Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or ca...Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil （gas） saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone （oil displacing water）, we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that： 1） Oil migration （oil displacing water） in low- permeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2） With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0, the percolation curve shows modified Darcy flow characteristics, while when the apparent fluidity up＂ non-Darcy percolation curve; 3） Oil-water is less than 1.0, the percolation curve is a ＂concave- two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4） The oil saturation of low- permeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.展开更多
Due to inherent limits of data acquisition and geophysical data resolution, there are large uncertainties in the characterization of subsurface fractures. However, outcrop analogies can provide qualitative and quantit...Due to inherent limits of data acquisition and geophysical data resolution, there are large uncertainties in the characterization of subsurface fractures. However, outcrop analogies can provide qualitative and quantitative information on a large number of fractures, based on which the accuracy of subsurface fracture characterization can be improved. Here we take the tectonic fracture modeling of an ultra-low permeability sandstone reservoir based on an outcrop analogy, a case study of the Chang6t~ Formation of the Upper Triassic Yanchang Group of the Wangyao Oilfield in the Ordos Basin of China. An outcrop at the edge of the basin is a suitable analog for the reservoir, but the prerequisite is that they must have equivalent previous stress fields, similar final structural characteristics, relative timing and an identical depositional environment and diagenesis. The relationship among fracture density, rock type and bed thickness based on the outcrop is one of the most important fracture distribution models, and can be used to interpret fracture density in individual wells quantitatively. Fracture orientation, dip, geometry and scale, also should be described and measured in the outcrop, and can be used together with structure restoration and single well fracture density interpretation to guide fracture intensity prediction on bed surfaces and to constrain the construction of the 3D fracture geometry model of the subsurface reservoir. The application of the above principles shows the outcrop-based tectonic fracture models of the target ultra-low permeability sandstone reservoir are consistent with fractures inferred from microseismic interpretation and tracer tests. This illustrated that the fracture modeling based on the outcrop analogy is reliable and can reduce the uncertainty in stochastic fracture modeling.展开更多
According to the characteristics of"structural elements"(framework grain,interstitial material and pore throat structure)of low-permeability sandstone reservoir,the"step by step dissolution and separati...According to the characteristics of"structural elements"(framework grain,interstitial material and pore throat structure)of low-permeability sandstone reservoir,the"step by step dissolution and separation"acidification and acid fracturing technology has been developed and tested in field.There are three main mechanisms affecting permeability of low-permeability sandstone reservoir:(1)The mud fillings between the framework grains block the seepage channels.(2)In the process of burial,the products from crystallization caused by changes in salinity and solubility and uneven migration and variation of the syn-sedimentary formation water occupy the pores and throat between grains.(3)Under the action of gradual increase of overburden pressure,the framework grains of the rock is compacted tighter,making the seepage channels turn narrower.The"step by step dissolution and separation"acidification(acid fracturing)technology uses sustained release acid as main acidizing fluid,supramolecular solvent instead of hydrochloric acid to dissolve carbonate,and a composite system of ammonium hydrogen fluoride,fluoroboric acid,and fluorophosphoric acid to dissolve silicate,and dissolving and implementing step by step,finally reaching the goal of increasing porosity and permeability.By using the technology,the main blocking interstitial material can be dissolved effectively and the dissolution residual can be removed from the rock frame,thus expanding the effective drainage radius and increasing production and injection of single well.This technology has been proved effective by field test.展开更多
Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan’an Formation and the lowstand system tract of the Zhiluo Formation, and there is a regio...Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan’an Formation and the lowstand system tract of the Zhiluo Formation, and there is a regional unconformity between them. The Dongsheng uranium deposit is associated with the Jurassic coal measures. Research data indicate that the Jurassic coal measures in the study area have a certain hydrocarbon-generating capacity, although the metamorphic grade is low （Ro=0.40%–0.58%）. In the Dongsheng region alone, the accumulative amount of generated coalbed methane （CBM） is about 2028.29 × 108 –2218.72 × 108 m3; the residual amount is about 50.92 × 108 m3, and the lost amount is about 1977 × 108 m3. Analysis of the burial history of the host rocks and the evolutionary history of the Dongsheng uranium deposit suggests that the Jurassic coal measures generated hydrocarbon mainly from Middle Jurassic to Early Crataceous, which is the main mineralization phase of the Dongsheng uranium deposit. By the Late Cretaceous, a mass of CBM dissipated due to the strong tectonic uplift, and the Dongsheng uranium deposit stepped into the preservation phase. Therefore, the low-mature hydrocarbon-containing fluid in the Jurassic coal measures not only served as a reducing agent for the formation of sandstone-type uranium deposits, but also rendered the second reduction of paleo-interlayer oxidation zone and become the primary reducing agent for ore conservation. Regional strata correlation reveals that the sandstone-type uranium reservoir at the bottom of the Zhiluo Formation is in contact with the underlying industrial coal seams in the Yan’an Formation through incision or in the form of an unconformity surface. In the Dongsheng region with poorly developed fault systems, the unconformity surface and scour surface served as the main migration pathways for low-mature hydrocarbon-containing fluid migrating to the uranium reservoir.展开更多
