SlideShare a Scribd company logo
REPUBLIQUE DU CAMEROUN
Paix- Travail-Patrie
**********
MINISTERE DE L’ENSEIGNEMENTSUPERIEUR
**********
UNIVERSITE DE MAROUA
**********
FACULTE DES MINES ET DES INDUSTRIES
PETROLIERES
**********
DEPARTEMENT D’EXPLORATION MINIERE
PETROLIERE GAZIERE ET RESOURCES EN EAU
**********
REPUBLIC OF CAMEROON
Peace-Work- Fatherland
**********
MINISTRY OF HIGHER EDUCATION
**********
UNIVERSITY OF MAROUA
**********
FACULTY OF MINES AND PETROLEUM
INDUSTRIES
**********
DEPARTMENT OF MINING PETROLEUM AND GAS
EXPLORATION
**********
Tel: +237 653397589/656862354
THEME: SAMPLING PROBLEMATIC
Année Académique 2020/2021
ENCADREUR: Dr DOMRA KANA Xavier
DONNEES GEOLOGIQUES DE FORAGE ET FLUIDES DE
FORAGE
Tel :+237 653397589/656862354
Email: imip_uma@yahoo.fr
NAMES OF PARTICIPANTS
- SIHEU BEYO CEDRIC
- SO’OH MOUKOKO
- TANYI CLEMENTINE ADAH
INTRODUCTION
Sampling is defined as taking a small portion of a whole mass that
accurately represents the whole mass. Many general petroleum
engineering texts have sections covering the measurement of phase
behavior or pressure/volume/temperature (PVT) analysis, but few have
detailed descriptions of reservoir fluid-sampling practices. Our
assignment discusses the rationale for fluid sampling, general
guidance for establishing a sampling program, and some special cases
that go beyond the typical fluid sampling approaches. Sampling
problem can be define as obtaining a sample adequate for a given
investigation.
I. Overview
Pressure-volume-temperature(PVT) analysis, of fundamental importance to reservoir management,
measurements relating to corrosion potential, solids formation, and nonhydrocarbon constituents have the
potential to produce serious effects on:
• The design of production facilities;
• Compatibility with pipeline transport;
• Product sales value;
• Refinery maintenance costs;
• Reservoir asset values in general.
Fluid samples are thus required to enable advanced physical and chemical analyses to be carried out in
specialized laboratories. Samples must be collected from a wide range of locations such as:
• Separators;
• Pipelines;
• Tanks
• Wellbores;
• The formation.
This topic primarily targets the sampling of fluids under pressures above atmospheric, where numerous tools
and procedures have been developed that are essentially specific to the petroleum industry. Best practices are
proposed for fluid sampling, reporting of data, and quality control of samples.
Figure 1 is a schematic diagram illustrating some of the most common sources of error in relation to the
collection of production samples and data in the field.
Fig. 1 – A schematic view of wellsite sampling
and measurement error
The schematic in Fig. 1 emphasizes sampling activities in cased-hole wells, but pressurized samples are
also obtained with formation-test tools in openhole wells. Here, contamination by mud filtrate or excessive
pressure decrease (drawdown) during sampling means that it may not be possible to obtain quality PVT
samples. Contamination by oil-based mud (OBM) is especially problematic. Sampling from tanks or
pipelines also requires that care be taken to ensure that the fluid is representative of the location or
condition required to be studied.
II. Importance of reservoir fluid type
One of the principal variables in reservoir-fluid sampling is the type of reservoir fluid present. This is rarely
known with certainty and, in exploration wells, may be completely unknown at the start of testing.
Determining the exact nature of a reservoir fluid is, of course, a key objective of sampling and laboratory
study. Figure 2 shows the relation between the major classes of hydrocarbon reservoir fluid in terms of a
generalized phase diagram. Although the shape of the phase diagram is specific to the actual fluid
composition, it is the reservoir temperature compared to the temperature Tc of the critical point (Tc
determines if the fluid is an oil or a gas).
When the reservoir temperature is lower than Tc, the fluid is an oil and will exhibit a bubblepoint when
pressure is reduced into the two-phase region. If the reservoir-fluid temperature is above Tc, the fluid is a gas
and will either show gas/condensate behavior and a dewpoint on pressure reduction or, if the reservoir
temperature is also above the cricondentherm Tt, the fluid will behave as a one-phase gas with no liquid
formation in the reservoir on pressure reduction. If the fluid exists in the reservoir at or close to its critical
temperature, it is classified as a critical or near-critical fluid. These fluids exhibit neither bubblepoint nor
dewpoint, but on pressure reduction into the two-phase region, they immediately form a system comprising
large proportions of both gas and liquid (e.g., 60% gas and 40% liquid by volume).
Fig. 2 – A generalized phase diagram for reservoir fluids.
The reservoir pressure determines whether the fluid is at the boundary of the two-phase region (and
referred to as saturated) or at a higher pressure than the two-phase region (and referred to as
undersaturated). Saturated fluids will immediately enter the two-phase region when a well produces fluid
because of the reduction of pressure in the well and near-wellbore region. (See phase diagrams).
III. General guidelines for a sampling program
It may then be necessary to repeat some analyses during the appraisal stage, typically when wells
will yield samples that are more representative of likely production. In contrast, sampling late in
the appraisal phase may be needed only on occasions when surface measurements indicate
unexpected fluid character.
1. Selecting sampling sites
The composition of subsurface water commonly changes laterally, as well as with depth, in the same
aquifer. Changes may be brought about by the intrusion of other waters and by discharge from and
recharge to the aquifer. Therefore, it is generally necessary to obtain and analyze many samples. Also, the
samples may change with time as gases come out of solution and supersaturated solutions produce
precipitates. Sampling sites should be selected, if possible, to fit into a comprehensive network to cover an
oil-productive geologic basin.
2. Determining measurements required
The first priority in developing a sampling program, whether extensive or limited, is to establish
exactly what measurements are required. Generally, it is advisable to plan to perform all applicable
measurements unless sufficient information is already available from earlier tests of other wells. The fact
that a measurement proves to be "normal," or an unwanted component is not detected, should not be
regarded as a waste of resources because it can still provide essential information, especially if data are
different on other wells or changes are identified during production. On-site measurements are
recommended for all reactive components because concentrations may change with time (e.g., during a
well test), and losses frequently occur during sample transport and storage.
3. Set up a suitable sampling program
Having decided which fluid measurements are required, it is necessary to set up a suitable sampling
program, taking into account the cost of the work, the quality and quantity of samples and subsequent
measurements, the urgency with which data are required, and the application of safe practices. Thus, in
the case of a well test, the overall plan should include the following:
 Establish the production potential
 Determine the permeability
 Determine the skin
 Collect fluid samples
 Each objective should be defined in sufficient detail so that all parties involved are fully aware of
their obligations, thus increasing the likelihood of achieving the objective. Objectives must be
realistic and must allow for possible changes.
 Fluid-sampling operations are often handled by service-company personnel, but because significant
variation in levels of competence exists within the industry and within service companies themselves,
themselves, it is recommended either to use specialist laboratory personnel or to supervise the
service-company operations closely.
4. Sampling overview
Surface-separator sampling is the most common technique, but the reservoir-fluid sample
recombined in the laboratory is subject to errors in the measured GOR and any imprecision
