开江—梁平海槽演化阶段与构造沉积特征

Evolution stage and tectonic sedimentary characteristics of the Kaijiang-Liangping Trough

四川盆地开江—梁平海槽及其周缘地质资源丰富,分布有普光、龙岗等一系列大型气藏群,勘探开发潜力巨大。目前,针对海槽的发育时期、形成演化尚无统一观点,进一步明确其发育起始时期、演化阶段对推进海槽周缘油气勘探及地质研究具有重要意义。文中依据海槽周缘勘探最新进展,利用野外露头、钻井、测井及三维地震资料,综合分析区域构造演化与沉积充填特征,探讨海槽演化阶段及各阶段构造动力和沉积机制差异。研究表明:1)开江—梁平海槽内部可识别出3套典型的深水沉积,在四川盆地北部总体呈西北宽、东南窄的北西—南东向发育,海槽内部至周缘台地相区发育完整的深水—浅水沉积相序组合;2)海槽发育始于中二叠世晚期,持续发育于晚二叠世,在长兴期达到高峰,延续至早三叠世逐渐消亡,表现出多阶段继承性演化的特征,可分为3期构造沉积演化,即中二叠世海槽雏形萌芽期、晚二叠世海槽发育高峰期、早三叠世海槽充填消亡期;3)不同演化阶段的构造动力和沉积机制存在差异,与萌芽期横向迁移的空间变化模式不同,高峰期以纵向加积为主;4)环开江—梁平海槽周缘是海相碳酸盐岩大中型气田分布的主要区带之一,海槽纵向多产层发育,勘探开发潜力巨大。

The Kaijiang-Liangping trough and its periphery in Sichuan Basin are rich in geological resources,with a series of large gas reservoir groups such as Puguang and Longgang distributed and so on,which has great exploration and development potential.At present,there is no unified view on the development period,formation and evolution of the Trough.It is of great significance to further clarify the initial stage and evolution stage of its development for promoting oil and gas exploration and geological research around the Trough.Based on the latest progress of exploration around the Trough,this paper comprehensively analyzes the regional tectonic evolution and sedimentary filling characteristics through outcrop,drilling,logging and three-dimensional seismic data,and discusses the evolution stages of the Trough and the differences of tectonic dynamics and sedimentary mechanisms in each stage.The research shows that:(I)three sets of typical deep water sediments can be identified in the Kaijiang-Liangping Trough,which are generlly developed in a NW-SE direction,wide in the northwest and narrow in the southeast in the northerm Sichuan Basin,and a complete sequence of deep water to shallow water sedimentary facies is developed in the platform facies areas from the Trough to the periphery.(2)The development of the Trough began in the Late Middle Permian,continued in the Late Permian,reached its peak in the Changxing period,and gradually disappeared in the Early Triassic,showing the characteristics of multi-stage inheritance evolution,It can be divided into three stages of tectonic sedimentary evolution,namely,the embryonic stage of the Middle Permian Trough,the development peak of the Late Permian Trough,and the filling and disappearing stage of the Early Triassic Trough.(3)There are dfferences in tectonic dynamics and sedimentary mechanisms in different evolutionary stages,and the spatial change mode of lateral migration in peak period is different from mainly vertical accretion in the embryonic stage.(4)Kaijiang-Liangping Trough is one of the main distribution zones of large and medium-sized marine carbonate gas fields,and the longitudinal multiple beds are developed in the Trough,which has great potential for exploration and development.