The document presents a geomechanical wellbore stability model developed for an exploratory well in Colombia's Middle Magdalena Basin, which uses linear elastic theory, well log data, and laboratory tests to estimate mechanical properties and stress states. The model was calibrated using data from previously drilled wells and validated during drilling of the exploratory well. Developing this model allowed the company to formalize its geomechanical modeling methodology in Colombia.
The document discusses geomechanics applications throughout the lifecycle of oil and gas fields. It covers determining stress states, wellbore stability, fluid flow in fractured reservoirs, and 3D/4D geomechanical modeling. The author is Mark Zoback, a professor of geophysics at Stanford University who has published extensively on in situ stress measurements and their implications for wellbore stability, fault sealing, and induced seismicity from fluid injection.
Wellbore instability can be caused by mechanical, chemical, and man-made factors. Remedial actions may include improving drilling practices to minimize pressure fluctuations, controlling mud weight, reducing drill string vibrations, and monitoring trends to detect instability early. Case studies demonstrate how applying integrated approaches, including geomechanical modeling and updated drilling plans, can help solve instability problems and prevent issues like stuck pipe.
Rock mechanics for engineering geology part 1Jyoti Khatiwada
Rock mass classification systems are used to characterize rock masses for engineering design and stability analysis. The key systems discussed include the Rock Mass Rating (RMR) system, Q-system, Slope Mass Rating (SMR), and the New Austrian Tunnelling Method (NATM) classification. These systems aim to identify significant rock mass parameters, divide rock masses into classes of similar quality, and provide guidelines for design and communication between engineers and geologists. The advantages and limitations of each system are reviewed.
This paper analyzes geomechanical data from three offshore wells in Brazil to characterize in-situ stress and identify critically stressed fractures. The stress tensor was determined to be normal stress regime. Fracture modeling found no critically stressed fractures for two wells and one fracture plane for the third, requiring an unrealistically low friction coefficient. The study concludes fractures likely do not play a significant role in reservoir dynamics and more detailed analysis is needed.
The document discusses the use of the RMi rock mass characterization system for designing rock support in underground excavations. It begins by outlining the goals of underground excavation design and some current methods for stability analysis and rock support estimation. These include classification systems, ground-support interaction analysis using Fenner-Pacher curves, and key block analysis. The chapter then reviews factors influencing stability, defines key terms, and describes various modes of failure in underground openings including block failures, overstressing of intact rock or jointed materials, and special considerations for faults and weakness zones.
Rocks mechanics and its application in mining geology.
It aims at enhancing the mining process and higher yielding by reducing the chance of failures by providing information about the rocks of the mining area.
Laboratory modelling of rock joints under shear and constant normal loadingeSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The document discusses geomechanics applications throughout the lifecycle of oil and gas fields. It covers determining stress states, wellbore stability, fluid flow in fractured reservoirs, and 3D/4D geomechanical modeling. The author is Mark Zoback, a professor of geophysics at Stanford University who has published extensively on in situ stress measurements and their implications for wellbore stability, fault sealing, and induced seismicity from fluid injection.
Wellbore instability can be caused by mechanical, chemical, and man-made factors. Remedial actions may include improving drilling practices to minimize pressure fluctuations, controlling mud weight, reducing drill string vibrations, and monitoring trends to detect instability early. Case studies demonstrate how applying integrated approaches, including geomechanical modeling and updated drilling plans, can help solve instability problems and prevent issues like stuck pipe.
Rock mechanics for engineering geology part 1Jyoti Khatiwada
Rock mass classification systems are used to characterize rock masses for engineering design and stability analysis. The key systems discussed include the Rock Mass Rating (RMR) system, Q-system, Slope Mass Rating (SMR), and the New Austrian Tunnelling Method (NATM) classification. These systems aim to identify significant rock mass parameters, divide rock masses into classes of similar quality, and provide guidelines for design and communication between engineers and geologists. The advantages and limitations of each system are reviewed.
This paper analyzes geomechanical data from three offshore wells in Brazil to characterize in-situ stress and identify critically stressed fractures. The stress tensor was determined to be normal stress regime. Fracture modeling found no critically stressed fractures for two wells and one fracture plane for the third, requiring an unrealistically low friction coefficient. The study concludes fractures likely do not play a significant role in reservoir dynamics and more detailed analysis is needed.
The document discusses the use of the RMi rock mass characterization system for designing rock support in underground excavations. It begins by outlining the goals of underground excavation design and some current methods for stability analysis and rock support estimation. These include classification systems, ground-support interaction analysis using Fenner-Pacher curves, and key block analysis. The chapter then reviews factors influencing stability, defines key terms, and describes various modes of failure in underground openings including block failures, overstressing of intact rock or jointed materials, and special considerations for faults and weakness zones.
Rocks mechanics and its application in mining geology.
It aims at enhancing the mining process and higher yielding by reducing the chance of failures by providing information about the rocks of the mining area.
Laboratory modelling of rock joints under shear and constant normal loadingeSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Exposición de José Marín, geólogo de reservorios y especialista en Geomodelación ; fue transmitida en VIVO para la comunidad del Portal de Ingeniería. Para poder ver la charla, ingresa al siguiente enlace: https://www.youtube.com/watch?v=3YJYPQWfuBM
This document discusses several applications of slope stability analysis using the finite element method. It begins by introducing slope stability analysis and some traditional limit equilibrium methods. It then discusses two main advantages of the finite element method: it does not require assumptions about the failure surface shape or location, and it can model complex geometries and soil properties. The document presents several examples of applying the finite element method to analyze slope stability under various conditions, including accounting for drainage, brittle soil behavior, and engineering interventions. It compares results to traditional methods and notes the additional data on stresses, strains, and progressive failure that finite element analysis can provide.
1. Three new porosity models are proposed to model the relationship between accumulative porosity and pore size in rocks. Experimental results show that one of the models, which relates porosity to the maximum pore size, most closely matches measured pore size distribution data.
2. Pore geometry, orientation, and aspect ratio influence the strength and stiffness of porous rock. Numerical simulations show that compressive strength and Young's modulus decrease as the angle between the major axis of elliptical pores and applied stress increases from 0 to 90 degrees. Strength and stiffness also depend on pore aspect ratio.
3. Two methods for modeling dry bulk modulus at varying porosities are compared - the pore space stiffness method and critical porosity
Rock Mass Classification and also a brief description of Rock Mass Rating (RMR), Rock Structure Rating (RSR), Q valves and New Austrian Tunneling method(NATM)
Rock Mechanics and Rock Cavern Design_ICE HKAKeith Kong
This document discusses rock mechanics and rock cavern design. It provides details on 20 underground space projects Black & Veatch has been involved with over the past 20 years in Hong Kong and Singapore. These include tunnels, storage tanks, reservoirs, and other underground structures. The document then covers topics such as ground investigation, in-situ rock stresses, joint orientations, rock mass classification, and field testing methods for measuring rock and soil parameters and in-situ stresses.
Shear Strength Of Rockfill, Interfaces And Rock Joints, And Their Pointsguest963b41
The document discusses the shear strength of rockfill, rock joints, and their interfaces and contact points. It finds that the peak shear strength of rockfill and rock joints have similar non-linear strength envelopes when interpreted from large-scale triaxial tests and direct shear tests, respectively. Index tilt tests can also characterize the extremely low stress-dependent shear strength of rockfill and joints. The actual contact stresses when peak shear strength is reached are very high due to small contact areas. Equations are presented to estimate the shear strength of rockfill, rock joints, and their interfaces using characteristics measured from index tests. The non-linear strength envelopes mean that stability factors of safety will reduce from top to bottom and outside to inside
This document discusses the Hoek-Brown failure criterion for estimating the strength and deformation properties of rock masses. It provides details on:
1) Estimating the intact rock strength (ciσ) and Hoek-Brown constant (mi) from triaxial test data on rock cores.
2) Methods for estimating ciσ and mi when direct testing is not possible.
3) Factors that influence rock mass strength estimates such as rock type, discontinuity spacing, and scale of the structure being analyzed.
Rock mechanics focuses on studying the properties and behavior of intact rock and rock masses. Testing of intact rock samples involves destructive strength tests like uniaxial compression and triaxial tests as well as nondestructive tests like Schmidt hammer and sonic wave propagation. The compressive strength test is widely used in rock engineering to determine parameters like the Young's modulus. The complete stress-strain curve obtained from compression testing provides information on the rock's strength, stiffness and failure behavior. Other tests like point load and Brazilian tests are also used to indirectly measure the tensile strength of rock samples.
