Environmental Control of Drilling Mud Discharge Through Dewatering In Cold Weather Climates: Effect of Ambient Temperature

Abstract

Abstract This paper presents results of an experimental study into the effect of drilling mud temperature upon dewatering performance. Three temperature ranges were considered: from flowline temperature to room temperature, from room temperature to freezing point, and the freeze -20 ° C (-4 ° F) thaw 12 ° C (54 ° F) cycle. The tested drilling fluids included unweighted and weighted fresh water muds and a weighted salt water mud. A sealed laboratory batch reactor was used in the experiments to prevent rapid vapourization of separated water at temperatures above 60 ° C (140 °F). Also, ice or ice-salt baths were utilized for deep freezing. The dewaterability (net water removal) was measured with a bench-top plate press under constant expression pressure 207 kPa (30 psi). The freeze/thaw treatment greatly enhanced dewaterability by releasing 34 – 39% by volume of the mud water. Mechanical dewatering followed; it required half the chemicals and released an additional 36 – 43% of water. The process proved to be very effective, reducing waste mud volume by 64 – 72%. It is wellsuited for the Arctic with its natural freeze/thaw cycles. The results of experiments at temperatures above 21 ° C (70 °F) showed that there is little advantage to dewatering hot drilling mud diverted from active system. A 10% increase of water removal was observed above 60 ° C (140 °F). The experiments at temperatures below 21 ° C (70 °F) showed that in cold weather climates the waste drilling mud diverted from active system should be dewatered when its temperature is still above 40 °F. Otherwise, more chemicals will be needed for separation enhancement or the dewatering process will become entirely ineffective. Introduction The dewatering process has become increasingly popular in oilfield drilling practices. Its first field applications in the early 1980s were related to oilfield pit closure procedures, where drilling waste from reserve pits was processed by portable dewatering units. In this application, the dewatered pit solids can be directly disposed on-site using burial, trenching, or land treatment practices, or they can be initially solidified to prevent any potential leaching of toxicants. The dewatering effluent may be either directly disposed to the land or surface waters, or, when the effluent limitation guidelines are not met, can be injected underground. Several configurations of the pit dewatering processes commercially offered to the oilfield petroleum industry in the US and abroad have been reviewed in the literature(1). Later, the dewatering process was included into the active mud processing systems for separation and recycling of the mud water phase to minimize the drilling waste discharge volume(2–5). The dewatering of circulating active muds proved to be more difficult than the dewatering of reserve pit sludges, particularly when the mud systems contained high concentrations of surface-active solids(3) after being heavily treated with the suspension stabilitycontrol agents, as is the case for dispersed muds. Despite disadvantages, the dewatering of active mud offered an attractive alternative to drilling a well without a reserve pit, particularly in zerodischarge areas.