Instrument Design for Detecting the Inner Damage of Casing

Detecting and localizing the inner damage of the downhole casing is crucial for oil and gas production. The current methods for damage detection suffer from polarization effect, capacitance effect, and difficulty in measuring weak direct current signals. As an alternative, we propose a new instrument design based on a six-electrode array in this study. The basic detection principle is introduced, and the key factors that affect the detection performance are studied through modeling and simulation. Besides, the entire system of the instrument design consisting of several modules is presented. In addition, an experiment is conducted to demonstrate the detection capability of the proposed design. It is found that the detection dynamic of the instrument is 93 dB and a signal-to-noise ratio is 73 dB. It can detect damage when salinity is lower than 120 g/l and can identify the location of damage with high resolution in the longitudinal and radial directions.