四川盆地中西部雷口坡组油气地质条件及勘探方向探讨

Study on petroleum geological conditions and hydrocarbon exploration direction of Leikoupo Formation in the centre and west of Sichuan Basin,China

四川盆地中三叠统雷口坡组迄今为止只发现了中坝和磨溪两个大中型气田,但近年来,钻井过程中于雷口坡组油气显示活跃,展示了良好的勘探前景。盆地中西部雷口坡组主要为局限台地相沉积,部分地区为开阔台地和蒸发台地相,主要亚相为潟湖和潮坪;其沉积时该区地壳处于拉张状态。雷口坡组有良好的烃源岩条件,多种类型的优质储层(礁滩、热液白云岩、古喀斯特储层等),有膏岩层、泥岩层的良好封隔,具有形成大中型气藏的地质条件。寻找礁滩储层、热液白云岩储层和古喀斯特储层气藏是四川盆地中西部雷口坡组的勘探新方向,其重点勘探地区应是龙门山前缘(川西)地区。然而,雷口坡组源储距离较大,必须要有断穿龙潭组和下三叠统的断层裂缝系统作为运移通道,所以在预测有利勘探区时,应重视天然气输导体系的研究。

So far only two medium-large gas fields,i.e.Zhongba and Moxi gas fields,have been discovered in the Middle Triassic Leikoupo Formation in Sichuan Basin.However,evidences of oil and gas from Leikoupo Formation during recent drillings are common,showing a good petroleum exploration prospect in the formation.Most of Leikoupo Formation is restricted platform facies and a small part of the formation is open platform and evaporated facies in the centre and west of Sichuan Basin.Their main subfacies are lagoons and tidal flats.The crust of this area is in an extensional state during the Leikoupo Formation deposition.The source rocks of Leikoupo Formation are good.There are several types of high quality reservoirs in Leikoupo Formation,such as reef-bank reservoirs,hydrothermal dolostone reservoirs,paleokarst reservoirs,and so on.The gypsum and mudstone are the good covers of Leikoupo Formation.Therefore,Leikoupo Formation has good geological conditions and can form medium-large gas pools.The new exploratory directions of Leikoupo Formation are to look for reef-bank reservoir gas pools,hydrothermal dolostone gas pools and paleokarst reservoir gas pools in the centre and west of Sichuan Basin.The front regions of Longman Mountains（western Sichuan Basin） are the important exploratory areas.However,the distance between the source rocks（Upper Permian Longtan Formation） and reservoir rocks is so far that fault-fracture systems must act as migration pathways（conduit system） for petroleum and gas.The conduit systems must break through the Upper Permian Longtan Formation and Lower Triassic gypsum.Therefore,the study of conduit systems of gas is important in predicting the favorable exploration area in Leikoupo Formation.