in the laboratory recombination procedure. Downhole samples (or wellhead samples) are
not affected by such inaccuracies but require the fluid to be in monophasic condition when
sampled; this can be confirmed definitively only afterward in the laboratory. Also, there is
general reluctance to attempt downhole sampling in gas/condensate reservoirs because
many are saturated, and the phases are likely to segregate in the wellbore. The ideal
situation for a laboratory is to receive both surface and downhole samples because a choice
is then available, and a good idea can be obtained of how representative the resulting fluid
is. In certain circumstances, it can be good practice to collect "backup" fluid samples at the
earliest opportunity during a production test, even if a well has not cleaned up properly.
If there is concern about whether the fluid is homogeneous in a flow line or tank, the best
approach is to take samples from different locations and compare them. In a liquid flow line, take
samples from the top and bottom; in a tank, take samples at different depths. If samples are
indeed different, it is advisable to locate a better sampling point (e.g., where there is sufficient
turbulence to homogenize the fluid). Failing this, the only solution may be to mix the samples
together in an attempt to provide a representative average fluid. If, however, the purpose of the
sampling is to study the nonhomogeneity, then separate samples should be taken accordingly.
When samples are collected from drillstem tests (DSTs), which do not involve surface
production, the limited volume of fluid produced from the reservoir may be insufficient to
remove mud filtrate or other contaminated or changed fluid. Thus, even samples collected from
the last fluid that enters the drillstem may not be truly representative. This is especially the case
for formation-water samples, which are more widely susceptible to contamination from drilling
fluids, well-completion fluids, cements, tracing fluids, and acids, which contain many different
chemicals. The most representative formation-water samples are usually those obtained after the
oil well has produced for a period of time and all extraneous fluids adjacent to the wellbore have
been flushed out.
5. Sampling procedures
Sampling procedures differ based on whether the fluids are pressurized or not. For
applicable procedures as follows;
 Downhole fluid sampling
 Surface sampling of reservoir fluids
 Nonpressurized hydrocarbon fluid sampling
 Oilfield water sampling
6. Additional considerations
 Measurements affecting reservoir fluid sampling
 Quality control during reservoir fluid sampling
 Fluid sampling safety hazards
IV. Special topics and considerations in fluid sampling
1. Sampling of crude-oil emulsions
Samples of emulsions may be required for several reasons, including
 Verifying crude specifications
 Evaluating the performance of emulsion-treating systems
 For laboratory testing such as choice of demulsifiers and optimum concentration
Emulsions frequently must be sampled under pressure, and special procedures must be
used to obtain representative samples. For crude specification testing, it is not important to
maintain the integrity of the water droplets; however, the sample location point may be critical.
In general, samples should not be withdrawn from the bottom of the pipe or vessel, where free
water may accumulate, affecting the BS&W reading and, thus, the validity of the sample. In
addition, the sample should not be withdrawn from the top of the vessel or pipe, as it is likely
to contain primarily oil. The best position in the pipe to take an emulsion sample is from the
side at approximately midheight, preferably with a sampling probe (often known as a "quill").
Choosing a sampling point at which there is turbulence and high fluid velocity in the pipe may
also avoid problems caused by segregation and ensure that the sample is homogeneous.
Also, emulsions exhibit a wide range of stability, so samples of emulsions collected in
the field may separate partially or even totally during shipment to the laboratory.
The best sampling procedure to use for samples from pressurized sources, without
further emulsification of the liquids, is the technique based on a floating-piston cylinder,
as described in Surface sampling of reservoir fluids. A setup similar to that in Figure 3 is
used, with the hydraulic section of the cylinder filled with a pressurizing fluid (e.g., a
glycol/water mixture or a synthetic oil) and the top of the cylinder evacuated. Purging of
the sample line can be made but should be carried out at a bleed rate. The sample
collection should be performed slowly to obtain the sample with a minimum pressure
drop between the cylinder and the sampling point. Alternative methods use a simple
sample cylinder (without any floating piston), which is initially filled with water (or
mercury). Once the pressurized sample is captured, the cylinder can be depressurized, if
required, by removing further quantities of hydraulic fluid extremely slowly with little
effect on the sample
In situations in which sampling into a pressurized container is not possible, the
best method to take an emulsion sample is to bleed the sample line very slowly into the
sample container. The idea is to minimize shear and reduce emulsification that may be
caused by the sampling procedures.
Fig. 3 – Diagram of a liquid-sampling apparatus.
2. Waxy and asphaltenic fluids
Great care should be taken in sampling fluids that have potential for the precipitation of wax or
asphaltenes because loss of a solid or flocculated phase during sampling or handling will produce
fluids that are no longer representative. Because these tendencies may not be recognized until the
samples are being studied, the same precautions are advisable for all fluids that have not been
characterized previously in detail.
Asphaltene problems in particular are difficult to predict owing to a poor correlation between
asphaltene concentration and flocculation tendency. Because of the difficulty of homogenizing fluids
containing flocculated asphaltenes, it is highly recommended that downhole samples be collected
using single-phase samplers with the pressure raised well above reservoir pressure by the nitrogen
charge. Separator oils and atmospheric oils generally suffer from limited asphaltene deposition
problems because they contain very few of the light hydrocarbons that contribute to flocculation.
Paraffinic or waxy crude oils can be extremely difficult to sample, with separator liquids
occasionally solidifying in sampling lines and equipment, and the use of heated, short, large-diameter
sampling lines is recommended. At downhole temperatures, sampling is generally easier, and limited
availability of heated sampling tools exists. Single-phase sampling tools can be used, especially if
asphaltene and wax problems may occur, but pressure maintenance alone will not prevent wax
precipitation on cooling, as this is strongly dependent on temperature. Though rarer, gas/condensate
reservoirs can also produce liquids that show wax-forming tendencies, which require special handling
procedures
3. On-site measurements
It is worth giving some details of common on-site measurements because they must be
performed on representative samples or sample streams and are frequently included in sampling
programs.
The most common on-site gas analysis method is the "length-of-stain" detector tubes (often
called "sniffer" tubes or Drager tubes, after one of the suppliers) used primarily for H2S but available
for CO2 and a wide range of other gases and vapors. This method is relatively simple to use, and
principal errors derive from incorrect use of response factors or stroke counts.
The ASTM has a number of standards that apply to this method, and all propose a
sampling system based on a modified polythene wash bottle (or equivalent setup) to
ensure that measurements are performed on a representative sample stream. Flexible
tubing is connected from a control valve at the sample point to the wash-bottle delivery
tube, and the screw cap is removed (or perforated). Then, the control valve is opened
slightly to allow gas to flow into the bottom of the wash bottle, which purges air out of the
top.
