A New Generation of Shale Inhibitors for Water-Based Muds

Abstract

SPE Members Abstract New applications of structurally unique organic cationic materials (OCMs) have provided a highly efficient and economical technology for inhibiting the swelling and yielding of hydratable shales. These OCMs are compatible with all common drilling fluid additives, thermally stable, and environmentally acceptable. The laboratory determined properties and field tests of the OCMs are discussed in detail. Introduction For a variety of reasons, including economics, convenience, and logistics, it has always been desirable to drill with water-based muds whenever possible. However, drilling in certain environments, particularly in water-sensitive shale formations, with water-based muds has often been difficult to impossible, and has often been very costly. When water-sensitive shales are exposed to aqueous fluids, they adsorb water, which results in swelling and/or disintegration of the shale. Typical drilling problems which result from these phenomena are bit balling, high torque and drag, and stuck pipe. Historically, because water-based muds sufficiently inhibitive to eliminate or minimize the hydration of these shales have not been available, the only alternative for drilling such sensitive formations has been oil-based muds. Although more expensive than water-based muds, oil-based muds are very effective in controlling water-sensitive shales and generally allow trouble-free drilling through these difficult formations, thereby ameliorating the higher cost. Over the past several years, environmental regulations and concerns have increasingly restricted the use of oil based muds worldwide, making them a much less attractive alternative than before. These increasing environmental demands have resulted in greatly intensified interest in the development of highly inhibitive water-based drilling fluid systems, with the eventual goal of replacing oil-based muds. The drilling fluid industry's search for inhibitive waterbased mud systems has been a continuous endeavor for some time. Many approaches have been taken over the years, including the use of: calcium treated muds, such as lime and gypsum muds; relatively high concentrations of inorganic salts, such as NaCl, KCl and CaCl2 modified asphalts and gilsonites; a variety of polymeric additives, such as the functionally anionic PACs and PHPAs, functionally cationic polymers such as polyquaternary amines, amphoteric polymers (which exhibit both anionic and cationic characteristics) such as polyamino acids, and nonionic polymers such as polyols, glycerols, glucosides, polyvinyl alcohols (PVA), and HECs. However, even these approaches have not been completely successful in inhibiting the hydration of highly reactive water-sensitive shales and alleviating the resulting problems. Additionally, the usage of many of these materials is increasingly restricted for environmental reasons. P. 623