Digging Deep: Reading the Rocks that Host Natural Gas in British Columbia
Sedimentological and stratigraphic studies in the Western Canadian Sedimentary Basin
By: Carlos Salas, Executive Vice President & Chief Scientific Officer
BC's portion of the Western Canadian Sedimentary Basin (WCSB), includes the Montney Play, which contains some of North America’s most significant natural gas deposits. Several Geoscience BC energy research projects provide valuable public information that build understanding of the area’s sedimentology, stratigraphy and natural gas potential.
The Western Canadian Sedimentary Basin (WCSB) is a collection of sediments spanning 600 million years deposited on the western margin of the North American craton. It is more than six kilometres thick at its deepest point and underlies more than 1.4 million km2 of British Columbia, Alberta and Saskatchewan.
The Middle Triassic Period (~247-252 million years before present) marks a period when deep-water deposition of silts created the Montney Formation, hosting one of the most important unconventional gas plays of North America with estimated reserves of 449 TCF marketable gas, 14,521 MBBO of natural gas liquids and 1,125 MMB of oil (National Energy Board, 2013).
Economic extraction of these multi-phase, low permeability, low porosity and overpressured reservoirs necessitates a myriad of multi-disciplinary research. Understanding the stratigraphy and sedimentology is a critical first step in the assessment of an unconventional play.
Geoscience BC has supported several sedimentological and stratigraphic studies in BC's Northeast Region.
Evidence of Complex Sedimentation
Starting in 2008, the project Biostratigraphic and Sedimentological Studies of Natural Gas-Bearing Triassic Strata in the Halfway River Map Area, NE British Columbia analyzed surface and subsurface rock samples of Triassic age, including samples from the Doig and Montney formations.
A research team led by Dr. James Mortensen at the University of British Columbia dated detrital zircons to age the source rocks, analyzed fossil populations and lithological characteristics to understand depositional setting, and mapped facies distribution.
Within this research team, PhD student Martyn Golding examined the age and tectonic setting of the Doig and Montney formations using fossil conodonts and detrital zircon geochronology. His Biostratigraphy and sedimentology of Triassic Hydrocarbon-bearing Rocks in Northeastern British Columbia thesis published in 2014 identified new fossil species and expanded on our stratigraphic knowledge of the formations.
In a 2011 Summary of Activities paper, Golding et al. concluded the research by saying: "All of this indicates a more complex pattern of sedimentation in the WCSB during the Triassic than has previously been assumed, it is not just a simple case of sediment being deposited from the east to the west. This has implications both for sedimentological analysis of the natural gas-bearing Montney and Doig formations, as well as for the tracing of facies within the basin."
In order to better understand facies distribution and their interrelationships with reservoir development, researchers from the University of Calgary the conducted a field study Upper Paleozoic to Lowest Triassic Succession - Sukunka-Kakwa Area, BC project. It looked at outcrops in the foothills belt and available subsurface information in the Kakwa-Sukunka area to generate a predictive model for known and potential reservoir intervals in Upper Paleozoic strata of the WCSB.
The results, as described in this paper, incorporated the complex structural history, providing an all-encompassing story on the deposition, diagenesis, migration history, and fracture distribution of the rocks.
An ongoing Ph.D. study by P.D. Gonzalez, supported by Geoscience BC – Sedimentology, Chemostratigraphy and Stratigraphic Architecture of the Lower Triassic Montney Formation in the Western Canada Sedimentary Basin, British Columbia – focuses on the integration of chemostratigraphy, sedimentology, ichnology and detailed allostratigraphy within the Montney Formation in northeastern BC.
The 2019 project update (Gonzalez et al. 2019) discussed data from 38 drillcores, wireline data and 56 thin-section samples covering several important rock units. Analysis so far supports previous studies, suggesting the Montney Formation was deposited along a storm-dominated, mixed carbonate-siliciclastic ramp setting, between the offshore and shoreface depositional environments, intermittently influenced by upwelling processes. This contributes to our understanding of the sedimentology of the Montney Formation, and the complex allostratigraphy, all which effect reservoir development , and the implications for gas hosting.
What's Controlling Reservoir Quality?
These detailed sedimentological and stratigraphic analyses are key to understanding the complex internal architecture of the Montney Formation and the facies and ichnofacies-related variables controlling reservoir quality. The projects provide public information that improves our collective level of geoscience knowledge, identifies new potential resource opportunities and helps companies optimize development strategies.