川东南志留系小河坝组致密砂岩储层孔隙结构

Pore structures of the Xiaoheba Formation tight sandstone reservoirs in southeastern Sichuan Basin, China

针对川东南地区下志留统小河坝组致密砂岩储层,利用铸体薄片、扫描电镜、物性测试、高压压汞、恒速压汞等技术手段,结合前人的研究成果,对储层微孔隙类型和结构特征进行研究。结果表明:储层演化程度较高,原生孔隙发育较少,次生溶孔占总孔隙的80%,包括微米级粒间溶孔、微米-纳米级粒内溶孔和杂基溶孔;高压压汞屏蔽了半径较大的孔隙,表征的孔喉半径为0.01～1.26μm,半径>0.1μm的喉道所占比例<10%;恒速压汞测试表明,渗透率不同的样品孔隙半径大小及分布范围相近,孔隙半径主要集中在145μm左右,分布范围为40～260μm;喉道半径大小相差悬殊,且分布范围较大,为0.1～2.7μm。高压压汞和恒速压汞结合表征小河坝组致密砂岩的孔隙半径为0.01～260μm,喉道半径为0.01～2.7μm;致密储层孔隙度主要受单位体积有效孔隙数量、有效孔隙半径大小的影响,而渗透率主要受控于有效喉道半径的大小和分布,储层物性的差异则是这些孔-喉结构参数共同影响的综合体现。

Thin section analysis, scanning electron microscopy (SEM), physical property testing, high-pressure mercury penetration (HPMP) and constant speed mercury penetration (CSMP) are used to study the characteristics of micro pores and structures in Lower Silurian Xiaoheba Formation tight sandstone reservoir in southeastern Sichuan Basin. The results show that there are fewer primary pores in the sandstone due to higher-evolutionary of the reservoir and most of the reservoir pores are secondary dissolved pores, including micro intergranular dissolved pore, micro-nano intragranular dissolved pore and mudstone matrix dissolved pore, which account for 80 percent of the total pore space. The small parts of pore-throat sizes characterized by HPMP range from 0.01 to 1.26 μm, and the pore-throats with the radius>0.1 μm are less than 10%. CSMP analysis reveals that for the samples with different permeability, there pore radius distribution is relatively concentrated, ranging from 40 μm to 260 μm and with the peak radius of 145 μm, whereas throat radius displays a strong diversity (0.1~2.7 μm). The whole pore-throat size distribution characteristics of tight sandstone are characterized by combination of the HPMP and CSMP methods, and the pore sizes are in the range of 0.01~260 μm and the throat sizes are 0.01~2.7 μm. It is showed that the porosity of tight reservoir is mainly influenced by the numbers of effective pores per unit volume and the effective pore radius, while the permeability is controlled by the size and distribution of the effective throat radius. All kinds of parameters of pore-throat structures have a combined effect on physical property of tight reservoir.