Comprehensive Evaluation Of Sealing Of Oil And Gas Caprocks In The Southern Margin Of Junggar Basin

In addition to the sufficient supply of oil and gas resources,favorable reservoir conditions and effective transmission channels,good sealing ability is the most important for the formation of large oil and gas reservoir.Only in this way can oil and gas enter traps to gather and preserve.So far,the oil and gas resources discovered and proved in the southern margin of Junggar Basin are relatively low.Therefore,it is necessary to study the sealing property of the cap bed in the southern margin of Junggar Basin,and point out the direction of exploration and development in the next step.On the basis of making full use of seismic data and logging data,the macroscopical development and distribution characteristics of caprock are analyzed.According to the active period of the southern margin fault of Junggar Basin,the southern margin fault system of Junggar Basin is divided.Based on the macroscopic development characteristics of the caprock,the microcosmic sealing ability and the failure degree of the caprock caused by faults,the comprehensive evaluation of the caprock sealing ability in the study area is carried out according to the fuzzy mathematics evaluation method.In the basin,there are four sets of cap layers in the basin which block oil and gas,namely,the Taxihe formation,the Anjihaihe formation,the Tugulu formation,and the Jurassic cap rock.The distribution range of the cover is wide and the sedimentary thickness is large.Sedimentary environment in turn is alluvial fan,lake,shallow lake-deep lake,semi-deep lake and braided river delta.Due to the strong tectonic movement in the southern margin of Junggar basin,the first row tectonic belt has a serious denudation after uplift,and the structure of the east,middle and west segments is quite different.Therefore,the development of the cover layer in each tectonic belt is inconsistent,and the areas closed in each cover are different.In the first row of tectonic belt,there is a general lack of the covering layer above the Tugulu formation,and only the Jurassic cap layer is developed.In the second row of tectonic belts,there was a deficiency of the Tugulu formation and the Jurassic cap layer,which developed the cap layer of the Taxihe formation and the Anjihaihe formation.In the third row of tectonic belt,missing Jurassic cap layer,other developmen.The fracture of the study area can be divided into 2 types and 13 forms according to the fault break.When the fault is of the type of basement involvement,the failure degree of the caprock should be taken into account when other factors remain unchanged.When the fracture is a caprock slip type,it is not necessary to consider the effect of fracture on the caprock sealing.According to the comprehensive evaluation results,the cover layer of the Anjihaihe formation is a good covering layer,and the covering layer of the Tugulu formation is the middle layer,and the Taxihe formation and the Jurassic cover layer are the lower cover.It can be seen from the analysis of the relationship between cover layers and oil and gas distribution in the study area,the control of cap layers on typical oil and gas reservoirs and the comprehensive evaluation results,the quality of the middle section of the research area is good,the western and eastern sections is poor.Oil and gas reservoirs are mainly distributed in reservoirs with good caprock quality or lower than middle caprock.The cover layer controls the distribution of oil and gas in plane and longitudes,which is of great significance for exploration and development of oil and gas reservoirs.