Difference of micro-pore throat characteristics in extra-low permeability sandstone of different pore throat matching relationship

There are different pore throat matching relationship and micro-pore throat characteristics for similar or equal sandstones because of different deposition and diagenesis reconstruction. Taking the Chang6 sandstone of Yanchang Formation in Wuqi area and the X₂ sandstone of Xishanyao Formation in Niujuanhu area as the objects, the micro-pore throat characteristics in different pore throat matching relationships are evaluated quantitatively using physical property testing, cast section and constant rate mercury penetration technique. The results show that there are no obvious differences in pore parameters, and the differences of micro-pore throat characteristics are mainly presented in throat parameters for samples with different permeabilities. As to the X₂ sandstone, the generation of dissolution pores and intercrystal pores leads to high content of curved lamellar and tube bundle throat, small throat radius and narrow distribution, concentrated contribution of throat to permeability, fine average throat radius and main flow throat radius, high content of big pore throat ratio in Niujuanhu area. In the Chang6 sandstone, necking, flaky and curved lamellar throats develop, throat radius vary obviously, and big throats are in high content, which can be explained by the generation of primary intercrystal pores. Different steps should be taken in the development process for extra-low permeability sandstone reservoirs which present different pore throat matching relationships.