Response and multi-parameter determination of microresistivity scanning imaging logging while drilling in oil-based drilling fluid using numerical modeling and machine learning

Microresistivity scanning imaging logging while drilling (MRSI-LWD) in oil-based drilling fluid (OBDF) has been widely applied in unconventional reservoirs. To solve the problem of few evaluable parameters obtained by MRSI-LWD in OBDF, the response characteristics and multi-parameter determination of MRSI-LWD in OBDF are worthy of further exploration. The response characteristics of MRSI-LWD is firstly investigated based on numerical modeling . Subsequently, the multi-parameter determination method is extensively studied, and includes the establishment of multi-parameter response databases, the method for obtaining the OBDF resistivity and permittivity, and the establishment of three-parameter calculation models based on the back propagation neural network (BPNN) model. Finally, several cases are provided to test the multi-parameter determination method. The results show that the high frequency benefit the characterization of low-resistivity zones, and the large standoff weaken the responses to the change of formation properties. The real part of impedance and the equivalent resistance can be utilized jointly to characterize the full-range formation resistivity. The formation resistivity, the standoff and the formation permittivity at the high frequency can be perfectly determined and their determination coefficients can reach over 99%. However, the determination of the formation permittivity at the low frequency is unsatisfying with its determination coefficient reaching around 60%, due to the low proportion of displacement current. This study will benefit the reservoir evaluation and the reduction of operating costs by independently using MRSI-LWD in OBDF. • The influences of excitation frequency and standoff on the measured impedance amplitude and phase are systematically studied. • The combination of the real part of impedance and the equivalent resistance can characterize the full-range formation resistivity. • Not only the formation resistivity but also the standoff and the multi-frequency formation permittivities can be obtained simultaneously based on the multi-parameter determination method.