Characterization Of Compact Carbonate Pore-Throat And Aggregation Mechanism Of The Xiagou Formation In The Qingxi Sag,Jiuquan Basin,China

The Xiagou Formation(k₁g)in Qingxi Sag,Jiuquan basin primarily comprises compact carbonate reservoirs.In these reservoirs,micrometer-and nanometer-scale pore-throat systems are widely developed.Pore throats have complex interconnections.These interconnected pore-throat systems constitute the main reservoir spaces of the compact carbonate reservoirs.To characterize the microscopic pore-throat network systems of the compact reservoirs completely and finely,30 pieces of compact core samples were collected and investigated using nuclear magnetic resonance(NMR)and nanocomputed tomography(CT)techniques,and the samples in the study area were simulated by simulation experiments.The pores in the study area are mainly nanoscale pore,pore size distribution mainly in the range of 30?400nm,especially in the range of 50?200nm.The reservoir space of carbonate micro-and nanoscale pores in the Xiagou Formation predominantly includs primary porosity,dissolution pores,and microcracks,these are divided into five types:nanointragranular microfractures,nanoscale granule edge microfractures,interparticle primary porosity,carbonate dissolution pores and calcite intragranular dissolution pores.The connectivity of the pores are affected by the effective throat-pore ratio and the average coordination number.At the nanometer scale,these pores are columnar and spheroidal.Nanometer-scale spheroidal micropores shows poor connectivity and are isolated in terms of 3D space;most are used as reservoir spaces.However,nanometer-scale columnar micropores showed certain connectivity.The nanometer-scale columnar are connected with micrograde columnar micropores and are adjacent to isolated spheroidal nanometer-scale micropores to a certain degree and acted as both pore throats and pores.The simulation experiments show that in order to form a tight oil accumulation,these three conditions must be achieved:excellent configuration,excellent Crack and excellent source.It must be have dynamic for the accumulation of tight oil,and the accumulation is divided into several stages,at the same time is effected by the degree of pore development and the degree of throat development.