四川盆地中三叠统雷口坡组沉积特征及有利储集相带

为了查明四川盆地中三叠统雷口坡组沉积特征与有利储集相带分布规律，为该区天然气勘探寻找新的接替区，以海相碳酸盐岩层序地层学和储层沉积学理论体系为指导，在岩心标志、测录井标志以及不整合等层序界面标志的基础上，对中三叠统雷口坡组进行了沉积相识别和层序地层划分，进而圈定了各层序时期平面沉积相边界，并编制了四川盆地中三叠统雷口坡组各体系域内层序-岩相古地理图，预测了有利储集相带分布区。研究结果表明：四川盆地中三叠统雷口坡组为一套较浅水的碳酸盐岩台地相沉积体系，主要发育局限台地、蒸发台地、台地边缘和开阔台地等4种相类型。雷口坡期受到早印支运动的影响，盆地内部呈现东高西低、大隆大凹的沉积格局。地壳抬升作用使得部分地层遭受长期暴露剥蚀作用并在顶部形成风化壳，致雷口坡组顶部部分地层缺失。以沉积相划分、层序界面识别标志为依据，四川盆地中三叠统雷口坡组划分出4个三级层序和8个体系域。盆地中部古隆起及其周缘白云岩坪和西北部绵竹-剑阁隆起的台缘滩具有较好的储集物性和有效的储盖组合特征，为盆地有利储集相带分布区，因而成为四川盆地中三叠统雷口坡组最为有力的勘探目标。

Sedimentary characteristics and favorable reservoir facies distribution of the Middle Triassic Leikoupo Formation,Sichuan Basin

In order to look for new fairways for future gas exploration in the Sichuan Basin,we worked on revealling the sedimentary characteristics and distribution of favorable reservoir facies in the Middle Triassic Leikoupo Formation.The study took marine carbonate sequence stratigraphy and reservoir sedimentology theory as guidance.Based on the markers in logging data,from cores,and sequence boundaries including unconformity,we conducted the sequence stratigraphy division and identification of sedimentary facies.Then spatial boundaries of sedimentary facies in each sequence are delineated,and the lithofacies paleogeographic map of each system tract in every sequence are compiled to predict favorable reservoir facies distribution.The results show that the Middle Triassic Leikoupo Formation in the Sichuan Basin develops a set of shallow water carbonate platform sedimentary system,including 4 major sedimentary facies,namely,restricted platform,evaporitic platform,platform edge and open platform.In general,the formation appears to be higher in the east and plunges to the west,with significant uplift and sag within the platform driven by early Indosinian tectonic movement.Due to basement uplift,some of the upper sections of the formation are eroded by long-term exposure,companied by development of a weathering crust.Furthermore,based on sedimentary facies recognition and sequence interface markers,we divided the Middle Triassic Leikoupo Formation into 4 third-tier sequences and 8 system tracts:the paleo-uplift in the central basin and its surrounding dolomite flat,and the platform edge bank of the northwestern Mianzhu and Jiange uplifts,are favorable reservoir facies because of their better reservoir properties and effective coupling of reservoir and caprock.Therefore,we conclude that these fairways are the most favorable areas for future exploration in the Middle Triassic Leikoupo Formation in the Sichuan Basin.