四川盆地中江地区中侏罗统上沙溪庙组储层控制因素分析

CONTROL FACTORS OF SANDSTONE RESERVOIR OF UPPER SHAXIMIAO FORMATION IN ZHONGJIANG REGION,SICHUAN BASIN

上沙溪庙组是四川盆地中江地区勘探潜力较大的含油气层位之一。通过14口井231个样品普通薄片鉴定,79块铸体薄片面孔率统计,33个样品扫描电镜观察,42个砂岩样品孔隙度和渗透率实验结果,对中江地区中侏罗统上沙溪庙组砂岩储层进行研究,结果表明:研究区储层孔隙以次生孔隙为主,原生孔隙发育情况较差,其平均孔隙度为6.1%,平均渗透率为0.105×10-3μm2,总体表现为低孔、低渗特征。储集层性能的主要控制因素为沉积微相和成岩作用,机械压实、硅质胶结、碳酸盐胶结等使储层物性变差,早期的绿泥石环边胶结和溶蚀作用等则改善储集性能,三角洲前缘河道砂体储集性能较好。根据储层物性、孔隙结构参数等特征,中江地区上沙溪庙组砂岩可以划分为4种类型储层,其中Ⅰ类和Ⅱ类储集层最具勘探价值,Ⅰ类储集层见于曲流河三角洲前缘河道砂体,Ⅱ类储集层主要发育于辫状河三角洲前缘河道。

Upper Shaoximiao Formation is one of the gas stratigraphic horizons with great explo- ration potentiality in Zhongjiang region of Sichuan basin. This reservoir is investigated by analysis of lithology,thin sections,SEM and core properties. It is showed that the types of pore are mainly secondary pore, minor physical pore, and the reservoir is characterized by low porosity and permeability with average porosity of 6.1 %, average permeability of 0. 105 ×10.3 μm^2. Sedimentary microfacies and digenesis are the main factors which affect the quality of reservoir. Compaction, siliceous cementation, carbonate cementation are Unfavorable to the porosity and permeability of the sandstone, while denudation and chlorite cementation are favorable to the porosity and permeability of the sandstone. Distributary channel sandstone of delta front and delta plain are better microfacies for the reservoir development. According to petrophysical properties of reservoir and pore structure parameters,Upper Shaximiao Formation sandstone reservoir in Zhongjiang region could be classified into four types of reservoirs. The type Ⅰ and type Ⅱ reservoirs can be taken as the major target zones for exploration. Distributary channel sandstone of meandering delta front and meandering delta plain was type Ⅰ ,distributary channel sandstone of braided delta front and braided delta plain was type Ⅱ.