Reservoir Property Of The Special Lithologic Section In The Lower K₁bt¹ Formation In The A'nan Depression Of The Er'lian Basin

With the development in the techniques of horizontal drilling and hydraulic fracturing,has helped to unlock huge resources of oil and gas trapped in tight rock,e.g.,shale and tight sandstone,tight reservoirs has been showing increasingly economic importance.It has been indicated that the pore structure at nanometer-micron scale of tight rocks primarily determines the storage capacity and seepage flow of hydrocarbon.Therefore,quantitatively characterizing the pore size distribution?PSD?of tight rock is the cornerstone for tight hydrocarbon evaluation and exploration.The lithology of the lower section of Member 1 of Tengger Formation?K₁bt¹?in A'nan depression,er'lian basin is complex,is the potential reservoir strata.Taking AM2 well as an example,the size of mineral particle from bottom to top becomes smaller,it's characterized by fine sandstone,siltstone,silty mudstone,tuff,sedimentary tuff,dolomitic mudstone.The content of dolomite in the dolomitic mudstone is gradually increased by the influence of the increase of salinity,and it is evolved into argillaceous dolomite-microcrystalline dolomite.The dolomitic mudstone is source rock and cap rock,the sedimentary tuff,siltstone and fine sandstone are the reservoirs with a large number of dissolution holes,which is attributed to dissolution of diagenetic fluid.Different rocks constitute multiple sets of source-reservoir-cover matching combination.Gas adsorption method is the commonly used micro-mesoporous measurement technique,and optimal gas adsorption operation conditions of tight rock were explored.The results show that using N₂ as probe gas,the optimal testing equilibration time is 20s,80 ? degassing for 36 hours,and sample grain size ranges in 20?50 mesh,with the quenched solid density functional theory?QSDFT?analyzing gas adsorption isotherms,which can obtain accurate data of sample pore structure,such as PSD in micro-mesoporous range,specific surface area,etc.On this basis,the full PSD of tight rock samples can be obtained by combining the large pore PSD obtained by mercury intrusion method.Based on the optimized parameters of gas adsorption test and the test result of mercury injection method,the full PSD of various lithologic samples such as mudstone,sedimentary tuff and sandstone is obtained.Dark mudstone is the source rock and cap rock,and the PSD is concentrated in 4-30nm.The intergranular pores,microcracks and bedding planes developed in the rock can be used as the main hydrocarbon expulsion channel,the expulsed hydrocarbons are stored in adiacent reservoirs.The pores greater than 10nm and micro-cracks in the sedimentary tuff and sandstone are the main reservoir space of hydrocarbons.