Inhibitory effect of water-based drilling fluid on methane hydrate dissociation

Hydrate dissociation poses a significant problem during drilling operations in hydrate-bearing sediments. The drilling fluid is in direct contact with hydrates, and understanding its inhibitory effect on hydrate dissociation is important for stabilizing hydrates during drilling operations. In this work, an apparatus was designed for investigating hydrate dissociation in drilling fluids, and the effects of thermodynamic hydrate inhibitors (THIs), polyvinyl pyrrolidone (PVP), and soybean lecithin on hydrate dissociation were studied. The inhibitory effect of a water-based drilling fluid in the presence of the potential hydrate dissociation inhibitors was also studied. An unexpected inhibitory effect occurred with ethylene glycol (EG) at concentrations below 10 wt%, resulting from a range of factors including the dissociation driving force, and mass and heat transfers in the EG solution. PVP and lecithin reduced the hydrate dissociation rate and increased the time required for complete dissociation of hydrates. These can, therefore, be used in waterbased drilling fluids to inhibit hydrate dissociation. A combination of 0.1 wt% PVP and 0.5 wt% lecithin was selected as an optimal hydrate dissociation inhibitor, considering its inhibitory effect and compatibility with the drilling fluid. Using EG at a concentration below 10 wt% as a THI instead of NaCl can also help inhibit hydrate dissociation. The findings of this work provide a basis for the development and design of drilling fluids for drilling in hydrate-bearing sediments. (C) 2019 Elsevier Ltd. All rights reserved.