Characterization and Optimization of Tight Gas Frontier Reservoirs

along the Central Moxa Arch, Green River Basin, Wyoming

By

Stephen D. Sturm, William J. Clark, Barbara F. Keusch, and Lesley W. Evans

Schlumberger DCS, Denver, CO

Edward J. Biller

BP America Production Company, Houston,

Optimization of Frontier fluvio-deltaic reservoirs along the central Moxa Arch results from a combination of critical parameters including the influence of paleotectonics on deposition, the distribution of permeability, and effective completion design to maximize inherent mechanical rock properties, and flow capacity proximal to the wellbore. Detailed characterization of Frontier reservoirs in the area of the Shute Creek, Cow Hollow, and Whiskey Buttes Units including integration of stratigraphic data from well logs, ~2500 core data samples, petrophysical analysis, production analysis, and completion analysis within a sequence-stratigraphic framework identified both infill and restimulation opportunities to exploit unrecognized gas reserves.

Frontier reservoirs are comprised of composite marine shoreface sequence (2nd Bench), unconformably overlain by aggradational fluvial sequence (1st Bench). Deposition in both sequences was focused along northeast and northwest-trending paleostructural elements that resulted in similar trending accumulations of net sand with increased

reservoir potential. Routine core and log analysis indicated that reservoir quality (K/phi) in the fluvial sandstones is generally greater than that of the underlying marine sandstones, although discrete permeability sweetspots have resulted from dissolution of calcite in middle and lower shoreface zones. However, because marine reservoirs are thicker they have comparatively higher storage (phiH) and flow capacities (kH) than fluvial reservoirs.

By better understanding reservoir character and mechanical stress properties and parameters that explain existing gas production, more effective well stimulation techniques have been initiated to economically optimize remaining gas reserves. Current stimulation methodology has resulted in greater fracture conductivity and productivity.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming