鄂尔多斯盆地姬塬地区上三叠统延长组长8油层组成岩相

Diagenetic facies of the Chang 8 oil-bearing layer of the Upper Triassic Yanchang Formation in the Jiyuan area,Ordos Basin

在综合测试数据的基础上,系统地研究了姬塬地区长8油层组成岩作用类型、成岩期次与成岩流体性质,得到:①研究区长8油层组处于中成岩阶段A期,主要经历了压实-压溶、胶结、交代、溶蚀、自生矿物的充填及破裂等成岩作用;②沉积相对成岩作用的类型具有明显的控制作用,受古湖岸线位置控制的早期绿泥石环边胶结作用,是原生粒间孔得以保存的重要原因;③压实-压溶作用是造成孔隙缩减的主要原因,这一成岩作用贯穿整个成岩阶段;④自生矿物充填作用和碳酸盐胶结作用从早成岩阶段B期延续到中成岩阶段A1期,对储层造成不同程度的破坏;⑤溶蚀和破裂作用主要发生在早成岩阶段B期和中成岩阶段A1期,对改善储层物性意义重大。在上述研究基础上,将研究区长8油层组划为致密泥岩压实相、绿泥石环边胶结—溶蚀相、溶蚀—碳酸盐胶结相及方解石连生胶结相4个成岩相组合。储层的时空分布规律明显受沉积相和成岩相控制,研究区中部水下分流河道沉积区的绿泥石环边胶结—溶蚀成岩相带为最有利储集层发育相带。

Based on comprehensive testing data,this paper discussed diagenetic types,timing and fluid properties of the Chang 8 oil-bearing layer in the Jiyuan area,Ordos Basin.Several lines of novel cognition were made as follows： ①The Chang 8 oil-bearing layer in the study area is at Phase A of the middle diagenesis that consists mostly of various diagenetic processes,such as compaction-pressolution,cementation,metasomatism,corrosion,filling of autogenous minerals and fracture.②Sedimentary facies significantly dominate types of diagenesis,the early rim cementation of chlorites controlled by the location of paleo-lakeline is of importance to the preservation of primary intergranular pores.③Compaction-pressolution leads to the most reduction of pores that lasts through the whole diagenesis.④The filling of autogenous minerals and cementation of carbonates continue from Phase B of the early diagenesis to Phase A1 of the middle diagenesis and may destroy reservoirs in various degrees.⑤Corrosion and disruption occur mostly at Phase B of the early diagenesis and Phase A1 of the middle diagenesis,significantly improving physical properties of reservoirs.On the basis of the above study,the Chang 8 oil-bearing layer of the study area was divided into four diagenetic types of facies combination,including dense-mudstone compaction,rim cementation-corrosion of chlorites,corrosion and carbonate cementation,and poikilitic cementation of calcites.The time-space distribution of reservoirs was obviously controlled by sedimentary and diagenetic facies,and chlorite-rim cementation-corrosion belts distributed in subaqueous distributary channels of the middle study area were proposed to be the most favorable places for reservoir development.