Environmentally Acceptable Shale Inhibitors for High Performance Water-Based Muds

Abstract

The water reactivity of clay-containing shale minerals remains a long-standing problem when drilling wellbores with water-based fluid systems. Complicating this issue, the environmental effect of chemical additives used in water-based drilling fluids continues to receive heightened scrutiny in various regions across the world. This study addresses these challenges by expanding the molecular toolbox of environmentally friendly additives that are available to manipulate shale reactivity. To this end, a shale inhibitor package is introduced and discussed that leverages chemical synergy to impede the uptake of water in shale minerals while also increasing the structural integrity of shale cuttings. The main component, a natural-based hybrid organic/inorganic inhibitor blend, is highlighted. Simple fluids systems were prepared with potassium-based brines and combined with shale inhibitors for initial shale erosion screening experiments. These simple fluids isolated the shale inhibition effects of the inhibitors of interest and excluded the possible influence of additional chemical additives typically found in drilling fluids. Subsequently, fully formulated, water-based drilling fluids were prepared with these inhibitors and compared to fluids with traditional inhibitors. These fully formulated drilling fluids were characterized by rheological testing, fluid loss, shale erosion, accretion, and linear swell testing. An inhibitor combination of a hybrid organic/inorganic inhibitor blend, along with a nitrogen-rich oligomeric hydration suppressant, was determined to be the most effective inhibition mixture in simple fluid screening. The dual mode of action of the two inhibitors, disparate in both molecular size and chemistry, likely achieved optimal interfacial shielding on the clay minerals to effectively diminish the rate of reaction with water. More importantly, the shale inhibition was successfully translated to fully formulated fluid systems without affecting rheological properties or diminishing fluid loss control. The results achieved were comparable to a current high-performance, synthetic-based shale inhibitor; however, the new shale inhibitor package features a more favorable environmental profile. Natural-based materials and their derivatives are continually revealed to contain useful properties, particularly for water-based drilling fluids. In this study, high-performance functionality and environmental friendliness were united with an innovative natural-based hybrid organic/inorganic inhibitor blend that is believed to function by encapsulating shale minerals. In addition, a synergy was discovered between hybrid organic/inorganic inhibitor blends and nitrogen-rich oligomeric compounds. Ultimately, the materials developed have achieved yellow environmental ratings in the North Sea and have been successfully validated in field applications in Norway.