Reservoir Development Characteristics And Its Controlling Effect On Gas Accumulation Of Qigequan Formation Mud Shale Reservoir In Sanhu Area

Quaternary mud shale,as a new type of resource in the field of unconventional oil and gas,has huge resource potential and exploration and development value.The study of its reservoir development characteristics is conducive to enriching the geological theory of mud shale biogas reservoirs.Taking the Quaternary Qigequan Formation mud shale in the Sanhu area as the research object,the mud shale of the Qigequan Formation in the Sanhu area was comprehensively analyzed by means of geochemical analysis and testing,low temperature nitrogen adsorption,high pressure mercury intrusion,methane isothermal adsorption and other experiments.Based on the mineral composition,organic geochemistry and gas-bearing characteristics of the rock,the development characteristics of mud shale reservoirs and their controlling effects on accumulation were systematically studied,and the accumulation model of biological mud shale gas in Qigequan Formation was established.The main conclusions are as follows:(1)There are three types of lithofacies: clay mud shale,mixed mud shale and felsic mud shale in Qigequan Formation mud shale in Sanhu area of Qaidam Basin.There are brittle mineral intergranular pores,clay mineral pores,dissolution pores and organic pores.The pore volume of the Qigequan Formation mud shale is mainly contributed by macropores,and the specific surface area is mainly contributed by mesopores.The development characteristics of pore structure are mainly controlled by brittle minerals and clay minerals.(2)The development characteristics of mud shale reservoirs in Qigequan Formation control the occurrence and content of gas.Adsorbed gas is mainly affected by clay mineral content and mud shale pore structure.Different lithofacies mud shale reservoirs in Qigequan Formation have different pore structures,and different pore structure characteristics determine that free gas has various migration modes.(3)The continuous hydrocarbon generation of high-quality source rocks,the combination of dominant lithofacies and stratigraphic structural characteristics jointly control the accumulation of biological gas reservoirs.Mud shale at 1000～1600 m is the peak period of biogas and hydrocarbon generation;the superimposed combination of clay mud shale,mixed mud shale and felsic mud shale is a high-quality lithofacies combination,which is the storage and preservation of biogas space;current structural characteristics determine that the structural high part of the northern slope is a favorable sweet spot area for mud shale.(4)Combined with the analysis of the mud shale source rock hydrocarbon generation mechanism,reservoir development characteristics,stratigraphic structure and other characteristics,three types of mud shale-type biogas accumulation models can be established,which are the self-sealing and overpressure biologics of deep mud shale in the depression.Gas reservoirs,biological gas reservoirs formed by formation water sealing in slope belts,and superimposed dynamic normal-pressure gas reservoirs of mud shale unconventional gas reservoirs and sandstone conventional gas reservoirs in structural highs.The research on the development characteristics and accumulation mechanism of mudstone reservoirs has important theoretical and practical significance for guiding the exploration and development of biogas mudstone.