The Aleutian Basin, Bering Sea A Frontier Area For Hydrocarbon Exploration

Abstract

ABSTRACT The Aleutian Basin is the deep water (>3000 m) basin that lies north of the Aleutian Islands adjacent to the Bering Sea continental shalf. The basin, about the size of the state of Texas, is underlain by a 2-9-km-thick flat-lying sequence of mostly Cenozoic sediment and rock that includes diatomaceous silty clay interbedded with turbidities in the upper 1 km. Before 1974, geologic and geophysical investigations in the Aleutian Basin were directed at determining its geologic history; more recently, investigations have also been aimed at assessing the basin's hydrocarbon potential. The four major requirements for hydrocarbon accumulation may be present, namely, structural and stratigraphic traps, source rocks, reservoir beds, and an adequate thermal and sedimentation history. Energy resource investigations by the U.S. Geological Survey indicate that:numerous structural features (gentle folds, diapirs, basement ridges) are present in the central and eastern parts of the basin,acoustic features (VAMP?s - Velocity Amplitude features) that may be due to trapped gases within the sedimentary section are common (over 350 identified) in the central basin,concentrations of organic gases, primarily methane, in the upper 1–3 meters beneath the seafloor are very sma1f, they-increase with depth, and they are highest in areas near VAMP's, andboth the thermal gradient and the sediment thickness are sufficiently great to allow hydrocarbon maturation at depth, if source rocks are present. Adverse conditions in the Aleutian Basin such as excessive water depths and severe weather pose difficult technical problems for the recovery of hydrocarbons that may be present. Our data nevertheless suggest the basin is a promising site for hydrocarbon accumulations and therefore warrants further exploration. INTRODUCTION The deep water (>3000 m) part of the Bering Sea (Bering Sea Basin) is divided into three physiographic areas, the Aleutian, Bowers, and Komandorsky Basins (Fig. 1). Most of the area of the Aleutian and Bowers Basins lies on the American side of the U.S.-Russia Treaty Line of 1867, an area that may some day be suitable for seafloor resource development. During the past three years the U.S. Geological Survey has conducted energy resource investigations within the Aleutian Basin. These studies have focused on both a regional assessment of the basin's hydrocarbon potential and detailed analysis of specific acoustic and structural features. The initial results suggest that the major requirements for hydrocarbon accumulation are present in the basin. In this paper, we synthesize the results from earlier investigations in the Aleutian Basin as well as from the more recent field studies by the U.S. Geological Survey. Although the discussion concentrates on the Aleutian Basin, most of the observations are also applicable to the smaller Bowers Basin. These deep-water basins are 'frontier areas' in that severe technical difficulties may be expected in the recovery of potential hydrocarbons; nonetheless, we hope to show that the basins are promising hydrocarbons sites and therefore warrent further exploration for energy resources.