安塞油田长2油层成岩作用及其对储层物性的影响

Diagenesis and its effect on reservoir quality in Chang-2 reservoir of Ansai Oil Field

安塞地区长2油层储层以中细粒长石砂岩为主,主要成岩矿物为绿泥石环边、方解石胶结物、石英和长石加大生长、伊利石、伊-蒙混层、钠长石和高岭石等。绿泥石环边的发育对原生粒间孔的保存起到有利的作用。石英加大级别达 级,加大边含有丰富的有机包体,均一温度范围48.1～76.5oC,烃类进入储层的时间为早白垩世中期至晚白垩世。储层发育多种孔隙类型,面孔率平均为11.60%,主要类型有粒间孔、骨架颗粒溶孔和微裂缝等。残余粒间孔和骨架颗粒溶孔是本区长2储层的主要孔隙类型。根据成岩作用的矿物岩石学标志、有机质成熟度及古温度,将长2油层砂岩的成岩作用划分为3个成岩阶段:早成岩阶段、晚成岩阶段和表生成岩阶段。储层性质明显地受到沉积微相和成岩作用的影响,沉积物粒度较粗、厚度较大的分流河道储集物性明显优于各种粒度较细、厚度较薄的分流间席状砂体。

Chang-2 reservoir sandstones of Ansai Oil Field mainly consis of fine-middle grained arkoses. Sandstones contain a diagenetic mineral assemblage that record major diagenetic events during burial history. The main diagenetic minerals of the sandstones include chlorite, calcite, quartz and feldspar overgrowth, illite, and albite. Chlotite grain coats and grain rims retard quartz cementation and concomitant porosity and permeability reduction by inhibiting precipitation of quartz overgrowths on detrital grains. Authigenic quartz overgrowths contain a variety of organic fluid inclusions that indicate the petroleum filling history. The fluid inclusion temperatures measured in Chang-2 reservoir samples are 48.1~76.5(~oC). Secondary porosity has created mainly by feldspar, rock fragment and clay matrix dissolution. The mean porosity for the whole population of 165 samples is 11.6%. Based on diagenetic events related to temperature, reservoir diagenetic stages can be divided into early diagenesis ,later diagenesis and epidiagenesis. Reservoir quality is controlled mostly by sedimentary microfacies and diagenesis. Distributary channel sandbodies commonly have high porosity and permeability, whereas interdistributary and distal sandsheets may have low petrophisical properties.