Drilling Waste Disposal in the Arctic Using Below-Grade Freezeback

Abstract

The disposal of waste muds and cuttings has become increasingly difficult for operators world-wide. Disposal tasks are complicated by the great variety of operating environments as well as the multitude of local, state and national regulations governing any waste disposal. This paper describes the successful disposal method used by ARCO Alaska, Inc. (AAI), on two exploratory wells drilled on the North Slope of Alaska in early 1988. The disposal method, below-grade freezeback, involves burying waste muds and cuttings in the permanently frozen ground known as permafrost. When buried, the waste freezes, becoming part of the permafrost. When buried, the waste freezes, becoming part of the permafrost. This disposal method utilizes the ability of the natural permafrost. This disposal method utilizes the ability of the natural Arctic environment to isolate and permanently contain the waste muds and cuttings. Introduction In early 1988, AAI, as operator, drilled two exploratory wells on the North Slope of Alaska. These wells, Pipeline State #1 and Point McIntyre #3 (Fig. 1), were the first exploration wells permitted under newly promulgated Solid Waste Management Regulations (SWMR) of the Alaska promulgated Solid Waste Management Regulations (SWMR) of the Alaska Department of Environmental Conservation (ADEC). The permitted disposal method was below-grade freezeback. In this method, wastes were buried in excavated pits in the permafrost so they would freeze, becoming part of the permafrost. permafrost. The permafrost has formed due to the sub-freezing temperatures that dominate the Arctic climate. Near the Beaufort Sea coast, the ground is permanently frozen to about 2,000 ft. (656 m). During the short Arctic permanently frozen to about 2,000 ft. (656 m). During the short Arctic summer, only the top 2 ft (0.6 m) will thaw. If freezable wastes are buried below this seasonal thaw zone, they will remain frozen. In the permitting process an analysis of the thermal conditions at each site was permitting process an analysis of the thermal conditions at each site was performed. Verification of the actual thermal performance of each site was performed. Verification of the actual thermal performance of each site was a permit requirement and has been performed using vertical thermistor arrays. The two wells were drilled between February and April 1988. The disposal pits were closed out in late April 1988, and the thermistors were pits were closed out in late April 1988, and the thermistors were installed. Since pit closure, both sites have been visited several times and ground temperature readings have been obtained. The following discussion addresses the heat transfer regime, permit requirements, site preparation and pit closures. Results of post-closure thermal monitoring preparation and pit closures. Results of post-closure thermal monitoring are also presented. PHYSICAL AND GEOLOGICAL SETTING PHYSICAL AND GEOLOGICAL SETTING The North Slope of Alaska, described by many authors, is that area of Alaska bounded by the Beaufort Sea on the north and the Brooks Range foothills on the south. The Slope is characterized by little, if any, relief. The surface elevation increases inland, with increases of 10 ft/mi (2 m/km) being common. At the foothills, elevations up to 600 ft (183 m) are typical. P. 273

Rheological and filtration property evaluations of the nano-based muds for drilling applications in low temperature environments

“…The drawback from this thermally stable mud is that it is mostly formulated in the oil and synthetic-based mud systems due to their high lubricity and formation damage prevention benefits. However, oil itself is considered toxic and hazardous to the environment (Nesbitt and Sanders, 1981) which may result in a higher waste management cost for mud disposal, especially when used in the Arctic region (Maunder et al, 1990;Rakhmangulov et al, 2016). For this reason, designing a drilling mud that provides similar quality in the aqueous-based system is essential to reduce the excessive use of toxic or hazardous additives in drilling muds not only for the Arctic operations but also for the offshore deepwater drillings in general.…”

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

“…In cold weather climates the spent drilling mud undergoes intensive cooling until its temperature stabilizes at the ambient level. Active mud temperatures in the Arctic drilling are at least 27° C (80° F) while their storage temperatures before pit dewatering are only slightly above freezing point (7) . Since cooling in the Arctic is natural and costs nothing, a logical question is what temperature would be most beneficial to the dewatering.…”

“…Freeze back technology was reportedly used at two exploratory wells drilled on the North Slope of Alaska in 1988 (7) . The dewatered mud solids were buried in the on-site excavated pits, below the base of the seasonal active layer, in the permafrost.…”