Petrophysical Characterization of Bitumen-Saturated Karsted Carbonates: Case Study of the Multibillion Barrel Upper Devonian Grosmont Formation, Northern Alberta, Canada
- Alex J. MacNeil (Osum Oil Sands)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- December 2015
- Document Type
- Journal Paper
- 592 - 614
- 2015. Society of Petrophysicists & Well Log Analysts
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- 249 since 2007
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The Grosmont Formation in northern Alberta contains the largest carbonate-hosted bitumen deposit in the world. Reservoir quality is directly tied to karst overprint; multiple pore types, fractures, sinkholes, and other karst features are present. Significant effort is underway to establish commercial development and petrophysical evaluation of reservoir properties is critical. There are virtually no studies that document the petrophysical characterization of bitumen-saturated carbonates. It is found that the physical properties of bitumen have positive and negative impacts on the petrophysical techniques routinely used for carbonate reservoir characterization.
Accurate characterization of porosity relies on a high-resolution stratigraphic framework, the integration of core with different types of wireline log data, and a conceptual understanding of how features specific to karsted reservoirs may be expressed in the near-wellbore region. A simple approach restricted to porosity log interpretation accurately characterizes the reservoir facies but misses detection of “high-flow zones” that represent thin (typically 10 to 30 cm) zones of high porosity (up to 100%) and potentially 100s to 1000s of Darcies permeability that are major controls on flow. These zones cannot be detected downhole with conventional production logging techniques because the bitumen is essentially immobile. Water saturation is best characterized with an Archie equation that relies on modified cementation and saturation exponents when saturations measured from core are available to constrain the results. Advanced tools, including the multifrequency dielectric and magnetic resonance imaging tools, can also provide accurate results when their limitations are understood. It is found that when resistivity is measured with the correct type of logging tool, and core is available to constrain results, standard techniques for reservoir characterization can be applied to bitumen-saturated carbonates.
|File Size||59 MB||Number of Pages||23|