The document discusses slope mass rating (SMR) and its use in assessing the stability of rock slopes. SMR is calculated based on the basic rock mass rating (RMR) minus adjustment factors (F1, F2, F3) that account for discontinuity orientation plus an additional factor (F4) depending on excavation method. SMR values are used to classify slope stability into five classes, with recommended support measures depending on the class such as bolting, shotcrete, or retaining walls. The document also discusses factors that can affect slope stability and adaptations made to the SMR system for use in different regions.
The Fullbore Formation MicroImager (FMI) instrument provides high resolution images of bedding and fractures in borehole walls. It uses electrical resistivity contrasts to image features around the borehole at vertical resolutions of 5 mm. FMI data is processed using Schlumberger software to correct speed, equalize histograms, and enhance images. FMI can be used for structural analysis, reservoir characterization of natural fractures and porosity, thin bed detection, and other applications. It images features like dips, fractures, vugs, laminations, and other sedimentological structures.
This document provides guidance for analyzing the static stability of slopes, including slopes of earth and rock-fill dams, embankments, excavated slopes, and natural slopes. It describes methods for slope stability analysis, presents design criteria, and discusses considerations for calculations and presenting results. Factors that should be considered in site characterization, material characterization, and design are outlined. Limitations of analysis methods are also noted.
Topographic influence on stability for gas wells penetrating longwall mining ...legend314
Gas wells that penetrate mineable coal seams may be subject to distress caused by ground movements due to longwall mining. Especially important are the lateral shear offsets and axial distortion, which are most damaging for wellbores. To replicate typical conditions in the Appalachian basin, a geological model that considers the combined effects of topography, weak interfaces between monolithic beds and various mining depths is presented in the foregoing. These conditions adequately represent the principal features of the anticipated response of gas wells that are near-undermined by longwall panels. We examine the magnitudes of longitudinal distortions, lateral shear offsets, delaminations, and vertical and lateral strains along vertical wells drilled to intersect the seam at various locations within the longwall pillar. We analyze the distribution of these deformations and predict areas where the most severe deformation would occur.
The document discusses various rock mass classification systems used in rock engineering. It introduces Terzaghi, Stini, and Lauffer's early classification systems from the 1940s-1950s. It then focuses on more commonly used modern systems like the Rock Quality Designation (RQD) developed by Deere, the Rock Structure Rating (RSR) developed by Wickham et al, and the Rock Mass Rating (RMR) system. The document provides details on how to calculate and apply these different rock mass classification ratings which are used to evaluate rock mass quality and aid in rock engineering design.
Rock mass classification or rock mass rating of rock materials in civil and m...Ulimella Siva Sankar
1. Rock mass classification systems provide a methodology to characterize rock mass strength using simple measurements and allow geologic data to be converted into quantitative engineering parameters.
2. The most widely used systems are RQD, RMR, and Q-system which evaluate factors like rock quality, joint conditions, and groundwater to determine an overall classification.
3. Classification systems estimate the rock mass strength and deformability, which can then be input into numerical models to design underground mine openings and support requirements.
This article presents a workflow for predicting time-lapse stress effects in seismic data due to production-induced stress changes. The workflow involves building reservoir and geomechanical models, dynamically modeling fluid flow and reservoir compaction over time, calculating changes in elastic properties from stress changes, and using these to predict changes in seismic attributes. The workflow is demonstrated on a synthetic double-dipping anticline reservoir model. Modeling predicts vertical and horizontal subsurface displacement, changes in triaxial stress state in the overburden, and time-lapse changes up to 40ms in seismic attributes like P-wave and S-wave travel times that could be observed in field seismic data.
The document discusses rock mass classification using the Q-system. It begins by defining rock mass and describing different types based on discontinuities, from massive to heavily jointed rock. It then discusses the Q-system which evaluates rock mass quality based on factors like degree of jointing, joint roughness, alteration, water conditions and stresses. These factors are used to calculate a Q-value, with higher values indicating better rock mass stability. The Q-system provides guidelines for rock support design based on the Q-value. Overall, the document provides an overview of rock mass characteristics and classifications using the Q-system.
The document outlines 10 principles or "commandments" for properly using rock mass classification systems RMR and Q as outlined by Dr. N. Barton. The principles include: 1) Quantifying classification parameters from standardized tests; 2) Following established procedures for classifying rock mass; 3) Using both systems and checking published correlations; 4) Estimating support and reinforcement requirements; and 5) Performing mapping as construction proceeds and comparing to design.
This document discusses computer programs and computer-aided approaches used for slope stability analysis in rock slope engineering. It describes how programs can perform kinematic analysis using stereonets, limit equilibrium analysis using methods like Bishop and Janbu, and rockfall simulation. Specific programs mentioned include DIPS, DipAnalyst, SLIDE, SWEDGE, ROCPLANE, ROCFALL, Phase2, FLAC, UDEC, and 3DEC. These programs allow for conventional limit equilibrium methods, numerical continuum modeling, discontinuum modeling, and hybrid modeling approaches to slope stability analysis.
The document discusses slope stability analysis and modeling in FLAC3D. It provides an overview of key concepts like factors of safety, failure mechanisms, and analysis methods. It then describes a FLAC3D model of a slope showing the zones, material properties, and boundary conditions defined. The model is solved to determine the factor of safety and failure mechanism, with results showing shear strain contours and identifying circular failure with a safety factor of 1.05.
This document summarizes 9 cat breeds:
1. Savannah cats are a hybrid of domestic cats and African servals, weighing up to 30 pounds. They are social and loyal like dogs.
2. Cornish Rex cats have a unique coat with only down hair, making them soft. They are playful, active cats good for families with kids.
3. Sphynx cats are hairless with blue eyes and sweet personalities. They need weekly baths and to stay warm as they can't regulate temperature well.
4. LaPerm cats have curly coats from a spontaneous genetic mutation. They are friendly, calm cats that may be good for people with allergies.
5. Scottish Fold
Practical wellbore formation test interpretation; #120009 (2009)Tran Dang Sang
The document discusses practical interpretation of wellbore formation test (WFT) pressure data, which is important for defining proved reserves under new SEC regulations. It addresses issues like data quality from different tools, establishing high versus low confidence data, and examples of pressure trends that could indicate reservoir continuity. Topics covered include pretest pressure stability, depth correlation, gradient error, accuracy versus precision, interpreting gradients in low mobility environments, and avoiding compartmentalization. The author argues that integrated analysis of pressure trends with other data like fluid samples, geochemistry, and PVT properties provides a stronger case than pressure gradient analysis alone.
Exposición de José Marín, geólogo de reservorios y especialista en Geomodelación ; fue transmitida en VIVO para la comunidad del Portal de Ingeniería. Para poder ver la charla, ingresa al siguiente enlace: https://www.youtube.com/watch?v=3YJYPQWfuBM
This document discusses several applications of slope stability analysis using the finite element method. It begins by introducing slope stability analysis and some traditional limit equilibrium methods. It then discusses two main advantages of the finite element method: it does not require assumptions about the failure surface shape or location, and it can model complex geometries and soil properties. The document presents several examples of applying the finite element method to analyze slope stability under various conditions, including accounting for drainage, brittle soil behavior, and engineering interventions. It compares results to traditional methods and notes the additional data on stresses, strains, and progressive failure that finite element analysis can provide.
1. Three new porosity models are proposed to model the relationship between accumulative porosity and pore size in rocks. Experimental results show that one of the models, which relates porosity to the maximum pore size, most closely matches measured pore size distribution data.
2. Pore geometry, orientation, and aspect ratio influence the strength and stiffness of porous rock. Numerical simulations show that compressive strength and Young's modulus decrease as the angle between the major axis of elliptical pores and applied stress increases from 0 to 90 degrees. Strength and stiffness also depend on pore aspect ratio.
3. Two methods for modeling dry bulk modulus at varying porosities are compared - the pore space stiffness method and critical porosity
Rock Mass Classification and also a brief description of Rock Mass Rating (RMR), Rock Structure Rating (RSR), Q valves and New Austrian Tunneling method(NATM)
Rock Mechanics and Rock Cavern Design_ICE HKAKeith Kong
This document discusses rock mechanics and rock cavern design. It provides details on 20 underground space projects Black & Veatch has been involved with over the past 20 years in Hong Kong and Singapore. These include tunnels, storage tanks, reservoirs, and other underground structures. The document then covers topics such as ground investigation, in-situ rock stresses, joint orientations, rock mass classification, and field testing methods for measuring rock and soil parameters and in-situ stresses.
