The sandstones of the Permo-Carboniferous Shajara Formation form the main part of the Unayzah Reservoir in the Greater Arabian Basin. It is divided into three reservoirs, namely from base to top Lower, Middle, and Upper Shajara reservoirs. Mercury intrusion technique was carried out on representative sandstone samples collected from the type section and the three reservoirs are generally characterized as heterogeneous megaporous reservoirs. The best reservoir quality is assigned to the lower sand unit of the Lower Shajara followed by the Middle Shajara Reservoir. One sample collected from the upper part of the Lower Shajara was described as low quality due to its fine grain characteristic and its proximity to the unconformity surface. Reservoir quality is controlled to a large extent by the depositional facies and specifically by rock texture illustrated by petrophysical description. The quality of the three reservoirs of the Shajara Formation, increases with the increase of grain size and grain sorting.
Keywords Shajara Reservoirs Shajara Formation Unayzah Group Pore size distribution
The document summarizes research on the petrophysical properties of different formations in the Indus Basin. It discusses five research papers that analyzed porosity and permeability in formations like the Khewra Sandstone, Warchha Sandstone, Habib Rahi Limestone, Sui Main Limestone, and Wargal Limestone. The results found that the Warchha Sandstone had very high porosity ranging from 26.75-34.5%, while the Habib Rahi Limestone had very low porosity of 0.21%. Porosity in the Wargal Limestone ranged from 0.483-23.547% depending on the location. The document concludes by evaluating the petrophysical properties of reservoirs
Hydrocarbon prospects of punjab platform pakistan, with specialTahir Aziz
The document summarizes the hydrocarbon prospects of the Punjab Platform in Pakistan, with reference to the adjacent Bikaner-Nagaur Basin in India. Geoscientific data indicates the region has undergone tectonic activity and deposition conducive to hydrocarbon generation and accumulation from the Infra-Cambrian to Tertiary periods. Source rocks identified in various formations range from poor to good potential. Multiple trap types have been identified including fault blocks, stratigraphic traps, and salt-induced structures. Hydrocarbons have been found in Infra-Cambrian reservoirs that extend from India into the Punjab Platform.
This document provides information about the reservoir, source, and seal rocks of the Lower Indus Basin in Pakistan. The main reservoir rocks identified are the Pab Sandstone, Ranikot Sandstone, and limestones in the Kirthar and Ghazij Formations. The primary source rock is the Lower Cretaceous Sembar Formation shale, but other potential sources are also identified. Thick shale units in the Paleocene and Eocene successions serve as the main regional seals in the area.
Bombay High is an offshore oilfield located 160 km off the coast of Mumbai, India. It was discovered in 1964-1967 and is operated by ONGC. It supplied 14% of India's oil needs and accounted for 38% of domestic production until 2004. The field is located in the Bombay offshore basin and produces from limestone reservoirs of Miocene age. It has produced over 2 billion barrels of oil and 3 trillion cubic feet of gas to date. A major fire in 2005 destroyed the Mumbai High North platform, costing $1.2 billion to rebuild. ONGC continues exploration and production activities in the area through seismic surveys.
The Cambay Basin is an intracratonic rift graben located in northwest India that began forming following the Deccan Traps volcanic event in the late Cretaceous. The basin is filled with up to 8km of Tertiary sedimentary rocks. Major source rocks include the thick Cambay Shale deposited in the early Eocene during a transgression. Hydrocarbon reservoirs are found in the Olpad Formation, Hazad delta sands, and Miocene formations. Multiple petroleum plays exist, including those in the Paleocene-early Eocene, middle Eocene, and late Eocene-Oligocene sequences. The Cambay Shale is a prolific source of oil and gas in the
This technical paper provides an overview of the major sedimentary basins in India that contain hydrocarbon reserves. It divides the basins into four categories based on the status of hydrocarbon exploration and production. The key basins discussed in detail include the Assam Shelf Basin, Cambay Basin, Bombay Offshore Basin, and Krishna-Godavari Basin. For each basin, it summarizes the geological setting, stratigraphy, hydrocarbon source rocks and reservoir rocks. The paper provides a high-level technical summary of India's major sedimentary basins with proven oil and gas reserves.
This document provides an overview of advances in fan delta sedimentology. It discusses classifications of fan deltas and alluvial deltas. It reviews several fan delta depositional models proposed based on studies of modern and ancient examples, including subaqueous fan delta models, Gilbert-type fan delta models, and models affected by volcanism or glaciation. It also discusses research methods for studying fan delta sedimentology, such as flume experiments, ground penetrating radar, and computer simulations. In summary, the document reviews developments in understanding fan delta classifications, depositional environments, and research approaches.
The document summarizes research on the petrophysical properties of different formations in the Indus Basin. It discusses five research papers that analyzed porosity and permeability in formations like the Khewra Sandstone, Warchha Sandstone, Habib Rahi Limestone, Sui Main Limestone, and Wargal Limestone. The results found that the Warchha Sandstone had very high porosity ranging from 26.75-34.5%, while the Habib Rahi Limestone had very low porosity of 0.21%. Porosity in the Wargal Limestone ranged from 0.483-23.547% depending on the location. The document concludes by evaluating the petrophysical properties of reservoirs
Hydrocarbon prospects of punjab platform pakistan, with specialTahir Aziz
The document summarizes the hydrocarbon prospects of the Punjab Platform in Pakistan, with reference to the adjacent Bikaner-Nagaur Basin in India. Geoscientific data indicates the region has undergone tectonic activity and deposition conducive to hydrocarbon generation and accumulation from the Infra-Cambrian to Tertiary periods. Source rocks identified in various formations range from poor to good potential. Multiple trap types have been identified including fault blocks, stratigraphic traps, and salt-induced structures. Hydrocarbons have been found in Infra-Cambrian reservoirs that extend from India into the Punjab Platform.
This document provides information about the reservoir, source, and seal rocks of the Lower Indus Basin in Pakistan. The main reservoir rocks identified are the Pab Sandstone, Ranikot Sandstone, and limestones in the Kirthar and Ghazij Formations. The primary source rock is the Lower Cretaceous Sembar Formation shale, but other potential sources are also identified. Thick shale units in the Paleocene and Eocene successions serve as the main regional seals in the area.
Bombay High is an offshore oilfield located 160 km off the coast of Mumbai, India. It was discovered in 1964-1967 and is operated by ONGC. It supplied 14% of India's oil needs and accounted for 38% of domestic production until 2004. The field is located in the Bombay offshore basin and produces from limestone reservoirs of Miocene age. It has produced over 2 billion barrels of oil and 3 trillion cubic feet of gas to date. A major fire in 2005 destroyed the Mumbai High North platform, costing $1.2 billion to rebuild. ONGC continues exploration and production activities in the area through seismic surveys.