Jiyang depression, which is the main oil productive area of Shengli oil field, is located at the southeast part of the Bohai Bay Basin and is a terrestrial lacustrine rift subsidence basin formed in the late Mesozoic ...Jiyang depression, which is the main oil productive area of Shengli oil field, is located at the southeast part of the Bohai Bay Basin and is a terrestrial lacustrine rift subsidence basin formed in the late Mesozoic with fully developed fault system. The main hydrocarbon productive formations of this depression are the terrestrial clastic rocks of the Tertiary, which are of strong lateral variation. The complex fault reservoirs and subtle lithological reservoirs distributed extensively and are becoming the main exploration targets in recent years. The exploration and development practice in these years has formed the exploration technologies, mainly including detailed study and description of low grade faults, delineation of microstructures, facies constrained formation description and prediction and low resistivity oil bearing formation’s identification. These exploration technologies have resulted in remarkable effectiveness on the reserve and oil production increments.展开更多
The classification of low permeability-tight reservoirs is the premise of development. The deep reservoir of Shahejie 3 member contains rich low permeability-tight reserves, but the strong heterogeneity and complex mi...The classification of low permeability-tight reservoirs is the premise of development. The deep reservoir of Shahejie 3 member contains rich low permeability-tight reserves, but the strong heterogeneity and complex micro pore structure make the main controlling factors subjective and the classification boundaries unclear. Therefore, a new indicator considering the interaction between fluid and rock named Threshold Flow Zone Indicator(TFZI) is proposed, it can be used as the main sequence of correlation analysis to screen the main controlling factors, and the clustering algorithm is optimized combined with probability distribution to determine the classification boundaries. The sorting coefficient, main throat radius, movable fluid saturation and displacement pressure are screened as the representative parameters for the following four key aspects: rock composition, microstructure, flow capacity and the interaction between rock and fluid. Compared with the traditional probability distribution and clustering algorithm, the boundary of the optimized clustering algorithm proposed in this paper is more accurate.The classification results are consistent with sedimentary facies, oil levels and oil production intensity.This method provides an important basis for the development of low permeability-tight reservoirs.展开更多
The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South...The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South China Sea,is characterized by intense thermal fluid activities related to mud diapir and large-scale shallow-water gravity flow deposits.The multi-episodic invasion of high-temperature and CO_(2)-rich thermal fluid into the formation induces complex water-rock reaction during diagenetic pro-cess,providing a preferable investigation opportunity for revealing how thermal fluid affects reservoir quality.This study characterizes the reservoirs in the formation through core and thin section analyses as well as physical property test.The reservoirs are dominated by fine-grained sandstone characterized by medium porosity(15.2-21.3%)and lower permeability(0.56-15.75mD).Based on an analysis of casting thin section,cathode luminescence(CL),scanning electron microscope(SEM),carbon and oxygen isotope,inclusion test,and electron-probe microanalysis(EPMA),we systematically investigate the diagenetic patterns and pore evolution process for the reservoirs in the formation.The episodic invasion of thermal fluid occurred approximately 0.4 Ma ago plays an important role in controlling reservoir development:The CO_(2)-rich formation water induces massive late-stage dissolution,resulting in a higher proportion of dissolved pores(38.7-46.4%),which improves the porosity of reservoirs at a depth of 2600-3100 m.Nevertheless,the late dissolution together with carbonate cementation occurred in closed diagenetic system blocks most seepage channels.Furthermore,the relatively high level clay mineral transformation in the YF1 area leads to a higher content of authigenic illite(44-62%)in the formation.Massive authigenic illite severely blocks the pore throats in fine sandstone,reducing permeability.This study offers an insight to the understanding of mud diapir-derived thermal fluid affecting and controlling the quality of reservoirs in some areas of the Yinggehai Basin.展开更多
基金supported by the National Natural Science Foundation Project (No.40772088)the National Basic Research Program ("973" Program,Grant No. 2006CB202305)
文摘Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil （gas） saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone （oil displacing water）, we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that： 1） Oil migration （oil displacing water） in low- permeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2） With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0, the percolation curve shows modified Darcy flow characteristics, while when the apparent fluidity up＂ non-Darcy percolation curve; 3） Oil-water is less than 1.0, the percolation curve is a ＂concave- two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4） The oil saturation of low- permeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.
