扬子地块古生界泥页岩孔隙度和渗透率特征

Porosity and Permeability of Paleozoic Mudstone and Shale in the Yangtze Block

系统测量了浙江安吉下寒武统荷塘组、安徽泾县中奥陶统胡乐组、重庆下志留统龙马溪组、安徽昌桥上二叠统龙潭组的典型泥页岩样品的密度、孔隙度和渗透率。结果表明,扬子地块古生界泥页岩的孔隙度较低,介于0.73%-2.95%之间,有效孔隙度随压力增加而减小。在10MPa的有效压力下,渗透率介于（1.25-7.15）×10^-22 m2之间,微裂缝能显著提高样品的渗透率。由于加载过程中微裂隙的逐渐关闭,泥页岩的渗透率随有效压力增加而呈指数关系减小,但在卸载过程中渗透率的恢复具有滞后效应。低于20MPa的有效压力,孔隙压振荡法获得的页岩渗透率值显著低于压力脉冲衰减法。

We measured density,porosity and permeability of typical mudstone and shale samples from the Lower Cambrian Hetang Formation,Lower Ordovician Ningguo Formation,Middle Ordovician Hule Formation,Lower Silurian Longmaxi Formation,and Upper Permian Changqiao Formation in the Yangtze block.Our mudstone and shale samples have very low porosity between 0.73%-2.95%,and the effective porosity increases with pressure.Under the effective pressure of 10 MPa,the matrix permeability of sample ranges from 1.25×10^-22 m^2 to 7.15×10^-22 m^2.The occurrence of microcracks can remarkably enhance the permeability of samples.Permeability of mudstone and shale decreases exponentially with increasing effective pressure,which can be attributed to the gradual closure of microcracks and pores with pressure.Hysteresis of effective porosity and permeability were observed during the pressurization-depressurization cycle.Below 20 MPa,permeability derived from pore pressure oscillation method is significantly lower than that from the pressure pulse decay method.