Reactance Based Self Sensing Well Cement

Zonal isolation failure can have severe consequences for health, safety, and the environment. Therefore, long term monitoring of well cement is an active area of research. One potential solution is to convert the cement into an intrinsic sensor. Self-sensing cement can detect applied stress through changes in electrical response. While significant progress has been made in civil engineering, this technology has yet to be adopted by the oil and gas industry due to lack of standardization. Hence, this study presents a method for designing a cement sensor that follows the guidelines set by the American Petroleum Institute. The method involves use of multiscale carbon fibers and the alternating current (AC) two-probe approach to evaluate the impedance response to stress. The test results showed an improvement in cement compressive strength and that the reactance response is more sensitive than the resistance at the measured frequency of 300 kHz. For the bulk cement, the dielectric components were extracted using an equivalent AC circuit containing a resistor and a capacitor in parallel. It was found that the capacitance had the highest sensitivity to stress due to dielectric loss. These findings suggest that the self-sensing mechanism is related to changes in electric permittivity with stress through dielectric breakdown and that reactance is a crucial component. The potential for using electric impedance spectroscopy to monitor well cement deformation in real-time quantitatively shows promise and warrants further study.