靖边气田西北部下奥陶统马五段白云岩储层特征及其分类评价

Characteristics and Classification Evaluation of Dolomite Reservoir of Lower Ordovician Ma5 Member in Northwestern Jingbian Gasfield

鄂尔多斯盆地靖边气田西北部下奥陶统马家沟组经历了约130Ma的风化剥蚀淋滤作用,孔隙类型复杂多样,其中的马五1+2和马五14亚段白云岩是该区主要的天然气储产层段,研究其储层特征并对其进行评价具有重要的理论和生产意义。通过钻井岩心、铸体薄片、扫描电镜及压汞测试等方法,对该区的白云岩储层进行了深入研究,结果表明,储层的储集空间主要为孔隙和裂缝,可细分为晶间孔、晶间溶孔、溶蚀孔洞、膏模孔、构造缝、压溶缝和溶蚀缝;孔隙结构包括大孔中喉型、中孔中-细喉型、小孔细-微喉型和微孔微喉型4种类型。针对该区储层特征的复杂性,综合选取孔隙度、渗透率、孔隙结构参数、排驱压力、中值半径和最大进汞饱和度参数,采用聚类分析法,将储层分为4种类型,从而更客观地反映储层的储-渗能力。

Pore type of Lower Ordovician Majiagou Formation in northwestern Jingbian Gasfield, Ordos Basin, is complicated and consisting of a wide range since the Maiiagou Formation has been weathered, de- nuded and leached for approximately 130 Ma in the process of its geological evolution. Ma51＋2 and MaS1/4 submembers of Majiagou Formation are considered as the major natural gas reservoirs in this district, hence research on its reservoir characteristics and evaluation is significant to not only the theoretical study, but also the practical production. A deep study is carried out on dolomite reservoir by drilling cores, cast- ing thin section, scanning electron microscope and mercury injection test. The results show that pore and fracture are the major reservoir space, and it could be divided into intercrystalline pore, intercrystalline so- lution pore, solution pore, gypsum mouldic pore, structural fracture, pressolution fracture and dissolution fracture. Pore structure includes four types, namely, macropore and medium-sized throat, mesopore and medium-fine throat, small pore and fine-micro throat, micropore and microthroat. On the basis of such complicated reservoir characteristics, parameters including porosity, permeability, pore structure parame- ter, displacement pressure, median radius and maximum mercury instrusion saturation are comprehensive- ly considered and selected, according to which the reservoir is classified into four categories with clustering analysis, so that its storage-permeation ability is reflected in a more objective degree.