Reservoir Quality and Continuity, and Secondary Recovery Potential of the Mississippian Pekisko Formation at Twining Field, South-Central Alberta, Canada

Erika M. Josson, Stacy C. Atchley, and Julia A. Kahmann
Baylor University, Waco, TX

Twining field, located in south-central Alberta, Canada, and discovered in 1951, produces from four pools within the Mississippian Rundle Group. Estimates of original in-place oil are 913 million barrels, with 46 million barrels identified by the Alberta Energy Utilities Board as recoverable (5% recovery factor). Cumulative production to date from the Rundle Group is only 31 million barrels (67% of recoverable reserves), but programs for secondary recovery are absent.

This study evaluates secondary recovery potential within the Pekisko Formation of the Rundle Group by evaluating the sequence stratigraphic controls on reservoir distribution and continuity within a 47 square mile portion of Twining Field. The Pekisko Formation at Twining is a highly stratified limestone that includes 9 shallowing-upward decameter-scale parasequence sets. Reservoir is preferentially associated with shoal-water ooid grainstones at the top of each parasequence set, whereas non-reservoir skeletal and peloid subtidal packstones generally occur at the base. The Pekisko is unconformably overlain by the Lower Cretaceous Mannville Group. Dramatic erosional relief (up to 60 meters) is present and the Pekisko is in places karst-modified beneath the unconformity surface. Reservoir flow units coincide with the distribution of shoal-water ooid grainstones within parasequence sets, and are correlated within and between erosional interfluves. Strategies for secondary recovery must match injector-producer pairs within parasequence sets to maintain reservoir pressure and insure maximum sweep efficiency. Secondary recovery within karst-modified reservoir should be avoided because of the increased likelihood that water will by recycled through high permeability fracture and solution channel pore networks.