The Cambay Basin is an intracratonic rift graben located in northwest India that began forming following the Deccan Traps volcanic event in the late Cretaceous. The basin is filled with up to 8km of Tertiary sedimentary rocks. Major source rocks include the thick Cambay Shale deposited in the early Eocene during a transgression. Hydrocarbon reservoirs are found in the Olpad Formation, Hazad delta sands, and Miocene formations. Multiple petroleum plays exist, including those in the Paleocene-early Eocene, middle Eocene, and late Eocene-Oligocene sequences. The Cambay Shale is a prolific source of oil and gas in the
This technical paper provides an overview of the major sedimentary basins in India that contain hydrocarbon reserves. It divides the basins into four categories based on the status of hydrocarbon exploration and production. The key basins discussed in detail include the Assam Shelf Basin, Cambay Basin, Bombay Offshore Basin, and Krishna-Godavari Basin. For each basin, it summarizes the geological setting, stratigraphy, hydrocarbon source rocks and reservoir rocks. The paper provides a high-level technical summary of India's major sedimentary basins with proven oil and gas reserves.
This document provides an overview of advances in fan delta sedimentology. It discusses classifications of fan deltas and alluvial deltas. It reviews several fan delta depositional models proposed based on studies of modern and ancient examples, including subaqueous fan delta models, Gilbert-type fan delta models, and models affected by volcanism or glaciation. It also discusses research methods for studying fan delta sedimentology, such as flume experiments, ground penetrating radar, and computer simulations. In summary, the document reviews developments in understanding fan delta classifications, depositional environments, and research approaches.
This paper discusses geophysical imaging techniques for mapping sub-basalt strata, which remains an important but under-explored frontier for hydrocarbon exploration. Modern seismic acquisition and processing, along with integrated interpretation of multiple geophysical data sets, has improved imaging below basalt layers and revealed several productive sub-basalt reservoirs worldwide. The paper reviews key basins studied, technological advances enabling sub-basalt exploration, and presents examples of deepwater seismic sections demonstrating imaging capabilities.
This document provides an overview of a reservoir engineering course focused on fundamental rock properties. It discusses key topics like porosity, saturation, wettability, capillary pressure, and how they are determined through laboratory core analysis. Porosity refers to the pore space available to hold fluids and is classified as absolute or effective porosity. Saturation represents the fraction of pore space occupied by a fluid. Capillary pressure describes the pressure differential between immiscible fluids based on interface curvature. Laboratory tests on core samples are used to characterize these important rock properties.
This document summarizes key concepts related to reservoir phase behavior and interfacial phenomena. It includes:
- A typical pressure-temperature diagram showing the critical point, bubble point curve, and dew point curve used to classify reservoirs as oil or gas based on temperature.
- Definitions of surface tension, interfacial tension, and surface free energy as forces that exist at boundaries between phases.
- Explanations of liquid, solid, and liquid-liquid interfaces with examples. Wettability is also introduced as the preferential wetting of solids by liquids.
- Figures illustrating fluid distributions and interfacial energies in water-wet and oil-wet systems. Young's equation relates
This document summarizes a study that used a 2D hydrodynamic model to assess habitat suitability for spring Chinook salmon in alternatives for the San Joaquin River Restoration Project. The model reasonably simulated hydrodynamic conditions like flow velocities, depths, and water surface elevations. It calculated a Suitability Index for each alternative, finding Alternatives 2 and 3 provided better habitat. Correlations were found between the Index and upstream discharge and downstream water levels. The model can help evaluate how flows impact salmon migration and habitat under different restoration scenarios.
Proterozoic sedimentary basins of India in generalPramoda Raj
This document provides an overview of Proterozoic sedimentary basins in India. It discusses 10 major basins, including the Vindhyan, Cuddapah, and Kaladgi basins. These basins formed between 1.6 billion to 540 million years ago and contain important economic mineral deposits like limestone, coal, and diamonds. Fossils found in several basins provide evidence of early life in the Proterozoic Eon. The basins preserve records of crustal evolution and atmospheric change on the Indian subcontinent.
Rift Asymmetry in the Equatorial Atlantic by David Lewis, Maersk Oil: 2013/Th...The Rothwell Group, L.P.
1) Plate reconstructions in the Equatorial Atlantic provide constraints on basin geometries and play elements along the conjugate Brazilian and West African margins.
2) Rift asymmetry between the margins led to different structural styles, with the Brazilian basin being largely unstructured compared to more faulted basins in West Africa.
3) Understanding this rift asymmetry and plate model constraints is important for detailed play characterization and exploration concepts in the similar but non-equivalent basins along the margins.
This document analyzes the impact of rapid sea level changes in the Caspian Sea on the morphodynamic deformation of estuaries along the southern coasts. Sediment samples were collected from 8 main rivers and analyzed to classify the estuary shapes and sediment characteristics. Satellite images from 1983-2004, which correspond to a 2.5m sea level rise, were interpreted to measure estuary deformation. The results showed different estuary types, including barred, swollen, widened, and deltaic. Some estuary territories were limited by the sea level progression, while other estuary mouths widened or were displaced toward the beach. Overall, the rivers responded differently to the sea level rise depending on the beach steepness and sediment size.
From the Arctic to the Tropics: The U.S. UNCLOS Bathymetric Mapping ProgramLarry Mayer
Since CHC2006, the University of New Hampshire’s Center for Coastal & Ocean Mapping/Joint Hydrographic Center has mapped with multibeam, the bathymetry of an additional ~220,000 km2 of seafloor in areas as diverse as the Arctic, the Northern Marianas of the western Pacific and the Gulf of Mexico. The mapping supports any potential U.S. submission for of extended continental shelves under Article 76 of the United Nations Convention of the Law of the Sea. Consequently, the mapping has concentrated on capturing the complete extent of the 2500-m isobath and the zone where the Article 76-defined foot of the slope exists. In practice, the complete area between ~1500 and ~4500 m water depths is mapped in each region (with the exception of the Arctic Ocean). The data have been collected in conditions that range from harsh Arctic sea ice to the calms of the Philippine Sea tropics. Although, some of the conditions have limited the quality of some of the data, the data quality is generally quite good and geological surprises have been uncovered on each of the cruises.
Mp gw applying aquifer modification techniques like hydrofraking, bore blast...hydrologywebsite1
The document provides a final report on a groundwater study using hydrofracking in the Rohini watershed area of Madhya Pradesh, India. It details the pre-investigation activities including the local geology, hydrology, and existing groundwater problems. The objectives of the study were to assess hydrofracking's applicability, develop an optimal abstraction methodology, gain expertise in the technique, increase awareness of it among farmers, and test it on 15 borewells. The methodology section explains hydrofracking principles, procedures, testing done before and after, and factors controlling its success or failure. Results, analyses, evaluations, recommendations and conclusions are presented.
