Synthetic polymers: A review of applications in drilling fluids

With the growth of deep drilling and the complexity of the well profile, the requirements for a more complete and efficient exploitation of productive formations increase, which increases the risk of various complications. Currently, reagents based on modified natural polymers (which are naturally occurring compounds) and synthetic polymers (SPs) which are polymeric compounds created industrially, are widely used to prevent emerging complications in the drilling process. However, compared to modified natural polymers, SPs form a family of high-molecular-weight compounds that are fully synthesized by undergoing chemical polymerization reactions. SPs provide substantial flexibility in their design. Moreover, their size and chemical composition can be adjusted to provide properties for nearly all the functional objectives of drilling fluids. They can be classified based on chemical ingredients, type of reaction, and their responses to heating. However, some of SPs, due to their structural characteristics, have a high cost, a poor temperature and salt resistance in drilling fluids, and degradation begins when the temperature reaches 130 °C. These drawbacks prevent SP use in some medium and deep wells. Thus, this review addresses the historical development, the characteristics, manufacturing methods, classification, and the applications of SPs in drilling fluids. The contributions of SPs as additives to drilling fluids to enhance rheology, filtrate generation, carrying of cuttings, fluid lubricity, and clay/shale stability are explained in detail. The mechanisms, impacts, and advances achieved when SPs are added to drilling fluids are also described. The typical challenges encountered by SPs when deployed in drilling fluids and their advantages and drawbacks are also discussed. Economic issues also impact the applications of SPs in drilling fluids. Consequently, the cost of the most relevant SPs, and the monomers used in their synthesis, are assessed. Environmental impacts of SPs when deployed in drilling fluids, and their manufacturing processes are identified, together with advances in SP-treatment methods aimed at reducing those impacts. Recommendations for required future research addressing SP property and performance gaps are provided.