Hydraulic Fracturing the Nanushuk: Review of the Pikka Frac Campaign, North Slope Alaska

Abstract The Nanushuk reservoir, a thick accumulation of deltaic shoreface sandstones, interbedded siltstones, and shales, is the primary target for the new Pikka development on the North slope of Alaska. Due to the challenging and environmentally sensitive terrain, where the reservoir is located 4000 feet below the Colville River, the Pikka phase 1 wells are drilled from a single surface gravel pad. This serves to minimize the surface footprint consisting of 41 horizontal wells (21 producers and 20 injectors) with lateral lengths of 6000 ft on average. Hydraulic fracturing is the primary technology to connect hundreds of feet of laminated reservoir to the horizontal wells that will facilitate a line drive pattern water-alternating-gas development. Each well has between 9 and 12 hydraulic fractures with conventional treatment designs with large ceramic proppant (16/20 Lightweight Ceramic Proppant (LCP)) and a cross-linked borate gel. Diversion is achieved using a collet and ball system to isolate between stages within the frac liner. Mechanical set packers are used to isolate the formation between frac sleeves behind pipe. This paper reviews the design of the frac program, completion technology, real-time data collection, data integration, and lessons learned to improve decision making. The data collected from each frac is analyzed for impact on well productivity, and key learning's from challenges encountered in the field are presented with an emphasis on improved conductivity, diversion, frac height, and screen out prevention. The hydraulic fracturing design aims to achieve fracture heights of approximately 150 feet and half-lengths of around 250 feet. Fracture stage spacing ranges from 500 to 600 feet, typically resulting in about 11 stages per 6,000-foot horizontal lateral. To maximize conductivity and minimize non-Darcy and multiphase flow effects, 16/20 and 12/18 mesh lightweight ceramic proppants are used at concentrations of 10 to 12 pounds per gallon added (ppa). The fracturing fluid consists of a 26 pounds per thousand gallons (pptg) guar-based borate crosslinked gel, pumped at 40 barrels per minute, with pump rates constrained by friction in the 4-1/2" completion. Additionally, 40/70 lightweight ceramic proppant is used as a scour stage when required.