四川盆地震旦系—古生界古裂陷-古隆起交替演化与大型富油气区预测OA

Natural gas exploration in the Sinian-Paleozoic marine strata of the Sichuan Basin has made significant achievements,with several large gas fields discovered.However,as the operations progress,the marine gas exploration has again come under the challenge caused by indefinite prospects and zones for great addition of reserves.In this context,it is urgent to clarify how the alternating evolution of paleo-rifts and paleo-uplifts controls hydrocarbon accumulation and enrichment.Based on latest data from drilling and seismic survey,this study systematically elaborates the alternating evolution process of paleo-rifts and paleo-uplifts and its control effects on source rock,reservoir,and hydrocarbon accumulation,and predicts gas-rich zones.The following results are obtained.First,during different phases of the Sinian-Paleozoic,several large-scale tectonic units developed within the Sichuan Basin,including the Central Sichuan paleo-uplift,Kaijiang paleo-uplift,Deyang-Anyue rift,Kaijiang-Liangping trough,Pengxi-Wusheng platform-depression,and peripheral depressions surrounding the paleo-uplifts.The alternating evolution process of large paleo-rifts and paleo-uplifts can be divided into six stages.Second,the multi-phase uplift-depression transitions in the Sichuan Basin during the Sinian-Paleozoic were closely associated with the evolution of the Tethyan tectonic domain.The northern part of the basin was controlled by the closure of the Shangdan Ocean,a branch of the Proto-Tethys Ocean,and the extension-closure process of the Mianlue Ocean.The southern part was controlled by the far-field effects of the collision between the southern margin of the South China Block and Gondwana,and also by the Emeishan Large Igneous Province during the Permian.Third,the alternating evolution of paleo-rifts and paleo-uplifts controlled the development and distribution of three sets of regional high-quality source rocks,and eleven sets of large-scale reservoirs.Fourth,three major composite petroleum systems are established.Within these systems,nine conventional gas-rich zones and three shale gas-rich zones have been predicted across different strata,indicating clear directions with a huge quantity of resources for future exploration.It is concluded that the alternating evolution of paleo-rifts and paleo-uplifts in the Sichuan Basin is the core factor controlling the hydrocarbon accumulation in the Sinian-Paleozoic,and that the large geological units of paleo-rifts and paleo-uplifts will remain the important targets for large-scale natural gas exploration in the future.