This document summarizes the application of 2-D seismic interpretation to characterize the Meyal Oil Field in the Upper Indus Basin of Pakistan. The objectives were to perform 2-D seismic interpretation including time calculations, reflector marking, contour map preparation, and generating geoseismic sections. The methodology included data collection, analysis, identifying zones of interest, and manual 2-D seismic interpretation. Key findings include delineating formation depths, identifying major faults and structures, and observing pinch-outs of the Jurassic sands that indicate potential stratigraphic traps.
This document summarizes information about the Eastern Dharwar Craton (EDC) region of India. The EDC covers around 450,000 square kilometers and contains several greenstone belts formed from volcanic and sedimentary rocks. It is bounded by mobile belts and separated from the Western Dharwar Craton by the Chitradurga Shear Zone. The EDC contains older gneissic basement rocks overlain by the Warangal Group and greenstone belts of the Dharwar Supergroup, along with the large Closepet Granite intrusion and regions metamorphosed to amphibolite and granulite facies.
The document summarizes key information about the Cuddapah Supergroup, a large Proterozoic sedimentary basin in India. It describes the stratigraphy, tectonic setting, structure, sedimentation, and stratigraphic relationships of the basin. The Cuddapah Supergroup consists of a 12 km thick succession of sedimentary and volcanic rocks deposited in the basin. Younger groups in the west are less deformed compared to the tightly folded Nallamalai Group in the east. Widespread magmatism occurred during deposition, including basalt flows, sills, and felsic volcanism dated between 1862-1583 million years ago.
- The document discusses reservoir characteristics including rock and fluid properties that are important to understand for optimal hydrocarbon recovery. Techniques like seismic data, well logging, and testing provide valuable data to build reservoir models.
- Key rock properties that impact hydrocarbon storage and flow include porosity, permeability, and wettability. Core analysis in the lab and well logs provide data on these properties.
- Understanding fluid properties like phase behavior under reservoir conditions of pressure and temperature is also important for predicting production performance and fluid composition.
The document summarizes the Gondwana system of sedimentary rocks found in India. It describes the lithology, topography, sedimentation processes, flora and fauna of the different formations within the Gondwana group. These include the Talchir formation containing glacial deposits, the marine-influenced Bap and Badhaura formations, and the coal-bearing Damuda group. The climate changed from cold glacial conditions to warmer and wetter periods favorable for coal formation over the depositional period.
This document summarizes field experiences using selective hydraulic fracturing in deep directional wells in the Orocual Field in Venezuela. Three key wells (ORC-29, ORC-30) were directionally drilled into the San Juan Formation to a total depth of 14,000-16,000 feet. Hydraulic fracturing was performed in stages on 10-foot intervals to improve productivity. Initial fracturing attempts led to early screenouts, so perforating methods were modified. Production logging after each stage showed the effectiveness of the stimulations in creating a more homogeneous production profile from the heterogeneous reservoirs. The evaluation of these wells provided data to optimize future fracturing designs in the San Juan Formation.
This presentation provides an overview of the tectonics of the Aravali fold mountains in northwest India. The key points are:
1. The Aravali fold belt trends northeast-southwest and consists of folded Proterozoic sedimentary rocks ranging from 3,300-1,900 million years old.
2. The belt has undergone four phases of deformation and folding between 1,800-1,100 million years ago during the Aravali and Delhi orogenies.
3. Stratigraphy of the region includes the Banded Gneissic Complex at the base, overlain by the Bhilwara Supergroup and Aravali Supergroup, with the Delhi Supergroup
The document summarizes the geology of the Bundelkhand craton located in central India. The craton covers an area of 26,000 square kilometers and contains three main components: enclaves of supracrustal rocks within older gneisses, the Bundelkhand granite and associated quartz reefs and volcanic rocks, and mafic dyke swarms. The craton has undergone tectonic evolution characterized by three primary shear zone orientations: east-west, northeast-southwest, and northwest-southeast.
The document provides information on the Dharwar Craton located in southwest India. It discusses the classification of the craton into the Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC). Key differences between the WDC and EDC are noted, including larger greenstone belts in the WDC surrounded by older gneiss, compared to narrower greenstone belts in the EDC intruded by a Dharwar Batholith. The lithology of the cratons is also summarized, including the Sargur Group, Bababudan Group, Chitradurga Group, and younger granites like the Closepet Granite. Regional structures, met
This document is an assignment submitted by Kush Bakhat Subhani to Sir Muhammad kashif for a geology course. It discusses the reservoir, source, and seal rocks of the Lower Indus Basin, which includes the Sulaiman and Kirthar provinces. Potential reservoirs identified include limestone and sandstone formations from the Eocene to Cretaceous periods. The Sembar Formation is identified as the primary source rock, containing type-III kerogen capable of generating gas. Thick shale horizons in the Paleocene and Eocene are potential regional seals above the reservoirs in the Lower Indus Basin.
The document summarizes a study on lithology identification and gross rock volume (GRV) estimation of the B-Sand reservoir in the Lower Indus Basin of Pakistan. Well log and seismic data from two wells were analyzed using petrophysical and rock physics methods to identify the lithology and estimate reservoir properties. Cross-plots of elastic parameters helped differentiate lithologies including gas sand, oil sand, brine, and shale. GRV was calculated to estimate hydrocarbon volumes, showing the Dars West-01 well has more hydrocarbons and less water saturation than the Jumman Shah-01 well. The integrated analysis provides insights for accurate reservoir delineation, evaluation, and reserve estimation.
This paper discusses geophysical imaging techniques for mapping sub-basalt strata, which remains an important but under-explored frontier for hydrocarbon exploration. Modern seismic acquisition and processing, along with integrated interpretation of multiple geophysical data sets, has improved imaging below basalt layers and revealed several productive sub-basalt reservoirs worldwide. The paper reviews key basins studied, technological advances enabling sub-basalt exploration, and presents examples of deepwater seismic sections demonstrating imaging capabilities.
This document provides an overview of a reservoir engineering course focused on fundamental rock properties. It discusses key topics like porosity, saturation, wettability, capillary pressure, and how they are determined through laboratory core analysis. Porosity refers to the pore space available to hold fluids and is classified as absolute or effective porosity. Saturation represents the fraction of pore space occupied by a fluid. Capillary pressure describes the pressure differential between immiscible fluids based on interface curvature. Laboratory tests on core samples are used to characterize these important rock properties.
This document summarizes key concepts related to reservoir phase behavior and interfacial phenomena. It includes:
- A typical pressure-temperature diagram showing the critical point, bubble point curve, and dew point curve used to classify reservoirs as oil or gas based on temperature.
- Definitions of surface tension, interfacial tension, and surface free energy as forces that exist at boundaries between phases.
- Explanations of liquid, solid, and liquid-liquid interfaces with examples. Wettability is also introduced as the preferential wetting of solids by liquids.
