Geology and assessment of undiscovered oil and gas resources of the East Greenland Rift Basins Province, 2008

Abstract

In 2007 the U.S. Geological Survey (USGS) completed an assessment of undiscovered, technically recoverable oil and gas resources in the East Greenland Rift Basins Province of Northeast Greenland. The province was selected as the prototype for the U.S. Geological Survey Circum-Arctic Resource Appraisal (CARA). In collaboration with the Geological Survey of Denmark and Greenland (GEUS), the province was subdivided into nine geologically distinctive areas. Seven of these were defined as Assessment Units (AUs), of which five were quantitatively assessed. These are: North Danmarkshavn Salt Basin, South Danmarkshavn Basin, Thetis Basin, Northeast Greenland Volcanic Province, and Liverpool Land Basin. Jameson Land Basin and the Jameson Land Basin Subvolcanic Extension were defined as AUs but were not quantitatively assessed. Onshore studies by GEUS and other organizations suggest that at least four stratigraphic intervals may contain potential source rocks for petroleum. The geological history of related areas in western Norway and burial history modeling suggest that Upper Jurassic strata are most likely to contain petroleum source rocks. A wide variety of possible trapping mechanisms are expected within the province. Potential traps in the North Danmarkshavn Salt Basin AU are dominated by structures formed through salt tectonics; those in the South Danmarkshavn Basin and the Northeast Greenland Volcanic Province are characterized by extensional structures and by stratigraphic traps in submarine fan complexes. Prospective inversion structures of Tertiary age are present along the western margin of South Danmarkshavn Basin AU, and the large horst block structures that separate the Danmarkshavn and Thetis Basins may provide numerous opportunities for traps in fault blocks and along various facies-related permeability barriers. Possible reservoirs include shallow marine to nonmarine sandstones of Middle Jurassic age, sandstones in Upper Jurassic synrift deposits, Cretaceous sandstones in submarine fan complexes, sandstones in Paleogene progradational sequences, and in Upper Carboniferous to Lower Permian warm-water carbonate sequences, especially in northern Danmarkshavn Basin. Marine shales are expected to provide the main sealing lithologies in most AUs. Most of the undiscovered oil, gas, and natural gas liquids are likely to be in the offshore areas of the province and are inferred to belong to an Upper Jurassic Composite Total Petroleum System. The USGS estimated that the East Greenland Rift Basins Province contains approximately (mean) 31,400 million barrels oil equivalent (MMBOE) of oil, natural gas, and natural gas liquids. Of the five assessed AUs, North Danmarkshavn Salt Basin and the South Danmarkshavn Basin are estimated to contain most of the undiscovered petroleum. Introduction and Province Description Geological features of northeast Greenland suggest the possibility of large petroleum potential, as well as high uncertainty and risk. The area was the prototype for development of methodology used in the U.S. Geological Survey (USGS) Circum-Arctic Resource Appraisal (CARA), and the Northeast Greenland Rift Basins Province (fig. 1) was the first province to be evaluated. The new study was deemed necessary because of information made available through collaboration with the Geological Survey of Denmark and Greenland (GEUS), which significantly changed the geological understanding of the area. In collaboration with GEUS the province was subdivided into nine geologically distinct areas. From those, seven assessment units (AUs) were formally defined, five of which were quantitatively assessed. The CARA study superseded a previous USGS assessment of northeast Greenland completed in 2000 (Ahlbrandt and others 2005), from which it differs in several important respects: oil estimates were reduced and natural gas estimates were increased to reflect revised understanding of offshore geology. Despite the reduced oil estimates, the CARA indicates that northeast Greenland could be an important future petroleum province. The East Greenland Rift Basins Province extends for more than 1,200 kilometers (km) from south of the Blosseville 2 The 2008 Circum-Arctic Resource Appraisal Kyst Basin near 66° N to Kronprins Christian Land near 82o N (fig. 1), an area of approximately 500,000 km2, most of which lies beneath less than 500 meters (m) of water. The northern and northeastern boundary of the province is set along the approximate southern trace of the Greenland Fracture Zone/ Trolle Land Fault Zone, thus excluding the Wandel Sea Basin (fig. 2). The province is as wide as 600 km; its western boundary follows the approximate limit of sedimentary rocks onshore and its eastern boundary tracks the continent-ocean transition. The province encompasses the sedimentary basins of northeastern Greenland, including Jameson Land Basin (Christiansen and others, 1992; Mathiesen