Design and Development of Quaternary Amine Compounds: Shale Inhibition With Improved Environmental Profile

Abstract

Abstract Novel cationic-based drilling fluid additives that provide excellent shale inhibition with improved environmental profile have been developed and tested. Low-molecular-weight bis-quaternary amines that contain structures similar to naturally occurring cationic compounds provide low toxicity and excellent shale-inhibition properties. This paper describes both the laboratory development and chemistry of such shale inhibitors. Cationic shale inhibitors provide more effective shale inhibition by anchoring to the negatively charged shale surfaces as compared to traditional anionic products. However, cationic shale inhibitors are perceived to be more toxic in both onshore and offshore drilling applications than commonly used anionic drilling fluid additives. The toxic nature of many cationic amine compounds has limited their application as shale inhibitors in offshore and other environmentally sensitive areas. Along with toxicity-related issues of cationic compounds, these types of chemical additives are not compatible with conventional anionic drilling fluid additives such as polyanionic cellulose (PAC), polyacrylates, bentonite and various biopolymer additives. Thus, the utilization of cationic additives, specifically cationic shale inhibitors has been limited; yet, there is a need to develop such shale inhibitors which mitigate these limitations making them usable for environmentally sensitive areas. Extensions of the latest amine-shale inhibitor chemistries have enabled the design and development of cationic amine shale inhibitors, which provide efficient shale inhibition to water sensitive shale without the adverse environmental impact. The paper describes the chemistry and development of such modified cationic shale inhibitors, resolving the inherent environmental toxicity limitations and providing excellent shale inhibition to a variety of water-sensitive clays. The paper also includes various drilling fluid formulations containing these innovative shale inhibitors and compares their performance with state-of-the-art inhibitive water-based drilling fluids currently used in the field for similar applications. Introduction Drilling water-sensitive shale with water-based muds (WBM) can be a difficult and costly operation. Shales make up greater than 75% of the formations drilled and cause a majority of wellbore instability problems. An important consideration with these drilled formations is to protect the water-sensitive clays and reduce problems caused by water adsorption on the clay such as bit-balling, borehole washout, disintegration of cuttings, high torque and drag, wellbore instability, and stuck pipe.1,2 Two main families of chemicals, clay-controlling additives and clay stabilizers are used to combat the problematic, i.e., water-sensitive shale (clays). These are also sometimes classified as temporary (clay controlling) and permanent (clay stabilizers) shale inhibitors. Historically, either sodium chloride or potassium chloride has been the primary chemical of choice for temporary clay stabilization. These salts are only effective as long as the WBM containing these salts are in contact with the clays. However, as soon as either salt is depleted or the salt-containing WBM is displaced with freshwater mud, the clay will once again hydrate and swell, and destabilize the shale. The concentration of such additives between 2% to as high as 37% are frequently recommended in treating drilling fluids to minimize the swelling of the reactive clays. These salts retard the swelling of the clay through a variety of mechanisms. The cation exchange reaction reduces the amount of water that can be adsorbed by hydratable cations on the surface of the swelling clays.