Overview of a Steam-Assisted Gravity Drainage (SAGD) Reservoir Characterization Strategy for Horizontal Well Placement and Ranking Within the Surmont Lease, McMurray Oil Sands, Alberta

David Garner¹, Thomas J. Wheeler¹, Emmanuel Mus², and Jean-François Richy^2
1 ConocoPhillips Canada, Calgary, AB
² Total, seconded to ConocoPhillips Canada, Calgary, Canada,

The McMurray formation is a highly heterogeneous Cretaceous clastic reservoir with thick, bitumen-saturated sands. We applied a detailed quantitative workflow for integrating multi-scale data, building a geological model and managing uncertainties associated with planning and controlling a steam chamber for SAGD bitumen extraction. Our main goals in this study were to aid and improve the complex decision making for vertical placement of horizontal wells, for optimizing expected performance, and for ranking of the horizontal well pairs.

Let us consider that the SAGD wells can be studied as individual reservoirs, with a drainage volume surrounding each well pair. There is a line of sight (LOS) along the length of the horizontal path or vertical plane, and a width. Using the drainage volume and LOS we calculated parameters such as effective well length, net-to-gross, facies proportions, producible volumes, and a vertical discount factor on stranded volumes for each model realization. A comparison was made to the purely deterministic geological approach.

The evaluation focused on the uncertainties in the estimated or simulated reservoir parameters. To decide on placement, post-processing of the detailed geostatistical simulations provided uncertainty measures on the reservoir parameters as a function of elevation. A probabilistic model was used to simulate well pair performance and rank the well slots. The model used well placements, extracted reservoir parameter distributions, SAGD operating conditions, and Butler theory in a Monte Carlo framework.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005