- Figures illustrating fluid distributions and interfacial energies in water-wet and oil-wet systems. Young's equation relates
This document summarizes a study that used a 2D hydrodynamic model to assess habitat suitability for spring Chinook salmon in alternatives for the San Joaquin River Restoration Project. The model reasonably simulated hydrodynamic conditions like flow velocities, depths, and water surface elevations. It calculated a Suitability Index for each alternative, finding Alternatives 2 and 3 provided better habitat. Correlations were found between the Index and upstream discharge and downstream water levels. The model can help evaluate how flows impact salmon migration and habitat under different restoration scenarios.
Proterozoic sedimentary basins of India in generalPramoda Raj
This document provides an overview of Proterozoic sedimentary basins in India. It discusses 10 major basins, including the Vindhyan, Cuddapah, and Kaladgi basins. These basins formed between 1.6 billion to 540 million years ago and contain important economic mineral deposits like limestone, coal, and diamonds. Fossils found in several basins provide evidence of early life in the Proterozoic Eon. The basins preserve records of crustal evolution and atmospheric change on the Indian subcontinent.
Rift Asymmetry in the Equatorial Atlantic by David Lewis, Maersk Oil: 2013/Th...The Rothwell Group, L.P.
1) Plate reconstructions in the Equatorial Atlantic provide constraints on basin geometries and play elements along the conjugate Brazilian and West African margins.
2) Rift asymmetry between the margins led to different structural styles, with the Brazilian basin being largely unstructured compared to more faulted basins in West Africa.
3) Understanding this rift asymmetry and plate model constraints is important for detailed play characterization and exploration concepts in the similar but non-equivalent basins along the margins.
This document analyzes the impact of rapid sea level changes in the Caspian Sea on the morphodynamic deformation of estuaries along the southern coasts. Sediment samples were collected from 8 main rivers and analyzed to classify the estuary shapes and sediment characteristics. Satellite images from 1983-2004, which correspond to a 2.5m sea level rise, were interpreted to measure estuary deformation. The results showed different estuary types, including barred, swollen, widened, and deltaic. Some estuary territories were limited by the sea level progression, while other estuary mouths widened or were displaced toward the beach. Overall, the rivers responded differently to the sea level rise depending on the beach steepness and sediment size.
From the Arctic to the Tropics: The U.S. UNCLOS Bathymetric Mapping ProgramLarry Mayer
Since CHC2006, the University of New Hampshire’s Center for Coastal & Ocean Mapping/Joint Hydrographic Center has mapped with multibeam, the bathymetry of an additional ~220,000 km2 of seafloor in areas as diverse as the Arctic, the Northern Marianas of the western Pacific and the Gulf of Mexico. The mapping supports any potential U.S. submission for of extended continental shelves under Article 76 of the United Nations Convention of the Law of the Sea. Consequently, the mapping has concentrated on capturing the complete extent of the 2500-m isobath and the zone where the Article 76-defined foot of the slope exists. In practice, the complete area between ~1500 and ~4500 m water depths is mapped in each region (with the exception of the Arctic Ocean). The data have been collected in conditions that range from harsh Arctic sea ice to the calms of the Philippine Sea tropics. Although, some of the conditions have limited the quality of some of the data, the data quality is generally quite good and geological surprises have been uncovered on each of the cruises.
Mp gw applying aquifer modification techniques like hydrofraking, bore blast...hydrologywebsite1
The document provides a final report on a groundwater study using hydrofracking in the Rohini watershed area of Madhya Pradesh, India. It details the pre-investigation activities including the local geology, hydrology, and existing groundwater problems. The objectives of the study were to assess hydrofracking's applicability, develop an optimal abstraction methodology, gain expertise in the technique, increase awareness of it among farmers, and test it on 15 borewells. The methodology section explains hydrofracking principles, procedures, testing done before and after, and factors controlling its success or failure. Results, analyses, evaluations, recommendations and conclusions are presented.
This document summarizes the application of 2-D seismic interpretation to characterize the Meyal Oil Field in the Upper Indus Basin of Pakistan. The objectives were to perform 2-D seismic interpretation including time calculations, reflector marking, contour map preparation, and generating geoseismic sections. The methodology included data collection, analysis, identifying zones of interest, and manual 2-D seismic interpretation. Key findings include delineating formation depths, identifying major faults and structures, and observing pinch-outs of the Jurassic sands that indicate potential stratigraphic traps.
This document summarizes information about the Eastern Dharwar Craton (EDC) region of India. The EDC covers around 450,000 square kilometers and contains several greenstone belts formed from volcanic and sedimentary rocks. It is bounded by mobile belts and separated from the Western Dharwar Craton by the Chitradurga Shear Zone. The EDC contains older gneissic basement rocks overlain by the Warangal Group and greenstone belts of the Dharwar Supergroup, along with the large Closepet Granite intrusion and regions metamorphosed to amphibolite and granulite facies.
The document summarizes key information about the Cuddapah Supergroup, a large Proterozoic sedimentary basin in India. It describes the stratigraphy, tectonic setting, structure, sedimentation, and stratigraphic relationships of the basin. The Cuddapah Supergroup consists of a 12 km thick succession of sedimentary and volcanic rocks deposited in the basin. Younger groups in the west are less deformed compared to the tightly folded Nallamalai Group in the east. Widespread magmatism occurred during deposition, including basalt flows, sills, and felsic volcanism dated between 1862-1583 million years ago.
- The document discusses reservoir characteristics including rock and fluid properties that are important to understand for optimal hydrocarbon recovery. Techniques like seismic data, well logging, and testing provide valuable data to build reservoir models.
- Key rock properties that impact hydrocarbon storage and flow include porosity, permeability, and wettability. Core analysis in the lab and well logs provide data on these properties.
- Understanding fluid properties like phase behavior under reservoir conditions of pressure and temperature is also important for predicting production performance and fluid composition.
The document summarizes the Gondwana system of sedimentary rocks found in India. It describes the lithology, topography, sedimentation processes, flora and fauna of the different formations within the Gondwana group. These include the Talchir formation containing glacial deposits, the marine-influenced Bap and Badhaura formations, and the coal-bearing Damuda group. The climate changed from cold glacial conditions to warmer and wetter periods favorable for coal formation over the depositional period.
This document summarizes field experiences using selective hydraulic fracturing in deep directional wells in the Orocual Field in Venezuela. Three key wells (ORC-29, ORC-30) were directionally drilled into the San Juan Formation to a total depth of 14,000-16,000 feet. Hydraulic fracturing was performed in stages on 10-foot intervals to improve productivity. Initial fracturing attempts led to early screenouts, so perforating methods were modified. Production logging after each stage showed the effectiveness of the stimulations in creating a more homogeneous production profile from the heterogeneous reservoirs. The evaluation of these wells provided data to optimize future fracturing designs in the San Juan Formation.
This presentation provides an overview of the tectonics of the Aravali fold mountains in northwest India. The key points are:
1. The Aravali fold belt trends northeast-southwest and consists of folded Proterozoic sedimentary rocks ranging from 3,300-1,900 million years old.
