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Characterization of the Geothermal Resource at Clarke Lake Field Northeast British Columbia
- Author / Creator
- Renaud, Evan
Clarke Lake is a depleted gas fi eld developed in carbonate platform deposits of the Slave Point
Formation (Middle Devonian) in northeastern British Columbia, Canada. It displays anomalously high reservoir temperature and strong water drive, making it a candidate for repurposing as a
source of geothermal power. Porous and permeable reservoir near the platform margin developed
through the hydrothermal alteration of host limestone to dolomite. A geothermal resource requires
permeable reservoir rock that allows for fl ow rates that can sustain economic electricity generation. A depositional model in provides a basis for mapping the dolomite reservoir, and thus, permeability. Porosity and permeability measurements can be incorporated in a comprehensive suite
of fl ow simulations to test how reinjected water affects geothermal power production.
Nine depositional facies and two diagenetic facies are identifi ed, the former based on bioclast
assemblages, rock types, texture and composition and the latter based on rock fabric and the
degree of alteration to dolomite. Deposition of these facies occurred within lagoonal, reef-fl at and
foreslope settings associated with a rimmed carbonate platform. Dolomitized lagoon, reef fl at,
reef margin and shoal lithologies show enhanced porosity and permeability due to dissolution of
stromatoporoid bioclasts, forming mouldic and vuggy porosity. Diagenetic facies show high permeability but reduced porosity as a result of precipitation of porosity-occluding dolomite, fl uorite,
and sulphide minerals. High quality reservoir zones occur primarily at the reef margin, caused by
fabric-selective hydrothermal alteration of carbonate sediments near the contact with shales of the
Horn River and Muskwa formations.
Correlation of core descriptions and wireline log data allow the Slave Point Formation to be separated into successions that infl uenced dolomitization: an initial shoal unit, S1, three subsequent
reef units, R1, R2, R3, and terminal shoal units of D1, D2 and D3. Shoal units were deposited in
the transgressive systems tracts, whereas reef growth units were deposited in the highstand systems tracts. An initial transgression deposited shoals of the S1 unit across the carbonate platform.
As the rate of relative sea level rise waned, a well-defi ned reef margin developed at the platform
edge, which infl uenced depositional energy across the platform top and allowed deposition of
reef units (R1, R2, and R3). A subsequent transgression began to drown the reef, during which
spatially restricted shoals, D1, D2 and D3, were deposited near the reef margin before the rate of
relative sea level rise outpaced the rate of deposition.
We assessed the viability of geothermal energy production by simulating the water temperatures
in production scenarios that use different operation conditions, well confi gurations and grid sizes,
and by applying a Monte Carlo approach to different porosity and permeability realizations. Both
an injection-production well doublet and an array of 4 injection and 8 production wells were simulated. Temperature drops at production wells result from a migration of an injected cold water
plume and are most strongly related to fl ow rate. Varying fl ow rates result in a temperature drop
that ranges from 0.47 to 5.6 °C. Simulations using progressively fi ner grids predict longer thermal breakthrough time compared to coarser grids, while coarser grids predict greater temperature
drops at the production well.
The impact of thermal breakthrough at a geothermal production well is a reduction of the power
potential. Reduced power potentials using doublet production-injection scenarios are 465 kWe at
25 kg/s fl ow rates and 930 kWe at 50 kg/s fl ow rates, compared to baseline results (that assume
no thermal breakthrough) of 511 kWe and 1036 kWe, respectively . The four injection-eight production well scenarios estimate a power production of 3456 kWe at 200 kg/s fl ow rates, compared
to a baseline result of 4085 kWe without thermal breakthrough.
- Subjects / Keywords
- Graduation date
- Fall 2020
- Type of Item
- Master of Science
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