Control Of Oil And Gas Migration And Accumulation By Fracture Intersection Type Of Banqiao Slope In Qikou Depression

In petroliferous basins,the phenomenon of fault intersection is very common.Because of the structural deformation of two or more groups of faults superimposed,the degree of rock fracture,the intensity of activity and the width of fault zone at the intersection are more complex than those of a single fault,and their role in hydrocarbon accumulation is more complex.Based on the detailed analysis of 3D seismic interpretation data in Banqiao area,the geometric characteristics of the fault are analyzed.Three typical faults of Banqiao slope,Banqiao,Dazhangtuo and liugangzhuang fault,are selected in the comprehensive application of "three Diagrams".The "three Diagrams"(fault distance drop curve,drop / growth index buried depth curve and fault distance contour map)are analyzed comprehensively.The results show that the main body of a single fault of Banqiao slope experiences three periods of intense activity,namely: Sand Three,Shayi Dongying and Minghuazhen Formation.Based on the analysis of fault activity,the direction of tectonic stress field at that time can be determined by dividing the Kulun fault in the main active period of each fault in Qikou depression and analyzing its geometric characteristics.They are as follows: in the early stage(from the third member of Shahejie formation to the second member of Shahejie formation),under the action of NW-SE oriented tensile stress field,in the middle stage(from the first member of Shahejie formation to Dongying Formation),under the action of Sn oriented tensile stress field,under the action of tension and torsion deformation,and in the late stage(from Guantao formation to Minghuazhen Formation),under the action of Sn oriented weak extension and thermal subsidence.According to the division principle of fracture type and the main evolution process of Banqiao slope,a representative member of Shahejie formation is selected for plane calibration of fracture type.The analysis shows that there are four types of faults in the first member of Shahejie Formation: three active faults,the third member of Shahejie formation to the second member of Shahejie formation,the third member of Shahejie formation to Dongying Formation and the first member of Shahejie formation to Minghuazhen Formation.Combined with source rock,reservoir distribution and reservoir forming period,it shows that the fault type of the third stage activity is the main oil and gas source fault of the source rock of the third member of Shahejie Formation and the first member of Shahejie Formation in Banqiao area.Among them,Dazhangtuo fault is the main oil and gas source fault,while Banqiao fault is the blocking fault.Based on the determination of the history of the formation and evolution of the faults,theorigin of the faults and the source faults in Banqiao depression,this paper first divides the faults into three categories according to the change of the activity intensity(fault distance),the evolution stage and whether they are the source faults or not-Type A2-B2-C1 is the main combination type,that is,the strong active weak active intersection type formed by the oil-gas source fault intersection in the early stage of the later stage;type A3-B1-C3 and type A3-B2-C3,that is,the weak active weak active intersection type formed by the non oil-gas source fault intersection in the same period and the weak active weak active intersection type formed by the non oil-gas source fault intersection in the early stage of the later stage.Based on the geological models of Banqiao fault and Dazhangtuo fault,a finite difference numerical model is established by using numerical simulation method.Under the constraint of rock mechanics parameters,the paleostress of oil and gas accumulation period is loaded to simulate the stress distribution at the intersection of different combination types of faults.From the simulation results,it can be seen that the maximum principal stress,the minimum principal stress and the difference stress in the intersection of faults and other locations There are great differences,among them,the difference stress is significantly higher than other parts of the fault,indicating that the rocks in the intersection area are more prone to volume expansion deformation or expansion,on the one hand,it improves the permeability of the rocks,on the other hand,it is more conducive to the formation of traps.Obviously,it plays an important role in controlling the migration and accumulation of oil and gas.(1)When one or two faults in the combination type of fault intersection are oil and gas source faults,and the basic conditions such as strong activity strong activity or strong activity weak activity combination,large activity rate in reservoir forming period and stress concentration are met,they can be regarded as favorable parts of oil and gas migration.(2)The fault intersection area is an important part of fault trap development,which mainly includes three types of "fault step type" trap with inclined facies,relatively inclined "graben back type" trap and "Horst type" fault block trap with inclined facies.The favorable reservoir forming types can be predicted by comprehensively considering the structural shape,structural deformation degree or physical property increased by rock expansion,trap area and reservoir forming contribution.The fracture intersection type is mainly A2-B2-C1 type combination type,the trap type is the best Horst type,which is class I favorable area,the fault step type is class II favorable area,and the graben back type is class III favorable area.Five favorable fracture intersections,including three class II favorable areas and two class III favorable areas,were selected in the undrilled area of the lower Shaxia sub section of Banqiao slope.