Oil-Based Drilling Mud as a Gas-Hydrates Inhibitor

Abstract

Summary Gas-hydrates formation must be considered when petroleum reservoirs are developed in arctic regions and deepwater environments. This paper demonstrates that gas hydrates can form in oil-based muds, but that two major components—oil and dissolved solids in the aqueous phase—significantly inhibit this formation. This work identifies two major components in oil-based drilling mud that affect gas-hydrates formation. The temperature and extent of gas-hydrates formation both can be inhibited significantly, but not necessarily prevented, in oil-based drilling muds. A system that contained 20-vol% water and had an oil-continuous phase inhibited gas-hydrates formation 5 to 10°F. Dissolved solids in a 19.22-wt% calcium chloride (CaCl2) brine inhibited gas-hydrates formation 20 to 25°F and significantly reduced the extent of formation. Gas-hydrates formation in an oil-based drilling mud, prepared with 20- vol%, 19.22-wt% brine, was inhibited more than 30°F over the pressure range studied, 500 to 4, 500 psig. In most cases, oil-based mud can be prepared with sufficient concentrations of dissolved solids to prevent gas-hydrates formation under downhole conditions. Mud samples should be tested to determine the temperature of gas-hydrates formation before field use.