靖边气田北部奥陶系马五1亚段碳酸盐岩成岩作用及其孔隙结构特征

靖边气田碳酸盐岩储层原始沉积以泥微晶灰岩为主，物性极差而难以成为储层。其储集性能主要源于后期复杂成岩作用的影响，经历了不同类型的成岩作用，对应的孔隙结构复杂多样，这为有利储层的预测带来很大困难。采用铸体薄片、扫描电镜、阴极发光、物性和高压压汞等分析测试资料，综合研究了靖边气田北部马五₁亚段碳酸盐岩储层的成岩作用类型，及其形成的储集层微观孔隙结构特征。研究表明，马五₁亚段储层主要经历了机械压实和压溶作用、胶结充填作用、溶蚀作用和交代作用等成岩作用类型，并形成了白云石+石英+高岭石胶结-溶孔型(Ⅰ类)、白云石+方解石+石英胶结-溶孔型(Ⅱ类)、白云石+方解石胶结-晶间孔型(Ⅲ类)和方解石胶结-致密型(Ⅳ类)等4类储层。其中Ⅰ类储层内孔隙类型较单一，孔喉分选较好，有效可动喉道体积比例大，排驱压力和中值压力最小，为优势储集层；而Ⅳ类储层大-中孔隙基本被方解石充填，发育的孔喉基本没有渗流能力，储集性最差。

Diagenesis in Carbonate Reservoir and Pore Structure Characteristic from the Ordovician Ma51 Sub-member Reservoir in the Northern Jingbian Gasfield

Original deposition is dominated by micrite in carbonate reservoir in Jingbian Gasfield.Its physical property is poor and can′t become a reservoir.The reservoir property is mainly influenced by the late complex diagenesis,so the reservoir has gone through different diagenesis with different pore structure and is hard to predict favorable reservoir.In this paper,casting thin sections,scanning electron microscope,cathodoluminescence imaging,physical properties,high pressure mercury injection and other analytical testing methods were used to analyze the diagenesis and micro-pore structure of the reservoir in Ma5₁ sub-member reservoir from the northern Jingbian Gasfield.This study shows that,reservoir mainly experienced mechanical compaction and pressure solution,cementation filling,dissolution and metasomatism.And formed four types of reservoirs,namely dolomite-quartz-kaolinite cementation-dissoved pore type(Ⅰclass),dolomite-calcite-quartz cementation- dissoved pore type(Ⅱclass),dolomite+calcite cementation-intercrystalline pore type(Ⅲclass),and calcite cementation-dense reservoir type(Ⅳclass).ClassⅠreservoir is the most favorable reservoir because its pore type is single,pore throat sorting is better,effective throat volume ratio is large,drainage capillary pressure and median capillary pressure is low.Class Ⅳreservoir is the worst reservoir because its large-medium pore is filled by calcite,and pore throat has no permeability.