基金supported by Open Fund (PLC201203) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology)Major Project of Education Department in Sichuan Province (13ZA0177)
文摘Due to inherent limits of data acquisition and geophysical data resolution, there are large uncertainties in the characterization of subsurface fractures. However, outcrop analogies can provide qualitative and quantitative information on a large number of fractures, based on which the accuracy of subsurface fracture characterization can be improved. Here we take the tectonic fracture modeling of an ultra-low permeability sandstone reservoir based on an outcrop analogy, a case study of the Chang6t~ Formation of the Upper Triassic Yanchang Group of the Wangyao Oilfield in the Ordos Basin of China. An outcrop at the edge of the basin is a suitable analog for the reservoir, but the prerequisite is that they must have equivalent previous stress fields, similar final structural characteristics, relative timing and an identical depositional environment and diagenesis. The relationship among fracture density, rock type and bed thickness based on the outcrop is one of the most important fracture distribution models, and can be used to interpret fracture density in individual wells quantitatively. Fracture orientation, dip, geometry and scale, also should be described and measured in the outcrop, and can be used together with structure restoration and single well fracture density interpretation to guide fracture intensity prediction on bed surfaces and to constrain the construction of the 3D fracture geometry model of the subsurface reservoir. The application of the above principles shows the outcrop-based tectonic fracture models of the target ultra-low permeability sandstone reservoir are consistent with fractures inferred from microseismic interpretation and tracer tests. This illustrated that the fracture modeling based on the outcrop analogy is reliable and can reduce the uncertainty in stochastic fracture modeling.
基金Supported by the China National Science and Technology Major Project(2017ZX05049-004)
文摘According to the characteristics of"structural elements"(framework grain,interstitial material and pore throat structure)of low-permeability sandstone reservoir,the"step by step dissolution and separation"acidification and acid fracturing technology has been developed and tested in field.There are three main mechanisms affecting permeability of low-permeability sandstone reservoir:(1)The mud fillings between the framework grains block the seepage channels.(2)In the process of burial,the products from crystallization caused by changes in salinity and solubility and uneven migration and variation of the syn-sedimentary formation water occupy the pores and throat between grains.(3)Under the action of gradual increase of overburden pressure,the framework grains of the rock is compacted tighter,making the seepage channels turn narrower.The"step by step dissolution and separation"acidification(acid fracturing)technology uses sustained release acid as main acidizing fluid,supramolecular solvent instead of hydrochloric acid to dissolve carbonate,and a composite system of ammonium hydrogen fluoride,fluoroboric acid,and fluorophosphoric acid to dissolve silicate,and dissolving and implementing step by step,finally reaching the goal of increasing porosity and permeability.By using the technology,the main blocking interstitial material can be dissolved effectively and the dissolution residual can be removed from the rock frame,thus expanding the effective drainage radius and increasing production and injection of single well.This technology has been proved effective by field test.
基金sponsored by the National Natural Science Foundation Program of China (Nos.40772072 and 40802023)the Uranium Deposit Geological Program of Bureau of Geology,CNNC,the National Important Basic Research Program of China (No.2003CB214603 and No.2015CB453003)the Dongsheng coal and uranium exploration program of Central Geological exploration Fund (No.2008150013)
文摘Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan’an Formation and the lowstand system tract of the Zhiluo Formation, and there is a regional unconformity between them. The Dongsheng uranium deposit is associated with the Jurassic coal measures. Research data indicate that the Jurassic coal measures in the study area have a certain hydrocarbon-generating capacity, although the metamorphic grade is low （Ro=0.40%–0.58%）. In the Dongsheng region alone, the accumulative amount of generated coalbed methane （CBM） is about 2028.29 × 108 –2218.72 × 108 m3; the residual amount is about 50.92 × 108 m3, and the lost amount is about 1977 × 108 m3. Analysis of the burial history of the host rocks and the evolutionary history of the Dongsheng uranium deposit suggests that the Jurassic coal measures generated hydrocarbon mainly from Middle Jurassic to Early Crataceous, which is the main mineralization phase of the Dongsheng uranium deposit. By the Late Cretaceous, a mass of CBM dissipated due to the strong tectonic uplift, and the Dongsheng uranium deposit stepped into the preservation phase. Therefore, the low-mature hydrocarbon-containing fluid in the Jurassic coal measures not only served as a reducing agent for the formation of sandstone-type uranium deposits, but also rendered the second reduction of paleo-interlayer oxidation zone and become the primary reducing agent for ore conservation. Regional strata correlation reveals that the sandstone-type uranium reservoir at the bottom of the Zhiluo Formation is in contact with the underlying industrial coal seams in the Yan’an Formation through incision or in the form of an unconformity surface. In the Dongsheng region with poorly developed fault systems, the unconformity surface and scour surface served as the main migration pathways for low-mature hydrocarbon-containing fluid migrating to the uranium reservoir.
