| At present,the contradiction between international energy supply and demand is prominent,energy security has increasingly become the focus of attention of all countries,and the Sichuan Basin,as an important oil-bearing basin in China,has successively discovered a number of hundreds of billions of cubic meters of atmospheric fields.Among the total conventional oil and gas resources in the Sichuan Basin,the marine carbonate strata account for about 85% of the resources,of which the Lower Paleozoic Cambrian as an important oil and gas bearing layer,especially in the Middle and Upper Cambrian Xixiangchi Formation,since the discovery of natural gas in Weiyuan gas field in southern Shunan,and industrial gas flow has been obtained in Gaoshiti,Moxi and many wells north of Sichuan,showing good natural gas exploration potential.According to the gas content of the drilled wells,the Middle and Upper Cambrian Xixiangchi Formation in eastern Sichuan region has good accumulation conditions and resource potential.Based on the latest drilling and logging data,combined with field outcrop profile observation,indoor thin-section analysis and identification,carbon and oxygen isotope geochemical analysis and laboratory results and geophysical interpretation results,the sedimentary evolution characteristics of the Middle and Upper Cambrian Xixiangchi Formation in the high-frequency sequence strata lattice in eastern Sichuan were analyzed,and the favorable reservoir facies zone was predicted accordingly.The main research results achieved are as follows:(1)The sequence stratigraphy method was used to divide the Middle and Upper Cambrian Xixiangchi Formation in eastern Sichuan into three three-level sequences:SQ1,SQ2 and SQ3,which correspond to the first section of Xixiangchi,the second section of Xixiangchi and the third section of Xixiangchi,respectively;On this basis,it is further divided into five four-level sequences: sq1 and sq2 correspond to the first section of Xixiangchi,sq3 and sq4 correspond to the second section of Xixiangchi,and sq5 corresponds to the third section of Xixiangchi,which can more accurately divide the development period of the large set of dolomites in the Xixiangchi Formation in the study area under the tertiary-quaternal sequence stratigraphic lattice,and then study the sedimentary evolution characteristics of the strata,which is also of great significance for the prediction of the favorable zone of the reservoir.(2)It is concluded that the strata of the Xixiangchi Formation in eastern Sichuan are carbonate sediments formed under the background of a large "sea invasion-sea retreat" cycle,most of which are mainly confined terraces,and some open terraces are developed on the east side,and gradually transition to the terrace-edge and slope-basin facies with the deepening of the sea level to the east.The sedimentary pattern in eastern Sichuan is mainly inherited from the paleogeographical pattern of the sedimentary period of the lower stratum include the Longwangmiao Formation and the Gaotai Formation,and the facies changes are mainly affected by the rise and fall of sea level.(3)Combined with field profile and drilling core research results,the favorable reservoirs of the Xixiangchi Formation in eastern Sichuan have the characteristics of thin single-layer thickness and strong heterogeneity,and the distribution is mainly controlled by the dominant facies spread,and the granular beach is the main favorable reservoir development zone.Lithology plays an important role in reservoir development,and granular dolomite is the main rock type of favorable reservoir.In diagenesis,dolomitization,tectonic rupture and dissolution are favorable for reservoir development.Based on the distribution law of sedimentary facies,combined with drilling display and test data,it is predicted that the potential favorable development zones of the Xixiangchi Formation in eastern Sichuan are mainly distributed in the Kaijiang-Guang’an-Hechuan line and the Lichuan-Shizhu-Nanchuan line. |
PDF Full Text Request