A new DGGS exploration data portal – October 24, 2021
State agency publishes maps and database of all oil and gas exploration wells and their drill targets in the Alaska Arctic
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The Alaska Division of Geological and Geophysical Studies has released a comprehensive database, complete with maps and charts, for all exploration drilling that has been conducted at sea and on land in 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 Geological Materials Center, maintains a massive inventory of rock samples, including drill core, from exploration activities in Alaska.
DGGS says data in its new database comes from public sources, mainly state and federal well stories, Alaska Oil and Gas Division unit decisions, articles published by Petroleum News, industry news articles from Alaska, summary reports on federal wells. and press releases issued by oil and gas tenants. After collating data from these sources, the authors of the new database evaluated the data, performing additional research if necessary, before documenting the determined well exploration targets. Data from some wells is kept confidential under the rules of the Alaska Oil and Gas Conservation Commission.
Ultimately, the DGGS authors classified 346 wells as having publicly available drill target information. Drill targets could be inferred from data such as core and drill pipe tests for an additional 161 wells. Data from well testing and oil and gas exposures are available for 21 wells. Exploration targets for 11 wells could not be determined, despite the availability of public data for these wells. And the data remains confidential for eight wells. The authors also identified the discovery well for each oil field that subsequently went into production. The identification of discovery wells also includes a few development wells that had themselves made new discoveries.
In sync with assessments of Alaska’s oil and gas resources conducted by the US Geological Survey and the Bureau of Ocean Energy Management (formerly the Minerals Management Service), the DGGS authors ranked the drill targets into five main ones. types of zones, plus an “other”? category for targets that did not match any of these types. The five main types are the Ellesmerian clastics and carbonates; Sands of the Jurassic coast; Cretaceous rift sands; Brookian turbidites; and Brookian topsets. ?? Other types ?? include exploration wells for methane hydrate and coal bed methane.
Ellesmerian clastics and carbonates
The Ellesmerian forms the deepest and oldest of the North Slope oil rock sequences and includes 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 sparked major interest in Ellesmerian exploration, with exploration drilling in this area peaking in the mid-1980s. North Slope oil produced since the Trans-Alaska Pipeline came into service in 1977.
Jurassic and Cretaceous
The facies of the Jurassic littoral face, which shelters the principal alpine oil field in the area of the delta of the Colville river, is in the rocky sequence of Beaufort, above the Ellesmérien. The discovery of the Alpine field in 1994 fueled interest in exploration in Jurassic targets, with exploration moving westward into the northeast of the National Petroleum Reserve-Alaska. The Jurassic Coastal Facies was also the target of US military exploration in the 1940s and early 1950s. The facies is home to the South Barrow and East Barrow gas fields towards the western end of the North Slope.
The sands of the Cretaceous rift are also in the Beaufortian sequence and contain reservoir rocks from the huge Kuparuk River and Milne Point fields, discovered in 1969. The greatest number of exploration wells targeting this area were drilled between 1969 and the early 1980s, with development at Kuparuk starting in 1981. The finds in the room are associated with a major geological structure called Barrow Arch and encompass a large area, stretching from the NPR-A to the border west of the Arctic National Wildlife Refuge. Exploration in the area in the late 1980s and 1990s resulted in several discoveries, including the Point McIntyre field. Exploration in the early 2000s led to further discoveries. The Burger gas field, discovered off the Chukchi Sea, also has a reservoir associated with this area.
The Brookian turbidites are part of the Brookian sequence, the shallowest and youngest of the North Slope oil-bearing rock sequences. Turbidites are made up of thin-layered sands deposited by turbidity currents at the base of an ancient marine basin. Initially explored in the early 1950s, this area has aroused almost continuous interest since the early 1960s, with discoveries in the 1990s leading to the development of the Badami field east of the central northern slope, and the Tarn field. to the southwest part of the Kuparuk River unit.
The upper layers of the Brookian, also in the Brookian sequence, were deposited from rivers as vast masses of sand on the edge of a sea basin. In recent years, this area has become the center of important oil discoveries in the Nanushuk Formation, including the discovery of Pikka east of the Colville River delta and the discovery of Willow in the northeast of the NPR-A. In the 1940s and early 1950s, the US Navy made several minor gas discoveries in this area in the NPR-A and Brooks Range foothills, while also discovering a large oil deposit at Umiat. The discovery of viscous oil in the West Sak Formation near the Beaufort Sea coast led to the development of viscous oil which has continued to this 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 associated with each type of zone generally follows a pattern in which there is an initial peak sometime after initial exploration in the zone and shortly after initial development drilling. Production gradually declines thereafter, while play-type exploration and development drilling continues. The exception to this profile is the Brookian topset type of set, where production continues to increase following extensive development drilling in, for example, the Schrader Bluff and West Sak formations, while Pikka and Willow did not yet developed.
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