伊拉克A油田Asmari组混积型碳酸盐岩储层隔夹层研究

伊拉克A油田Asmari组为大型混积型碳酸盐岩油藏,发育灰岩、白云岩、砂岩、泥岩和硬石膏等多种岩性,储层复杂、非均质性强,存在多种类型的隔夹层。基于岩心、薄片、测井和分析测试等资料,对研究区隔夹层类型及特征展开综合分析,识别出了泥岩、硬膏岩和泥-微晶碳酸盐岩3类隔夹层。泥岩和硬石膏致密无孔隙、基本不具有渗流能力,对流体流动可以起到阻挡作用;泥-微晶碳酸盐岩属于细粒碳酸盐岩沉积,孔隙度低,但一般裂缝较发育,具有一定渗流能力,不能对流体起到有效的隔挡作用。硬石膏主要在油田中部及北部A段发育,其对油田北部储层纵向连通起到一定隔挡作用,导致纵向压力衰竭不一致。泥岩主要在C段顶部、B4和B1层发育,平面上主要在油田南部较发育。C段顶部发育一套厚度较大、稳定分布的泥岩隔层,将C段和上部B段及A段分隔为两个独立的油水系统,并有效阻挡了C段水层锥进到B段;B4和B1层泥岩较发育,但由于油田南部区域断层和裂缝较发育,导致泥岩隔夹层未能起到有效隔挡作用。搞清研究区隔夹层类型、分布及是否起隔挡作用,对A油田各区域各小层有效动用开发、见水规律研究具有很好的指导意义。

Study on interbeds of mixed carbonate reservoir in Asmari formation for A oilfield,Iraq

Asmari formation of A oilfield in Iraq is a large mixed carbonate reservoir,which is characterized by multiple lithologies such as limestone,dolomite,sandstone,mudstone and anhydrite.The reservoir is complex and heterogeneous,and various types of interbeds are developed.Based on the data of core,thin section,logging and test,the types and features of interbeds in Asmari formation of A oilfield are comprehensively analyzed.Three types of interbeds are identified,mudstone,anhydrite and micrite and microcrystalline carbonate.Mudstone and anhydrite are dense,without porous and permeable,and can block fluid flow.Micrite and microcrystalline carbonate belongs to fine-grained carbonate sediments with low porosity,but generally developed fractures with certain seepage capacity,which can not effectively block fluid flow.Anhydrite is mainly developed in the member A at the middle and north area of A oilfield.The pressure data shows that the anhydrite plays a certain role in blocking the vertical connection of the reservoir in the north of the oilfield,resulting in inconsistent vertical pressure depletion.Mudstone is mainly developed at the top of member C,B4 and B1 layers,and distributed in the south area of A oilfield.One mudstone interlayer,thick and stable,is developed at the top of member C,which separates member C with upper member B and A,resulting in two independent oil-water systems,and effectively prevents the water in member C coning into member B.The mudstone is relatively developed in B4 and B1 layers at south area of A oilfield.Due to the development of faults and fractures in the southern region of A oilfield,the mudstone interlayer fails to play an effective role in blocking the vertical connection of the reservoir.To make clear the types and distribution of interlayer and whether it plays the role of blocking the reservoir connection is very important for the development,and water breakthrough study of A oilfield.