The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is control...The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is controlled by sedimentation, diagenesis, and tectonics, and show complex pore structure and strong heterogeneity, thereby hindering effective natural gas exploration and development. Core, thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), conventional well logs and image logs are used to characterize the petrological characteristics and pore systems. Then a comprehensive analysis integrating sedimentation, diagenesis, and tectonics is performed to unravel the reservoir formation mechanism and distribution of reservoir quality. Results show that reservoir properties are generally environmentally selective. Coarse grained sandbodies (gravelly sandstones) formed in high depositional-energy have the best physical properties, while fine sandstone and mudstone with low depositional energy is easily to be tightly compacted, and have poor reservoir quality. Porosity usually decreases with compaction and cementation, and increases due to dissolution. Clay minerals filling pores result in a deterioration of the pore structure. Microfracture formed by fracturing can connect the matrix pores, effectively improving the reservoirs’ permeability. The differential distribution of fractures and in-situ stress plays an important role in modifying reservoir quality. The in-situ stress has obvious control over the matrix physical properties and fracture effectiveness. The matrix physical properties are negatively correlated with the value of horizontal stress difference (Δσ). As the value of Δσ increases, the pore structure becomes more complex, and the macroscopic reservoir quality becomes poor. The smaller the strike divergence between the natural fracture and SHmax, the lower the value of Δσ in the fracture layers is, and the better the fracture effectiveness is. Under the control of ternary factors on the reservoir, sedimentation-diagenesis jointly affect the matrix reservoir quality, while fractures and in-situ stress caused by tectonism affect the permeability and hydrocarbon productivity of the reservoir. Affected by ternary factors, reservoir quality and hydrocarbon productivity show obvious differences within the various structural location. Reservoir quality in tight sandstones can be predicted by integrating sedimentation, diagenesis, and tectonics (fracture and in-situ stress) in a compressional tectonic setting like Kuqa Depression. The research results will provide insights into the efficient exploration of oil and gas in Kuqa Depression as well as similar compressional tectonic settings elsewhere.展开更多
Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields.As a clastic reservoir,the water effect of Ahe formation in the northern structural belt of Kuqa is...Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields.As a clastic reservoir,the water effect of Ahe formation in the northern structural belt of Kuqa is strong as a whole,but the mechanism analysis of medium and strong water-sensitivity effect is restricted by the evaluation method with permeability damage rate as the main parameter.Taking the shape of water-sensitivity test curve as the starting point,combined with the analysis of microscopic pore throat and clay minerals,the difference of permeability change rate measured by samples is characterized.The strong to medium water-sensitivity effects in the study layer are divided into three types:The permeability gradually decreases in the early stage-the rapid decrease in the late stage,the continuous decrease in the permeability,and the rapid decrease in the early stage-the slow decrease in the later stage.As awidely developed reservoir space in the study section,the micropore not only has the characteristics of fine pore size and easy blockage,but also serves as the occurrence space of the main water-sensitive mineral illite-smectite mixed layer.Therefore,the change types of the above different water sensitivity test curves are mainly controlled by the difference of micropore content.When the micropore content is low,the permeability decreases slowly in the early stage and decreases rapidly in the later stage(type Ⅰ),while when the micropore content is high,the permeability decreases rapidly in the early stage and slowly decreases in the later stage(type Ⅱ),while when the micropore content is medium,the permeability decreases continuously,and there is no obvious rate change(type Ⅲ)before and after the micropore content.The results show that the structural characteristics and relative content differences of micropores in the samples are the internal mechanism of the difference of water sensitivity effect types.展开更多
基金supported by Science Foundation of China University of Petroleum,Beijing(No.2462023QNXZ010,No.2462023XKBH012,No.2462024XKBH009)China Postdoctoral Science Foundation(No.2024M753612,No.GZC20233101).
文摘The northern structural belt of Kuqa Depression is adjacent to the South Tianshan orogenic belt, which are characterized by complex geological conditions. The reservoir quality of the Jurassic Ahe Formation is controlled by sedimentation, diagenesis, and tectonics, and show complex pore structure and strong heterogeneity, thereby hindering effective natural gas exploration and development. Core, thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), conventional well logs and image logs are used to characterize the petrological characteristics and pore systems. Then a comprehensive analysis integrating sedimentation, diagenesis, and tectonics is performed to unravel the reservoir formation mechanism and distribution of reservoir quality. Results show that reservoir properties are generally environmentally selective. Coarse grained sandbodies (gravelly sandstones) formed in high depositional-energy have the best physical properties, while fine sandstone and mudstone with low depositional energy is easily to be tightly compacted, and have poor reservoir quality. Porosity usually decreases with compaction and cementation, and increases due to dissolution. Clay minerals filling pores result in a deterioration of the pore structure. Microfracture formed by fracturing can connect the matrix pores, effectively improving the reservoirs’ permeability. The differential distribution of fractures and in-situ stress plays an important role in modifying reservoir quality. The in-situ stress has obvious control over the matrix physical properties and fracture effectiveness. The matrix physical properties are negatively correlated with the value of horizontal stress difference (Δσ). As the value of Δσ increases, the pore structure becomes more complex, and the macroscopic reservoir quality becomes poor. The smaller the strike divergence between the natural fracture and SHmax, the lower the value of Δσ in the fracture layers is, and the better the fracture effectiveness is. Under the control of ternary factors on the reservoir, sedimentation-diagenesis jointly affect the matrix reservoir quality, while fractures and in-situ stress caused by tectonism affect the permeability and hydrocarbon productivity of the reservoir. Affected by ternary factors, reservoir quality and hydrocarbon productivity show obvious differences within the various structural location. Reservoir quality in tight sandstones can be predicted by integrating sedimentation, diagenesis, and tectonics (fracture and in-situ stress) in a compressional tectonic setting like Kuqa Depression. The research results will provide insights into the efficient exploration of oil and gas in Kuqa Depression as well as similar compressional tectonic settings elsewhere.
文摘Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields.As a clastic reservoir,the water effect of Ahe formation in the northern structural belt of Kuqa is strong as a whole,but the mechanism analysis of medium and strong water-sensitivity effect is restricted by the evaluation method with permeability damage rate as the main parameter.Taking the shape of water-sensitivity test curve as the starting point,combined with the analysis of microscopic pore throat and clay minerals,the difference of permeability change rate measured by samples is characterized.The strong to medium water-sensitivity effects in the study layer are divided into three types:The permeability gradually decreases in the early stage-the rapid decrease in the late stage,the continuous decrease in the permeability,and the rapid decrease in the early stage-the slow decrease in the later stage.As awidely developed reservoir space in the study section,the micropore not only has the characteristics of fine pore size and easy blockage,but also serves as the occurrence space of the main water-sensitive mineral illite-smectite mixed layer.Therefore,the change types of the above different water sensitivity test curves are mainly controlled by the difference of micropore content.When the micropore content is low,the permeability decreases slowly in the early stage and decreases rapidly in the later stage(type Ⅰ),while when the micropore content is high,the permeability decreases rapidly in the early stage and slowly decreases in the later stage(type Ⅱ),while when the micropore content is medium,the permeability decreases continuously,and there is no obvious rate change(type Ⅲ)before and after the micropore content.The results show that the structural characteristics and relative content differences of micropores in the samples are the internal mechanism of the difference of water sensitivity effect types.
