安塞油田长2、长3浅油层成岩作用及孔隙结构特征

Diagenesis and pore structure characteristic of Chang 2 and Chang 3 Oil-beds in Ansai Oilfield

目的揭示安塞油田长2、长3油层组储层的微观特征,为改善开发效果提供依据。方法通过薄片观察、扫描电镜及阴极发光等进行岩石学特征、成岩作用及孔隙结构特征研究。结果砂岩储层物性明显受埋藏-成岩作用事件的影响,主要成岩作用有压实-压溶、胶结充填和溶解作用等。压实-压溶及胶结充填作用是导致砂岩孔隙丧失的主要原因,其中碳酸盐胶结物和石英、长石加大是造成砂岩物性降低的主要原因,晚期成岩阶段有机质分解形成的酸性流体及表生成岩作用阶段的大气降水是形成次生孔隙的主要原因,从而使砂岩的物性得到改善。另外,在压实过程中碎屑颗粒周围形成的绿泥石衬边阻止了部分石英、长石次生加大及碳酸盐胶结物的沉淀,使部分原生粒间孔隙得以保存。结论安塞油田长2、长3油层组孔隙类型主要为原生粒间孔和次生粒间溶孔,孔喉结构主要属中小孔中细喉型和小孔微喉型,属于中上等和中等储层。

Aim To announce the micro characteristic of reservoir of the Chang 2 and Chang 3 Oil-beds in Ansai Oilfield and offer the basis for improving the result of exploitation. Methods Study the lithological, diagenesis and pore structure are studied based on bore core＇s and slice＇s observing and accounting, analysis of scanning electron microscope and cathodoluminescence spectroscopy. Results The reservoir quality is strongly influenced by the bur- ial history and facies-related diagenetic events which include mechanical-chemical impaction, consolidated fill and dissolution. The mechanical-chemical impaction and consolidated fill are the main factor causing the loss of porosity for the sandstones. In the cements, carbonate and quartz-feldspar overgrowths are the main cements that reduced the reservoir quality of the sandstones. The acidic liquid related to decomposition of organic mater during hydrocarbon enrichment in the late diagenesis and meteorico-waters during epidiagenesis, have resulted in dissolution of detrital feldspars and carbonate cements, and in the formation of kaolinite, contributing a better retention of reservoir quality for the sandstones. In addition, thin chlorite film around detrital grains prevented part of quartz and feldspar overgrowth and carbonate cement precipitation, which resulted in a part of primary pore preservation and hence caused a better reservoir quality. Conclusion Pore types of Chang 2 and Chang 3 Oil-beds sandstones in the Ansai Oil Field are syngenetic open space and vugular-solution pore mainly. Chang 2 and Chang 3 sandstone belong to better-medium reservoir in which pore-throat structure belongs to medium-thin throat-eyelet type and thin-small throat-eyelet type mainly.