After purging for at least 3 minutes, the length-of-stain detector can be inserted
through the top of the wash bottle and the pump operated to perform the measurement.
This arrangement ensures that the gas sampled is at atmospheric pressure. Detector tubes
have a limited life and should not be used beyond the date limit. Care must be taken to
avoid contacting any liquids with the end of the tube. An alternative approach used a gas
bag, which must be made from an inert material and purged completely at least five times
immediately before the measurement. In some circumstances, gas concentrations above
the detector-tube limit can be estimated by using fewer or fractional pump strokes, but
such practices must be recorded clearly to help interpret measurements. For reactive
species like H2S, there is significant justification for making on-site concentration
measurements by two independent techniques, as this provides on-site quality assurance.
Portable gas chromatographs are becoming more common at the
wellsite, and they bring the advantage of early characterization of gas
composition, together with an identification of most nonhydrocarbons
present (depending on the carrier gas used). However, such instruments are
accurate only when operated by trained personnel and when properly
calibrated. Also, the additional cost of the service must be justified, though
this could occur in the following cases:
 high nitrogen or helium is anticipated,
 early decisions must be made on the basis of gas sales value,
 variable nonhydrocarbon concentrations occur within a field and will contribute to
property mapping or be used to determine if fluid sampling is required,
 sample transport logistics mean that laboratory analyses may take a very long time.
4. Drilling-mud gas
During drilling operations, returning drilling mud is commonly monitored for the
presence of hydrocarbons, both for formation-evaluation purposes and for safety concerns.
Generally, hydrocarbons are extracted from the mud to provide an air sample containing
hydrocarbons, and as the extraction technique is dependent on equipment design and
installation, measured compositions are rarely quantitatively representative of the
concentrations in the drilling mud. This limitation is commonly accounted for by the use of
hydrocarbon ratios when interpreting drilling-mud hydrocarbon analyses and logs, but it
has been shown that effective quantitative measurements can be obtained with careful
location of the mud-sampling point, the use of a special extraction device, and care to
account for losses of hydrocarbon gas from the return line before the mud-sampling point.
Mud logging is covered in detail elsewhere in this Handbook.
5. Water-cut measurements
Downhole sampling can be used as a means to measure water cut in producing oil
wells, especially when there are no separation facilities or suitable measuring
instruments at the wellsite or when measurements with depth are required as an
alternative to (or validation for) production logs. In these cases, the well should be
flowing at normal producing conditions, unless the purpose of the sampling is to
investigate the water cut at other production conditions. As in all cases in which
sampling is attempted from two-phase flow, there is the potential for preferential
collection of one of the phases; this is especially likely if the two phases are not well
distributed. It may be advisable to set the sampler to collect the sample in the shortest
time to minimize any segregation. Care also should be taken in high-angle well sections,
where the sampler will lie in the lowest part and is likely to sample water preferentially.
For a measurement of total water cut, it is advisable to sample from a depth a
moderate distance [e.g., 20 ft (6 m)] above the top of the perforated interval. Also, it is
good practice to take a number of separate samples under identical flow conditions to
allow evaluation of the repeatability of water-cut measurements. Good agreement between
replicate samples, although not absolute proof, gives high confidence in the reliability of
the measurements, whereas significant variation is a clear sign of unrepresentative
sampling or of variable water cut in the fluids entering the wellbore. Sampling from a
range of depths both above and within the perforated interval in a well can provide more-
detailed information on water production, but it does not give production-rate information
on its own.
Volumetric measurement of water cut should ideally be made on site so that repeat
measurements can be made as required. If emulsion is present in the sampled fluid, this
should be given time to break, or suitable chemicals should be used to demulsify the
sample before the definitive water-cut measurement
V. Future developments
Optimizing costs in all petroleum-industry activities continues to have a major effect on
sampling operations, with competition between production testing and formation-test-tool
operations leading to widespread industry acceptance of lower-quality fluid samples from the
latter. A key challenge at present is to get better-quality formation-test-tool samples not simply
by advanced tool capability but by better planning and preparation for the test. Increasing
efforts to obtain reservoir information from short well cleanups is also putting pressure on fluid-
sampling operations, but in some cases (such as on-site measurements), this change in
emphasis may provide opportunities for measurements that otherwise would not be available.
Multiphase metering is likely to have an increasing impact on sampling operations because
the accuracy of flow-rate measurement is seen to be improving, and the economic benefits of
avoiding the use of separators will be major. However, even with significant development of
special sampling approaches (such as isokinetic sampling), it seems unlikely that the same
quality of samples will be available as with traditional separator methods.
conclusion
Both the reservoir-fluid type and the saturation condition influence the way fluid samples
must be collected, yet this information can be estimated only at the time of the sampling
program and is especially uncertain when fluids are close to the boundaries between the
different types. Numerous correlations are available for estimating reservoir-fluid type and
condition from produced-fluid flow rates and properties measured at the wellsite (such as
those developed by Standing), but you should be careful in using these methods, especially
when the fluid properties differ significantly from those used to develop the correlation. For
this reason, it is good practice to allow for significant error in the reservoir-fluid character when
designing and implementing sampling programs. With the tremendous pace of the
development and functionality of new downhole tools, there is a need for speedy updating of
industry standards documentation to allow broad dissemination of new sampling knowledge
and practices; however, it is clear that this is not a role readily filled by traditional standards
organizations such as API. Working groups and forums involving service companies and
operators may provide the best prospect of developing standards updates, which can be
published in peer-reviewed petroleum engineering journals.
References
 Moffatt, B.J. and Williams, J.M. 1998. Identifying and Meeting the Key Needs for Reservoir
Fluid Properties A Multi-Disciplinary Approach. Presented at the SPE Annual Technical
Conference and Exhibition, New Orleans, 27-30 September. SPE-49067-MS.
http://dx.doi.org/10.2118/49067-MS
 Williams, J.M. 1998. Fluid Sampling under Adverse Conditions. Oil & Gas Science and
Technology - Rev. IFP 53 (3): 355-365. http://dx.doi.org/10.2516/ogst:1998031
 Standing, M.B. 1951. Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, 10–
19. Richardson, Texas: SPE.
 ASTM D4810-88(1999) Standard Test Method for Hydrogen Sulfide in Natural Gas Using
Length-of-Stain Detector Tubes. 1999. West Conshohocken, Pennsylvania: ASTM
International. http://dx.doi.org/10.1520/D4810-88R99
 ASTM D4984-89(1999) Standard Test Method for Carbon Dioxide in Natural Gas Using
Length-of-Stain Detector Tubes. 1999. West Conshohocken, Pennsylvania: ASTM
International. http://dx.doi.org/10.1520/D4984-89R99

