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The History and Areal Distribution of Exploration Drilling Targets Categorized by Play Type, North Slope and Offshore Arctic Alaska


News headlines touting large oil discoveries, such as the recently announced 0.5-1 billion-barrel oil accumulations in the Nanushuk topset play, have a history of influencing exploration drilling in North Alaska. Interested explorers ask, what wells targeted this play? Where are the producing analogues? Who successfully or unsuccessfully targeted this play in the past? This comprehensive study documents the drilling target by play type from public domain information for 548 exploration wells on the North Slope of Alaska, Beaufort Sea and Chukchi Sea. The discovery well and production data for each producing pool are integrated into the study to address the explorers’ questions. To date, 17.9 billion barrels of liquid hydrocarbons have been produced from North Alaska. Wells have targeted five main play types: Ellesmerian clastics and carbonates (Kekiktuk, Lisburne, Ivishak, Shublik, and Sag River), Jurassic shoreface sands (Barrow, Simpson, Kugrua, Nechelik, Nuiqsut, and Alpine), Cretaceous rift sands (Walakpa, Kuparuk, Put River, Kemik, and Thomson), Brookian turbidites (Torok, Seabee, and Canning), and Brookian topsets (Nanushuk, Tuluvak, Schrader Bluff, West Sak, Ugnu, Prince Creek, and Sagavanirktok). A sixth category called ‘Other’ includes the remaining targets (e.g., basement and methane hydrates). A series of maps and diagrammatic cross sections show the spatial distribution of wells targeting each play type. Drilling target timelines illustrate the progression from exploration to discovery to delineation and then production. In each play type, key discoveries ignite a flurry of drilling activity. Exploration activity targeting the Ellesmerian was greatest after the discovery of Prudhoe Bay in 1968 and continued at an elevated rate through 1986. Exploration of the Jurassic shoreface sands saw two pulses in the early and mid-1980s that led to the oil discovery in the Nuiqsut sands at Oooguruk. Jurassic exploration continued from 1992 to 2015, spurred by the giant Alpine field discovery in 1994. Cretaceous rift sands have regularly been a drilling target since the Kuparuk River field was discovered 1969. Brookian topset and turbidites were the earliest targets starting in the 1940s with spikes in exploration activity in every decade since 1964. Exploration wells delineating recently announced Nanushuk topset discoveries out-numbered every other play in 2018.