碳酸盐岩不同孔隙类型储层特征及孔隙成因:以伊拉克西古尔纳油田中白垩统Mishrif组为例

Characteristics of Different Pore Type Carbonate Reservoirs and Pore Origins:A Case Study of Middle Cretaceous Mishrif Formation in West Qurna Oilfield,Iraq

伊拉克西古尔纳油田中白垩统Mishrif组孔隙型生屑灰岩储层岩石类型、孔隙类型复杂多样,非均质性强。利用薄片、物性和压汞测试等技术手段,识别孔隙类型,基于主控孔隙类型划分储层类型,研究不同孔隙类型储层特征和孔隙成因。研究区主要发育粒内孔、铸模孔、残余铸模孔、粒间孔、微孔、晶间孔。在目的层不同孔隙类型易伴生出现的背景下,根据主控孔隙类型,将Mishrif组划分为6种储层类型:残余铸模孔储层、粒内孔储层、微孔储层、铸模孔储层、混合孔储层和粒间孔储层,其中铸模孔储层和微孔储层最发育,混合孔储层、粒内孔储层和残余铸模孔储层较发育,粒间孔储层发育相对少。每类储层包含多种岩石类型和生屑类型,具有相似的物性和孔隙结构特征,揭示了孔隙类型的差异是造成储层强非均质性的重要原因。各类孔隙形成演化受控于沉积环境和以溶蚀作用为主的多种成岩作用,不同沉积环境控制着泥质含量、生屑结构、种类和丰度的差异,是控制孔隙类型的因素;溶蚀作用受生屑化学组分影响,是控制孔隙形成的主要原因,同生期泥晶化作用、埋藏期胶结作用、压实作用和白云石化作用不同程度地改造了孔隙。

The carbonate reservoirs of Middle Cretaceous Mishrif Formation of West Qurna Oilfield in Iraq are characterized by diversified pore types and complicated pore structure with strong heterogeneity.By means of thin sections,physical properties test and mercury injection tests,the main pore types are identified,and reservoir types based on dominant pore types are classified,and the characteristics of different types of reservoirs are studied,including petrological,physical properties and pore structure.The origins of pores are analyzed.And the pore types identified in Mishrif Formation are intraparticle pores,residual moldic pores,micropore,moldic pores,interparticle pores,intracrystalline pores.According to dominant pore type,Mishrif Formation can be classified to contain six types of reservoir,and they are intraparticle pore,residual moldic pore,micropore,moldic pore,mixing pore and interparticle pore dominated reservoir.Each type of reservoir contains two or more rock types and multiple bioclastic types,with similar physical properties and pore structure respectively.The study reveals that the pore types are the crucial cause for the strong heterogeneity of reserviors.The study verifies that pore formation and evolution are controlled by the sedimentary environment and diagenesis.Different pore types are formed because of the various environments which are responsible for the difference in lime and mud contents,bioclastic textures,types and abundance,controlled by water dynamics and biological living conditions.Pore occurrence is determined by various diagenesis,while pore occurrence was mainly attributed to dissolution,influenced by the mineral composition of bioclastics.In addition,pores are altered by micritization,cementation,compaction and dolomitization.