四川盆地广安—石柱古隆起的发现及油气地质意义

Discovery of Guang’an-Shizhu paleo-uplift in Sichuan Basin and its oil and gas geological significance

根据地震剖面、航磁资料、钻井资料和野外露头,在四川盆地东部发现了广安—石柱古隆起,并对其进行了详细论证,认为该古隆起属于川中古隆起向东部的延伸。通过恢复四川盆地龙王庙组厚度,明确了广安—石柱古隆起的平面展布特征,其形态总体呈NW—SE向的鼻状,EW向延伸较远,而SN向较窄,在东侧存在局部古高点。井-震结合的精细解释结果表明,广安—石柱古隆起形成于震旦纪早期,终止于寒武纪晚期。震旦纪—寒武纪,广安—石柱古隆起区沉积具有从斜坡向核部超覆的特征,在多次构造挤压作用下发生褶皱变形,并在古隆起东侧的石柱地区形成一个隆起幅度不大的自成古圈闭。结合广安—石柱古隆起的发育特征,重建的地质过程显示古隆起共经历了4个演化阶段,包括早震旦世的雏形阶段、晚震旦世—早寒武世中期的发育阶段、早寒武世晚期—晚寒武世的调整定型阶段和奥陶纪的隆升活动消亡阶段。广安—石柱古隆起的形成受基底隆升、板块运动、构造活动和隐伏花岗岩侵位等因素控制。在古隆起发育区,灯影组、龙王庙组和洗象池组发育大规模丘滩体沉积,且受后期白云石化作用和表生岩溶作用改造,可形成川东地区优质的储集层,具有重要的油气地质意义。

Based on seismic profiles,aeromagnetic data,drilling data and field outcrops,Guang’an-Shizhu paleo-uplift was discovered in the eastern Sichuan Basin and demonstrated in detail.It is believed that the paleo-uplift is an extension of the central Sichuan paleo-uplift to the east.By restoring the thickness of Longwangmiao Formation in Sichuan Basin,the planar distribution of Guang’an-Shizhu paleo-uplift was demonstrated,generally shown as a NW-SE trending nose structure,characterized with far EW-trending extension,narrow SN-trending expansion,and local paleo-highs in the east.The fine interpretation results based on logging and seismic data show that the evolution of Guang’an-Shizhu paleo-uplift began in the Early Sinian and ended in the Late Cambrian.During the Sinian to Cambrian period,the sedimentation in Guang’an-Shizhu paleo-uplift was characterized by overlapping from the slope to the core,fold deformations were formed under multiple tectonic compressions,and a paleo-trap with small uplift was formed in Shizhu area on the east side of the paleo-uplift.Based on the development characteristics of Guang’an-Shizhu paleo-uplift,the reconstructed geological process shows that the paleo-uplift has undergone four evolution stages,including the prototype stage in the Early Sinian,the development stage from the Late Sinian to the Middle Early Cambrian,the adjustment and formation stage from the Late Early Cambrian to the Late Cambrian,and the uplifting activity termination stage in the Ordovician.The formation of Guang’an-Shizhu paleo-uplift was controlled by the factors such as basement uplift,plate movement,tectonic activity and granite emplacement.In the paleo-uplift development area,a large scale of mound and shoal deposits were developed in Dengying Formation,Longwangmiao Formation and Xixiangchi Formation,and transformed by late dolomitization and epigenic karstification.They are high-quality reservoirs in the eastern Sichuan Basin and are of important petroleum geological significance.