2. The belt has undergone four phases of deformation and folding between 1,800-1,100 million years ago during the Aravali and Delhi orogenies.
3. Stratigraphy of the region includes the Banded Gneissic Complex at the base, overlain by the Bhilwara Supergroup and Aravali Supergroup, with the Delhi Supergroup
The document summarizes the geology of the Bundelkhand craton located in central India. The craton covers an area of 26,000 square kilometers and contains three main components: enclaves of supracrustal rocks within older gneisses, the Bundelkhand granite and associated quartz reefs and volcanic rocks, and mafic dyke swarms. The craton has undergone tectonic evolution characterized by three primary shear zone orientations: east-west, northeast-southwest, and northwest-southeast.
The document provides information on the Dharwar Craton located in southwest India. It discusses the classification of the craton into the Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC). Key differences between the WDC and EDC are noted, including larger greenstone belts in the WDC surrounded by older gneiss, compared to narrower greenstone belts in the EDC intruded by a Dharwar Batholith. The lithology of the cratons is also summarized, including the Sargur Group, Bababudan Group, Chitradurga Group, and younger granites like the Closepet Granite. Regional structures, met
This document is an assignment submitted by Kush Bakhat Subhani to Sir Muhammad kashif for a geology course. It discusses the reservoir, source, and seal rocks of the Lower Indus Basin, which includes the Sulaiman and Kirthar provinces. Potential reservoirs identified include limestone and sandstone formations from the Eocene to Cretaceous periods. The Sembar Formation is identified as the primary source rock, containing type-III kerogen capable of generating gas. Thick shale horizons in the Paleocene and Eocene are potential regional seals above the reservoirs in the Lower Indus Basin.
The document summarizes a study on lithology identification and gross rock volume (GRV) estimation of the B-Sand reservoir in the Lower Indus Basin of Pakistan. Well log and seismic data from two wells were analyzed using petrophysical and rock physics methods to identify the lithology and estimate reservoir properties. Cross-plots of elastic parameters helped differentiate lithologies including gas sand, oil sand, brine, and shale. GRV was calculated to estimate hydrocarbon volumes, showing the Dars West-01 well has more hydrocarbons and less water saturation than the Jumman Shah-01 well. The integrated analysis provides insights for accurate reservoir delineation, evaluation, and reserve estimation.
The document summarizes the petroleum play of the Lower Indus Basin in Pakistan. It describes the tectonic evolution and stratigraphy of the basin, including the source rocks like the Sembar Formation. It details the production history from fields like Sui producing from Eocene reservoirs. Key reservoirs included sandstones in the Jurassic to Eocene formations. Traps are structural like anticlines. Source rock evaluation of wells like Sann #1 showed good hydrocarbon generation potential from source rocks like the Sembar Formation and upper Goru Formation.
K.E. Al-Khidir, M.S. Benzagouta
Department of Petroleum Engineering and Natural Gas, College of Engineering,
King Saud University, Saudi Arabia
К.Е. Аль-Хидир, М.С. Бензагута
Инженерный колледж, Университет короля Сауда
Abstract. With reference to the reservoir characterization regarding the Khuff Formation – Khurtam Member (KSA), better reservoir quality prediction can be assigned to
the characterization of its physical properties. These properties determination are depending on facies description. These properties can be erratic according to the diagenetic change and control on pore geometrical attributes and reservoir characterization. In this
investigation, permeability and porosity have been measured in the laboratory. Rock Quality Index (RQI), flow zone index (FZI) as well as porosity groups have been
calculated. The use of different determined physical and petrophysical parameters and their plots have defined two Flow Zone Indicators (FZI) characterized by a restricted distribution of porosity permeability and rock quality index. Different approval statements were made by correlation process. These confirmation and data support made of the considered reservoir as relative tight reservoir and tight reservoir. The use of the R35 was organized to
make an approval to different statements with reference to the considered reservoir which can be classified as relative tight reservoir and tight reservoir. The R35 was carried out to approve not only that the reservoir is relative tight and tight but it can be classified in the range within the range of nano to microporous system.
Delineation of Hydrocarbon Bearing Reservoirs from Surface Seismic and Well L...IOSR Journals
Hydrocarbon reservoir has been delineated and their boundaries mapped using direct indicators from 3-D seismic and well log data from an oil field in Nembe creek, Niger Delta region. Well log signatures were employed to identify hydrocarbon bearing sands. Well to seismic correlation revealed that these reservoirs tied with direct hydrocarbon indicators on the seismic section. The results of the interpreted well logs revealed that the hydrocarbon interval in the area occurs between 6450ft to 6533ft for well A, 6449ft to 6537ft for well B and 6629ft to 6704ft for well C; which were delineated using the resistivity, water saturation and gamma ray logs. Cross plot analysis was carried out to validate the sensitivity of the rock attributes to reservoir saturation condition. Analysis of the extracted seismic attribute slices revealed HD5000 as hydrocarbon bearing reservoir.
Integrated Petrophysical Parameters and Petrographic Analysis Characterizing ...IJERA Editor
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The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
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units. The units from base to top are: Lower Shajara Fractal
Dimension Unit, Middle Shajara Fractal Dimension Unit,
and Upper Shajara Fractal Dimension Unit. The thermodynamic model and 3-D fractal model were effectively used to characterize the porous structures of Shajara sandstones in logical and quantitative way.
Keywords Heterogeneity . Shajara formation . Shajara
fractal dimension units . Permeability
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Bimodal pore size behavior of the shajara formation reservoirs of the permo carboniferous unayzah group
1. ORIGINAL PAPER - EXPLORATION GEOLOGY
Bimodal pore size behavior of the Shajara Formation Reservoirs
of the Permo-Carboniferous Unayzah Group, Saudi Arabia
K. E. Al-Khidir • A. A. Al-Quraishi •
A. A. Al-Laboun • M. S. Benzagouta
Received: 29 September 2010 / Accepted: 21 March 2011 / Published online: 5 April 2011
Ó The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract The sandstones of the Permo-Carboniferous
Shajara Formation form the main part of the Unayzah
Reservoir in the Greater Arabian Basin. It is divided into
three reservoirs, namely from base to top Lower, Middle,
and Upper Shajara reservoirs. Mercury intrusion technique
was carried out on representative sandstone samples col-
lected from the type section and the three reservoirs are
generally characterized as heterogeneous megaporous res-
ervoirs. The best reservoir quality is assigned to the lower
sand unit of the Lower Shajara followed by the Middle
Shajara Reservoir. One sample collected from the upper
part of the Lower Shajara was described as low quality due
to its fine grain characteristic and its proximity to the
unconformity surface. Reservoir quality is controlled to a
large extent by the depositional facies and specifically by
rock texture illustrated by petrophysical description. The
quality of the three reservoirs of the Shajara Formation,
increases with the increase of grain size and grain sorting.
