Abstract: Quantitative Geological Modelling of a Large Scale Estuarine Point Bar Reservoir, North East Alberta, Canada

R. S. Strobl, M. Attalla, L. P. Yuan, D. Cotterill, S. Lorimer, J. Stevens

Reservoir characterization based on drill hole information alone is commonly limited to broadly defined flow units and best guess estimates of the geometries of key lithofacies. Reservoirs consisting of fluvial and estuarine successions are particularly challenging to characterize due to lithofacies changes over short distances. Reservoir simulations based on a preliminary geological model are likely to result in significant errors and a poor production history match.

The Alberta Oil Sands Technology and Research Authority's Underground Test Facility provides a prime opportunity to characterize an estuarine channel reservoir on both a pool and interwell scale. Core holes spaced 50 m to 80 m apart, with detailed dipmeter interpretation, combined with core and outcrop examination, provide the level of confidence needed to produce a quantitative geologic model. In this example the outcrop analogue is virtually identical to the reservoir. Distinctive lithologies, lithofacies relationships, and consistent dipmeter responses support the correlation from outcrop to in situ.

Three major units are recognized for the reservoir: trough cross beds, a transition zone and continuous heterolithic dipping beds (lateral accretion) associated with the lower, middle and upper units, respectively. The model accurately predicts the geometries of each flow unit and estimates the lateral extent of heterogeneities such as mudstone beds and clast zones. The lateral accretion beds are especially problematic because of an associated three order magnitude reduction in vertical permeability and difficulty in representing dipping surfaces in the simulator. A variable depth-variable thickness simulation model is proposed and tested.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994