开江—梁平海槽东侧飞仙关组岩相分区及地质意义

Feixianguan Formation lithofacies zoning and its geological significance of eastern side of Kaijiang-Liangping Trough,NE Sichuan Basin

沉积相带演化规律一直是制约环开江—梁平海槽二叠系—三叠系礁滩储层发育及分布的重要因素。基于钻井、岩心、地震资料,认为海槽东侧下三叠统飞仙关组以罗家寨—正坝—赵家湾一线为界,南、北岩相具有分区的性质,地震振幅属性表明该线为沉积地貌高低转折带,以残余鲕粒云岩和亮晶鲕粒灰岩的高能沉积岩相组合为主,该线以北为石膏岩—膏质泥晶云岩—膏质残余鲕粒云岩的蒸发岩岩相组合,以南为泥晶灰岩—泥质灰岩的低能沉积岩相组合。长兴组中—晚期为缓坡开放型有镶边台地沉积背景下的低位体系域沉积;飞一段沉积早期为海侵体系域,即长兴组沉积古地貌基础上的缓坡开放型无镶边台地沉积,膏质鲕粒白云岩组成的鲕粒滩集中在台地内部(月溪1井—金珠1井—高张1井区),储集性相对较差。飞一段沉积晚期—飞二段沉积期是鲕滩储层发育关键期,为高位体系域下的缓坡封闭型有镶边台地沉积,受NW向基底断裂和NE向地貌高地的共同控制,沿台缘带发育"U"型厚层台缘鲕粒滩,鲕粒滩障壁作用导致台缘带以北为蒸发潟湖环境,以南沿天成1井—门南1井—新兴1井一线发育上斜坡沉积环境,向南过渡为下斜坡沉积环境。

The evolution of sedimentary facies has always been an important factor restricting the development and distribution of Permian-Triassic reef-shoal reservoirs around Kaijiang-Liangping Trough.Based on drilling and core data,it is demonstrated that the Lower Triassic Feixianguan Formation in the eastern side of the Trough is divided into two parts by Luojiazhai-Zhengba-Zhaojiawan.Lithofacies zoning is obvious in both northern and southern parts.The seismic amplitude attribute indicates that the line is a high and low transition zone of sedimentary geomorphology which is characterized by the high energy deposition combination of residual oolitic dolomite and bright crystal oolitic limestone.The north of the line is an evaporation lithofacies combination consisting of gypsum,gypsum-bearing dolomicrite and gypsum-bearing residual oolitic dolomite.The south is a low energy lithofacies combination consisting of micrite and muddy limestone.The middle-late stage of Changxing Formation is a LST deposition under sedimentary background of the gentle slope and open platform with rims and the early stage of Feixianguan 1 st is TST on the basis of sedimentary paleogeomorphology of the Changxing Formation.Meanwhile the oolitic shoals which consist of gypsum-bearing residual oolitic dolomite concentrate in carbonate terrace such as Yuexi 1-Jinzhu1-Gaozhang 1 well area.The late stage of Feixianguan 1 st to Feixianguan 2 ndis the key stage of oolitic shoal reservoir development which is HST deposition of the gentle slope and restricted platform with rims.Under the jointly control of NW-trending basement fracture and NE-trending geomorphic highland,thick oolitic shoals of＂U＂shape develop along the platform margin.The north of the platform margin is the evaporation lagoon environment and the south is upper glacis sedimentary environment along Tiancheng 1-Mennan 1-Xinxing 1,and the southward transition to the lower glacis sedimentary environment.