N21 reservoir characteristics of Erboliang-Ⅲ region in Qaidam basin

N21 reservoir is the main target layer of Erboliang-III region in Qaidam basin,and it belongs to shore and shallow lacustrine facies, with characteristics of fine grain sizes mainly of argillaceous siltstone,siltstone and fine sandstone,the deepest buried depth is up to 4000 m,while the intergranular pore preservation is good.The research on microscopic characteristics and controlling factors of the reservoirs plays a crucial role in expanding exploration to deep formations.Through a series of microscopic reservoir geological study,such as rock slice polarizing microscope observation,conventional physical properties test,and capillary pressure analysis,combined with core observation,macro distribution of sedimentary facies study,it can be concluded that the average porosity of reservoir is about 10%,permeability is mainly about(0.1 ~ 10)×10-3μm2,being of extra low permeability reservoir.The rock pore throat radius is small,but with good connectivity.The quality of the reservoirs is mainly controlled by two factors,the sedimentary environment and the diagenesis.Because of shore and shallow lacustrine sedimentary and remote transportation,the rock is mainly composed of fine grained sediments.Under continuous screening and segregation of the lacustrine effect,the clastic particles separation and granding are generally good.More rigid particles and early carbonate cementation can increase the rock compaction resistance in a certain extent.