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延长组是鄂尔多斯盆地重要储油层系,而长8油层组为下组合最重要的含油层位,长8储层岩石类型主要为细粒长石砂岩,填系物以自生矿物为主,胶结物有方解石、绿泥石等,以泥质胶结为主。储层孔隙度平均值为8.6%,渗透率平均值为0.27mD,属于特低孔-超低渗储层。研究区不同沉积微相物性特征具有较大差异,高孔高渗主要集中在水下分流和河口坝优势微相。孔隙类型以粒间溶孔为主,这种孔隙对孔隙度的贡献较大,是研究区最主要的储集空间;粒内溶孔也是研究区孔隙类型之一,这种孔隙对提高储层孔隙度有限。微裂缝在研究区较常见,主要是由压实作用形成的,它们的存在改善了储层物性。依据层次分析方法 ,选取构造部位、微相部位、烃源岩厚度、砂体厚度、孔隙度和渗透率作为评价有利区指标,确定各评价指标的权重,采用模糊综合评判方法对研究区有利区进行了预测,其中长81预测Ⅰ类有利区2个,Ⅱ类有利区3个;长82预测Ⅰ类有利区3个,Ⅱ类有利区3个。
The Yanchang Formation is an important reservoir system in the Ordos Basin. The Chang 8 reservoir is the most important oil-bearing formation in the Lower Ordos Basin. The Chang 8 reservoir is mainly composed of fine-grained feldspathic sandstones. The fillings are mainly composed of authigenic minerals, cements There are calcite, chlorite, mud-based cementation. The average porosity of the reservoir is 8.6% and the average permeability is 0.27mD, belonging to the ultra-low porosity and ultra-low permeability reservoir. The characteristics of different sedimentary microfacies in the study area are quite different. The high porosity and high permeability are mainly concentrated in the underwater distributary and the dominant microfacies of the mouth bar. The pore type is dominated by intergranular dissolved pores, which contribute more to the porosity and are the most important reservoir space in the study area. Intragranular dissolution is also one of the pore types in the study area. Porosity is limited. Microfractures are more common in the study area and are mainly formed by compaction. Their existence improves reservoir physical properties. According to the analytic hierarchy process (AHP), the tectonic site, microfacies, source rock thickness, sand body thickness, porosity and permeability are selected as the indexes for evaluating the favorable areas, and the weights of each evaluation index are determined. The fuzzy comprehensive evaluation method is used to evaluate the favorable areas The prediction was made in the following two aspects. Among them, Chang 81 predicted two favorable areas of Category I and three favorable areas of Type II; three of the favorable areas of Category I and three of Type II were predicted by Chang 82.