Research On The Inversion Method Of The P-wave And S-wave Velocity Profiles Around The Wellbore

In the process of petroleum exploration and development,due to drilling,mud filtrate invasion and other reasons,the formation around the well will be heterogeneous in the radial direction,which is specifically manifested in the change of formation wave velocity in the radial direction.The inversion of formation radial velocity profile has important guiding significance in the identification of invasion depth and the evaluation of borehole stability.The traditional method needs to determine the formation wave velocity and the corresponding radial distance at the same time,which is more complex in the actual processing and calculation process.Based on a stepwise inversion method,this thesis inverses the velocity profiles of P-wave and S-wave in the formation near the wellbore.Firstly,the adjacent receiving arrays are grouped,and the velocity sequences of P-wave and S-wave are obtained for each group by STC method,and then the corresponding radial positions are obtained by ray theory.The staggered grid finite difference method is used to combine with multiple formation models for forward simulation,and the factors affecting the inversion results are deeply explored.The simulation results show that the detection depth of the radial velocity profile is related to the offset distance between the transmitting source and the receiver in the instrument,the larger the offset distance is,the deeper the radial depth of the formation can be detected.In a specific detection depth,the offset distance required by the instrument is affected by the velocity change in the formation,the smaller the velocity change,the greater the offset distance required by the instrument.In the process of grouping,a small number of receiver groups can improve the resolution of the inversion results,but when the number of receivers in the group is large,the results can be more robust.In addition,this thesis makes an in-depth exploration of this method by establishing a longitudinal heterogeneous formation model with more complex conditions.Finally,the data processing method is proposed according to the existing instruments and applies it in combination with the actual logging data,which has achieved good results and verified the effectiveness of the stepwise inversion method.