Neil F. Hurley¹, Alex Aviantara², Dennis Kerr²

(1) Colorado School of Mines, Golden, CO
(2) The University of Tulsa, Tulsa, OK

ABSTRACT: Structural and Stratigraphic Compartments Determined from Horizontal Drilling in an Eolian Reservoir, Tensleep Sandstone, Wyoming

The eolian Tensleep Sandstone (Pennslyvanian) is a major oil and gas producer in the Bighorn basin, Wyoming. In 1992, the operator of Byron field drilled a medium-radius lateral hole along a NE trend. The well reached 90 degrees deviation where it encountered the Tensleep Sandstone on the flank of the anticlinal structure. Casing was set at that point. The remainder of the well, which was drilled for roughly 500 ft (150 m) on an uphill slant, stayed in the uppermost Tensleep Sandstone within a 20 ft (6 m) thick stratigraphic section. This part of the borehole was left uncased. The general shape of the borehole is that of a "fishhook," where the structural high is at TD (total depth).

The last 150 ft (45 m) of the borehole was full of oil. This level probably represents the height of the oil-water contact in the fractures. If so, this would put the oil-water contact in the fractures at an elevation several hundred feet above the oil-water contact in the matrix. This suggests an innovative, although untested, method of completing the well. The oil will gravity segregate towards the top (TD) of the fishhook-shaped well. Tubing could be run to a point near TD, and the rate at which the borehole is charged with oil can be determined by using step-rate pump tests. If the rate is economically viable, then the well could be produced with minimal water production. The upside potential for similar horizontal wells could be very high in Bighorn basin fields and in other fractured anticlines.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado