Responses Simulation of Through-Casing Resistivity Logging in Heterogeneous Casing Wells

Because the potential distribution on the metal casing contains the information of metal casing and formations, the change of resistivity of metal casing has an important effect on through-casing resistivity logging responses. The effect due to the change of casing resistivity on the coefficients of transmission line equation (TLE) is considered, and the calculation method of potential distribution on the heterogeneous casing is also given. On the basis of the potential distributions obtained from TLE, through-casing resistivity logging responses of heterogeneous casing are calculated, and the effects of the change of metal casing resistivity on the resistivity logging response are analyzed. The computation results show that the casing change whether thinner or thicker has an obvious effect on the logging responses, and the abnormality of logging response appears where the casing resistance suddenly decreases or increases. The computation results also show that the spacing of electrodes has an important effect on through-casing resistivity logging responses.