Characteristics and hydrocarbon geological significances of paleo-bay in the fourth member of Middle Triassic Leikoupo Formation,western Sichuan Basin,SW China
Characteristics and hydrocarbon geological significances of paleo-bay in the fourth member of Middle Triassic Leikoupo Formation,western Sichuan Basin,SW China
The depositional facies types of the fourth member of the Middle Triassic Leokoupo Formation(Lei-4 Member)in westem Sichuan Basin are examined through the methods of sedimentology,lithology and analysis of well-logging data,as well as the special lithofacies indicators such as microbialite,gypsum-salt rock and tempestites,using the data of about 400 wells and 11 outcrop sections.The distribution and evolution and its hydrocarbon geological significances of the bay facies have been discussed.The Lei-4 Member in westem Sichuan Basin has an ocean-bay-flat depositional model,with the presence of evaporated tidal flat,restricted tidal flat and paleo-bay facies from east to west.The subfacies such as bay margin,subtidal bay and bay slope are recognized within the paleo-bay,with microbial reef and grain bank microfacies in the bay margin,microbial flat,deep-water spongy reef and hydrostatic mudstone microfacies in the subtidal bay,and tempestites and collapsed deposits in the upper bay slope.The bay boundary covered the Guangyuan-Zitong-Dujiangyan area in the period of the first submember of the Lei-4 Member(Lei-4-1)with falling sea level,regressed westward into the Shangsi-Jiangyou-Dujiangyan area in the period of Lei-4-2,and expanded to the Shangsi-Zitong-Langzhong-Wusheng-Yanting-Chengdu area in the northern part of central Sichuan Basin in the period of Lei-4-3 along with a small-scale transgression.The topographic pattern of"one high and two lows"is confirmed in the Lei-4 Member,corresponding to a configuration of source rocks and reservoir rocks alternated horizontally and superimposed vertically.Two efficient source-reservoir configuration models,i.e.side source & side reservoir,and self-generating & self-storing,are available with the microbial reef and grain bank reservoirs at the bay margin and the high-quality source rocks within the sags on both sides of the bay.The research findings will inevitably open up a new situation for the hydrocarbon exploration in the Leikoupo Formation.
维普
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