Gladys W. Fong1, S. George Pemberton1, Murray K. Gingras2, Bo Hank1
(1) University of Alberta, Edmonton, AB
(2) University of New Brunswick, Fredricton, NB
ABSTRACT: Assessing the Reservoir Quality of Burrow-Mottled Carbonates in the Devonian Wabamun Group, Pine Creek Area, Northwest Alberta, Canada
The Devonian (Famennian) Wabamun Group (upper Three Forks Group or Palliser Formation) consists of a series of stacked cyclical shallow water ramp carbonates and evaporates which were deposited during a regressive cycle. In the Pine Creek Field (Township 56-58, Range 19-20), the Wabamun hydrocarbons are produced from the Stettler Formation (cumulative gas production 4.5x10^5 MMCF). Stettler Formation sediments consists of cyclical wackestones, packstones and grainstones which are tan to brown in color. They were deposited on a large, semi-restricted shelf, and are characterized by extensive bioturbation, scarce shelly fossils, and by the pervasive presence of pellets and intraclasts. The partly dolomitized peloidal grainstone zones are found at different levels within the platform and constitute the major reservoirs in this play. Relationships between the biogenically-mediated substrate and porosity enhancement within the Wabamun Group suggest paleobiological controls on the reservoir development. Preferential dissolution and precipitation of dolomite are found within and adjacent to burrow fabrics. The local diagenetic heterogeneities suggest intrinsic paleobiological control on dolomitization patterns. Fluid flow through burrow-mottled carbonates is notably tortuous and is very similar to that seen in fractured reservoirs. These strata act as dual permeability systems (high permeability within the burrow networks and low permeability in surrounding matrix). An understanding of burrow fabrics, and paleobiological influenced dolomites and their distribution patterns provide a useful tool to exploration and improve reservoir characterization accuracy. In the Stettler Formation the ichnofossils constitute the reservoir and the understanding of anisotropic permeability trends is of fundamental importance to the successful exploitation of this and similar carbonate reservoirs.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado