不同孔喉匹配关系下的特低渗透砂岩微观孔喉特征差异

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

因沉积和成岩作用改造不同,渗透率相近或相等的砂岩,微观孔喉特征参数存在明显差异。以吴起地区延长组长6砂岩和牛圈湖地区西山窑组X2砂岩为对象,综合利用物性、铸体薄片和恒速压汞对不同孔喉匹配关系下的微观孔喉特征参数进行了定量对比。结果表明,各渗透率级别样品的孔隙参数差异不大,微观孔喉特征的差异主要体现在喉道上。发育的溶蚀孔和晶间孔造成X2砂岩的弯片状、管束状喉道含量高,喉道半径小且分布范围窄,对渗透率贡献集中,平均喉道半径和主流喉道半径小、大孔喉比含量高。长6砂岩缩颈状、片状和弯片状喉道发育,喉道半径差异大、大喉道含量高的特征归因于发育的原生粒间孔。不同孔喉匹配关系下的特低渗透砂岩,开发过程中应区别对待。

There are different pore throat matching relationship and micro-pore throat characteristics equal sandstones because of different deposition and diagenesis reconstruction. Taking the Chang6 for similar or 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.