Lithofacies palaeogeographic characteristics and favorable reservoir facies of the Leikoupo Formation in Sichuan Basin
XU Kang1,2, GONG Hanning1,2
1 Wuxi Research Institute of Petroleum Geology,SINOPEC,Jiangsu Wuxi 214126,China; 2 Key Laboratory of Hydrocarbon Accumulation,SINOPEC,Jiangsu Wuxi 214126,China
Abstract：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 palaeogeographic 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 evaporate platform. The palaeogeographic pattern changed from “high in the west and low in the east”during 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 western 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 Formation in northeastern Sichuan,the karst reservoirs in the structural superimposed unconformity are favorable to be formed.
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