--> --> Lithofacies of Deepwater Fine-Grained Depositional System and Its Significance for Shale Gas and Oil Exploration in Lacustrine Basin: An Insight from Qingshankou Formation, Qijia-Gulong Depression, Songliao Basin, Northeast China

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Lithofacies of Deepwater Fine-Grained Depositional System and Its Significance for Shale Gas and Oil Exploration in Lacustrine Basin: An Insight from Qingshankou Formation, Qijia-Gulong Depression, Songliao Basin, Northeast China

Abstract

In order to clarity the types of lithofacies in deepwater area of continental lacustrine basin and its affection towards shale gas/oil exploration, fine core observation, well logging analysis, interpretation of high resolution 3D seismic data, determination of whole core macerals and field emission scanning electron microscope pore research have been carry out in the shale area of Qingshankou Formation in Qijia-Gulong Depression, Songliao Basin. The results show that, six lithofacies can be identified in deepwater fine-grained depositional system, including oil shale, deepwater mud, bottom current rework sand (BCRS), shelly beach, turbidite, and mass transport deposits (MTD). Based on maceral analysis of 36 samples in deep water area of Qingshankou Fm in the study area, the occurrence of organic matter was divided into three types, which were enriched along the layer, disperse and enriched along layer-reworked. Hydrocarbon accumulation types of shale oil/gas were divided into three types on the basis of former study and division, which were matrix-dominated type, interlayer-dominated type and pore-dominated type. Good correlation has been found between lithofacies and the occurrence of organic matter, reservoir space types, and hydrocarbon accumulation types. Reservoir space types of oil shale and deepwater mud are dominated by organic matter pores, intergranular pores between clay minerals, intergranular pores between authigenic pyrite, and microfractures, which belonged to matrix-dominated hydrocarbon accumulation; shelly beach, bottom current rework sand (BCRS), and turbidite lithofacies were interlayer-dominated hydrocarbon accumulation, which were the favorable targets of shale gas and oil exploration; while mass transport deposits (MTD) were pore-dominated hydrocarbon accumulation with well developed primary pores and secondary dissolved pores.