Keywords Shajara Reservoirs Á Shajara Formation Á
Unayzah Group Á Pore size distribution
Introduction
The Permo-Carboniferous Unayzah Reservoirs are oil and
gas bearing in more than 30 oil and gas fields in Saudi
Arabia. These reservoirs are partially represented in out-
crops by the Shajara, Safra, and Shiqqah sandstones of the
Unayzah Group. These formations are exposed as a thin
belt below the Khuff carbonates in central Arabia.
Fossil plants of the late Carboniferous–early Permian
age were first reported at the town of Unayzah by El-
Khayal et al. (1980). Later, the term Unazyah Formation
was informally introduced by Al-Laboun (1982) as sili-
ciclastics and minor carbonate section at the base of the
Khuff Formation. This definition was adopted by Aramco
Stratigraphic Committee (1983) and formally defined by
Al-Laboun (1987)in the American Association of Petro-
leum Geologist (AAPG). The Unayzah Formation was then
correlated with its equivalent units in different parts of the
Greater Arabian basin (Al-Laboun 1988) and its type
locality was established within Unayzah town with a ref-
erence section assigned at Wadi Ash-Shajara at the
Qusayba depression, Al-Qasim region (Fig. 1).
The subsurface informal reference section (Hawtah-1) of
the Unayzah Formation was studied by Ferguson and
Chambers (1991). The section consists of two sandstone
intervals separated by a coarsening upward siltstone unit.
Similarly, McGillivray and Husseini (1992) divided the
Unayzah Formation in the Hawtah–Hazmiyah fields into
two informal sequences identified as Unayzah A and
Unayzah B members. The two members are separated by a
red-brown siltstone or fine-grained silty sandstone. Senalp
and Al-Dauji (1995) studied the stratigraphy and sedimen-
tation of the Unayzah Reservoir in central Arabia. They
redefined the Unayzah Formation at its type locality by
introducing the term ‘‘basal Khuff clastics’’ (Ash-Shiqqah
K. E. Al-Khidir (&) Á M. S. Benzagouta
Department of Petroleum and Natural Gas Engineering,
King Saud University, Riyadh, Saudi Arabia
e-mail: kalkhidir@ksu.edu.sa
A. A. Al-Quraishi
Oil and Gas Research Institute, King Abdulaziz City for Science
and Technology, Riyadh, Saudi Arabia
A. A. Al-Laboun
Department of Geology, King Saud University,
Riyadh, Saudi Arabia
123
J Petrol Explor Prod Technol (2011) 1:1–9
DOI 10.1007/s13202-011-0007-5
2. member) of the Khuff Formation to be the upper contact of
the Unayzah Formation.
Evans et al. (1997) studied the stratigraphic trap in the
Permian Unayzah Formation, in Usaylah-1, central Arabia,
and they reported that the trap is an up dip pinch out. An oil
column 31 ft thick is encountered in the eolian sandstone
facies of the upper part of the Unayzah Formation. Later,
Wender et al. (1998) divided the Early Permian Unayzah
Formation into three units, the Unayzah-A Reservoir,
Unayzah Siltstone Member, and Unayzah-B Reservoir.
Melvin and Spraque (2006) studied origin and stratigraphic
architecture of glaciogenic sediments in Permian–Carbon-
iferous lower Unayzah sandstones in eastern central Saudi
Arabia. They subdivided the lower Unayzah sandstones
into three members, from base to top are: Unayzah C
Member, Unayzah B Member, and an un-named middle
Unayzah member.
Reservoir characteristics of the Permo-Carboniferous
Unayzah Formation, at Wadi Shajara was thoroughly
investigated through field and petrophysical examinations.
An exposed clastic sequence consisting of three sandstone
intervals separated by two mudstone units were observed
(Fig. 2). The clastic sequence is bounded from top and
bottom, by two regional unconformities, namely sub-Khuff
and sub-Unayzah unconformity, respectively. Based on
Saudi Stratigraphic Code (1983), a group is defined as a
lithostratigraphic unit bounded by two regional unconfo-
rmities. Therefore, we propose raising the Permo-Carbon-
iferous Unayzah Formation to a group status and identify a
new formation named Shajara Formation (Al-Khidir 2007).
The term Unayzah Formation was restricted to the upper
unit of the group which is best represented in its original
type locality in Unayzah town, while the term Shajara
Formation was assigned to the Lower unit which is best
represented at Wadi Ash-Shajara (Laboun 2010). Depend-
ing on sub-Unayzah unconformity, sub-middle Shajara
local unconformity, the lower mudstone interval, and sub-
Khuff unconformity (Fig. 2), the Shajara Formation was
divided into three members, from base to top: the Lower
Shajara, the Middle Shajara, and the Upper Shajara
(Al-Khidir 2007).
The Shajara Reservoirs of the Shajara Formation is oil
and gas bearing in many fields in Saudi Arabia. In addition,
it is the principal Paleozoic clastic reservoir. To our
knowledge no petrophysical examination was conducted on
the surface samples of the Shajara Formation. The aim of
this work is to categorize the Shajara reservoirs by char-
acterizing the pore geometry and the pore aperture sizes of
the sandstones. This is done by integrating capillary pres-
sure obtained by the mercury injection porosimetry tech-
nique, petrofacies determination and lithofacies description
of outcrop samples collected.
Experimental work
The most obvious and straightforward measurements of
pore size are with geometric analysis of images of indi-
vidual pores. This can be done using various types of
microscopy on thin sections or other flat soil surfaces, or
tomography. Image-based techniques can be prohibitively
tedious because enough pores must be analyzed to give an
adequate statistical representation. Therefore, the determi-
nation of pore geometry and pore aperture size using
mercury injection technique is believed to be more helpful
in categorizing rocks by pore types (i.e. nanno, micro,
meso, macro or mega). Autopore III 9420 mercury intru-
sion unit was used to determine the capillary pressure,
porosity, pore throat accessibility, and pore level hetero-
geneity of the three reservoirs comprising the Shajara
Formation. This was conducted on nine outcrop sandstone
samples selected among 13 samples from the type section.
All samples except for one (SJ3) are friable sand and their
locations are presented in stratigraphic column illustrated
in Fig. 2.
Samples’ permeability (k) was calculated utilizing Pur-
cell’s equation (1948) stated as:
K ¼ 14; 260  k  / Â
Zs¼1
s¼0
dSHg
Pc
ð1Þ
where, k is a lithology factor (equal to 0.216), dSHg is
incremental mercury saturation and Pc is the capillary
pressure measured in psi.
The pore aperture size is calculated utilizing Washburn
equation expressed as:
Fig. 1 Location map of the studied area
2 J Petrol Explor Prod Technol (2011) 1:1–9
123
3. r ¼
2  r  cos h
Pc
ð2Þ
where, r is the pore radius in micron, r is the surface tension
of mercury in Dynes/cm, h is the contact angle of mercury
in air and Pc is the capillary pressure in Dynes/cm2
.
