Study On Geological Conditions Of Shale Gas Accumulation In The Lower Cambrian Shuijing Formation Of The Huangling Domal In Western Hubei Province

Western Hubei is an important shale gas exploration area in southern China.The shale is widely developed in the region,with large thickness,rich organic carbon content,high thermal evolution,large hydrocarbon generation,and shale gas bearing geological characteristics.The parameters are very similar to those of the foreign gas-bearing shale.Therefore,the exploration of the geological conditions of the reservoir and the exploration of its regularities of distribution are likely to achieve breakthroughs in the exploration and development of shale gas in this area.This paper focuses on the Lower Cambrian Shuijingtuo Formation in the Huangling domal structure,western Hubei,and combines petrology,sedimentology,petroleum geology,and shale on the basis of field sampling,microscopic slice identification,Mineral composition and petrophysical analysis and organic geochemical experimental data analysis.The multi-disciplinary theory of mineralogy and other disciplines systematically studied the geological conditions of shale gas accumulation in the Shuijingtuo Formation.The petrological characteristics,diagenesis type,sedimentary facies characteristics,organic geochemical characteristics and physical properties of shale reservoirs of organic-rich shale in the study area were carefully analyzed,and the sedimentary facies,diagenesis,rupture and region were summarized.The control of the reservoir is constructed.The reservoir pores of the reservoir and the reservoir properties such as porosity and permeability are analyzed in detail,and the favorable blocks and resources of the Shuijingtuo Formation are estimated.The black shale of the Shuijingtuo Formation in the study area is relatively developed,and the sedimentary environment is mainly shallow water-deep water shelf.The organic-rich black shale is mostly developed in the deep-water continental shelf,and the horizontal bedding is generally developed.The high content of brittle minerals such as quartz and pyrite in the mineral component is conducive to the later fracturing transformation.The reservoir development of the Shuijingtuo Formation is controlled by factors such as sedimentary facies,diagenesis,rupture and tectonic action.The diagenesis mainly includes compaction,cementation,dissolution,metasomatism,thermal evolution of organic matter and transformation of clay minerals.The wells in the study area are widely distributed,with large thickness and moderate buried depth.The organic geochemical characteristics show that they are more favorable for gas,and the physical characteristics indicate that the reservoir belongs to low porosity and low permeability.The pore types in shale are divided into organic pores,intragranular pores,and intergranular pores,The fractures formed under tectonic stress and diagenesis are also relatively developed,so reservoir storage space is more favorable for the occurrence of shale gas reservoirs.It is believed that the favorable shale gas block of the Shuijingtuo Formation in the study area should be in the zone where the reservoir depth is around 1500-3000m.There are many locations in the structural slope zone or stable zone,and the formation is stable and gentle and away from the fault development area.Such as the Yichang Slope Belt Area in the study area and the southern part of the Huangling domal structure area.The shale gas resources of the Shuijingtuo Formation in the study area were estimated by the volumetric method,and the estimated shale gas resources of the wells in the area were 0.2832×10~122 m~3.