Investigation of Stress State During Cement Hardening and Its Effect on Failure of Cement Sheath in Shale Gas Wells

Abstract

Consideration of initial stress state after cement hardening provides a vital basis for the prediction of cement failure, which has been overlooked in previously published methodologies partly due to the difficulties in examining this problem rationally. In the present study, the hoop stress at casing-cement interface during cement hardening is investigated experimentally based on the full-scale casing-cement sheath-formation system (CCFS) facility, which is equipped with the real-time stress-strain measurement capability. The hoop stress at casing-cement interface during cement hardening drops sharply, rather than equating with the initial annulus pressure of cement slurry. It presents a higher drawdown under higher annulus pressure and thinner casing, and a lower drawdown under elastic cement slurry and thicker cement sheath. Furthermore, an analytical model taking the effect of cement hardening into account is developed to predict the integrity of cement sheath. Reliability of the model is verified by comparison with field observations. Excellent agreements are observed. The results illustrate that the tensile cracks are likely to occur at the inner cement (inner surface of cement sheath) by the effect of cement hardening, since the hoop stress at inner cement during cement hardening drops greatly and even becomes tensile. A detailed sensitivity analysis illustrates that an elastic cement slurry with a lower elastic modulus works more effectively, which can resolve the SCP problem in shale gas wells.

Improving the Rheological and Mechanical Properties of Oil Well Cement Slurries Using Multiple Chemical Admixtures for Enhancing Zonal Isolation: A Laboratory Evaluation

“…The global oil demand has been rising steadily during the last few years. Between 1965 and 2008, it increased by 171 percent [4,10,28]. Throughout the previous two decades, the estimate of recently found oil reserves has been exceeded by the annual assessment of oil consumption [12, 15, and 29].…”

Evaluating Methane Emissions From Decommissioned Unconventional Petroleum Wells in British Columbia, Canada

“…This in turn introduces additional risks to integrity, including; wellbore tortuosity, eccentricity, improper cement placement and inadequate zonal isolation (Jung & Frigaard, 2022;Renteria et al, 2022;Sabins, 1990;Yu et al, 2019). Similarly, the hydraulic fracturing process involves injecting fluids through the well structure at high pressures to enhance hydrocarbon production, a process that can potentially affect well integrity by inducing stress on wellbore materials, affecting cement quality and creating pathways for fugitive fluid migration (Wang & Dahi Taleghani, 2017;Xi et al, 2022;Zhao et al, 2022). Uncertainty surrounding the integrity of unconventional wells is further confounded by the fact that such wells are still very young, to date few have been decommissioned for any extended period and few, if any, have been examined in detail post-abandonment.…”