四川盆地雷口坡组岩相古地理特征及有利储集相带

Lithofacies palaeogeographic characteristics and favorable reservoir facies of the Leikoupo Formation in Sichuan Basin

四川盆地中三叠统雷口坡组近年来取得重大勘探突破。基于野外露头、录井、测井及地震资料,以三级层序体系域为单元编制岩相古地理图,分析有利储集相带展布。研究表明:四川盆地雷口坡组可划分为2个三级层序,主要沉积环境为局限—蒸发台地。局限台地内发育潮间上带、潮间下带、局限潟湖及台内滩。蒸发台地内发育潮上带和蒸发潟湖。古地理格局由SQ1时期的西高东低,演变为SQ2-TST时期的东西高、中间低,最后在SQ2-HST时期转变为西低东高。岩相在雷口坡组沉积的早、晚期以云-膏岩组合为主,中期以灰-膏岩组合为主。川西广汉斜坡北部是雷四3亚段发育藻云坪岩性圈闭有利目标区,川西梓潼凹陷西北部雷三2-3亚段、泸州古隆起周缘雷一1亚段是滩相白云岩储集层发育的有利区,川东北雷口坡组顶部不整合面之下是构造叠合不整合面岩溶储集层发育的有利区。

In recent years,important exploration findings have been made in the Middle Triassic Leikoupo Formation in Sichuan Basin.Based on the database consisting of outcrops,logging data,and seismic data and taking the thirdorder sequences stratigraphic framework as unit,the lithofacies palaeogeographic map of Leikoupo Formation is compiled and the characteristics of favorable reservoir facies are analyzed.The results suggest that the Leikoupo Formation in Sichuan Basin can be divided into two thirdorder sequences and that the main sedimentary environments are restricted platform and evaporate platform.In the restricted platform,the upper intertidal zone,the lower intertidal zone,the limited lagoon and the beach within the platform are developed.The supratidal zone and evaporate lagoon are developed in the evaporate platform.The palaeogeographic pattern changed from“high in the west and low in the east”during the SQ1 period through“high in the east and low in the middle”during the SQ2-TST period to“low in the west and high in the east”during the SQ2-HST period.In the early and later periods during the deposition of Leikoupo Formation,the lithofacies are dominated by dolomite and gypsum,however,in the middle period they are dominated by Limestone and gypsum.The north part of Guanghan slope in western Sichuan is a favorable area for the development of algal dolomite flat traps of the third period of the Member 4 of Leikoupo Formation.The Member 3 of Leikoupo Formation in the northwest of Zitong sag in western Sichuan and the Member 1 of Leikoupo Formation around Luzhou ancient uplift are favorable areas for the development of beach facies dolomite reservoir.Under the top unconformity of the Leikoupo Formation in northeastern Sichuan,the karst reservoirs in the structural superimposed unconformity are favorable to be formed.