Compensation effect analysis in DIE method for through-casing measuring formation resistivity

The measuring technique based on Double-Injection-Electrodes (DIE) and its compensation arithmetic method have been proven to be very useful for eliminating the errors caused by electrode-scale mechanical tolerances in formation resistivity measurement through metal case. In this paper, we found that even minor casing joint or casing corrosion may deteriorate the measurement accuracy. Based on theoretical analysis and self-adaptive goal oriented hp-Finite Element (FE) simulations, the compensation effects of DIE measurement technique were estimated. The calculated results from this measuring method are always close to the real formation resistivity, regardless of whether the metal casing is ideal or not. Meanwhile, large errors occur when recording measurements based on Single-Injection-Electrodes (SIE), since the calculated formation resistivity may provide negative values when casing joint or casing corrosion exists. The Double-Injection-Electrode (DIE) measurement technique is predicted to have good compensation effects in many non-ideal situations with uneven metal casing besides electrode-scale mechanical tolerances.

Research highlights
► This paper presents the principles of Double-Injection-Electrodes (DIE) compensating model for through-casing resistivity (TCR) measurement. TCR measurement technology is very important in oil and gas exploitation. However, traditional Kaufman's Single-Injection-Electrode (SIE) measurement model is proven to have some obvious disadvantages: large error will occur when little electrode-scale mechanical tolerance exists.
► Through theoretical analysis, we find that the DIE model and its algorithm can eliminate the errors caused by casing corrosion or casing joints besides mechanical tolerances.
► Through self-adaptive goal oriented hp-Finite Element (FE) simulations, we find that the calculated results from DIE model are always close to the real formation resistivity no matter the metal casing is ideal or not. The Double-Injection-Electrode (DIE) model is predicted to have good compensation effects to many non-ideal situations.