Research On PeriScope Edge Inversion Of Electromagnetic Logging Tool While Drilling

With the development of petroleum industry,most oil and gas fields have entered the middle and late stage of development.In the face of complex reservoirs such as thin beds,fractures,faults,etc.,the parameters measured in logging while drilling can not only be used for underground evaluation,but also for geological steering in combination with borehole trajectory parameters.According to the changes in formation parameters measured in real time,the drilling bit location and the distance from the boundary between layers can be determined.It is of great significance for efficient development of complex oil and gas reservoirs to guide drilling engineers to adjust the drilling direction of the bit at any time so that the bit can drill in the zone with the best value in the reservoir to the maximum extent.Based on the electromagnetic wave resistivity logging tool Peri Scope,this paper studies the response analysis of logging while drilling in layered formation and realizes the formation edge inversion.Firstly,by means of the expression of each component of the electromagnetic field intensity and magnetic field intensity generated by magnetic dipole in any direction at any receiving position in the horizontal uniform layered anisotropic medium,the measurement principle of the instrument is analyzed,and the response of electromagnetic wave logging while drilling is numerically simulated in the anisotropic layered formation.The output amplitude ratio and phase difference resistivity curves of the Peri Scope electromagnetic logging instrument are obtained under the condition of different frequency and different coil distance.The edge detection capability and logging response characteristics of the Peri Scope electromagnetic logging instrument while drilling are analyzed.Secondly,the inverse algorithm of electromagnetic logging while drilling based on Newton method is studied.Electromagnetic inversion minimization problem is studied from the aspects of mathematical principles of general algorithm framework,and considering the actual logging conditions,the objective function with Lagrange multiplier,increased the priori information related matrix（?）and data measurement noise correlation matrix（?）,to overcome the ill-posed nature of inversion problem,and avoid the nonlinear problem of local minimum values.The basic principles,advantages and disadvantages of Newton method,improved Newton method,Gauss Newton method and fastest descent method are analyzed.Finally,the principle of multiplicative regularization of the objective function is analyzed,the selection principle of regularization factor is given,the iterative steps are adjusted by using the line search algorithm,and the criteria for terminating the iteration are given.Pretreatment of logging data.The dimensionality of the actual stratigraphic model is reduced to a series of one-dimensional inversion problems of the layered model,and appropriate model parameters are selected and corresponding petrophysical constraints,physical constraints,geological constraints and instrument constraints are applied.The?matrix and?matrix,which are formed by combining the Jacobi matrix J of the objective function,represent respectively the total amount of formation information contained in the logging data of the sampling point and the sensitivity of all logging data to a certain formation parameter.Combining with the logging response characteristics,the purpose of selecting the optimal inversion curve for logging data analysis is to be achieved.The initial value selection and iteration steps of the improved regularization Gauss-Newton square optimization method are given.Finally,the borehole edge inversion of electromagnetic logging while drilling is realized by Gaussian Newton optimization method based on regularization.The single-layer interface formation model and double-layer interface model were designed,the optimized log curves were selected to participate in inversion for different formation models.The results show that the inversion results are good under different formation conditions.It can not only reflect the stratigraphic boundary,but also reflect the stratigraphic characteristics.