Self-Sealing Isn’t Just for Cracks: Recent Advance in Sour Well Protection

Abstract

Cementing sour wells can be very challenging; even when best practices are followed, the integrity of the cement, casing, and/or tubing can be jeopardized. In such cases, challenging and costly remedial work is necessary due to the complicated nature of the environment. A safe, cost effective way to prevent the need for remedial work is the use of self-sealing systems; however, until now, there was no data that validated self-sealing systems’ capability to tolerate exposure to H2S. This paper focuses on the newly discovered ability for the self-sealing systems to withstand exposure to H2S while maintaining self-sealing properties. To confirm that the self-sealing material is uninhibited by H2S, a gas mixture of H2S in nitrogen was bubbled through a mixture of self-sealing material and water. The concentration and rates used were picked to mimic a standard sour well’s condition allowing the testing to recreate the challenging well environment. The self-sealing material was then added to the cement slurry and transferred to the crack/seal equipment for testing. The results from the experiment were compared to a self-sealing slurry with the same components but in which the self-sealing material had not been exposed to H2S. Both systems were able to seal multiple times, validating the ability of the exposed material to withstand H2S exposure. The finding from this study opens the door for self-sealing cements to address several kinds of corrosive gases. Because the system was able to withstand exposure to such a strong gas, it will likely be able to tolerate weaker corrosive gases such as CO2. The discovery from this experiment promotes a new use for self-sealing cements. No longer will their use be limited to cracks in the cement matrix but also as an extra precaution when working in sour wells and corrosive environments.

Specification for Permanent Plugging Materials

“…The source of Ca 2+ is supplied in two ways: the dissolution of Ca(OH) 2 broadly known as CH, and decomposition of hydrated silicate and aluminate phases or broadly known as calcium silicate hydrate (C-S-H) gel. The Ca(OH) 2 becomes unstable at a pH below 12.6 and Ca 2+ is leached out and if the pH becomes less than 8, the strength giving C-S-H phases are destabilized and Ca 2+ is leached out [35]. Taylor [34] explains the reactions as following:…”