Reconstruction and petroleum geological significance of lithofacies paleogeography and paleokarst geomorphology of the Middle Permian Maokou Formation in northwestern Sichuan Basin,SW China

Based on analysis of outcrop,drilling,logging and seismic data,and geotectonic background,the lithofacies paleogeography and paleokarst geomorphology of the Middle Permian Maokou Formation in the northwestern Sichuan Basin were reconstructed,and the petroleum geological significance of the lithofacies paleogeography and paleokarst geomorphology were discussed.The Maokou Formation is divided into 3 long-term cycles,namely LSCl,LSC2 and LSC3,which correspond to the Member 1,Member 2 and Member 3 of the Maokou Formation,respectively.Controlled by the extensional structure caused by opening of the Mianlue Ocean in the north margin of the upper Yangtze blocks and basement faults produced by mantle plume uplifting,the area had tectonic differentiation in NWW and NE,and sedimentary basement took on episodic settlement from north to south,as a result,the sedimentary systems of Member 1 to Member 3 gradually evolved from carbonate platform to platform-slope-continental shelf.According to the residual thickness,paleokarst geomorphologic units such as karst highland,karst slope and karst depression at different stages were reconstructed.The karst geomorphological units were developed successively on the basis of sedimentary geomorphology.Sedimentary facies and paleokarst geomorphology are of great significance for oil and gas accumulation.The Maokou Formation in northwestern Sichuan has two kinds of most favorable reservoir zone combinations:high energy grain shoal and karst monadnock,platform margin slope and karst slope.Based on this understanding,the planar distribution of the two kinds of reservoir zones were predicted by overlapping the favorable reservoir facies belt with paleokarst geomorphology.The study results provide a new idea and reference for the exploration deployment of the Middle Permian Maokou Formation in the Sichuan Basin.

松辽盆地青山口组三段底界不整合面的发现及石油地质学意义

基于地震资料、岩芯观察、测井资料,并结合微体古生物和地球化学分布特征,通过开展高分辨率层序地层学研究,在松辽盆地北部的西部斜坡区、泰康隆起带、龙虎泡阶地以及滨北地区,发现青三段底界发育一区域性不整合面。该不整合面可作为松辽盆地南、北两大探区(大庆、吉林探区;松辽盆地南部的西部斜坡区和红岗阶地也发育大规模区域不整合面)青二、三段划分和对比的标志,同样也可作为三级层序划分的重要理论依据。该不整合面的形成由差异沉积速率和地壳的差异沉降作用共同控制,属于沉积型不整合面。该不整合面控制青二、三段高频层序的时空分布;宏观控制沉积相带分布;控制青二段高位域砂体在水下的分布,进一步控制油藏类型的形成和油气规模的分布。青三段底界不整合面的发现和提出无疑具有重要的地质理论和油气勘探实践意义。

鄂西娄山关组顶部古岩溶不整合面的发现及层序地层学意义

鄂西娄山关组顶部存在古岩溶不整合面，有众多陆上暴露和溶蚀标志，表明其产生受寒武纪末海平面下降事件的控制。它不仅形成了碳酸盐台地上典型的Ⅱ型层序界面，而且恰与寒武—奥陶纪年代地层界线相重合，体现了层序界面。

湘黔交界娄山关组层序地层学研究

传统上认为湘黔交界处的中寒武统—下奥陶统娄山关组为均一性极强的厚层白云岩,可分性极差。但笔者新近研究发现,其顶、底均为古岩溶不整合面,并有大量颗粒(鲕、豆、核形石)白云岩和藻纹层白云岩夹层,还有许多鸟眼构造、叠层石构造、交错层理、帐蓬构造存在。据其垂向组合规律,将娄山关组分为三段。认为娄山关组由7个三级层序组成,层序界面为古岩溶不整合面或暴露带,每个层序都由海进体系域和高水位体系域构成。

北京西山淹没不整合型高频旋回层序地层研究

以北京西山寒武系张夏组地层为例,运用米兰柯维奇高频旋回层序地层分析方法与地球化学结合研究的手段,对三级快速海侵背景下的寒武系张夏组高频旋回层序地层格架进行划分。研究认为,该区张夏组灰岩地层并非传统的I、II型碳酸盐岩层序模式,应为典型淹没不整合型层序。建立了从三级层序到六级米级旋回的张夏组淹没不整合型高频旋回层序地层格架。淹没不整合型层序格架内有利储层主要发育于三级、四级层序的高水位体系域中。快速海侵事件标志着碳酸盐岩台地的沉积间断。通过对淹没不整合型碳酸盐岩层序地层的研究来指导未来的石油勘探生产,具有现实的研究意义。

四川盆地西北部中二叠统茅口组岩相古地理、古岩溶地貌恢复及其油气地质意义

基于野外剖面、地震、测井及钻井等资料分析,结合大地构造背景,对四川盆地西北部(简称川西北)地区中二叠统茅口组岩相古地理及古岩溶地貌特征进行恢复并探讨其油气地质意义。研究表明,川西北地区茅口组可进一步划分为LSC1、LSC2、LSC3共3个长期旋回,分别对应茅一段、茅二段、茅三段。受上扬子地块北缘勉略古洋盆扩张所形成的伸展构造及地幔柱隆升产生的基底断裂控制,在北西西及北东方向产生构造分异,沉积基底自北向南呈幕式沉降,导致茅一段—茅三段沉积体系由碳酸盐台地逐渐演变为台地-斜坡-广海陆棚共存的特征。根据残余厚度恢复出岩溶高地、岩溶斜坡、岩溶洼地等古岩溶地貌单元,岩溶地貌单元是在沉积地貌基础上继承性发展形成的。沉积相及古岩溶地貌对于油气储集具有重要意义,高能滩与溶丘组合、台缘斜坡与岩溶斜坡组合是川西北地区茅口组最优质的储集区带组合类型,将优质储集相带叠合古岩溶地貌,对这两类储集区带平面展布特征进行预测。研究结果将为四川盆地中二叠统茅口组勘探部署提供新的思路与借鉴。