Thermally stable and salt-resistant synthetic polymers as drilling fluid additives for deployment in harsh sub-surface conditions: A review

Conventional drilling fluid (DF) technologies commonly fail to meet many of the requirements of modern drilling under various harsh subsurface conditions, particularly those associated with high pressure and temperature (HPHT), and highly saline conditions. Such conditions have a great influence on the efficiency of DF by causing adverse changes to their properties that can increase the risk of gas kicks, stuck drill pipes, and pipe twist-offs. As a consequence, more research is now being directed to develop and test new materials that can improve DF performance in harsh conditions. Recent developments and applications associated with polymeric treatment agents (synthetic polymers; SP) as DF additives have met with some success in HPHT and excessively saline conditions with respect to preventing lost circulation. However, certain challenges remain regarding the quality and sustainability of SP in harsh environments. This review describes the evolution of DF compositions and additives, with particular emphasis on the types of SP deployed, and their advantages and disadvantages, considering the major obstacles they must combat in the harsh subsurface conditions that are typically encountered, which mainly are HPHT, salt contamination, and lost circulation. This review reveals the key monomers that can be used to generate SPs, combat salt contamination and be deployed in HPHT conditions, as well as identifying their advantages and disadvantages. Combating lost circulation risks and the remedial actions and the SP materials required to do so in harsh conditions is addressed in detail. The most important monomers used in the polymerization SP that are deployed in harsh conditions are identified and their benefits and drawbacks are contrasted. Moreover, new advances in SP and their modification to address DF problems are discussed. Environmental aspects of the toxicological value and class of utilized monomers in the synthesis of SPs are evaluated. The economic aspects of SP deployments in DF and the cost of the most utilized monomers in the synthesis of SPs are assessed. The information reviewed leads to recommendations for future research addressing the prevailing knowledge and SP property gaps.