鄂尔多斯盆地姬塬地区延长组长8_1段储层特征及控制因素分析

RESERVIOR CHARACTERISTICS AND CONTROL FACTORS OF CHANG 8_1 OF YANCHANG FORMATION OF TRIASSIC IN JUYUAN REGION OF ORDOS BASIN

长81油层是鄂尔多斯盆地姬塬地区勘探潜力较大的含油层位之一。通过10口井的岩心观察、63个铸体染色薄片的鉴定、7个样品的扫描电镜观察、32个样品的薄片鉴定报告和44口井的岩心分析数据的统计等方法,对鄂尔多斯盆地姬塬地区延长组长81段储层进行研究,结果表明:研究区储层孔隙类型以粒间孔为主,偶见次生溶孔,其平均孔隙度为7.81%,平均渗透率为0.26×10-3μm2,总体表现为低孔、低渗特征。沉积条件是储层原始矿物成分和岩石结构形成的基础,它使得分流河道、水下分流河道、河口坝和远砂坝4个微相的储层原始物性产生了一定的差异。成岩作用是影响储层物性好坏的关键因素,其中压实和碳酸盐、硅质、高岭石胶结使得原始孔隙度平均损失分别达23.15%和13.22%;绿泥石薄膜对储层物性有一定的积极作用;溶蚀作用对储层物性的改善有限,孔隙度增加平均只有0.58%,其重要原因是研究区异常热演化史导致早期碳酸盐胶结物后期不被溶蚀。

The Chang 81 reservoir is one of the oil stratigraphic horizons with great exploration potentiality in jiyuan region of the Ordos basin. This reservoir is investigated by analysis of lithol- ogy,thin sections,SEM and core properties. It is showed that the types of pore are mainly interg- ranular pores with minor secondary solution pores, and the reservoir is characterized by low po- rosity and permeability with average porosity of 7.81%, average permeability of 0.26×10-3μm2. Sedimentary condition is the basis for the formation of original mineral compositions and rock tex- ture, which plays some control action on reservoir physical property and creates the differences a- mong original reservoir physical property of distributary channel, underwater distributary chan- nel,mouth bar and distal bar. Diagenesis was the key factor affecting reservoir physical property. In fact, compaction, carbonate cementation, siliceous cementation and kaolinite cementation were the dominant diagenesis types which destroyed the reservoir physical property, and chlorite thin films play a positive role in protecting the reservoir physical property. The primary porosity of the reservoir is reduced by 23.15% by compaction and 13.22% by cementation respectively. The sec- ondary pores were produced by dissolution, resulting in an increase of porosity by 0.58%, which scarcely improved the reservoir physical property. The abnormal thermal evolution history was the important cause for later none dissolution of earlier-stage carbonate cements.