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Liard Basin

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Location map of Liard Basin in the northwestern Western Canada Sedimentary Basin.

The Liard Basin lies between the Rocky Mountains to the south and the Mackenzie and Franklin Mountains to the north. The area includes the physiographic feature of the Liard Plateau and portions of the southernmost Mackenzie and Franklin Mountains. The basin constitutes the northernmost extension of the Western Canada Sedimentary Basin and in the Yukon the Liard Basin is approximately 8,000 km2 in area.

Depositional basement consists of the Neoproterozoic Pool Creek syenite and un-named Proterozoic siliciclastic and volcaniclastic sediments. These are unconformably overlain by a Cambrian through Middle Devonian sedimentary sequence consisting dominantly of continental shelf platformal limestones and dolostones which transition westward into marine shales and source rocks that correlate well with source rocks in the Western Canada Sedimentary Basin to the south. Locally within the carbonates are coarsely crystalline, diagenetic, hydrothermal dolomites termed the Manetoe facies. This diagenetic facies has primary and vuggy to cavernous porosity and is one of two principal reservoirs and targets for conventional natural gas prospects within the Liard Basin.

Conformably overlying the carbonates are fissile, grey to black marine shales of the Devonian to Carboniferous Besa River Formation, a generic historical unit that incorporated the distal basin equivalent shales of the Horn River Group and Fort Simpson, Kotcho, Exshaw, Banff, Prophet and Golata formations in Yukon and northeastern BC.  New electric log and cuttings analyses have facilitated differentiation of these individual shale units and the construction of a robust, basin-wide correlative framework across Yukon, BC and NWT. The Carboniferous Prophet Formation is the basinal equivalent of the platformal Pekisko to Debolt formations of the Rundle Group, and in Yukon is thick and limestone-prone. It represents the second principal reservoir for conventional natural gas prospects within Liard Basin.

The Liard Basin contains hydrocarbon bearing shales (source rocks) of Middle Devonian to Carboniferous age within: the Horn River Group (Evie, Otter Park and Muskwa formations), the middle unit of the Fort Simpson Formation, the Patry shale (Kotcho Formation basinal equivalent) and the Exshaw Formation. The current NEB resource assessment of Liard Basin recognizes two shale units as having the most potential for unconventional natural gas in Yukon’s Liard Basin: the Horn River shale and the Exshaw-Patry shale (NEB et al. in prep.). These shales are restricted marine source rocks that correlate well across the Western Canada Sedimentary Basin.

The Golata Formation overlies the Rundle Group carbonate/shale facies in the basin. In outcrop it is gradational with the Middle to Upper Mississippian Mattson formation, and is considered to be the distal basinal shale equivalent of the proximal Mattson Formation deltaic complex. The Mattson delta prograded to the west-southwest and contains friable and porous sandstones interbedded with siltstones, shales and minor chert, limestone and dolostone units.

Permian and Triassic strata consist dominantly of chert and shallow water shales and siltstones of the Fantasque and Toad-Grayling formations respectively. Cretaceous marine sandstones and shales unconformably overlie all other units in the map area. Structures within the Liard Basin are characterized by northwesterly to northeasterly trending box folds and east-verging and west-verging thrust faults. Topographic lows are typically underlain by synclines containing Triassic and Cretaceous siliclastic sedimentary rocks.

Liard Basin exploration history 
The first recorded evidence of active petroleum exploration was in 1955 with reconnaissance field work by California Standard, the predecessor to Chevron. The first well in the Yukon was SOBC Shell Beavercrow YT K-02 completed in 1963. A total of 13 wells have been completed in the Liard Basin in southeast Yukon. Approximately 570 line-kilometers of two-dimensional seismic has also been acquired by the industry.

The Yukon contains portions of three discovered gas fields: Beaver River Field, Kotaneelee Field, and La Biche Field. The Beaver River Field in Yukon is a former producer from well PanAm C-1 Beaver River YT G-01. Production from the Kotaneelee gas field is currently suspended. Both of these fields consist of pools and prospects hosted in fractured, diagenetic hydrothermal dolomites of the Manetoe facies within carbonates of the Middle Devonian Arnica, Landry and Nahanni formations. The gas is structurally trapped in closures formed by anticlines, normal faults, and reverse faults. Seal and source for the reservoirs is provided by shales of the Horn River Group. Commonly, gas is trapped on top of water.

The potential for unconventional exploration opportunities exists in the Liard Basin.  From 2009 to 2012, Apache Corporation drilled and validated a new unconventional Devonian age ‘Besa River’ shale gas play in the Liard Basin of northeastern BC with net estimated sales gas of 48 Tcf over an area of 175,000 ha. Apache’s D-34-K/94-O-5 well had a thirty-day initial production rate of 21 mmcf/d. More than 400 wells have been drilled in the northeastern portion of Liard Basin.

Exploration targets for Devonian shale gas in the Yukon’s portion of the Liard Basin have been identified by EFL Overseas Inc. at Kotaneelee and by Lone Pine Resources Inc. at Pointed Mountain, in the Northwest Territories.  To date, these unconventional reservoirs remain untested for their potential in the Yukon or Northwest Territories.

Liard Basin exploration play types
Five expected gas plays are identified in the Liard Basin area for conventional exploration opportunities. One play, the Manetoe facies dolomite, within the Nahanni Formation is established with proven discoveries and former production from the Beaver River gas field and Kotaneelee gas field (NEB 2001). This play is a sour, acid, 6-10% CO2, dry gas play and is considered the most significant one for the region. Established pool size distributions for the play type range between ~300 Bcf (at Pointed Mountain in southwest NWT) to ~200 Bcf (at Kotaneelee in southern Yukon, and at the Beaver River Gas Field that straddles the Yukon British Columbia border).

Unconventional play potential exists in a number of high quality source rocks within the Devonian-aged basinal shale succession: the Exshaw-Patry and Horn River shales. Although there has been no unconventional exploration drilling within the Yukon, core and cuttings samples and electric log signatures from wells that have drilled through these source rocks indicate that these unconventional reservoirs align very well with those drilled in the Liard Basin in northeastern British Columbia (e.g. Hutchison & Fraser 2016).

References
• NEB 2001. Petroleum resource assessment of the Liard Plateau, Yukon Territory, Canada. Oil & Gas Resources Branch, Department of Economic Development, Government of Yukon.
• NEB, BCOGC, BCMNGD, NWTGS & YGS in prep. The unconventional gas resources of Mississippian-Devonian shales in the Liard Basin of British Columbia, the Northwest Territories and Yukon. To be published March 2016.
• Hutchison, M. P. & Fraser, T. A. 2016. Frontier shale gas plays of Yukon’s Liard Basin, Canada. Presentation, Canadian Society of Petroleum Geologists GeoConvention 2016, 7-11 March 2016, Calgary, Canada.
• Ferri, F., McMechan, M. & Creaser, R. 2015. The Besa River Formation in Liard Basin, British Columbia. Oil & Gas Geoscience Reports, BC Ministry of Natural Gas Development, 1-27.