Shear Strength Of Rockfill, Interfaces And Rock Joints, And Their Pointsguest963b41
The document discusses the shear strength of rockfill, rock joints, and their interfaces and contact points. It finds that the peak shear strength of rockfill and rock joints have similar non-linear strength envelopes when interpreted from large-scale triaxial tests and direct shear tests, respectively. Index tilt tests can also characterize the extremely low stress-dependent shear strength of rockfill and joints. The actual contact stresses when peak shear strength is reached are very high due to small contact areas. Equations are presented to estimate the shear strength of rockfill, rock joints, and their interfaces using characteristics measured from index tests. The non-linear strength envelopes mean that stability factors of safety will reduce from top to bottom and outside to inside
This document discusses the Hoek-Brown failure criterion for estimating the strength and deformation properties of rock masses. It provides details on:
1) Estimating the intact rock strength (ciσ) and Hoek-Brown constant (mi) from triaxial test data on rock cores.
2) Methods for estimating ciσ and mi when direct testing is not possible.
3) Factors that influence rock mass strength estimates such as rock type, discontinuity spacing, and scale of the structure being analyzed.
Rock mechanics focuses on studying the properties and behavior of intact rock and rock masses. Testing of intact rock samples involves destructive strength tests like uniaxial compression and triaxial tests as well as nondestructive tests like Schmidt hammer and sonic wave propagation. The compressive strength test is widely used in rock engineering to determine parameters like the Young's modulus. The complete stress-strain curve obtained from compression testing provides information on the rock's strength, stiffness and failure behavior. Other tests like point load and Brazilian tests are also used to indirectly measure the tensile strength of rock samples.
The document discusses slope mass rating (SMR) and its use in assessing the stability of rock slopes. SMR is calculated based on the basic rock mass rating (RMR) minus adjustment factors (F1, F2, F3) that account for discontinuity orientation plus an additional factor (F4) depending on excavation method. SMR values are used to classify slope stability into five classes, with recommended support measures depending on the class such as bolting, shotcrete, or retaining walls. The document also discusses factors that can affect slope stability and adaptations made to the SMR system for use in different regions.
The Fullbore Formation MicroImager (FMI) instrument provides high resolution images of bedding and fractures in borehole walls. It uses electrical resistivity contrasts to image features around the borehole at vertical resolutions of 5 mm. FMI data is processed using Schlumberger software to correct speed, equalize histograms, and enhance images. FMI can be used for structural analysis, reservoir characterization of natural fractures and porosity, thin bed detection, and other applications. It images features like dips, fractures, vugs, laminations, and other sedimentological structures.
This document provides guidance for analyzing the static stability of slopes, including slopes of earth and rock-fill dams, embankments, excavated slopes, and natural slopes. It describes methods for slope stability analysis, presents design criteria, and discusses considerations for calculations and presenting results. Factors that should be considered in site characterization, material characterization, and design are outlined. Limitations of analysis methods are also noted.
Topographic influence on stability for gas wells penetrating longwall mining ...legend314
Gas wells that penetrate mineable coal seams may be subject to distress caused by ground movements due to longwall mining. Especially important are the lateral shear offsets and axial distortion, which are most damaging for wellbores. To replicate typical conditions in the Appalachian basin, a geological model that considers the combined effects of topography, weak interfaces between monolithic beds and various mining depths is presented in the foregoing. These conditions adequately represent the principal features of the anticipated response of gas wells that are near-undermined by longwall panels. We examine the magnitudes of longitudinal distortions, lateral shear offsets, delaminations, and vertical and lateral strains along vertical wells drilled to intersect the seam at various locations within the longwall pillar. We analyze the distribution of these deformations and predict areas where the most severe deformation would occur.
The document discusses various rock mass classification systems used in rock engineering. It introduces Terzaghi, Stini, and Lauffer's early classification systems from the 1940s-1950s. It then focuses on more commonly used modern systems like the Rock Quality Designation (RQD) developed by Deere, the Rock Structure Rating (RSR) developed by Wickham et al, and the Rock Mass Rating (RMR) system. The document provides details on how to calculate and apply these different rock mass classification ratings which are used to evaluate rock mass quality and aid in rock engineering design.
Rock mass classification or rock mass rating of rock materials in civil and m...Ulimella Siva Sankar
1. Rock mass classification systems provide a methodology to characterize rock mass strength using simple measurements and allow geologic data to be converted into quantitative engineering parameters.
2. The most widely used systems are RQD, RMR, and Q-system which evaluate factors like rock quality, joint conditions, and groundwater to determine an overall classification.
3. Classification systems estimate the rock mass strength and deformability, which can then be input into numerical models to design underground mine openings and support requirements.
This article presents a workflow for predicting time-lapse stress effects in seismic data due to production-induced stress changes. The workflow involves building reservoir and geomechanical models, dynamically modeling fluid flow and reservoir compaction over time, calculating changes in elastic properties from stress changes, and using these to predict changes in seismic attributes. The workflow is demonstrated on a synthetic double-dipping anticline reservoir model. Modeling predicts vertical and horizontal subsurface displacement, changes in triaxial stress state in the overburden, and time-lapse changes up to 40ms in seismic attributes like P-wave and S-wave travel times that could be observed in field seismic data.
The document discusses rock mass classification using the Q-system. It begins by defining rock mass and describing different types based on discontinuities, from massive to heavily jointed rock. It then discusses the Q-system which evaluates rock mass quality based on factors like degree of jointing, joint roughness, alteration, water conditions and stresses. These factors are used to calculate a Q-value, with higher values indicating better rock mass stability. The Q-system provides guidelines for rock support design based on the Q-value. Overall, the document provides an overview of rock mass characteristics and classifications using the Q-system.
The document outlines 10 principles or "commandments" for properly using rock mass classification systems RMR and Q as outlined by Dr. N. Barton. The principles include: 1) Quantifying classification parameters from standardized tests; 2) Following established procedures for classifying rock mass; 3) Using both systems and checking published correlations; 4) Estimating support and reinforcement requirements; and 5) Performing mapping as construction proceeds and comparing to design.
This document discusses computer programs and computer-aided approaches used for slope stability analysis in rock slope engineering. It describes how programs can perform kinematic analysis using stereonets, limit equilibrium analysis using methods like Bishop and Janbu, and rockfall simulation. Specific programs mentioned include DIPS, DipAnalyst, SLIDE, SWEDGE, ROCPLANE, ROCFALL, Phase2, FLAC, UDEC, and 3DEC. These programs allow for conventional limit equilibrium methods, numerical continuum modeling, discontinuum modeling, and hybrid modeling approaches to slope stability analysis.
The document discusses slope stability analysis and modeling in FLAC3D. It provides an overview of key concepts like factors of safety, failure mechanisms, and analysis methods. It then describes a FLAC3D model of a slope showing the zones, material properties, and boundary conditions defined. The model is solved to determine the factor of safety and failure mechanism, with results showing shear strain contours and identifying circular failure with a safety factor of 1.05.
This document summarizes 9 cat breeds:
1. Savannah cats are a hybrid of domestic cats and African servals, weighing up to 30 pounds. They are social and loyal like dogs.
2. Cornish Rex cats have a unique coat with only down hair, making them soft. They are playful, active cats good for families with kids.
3. Sphynx cats are hairless with blue eyes and sweet personalities. They need weekly baths and to stay warm as they can't regulate temperature well.
4. LaPerm cats have curly coats from a spontaneous genetic mutation. They are friendly, calm cats that may be good for people with allergies.
5. Scottish Fold
Practical wellbore formation test interpretation; #120009 (2009)Tran Dang Sang
The document discusses practical interpretation of wellbore formation test (WFT) pressure data, which is important for defining proved reserves under new SEC regulations. It addresses issues like data quality from different tools, establishing high versus low confidence data, and examples of pressure trends that could indicate reservoir continuity. Topics covered include pretest pressure stability, depth correlation, gradient error, accuracy versus precision, interpreting gradients in low mobility environments, and avoiding compartmentalization. The author argues that integrated analysis of pressure trends with other data like fluid samples, geochemistry, and PVT properties provides a stronger case than pressure gradient analysis alone.