More Related Content

Similar to TPE DRILLING.pptx

Water sampling methods and tools
Water sampling methods and toolsWater sampling methods and tools
Water sampling methods and tools
Praveen Kumar Singh
 
IMWA2013_Swanson_511
IMWA2013_Swanson_511IMWA2013_Swanson_511
IMWA2013_Swanson_511
Eric Swanson
 
361
361361
361
361361
Amb 017
Amb 017Amb 017
Amb 017
FreddyMotta2
 
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
Mohanned Mahjoup
 
registro de pozoz
registro de pozozregistro de pozoz
registro de pozoz
opulento22
 
SPE-942221-G-P.pdf
SPE-942221-G-P.pdfSPE-942221-G-P.pdf
SPE-942221-G-P.pdf
AdianAndrews1
 
Porosity by saturation method
Porosity by saturation methodPorosity by saturation method
Porosity by saturation method
Kamal Abdurahman
 
HPTLC method development.pptx
HPTLC method development.pptxHPTLC method development.pptx
HPTLC method development.pptx
SunaynaChoudhary
 
ReverseOsmosisLabReport
ReverseOsmosisLabReportReverseOsmosisLabReport
ReverseOsmosisLabReport
Janet Mok
 
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas DrillingRecommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
Marcellus Drilling News
 
SPE_97314HPWBM
SPE_97314HPWBMSPE_97314HPWBM
SPE_97314HPWBM
Abdelkhalek Gomaa
 
Slug Test Procedures
Slug Test ProceduresSlug Test Procedures
Slug Test Procedures
tpttk
 
1st poster example of core analysis program
1st poster example of core analysis program1st poster example of core analysis program
1st poster example of core analysis program
Dr. Arzu Javadova
 
Intern Report
Intern ReportIntern Report
Intern Report
Akshay Gupta
 
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
Uchenna Odi, PhD, MBA
 
Flow assurance
Flow assuranceFlow assurance
Flow assurance
Katherine Prada
 
GC introduction and instrumentation part
GC introduction and instrumentation partGC introduction and instrumentation part
GC introduction and instrumentation part
nivedithag131
 
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
PerkinElmer, Inc.
 

Similar to TPE DRILLING.pptx (20)

Water sampling methods and tools
Water sampling methods and toolsWater sampling methods and tools
Water sampling methods and tools
 
IMWA2013_Swanson_511
IMWA2013_Swanson_511IMWA2013_Swanson_511
IMWA2013_Swanson_511
 
361
361361
361
 
361
361361
361
 
Amb 017
Amb 017Amb 017
Amb 017
 
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
UntitledExcessive Water Production Diagnostic and Control - Case Study Jake O...
 
registro de pozoz
registro de pozozregistro de pozoz
registro de pozoz
 
SPE-942221-G-P.pdf
SPE-942221-G-P.pdfSPE-942221-G-P.pdf
SPE-942221-G-P.pdf
 
Porosity by saturation method
Porosity by saturation methodPorosity by saturation method
Porosity by saturation method
 
HPTLC method development.pptx
HPTLC method development.pptxHPTLC method development.pptx
HPTLC method development.pptx
 
ReverseOsmosisLabReport
ReverseOsmosisLabReportReverseOsmosisLabReport
ReverseOsmosisLabReport
 
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas DrillingRecommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
Recommended Practices for Pre-Drill Water Supply Surveys in Shale Gas Drilling
 
SPE_97314HPWBM
SPE_97314HPWBMSPE_97314HPWBM
SPE_97314HPWBM
 
Slug Test Procedures
Slug Test ProceduresSlug Test Procedures
Slug Test Procedures
 
1st poster example of core analysis program
1st poster example of core analysis program1st poster example of core analysis program
1st poster example of core analysis program
 
Intern Report
Intern ReportIntern Report
Intern Report
 
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
Peer Reviewed CETI 14-045: Experimental Investigation of Wet Gas Dew Point Pr...
 
Flow assurance
Flow assuranceFlow assurance
Flow assurance
 
GC introduction and instrumentation part
GC introduction and instrumentation partGC introduction and instrumentation part
GC introduction and instrumentation part
 
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
Analysis of Volatile Organic Compounds (VOCs) in Air Using US EPA Method TO-17
 

Recently uploaded

一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
upoux
 
Presentation on Food Delivery Systems
Presentation on Food Delivery SystemsPresentation on Food Delivery Systems
Presentation on Food Delivery Systems
Abdullah Al Noman
 
Supermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdfSupermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdf
Kamal Acharya
 
Introduction to Computer Networks & OSI MODEL.ppt
Introduction to Computer Networks & OSI MODEL.pptIntroduction to Computer Networks & OSI MODEL.ppt
Introduction to Computer Networks & OSI MODEL.ppt
Dwarkadas J Sanghvi College of Engineering
 
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
PriyankaKilaniya
 
Blood finder application project report (1).pdf
Blood finder application project report (1).pdfBlood finder application project report (1).pdf
Blood finder application project report (1).pdf
Kamal Acharya
 
Butterfly Valves Manufacturer (LBF Series).pdf
Butterfly Valves Manufacturer (LBF Series).pdfButterfly Valves Manufacturer (LBF Series).pdf
Butterfly Valves Manufacturer (LBF Series).pdf
Lubi Valves
 
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptxEV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
nikshimanasa
 
