Recent advances in polymers as additives for wellbore cementing applications: A review

Abstract

In recent years, more deep and ultra-deep gas and oil wells have been drilled. The high-temperature and high-pressure (HPHT) conditions encountered in such wells frequently contribute to drilling problems being encountered. Sub-surface problems such as loss circulation, gas migration, fluid inflows, and wellbore wall swelling and collapse impact the quality of wellbore cementing. Such complex wellbore conditions place higher demands on cement, water, and drilling fluid admixtures. Cement slurries (CS) tend to become unstable as the thermal movements of the component increase above certain critical levels. Ultimately, thermal degradation of the CS under harsh conditions leads to the release of free fluids and hydration effects. These negatively impact CS performance, reducing its ability to generate effective fluid seals in the wellbore walls. Chemical additives are used in CS in attempts to address certain issues such as retardation, fluid loss, dispersion, settling prevention, and gas migration control. However, many additives become less effective in HPHT subsurface conditions. Recently, the involvement of synthetic polymers (SP) as CS additives has demonstrated their ability to respond more favorably to harsh sub-surface conditions. However, issues remain with SP requiring further improvements to make them more effective as CS additives in harsh conditions. Therefore, this review describes the main challenges CS faces in a wellbore: fluid loss, hydration, high salinity, HPHT, gas migration, and adverse rock formation responses. The SP additives, which are now able to overcome most of these challenges, are explained. The functions and mechanism of SP in gas and oil borehole CS, together with their benefits and drawbacks, are addressed in detail. The principal suitable monomers used to polymerize SPs for beneficial use as CS additives are identified, and their properties are compared.Moreover, a new four-category classification is proposed for polymers used as wellbore cement additives, which distinguishes SP, nano-SP, self-repairing polymers, and geopolymer materials. Economic factors and environmental impacts associated with SP use as CS additives are also identified. Based on the review’s findings, recommendations are made for further research and development work required to address outstanding concerns with respect to such SP applications.