The API RP 78 document aims to establish industry standards for wellbore positioning. It was created in response to an identified need by the Operator Wellbore Survey Group committee. The document will provide minimum guidelines for planning, acquiring, analyzing and using wellbore position data throughout the well lifecycle. It will cover effective representation of well trajectories and proximity assessments while not addressing advanced techniques beyond mainstream practices. Development involves dividing the work into sections led by subject matter experts to draft content before combining into a final recommended practice document.
Stress analysis is the essence that is needed while planning exploration, drilling and development operations in oil and gas industries. Proper knowledge of Geomechanics will help us to reduce the risk of failure as well as provide a better picture of stresses inside the earth. From Hydrofracturing to directional drilling, stresses play their parts.
1) Waterstones S.r.l. offers a wide range of geophysical well log services to analyze boreholes and wells up to 1400 m deep.
2) They perform logs in horizontal, variably oriented, and vertical boreholes using tools like optical and acoustic televiewers, sonic logs, resistivity logs, and more.
3) The logs are used for applications like fracture detection, lithology analysis, cement bond evaluation, and hydrogeological surveys.
Laboratory-scale geochemical and geomechanical testing of near wellbore CO2 i...Global CCS Institute
To highlight the research and achievements of Australian researchers, the Global CCS Institute together with ANLEC R&D will hold a series of webinars throughout 2016 and 2017. Each webinar will highlight a specific ANLEC R&D research project and the relevant report found on the Institute’s website. This is the sixth webinar of the series and presented the results of chemical and mechanical changes that carbon dioxide (CO2) may have at a prospective storage complex in the Surat Basin, Queensland, Australia.
Earth Sciences and Chemical Engineering researchers at the University of Queensland have been investigating the effects of supercritical CO2 injection on reservoir properties in the near wellbore region as a result of geochemical reactions since 2011. The near wellbore area is critical for CO2 injection into deep geological formations as most of the resistance to flow occurs in this region. Any changes to the permeability can have significant economic impact in terms of well utilisation efficiency and compression costs. In the far field, away from the well, the affected reservoir is much larger and changes to permeability through blocking or enhancement have relatively low impact.
This webinar was presented by Prof Sue Golding and Dr Grant Dawson and will provide an overview of the findings of the research to assist understanding of the beneficial effects and commercial consequences of near wellbore injectivity enhancement as a result of geochemical reactions.
Simulating Reservoir Structure using Well Log DataYien Tiong
The document provides an outline and objectives for constructing a reservoir model from well data using stochastic simulation. It presents well location and data quality control results, including boxplots and histograms of porosity and permeability which show uniform porosity distributions and lognormal permeability distributions with some outlier data. A top reservoir surface is generated through stochastic simulation after removing regional eastward dipping trend and faults identified from compartmentalization.
Wireline logging provides continuous and repeatable imaging of subsurface conditions and is immediately available at wellsites. Borehole geophysical logs can identify aquifers and contaminant plumes as well as provide information on formation properties, borehole characteristics, stratigraphy, water content, porosity, water saturation, water chemistry, salinity, lithology, and temperature to aid in tasks such as well design, testing, completion, and remediation. Hughbert Collier is a senior vice president at Collier Consulting in Stephenville, Texas who provides wireline logging services.
Geomechanical Study of Wellbore StabilityVidit Mohan
This document provides an overview of geomechanical modeling and wellbore stability analysis. It discusses the need for geomechanical models to incorporate in-situ stress data, pore pressure, rock properties, and geology. The key aspects of developing a geomechanical model are outlined, including the variation of effective hoop stress around wellbores. Different failure criteria for compressional and tensile failures are presented. Methods for estimating pore pressure from logs using normal compaction trends and for determining fracture pressure from correlations with overburden stress are summarized. The sensitivity of results to pore pressure is highlighted. Top-down and bottom-up approaches to casing design based on pore pressure and fracture pressure are contrasted.
This study used finite element modeling to analyze swelling behavior in a tunnel excavated through marl rock. Laboratory tests on marl rock samples were used to calibrate two finite element programs, FISS and Nisa-II. FISS modeled the tunnel using the laboratory swelling test results. Nisa-II modeled time-dependent creep behavior by defining a creep function relating stress, strain, and time. Both programs analyzed stresses around the tunnel and indicated higher stresses in the sidewalls compared to the roof and floor. The study demonstrated a method to numerically model swelling behavior in tunnels using laboratory test data.
Laboratory experimental study and elastic wave velocity on physical propertie...HoangTienTrung1
Pressure grouting has gained popularity as a soil reinforcement method. However, the behavior of the interface between rock and grout is not well known. This study investigates the interaction of pressure grouting and rock, through a series of laboratory tests performed on specially designed and fabricated equipment and using standard testing methods. The test measures the density, compressional strength, and frictional resistance of grout relative to the applied pressure and curing time. Simultaneously, the velocities of the elastic wave traveling through the grout are obtained to develop correlations between the physical properties of the grout and the test conditions. The results of the tests show that the density, compressional strength, and frictional resistance of the grout increase with applied pressure and curing time. The strengths of the influencing factors are seen to be correlated within the range of the test conditions. Using the results of these tests, the potential development of a new method that requires less cement was discussed.
1) The study investigates the effect of reservoir hydrostatic pressure on the seismic response of roller compacted concrete (RCC) dams using finite element analysis.
2) Analysis of the Kinta RCC dam in Malaysia shows that hydrostatic pressure increases stresses by 25% and changes displacement response from negative to positive direction. It also causes more damage at the heel of the dam.
3) Consideration of hydrostatic pressure leads to a 13% increase in maximum horizontal deformation, from 76.5 mm to 86.6 mm, and changes the zone of peak deformation from the base to the crest of the dam. It also changes the displacement response of nodes from negative to positive.
This document summarizes the methodology used to optimize hydraulic fracturing in the San Jorge Basin in Argentina. State-of-the-art well logging tools and collaboration between operating and service companies were used to better understand reservoir conditions and design fractures. NMR logging, sonic logs, and pressure diagnostics during fracturing were integrated to determine fracture heights and calibrate models. This approach resulted in improved well performance through more accurate fracture design tailored to each reservoir's characteristics.
Lyapichev. Problems in numerical analysis of CFRDs (ICOLD Bull.155)6 p.)Yury Lyapichev
The document discusses several challenges and developments in numerically analyzing concrete faced rockfill dams (CFRDs). It notes that until recently, CFRDs were designed based on experience rather than analysis. Accurate models have since shown issues like excessive compressibility of downstream rockfill adversely impacting the concrete face. The document also discusses modeling earthquakes, the need for structure-specific models in some cases, and ensuring nonlinear analysis convergence. Overall, it emphasizes the importance of numerical analysis as a tool to supplement—not replace—engineering judgment, especially for extrapolating lessons from incidents at high CFRDs.
This document analyzes wellbore instability in vertical, directional, and horizontal wells using field data from an offshore field being redeveloped by drilling horizontal wells. The analysis identified the major causes of instability in the wells as tight holes, stuck pipes, and hole pack offs. Rock mechanical simulations predicted a safe mud weight window for horizontal wells, but all wells were drilled using the same mud weight. The document then describes analyzing drilling data from the vertical, directional, and horizontal wells to identify instability mechanisms and design optimized safe mud weight windows for each well type and orientation.
This document describes a numerical modeling study to predict the strength of St. Peter Sandstone pillars used in underground mining. Finite difference models were created of pillars with dimensions of 12.192 m x 12.192 m x 9.144 m and a room width of 10.3632 m, based on dimensions used successfully in an abandoned Iowa mine. The models applied varying overburden loads to the pillars to determine stress-strain behavior and peak stress. An empirical pillar strength formula was developed and used to establish a relationship between pillar stress, safety factor, and maximum stable overburden depth for factors of safety of 1.5 and 2.
This project characterized an unconventional Upper Jurassic reservoir in northern Mexico through an integrated geoscience analysis. The analysis included well log evaluation, seismic analysis, and geological modeling to predict total organic carbon (TOC) and brittleness distributions in 3D and characterize natural fractures and in situ stresses. TOC and brittleness predictions from well data correlated highly with seismic attributes and rock properties. While the seismic survey was not wide-azimuth, fracture information could still be extracted and correlated with wellbore images. The results provide insights into the reservoir's potential for hydraulic fracturing and hydrocarbon production from the shale formation.
