Title : Evaluation of effective sealing length of cement sheath in gas storage well
Abstract:
The alternating internal pressure caused by the periodic injection and production significantly negatively impacts the sealing performance of cement sheaths in gas storage wells. Based on typical working conditions in the gas storage wells, a method and test device for evaluating the cement sheath's integrity and sealing performance are proposed to clarify the influence mechanism of cement sheath sealing performance under complex underground cementing conditions. Based on the test device, the sealing performance of the cement sheath under five curing temperatures, three pouring types, six bonding lengths, two alternating loads, and five cycles is evaluated. Cement sheath's integrity and sealing performance are characterized by interface micro gap, body crack, leakage position, leakage flow rate, gas breakthrough pressure, and residual sealing pressure. The sealing ability relationship between the cement's successive high-quality section and the cumulative high-quality section is clarified, the evolution characteristics of sealing performance of cement sheath with different bonding lengths before and after alternating loads, and the intrinsic damage mechanism of cement sheath under alternating loads are revealed. Based on experimental data, a method for evaluating the effective sealing length of the cement sheath is developed. An effective sealing length of cement sheath prediction model for cement sheath is established using the global optimization algorithm, by which the minimum length of successive high-quality sections and cumulative high-quality sections under different sealing years is calculated in a gas storage well. The results show that the evaluation method for the effective sealing length of cement sheath based on experimental data can more scientifically determine the minimum effective sealing length under different working conditions