Height and depth gauge linear metrology.pdf
Height and depth gauge linear metrology.pdfHeight and depth gauge linear metrology.pdf
Height and depth gauge linear metrology.pdf
q30122000
 
Object Oriented Analysis and Design - OOAD
Object Oriented Analysis and Design - OOADObject Oriented Analysis and Design - OOAD
Object Oriented Analysis and Design - OOAD
PreethaV16
 
Digital Image Processing Unit -2 Notes complete
Digital Image Processing Unit -2 Notes completeDigital Image Processing Unit -2 Notes complete
Digital Image Processing Unit -2 Notes complete
shubhamsaraswat8740
 
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
upoux
 
Open Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surfaceOpen Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surface
Indrajeet sahu
 
Assistant Engineer (Chemical) Interview Questions.pdf
Assistant Engineer (Chemical) Interview Questions.pdfAssistant Engineer (Chemical) Interview Questions.pdf
Assistant Engineer (Chemical) Interview Questions.pdf
Seetal Daas
 
Applications of artificial Intelligence in Mechanical Engineering.pdf
Applications of artificial Intelligence in Mechanical Engineering.pdfApplications of artificial Intelligence in Mechanical Engineering.pdf
Applications of artificial Intelligence in Mechanical Engineering.pdf
Atif Razi
 
Sri Guru Hargobind Ji - Bandi Chor Guru.pdf
Sri Guru Hargobind Ji - Bandi Chor Guru.pdfSri Guru Hargobind Ji - Bandi Chor Guru.pdf
Sri Guru Hargobind Ji - Bandi Chor Guru.pdf
Balvir Singh
 
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICSUNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
vmspraneeth
 
AI in customer support Use cases solutions development and implementation.pdf
AI in customer support Use cases solutions development and implementation.pdfAI in customer support Use cases solutions development and implementation.pdf
AI in customer support Use cases solutions development and implementation.pdf
mahaffeycheryld
 
Ericsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.pptEricsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.ppt
wafawafa52
 
SENTIMENT ANALYSIS ON PPT AND Project template_.pptx
SENTIMENT ANALYSIS ON PPT AND Project template_.pptxSENTIMENT ANALYSIS ON PPT AND Project template_.pptx
SENTIMENT ANALYSIS ON PPT AND Project template_.pptx
b0754201
 

Recently uploaded (20)

一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
一比一原版(osu毕业证书)美国俄勒冈州立大学毕业证如何办理
 
Presentation on Food Delivery Systems
Presentation on Food Delivery SystemsPresentation on Food Delivery Systems
Presentation on Food Delivery Systems
 
Supermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdfSupermarket Management System Project Report.pdf
Supermarket Management System Project Report.pdf
 
Introduction to Computer Networks & OSI MODEL.ppt
Introduction to Computer Networks & OSI MODEL.pptIntroduction to Computer Networks & OSI MODEL.ppt
Introduction to Computer Networks & OSI MODEL.ppt
 
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...
 
Blood finder application project report (1).pdf
Blood finder application project report (1).pdfBlood finder application project report (1).pdf
Blood finder application project report (1).pdf
 
Butterfly Valves Manufacturer (LBF Series).pdf
Butterfly Valves Manufacturer (LBF Series).pdfButterfly Valves Manufacturer (LBF Series).pdf
Butterfly Valves Manufacturer (LBF Series).pdf
 
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptxEV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
EV BMS WITH CHARGE MONITOR AND FIRE DETECTION.pptx
 
Height and depth gauge linear metrology.pdf
Height and depth gauge linear metrology.pdfHeight and depth gauge linear metrology.pdf
Height and depth gauge linear metrology.pdf
 
Object Oriented Analysis and Design - OOAD
Object Oriented Analysis and Design - OOADObject Oriented Analysis and Design - OOAD
Object Oriented Analysis and Design - OOAD
 
Digital Image Processing Unit -2 Notes complete
Digital Image Processing Unit -2 Notes completeDigital Image Processing Unit -2 Notes complete
Digital Image Processing Unit -2 Notes complete
 
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
一比一原版(uofo毕业证书)美国俄勒冈大学毕业证如何办理
 
Open Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surfaceOpen Channel Flow: fluid flow with a free surface
Open Channel Flow: fluid flow with a free surface
 
Assistant Engineer (Chemical) Interview Questions.pdf
Assistant Engineer (Chemical) Interview Questions.pdfAssistant Engineer (Chemical) Interview Questions.pdf
Assistant Engineer (Chemical) Interview Questions.pdf
 
Applications of artificial Intelligence in Mechanical Engineering.pdf
Applications of artificial Intelligence in Mechanical Engineering.pdfApplications of artificial Intelligence in Mechanical Engineering.pdf
Applications of artificial Intelligence in Mechanical Engineering.pdf
 
Sri Guru Hargobind Ji - Bandi Chor Guru.pdf
Sri Guru Hargobind Ji - Bandi Chor Guru.pdfSri Guru Hargobind Ji - Bandi Chor Guru.pdf
Sri Guru Hargobind Ji - Bandi Chor Guru.pdf
 
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICSUNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
UNIT 4 LINEAR INTEGRATED CIRCUITS-DIGITAL ICS
 
AI in customer support Use cases solutions development and implementation.pdf
AI in customer support Use cases solutions development and implementation.pdfAI in customer support Use cases solutions development and implementation.pdf
AI in customer support Use cases solutions development and implementation.pdf
 
Ericsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.pptEricsson LTE Throughput Troubleshooting Techniques.ppt
Ericsson LTE Throughput Troubleshooting Techniques.ppt
 
SENTIMENT ANALYSIS ON PPT AND Project template_.pptx
SENTIMENT ANALYSIS ON PPT AND Project template_.pptxSENTIMENT ANALYSIS ON PPT AND Project template_.pptx
SENTIMENT ANALYSIS ON PPT AND Project template_.pptx
 

