Usgs Assessment: Undiscovered Petroleum Resources of the Laptev Sea Shelf Province, 2007

In 2007, the U.S. Geological Survey (USGS) completed an assessment of potential undiscovered, technically recoverable (assuming the absence of sea ice) crude oil, natural gas, and natural gas liquids (collectively referred to as petroleum) resources in the Laptev Sea Shelf Province of the Russian Federation. As with other areas assessed in the USGS Circum-Arctic Oil and Gas Resource Appraisal (CARA), this area shares important characteristics with many Arctic basins, including sparse data, significant petroleum-resource potential, geologic uncertainty, and technical barriers that impede exploration and development. As defined for CARA, the province includes an area of approximately 500,000 km2, most of which underlies less than 500 m of water offshore of northern Russia between long. 110º and 150º E and between lat. 70º and 80º N.

Assessment Units
The Laptev Sea Shelf Province contains a composite sedimentary basin, in which sediments were deformed by compression during Early Cretaceous time; later, in Paleogene and Neogene time, a superimposed rift/sag system developed in the area. The province was subdivided into three geologically distinctive assessment units based on structural style—the West Laptev Grabens, East Laptev Horsts, and Anisin-Novosibirsk Basins assessment units (AUs) (fig. 1).
The West Laptev Grabens AU was evaluated using two different geological scenarios (table 1) because geologic models for petroleum occurrence considered for this AU are mutually exclusive. The differences between the two scenarios are so extreme that the populations of undiscovered accumulations cannot be statistically combined into a single distribution. The Anisin-Novosibirsk Basins AU was also assessed.
The East Laptev Horsts AU, although defined, was not quantitatively assessed because of the extremely low assessment-unit probability for the existence of an undiscovered accumulation exceeding the defined minimum size of 50 million barrels of oil equivalent.

Petroleum System Elements
Onshore field work and interpretation of geophysical data gathered from offshore areas by geologists from several countries and organizations indicate that two or more total petroleum systems might exist in the study area. Because of possible mixing of petroleum, the Jurassic-Cretaceous-Paleogene Composite Total Petroleum System (TPS) was identified for the West Laptev Grabens AU. Geologic scenarios evaluated for the assessment were based on the existence and distribution of source rocks of these ages. The Paleogene TPS was identified for the Anisin-Novosibirsk Basins AU. The greatest geologic uncertainty for the assessment of both assessment units is with respect to the petroleum charge.

Analyses of natural gas collected from bottom sediments and near-bottom waters of the Laptev Sea Shelf indicate the presence of mature oil-prone marine source rocks, presumably of Paleogene age. Upper Jurassic (Volgian) organic-rich mudstone might also be an important petroleum source rock in the study area, as are synrift Lower Cretaceous and Paleogene carbonaceous and coaly rocks. Major synrift reservoir rocks are likely to be shelf and slope siliciclastic sediments deposited by deltas of the paleo- and present-day Lena River. Whether prerift reservoir rocks are present is uncertain. Traps for petroleum accumulation could include extensional structures and stratigraphic traps associated with shelf sediments.

Resource Summary
The U.S. Geological Survey assessed undiscovered conventional, technically recoverable petroleum (discovered reserves not included) resulting in the estimated mean volumes of a probability distribution of approximately 3,069 million barrels (419 million metric tons) of crude oil, 32,252 billion cubic feet (913 billion cubic meters) of natural gas, and 861 million barrels (117 million metric tons) of natural gas liquids (table 1). The greatest volume of undiscovered petroleum is estimated to be in the West Laptev Grabens AU.

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