万花-劳山区长8油层组储层特征及有利区预测

Characteristics of Reservoir and Prediction of Favorable Exploration Area of Chang 8 Member in Wanhua-Laoshan Area

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。

Yanchang Formation is an important reservoir of Ordos Basin ,and Chang 8 Member is the most importand reservoir of lower assemblage of Yanchang Formation.In Chang 8 reservoir,the rock types are mainly fine-grained feldspar sandstone,filling material is authigenic mineral mainly,and calcite,chlorite and other cement has mud cementation.The average porosity and permeability of the reservoir is 8.6% and 0.27mD re- spectively.The reservoir in the study area belongs to extra-low porosity and ultra-low permeability one.The physical property characteristics of sedimentary microfacies in the study area are quite different,and the high porosity and high permeability mainly distributes at the microfacies of the underwater distributary and the mouth bar.Pore type is mainly intergranular dissolution pore,which has great contribution to the porosity and is the main reservoir space in the study area.Intragranular dissolved pores are also one of the pore types in the study area,which has little contribution to reservoir porosity increase.Microfractures that are mainly formed by compaction are more common in the study area,and they improved the reservoir physical property.Based on the analytic hierarchy process ,the location of the structure ,the location of the microfacies ,the thickness of the hydrocarbon source rocks,the thickness of the sandbody,the porosity and permeability were selected as the evaluation index of the favorable area,and the weight of each evaluation index was determined.The favor- able area of each sedimentary unit was predicted by fuzzy comprehensive evaluation method,where 2 favorable areas I and 3 favorable areas II were predicted in the Chang 81 unit,3 favorable areas I and 3 favor- able areas II were predicted in the Chang 82 unit.