Arithmetic method of double-injection-electrode model for resistivity measurement through metal casing

Through-casing resistivity (TCR) measurement instruments such as Cased Hole Formation Resistivity are extensively used for the dynamic monitoring of oil reservoirs during the production phase in oil wells to evaluate the residual oil distribution. However, two shortcomings still exist in the common TCR model based on single-injection electrodes: The real value of steel-casing resistance is difficult to acquire, and the effect from mechanical tolerances of electrode scale is unpredictable. This paper proposes an innovative model based on doubleinjection electrodes. In this new model, all the required variables can be measured simultaneously; furthermore, a compensating arithmetic method is employed to obtain the real casing resistance. Self-adaptive goal-oriented hp-finite-element simulations have been performed to prove that the influence of mechanical tolerances of electrode scale can be reduced effectively. Therefore, the TCR measurement accuracy is highly improved. © 2009 IEEE