This paper addresses the fracture toughness ( ), or also known as critical stress intensity Factor, according to
conditions of Lineal Elastic Fracture Mechanics (LEFM). The characterization of the mechanical properties in
tensile and fracture toughness of structural steel pipes API-5L used in hydrocarbons transportation was
performed. For fracture toughness, the material was tested through fatigue crack propagation on standardized
compact specimen (CT) according to ASTM E-399 norm. A thickness (B) equal to and a crack size (a) equal
to 0.5w were used. With the porpoise of establishing the adequate conditions at the crack tip, the specimens were
subjected to fatigue pre-cracking by application of repeated cycles of load in tensile-tensile and constant load
amplitude with a load ratio of R = 0.1. The experimental Compliance method was used based on data obtained
from load vs. Crack Mouth Opening Displacement (CMOD). The results show a Stress Intensity factor of 35.88
MPa√m for a 25 mm crack size specimen. The device used for testing is a MTS-810 machine with capacity of
100KN and 6 kHz sampling rate, which meets the conditions of the ASTM E-399 standard. The cracking
susceptibility of steel is influenced by the size, morphology and distribution of non-metallic inclusions,
thermochemical interaction with the environment and microstructure.
Evaluation of shear strength of model rock joints by experimental studyeSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
This document summarizes a methodology for predicting stress corrosion crack growth rates when linear elastic fracture mechanics conditions are not met. The methodology relates crack tip opening angle to growth rate based on theoretical results under small-scale yielding, coupled with experimental data relating stress intensity factor to growth rate under LEFM conditions. It then predicts growth rates by determining crack tip opening angle under non-LEFM conditions. The paper analyzes a model of a solid with two deep cracks under tension to examine how plastic deformation extent and loading pattern (displacement or load control) affect predicted and LEFM-based growth rates throughout the plasticity range. It finds LEFM approaches can over or under-predict growth rates depending on conditions.
Full Paper - Ratcheting Uplift of Buried Pipelines in Sand (P. Chitas)Pagkratios Chitas
This document summarizes an experimental study on the ratcheting failure mechanism of buried offshore pipelines in sand. Small-scale laboratory tests were conducted using a pipe section buried in dry silica sand at various densities and embedment depths. Both monotonic and cyclic (load-controlled) pull-out tests were performed to simulate upheaval buckling and ratcheting failure. The test results were analyzed to investigate controlling parameters, validate prediction methods, and determine adequate soil cover required to resist ratcheting. The experimental setup, soil sample preparation, and testing procedure are described in detail.
This document summarizes a study that used centrifuge modeling to analyze the seismic loading response of layered brick soil. Centrifuge modeling allows for scaled physical modeling of geotechnical problems involving gravity effects. The study involved constructing a layered brick soil model in a centrifuge and subjecting it to simulated earthquake motions while monitoring soil responses like settlement, pore pressure, and acceleration. The results provided data on how the layered soil responded dynamically to seismic loads at different frequencies and strain levels, helping to validate numerical models and further the understanding of soil failure mechanisms during earthquakes.
This document summarizes a study that used centrifuge modeling to analyze the seismic loading response of layered brick soil. Centrifuge modeling allows for scaled physical modeling of geotechnical problems involving gravity effects. The study constructed a layered brick soil model in a flexible shear box container and subjected it to various ground motions up to an acceleration of 58g using a shaking table. A variety of sensors measured soil responses like settlement, pore pressure, and acceleration at different depths during testing. The results provide data on how the layered soil responds nonlinearly to seismic loads and frequencies, with implications for seismic design of offshore structures.
A fracture mechanics based method for prediction ofSAJITH GEORGE
The document presents a fracture mechanics-based method for predicting cracking in circular and elliptical concrete rings undergoing restrained shrinkage. It describes an experimental program using different ring geometries and material tests to determine properties. A numerical model is developed using ANSYS to model the restrained shrinkage process and calculate stress intensity factors. The model uses a fictitious temperature field to simulate shrinkage and determines cracking age by comparing driving and resistance curves. It finds cracking occurs earlier in elliptical rings and the method accurately predicts experimental cracking ages.
3 d seismic method for reservoir geothermal exploration n assessmentMuhammad Khawarizmi
1) 3-D seismic reflection methods have potential to image fractures controlling geothermal reservoirs but past studies often failed to identify drill targets due to scattering and heterogeneity.
2) Recent advances in 3-D seismic acquisition and processing, as well as modeling of fracture effects on seismic waves, may enable more detailed subsurface imaging capable of locating productive fracture pathways.
3) Methods analyzing amplitude versus offset, azimuth, and frequency content across 3-D volumes can help characterize fracture orientations that may control fluid flow. However, higher resolution is still needed to define the specific fractures controlling permeability.
This document presents a simplified method for estimating the entire load profile of a fully grouted anchor bolt based on strain measurement data from two points near the loaded end. Pullout tests were conducted on anchor bolts grouted in concrete with two different grout types. Strain gauges attached to the bolts recorded data during loading. Interpolation of data from two gauges was able to estimate the full load profile along the bolt, matching the profile obtained from multiple gauges. This method provides a simplified way to determine an anchor bolt's load profile without needing data from along its entire length.
1. 85CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
GEOMECHANICALWELLBORE
STABILITY MODELING OF
EXPLORATORYWELLS – STUDY
CASEAT MIDDLE MAGDALENA
BASIN
Jenny-Mabel Carvajal Jiménez1*, Luz-Carime Valera Lara2, Alexander Rueda3,
and Néstor-Fernando Saavedra Trujillo1
1Ecopetrol S.A. - Instituto Colombiano del Petróleo, A.A. 4185, Bucaramanga, Santander, Colombia
2DTH Ltda., Calle 91 # 24-69, Bucaramanga, Santander, Colombia
3Ecopetrol S.A. Reservoir and Production Engineering Office, Calle 37 # 8-43, Bogotá, Cundinamarca, Colombia
e-mail: jenny.carvajal@ecopetrol.com.co
(Received May 30, 2006; Accepted Oct. 11, 2007)
T
his paper presents the geomechanical wellbore stability model of an exploratory well sited at Middle
Magdalena Basin (MMB), which is based on the validity of linear elastic deformational theory for porous
media; the use of correlations and field tools such as well and image logs to indirect determination
of mechanical properties and stress state. Additionally, it is shown the model calibration and validation using
drilling events which occurred at other previously drilled wells in the study area, at the exploratory well itself
and experimentally evaluated mechanical properties on outcrop and core samples from the basin formations.
This application allowed the Instituto Colombiano del Petróleo (ICP) at Ecopetrol S.A. to formally perform
the geomechanical modeling of Colombian formations and to accomplish a complete and appropriate
methodology to do so; such methodology has been standardized as part of the drilling support process at
Ecopetrol S.A., supplying the possibility for taking decisions that contribute to reduce drilling costs and risks
during operations.
* To whom correspondence may be addressed
Keywords: exploratory well, rock mechanics, modeling, stability, drilling, Middle Magdalena Basin, Cagüi 1.
* To whom correspondence may be addressed
2. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 200786
E
n este artículo se presenta el modelamiento geomecánico durante la perforación de un pozo explo-
ratorio, ubicado en la cuenca del Valle Medio del Río Magdalena; el cual supone la validez de la
teoría elástica lineal para determinar el comportamiento deformacional de las rocas, soportado en
el uso de correlaciones para la obtención indirecta de las propiedades geomecánicas de las formaciones y
el estado de esfuerzos in situ, a partir de herramientas de pozo como los registros eléctricos y de imágenes.
Adicionalmente, se presenta la calibración de dicho modelo con los eventos de perforación observados en
pozos perforados previamente en el área de estudio y con pruebas de laboratorio realizadas en muestras de
afloramiento de la cuenca. La validación del modelo extrapolado se basó en la experiencia de perforación y
en pruebas de laboratorio adicionales realizadas en el corazón extraído del prospecto perforado. Con este
ejercicio, el Instituto Colombiano del Petróleo de Ecopetrol S.A. incursionó de manera formal en el área del
modelamiento geomecánico de las formaciones colombianas, lo que permitió el desarrollo de una meto-
dología robusta y apropiada para la región de estudio y la estandarización de este proceso como apoyo a
la perforación en Ecopetrol S.A., brindando la posibilidad de establecer acciones que permiten reducir el
costo de perforación y los riesgos inherentes a las diferentes operaciones desarrolladas.
Palabras clave: pozos exploratorios, mecánica de rocas, modelamiento, estabilidad, perforación, cuenca del Valle
Medio del Magdalena, Cagüi 1.
3. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 87
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
NOMENCLATURE
Sh Minimum horizontal stress, psi
SV Overburden stress gradient, psi/ft
g Gravity
ρsea Sea water density
ρb Formation density
D Depth, ft
P/D Pore pressure gradient, psi/ft
S/D Overburden stress gradient or lithology pressure gradient, psi/ft
Δtn Normal transit time
Δto Observed transit time
VP Compressive seismic velocity
VS Shear seismic velocity
ν Poisson ratio
K Bulk modulus
ρ Rock density average
E Young´s Moduli
To Tensile strength
P Maximum stress
D Sample diameter
t Sample thickness
Vshale Shale content
GRread Gamma ray reading
GRclean Clean gamma ray
GRshale Dirty gamma ray
σV Overburden stress
e Lithology thickness
σ1 Maximum stress
σ3 Minimum stress
UCS Unconfined compressive strength
φ Internal friction coefficient
β Rock failure angle
pW
T Mudweigth Pressure
σh Minimun horizontal stress
σH Maximum horizontal stress
P0 Pore pressure
4. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
88
INTRODUCTION
Rock mechanics has become one of the support
technologies applied in order to obtain an efficient ex-
ploitation of hydrocarbons due to the changes induced
by petroleum industry activities performed on oil and
gas reservoirs. Early applications of geomechanics in
petroleum industry were made to prevent and control
sanding and stability problems of wells (Roegiers,
1995).
Wellbore stability is considered when the well di-
ameter fits the bit sizes and it remains constant while
drilling. In constrast to this, geomechanical instabil-
ity refers to mechanical conditions such as wellbore
collapse or failure. In general, wellbore instability is
related to drillpipe sticking, tight spots, caving produc-
tion, wellbore collapse and unscheduled sidetracks,
these conditions are mostly caused by unknown rock
mechanics and lead to increased costs during drilling
and completion operations.
Hubbert and Willis (1957) developed a mechani-
cal wellbore stability model in which the primary as-
sumption was the linear elastic stress pathway around
the borehole. From this model, Geertsma (1966) and
other researchers stated methodologies to couple pore
pressure effects and improve the stress prediction on
the borehole using non linear elastic hypothesis and
anelastic strain. Most recent models include wellbore
instability numerical simulation (Vásquez, Castilla, &
Osorio, 2004). A comparative outline of current insta-
bility models available is shown in Table 1.
The proposed methodology assumes the validity
of linear elastic theory for porous media in order to
predict geomechanical rock behavior. In addition to
this, to reduce solution uncertainties in the model a set
of data is used, which is obtained from drilling reports,
well logging, laboratory tests, well tests such us LOT
(Leak off Test), FIT (Formation Integrity Test) and
microfracturing. The main goal of this method is to
obtain representative models to be used while drilling,
so it would be possible to prevent instability problems
and to reduce non productive time and drlling costs.
This paper describes the methodology used by Eco-
petrol S.A. to perform and calibrate the geomechanical
wellbore stability models and its application to an
exploratory well sited at MMB – Colombia, called
Cagüi 1. This application demonstrated the validity
of hypothesis such as: I) applicability of linear elastic
theory in mechanical stability simulation while drill-
ing, II) applicability of well logging to rock mechanic
features modeling, III) applicability of laboratory
test to calibrate rock mechanical modeling and iv)
applicability of drilling reports to calibrate wellbore
stability models.
FUNDAMENTAL THEORY
Wellbore instability modeling
According to rock mechanics, drilling generates
changes in the stress field of the formation due to
supporting material losses. In fact, drilling induces
radial and tangential stresses that result in additional
shear stresses. At certain point induced stress may be
higher than the rock strength and rock will fail caus-
ing borehole collapse and stuck piping. This mechanic
behavior can be addressed to know the rock feature so
it would be possible to prevent and to reduce instabil-
ity problems.
The following items help to state a stability model
(Adam, Bourgoyne, Keith, Martin, & Young, 1986):
Table 1. Comparative outline of instability models
Proposed
Model
Representative
Solution
Modeling
Data
Availability
Solution
Availability
Linar
elastic
model
Low High
Comercial
software
Bilinear
elastic
model
Middle Low
Comercial
software
Poroelastic
model
Middle - High Very high
Comercial
software
Non linear
elastic
model
Middle - High Very low
Comercial
software
Numeric
model
High Minimum Yes
5. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 89
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
1. To evaluate the acting forces on objective area (grav-
ity and tectonic stresses).
2. To assess the rock strength.
3. To calculate resulting stress field.
4. To use the constituve laws to relate stress field and
strain.
5. To state boundary conditions for stresses and
strains.
6. To identify the failure mode.
7. To determine the mudweight window and to calcu-
late the best mud density.
8. To define activities to control of instability.
Calculating overburden stress. To do so, the density
well logging is integrated with respect to vertical depth
using the following equation:
(1)
Minimum horizontal stress assessment (Sh). This
stress is read from LOT and FIT results, Figure 1 shows
a type curve of these tests (Aird, 2001) and the point
corresponding to Sh.
sure, minimum horizontal stress, UCS, tensile strength
and failure conditions observed at previously drilled
wells. To draw the stress polygon (Figure 2) it must be
calculated the strike-slip, normal and thrust regime limits,
then the polygon area is closed using the vertical stress
and pore pressure and finally with rock properties it is ap-
proached the maximum horizonta stress for each depth.
Figure 1. LOT Type Curve (from Aird, 2001 )
Figure 2. Stress Polygon (modified from Zoback et al., 2003)
Maximum horizontal stress calculation (Zoback et al.,
2003). In order to quantify this stress the stress polygon
definition is used, in wich is possible to identify various
magnitude ranges based on overburden stress, pore pres-
Horizontal stress orientation. Finally to complete
the horizontal stress determination the orientation
of them must be known. This can be achieved from
image well logging (UBI or FMI), geometry well log-
ging (four arms caliper or higher calipers), regional
or structural studies. When well logging are available
the current orientation can be obtained. On the other
hand, when regional and structural studies are used the
orientation will depend on tectonic conditions (Muñoz
et al., 1996).
Pore pressure calculations. To estimate the pore pres-
sure profile the Eaton’s correlation (1969) is used:
(2)
(3)
Geomechanical properties modeling of rock forma-
tions
The geomechanical properties can be modeled from
rock features such as composition (shale content), den-
sity and acoustic velocities based on well logging tools
6. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
90
– Gamma Ray, Neutron Density and Sonic log – and
experimentally evaluated petrophysic properties on well
samples. Rock composition, porosity and density can be
obtained from well logging or laboratory tests, however
acoustic velocities require special data treatment, which
isaccomplishedusingtheequationsproposedbyNielsen,
and Kohlhaas (1979).
Elastic Moduli assessment (Biot, 1956).According
to elastic theory it is possible to obtain all the elastic
moduli from two of them (as it can be seen at Table 2,
published by T. Bourbiē, Coussy, & Zinszner, 1987).
A common array is the Poisson ratio and Volumetric
moduli which can be calculated from acoustic velocities
as shown in Equations 4 and 5).
(4)
(5)
and Mohr-Coulomb failure envelope. The parameters
from geomechanic tests are representative of rock
behavior and can be used to calibrate geomechanical
models built from well logging. Table 3 lists the tests
to evaluate wellbore stability parameters.
E G
K, v
Table 2. Mathematical expressions for elastic moduli
The values obtained by the earlier equations are
greater than pseudostatic measurements of mechani-
cal properties. The dynamic measurements need to be
upscaled in order to fit the corresponding pseudostatic
properties since those are the data used in geomechani-
cal modeling.
Mohr-Coulomb failure envelope and rock strengths.
These parameters are computed from Tixier, Loveless,
and Anderson (1975) equations which are based on
experimental correlations.
Experimental geomechanic evaluation
Experimental geomechanic evaluation is used to de-
termine straightforward elastic moduli, rock strengths
Test Name Evaluated Parameter
Uniaxial
compressive test
Young Moduli
Poisson ratio
UCS
Strains: Axial, Circumferencial,
Volumetric
Velocities: Compressive and Shear
Brazilian test Tensile strength
Triaxial
compressive test
Young Moduli
Poisson ratio
CCS
Strains: Axial, Circumferencial,
Volumetric
Multiple failure
envelope
Cohesion, Internal friction coefficient
Table 3. Geomechanic tests for wellbore stability study
Uniaxial compressive test. This experimental
evaluation consists in applying axial force on the
rock in a continous way increasing the stress until the
sample shows shear failure. The strains of the rock
are measured during the test so Young moduli and
Poisson ratio can be calculated from them (Charlez,
1991; ASTM D2938 – 95 (Reapproved 2002), ASTM
D 3148, 2002).