TPE DRILLING.pptx

  • 1. REPUBLIQUE DU CAMEROUN Paix- Travail-Patrie ********** MINISTERE DE L’ENSEIGNEMENTSUPERIEUR ********** UNIVERSITE DE MAROUA ********** FACULTE DES MINES ET DES INDUSTRIES PETROLIERES ********** DEPARTEMENT D’EXPLORATION MINIERE PETROLIERE GAZIERE ET RESOURCES EN EAU ********** REPUBLIC OF CAMEROON Peace-Work- Fatherland ********** MINISTRY OF HIGHER EDUCATION ********** UNIVERSITY OF MAROUA ********** FACULTY OF MINES AND PETROLEUM INDUSTRIES ********** DEPARTMENT OF MINING PETROLEUM AND GAS EXPLORATION ********** Tel: +237 653397589/656862354 THEME: SAMPLING PROBLEMATIC Année Académique 2020/2021 ENCADREUR: Dr DOMRA KANA Xavier DONNEES GEOLOGIQUES DE FORAGE ET FLUIDES DE FORAGE Tel :+237 653397589/656862354 Email: imip_uma@yahoo.fr NAMES OF PARTICIPANTS - SIHEU BEYO CEDRIC - SO’OH MOUKOKO - TANYI CLEMENTINE ADAH
  • 2. INTRODUCTION Sampling is defined as taking a small portion of a whole mass that accurately represents the whole mass. Many general petroleum engineering texts have sections covering the measurement of phase behavior or pressure/volume/temperature (PVT) analysis, but few have detailed descriptions of reservoir fluid-sampling practices. Our assignment discusses the rationale for fluid sampling, general guidance for establishing a sampling program, and some special cases that go beyond the typical fluid sampling approaches. Sampling problem can be define as obtaining a sample adequate for a given investigation.
  • 3. I. Overview Pressure-volume-temperature(PVT) analysis, of fundamental importance to reservoir management, measurements relating to corrosion potential, solids formation, and nonhydrocarbon constituents have the potential to produce serious effects on: • The design of production facilities; • Compatibility with pipeline transport; • Product sales value; • Refinery maintenance costs; • Reservoir asset values in general. Fluid samples are thus required to enable advanced physical and chemical analyses to be carried out in specialized laboratories. Samples must be collected from a wide range of locations such as: • Separators; • Pipelines; • Tanks • Wellbores; • The formation.
  • 4. This topic primarily targets the sampling of fluids under pressures above atmospheric, where numerous tools and procedures have been developed that are essentially specific to the petroleum industry. Best practices are proposed for fluid sampling, reporting of data, and quality control of samples. Figure 1 is a schematic diagram illustrating some of the most common sources of error in relation to the collection of production samples and data in the field. Fig. 1 – A schematic view of wellsite sampling and measurement error
  • 5. The schematic in Fig. 1 emphasizes sampling activities in cased-hole wells, but pressurized samples are also obtained with formation-test tools in openhole wells. Here, contamination by mud filtrate or excessive pressure decrease (drawdown) during sampling means that it may not be possible to obtain quality PVT samples. Contamination by oil-based mud (OBM) is especially problematic. Sampling from tanks or pipelines also requires that care be taken to ensure that the fluid is representative of the location or condition required to be studied. II. Importance of reservoir fluid type One of the principal variables in reservoir-fluid sampling is the type of reservoir fluid present. This is rarely known with certainty and, in exploration wells, may be completely unknown at the start of testing. Determining the exact nature of a reservoir fluid is, of course, a key objective of sampling and laboratory study. Figure 2 shows the relation between the major classes of hydrocarbon reservoir fluid in terms of a generalized phase diagram. Although the shape of the phase diagram is specific to the actual fluid composition, it is the reservoir temperature compared to the temperature Tc of the critical point (Tc determines if the fluid is an oil or a gas).
  • 6. When the reservoir temperature is lower than Tc, the fluid is an oil and will exhibit a bubblepoint when pressure is reduced into the two-phase region. If the reservoir-fluid temperature is above Tc, the fluid is a gas and will either show gas/condensate behavior and a dewpoint on pressure reduction or, if the reservoir temperature is also above the cricondentherm Tt, the fluid will behave as a one-phase gas with no liquid formation in the reservoir on pressure reduction. If the fluid exists in the reservoir at or close to its critical temperature, it is classified as a critical or near-critical fluid. These fluids exhibit neither bubblepoint nor dewpoint, but on pressure reduction into the two-phase region, they immediately form a system comprising large proportions of both gas and liquid (e.g., 60% gas and 40% liquid by volume). Fig. 2 – A generalized phase diagram for reservoir fluids.
  • 7. The reservoir pressure determines whether the fluid is at the boundary of the two-phase region (and referred to as saturated) or at a higher pressure than the two-phase region (and referred to as undersaturated). Saturated fluids will immediately enter the two-phase region when a well produces fluid because of the reduction of pressure in the well and near-wellbore region. (See phase diagrams). III. General guidelines for a sampling program It may then be necessary to repeat some analyses during the appraisal stage, typically when wells will yield samples that are more representative of likely production. In contrast, sampling late in the appraisal phase may be needed only on occasions when surface measurements indicate unexpected fluid character.
  • 8. 1. Selecting sampling sites The composition of subsurface water commonly changes laterally, as well as with depth, in the same aquifer. Changes may be brought about by the intrusion of other waters and by discharge from and recharge to the aquifer. Therefore, it is generally necessary to obtain and analyze many samples. Also, the samples may change with time as gases come out of solution and supersaturated solutions produce precipitates. Sampling sites should be selected, if possible, to fit into a comprehensive network to cover an oil-productive geologic basin. 2. Determining measurements required The first priority in developing a sampling program, whether extensive or limited, is to establish exactly what measurements are required. Generally, it is advisable to plan to perform all applicable measurements unless sufficient information is already available from earlier tests of other wells. The fact that a measurement proves to be "normal," or an unwanted component is not detected, should not be regarded as a waste of resources because it can still provide essential information, especially if data are different on other wells or changes are identified during production. On-site measurements are recommended for all reactive components because concentrations may change with time (e.g., during a well test), and losses frequently occur during sample transport and storage.
  • 9. 3. Set up a suitable sampling program Having decided which fluid measurements are required, it is necessary to set up a suitable sampling program, taking into account the cost of the work, the quality and quantity of samples and subsequent measurements, the urgency with which data are required, and the application of safe practices. Thus, in the case of a well test, the overall plan should include the following:  Establish the production potential  Determine the permeability  Determine the skin  Collect fluid samples  Each objective should be defined in sufficient detail so that all parties involved are fully aware of their obligations, thus increasing the likelihood of achieving the objective. Objectives must be realistic and must allow for possible changes.  Fluid-sampling operations are often handled by service-company personnel, but because significant variation in levels of competence exists within the industry and within service companies themselves, themselves, it is recommended either to use specialist laboratory personnel or to supervise the service-company operations closely.
