Production-Induced Water Migration into Gas Pools Overlying the Athabasca Oil Sands, McMurray Formation, Alberta: Implications for Steam-Assisted Gravity Drainage (SAGD) Production

Edward L. Etris
Core Laboratories, Calgary, AB

Subsurface exploitation of the oil sands in Alberta, Canada, is expanding dramatically as in-situ recovery processes such as Steam Assisted Gravity Drainage (SAGD) are applied to this multi-trillion barrel resource. The best areas for thermal recovery are those that contain bitumen deposits capped by impermeable sediments that act as a vertical barrier to steam. Less desirable are areas where bitumen is overlain by gas intervals or—worse yet—water intervals that are in direct communication with the bitumen in the same reservoir zone: so-called “thief” zones because they “rob” steam chambers of their effectiveness in mobilizing bitumen. It is well known that such situations occur in the Athabasca oil sands, but it is commonly assumed that the presence or absence of so-called “top water” (water above bitumen) remains a stable dichotomy over the timeframe of production of gas pools above bitumen.

A recent study, however, has uncovered a case where top water was not present at the time of discovery of a gas pool in the Athabasca oil sands, but has migrated in below the gas, emplacing water above a thick bitumen zone attractive to SAGD development, thus decreasing its attractiveness. Recognition of this production-induced migration required careful, detailed log evaluation, knowledge of the unusual aspects of the sediments of the McMurray Formation, and ordering of the wells by drilling sequence (dates) during log correlation, generating a new kind of “chronostratigraphic” section, which will be described in detail. Such situations may be more common than previously thought.

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