Study On Wellbore Stability Of Igneous Formation In Bozhong Oilfield

Bozhong Oilfield has good oil and gas reserves.However,the wellbore instability of igneous rock formation in Bozhong Oilfield occurs frequently,which seriously affects the safety and effectiveness of drilling operation.Therefore,the study on wellbore stability of igneous rock formation in Bozhong Oilfield has a certain reference significance for safe and efficient drilling in igneous rock formation in Bozhong Oilfield.In this paper,the rock mechanical characteristics of igneous rock formation in Bozhong Oilfield are studied.The rock strength parameters,component information and the influence of hydration are obtained through rock mechanics experiment.The vertical distribution law of in-situ stress and rock strength parameters of igneous rock formation is obtained by combining the experimental results with logging data.The calculation model of safety density window of directional well in igneous formation is studied,and the influence law of directional well trajectory on the safe mud window of the formation is revealed.Based on ABAQUS software,the numerical simulation model of wellbore stability in igneous rock formation with weak interlayer is established.The effects of strength,permeability,horizontal in-situ stress ratio and abnormal formation pressure on wellbore stability are numerically simulated and analyzed.The results show that the equivalent density range of collapse pressure of igneous rock formation in Bozhong Oilfield is 1.10-1.39g/cm~3,and the equivalent density range of fracture pressure is 1.72-2.1g/cm~3;the optimal drilling azimuth of directional well should be consistent with the minimum in-situ stress azimuth as far as possible.At the same time,attention should be paid to the high-risk area of wellbore instability when the inclination angle of the well in the maximum in-situ stress azimuth is greater than 50°.According to the numerical simulation results,the existence of weak interlayer changes the stress-strain state of rock mass around the well and increases the risk of wellbore instability.At the same time,the smaller the strength of weak interlayer,the stronger the permeability,the larger the horizontal in-situ stress ratio and the occurrence of abnormal formation pressure will lead to the decline of wellbore stability.