  • 10. 4. Sampling overview Surface-separator sampling is the most common technique, but the reservoir-fluid sample recombined in the laboratory is subject to errors in the measured GOR and any imprecision in the laboratory recombination procedure. Downhole samples (or wellhead samples) are not affected by such inaccuracies but require the fluid to be in monophasic condition when sampled; this can be confirmed definitively only afterward in the laboratory. Also, there is general reluctance to attempt downhole sampling in gas/condensate reservoirs because many are saturated, and the phases are likely to segregate in the wellbore. The ideal situation for a laboratory is to receive both surface and downhole samples because a choice is then available, and a good idea can be obtained of how representative the resulting fluid is. In certain circumstances, it can be good practice to collect "backup" fluid samples at the earliest opportunity during a production test, even if a well has not cleaned up properly.
  • 11. If there is concern about whether the fluid is homogeneous in a flow line or tank, the best approach is to take samples from different locations and compare them. In a liquid flow line, take samples from the top and bottom; in a tank, take samples at different depths. If samples are indeed different, it is advisable to locate a better sampling point (e.g., where there is sufficient turbulence to homogenize the fluid). Failing this, the only solution may be to mix the samples together in an attempt to provide a representative average fluid. If, however, the purpose of the sampling is to study the nonhomogeneity, then separate samples should be taken accordingly. When samples are collected from drillstem tests (DSTs), which do not involve surface production, the limited volume of fluid produced from the reservoir may be insufficient to remove mud filtrate or other contaminated or changed fluid. Thus, even samples collected from the last fluid that enters the drillstem may not be truly representative. This is especially the case for formation-water samples, which are more widely susceptible to contamination from drilling fluids, well-completion fluids, cements, tracing fluids, and acids, which contain many different chemicals. The most representative formation-water samples are usually those obtained after the oil well has produced for a period of time and all extraneous fluids adjacent to the wellbore have been flushed out.
  • 12. 5. Sampling procedures Sampling procedures differ based on whether the fluids are pressurized or not. For applicable procedures as follows;  Downhole fluid sampling  Surface sampling of reservoir fluids  Nonpressurized hydrocarbon fluid sampling  Oilfield water sampling 6. Additional considerations  Measurements affecting reservoir fluid sampling  Quality control during reservoir fluid sampling  Fluid sampling safety hazards
  • 13. IV. Special topics and considerations in fluid sampling 1. Sampling of crude-oil emulsions Samples of emulsions may be required for several reasons, including  Verifying crude specifications  Evaluating the performance of emulsion-treating systems  For laboratory testing such as choice of demulsifiers and optimum concentration Emulsions frequently must be sampled under pressure, and special procedures must be used to obtain representative samples. For crude specification testing, it is not important to maintain the integrity of the water droplets; however, the sample location point may be critical. In general, samples should not be withdrawn from the bottom of the pipe or vessel, where free water may accumulate, affecting the BS&W reading and, thus, the validity of the sample. In addition, the sample should not be withdrawn from the top of the vessel or pipe, as it is likely to contain primarily oil. The best position in the pipe to take an emulsion sample is from the side at approximately midheight, preferably with a sampling probe (often known as a "quill"). Choosing a sampling point at which there is turbulence and high fluid velocity in the pipe may also avoid problems caused by segregation and ensure that the sample is homogeneous.
  • 14. Also, emulsions exhibit a wide range of stability, so samples of emulsions collected in the field may separate partially or even totally during shipment to the laboratory. The best sampling procedure to use for samples from pressurized sources, without further emulsification of the liquids, is the technique based on a floating-piston cylinder, as described in Surface sampling of reservoir fluids. A setup similar to that in Figure 3 is used, with the hydraulic section of the cylinder filled with a pressurizing fluid (e.g., a glycol/water mixture or a synthetic oil) and the top of the cylinder evacuated. Purging of the sample line can be made but should be carried out at a bleed rate. The sample collection should be performed slowly to obtain the sample with a minimum pressure drop between the cylinder and the sampling point. Alternative methods use a simple sample cylinder (without any floating piston), which is initially filled with water (or mercury). Once the pressurized sample is captured, the cylinder can be depressurized, if required, by removing further quantities of hydraulic fluid extremely slowly with little effect on the sample
  • 15. In situations in which sampling into a pressurized container is not possible, the best method to take an emulsion sample is to bleed the sample line very slowly into the sample container. The idea is to minimize shear and reduce emulsification that may be caused by the sampling procedures. Fig. 3 – Diagram of a liquid-sampling apparatus.
  • 16. 2. Waxy and asphaltenic fluids Great care should be taken in sampling fluids that have potential for the precipitation of wax or asphaltenes because loss of a solid or flocculated phase during sampling or handling will produce fluids that are no longer representative. Because these tendencies may not be recognized until the samples are being studied, the same precautions are advisable for all fluids that have not been characterized previously in detail. Asphaltene problems in particular are difficult to predict owing to a poor correlation between asphaltene concentration and flocculation tendency. Because of the difficulty of homogenizing fluids containing flocculated asphaltenes, it is highly recommended that downhole samples be collected using single-phase samplers with the pressure raised well above reservoir pressure by the nitrogen charge. Separator oils and atmospheric oils generally suffer from limited asphaltene deposition problems because they contain very few of the light hydrocarbons that contribute to flocculation.
  • 17. Paraffinic or waxy crude oils can be extremely difficult to sample, with separator liquids occasionally solidifying in sampling lines and equipment, and the use of heated, short, large-diameter sampling lines is recommended. At downhole temperatures, sampling is generally easier, and limited availability of heated sampling tools exists. Single-phase sampling tools can be used, especially if asphaltene and wax problems may occur, but pressure maintenance alone will not prevent wax precipitation on cooling, as this is strongly dependent on temperature. Though rarer, gas/condensate reservoirs can also produce liquids that show wax-forming tendencies, which require special handling procedures 3. On-site measurements It is worth giving some details of common on-site measurements because they must be performed on representative samples or sample streams and are frequently included in sampling programs. The most common on-site gas analysis method is the "length-of-stain" detector tubes (often called "sniffer" tubes or Drager tubes, after one of the suppliers) used primarily for H2S but available for CO2 and a wide range of other gases and vapors. This method is relatively simple to use, and principal errors derive from incorrect use of response factors or stroke counts.
  • 18. The ASTM has a number of standards that apply to this method, and all propose a sampling system based on a modified polythene wash bottle (or equivalent setup) to ensure that measurements are performed on a representative sample stream. Flexible tubing is connected from a control valve at the sample point to the wash-bottle delivery tube, and the screw cap is removed (or perforated). Then, the control valve is opened slightly to allow gas to flow into the bottom of the wash bottle, which purges air out of the top. After purging for at least 3 minutes, the length-of-stain detector can be inserted through the top of the wash bottle and the pump operated to perform the measurement. This arrangement ensures that the gas sampled is at atmospheric pressure. Detector tubes have a limited life and should not be used beyond the date limit. Care must be taken to avoid contacting any liquids with the end of the tube. An alternative approach used a gas bag, which must be made from an inert material and purged completely at least five times immediately before the measurement. In some circumstances, gas concentrations above the detector-tube limit can be estimated by using fewer or fractional pump strokes, but such practices must be recorded clearly to help interpret measurements. For reactive species like H2S, there is significant justification for making on-site concentration measurements by two independent techniques, as this provides on-site quality assurance.
  • 19. Portable gas chromatographs are becoming more common at the wellsite, and they bring the advantage of early characterization of gas composition, together with an identification of most nonhydrocarbons present (depending on the carrier gas used). However, such instruments are accurate only when operated by trained personnel and when properly calibrated. Also, the additional cost of the service must be justified, though this could occur in the following cases:  high nitrogen or helium is anticipated,  early decisions must be made on the basis of gas sales value,  variable nonhydrocarbon concentrations occur within a field and will contribute to property mapping or be used to determine if fluid sampling is required,  sample transport logistics mean that laboratory analyses may take a very long time.
  • 20. 4. Drilling-mud gas During drilling operations, returning drilling mud is commonly monitored for the presence of hydrocarbons, both for formation-evaluation purposes and for safety concerns. Generally, hydrocarbons are extracted from the mud to provide an air sample containing hydrocarbons, and as the extraction technique is dependent on equipment design and installation, measured compositions are rarely quantitatively representative of the concentrations in the drilling mud. This limitation is commonly accounted for by the use of hydrocarbon ratios when interpreting drilling-mud hydrocarbon analyses and logs, but it has been shown that effective quantitative measurements can be obtained with careful location of the mud-sampling point, the use of a special extraction device, and care to account for losses of hydrocarbon gas from the return line before the mud-sampling point. Mud logging is covered in detail elsewhere in this Handbook.
  • 21. 5. Water-cut measurements Downhole sampling can be used as a means to measure water cut in producing oil wells, especially when there are no separation facilities or suitable measuring instruments at the wellsite or when measurements with depth are required as an alternative to (or validation for) production logs. In these cases, the well should be flowing at normal producing conditions, unless the purpose of the sampling is to investigate the water cut at other production conditions. As in all cases in which sampling is attempted from two-phase flow, there is the potential for preferential collection of one of the phases; this is especially likely if the two phases are not well distributed. It may be advisable to set the sampler to collect the sample in the shortest time to minimize any segregation. Care also should be taken in high-angle well sections, where the sampler will lie in the lowest part and is likely to sample water preferentially.
  • 22. For a measurement of total water cut, it is advisable to sample from a depth a moderate distance [e.g., 20 ft (6 m)] above the top of the perforated interval. Also, it is good practice to take a number of separate samples under identical flow conditions to allow evaluation of the repeatability of water-cut measurements. Good agreement between replicate samples, although not absolute proof, gives high confidence in the reliability of the measurements, whereas significant variation is a clear sign of unrepresentative sampling or of variable water cut in the fluids entering the wellbore. Sampling from a range of depths both above and within the perforated interval in a well can provide more- detailed information on water production, but it does not give production-rate information on its own. Volumetric measurement of water cut should ideally be made on site so that repeat measurements can be made as required. If emulsion is present in the sampled fluid, this should be given time to break, or suitable chemicals should be used to demulsify the sample before the definitive water-cut measurement
  • 23. V. Future developments Optimizing costs in all petroleum-industry activities continues to have a major effect on sampling operations, with competition between production testing and formation-test-tool operations leading to widespread industry acceptance of lower-quality fluid samples from the latter. A key challenge at present is to get better-quality formation-test-tool samples not simply by advanced tool capability but by better planning and preparation for the test. Increasing efforts to obtain reservoir information from short well cleanups is also putting pressure on fluid- sampling operations, but in some cases (such as on-site measurements), this change in emphasis may provide opportunities for measurements that otherwise would not be available. Multiphase metering is likely to have an increasing impact on sampling operations because the accuracy of flow-rate measurement is seen to be improving, and the economic benefits of avoiding the use of separators will be major. However, even with significant development of special sampling approaches (such as isokinetic sampling), it seems unlikely that the same quality of samples will be available as with traditional separator methods.
  • 24. conclusion Both the reservoir-fluid type and the saturation condition influence the way fluid samples must be collected, yet this information can be estimated only at the time of the sampling program and is especially uncertain when fluids are close to the boundaries between the different types. Numerous correlations are available for estimating reservoir-fluid type and condition from produced-fluid flow rates and properties measured at the wellsite (such as those developed by Standing), but you should be careful in using these methods, especially when the fluid properties differ significantly from those used to develop the correlation. For this reason, it is good practice to allow for significant error in the reservoir-fluid character when designing and implementing sampling programs. With the tremendous pace of the development and functionality of new downhole tools, there is a need for speedy updating of industry standards documentation to allow broad dissemination of new sampling knowledge and practices; however, it is clear that this is not a role readily filled by traditional standards organizations such as API. Working groups and forums involving service companies and operators may provide the best prospect of developing standards updates, which can be published in peer-reviewed petroleum engineering journals.
  • 25. References  Moffatt, B.J. and Williams, J.M. 1998. Identifying and Meeting the Key Needs for Reservoir Fluid Properties A Multi-Disciplinary Approach. Presented at the SPE Annual Technical Conference and Exhibition, New Orleans, 27-30 September. SPE-49067-MS. http://dx.doi.org/10.2118/49067-MS  Williams, J.M. 1998. Fluid Sampling under Adverse Conditions. Oil & Gas Science and Technology - Rev. IFP 53 (3): 355-365. http://dx.doi.org/10.2516/ogst:1998031  Standing, M.B. 1951. Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, 10– 19. Richardson, Texas: SPE.  ASTM D4810-88(1999) Standard Test Method for Hydrogen Sulfide in Natural Gas Using Length-of-Stain Detector Tubes. 1999. West Conshohocken, Pennsylvania: ASTM International. http://dx.doi.org/10.1520/D4810-88R99  ASTM D4984-89(1999) Standard Test Method for Carbon Dioxide in Natural Gas Using Length-of-Stain Detector Tubes. 1999. West Conshohocken, Pennsylvania: ASTM International. http://dx.doi.org/10.1520/D4984-89R99