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Vol. 26, No.43 Week of October 24, 2021
Providing coverage of Alaska and northern Canada's oil and gas industry

A new DGGS exploration data portal

State agency publishes maps and database of all oil and gas exploration wells and their drilling targets in Arctic Alaska

Alan Bailey

for Petroleum News

Alaska’s Division of Geological and Geophysical Surveys has published a completed database, with accompanying maps and charts, for all of the exploration drilling that has been conducted offshore and onshore Arctic Alaska over the years. The agency’s goal in publishing the database is to provide a window into publicly available oil and gas exploration data. In addition to its data portal, DGGS, through its Geologic Materials Center, maintains a massive inventory of rock samples, including drilling cores, from exploration activities in Alaska.

DGGS says that the data in its new database have come from public sources, primarily state and federal well histories, unit decisions by Alaska’s Division of Oil and Gas, articles published by Petroleum News, Alaska industry news articles, federal well summary reports and press releases issued by oil and gas lessees. After gathering data from these sources, the authors of the new database assessed the data, conducting additional research as necessary, before documenting the determined well exploration targets. Data for some wells remain confidential under Alaska Oil and Gas Conservation Commission rules.

Wells categorized

Ultimately, the DGGS authors categorized 346 wells as having publicly available drilling target information. Drilling targets could be inferred from data such as core and drill stem tests for an additional 161 wells. Well test and oil or gas show data are available for 21 wells. It did not prove possible to determine the exploration targets for 11 wells, despite the availability of public data for these wells. And data remain confidential for eight wells. The authors also identified the discovery well for each oil pool that subsequently went into production. The identification of discovery wells also encompasses a few development wells that had themselves made new discoveries.

In synchronization with Alaska oil and gas resource assessments conducted by the U.S. Geological Survey and the Bureau of Ocean Energy Management (formerly the Minerals Management Service), the DGGS authors categorized drilling targets into five main play types, plus an “other” category for targets that did not fit into one of these types. The five main types consist of Ellesmerian clastics and carbonates; Jurassic shoreface sands; Cretaceous rift sands; Brookian turbidites; and Brookian topsets. “Other types” include methane hydrate and coalbed methane exploratory wells.

Ellesmerian clastics and carbonates

The Ellesmerian forms the deepest and oldest of the North Slope petroleum bearing rock sequences and includes the reservoirs for several fields including the giant Prudhoe Bay oil field and the huge Endicott field. The discovery of the Prudhoe Bay field in 1968 led to major interest in Ellesmerian exploration, with exploration drilling in this play peaking in the mid 1980s. Oil production from the Ellesmerian dominates the total North Slope oil volume produced since the trans-Alaska oil pipeline went into operation in 1977.

Jurassic and Cretaceous

The Jurassic shoreface facies, which holds the major Alpine oil field in the Colville River Delta region, is found within the Beaufortian rock sequence, above the Ellesmerian. The discovery of the Alpine field in 1994 fueled interest in exploration in Jurassic targets, with this exploration moving west into the northeastern National Petroleum Reserve-Alaska. The Jurassic shoreface facies also formed the target of U.S. military exploration in the 1940s and early 1950s. The facies hosts the South Barrow and East Barrow gas fields, towards the western end of the North Slope.

The Cretaceous rift sands also lie within the Beaufortian sequence and hold the reservoir rocks for the huge Kuparuk River and Milne Point fields, discovered in 1969. The largest number of exploration wells targeting this play were drilled between 1969 and the early 1980s, with development at Kuparuk beginning in 1981. Discoveries in the play are associated with a major geologic structure called the Barrow Arch and encompass a large region, extending from NPR-A to the western border of the Arctic National Wildlife Refuge. Exploration in the play in the late 1980s and 1990s resulted in several discoveries, most notably the Point McIntyre field. Exploration in the early 2000s resulted in some further discoveries. The Burger gas field, discovered offshore in the Chukchi Sea, also has a reservoir associated with this play.

Brookian plays

The Brookian turbidites are in the Brookian sequence, the shallowest and youngest of the North Slope petroleum bearing rock sequences. The turbidites consist of thinly layered sands deposited by turbidity currents at the base of an ancient marine basin. Initially explored in the early 1950s, there has been almost continuous interest in this play since the early 1960s, with discoveries in the 1990s leading to the development of the Badami field to the east of the central North Slope, and the Tarn field in the southwestern part of the Kuparuk River unit.

The Brookian topsets, also in the Brookian sequence, were deposited from rivers as large sand bodies on a marine basin edge. In recent years this play has become the focus of major oil discoveries in the Nanushuk formation, including the Pikka discovery to the east of the Colville River Delta and the Willow discovery in the northeastern NPR-A. In the 1940s and early 1950s the U.S. Navy made several minor gas discoveries in this play in the NPR-A and the Brooks Range foothills, while also discovering a sizable oil field at Umiat. The discovery of viscous oil in the West Sak formation near the Beaufort Sea coast led to viscous oil development that has continued to the present day in the West Sak and Schrader Bluff formations. The Nikaitchuq field, discovered in 2004, has a reservoir in the Schrader Bluff formation.

Oil production

Oil production associated with each play type in general follows a profile, in which there is an initial peak some time after initial exploration in the play and shortly after initial development drilling. Production gradually drops thereafter, while exploration and development drilling in the play type continue. The exception to this profile is the Brookian topset play type, where production is still climbing following much development drilling in, for example, the Schrader Bluff and West Sak formations, while Pikka and Willow have yet to be developed.



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