Characterization of the Grosmont Formation: A Carbonate Bitumen Reservoir

The Upper Devonian Grosmont Formation hosts an estimated 406 billion barrels of bitumen. This carbonate platform was dolomitized, fractured during burial and exhumation, then intensely altered by meteoric diagenesis. Oil migration occurred soon after porosity enhancement, which slowed or stopped further alteration of the mineralogy and pore space. Our study area of 35 km2 includes a high-resolution seismic volume and 18 delineation wells with a full suite of logs and core. The ultimate economic objectives of the study are to identify porous strata and select the optimal thermal process for development.

The Grosmont has been interpreted as a shallowing-up carbonate sequence with multiple parasequence sets. Progradation of the gently-dipping carbonate platform resulted in wide bands of laterally-consistent sediments. Meteoric dissolution has preferentially enhanced permeable strata and the resulting flow units are easily mappable over the full study area. Depositional and diagenetic facies have been tied to the acoustic impedance volume derived from seismic inversion, which in the Grosmont carbonates is primarily modulated by porosity.

Common vertical to sub-vertical bitumen-filled fractures observed in the resistivity image logs and in the core of the vertical delineation wells suggest that these fractures are ubiquitous and vertical permeability is high. To estimate the fracture density and orientation, azimuthal AVO and velocity variations were estimated in the compressional wave seismic. This has identified zones of higher fracture density that will be tested by wells in 2012. The high vertical permeability combined with the laterally-predictable flow units makes this an ideal reservoir for steam assisted gravity drainage (SAGD). This technique is currently being piloted in a joint project by Osum Oil Sands Corp. and Laricina Energy Ltd.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California