Research On Reservoir Characteristics And Favorable Traps Of Changxing Formation In Dongtieshan~Longmen Block, Longgang

The gas reservoir of the Permian Changxing Formation on the platform margin around the Kaijiang-Liangping trough is one of the important areas for gas exploration in the Northeast Sichuan Basin.After breakthrough of the Changxing Formation reservoir in Longhuichang on the west side of the trough in 2013,a number of pre-exploration wells were deployed for the Changxing Formation reservoir,but failed to achieve anticipated exploration results.Based on the drilling wells,logging data,seismic profiles and other test data,through the outcrops,core description,thin observation and seismic data interpretation of the study area,the stratigraphic and sedimentary facies distribution,reservoir characteristics and distribution,gas water relation characteristics and favorable trap optimization in the study area are studied in detail in five aspects,made the following conclusions and understanding:The top and bottom boundaries of the Changxing Formation are recognized.The Changxing Formation can be divided into three members,the first member of the Changxing Formation mainly is manily composed of micritelimestones with some chert nodules.The second and third member of the Changxing Formation is characterized by bioclastic limestone,residual bioclastic dolomite and reef limestone.Both are distinguished by thin mudstone or rocky debris at the top of the reef.Open platform facies,platform margin facies,slope?trough facies and gentle slope facies were developed during the Changxing Formation period.The platform margin was spread along the northwest to the south east.The reefs are mainly developed on the platform margin.The reefs are developed in the second and third member of Changxing Formation,and the reefs show migrating from the open platform to the slope?trough.The main types of reservoirs rocks in the Changxing Formation are residual bioclastic dolomite and crystalline dolostone.The mian pore type is intergranular pore and intergranular dissolution pore,and the porosity is between 2%and 15%.The reservoir type is crack-pore type.The reservoirs of the Changxing Formation are classified.The main reservoirs of the Changxing Formation in the study area are the third class reservoir types,its porosity ranges from 2%to 6%.It shows low porosity and low permeability,but it has high porosity and permeability in the local areas.The key of reservoirs formation are seepage-reflux dolomitization and dissolution.The Changxing Formation reservoirs are mainly distributed along the platform margin,and the horizontal changes are large and the heterogeneity is strong.Vertically,the reservoirs always are developed in the second and third member of the Changxing Formation.On the development of higher degree research area in southern Tieshan and Shuangjiaba Changxin formation gas reservoir,two gas reservoirs are structural-lithologic reservoir,the gas components are different,and there is no uniform gas water interface,each has its own gas?water relationship.The activity of the fault has a great influence on the enrichment of natural gas,the fault which was active in oil and gas filling period is not conducive to the preservation of oil and gas.In this study,based on the prediction results of 3D seismic interpretation,combined with the reservoir zero line as the boundary,Changxing Formation traps were sorted out in the study area.A total of 11 traps have been sorted out.The traps are evaluated by trapping area,trap reservoir thickness and trap preservation condition and three favorable traps are evaluated.