摘要： 四川盆地二叠系和三叠系的接触关系以及长兴组岩溶成因的认识,地质界一直存在较大分歧。通过野外露头、钻井、岩心、成像测井、C-O同位素等资料研究发现,普光气田长兴组发育大规模溶沟、溶洞、囊状溶洞、岩溶角砾岩;P/T界线附近长兴组溶蚀灰岩碳同位素发生严重负偏移;长兴组顶见不整合面,成像测井岩溶相带划分明显;长兴组顶部存在地层缺失。综合分析认为,普光气田长兴组发生过表生岩溶作用,长兴阶晚期重大海退事件是引起表生岩溶的主要因素。长兴组长期接受表生岩溶作用的改造,除形成台地边缘礁滩相储集层外,在礁滩欠发育的台地内部和台地前缘上斜坡等区带,是寻找不整合岩溶储集层的有利地区。

关键词: 表生岩溶, 海退, P/T界线, 长兴组, 普光气田, 四川盆地

Abstract: There is a great dispute in understanding the contact relationship between the Permian and Triassic, and origins of the karst of Changxing Formation in Sichuan Basin for a long time. Through the analysis of field outcrops, drilling, cores, imaging logging, C-O isotope and other data, this paper finds that large-scale karst gullies, karst caves, cystic karst caves and karst breccias occurred in Changxing Formation of Puguang Gasfield. The carbon isotopes of the dissolved limestone in Changxing Formation were negatively excursed near the Permian-Triassic boundary. The top of Changxing Formation is an obvious unconformity, and the karst facies variations are obvious on the imaging logging map. Furthermore, at the top of Changxing Formation, some strata is missing. According to the comprehensive analysis, the results reveal that the supergene karst had occurred in the Changxing Formation of Puguang Gasfield, and that the major factor causing the supergene karst is the great regression event at late Changxing Stage. Changxing Formation had been modified by the supergene karst for a long time. In addition to the reef-bank reservoirs at the edge of the platform, the interior of the platform and the up-slope at the front of the platform where the reef-bank is not occurred are also the favourable areas to search for the unconformity karst reservoirs.

Key words: supergene karst, regression, P/T boundary, Changxing Formation, Puguang Gasfield, Sichuan Basin

中图分类号: 

• P512.2