Permeability Heterogeneity in Bioturbated Sediment, Cardium Formation, Pembina Field, and Implications for Waterflooding of Tight Oil Reservoirs

Abstract

Bioturbated sediments representing distal expressions of paralic depositional environments are increasingly being exploited for oil in the supergiant Cardium Formation reservoir, Pembina Field, Alberta, Canada. These sedimentary strata were previously considered unproductive due to the limited vertical and horizontal connectivity between permeable beds. In these “tight oil” plays (0.1 – 10 md), sand-filled burrows connect bioturbated and parallel laminated sandstone beds creating hydrocarbon migration pathways exploitable via horizontal drilling and multi-stage fracking. As the exploitation of bioturbated strata progresses, waterflooding is being considered, although the response to enhanced oil recovery schemes in unconventional plays is limited. To assess the viability of waterflooding the bioturbated strata of the Cardium Formation, a regional-scale core-based study was undertaken. Thirty-eight cores were logged and seven lithofacies identified, including four bioturbated facies that range from 5–75% total sandstone and siltstone content. An additional 629 Pressure Decay Profile Permeametry (microperm) measurements were acquired from three of the bioturbated facies in eleven wells distributed throughout the study area. Microperm values enable correlation of bulk permeability from plugs and full diameter samples to the heterogeneous permeability distributions in intensely bioturbated strata. Bulk and microperm permeability data are graphically compared, and permeability distributions are mapped across the field. Using isopach thicknesses of bioturbated facies, production data, and permeability data, “sweet spots” are identified for placement of effective waterfloods. Production information for recently drilled horizontal wells in the Pembina field demonstrate that bioturbated muddy sandstones and sandy mudstones in paralic environments can be economically exploited when sand-filled burrows provide connectivity between sand beds. However, well performance within these poorly understood unconventional tight oil plays can better be predicted with an in depth characterization of their facies and complex permeability heterogeneities. Based on our results, it is clear that micropermeability analysis can be effectively employed to differentiate between economic and sub-economic plays, identify areas with high effective permeability, and to high-grade areas for enhanced oil recovery schemes.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015