Relationship of Faults, Fractures, and Critical Stress to Mesaverde Reservoir Performance, North La Barge Field, Sublette County, Wyoming

Connie N. Knight¹ and Jennifer Miskimins^2
1True North Energy Corp., Golden, CO
²Colorado School of Mines, Golden, CO

The North La Barge Shallow Unit (NLBSU), located on the northern extension of the Moxa Arch, , produces oil from the Mesaverde formation at depths of 2000 ft (610 m). Three-dimensional seismic data, borehole images, and cores were used to identify fault and fracture controls on reservoir performance.

The NLBSU is dissected by several subtle strike-slip faults. One such fault compartmentalizes the field. Detailed sedimentologic mapping demonstrate that this sealing fault has a complex history of reactivation.

The NLBSU exhibits four types of production behavior including fracture-dominated, matrix-dominated, fracture/matrix combination, and significantly reduced production near faults. The fracture-dominated production behavior is centralized in a structurally complex, highly stress-controlled region, which includes a horsetail splay termination of a strike-slip fault. This faulted region results in critically stressed natural fracture production.

Faulting and fault-related fracturing play a complex role in controlling production histories at the NLBSU. In addition to critically stress natural fracture production, several producing wells that were drilled in fault damage zones exhibit significantly reduced production performance. The presence of fault damage zones takes precedence over the occurrence of natural fractures in terms of reservoir enhancement and results in poor production performance. Knowledge of these types of production controls can aid in reservoir management throughout the life of a field.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas