四川盆地南部中三叠统雷口坡组岩相古地理与常规—非常规双领域勘探意义

Lithofacies paleogeography of Middle Triassic Leikoupo Formation in the southern Sichuan Basin and its implications for conventional and unconventional dual-domain exploration

宋晓波 陈安清 苏成鹏 刘勇 孙娜 王泽宇 李雯 王宪峰 黄光辉 孙诗

SONG Xiaobo CHEN Anqing SU Chengpeng LIU Yong SUN Na WANG Zeyu LI Wen WANG Xianfeng HUANG Guanghui SUN Shi

中国石化 西南油气分公司 勘探开发研究院, 成都 610059 成都理工大学 自然资源部深时地理环境重建与应用重点实验室, 成都 610059 成都理工大学 油气藏地质及开发工程全国重点实验室, 成都 610059

Exploration and Development Research Institute, SINOPEC Southwest Branch Company, Chengdu, Sichuan 610059, China Key Laboratory of Deep-Time Geography and Environment Reconstruction and Applications, Ministry of Natural Resources, Chengdu University of Technology, Chengdu, Sichuan 610059, China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China

中三叠统雷口坡组是四川盆地油气勘探最早的层系之一，但长期处于小气藏多点开花的勘探局面。近期研究表明雷口坡组发育海相常规与非常规油气藏的双重前景，已有的古地理格局认识难以满足新的勘探需求。以四川盆地南部雷口坡组为研究对象，在详细的野外露头和钻井岩心沉积相分析的基础上，开展了岩相古地理重建和沉积—储层发育模式研究。四川盆地南部中三叠统雷口坡组的沉积环境类型包括台地潮坪、潮缘滩、陆棚海湾、咸化潟湖。海侵期(雷口坡组一段和三段)陆表海相对能量较高，有利于高能滩相和富有机质泥岩或泥灰岩发育；海退期(雷口坡组二段和四段)能量相对较低，有利于白云岩—蒸发岩系发育。川南雷口坡组常规碳酸盐岩储层的发育主要受古地貌格局控制，波浪—潮汐复合作用形成了广泛分布的薄滩相白云岩储层。雷三段沉积期的海侵作用是富有机质泥岩或泥灰岩非常规储层形成的重要影响因素，既改变了原有的古地貌格局，又携带巴东组富有机质碎屑物源进入上扬子克拉通内部，并在后期强烈的蒸发作用下形成具有“盐岩—泥灰岩”旋回的盐间油气藏。四川盆地南部雷口坡组常规—非常规双领域的古地理重建，不仅揭示了雷口坡组海相非常规盐间油气藏的勘探新领域，同时也证实了雷口坡组本身具备发育优质烃源岩的条件。

The Leikoupo Formation of the Middle Triassic is one of the earliest strata for oil and gas exploration in the Sichuan Basin, but its exploration has long been limited to scattered small gas fields. Recent studies reveal that the Leikoupo Formation holds dual prospects for marine conventional and unconventional oil and gas reservoirs, but the existing paleogeographic pattern is inadequate for the new exploration needs. This study focused on the Leikoupo Formation in the southern Sichuan Basin. Based on the detailed analysis of sedimentary facies in outcrops and drill cores, the lithofacies paleogeography was reconstructed and the sediment and reservoir development patterns were studied. The sedimentary environment types in the Middle Triassic Leikoupo Formation of the southern Sichuan Basin included platform tidal flats, tidal shoals, shelf bays, and saline lagoons. During the transgression period (members 1 and 3 of the Leikoupo Formation), relatively high-energy marine conditions favored the development of high-energy shoal facies and organic-rich mudstone or marl. During the regressive period (members 2 and 4 of the Leikoupo Formation), the energy was relatively lower, favoring the development of dolomite and evaporite successions. The development of conventional carbonate rock reservoirs in the Leikoupo Formation of the southern Sichuan Basin was primarily controlled by the paleogeomorphic pattern. The combined effects of wave and tidal actions led to the extensive distribution of thin shoal-facies dolomite reservoirs. The transgression during the depositional period of member 3 of the Leikoupo Formation played a significant role in the formation of unconventional reservoirs of organic-rich mudstone or marl. It not only altered the original paleogeomorphic pattern but also transported organic-rich clastic materials from the Badong Formation into the interior of the Upper Yangtze Craton. Under intense evaporation during the later stages, intersalt hydrocarbon reservoirs with a "salt rock and marl" cycle were formed. The paleogeographic reconstruction in both conventional and unconventional domains of the Leikoupo Formation in the southern Sichuan Basin not only reveals a new exploration area for marine intersalt unconventional resources, but also confirms the favorable conditions for the development of high-quality source rocks within the formation.

国家自然科学基金项目 U24A20591;国家自然科学基金项目 42272132;中国石化西南油气分公司勘探开发研究院项目 34450000-22-ZC0607-0038

https://doi.org/10.11781/sysydz2025040731