KNIGHT, CONSTANCE N., and NEIL F. HURLEY
Colorado School of Mines, Golden, CO

Abstract: Relationships of Faulting, Fracturing, and Sedimentation Patterns to Hydrocarbon Production: Mesaverde Sandstone, North La Barge Field, Sublette County, Wyoming

North La Barge field production is characterized by "sweet spots", which are related to complex faulting and sedimentologic variations. The field is dissected by thrusts and tear (strike-slip) faults. Also subtle changes in depositional environments exert a primary control on reservoir performance. New technologies, including 3-D seismic and Formation Micro Imager (FMI) logging have been used to interpret complex structural and sedimentologic relationships for this field.

Subtle, yet critical changes in depositional environments of productive Mesaverde facies have been interpreted using core and FMI logs. Permeable upper and lower shoreface Mesaverde sandstones have been mapped in the subsurface. These have been related to outcrop facies equivalents. Sedimentation patterns suggest structural control. Fracture density and fracture orientation, which in part control reservoir performance, are functions of proximity to the La Barge thrust, and to tear faults. In situ stress orientations from borehole breakouts are mixed. Some stress orientations relate to thrusting; whereas others relate to tear faulting. Proximity of Mesaverde sandstone reservoirs to the overlying Cretaceous-Tertiary unconformity affects production in a negative manner, apparently due to alteration/diagenesis.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas