Forward Modeling For Borehole Surface Logging With Vertical Line Source In Anisotropic Formation

Borehole surface electromagnetic method refers to a detection method of power supply in well and receiving electromagnetic field on the ground.In the process of oil and gas exploration and development,well electromagnetic logging data can be used to assist in the identification of reservoir boundary or exploration of residual oil and gas.With the deepening of unconventional oil and gas exploration and development in recent years,how to carry out underground electromagnetic logging in complex anisotropic formation is a new challenge,and the research work on the electromagnetic forward modeling of well in anisotropic formation can provide an important theoretical basis for this application.In this thesis,firstly,we use the analytic method to deduce the electric field response of the vertical electric dipole(VED)source logging in the anisotropic formation,obtain the electromagnetic response of the frequency domain and compare the correctness of the verification formula.I consider the transient electromagnetic method that has the advantages of sensitivity to the low resistance body and strong resolution and uses the cosine transform method to convert the frequency domain electromagnetic response.The discrete expressions of electric field and magnetic field in time domain are obtained,and the response of VED source well logging is calculated in time domain by numerical simulation method,and the influence of different model parameters such as thin mutual reservoir,overlayer and basement layer on forward response is analyzed.In order to detect deep anisotropic oil and gas,in this thesis,the electric field response analytic solution of finite length line source in anisotropic formation model is calculated.The correctness of the analytic solution is verified by numerical simulation software and the forward model analysis and summary of the finite long line source with casing are carried out by using the finite element simulation software.Through theoretical analysis and numerical simulation,it is shown that vertical and finite length line sources,as excitation sources,play a leading role in the electric filed response of the surface,and the transverse resistivity has little effect.The influence of VED transient electric field response on anisotropic overlay is significantly higher than that of anisotropic basement layer.Using the VED source compared with the finite length line source,the identification ability for oil and gas layer is stronger and the sensitivity is higher.For the finite length line source logging model with casing,under the condition of casing thickness and casing resistivity,the influence of casing on electromagnetic response decreases gradually with the increase of formation resistivity,the lower the frequency,the smaller the electric field is affected by the casing,and the sensitivity to the abnormal body will be reduced.The results of these forward model analysis can provide theoretical basis and reference basis for the work of underground electromagnetic logging carried out in anisotropic formation.and the results have important research significance and value.