鄂尔多斯盆地华庆地区长8致密砂岩储层特征及其成因

鄂尔多斯盆地华庆地区长8段砂岩为一套典型的低孔、低渗到特低孔、特低渗的储层,平均孔隙度为8.27%,平均渗透率为0.51×10^-3 μm²,主要孔隙类型为剩余粒间孔隙,孔隙结构以小型小孔喉和微型小孔喉为主。长8致密砂岩储层经历了压实、胶结、溶解等复杂的成岩作用,其中压实和胶结等破坏性成岩作用使储层的原生孔隙大大减少,且长8储层在镜下发现沥青充填孔隙,降低了储层的物性,导致储层致密。成岩作用对储层的致密化起决定性作用,沉积环境是控制致密砂岩储层形成的基本因素,三角洲前缘砂体中的水下分流河道砂体物性最好;主砂体展布带内中心部位物性好,向两边逐渐变差。随着填隙物含量的增加,储层物性逐渐变差。

Characteristics of the Chang 8 tight sandstone reservoirs and their genesis in Huaqing area,Ordos Basin

Chang 8 sandstone of the Upper Triassic Yanchang Formation in Huaqing area,Ordos Basin,is a typical set of reservoirs with low-ultra low porosity and permeability.Its average porosity is 8.27% and average permeability is 0.51×10^-3 μm².The main type of pore space is residual inter-granular pore,and the main type of pore structure is tiny and micro throat.The Chang 8 reservoir has experienced complex diagenesis,such as compaction,cementation,and dissolution.The destructive diagenesis of compaction and cementation sharply reduce the primary pores of the reservoir,besides,some pores are filled with bitumen,resulting in the lowering of porosity and permeability and the tightness of the reservoir.Diagenis is a determining factor in reservoir tightening,while depositional environment is the basic controlling factor of the reservoir physical property.The underwater distributary channel sands in delta front have the best physical property,and the central part of the sandbody is better than its two sides.With the increasing of interstilital matter,the physical properties get poorer.