Evaluation of liner hanger seal assembly and cement sheath as a dual barrier system: Implications for industry standards

Abstract

Liner hanger seal assembly and cement sheath are essential barrier elements for well drilling and completions. During installation, the liner hanger seal assembly is set up-stream to the cement column. This arrangement prevents the evaluation of both the liner hanger seal assembly and cement sheath independently. Currently, there are no testing procedures, industry standards, or regulatory guidelines for testing this type of dual barrier system independently.The primary objective of this study is to establish that cement sheath can act as a secondary barrier element in a dual barrier (elastomer seal and cement sheath) zonal isolation system, if the elastomer seal (primary barrier) is faulty. In the context of this study, the term "barrier" describes the use of cement sheath and elastomer sealing element in a liner hanger to prevent uncontrolled migration of formation fluid to a shallow formation or surface facilities. Another objective is to evaluate the effect of using an anti-gas migration additive on cement sealability. To achieve these objectives, experimental testing procedures were developed to evaluate the performance of a liner hanger seal assembly and cement sheath. Two experimental scenarios were considered in this study. The first scenario included testing faulty ethylene propylene diene monomer (EPDM) elastomer with neat Class H cement and the second scenario included testing faulty EPDM elastomer and Class H cement mixed with a commercial gas migration control additive. The tests were conducted at different pressures and wait on cement (WOC) intervals.The results revealed that neat Class H cement cannot act as a secondary barrier and prevent gas migration in the case that the primary barrier (elastomeric element of the liner hanger) is faulty. The cement slurry with the commercial gas migration control additive can act as a secondary barrier in case the primary barrier is faulty. The results also showed that WOC time improves cement sheath sealability. In addition, pipe material and surface roughness play key roles in the cement slurry bonding process. The major addition to the literature from this study is that for cement sheath to be considered a secondary barrier element in a dual barrier zonal isolation system, it must contain a specific anti-gas migration additive in addition to other cement additives. This specification should be included as a standard regulatory practice and should be adopted for every well section.