Indirect tensile test. It is also called Brazilian Test
and it implies the progressive increase of compressive
force applied transversely to the axial axis of the sample
at one point of the diameter until the rock fails on indi-
rect tensile mode (ASTM D 3967 – 05, 2002).
Triaxial compressive test. At the beginning of this
test the sample has confining pressure and axial force
applied on it – the value of this stress is similar to
average in situ stress state. Next to this, axial force is
increased until the rock fails in a shear mode (ASTM
D 2664 – 04, 2004; ASTM D 5407 – 95 Reapproved
2000).
7. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 91
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
In addition, to obtain the Mohr-Coulomb failure
envelope, a series of triaxial compressive tests must
be carried out by applying different initial stress states
on the specimens. This is possible to achieve using
either as many samples as stress states are evaluated
or using just one specimen in a special triaxial known
as multiple failure envelope test.
EXPERIMENTAL PROCEDURE
This methodology consists in three stages. First step
is to build up the model based on the correlation wells
available (Figure 3) which are sited next to the studied
well and have similar behavior respect to it. Further-
more, correlation wells must have as much information
as possible to obtain the geomechanical model. This
means well logging (density log, sonic log, gamma ray
log, resistivity log, porosity log), drilling reports and
formation tests.
Geomechanical model building up
Primary assumptions during this stage are the
validity of linear elastic theory for porous media, the
uniformity of rock formations, the representativity of
formation test and well logging. Based on these, the
geomechanical model building up consists of the next
items:
1. To choose the correlation wells.
2. To determine the lithologies at wells.
3. To assess shale content at different lithologies
(Vshale).
4. To calculate shear and compressive acoustic velocity
on wells.
5. To compute elastic moduli, rock strength and Mohr-
Coulomb faillore envelope.
6. To get well in situ stresses (overburden stress,
minimum horizontal stress, maximum horizontal
Figure 3. Wellbore stability model building up
Thesecondstageismodelcalibration(Figure4)which
is the replication of drilling conditions on the correlation
wells,basedonthefollowinginformation:formationtests
data, daily drilling reports, and experimental tests data
(both petrophysics and geomechanics data).
At last, the model is extrapolated to the exploratory
well (Figure 5) by taking into account geologic features,
well configurations and the different drilling condi-
tions occured at correlation wells. In order to update
the model, the behavior of rocks is observed while
exploratory well drilling. This may help to support the
decision making on the operation.
Figure 4. Wellbore stability model calibration
Figure 5. Wellbore stability model extrapolation
8. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
92
stress, orientation of horizontal stresses and pore
pressure).
7. To evaluate the mudweight window, which has three
parameters: I) minimum mudweight, II) maximum
mudweight and III) optimum mudweight while
drilling.
Correlation wells are sited in the surrounding area of
the exploratory well, to choose the main correlation well
it is assumed that formations are uniform so wells near to
the prospect will behave similarly. Once the correlation
well is chosen, the lithology of it must be determined
from core and cutting samples description, composite
well log and gamma ray log. Based on this information,
the shale content can be calculated using the value of
clean gamma ray – which corresponds to gamma ray
reading at non shaly zones – and dirty gamma ray – read-
ing at shaly zones – applying Equation 6.
(6)
The sonic well log is used to get the compressive
acoustic velocity and after this calculation it is possible
to assess the shear acoustic velocity according to the
well lithologies. Once these velocities are computed,
the elastic moduli can be determined from the expres-
sions in Table 2. Finally, rock strength must be defined
for each well lithology.
To determinate the in situ stress state it is required
to calculate first of all the overburden stress (Equation
1). If there is not enough density information to use
Equation 1, it is possible to build up this stress from
lithological description, core petrophysics data and
cuttings using the following equation:
(7)
Whereas 0,433 is the unit conversion constant from
g/cc to psi/ft. Table 4 lists various lithology densities
assuming 100 % of purity on each.
After calculating overburden stress, the minimum
horizontal stress magnitude can be defined from LOT
and FIT at correlation wells. To extrapolate the mini-
mum stress gradient it is assumed that its magnitud is
constant at each rock formation. Once the previous
stresses are computed, it is possible to approach maxi-
mum horizontal stress magnitude using stress polygon
(Figure 2). The orientation of horizontal stresses is
defined based on well logs or regional studies. Finally,
the stress state is completed when pore pressure profile
is obtained from Eaton method (Equations 2 and 3).
According to geomechanical definitions mudweight
window is the value or range of values that might be
used to keep a safe operation while drilling. Minimum
values of this window correspond to the minimum
mudweight required to avoid collapse formation in the
borehole; maximum values address to prevent hydraulic
fracturing while drilling and optimum mudweight is the
suggested mud density to perform drilling.
The minimum mudweight is calculated from Mohr-
Coulomb failure criteria using the following equations
(Muñoz et al., 1996):
(8)
(9)
Taking into account the relative magnitude of in-
duced stresses (failure regimes) and the Mohr-Coulomb
parameters (Equations 8 and 9) there can be six dif-
ferent possible conditions for borehole collapse. these
conditions are listed in Table 5.
The maximum mudweight for a vertical well can be
defined considering hydraulic failure condition (tensile
fracture), which is calculated upon the next equation
(Muñoz et al., 1996):
(10)
The mudweight window is favorable when the
collapse density is lower than the fracture density in
any other case such mudweight window will be non
Table 4. Lithology densities (modified from Schlumberger, 1972)
Lithology Apparent Log Density (Kg/m3)
Shale 2200 – 2750
Sandstone 2485
Bituminous Coal 1300 – 1500
Limestone 2540
Dolomite 2683
9. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 93
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
favorable. In the Figure 6 is shown a skematic drawing
of these cases.
When the mudweight window is favorable the op-
timum mud density is the range average. In the other
cases the optimum mud density corresponds to either
fracturing or collapse values, taking into account which
is the most critical situation under drilling conditions
and trying to minimize mechanical failure.
Geomechanical model calibration
In order to calibrate a geomechanical model, it is
necessary to identify the drilling conditions on correla-
tion wells.To do so, the primary information is obtained
from daily drilling reports, operative reports and final
drilling reports. After this information is extracted the
model is tested and fitted so it accurately reflects the
observed behavior.
Extrapolating the model to the exploratory well and
updating the model while drilling
The geomechanical model can be extrapolated once
the initial model is calibrated. This can be addressed
from the geomechanical and petrophysical behavior of
the rocks to be drilled, their width and their structural
Table 5. Conditions for borehole collapse on vertical wells
Case
Stress Regime
on the Wellbore Wall
Failure Conditions
1
2
3
4
5
6
Figure 6. Mudweight window
conditions on the new well. Here, the primary assump-
tion is the lithological and mechanical uniformity of the
10. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
94
formations since this allows to calculate the necessary
parameters to obtain the new model.
While drilling it is necesary to update the model.
This issue can be accomplished using drilling param-
eters, well logging, lithological description of the
rocks from cuttings and LOT/FIT performed on the
exploratory well. Once this information is recorded
the geomechanical model and its parameters can be
updated. Finally, the initial model is compared to the
updated model and the model parameters can be vali-
dated with the actual data to obtain an accurate model
that represents the drilled zone behavior.
STUDY CASE: EXPLORATORY WELL ON
MMB
The methodology presented in this paper was applied
on one exploratory well sited at MMB named Cagüi 1.
Geomechanical model building up
This exploration well is sited in the north depression
of MMB, in the surroundings to Playon town – San-
tander, Colombia. According to the geological studies
(Suárez, 1998), this sector has three structural and
stratigraphic features which are:
• Triassic-Jurassic. Constituted by Girón Formation,
this sector shows normal faulting systems enclosed
by subvertical faults.
• Cretaceous-Paleocene. It is composed by Tambor,
Rosablanca, Paja, Tablazo, Simití, La Luna, Umir
and Lisama Formations. this region is conformed
by inverse strike-slip faulting system.
• Middle Post-Eocene. The formations found in this
sector are: La Paz, Esmeralda, Mugrosa, Colorado,
Real Inferior, Medio y Superior. These formations
dip to east and present inverse faulting system
caused by Lebrija faulting system.
Correlation wells. Based on the structural and stra-
tigraphyc information the correlation wells chosen to
accomplish the geomechanical model were Puntapiedra
1 and 2 and Bosques 3. Puntapiedra 1 was chosen as
the primary correlation well since it has the largest
amount of best quality information, however due to the
final drilled depth of this well it was necesary to model
Paja and Rosablanca Formations from Bosques 3 well.
