Structural Characteristics Of Steep Slope Zone In Dongying Sag And Study On Densification Process Of Glutenite Reservoir Of Es₄

A set of compact glutenite reservoirs is developed in the fourth member of Shahejie Formation in the steep slope zone of northern Dongying Depression,which is one of the important reservoir types in unconventional oil and gas exploration.It is important to clarify the densification process and control factors of glutenite reservoirs for promoting the exploration of tight glutenite.Therefore,on the basis of many predecessors'research results,this paper takes the tight glutenite reservoir of the fourth member of Shahejie Formation in the steep slope zone of Dongying Sag as the research object,uses seismic data to analyze the structural evolution and structural characteristics of the steep slope zone area,analyses the sedimentary background and sedimentary model of the steep slope zone area through drilling cores,conventional thin sections and logging data,and adopts casting thin sections,scanning electron microscopy and overburden pressure hole.The characteristics and diagenesis of glutenite reservoir are analyzed by permeability and mercury injection analysis,and the densification process and controlling factors are studied by combining the above research with casting image analysis and fluid inclusion temperature measurement.The main achievements and understandings are as follows:1.The Shengbei Fault in the northern steep slope zone of Dongying Depression began to develop during the sedimentary period of the fourth member of Shahejie Formation,and arranged in parallel with the middle section of the Chennan Fault of the boundary faults in the East-West direction,forming the high and low steps of the reverse faults,forming the FAULT-STEPPED structural characteristics of the northern steep slope zone.2.The compact glutenite reservoir of Es₄ member in the northern steep slope zone of Dongying Depression is characterized by complex rock composition,low structural maturity and poor reservoir stratification.The glutenite of offshore underwater fan origin is formed at high steps,and the glutenite of slump turbidite fan origin is formed at low steps.Over 82%of the glutenite reservoirs in the northern steep slope zone of Dongying Depression belong to tight reservoirs.The throat types of glutenite reservoirs include necking throat,sheet throat and tubular throat.The pore types can be divided into fracture,primary intergranular pore and dissolution pore according to their genesis.The diagenesis types of tight sandstone reservoirs mainly include compaction,cementation and dissolution.3.The diagenesis sequence and hydrocarbon filling of tight sandstone reservoirs are analyzed.The diagenesis-filling sequence of offshore subaqueous fan sandy conglomerate is lithic dissolution-quartz enlargement-calcite cementation-compaction-oil and gas filling I-early feldspar dissolution-authigenic quartz-carbonate cementation-clay cementation-quartz solution-oil and gas filling II-late feldspar dissolution;slump turbidite fan sandy conglomerate The diagenesis sequence is chlorite cementation-calcite cementation-hydrocarbon filling I-debris dissolution-quartz augmentation/authigenic quartz-compaction-feldspar dissolution-carbonate cementation-clay cementation-quartz dissolution-hydrocarbon filling II-late pyrite cementation.Restoring the original porosity of glutenite reservoir in the early stage of sedimentation,the original porosity of offshore subaqueous fan glutenite reservoir is33.28%,and the original porosity of slump turbidite fan glutenite is 36.07%.According to the diagenesis-filling sequence,the process of reservoir physical property evolution is restored.4.Structural-sedimentary pattern controls the initial conditions for the formation of glutenite;compaction destroys the reservoir most at the initial stage of burial and tends to be gentle at the later stage;carbonate cementation has a greater impact on the decrease of porosity,clay cementation has a greater impact on the decrease of permeability,and hydrocarbon invasion and dissolution play a constructive role in the preservation and transformation of reservoirs.