文摘Jiyang depression, which is the main oil productive area of Shengli oil field, is located at the southeast part of the Bohai Bay Basin and is a terrestrial lacustrine rift subsidence basin formed in the late Mesozoic with fully developed fault system. The main hydrocarbon productive formations of this depression are the terrestrial clastic rocks of the Tertiary, which are of strong lateral variation. The complex fault reservoirs and subtle lithological reservoirs distributed extensively and are becoming the main exploration targets in recent years. The exploration and development practice in these years has formed the exploration technologies, mainly including detailed study and description of low grade faults, delineation of microstructures, facies constrained formation description and prediction and low resistivity oil bearing formation’s identification. These exploration technologies have resulted in remarkable effectiveness on the reserve and oil production increments.
基金supported by China Natural Science Foundation(Grant No.51704303)Beijing Natural Science Foundation(Grant No.3173044)。
文摘The classification of low permeability-tight reservoirs is the premise of development. The deep reservoir of Shahejie 3 member contains rich low permeability-tight reserves, but the strong heterogeneity and complex micro pore structure make the main controlling factors subjective and the classification boundaries unclear. Therefore, a new indicator considering the interaction between fluid and rock named Threshold Flow Zone Indicator(TFZI) is proposed, it can be used as the main sequence of correlation analysis to screen the main controlling factors, and the clustering algorithm is optimized combined with probability distribution to determine the classification boundaries. The sorting coefficient, main throat radius, movable fluid saturation and displacement pressure are screened as the representative parameters for the following four key aspects: rock composition, microstructure, flow capacity and the interaction between rock and fluid. Compared with the traditional probability distribution and clustering algorithm, the boundary of the optimized clustering algorithm proposed in this paper is more accurate.The classification results are consistent with sedimentary facies, oil levels and oil production intensity.This method provides an important basis for the development of low permeability-tight reservoirs.
文摘The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South China Sea,is characterized by intense thermal fluid activities related to mud diapir and large-scale shallow-water gravity flow deposits.The multi-episodic invasion of high-temperature and CO_(2)-rich thermal fluid into the formation induces complex water-rock reaction during diagenetic pro-cess,providing a preferable investigation opportunity for revealing how thermal fluid affects reservoir quality.This study characterizes the reservoirs in the formation through core and thin section analyses as well as physical property test.The reservoirs are dominated by fine-grained sandstone characterized by medium porosity(15.2-21.3%)and lower permeability(0.56-15.75mD).Based on an analysis of casting thin section,cathode luminescence(CL),scanning electron microscope(SEM),carbon and oxygen isotope,inclusion test,and electron-probe microanalysis(EPMA),we systematically investigate the diagenetic patterns and pore evolution process for the reservoirs in the formation.The episodic invasion of thermal fluid occurred approximately 0.4 Ma ago plays an important role in controlling reservoir development:The CO_(2)-rich formation water induces massive late-stage dissolution,resulting in a higher proportion of dissolved pores(38.7-46.4%),which improves the porosity of reservoirs at a depth of 2600-3100 m.Nevertheless,the late dissolution together with carbonate cementation occurred in closed diagenetic system blocks most seepage channels.Furthermore,the relatively high level clay mineral transformation in the YF1 area leads to a higher content of authigenic illite(44-62%)in the formation.Massive authigenic illite severely blocks the pore throats in fine sandstone,reducing permeability.This study offers an insight to the understanding of mud diapir-derived thermal fluid affecting and controlling the quality of reservoirs in some areas of the Yinggehai Basin.
