【摘要】 通过对四川盆地寒武系、奥陶系野外露头剖面、钻井岩心、录井和测井等资料的详细分析,认为寒武系—奥陶系主要发育局限台地相、开阔台地相和台地边缘相。结合地震资料,应用层序地层学理论和方法将寒武系划分为5个三级层序,奥陶系划分为6个三级层序。以三级层序为单元,采用单因素编图、多因素综合的方法,编制了四川盆地及邻区寒武系—奥陶系层序岩相古地理图,认为寒武纪—奥陶纪总体呈现西部以陆源碎屑沉积为主、东部以碳酸盐岩沉积为主的格局,碳酸盐台地演化呈现出由早寒武世早期(梅树村期—筇竹寺期)碎屑-混积陆棚、早寒武世中期(沧浪铺期)缓坡台地向早寒武世晚期(龙王庙期)至中奥陶世镶边台地的转变,在晚奥陶世,因全球海平面上升再加上扬子板块东南被动陆缘向华夏陆块之下俯冲聚敛的构造沉降效应,导致沉积水体快速加深,致使上扬子(四川)台地被淹没而成为较深水缓坡—盆地相。寒武纪从早期陆源碎屑和碳酸盐混积为主转变到晚期清水碳酸盐沉积为主,盆地内部大面积发育局限台地相台内滩和台内白云岩有利储集体;奥陶纪受海侵影响,盆地内部以开阔台地沉积为主,台内滩呈带状分布;晚奥陶世台地被淹没沉积了宝塔组、临湘组及五峰组泥晶灰岩、泥质灰岩及泥岩,成为遍及全盆地的区域盖层,五峰组还可作为优质烃源岩。有利天然气储层为砂屑白云岩、鲕粒白云岩和细粉晶白云岩,溶蚀孔洞发育,储层平均孔隙度2%～6%,储层单层厚度较大,空间上连续性较好。在有利储集体评价的基础上,通过成藏条件综合分析,优选了4个寒武系—奥陶系有利勘探区带,其中乐山—龙女寺古隆起有利区带和泸州古隆起有利区带发育大型构造圈闭,有利储集体大面积分布,有较大勘探潜力。更多还原

【Abstract】 In this study,a detailed analysis of the field outcrop profiles,drilling cores and well logging data showed that the Sichuan Basin in Cambrian and Ordovician mainly developed restricted platform facies,open platform facies,and platform marginal facies.Combined with seismic data,the Cambrian and Ordovician were respectively divided into five and six 3rd order sequences in accord with the theory and method of sequence stratigraphy.With the 3rd-order sequence as the unit,the map of sequence lithofacies paleogeography was prepared for Sichuan Basin and adjacent areas in Cambrian and Ordovician using the single factor analysis and multifactor comprehensive mapping method.In the Cambrian and Ordovician,terrigenous clastic rocks mainly deposited in the west,and carbonate rocks dominated the east.Regarding the evolution of carbonate platform,clastics-hybrid shelf in the early stage of Early Cambrian(Meishucun Age and Qiongzhusi Age) and carbonate ramp in the middle stage of Early Cambrian(Canglangpu Age) evolved to rimmed platform from the late Early Cambrian(Longwangmiao Age) to the Middle Ordovician.In the Late Ordovician,the combined effects of global sea level rise and tectonic subsidence of Yangtze plate southeast passive continental margin subducted to Cathaysia led to rapid rise of sea level and increase in deposition water depth.As a result,the upper Yangtze(Sichuan) platform was submerged,further developing into a deep-water ramp-basin facies.In the Early Cambrian,terrigenous clastic rocks and carbonate hybrids mainly deposited in the early stage,whereas carbonate rocks mainly deposited in clear water areas in the late stage.A large area of favorable reservoirs(i.e.,intra-platform shoals and intra-platform dolomites) of restricted platform facies was developed in the basin.As affected by the Ordovician transgression,the basin mainly developed open platform facies with intra-platform shoal facies in banded distribution.In the Late Ordovician,the platform was submerged and deposited with micritic limestone,argillaceous limestone,mudstone of Baota Formation,Linxiang Formation,and Wufeng Formation,which became the regional cap rocks throughout the entire basin.Argillaceous limestone and mudstone of Wufeng Formation are the important high quality source rock in Sichuan Basin.The favorable reservoirs of natural gas consist of dolarenite,oolitic dolomite,and silty-fine crystal dolomite,with well-developed dissolution pores(average porosity 2%~6%),large monolayer thickness,and good spatial continuity.Based on the evaluation of favorable reservoirs,four favorable exploration zones of the Cambrian and Ordovician were selected through comprehensive analysis of the hydrocarbon accumulation conditions,and the favorable exploration zones of Leshan-Longnüsi Palaeouplift and Luzhou Palaeouplift have developed large-scale structural traps and widely distributed favorable reservoirs,thus are of great exploration potential.更多还原