上扬子克拉通内裂陷的发现及对安岳特大型气田形成的控制作用

利用钻井和地震资料,在上扬子克拉通德阳-安岳地区发现晚震旦世-早寒武世克拉通内裂陷,受张性断裂控制,呈NNW向展布,南北长320 km、东西宽50~300 km。裂陷演化经历了形成期、发展期、消亡期3个阶段,形成有利的近源成藏组合。研究结果表明:1晚震旦世灯影组沉积期为裂陷形成期,裂陷内发育槽盆相沉积,两侧发育台地边缘相丘滩体,控制了灯影组优质储层的形成与分布;2早寒武世梅树村组沉积期-筇竹寺组沉积期为裂陷发展期,充填500~1000 m的深水陆棚相泥质岩,是优质烃源岩沉积期;3沧浪铺组沉积期为裂陷消亡期,经填平补齐,结束了克拉通内裂陷的演化历史。克拉通内裂陷是安岳特大型气田形成的关键因素,裂陷内优质烃源岩为特大型气田提供了充足的气源,在晚燕山期-喜马拉雅期川中古隆起西部快速隆升过程中形成区域性侧向封堵,有利于裂陷东翼的高石梯-磨溪地区特大型气田的保存。克拉通内裂陷及其大气田成藏作用对古老克拉通盆地深层油气勘探有重要的参考价值。

Discovery of intra-cratonic rift in the Upper Yangtze and its coutrol effect on the formation of Anyue giant gas field

According to the drilling and seismic data,the Late Sinian-Early Cambrian intra-cratonic rift was found in Deyang-Anyue area of the Upper Yangtze craton.This rift is controlled by tensional fault and distributed in NNW trending with the NS length of 320 km and EW width of 50-300 km.After three stages of rift evolution,i.e.,the forming stage,developing stage and dying stage,a favorable near-source accumulation assemblage was formed.The research results indicate that:(1) the sedimentary stage of Late Sinian Dengying Formation is the rift forming stage,during which trough-basin facies sedimentation is developed in the rift,while platform marginal facies mounds and shoals are developed on both side,controlling the formation and distribution of high-quality reservoirs in Dengying Formation;(2) the sedimentation stage of Early Cambrian Meishucun-Qiongzhusi Formation is the rift development stage,during which deep-water continental shelf facies argillaceous rocks are filled in the rift with a thickness of 500-1000 m,indicating the sedimentation stage of high-quality source rocks;(3) the sedimentation stage of Canglangpu Formation is the rift dying stage,terminating the evolution history of intra-cratonic rift by gap filling.The intra-cratonic rift is a key factor for the formation of Anyue giant gas field,where the high-quality source rocks provide abundant gases for the giant gas field.A regional lateral sealing occurred during the rapid rising of the western paleo-uplift in Central Sichuan during the Late Yanshan-Himalayan period,favorable to the preservation of the Gaoshiti-Moxi giant gas field on the east wing of the rift.The intra-cratonic rift and its role in giant gas accumulation provides a significant reference for deep oil and gas exploration in paleo-craton basins.