滨里海盆地东缘北特鲁瓦油田石炭系层序地层与沉积演化特征

Carboniferous sequence stratigraphy and sedimentary evolution in the North Troyes Oilfield,eastern margin of the Pre-Caspian Basin

根据三维地震、测井及钻井取心等资料,结合Vail的层序划分方案,在滨里海盆地东缘北特鲁瓦油田石炭系碳酸盐岩台地内识别出7个地震层序界面及7个钻井层序界面,并将KT-Ⅰ油层组划分为3个半三级层序,KT-Ⅱ油层组划分为3个三级层序。纵向上层序格架内沉积环境由开阔台地、局限台地至蒸发台地演化。根据研究区层序格架内的古地貌恢复及沉积演化研究,将研究区古地貌—沉积演化划分为3个阶段:台地初始隆坳分异期(SQ2-SQ3层序)、差异抬升与沉积分异定型期(SQ4层序)及继承发育期(SQ5-SQ7层序)。进一步分析认为,层序格架控制下的隆坳格局分异控制了白云岩亚类在平面上的分布,低部位以泥晶云岩—膏盐岩组合和泥晶云岩—泥晶灰岩组合为主,主要为潟湖相沉积;而高部位则以泥粉晶云岩、细粉晶云岩和残余颗粒泥晶云岩为主,发育云坪相及云化颗粒滩相沉积。结果表明,区内KT-Ⅰ油层组沉积期并非前人认为的西高东低剥蚀后沉降充填,而是继承性差异沉降的结果,古地理格局总体具有“东台西槽、北高南低”特征,其始终控制着有利相带和优质储集层的发育展布。这一认识对滨里海地区油气勘探开发战略选区具有重要的指导作用。

Based on 3D seismic and borehold data,seven seismic sequence boundaries and seven drilling sequence boundaries are identified in the Carboniferous carbonate platform of North Troyes Oilfield.The KT-I reservoir group is divided into three and a half third-order sequences,and the KT-Ⅱreservoir group is divided into three third-order sequences.The sedimentary environment evolved stratigraphically from open platform,through restricted platform,to evaporative platform.According to the palaeo-geomorphic restoration and sedimentary evolution within the sequence framework of the study area,the palaeogeomorphic and sedimentary evolution of the study area can be divided into three stages:the initial phase of differential platform uplift and depression(SQ2-SQ3 sequence),the finalizing phase of differential uplift and sedimentary differentiation fixing period(SQ4 sequence),and the inherited development phase(SQ5-SQ7 sequence).Further analysis shows that the uplift and depression pattern under the control of sequence framework controls the plan-view distribution of dolomite subclasses.The lower part of the sequences are dominated by micritic dolomite-gypsum and micritic dolomite-micritic limestone assemblages,which are characteristic of mainly lagoonal lacustrine deposits,while the higher part of the sequences are dominated by micritic dolomites,fine micritic dolomites and residual micritic dolomites.The results show that deposition of the KT-I oil formation in the study area results from inherited differential subsidence,rather than erosion and subsidence of the“western highland and eastern lowland”as previously thought.The overall palaeogeographical pattern is characterized by“Platform in the east,trough in the west,high in the north and low in the south”,which consistently controls the development and distribution of favorable facies and high-quality reservoirs.This finding is vitally important in screening for hydrocarbon exploration and production prospects in Pre-Caspian Basin.