川东地区侏罗系自流井组大安寨段页岩气(油)储层评价

Evaluation of reservoirs in the Da'anzhai Member of the Jurassic Ziliujing Formation in eastern Sichuan Basin

以野外剖面观测和室内薄片鉴定为基础,结合沉积相、薄片鉴定、X-衍射、物性、孔隙结构和岩石力学分析,确定川东地区大安寨段有利储层为各类介壳灰岩与碳质页岩的不等厚互层组合体,以发育于大安寨段第二亚段(简称大二亚段)上部湖坡亚相的湖退型灰岩与页岩互层组合为相对优质的储集体,其脆性矿物含量明显高于下部,更易产生天然裂缝和进行储层的压裂改造。有机碳含量平均值为1.07%,明显大于下部的0.38%,对应的实测总含气量平均值为0.71 m3/t,明显大于下部的0.41 m3/t。运用岩石薄片、压汞资料、物性资料等多种常规技术分析大安寨段页岩储层储集物性特征,分析结果表明大安寨段储层均具有特低孔-特低渗性质。场发射扫描电镜分析结果证明了储集体纳米级孔隙的发育和分布规律。粒间孔隙中的粘土矿物层间孔在大二亚段最为发育,且连通性最好,与有机质有关的孔缝及刚性矿物边缘缝在大二亚段上部较为发育,颗粒内孔仅在大二亚段上部零星发育。综合分析确定大二亚段上部相对大安寨其他层位更具页岩气(油)勘探开发潜力,应给于足够重视。

Reservoirs of interest in the Da＇anzhai Member of the Ziliujing Formation in eastern Sichuan Basin were determined to be interbeds of shell limestone and carbonaceous shale of various thickness based on outcrop observation and thin section authentication with analyses of sedimentary facies,X-diffraction,physical properties,pore structure,and rock mechanics. The assemblage of lake regression limestone interbedded with shale of the sub-lacustrine-slope facies at the upper part of the second sub-member of the Da＇anzhai was considered to be the relative good reservoirs as their content of brittle minerals were obviously higher than that of the lower part and were easily cracked and stimulated. Average TOC of the upper part was 1. 07% contrasting with a 0. 38% at the lower part. Measured total gas concentration of the upper was averaged at 0. 71 m3/ t,higher than 0. 41 m3/ t taken from the lower part. Thin section analyses,mercury injection test data as well as physical properties of the samples from the sub-member showed that the reservoirs were extra-low porosity and extra-low permeability. FESEM（ field emission scanning electron microscopy） results confirmed the suspect of nanoscale pore structure. Interbedded pores of clay minerals among intergranular pores were considered to have the best connectivity in the sub-member and pores and cracks associated with organic matter as well as perimetral joints of rigid minerals were proved to be well developed at the upper part of the sub-member. The upper part of the sub-member also found to contain some sporadically distributed intragranular pores. It is therefore suggested that the upper part of the sub-member is more promising in terms of exploration potential than any other layers of the Da＇anzhai Member.