川中-川西过渡带沙溪庙组第二段致密砂岩储层物性控制因素及孔隙演化

Control factors and pore evolution of tight sandstone reservoir of the Second Member of Shaximiao Formation in the transition zone between central and western Sichuan Basin,China

探讨川中-川西过渡地区中侏罗统沙溪庙组第二段绿泥石相和溶蚀相储层物性控制因素及孔隙演化过程。通过铸体薄片鉴定、扫描电镜分析、包裹体均一温度以及碳氧同位素等手段,开展了储层压实作用、胶结作用损失孔隙度以及溶蚀作用增加孔隙度的定时-定量研究。结果表明,压实作用是沙二段储层物性变差的第一重要因素,分别造成了溶蚀相和绿泥石相储层28.18%和22.18%的孔隙度损失;由胶结作用造成的孔隙度损失分别为8.25%和9.11%;溶蚀作用是储层物性改善的重要因素,由溶蚀作用所增加的次生孔隙度分别为5.64%和1.54%。绿泥石相和溶蚀相储层的孔隙演化有明显差异。绿泥石相储层抗压实能力较强,早期压实损失孔隙较少,在1 km埋深时,孔隙度下降至19.8%;而溶蚀相储层在1 km埋深时,孔隙度下降至16.5%左右。溶蚀作用对二者的影响也存在明显差异,绿泥石相储层增加了1.54%左右的溶蚀孔隙度,在1.7 km埋深时,孔隙度保持在18.5%左右;溶蚀相储层则增加了5.64%左右的溶蚀孔隙度,在1.7 km埋深时,孔隙度为18%左右。在晚期胶结物的作用下,储层孔隙度进一步下降,绿泥石相储层在埋深为2.48 km左右时孔隙度下降至12%,直至目前的10.25%;溶蚀相储层在埋深为2.2 km左右时孔隙度下降至12%,现今孔隙度为9.21%。储层致密化均在烃源岩生排烃高峰期之后。

Quantitative study of porosity variation in Member 2 of the Upper Jurassic Shaximiao Formation(J2s2),caused by compaction,cementation and dissolution is carried out on the basis of thin section observation,analysis of SEM,fluid inclusion homogeneous temperature and carbon and oxygen isotopes of carbonate cement.It shows that the compaction is the most important factor affecting the physical property of reservoir.In fact,compaction brings about 28.18%and 22.18%porosity losses in denudation facies and chlorite facies reservoirs respectively,while dissolution is an important factor improving the physical property of reservoirs.Dissolution leads to the formation of secondary pores and creates porosity of 5.64%and 1.54%.The pore evolution of denudation facies and chlorite facies reservoirs shows significant difference.In fact,the chlorite facies reservoir has stronger ability to resist the compaction with less loss of porosity and at the depth of 1 km,the porosity falls to 19.8%.However,for the denudation facies the porosity falls to 16.5%at the same depth.The porosity of dissolution pores in chlorite facies reservoir reaches to 1.54%,and keeps to about 18.5%at 1.7 km depth.While the porosity of dissolution pores in denudation facies reservoir reaches to 5.64%,and keeps to 18%at 1.7 km depth.The late cement results in decease of reservoir porosity and the porosity of chlorite facies reservoir falls to 12%at the depth of 2.48 km,and the porosity of denudation facies reservoir falls to 12%at the depth of 2.2 km.It is considered that the reservoir densification occurred after the peak of hydrocarbon generation and expulsion of the source rocks.