靖边气田北部下奥陶统马五_4~1层孔隙特征

PORE CHARACTERISTICS OF THE RESERVOIR O_1m^5_4~1 (LOWER ORDOVICIAN MAJIAGOU FORMATION) IN NORTHERN JINGBIAN GAS FIELD,THE ORDOS BASIN

下奥陶统马家沟组马五41层是鄂尔多斯盆地靖边气田北部的主要产气层之一,确定其主要孔隙类型及孔隙组合类型、分析储层影响因素对储层预测具有重要的作用。通过岩心观察以及铸体薄片、扫描电镜分析鉴定,将其储集空间划分为孔隙和裂缝两大类,以及晶间孔、晶间溶孔、溶蚀孔洞、铸模孔、溶蚀裂缝、角砾间微孔(缝)、构造缝、缝合线、收缩缝等9小类,并结合压汞分析资料进一步细分为溶蚀孔(洞)—裂缝复合型、孔隙—裂缝复合型、孔隙型、微孔—裂缝复合型、致密微孔型这5种组合类型。该区孔隙发育主要受沉积微相和成岩作用的双重影响:沉积微相为孔隙形成的基础,潮上云坪为最有利的孔隙发育相带,潮上膏云坪、灰云坪次之;成岩作用决定其储集能力,白云石化、溶蚀作用、去膏化、构造应力使储层物性得到改善,而去白云化作用、充填作用、胶结作用、交代作用则对储层具有破坏性影响。

The reservoir O1m541 in the Lower Ordovician Majiagou Formation is one of the major gas pay zone in the northern part of Jingbian gas field,the Ordos basin.The determination of its main types of pores and pore combination and analysis of the factors influencing the reservoirs are critical to reservoir prediction.Based on core observation,cast thin-section and SEM analysis,the pore spaces can be divided into two types,including pore and fracture,and 9 subtypes,including intercrystal pore,intercrystal solution pore,solution pore and cavity,mould pore,dissolution fracture,interbreccia pore or fracture,structural fracture,suture and shrinkage joint.In combination with mercury penetration analysis,5 types of pore combinations are recognized,including dissolution pore/cavity-fracture,pore-fracture,pore,micropore-microfracture,and tight micropore.The pore development in the study area is mainly controlled by sedimentary microfacies and diagenesis.Sedimentary microfacies are the basis of pore formation,with supratidal dolomitic flat as the best facies belt for pore development followed by supratidal gypseous-dolomitic flat and calciferous-dolomitic flat.Diagenesis determines the reservoir capability,with dolomitization,dissolution,degypsumization and tectonic stress as the main constructive diagenesis,while dedolomitization,filling process,cementation and metasomatism as the main destructive diagenesis.