To reveal the heterogeneity of the investigated reser-
voirs, the pore aperture distribution (PSD) was plotted as a
function of pore radius. The PSD function is defined as the
rate of change of mercury intrusion volume with respect to
the difference of pore radius logarithm relative to the
maximum value of that term. To confirm the findings of the
PSD plots, the cumulative percent of mercury saturation
was plotted with respect to log pore radius.
On average, the pore throats entered by a non-wetting
fluid (mercury) at 35% saturation (R35) or less during a
capillary analysis, represent the pores that dominate fluid
flow in a reservoir samples (Kolodzie 1980). The pore
throat corresponding to a mercury saturation of 35% was
evaluated using Winland equation expressed as:
LogR35 ¼ 0:732 þ 0:588 Â log k À 0:864 Â log / ð3Þ
Pittman (2001) reported that, pore throat radius
corresponding to the apex has the potential for delineating
Fig. 2 Stratigraphic column of
the type section of the Permo-
carboniferous Shajara
Formation of the Unayzah
Group, Wadi Shajara, Qusayba
area, al Qassim district, Saudi
Arabia, N 26°52 17.4, E 43°36
18
J Petrol Explor Prod Technol (2011) 1:1–9 3
123
4. stratigraphic traps in the same manner as the pore aperture
corresponding to 35th percentile of a cumulative mercury
saturation curve, which was developed by Winland.
Therefore, the pore aperture size corresponding to the
apex (Rapex) was determined from Pittman equation stated
as follows:
LogRapex ¼ À0:117 þ 0:475 Â Logk À 0:099 Â Log/
ð4Þ
Results and discussion
In order to determine the behavior of the pore geometry of
Shajara Reservoirs, samples capillary pressures were
measured and the measurements were used to determine
the pore size distribution. Figure 3 is the pore size distri-
bution of sample SJ1 representing the Lower Shajara
Reservoir. This sample is characterized as red in color,
medium grain size and moderately well sorted. The figure
indicates a bimodal pore size distribution of two distinct
pore sizes, minor macro pores of sizes less than 10 lm and
major mega pores with size greater than 10 lm according
to Libny et al. classification (2001). Within the mega pores
there exist a variation in pore size. The sample is charac-
terized with maximum pore radius of 173.9 lm, and a
minimum radius of 0.01 lm, and an average pore size of
41.6 lm. Variation in pore size distribution demonstrates
the possibility of anisotropy. This anisotropy is well
defined in Fig. 4 where three distinct tracks have been
obtained. The pore radii of the first track ranges from 60.2
to 173.9 lm. The second represents pore radii varying from
0.1 to 60.2 lm, whereas the third track is characterized by
very low pore radii ranging in size from 0.1 to 0.01 lm.
Sample SJ2 is the second sample representing the Lower
Shajara Reservoir. It is described as medium-grained, well
sorted sandstone. Figure 5 is the pore size distribution of
the sample indicating a bimodal pore size distribution with
Fig. 3 Incremental and cumulative PSD versus pore radius of sample
SJ1 from the Lower Shajara Reservoir
Fig. 4 Cumulative % SHg versus pore radius of sample SJ1 from the
Lower Shajara Reservoir
Fig. 5 Incremental and cumulative PSD versus pore radius of sample
SJ2 from the Lower Shajara Reservoir
Fig. 6 Cumulative % SHg versus pore radius of sample SJ2 from the
Lower Shajara Reservoir
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5. a maximum pore radius of 173.9 lm, and an average pore
size of 25.4 lm. Again two distinct pore sizes exist with
majority of the sizes classified as megapores. Figure 6
confirms the heterogeneity of the sample as presented by
multiple tracks with distinctive pore radius ranges.
Sample SJ3 of the Lower Shajara Reservoir is charac-
terized with finer grain size when compared to samples SJ1
and SJ2. Such grain size variability as well as compaction
noticed through grains visual inspection is believed to be
due to the sample proximity to the unconformity surface.
This is reflected in a drastic drop in permeability of sample
SJ3 as stated in Table 1. The sample is also identified with
bimodal pore size distribution with skewness towards finer
pore size as indicated in Fig. 7. The sample is characterized
with narrower range of pore radii variation and smaller
pore sizes compared to that of samples SJ1 and SJ2. Again,
Fig. 8 exhibits two tracks of pore radii ranging in size from
10 to 45 lm, and from 1 to 10 lm.
Grain size assessment, pore size distributions and calcu-
lated petrophysical properties of porosity and permeability
of samples SJ1, SJ2 and SJ3 can help assessing the Lower
Shajara Reservoir. This can be confirmed by the Winland
R35 and Pittman Rapex (Table 1). Based on the grain size
description and the obtained porosity and particularly per-
meability, it can likely be stated that the average pore size
decreases as the grain size gets finer and as a consequence
flow capacity declines. This is observed as we proceed
upward in the reservoir. Based on that and the reservoir
classification utilizing the Winland R35, the lower part of the
reservoir can be classified as megaporous (pore radius
greater than 10 lm), whereas the upper portion of the res-
ervoir represented by sample SJ3 is classified as macropo-
rous (pore radius between 2 and 10 lm) with lower flow
capacity as stated by the low permeability value (Table 2).
Middle Shajara Reservoir were characterized using
samples SJ7, SJ8 and SJ9. Sample SJ7 is described as
coarse-grained, moderately well sorted sandstone. This
sample is characterized by bimodal pore size distribution as
shown in Fig. 9 with pore radii ranging from 1.2 to
180.8 lm with an average value of 46.15 lm. The sample
heterogeneity is revealed in Fig. 10, where two tracks of
pore radii exists. The first represents a pore radii ranging
from 10 to 180.8 lm, whereas the second represents pore
radii that vary from 1.2 to 10 lm.