Puntapiedra 2 well was used to correlate drilling events
and validate the geomechanical model.
Lithostratigraphic description of correlation wells
(Ortega and Ramírez, 2002, Rubiano et al., 2001).
While drilling of Puntapiedra 1 well next formations
were found (from base to top): Simití, La Paz, Es-
meralda, Mugrosa, Colorado and Grupo Real. These
formations are primary shales and sandstones buried
on river channels which have certain content of calcare-
ous material.
Shale content and acoustic velocities assessment.The
Equation 6 was used to obtain shale content. After that,
the compressive acoustic velocity profile was computed.
Finally,usingthistwodatatheshearacousticvelocitywas
addressed. In Figure 7 the Vshale, Vp and Vs profiles ob-
tained for Puntapiedra 1 well are shown. From this figure
it is possible to state that velocities behavior is consistent
to shale content in rocks and its lithological features.As a
result rocks with low shale content have higher velocities
values than rocks with high shale content.
Elastic moduli, rock strength and Mohr-Coulomb
failure envelope. In order to build up the geomechanical
model it is necessary to assess the elastic rock features
in the correlation well. This can be accomplished us-
Figure 7. Puntapiedara 1 shale content, compressive seismic velocity and
shear seismic velocity logs
11. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 95
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
ing the Equations 4 and 5 and the expresions on Table
2. On the other hand to compute the Mohr-Coulomb
failure envelope and rock strength it was necessary to
know in advance the shale content and compressive and
shear acoustic velocities. Figure 8 shows the profiles
obtained for these properties. It can be observed that for
Puntapiedra 1 well the Grupo Real y Colorado forma-
tions are weaker than the other well formations, this
formations could be the most problematic ones during
drilling. It also can be seen that Mugrosa Formation
has a higher strength than the previous formations and
Esmeralda Formation has a decrease in strength as its
depth increases, in the other hand La Paz Formation
shows opposite behavior to Esmeralda Formation,
finally Simití Formation has a mixed behavior, first
it decreases it strength down to a minimum value at
about 11300 ft and then starts increasing its strength
up progressively until the end of the well.
Figure 8. Puntapiedra 1 mechancial properties logs (from left to right ucs,
cohesion, tensile strength and young moduli)
Stress field calculation. This issue was accomplished
by first calculating the overburden stress using the den-
sity log from Puntapiedra 1 well, the lithology densities
from Table 4 and Equations 1 and 7. In figure 9 the
density log (left side) and the overburden stress – right
side – for this well are presented. The densities from
the log vary between 2,45 and 2,68 gr/cc which are
tipical values for drilled formations in the well. The
overburden gradient obtained from density log varies
Figure 9. Puntapiedra 1 ROHB log (left) and overburden
stress gradient (right)
between 0,983 and 1,01 psi/ft which is also very com-
mon value for this stress magnitud.
In second instance, the minimum horizontal stress
gradient was calculated using three LOT and three FIT
from Puntapiedra 1 and Puntapiedra 2 wells. The data
obtained in these test are listed in Table 6. The value
obtained for the minimum horizontal stress gradient
varies from 0,84 psi/ft to 1,01 psi/ft.
In third place, to determine the maximum horizontal
stress magnitude the stress polygon was evaluated at
each FITfrom Puntapiedra 1 well.The results from these
calculations are shown in Table 7. It can be noticed that
the maximum horizontal stress gradient varies between
1,61 psi/ft and 1,08 psi/ft. It can be notice that for Simití
Formation (11 475 ft and 11 790 ft) the maximum stress
gradient is lower than for the Grupo Real Formation
(3000 ft), the reason for this behavior is the lower values
of tensile strength in Simití Formation.
Fourthly, the horizontal stress orientation was de-
fined based on the regional study “Levantamiento de
12. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
96
True Vertical
Depth (ft)
Mudweight (LPG) Gradient (psi/ft)
Pump Pressure
at leak off (psi)
Calculated
Pressure (psi)
Well
3000 13 0,676 2000 4028 Puntapiedra 1
11475 16 0,832 1000 10547,2 Puntapiedra 1
11790 17,9 0,931 1000 11976,5 Puntapiedra 1
3091 14,7 0,764 2361,5 Puntapiedra 2
3106 15 0,78 2422,7 Puntapiedra 2
11153 18,3 0,952 10617,7 Puntapiedra 2
Table 6. Formation tests data
Table 7. Maximum horizontal stress for Puntapiedra 1
Test Integrity 1 Integrity 2 Integrity 3
Depth (ft) 3000 11475 11790
Pore pressure gradient (psi/ft) 0,433 0,617 0,522
Pore pressure (psi) 1299 7076,6 6153,2
Minimum horizontal stress gradient (psi/ft) 0,84 0,84 0,84
Mudweight (lb/gal) 13 16 17,9
Maximum horizontal stress (psi) 4837,5 12354,8 12627,9
Maximum horizontal stress gradient (psi/ft) 1,612 1,077 1,071
Secciones Estratigráficas, Control de Cartografía Ge-
ológica y Medición de Fracturas, Pliegues y Fallas en
el Bloque Torcoroma” (Technical Report), in which the
maximum horizontal stress orientation is inferred from
natural fracture orientation.According to this study the
maximum horizontal stress orientation resulted to be
about N85°E - S85°W.
Finally, the pore pressure was calculated from the
Eaton method. Figure 10 shows the results obtained for
this property. In general, most of the correlation well
presents normal pore pressure or slightly overpres-
sured gradient (0,433 psi/ft to 0,502 psi/ft) excepting
the Simití Formation in which pore pressure gradient
goes up to 0,82 psi/ft.
Mudweight window. To model the geomechani-
cal behavior while drilling of Puntapiedra 1 well, the
software AGE was used. The results of this modeling
are shown in Figure 11. From this information it can
be stated that there was a risk during drilling due to
overpressure on the Simití formation and that mud
density necessary to prevent wellbore collapse failure
in the lower part of Real Inferior Formation was very
close to pore pressure, so it would be necessary to drill
the well with a high density mud. In fact, Puntapiedra
1 well was geomechanically stable while drilling and
the drillers used high density muds which prevent both
kickings and collpse during the drilling operations.
Geomechanical model calibration
To do the model calibration, information from the
next sources was used: well drilling reports, well tests
and experimental tests.
From experimental geomechanical data the Mohr-
Coulomb failure envelope was obtained (evaluated
at the Rosablanca formation which was the reservoir
target formation). This failure envelope was used to
calibrate geomechanical properties in the wellbore
stability model. In a related fashion, the well tests
available supply enough data to calibrate pore pressure
profile as shown in Figure 10. From this calibration the
13. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007 97
GEOMECHANICAL WELLBORE STABILITY MODELING OF EXPLORATORY WELLS
Figure 10. Puntapiedra 1 pore pressure profile
Figure 11. Puntapiedra 1 mudweight window
Eaton exponent was changed to a value of 2,0. Finally,
the drilling reports did not reference any instability
conditions while drilling so at the end of this procedure
the model was considered to fit the actual geomechanic
behavior of the correlation wells.
Extrapolation to Cagüi 1 well
The geomechanical model extrapolation to Cagüi 1
well was based on the Puntapiedra 1 well geomechani-
cal data. According to geological uncertainties it was
necessary to perform two different scenarios. In the
first one, the Paja Formation appeared overlying the
14. CT&F - Ciencia, Tecnología y Futuro - Vol. 3 Núm. 3 Dic. 2007
JENNY-MABEL CARVAJAL JIMÉNEZ et al.
98
• Theperformedapplicationdemonstratedthelinearelas-
tic theory validity for wellbore instability modeling.
• This application verifies that well logging and for-
mation tests can be used to obtain necessary data
for geomechanical formation modeling.
• It was proved that the obtained data from laboratory
tests and drilling reports can be used for wellbore
stability calibrations.
• Continuous updating of geomechanical models
leads to more accurate predictions, therefore better
models.
ACKNOWLEDGMENT
The authors are greatly indebted to the Cagüi 1
exploration well workteam (Exploration Department,
Ecopetrol S.A.), to the Geomechanical and Naturally
Fractured Reservoirs research workteam (ICP, Eco-
petrol S.A.) and to the exploratory wells supporting
technologies workteam (ICP, Ecopetrol S.A.) who
contributed to this study over an one-year period.
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100
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