Abnormal Pressure, Natural Fractures, and Prolific Hydrocarbon Production in Fall River Sandstone, Deep Powder River Basin, Wyoming: ABSTRACT

Abstract

Prolific hydrocarbon production from the Lower Cretaceous Fall River (Dakota) sandstone occurs in several fields in the deep overpressured portion of the Powder River basin. Most of the production to date comes from Buck Draw field at depths greater than 12,000 ft (3657 m). Individual wells in the field are capable of producing more than 2000 BOPD and have cumulatively produced in excess of 1 million bbl. Production comes mainly from stratigraphic traps. The Fall River Formation consists of fluvial, deltaic, and marine sandstones. Most of the productive sandstones in the Buck Draw area are interpreted to be fluvial (point bar) in origin. This interpretation is based upon log-curve shape, mapped subsurface trends, and the vertical sequence of sedimentary structures, lithologic textures, and mineralogic composition that was observed in cores. The fluvial sandstones were deposited by a meandering river that incised through previously deposited delta-front and marine sandstones. The delta-front and marine sandstones are in transitional contact with the underlying Fuson Shale, whereas the fluvial sandstones are in erosional contact with the Fuson. The updip traps to the fluvial sandstones are clay plugs in abandoned meander loops and the less-permeable delta-front and marine sandstones.