and others, 1995; Stemmerik and others, 1993), and the less well known offshore basins of the northeast Greenland shelf: Danmarkshavn Basin, Thetis Basin (Hamann and others, 2005), Liverpool Land Basin (Larsen, 1990) and the Blosseville Kyst Basin (Larsen, 1985) (fig. 2). The Tertiary volcanic rocks found offshore between 67° and 75° N are included in the province and are presumed to cover thick sedimentary successions. The Caledonian deformational belt (fig. 2), which formed as a consequence of the closing of the proto-Atlantic Ocean and the collision of the Laurentia and Baltica continents, is known to include more than 4,000 m of intensely folded and faulted sedimentary rocks of Cambrian to Devonian age. For the purposes of this study, deformed Caledonian rocks are assumed to be economic basement; the oldest strata considered in this assessment are Middle to Upper Devonian continental deposits (fig. 3), which accumulated during the crustal relaxation and extensional faulting that followed the Caledonian orogeny. Since the Caledonian collision, northeastern Greenland has been the site of numerous episodes of multi-phase lithospheric extension, the most prominent of which were in the late Permian to Triassic, Late Jurassic to Early Cretaceous, and in mid-Cretaceous time (Surlyk, 1990; Blystad and others, 1995; Doré and others, 1999; Brekke, 2000; Surlyk, 2003), culminating in crustal separation during the Paleocene. The outer (easternmost) part of the shelf has been a passive margin since the early Eocene (Tsikalas and others, 2005). The petroleum potential of northeast Greenland has long been postulated (Ulmishek, 1984; Haimilia and others, 1990) on the basis of (1) the plate tectonic model of the opening of the North Atlantic Ocean Basin (Kay, 1969; Talwani and Eldholm, 1977; Hinz and others, 1987); (2) investigations of outcrops onshore (Stemmerik and others, 1993; and (3) the geologic similarity of northeastern Greenland and the petroliferous basins of northwestern Europe (Hinz and Schlüter 1980, Larsen 1984). As of 2011, with the exception of a few shallow research cores, the sedimentary basins of the province remain undrilled owing largely to their remote location and the possibility of sea ice any month of the year. The northeast Greenland shelf is of particular interest; potential field data have been used to identify major northeast-trending structural features (Larsen 1984, 1990) and, more recently, these features have been examined in greater detail following analysis of the proprietary KANUMAS seismic data (Hamann and others, 2005). South of Shannon Island, thick Tertiary volcanic rocks of the East Greenland Volcanic Province largely cover the shelf. The Koldewey Platform, on the westernmost part of the shelf, is an area of relatively shallow (2 to 5 km) Caledonian rocks, overlain by a thin sedimentary cover thought to include upper Carboniferous to Permian carbonate rocks and lower Carboniferous siliciclastic sequences (fig. 4). In the eastern part of the Koldewey Platform, the Paleozoic section is overlain by various thicknesses of discontinuous and incompletely preserved Mesozoic strata. In some places, such as on Store Koldewey, Mesozoic rocks directly overlie Caledonian basement. North-trending en echelon faults separate the Koldewey Platform from the Danmarkshavn Basin, which is a large, deep, northeast-trending sedimentary basin that is bounded by the Koldewey Platform on the west and by Danmarkshavn Ridge on the east (fig. 4). South of Store Koldewey the basin is limited by the Shannon High, a basement horst that probably extends southward beneath the volcanic field. The basin is at least 400 km long in a northeast-southwest dimension, 50 km wide in the south, and 100 km wide at about 78° N. The central axis and principal depocenter of the basin is thought to contain a largely conformable section, more than 13 km thick, of (probable) Devonian to Holocene age sedimentary rocks. Numerous unconformities increase in significance and the sedimentary strata thin and unconformities increase in magnitude northward and westward of the central Danmarkshavn Basin. Interpretation of the KANUMAS seismic data and unpublished research seismic data acquired by the Alfred Wegener Institute has led to the identification of a major salt province in the northern part of Danmarkshavn Basin (Hamann and others, 2005; W. Jokat, written commun., 2007). The salt is inferred to be of late Carboniferous or possibly earliest Permian age (fig. 3) based upon regional paleogeographic reconstructions (Stemmerik, 2000). The evaporite sequence is, therefore, a likely equivalent to the lower part of the carbonate succession found onshore in North Greenland (Stemmerik, 2000), closely related to similar salt accumulations in Tromsø and Nordkapp Basins in the Barents Sea, and related to the Sverdrup Basin of northern Canada (Larssen and others, 2002). The salt is believed to have accumulated in a rapidly subsiding sag basin along the rift axis between Norway and Greenland (Gudlaugsso