致密砂岩微观孔隙结构参数对有效应力变化的响应

致密砂岩气层孔喉细小，开发过程中孔隙压力下降导致储层孔喉体积压缩，使得气层渗透率快速降低，储层损害问题十分严重。鉴于常规毛细管压力测试不能反映开发中有效应力增加时储层岩石孔隙结构的变化情况，故引入有效应力单面进汞毛细管压力测试对原地应力条件致密砂岩孔喉分布规律进行研究。测定有效应力为5 MPa、15 MPa和25 MPa的单面进汞毛细管压力参数，并与相应常规四面进汞样毛细管压力曲线参数对比，结果表明同一汞饱和度条件下单面进汞毛细管压力高于四面进汞，毛细管压力曲线表现为向右向上发生偏移，且随有效应力增加曲线的偏移程度增大。与四面进汞相比较，单面进汞排驱压力和饱和度中值压力增加，最大进汞饱和度降低，孔喉分布单面进汞孔喉偏粗部分体积比例减少、偏细部分体积比例增加，孔隙度及渗透率值大大降低。对具有应力敏感特征的致密砂岩气层的开发而言，储层评价和储层保护技术方案设计应考虑原地有效应力条件下的孔隙结构参数。

THE RESPONSE OF MICRO-PORE STRUCTURE PARAMETERS OF TIGHT SANDSTONE TO EFFECTIVE STRESS CHANGES

The pore throat of gas-filled tight sandstone is very slim, and the pore throat volume of the reservoir is compressed with the decline of the pore pressure during the process of exploitation, which results in rapid permeability decrease in the gas-filled reservoir and serious reservoir damages. As the conventional capillary pressure test can't reflect the changes of rock pore structure in the reservoir with the raise of the effective stress during the exploitation, the paper introduced capillary pressure test method of one-edge hydrargyrum-injection of effective stress to research the pore throat distribution rule in the tight sandstone under the autochthonous stress condition. The capillary pressure parameters of one-edge hydrargyrum-injection are measured with effective stress of 5 MPa, 15 MPa and 25 MPa respectively, and are compared with that resulted from the corresponding conventional four-edge hydrargyrum-injection method. The results shows if the hydrargyrum saturations are unchanged, compared with the method of four-edge hydrargyrum-injection, the capillary pressure of one-edge hydrargyrum-injection is higher, the capillary pressure curve offsets rightward and upwardly, and the curve offset extents increase with the raise of the effective stress. The expulsion pressure and saturation medium pressure become higher, the maximum hydragyrum saturation declines, and the volume proportion of wide pore throat parts becomes lower and that of thin pore throat part becomes higher, at the same time, the porosity and permeability decrease rapidly. For the exploitation of gas reservoirs in the tight sandstone which is sensitive to the stress, the pore structure parameters under the condition of autochthonous effective stress should be considered when the technical scheme for reservoir evaluation and reservoir protection is worked out.