Abstract
In the middle and late stages of oil and gas field development, improving the accuracy of resistivity measurement is of great significance in assessing the residual oil saturation of reservoirs. The traditional over-casing resistivity logging technology has the disadvantages of low time efficiency, great influence by casing contact resistance, poor environmental adaptability and limited detection depth. Transient EM is based on the theory of electromagnetic induction and obtains formation resistivity parameters by emitting a transient EM field and measuring changes in the induced EM field in the formation. However, the high electrical and magnetic conductivity of the casing will seriously interfere with the electromagnetic signal and affect the formation resistivity measurement. For this reason, this paper proposes a new method of signaling the casing by using a combination of multiple coil systems in the pre-compression of the formation response, and adopts finite element simulation to deeply investigate the transient electromagnetic response curves as well as the transient electromagnetic radial probing depths and longitudinal resolutions under the variations of different formation resistivities and casing parameters. The results show that this technique can effectively suppress the casing response in the pre-transient electromagnetic response, making the formation response clearer, providing an accurate and reliable means for the measurement of formation resistivity in cased wells, and further enhancing the accuracy of residual oil evaluation in oil exploration and development.