Summary

Drill cuttings collected during drilling of two development wells at Prudhoe Bay were processed through an auxiliary unit to dry processed through anauxiliary unit to dry and sort the material. Construction-grade gravel and sandwere collected from the processing unit and stored for future use as fillmaterial on roads and pads. Material too small to use for construction wasslurried and disposed of by approved subsurface techniques. Chemical tests ofthe processed drill cuttings indicate that processed drill cuttings indicatethat they are an environmentally sound alternative for quarried gravel.

Introduction

Finding an environmentally acceptable method for drill-cuttings disposal isa major concern for operators worldwide, particularly in the Arctic. This paperreports the particularly in the Arctic. This paper reports the results of apilot program designed to reclaim and recycle gravel excavated duringdevelopment drilling of wells in Prudhoe Bay's eastern operating area (EOA) on Prudhoe Bay's eastern operating area (EOA) on Alaska's North Slope.

Recycling drill cuttings minimizes drilling waste, conserves naturalresources, and greatly reduces the need for waste disposal. It also reduces theoperational costs associated with waste disposal and pad and road maintenanceand the demand for quarried gravel. Overall, recycling reduces theenvironmental impact of drilling and construction operations.

On the basis of results from the pilot project, the Alaska Dept. of Environmental project, the Alaska Dept. of Environmental Conservation (ADEC)approved an expanded testing program for 1991. With continued success, thisprogram could result in the opportunity to reclaim sand and gravel routinelyand thus reduce drilling waste significantly.

North Slope Environment.

The Prudhoe Bay field is located on the Teshekpukportion of the Arctic coastal plain-i.e., the portion of the Arctic coastalplain-i.e., the North Slope of Alaska (Fig. 1). The coastal plain ischaracterized by low relief with plain is characterized by low relief withelevations of less than 30 ft at the sea coast and up to 500 ft at the base ofthe northern foothills province. The undulate tundra contains thousands ofsmall thaw lakes that, with polygonal ground patterns, make up the polygonalground patterns, make up the smaller-scale features of the physiography. Bothfeatures are related to the presence of permafrost. permafrost. The Prudhoe Bayclimate is characterized by extreme temperatures and low levels ofprecipitation. Temperatures range from 20 precipitation. Temperatures rangefrom 20 to 75 degrees F in the summer and -20 to -60 degrees F in the winter. Annual precipitation along the coastal plain ranges from precipitation alongthe coastal plain ranges from 4 to 10 in., with maximum precipitation occurringin July and August.

Geology.

This project focuses on the surface hole section, the upper 3,500ft true vertical depth (TVD) of strata, including 2,000 ft of permafrost. Permafrost is virtually continuous throughout the Alaskan North Slope, extending from near the surface to a vertical depth of roughly 2,000 ft near Prudhoe Bay. The most significant characteristic of permafrost in regard tothis project is its susceptibility to thaw. project is its susceptibility tothaw. Thawing causes the wellbore to enlarge during drilling, whichsignificantly influences the volume of material recovered. Permafrost consistsof shales, sands, and gravels and contains most of the material with thepotential to substitute for mined gravel. The potential to substitute for minedgravel. The drilled surface hole section generally consists of 70 % sand andgravel.

The entire North Slope is overlain by poorly stratified sand and gravel, thought to poorly stratified sand and gravel, thought to be glacial outwash, extending from the surface to 40 ft. The Gubik formation occurs in Prudhoe Bayfrom below the glacial outwash to 600 ft. The Gubik formation is primarilyclean, crossbedded sand with primarily clean, crossbedded sand with smallpebbles of black chert in the upper part. The 5–10-ft-thick sand unitsarseparated part. The 5–10-ft-thick sand units arseparated by thin beds of darkgray, laminated marine silt and clay. The Gubik formation consists mainly ofcoarse gravel, with clasts that are primarily roller-shaped, 3 to 5 in. long, and composed of gray quartzite, tuff, chert, and highly weathered minorlimestone. The remaining stratum, to below 3,500 ft TVD, consists of the Upper Sagavanirktok formation, which lies beneath the Gubik. The Sagavanirktokformation consists of poorly consolidated nonmarine and marine shale, sandstone, and conglomerate, with some carbonaceous shale, lignite, andbentonite clays (Fig. 2).

Pilot-Project Overview.

Development of Pilot-Project Overview. Developmentof the North Slope is regulated by U.S., State of Alaska, and North Slopeagencies to minimize long-term adverse effects on the environment. Recentchanges in U.S. environmental policies have focused this goal on three areas:protection of wetlands, reduction of waste, and maximization of resourcerecycling.

JPT

P. 722

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