Natural Gas Industry B (Oct 2020)
Design and plugging property of composite pressure activated sealant
Abstract
Pressure activated sealant (PAS), as a novel kind of sealing fluid, can provide rapid and self-adapting repair on the tiny damage of static seals (e.g., screws and pipelines) while encountering pressure difference of leakage sites, but its sealing property is affected more by the size of leakage site, so it exhibits limited application in the production and wellbore integrity recovery of oil & gas wells. To extend PAS's applicability, this paper put forward a composite PAS technology involving the cooperativity of solid and liquid sealing materials for enhancing large pore plugging based on the phase state transition and sealing behaviors of sealing fluid under differential pressure. In this technology, two types of solid sealing materials (bridging rigid particle and tension reinforcing fiber) were used jointly to modify the geometries of leakage pores and the migration paths of fluids, which can promote the formation of effective solid barrier from the PAS to fill in large leaking pores, so as to perform sealing repair. And the following laboratory experimental results were obtained. First, the newly prepared PAS is a kind of polydisperse system, and the core particles are regular in shape with the size distribution mainly in a range of 300–400 μm. Second, in the range of evaluation pressure, sepiolite fiber, as the structure promoter, reinforces the integrity of sealing solids. Third, mussel powder, as the pore structure modifier, improves the retention ability of the sealing fluid in the limited leakage space. These two sealing materials not only cooperatively improve the structure of solid barrier, but also markedly enhance the plugging capability of composite PAS in large pores. In conclusion, these results can provide theoretical and technical support for the development and application of novel multifunctional sealants in oil & gas wells.