Table 1 Petrophysical properties of samples tested
Petrophysical facies U (%) K (mD) R35 (lm) Rapex (lm) h (feet) U avg. (%) K avg. (mD) Reservoir
Sj-1 29.2 1,680 23 18.6 11.8 31.1 1,592 Lowe Shajara Reservoir
Sj-2 35.5 1,955 21.3 19.6 3.9
Sj-3 34.2 56 2.7 3.6 1.6
Sj-7 35.1 1,472 18.2 17.2 13.4 33.4 1,407 Middle Shajara Reservoir
Sj-8 31.9 1,344 18.7 16.8
Sj-9 31.5 1,395 19.3 16.9 0.9
Sj-11 36.2 1,197 15.7 15.5 13.1 29.9 1,204 Upper Shajara Reservoir
Sj-12 28.2 1,440 21.7 17.4
Sj-13 25.4 973 18.8 14.6 6.5
Fig. 7 Incremental and cumulative PSD versus pore radius of sample
SJ3 from the Lower Shajara Reservoir
Fig. 8 Cumulative % SHg versus pore radius of sample SJ3 from the
Lower Shajara Reservoir
J Petrol Explor Prod Technol (2011) 1:1–9 5
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6. Sample SJ8 is also identified as medium-grained, mod-
erately well sorted sandstone. This sample is characterized
with bimodal pore size distribution as shown in Fig. 11
with an average pore radius of 28.65 lm indicating smaller
average pore size than that of sample SJ7. The heteroge-
neity of this sample is affirmed in Fig. 12 which displays
Table 2 Lithofacies description of samples tested
Facies no. Color Grain size Sorting Hardness
SJ-1 Red Medium-grained Moderately well sorted Friable
SJ-2 Yellow Medium-grained Well sorted Friable
SJ-3 White–pink Fine-grained Poorly sorted Hard
SJ-7 Red Coarse-grained Moderately well sorted Friable
SJ-8 Red Medium-grained Moderately well sorted Friable
SJ-9 Yellow Medium-grained Moderately well sorted Friable
Sj-11 Yellow Medium-grained Poorly sorted Friable
SJ-12 Yellow Very coarse-grained Moderately sorted Friable
SJ-13 Light brown Coarse-grained Moderately sorted Friable
Fig. 9 Incremental and cumulative PSD versus pore radius of sample
SJ7 from the Lower Shajara Reservoir
Fig. 10 Cumulative % SHg versus pore radius of sample SJ7 from the
Lower Shajara Reservoir
Fig. 11 Incremental and cumulative PSD versus pore radius of
sample SJ8 from the Lower Shajara Reservoir
Fig. 12 Cumulative % SHg versus pore radius of sample SJ8 from the
Lower Shajara Reservoir
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7. two tracks of pore radii. The first is for a pore radii that
range in size from 37 to 180.8 lm, whereas the second is
characterized by pore radii varying in size from 1 to
10 lm.
Similar to the above two samples of the Middle Shajara
Reservoir, sample SJ9 is described as medium-grained,
moderately well sorted sandstone. This sample is charac-
terized with bimodal pore size distribution as indicated in
Fig. 13 with an average pore radius of 73.9 lm indicating
the largest mean pore size for this section of the reservoir.
Further verification of heterogeneity of this sample is
indicated in Fig. 14 which indicates two tracks of pore
radii, ranging in size from 10 to 164.4 lm and 1 to 10 lm.
Based on the outcomes obtained and the Winland R35 and
Pittman Rapex (Table 1), the whole Middle Shajara Reser-
voir is classified as megaporous reservoir with good flow
capacity.
The Upper Shajara Reservoir is also represented by
three samples, namely from base to top SJ11, SJ12, and
SJ13. Sample SJ11 is identified as medium-grained, poorly
sorted sandstone. This sample is characterized with bimo-
dal pore size distribution as illustrated in Fig. 15. This
variation in pore size distribution is proved in Fig. 16
where three tracks of pore distribution are observed. The
first track is for pore radii varying in size from 30 to
173.9 lm. The second track represents distribution of pore
radii ranging in size from 0.1 to 30 lm. The third track
represents a very small pore radii range of 0.01–0.1 lm.
This sample has a mean pore radius of 42.9 lm.
Sample SJ12 is identified as very coarse-grained, mod-
erately sorted sandstone. This sample is also characterized
with bimodal pore size distribution as illustrated in Fig. 17.
This sample possesses an average pore radius of 67.7 lm.
The pore heterogeneity is verified in Fig. 18 where two
Fig. 13 Incremental and cumulative PSD versus pore radius of
sample SJ9 from the Lower Shajara Reservoir
Fig. 14 Cumulative % SHg versus pore radius of sample SJ9 from the
Lower Shajara Reservoir
Fig. 15 Incremental and cumulative PSD versus pore radius of
sample SJ11 from the Lower Shajara Reservoir
Fig. 16 Cumulative % SHg versus pore radius of sample SJ11 from
the Lower Shajara Reservoir
J Petrol Explor Prod Technol (2011) 1:1–9 7
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8. tracks of pore size distribution exist. The first having pore
radii ranging in size from 36 to 173.9 lm, whereas the
second ranges from 3.6 to 36 lm.
Sample SJ13 represents the upper section of the reser-
voir. It is described as coarse-grained, moderately sorted
sandstone. Again it is characterized with bimodal pore size
distribution as illustrated in Fig. 19 with an average pore
radius of 25.2 lm. This sample is also considered hetero-
geneous as indicated in Fig. 20 where three distinct tracks
of pore radii are observed. Reservoir classification of the
Upper Shajara can be considered as megaporous.
In an overall view, and based on the relationship of R35
and Rapex presented in Fig. 21, the reservoir quality of the
Shajara Formation increases with the increase in mean pore
radius corresponding to the apex and to that corresponding
to 35% mercury saturation. Good correlation was obtained
Fig. 17 Incremental and cumulative PSD versus pore radius of
sample SJ12 from the Lower Shajara Reservoir
Fig. 18 Incremental and cumulative % SHg versus pore radius of
sample SJ12 from the Lower Shajara Reservoir
Fig. 19 Incremental and cumulative PSD versus pore radius of
sample SJ13 from the Lower Shajara Reservoir
Fig. 20 Cumulative % SHg versus pore radius of sample SJ13 from
the Lower Shajara Reservoir
Fig. 21 Winland R35 versus Pittman Rapex
8 J Petrol Explor Prod Technol (2011) 1:1–9
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9. for the R35 versus Rapex and all samples mean pore sizes are
grouped at megaporous category except for sample SJ3
which falls on macroporous category confirming the pre-
viously discussed pore size identification. In conclusion,
grain and pore size variability are the controlling factor on
the Shajara reservoir quality assessment.
Conclusions
• The three reservoirs of the Shajara Formation are
characterized as heterogeneous reservoirs.
• In general, the three Shajara Reservoirs are classified as
megaporous, with average pore size of 22, 49 and
45 lm for the Lower, Middle, and Upper Shajara
Reservoirs, respectively. However, the best reservoir
quality is assigned to the lower sand unit of the Lower
Shajara followed by the Middle Shajara Reservoir.
• Pore radius corresponding to the apex and that corre-
sponding to the 35% mercury saturation confirms the
reservoir classification indicating megaporous reser-
voirs except for SJ3 of the Lower Shajara which has
low quality due to its fine grain characteristic and its
proximity to the unconformity surface.
• An excellent correlation factor of 0.93 was obtained
when Winland R35 was plotted versus Pittman Rapex.
• Reservoir quality is controlled to a large extent by the
depositional facies and specifically by rock texture
illustrated by petrophysical description. The quality of
the Shajara Formation reservoirs increases with the
increase in grain size and grain sorting.
Open Access This article is distributed under the terms of the
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mits any noncommercial use, distribution, and reproduction in any
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