The Evaluation Of Fault Stability In The Process Of Oil And Gas Safety Exploitation

Fault stability is the possibility of fault reactivation under the condition of current stress field.Fault reactivation is mainly triggered by pore pressure in field scale,whose quantitative evaluation index is the critical pressure,namely the additional fluid pressure,inducing fault reactivation under the condition of current pore pressure.When the fliud pressure reaches the critical pressure corresponding fault segement will be in the state of critical stress.Critically stressed faults are easy to slide causing leakage of oil and gas and casing damage along fault.Therefore,it is of vital significance for oil and gas production to figure out the degree of fault stability.In situ stress is the key parameter of fault stability evaluation.There are different ways to obtain in-situ stress field,including hydraulic methods,acoustic emission method,calculations through logging data and so on.Hydraulic fracturing can obtain the accurate magnitude of the minimum horizontal principal stress.Considering the feasibility this paper use logging data to calculate continuous in-situ stress profile.FAST,one of the method for fault stability evaluation,not only can evaluate fault stability quantitatively but also consider the effect of fault cohesion.There are many factors influence the stability of the fault.The relationship between the differential stress and rock tensile strength determines the type of fault reactivation,and the direction of stress field has a great effect on the fault stability.Argillaceous components can weaken the fault rock strength,therefore fault zone with a large number of clay minerals is easy to reactivate.Reservoir fluid pressure changing extensively will lead to the changes of horizontal principal stress and affect the stability of the fault eventually.Besides,the accuracy of seismic interpretation also will affect the evaluation results.In this paper,on the bases of fault stability mechanism and the influence factors analysis of fault stability,the in situ stress data,fluid pressure,and fault mechanical property data have been used to evaluate the degree of the fault reactivation in the ?,? and ? oil group of 2 block Bozhong 34-2/4 oil field quantitatively.The results show that,The optimal fault orientation is 160°?61.5° and 340°?61.5°,and with the continuously increase of fluid pressure the fault close to this orientation will reach the state of critical stress firstly.The range of additional fluid pressure of ? oil group is 6.1-29.8 MPa,the range of additional fluid pressure of ? oil group is 6.6-29.7 MPa,and the range of additional fluid pressure of ? oil group is 6.6-29.7 MPa in the north and center block of 2 block of Bozhong 34-2/4 oil field.The most risk fault segements is the position located on the west of the BZ34-2-1 well on fault F30 and the northeast of F31 fault tip,and the additional fluid pressure is 6.5 MPa and 6.1 MPa respectively.