Hydrodynamic Model for Pervasive Biogenic Gas Trapped in Low Permeability Sands - Western Plains of North America

Rakhit, Kaush and David Hume
Rakhit Petroleum Consulting Ltd, Calgary, AB

Pervasive Shallow Biogenic Gas Systems (PSBG) are becoming an increasingly important unconventional gas resource in the Western Plains and Rocky Mountain regions of North America. The resource has often been bypassed due to drilling fluid invasion, high water saturation, fresh formation waters and formation damage. In concert these issues have tended to reduce the reliability of conventional petrophysical analysis, testing and completion techniques. 

PSBG is most commonly hosted in Upper Cretaceous and Tertiary Clastic reservoirs generally at depths of less than 1,000 m (3,300 ft.). The signature trademark of the play is its broad areal extent and sub-normal formation pressures (25-75% of hydrostatic). Subnormally pressured PSBG systems often transition updip into normally pressured water wet systems. Downdip water flow is frequently observed in these systems which may aid in trapping and provide the potential for water imbibition.

A series of case studies from Western Canada will be presented as a means of characterizing the PSBG resource. Extending the play into new areas requires the integration of detailed stratigraphic analysis with hydrodynamic, petrophysical and basin evolution modeling.