Real-time forward modeling and inversion of logging-while-drilling electromagnetic measurements in horizontal wells

Abstract

Based on the pseudo-analytical equation of electromagnetic log for layered formation, an optimal boundary match method is proposed to adaptively truncate the encountered formation structures. An efficient integral method is put forward to significantly accelerate the convergence of Sommerfeld integral. By asymptotically approximating and subtracting the first reflection/transmission waves from the scattered field, the new Sommerfeld integral method has addressed difficulties encountered by the traditional digital filtering method, such as low computational precision and limited operating range, and realized the acceleration of the computation speed of logging-while-drilling electromagnetic measurements (LWD EM). By making use of the priori information from the offset/pilot wells and interactively adjusting the formation model, the optimum initial guesses of the inversion model is determined in order to predict the nearby formation boundaries. The gradient optimization algorithm is developed and an interactive inversion system for the LWD EM data from the horizontal wells is established. The inverted results of field data demonstrated that the real-time interactive inversion method is capable of providing the accurate boundaries of layers around the wellbore from the LWD EM, and it will benefit the wellbore trajectory optimization and reservoir interpretation.