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Pebble Creek Geothermal Prospect(North Meager Greek Reservoir)
The youngest (and therefore hottest) volcanic centre in Canada is located in the Pebble Creek area, where shallow and medium range have proved presence of a high-temperature geothermal resource. Eight temperature gradient holes drilled (by B.C. Hydro in late 1970's) to a maximum depth of 1297m show a high regional gradient of about 80 to 100 C/km. This suggests that a commercially viable geothermal reservoir can be located at a maximum depth of about 2500m, which is within the range of most developed commercial geothermal power fields around the world. After B.C. Hydro returning the prospect to the Province, Andrew E. Nevin acquired (in 1992) a geothermal permit on the Pebble Creek Prospect (also known as the North Meager Creak Reservoir or simply North Reservoir). With financial assistance of California Energy Commission, Nevin conducted a feasibility study of the site (Nevin, 1993). A low energy market and lack of real incentive for renewable energy, on the part of government, led Nevin to end his activities on the site. The project thus went to hibernation before coming back to life in 2002 due to increasing energy prices and rising interest in renewable and environmentally sounds energy alternatives. In February 2002, Gaea Energy Enterprises was granted two geothermal permits on the site. The permits cover the entire North Reservoir prospect, plus new prospects towards the east in the Lillooet Valley (Fig. 1) Gaea acquired another geothermal permit in 2004 to cover the entire north and northeast side of the Meager Creek geothermal complex (Fig. 1). Gaea has compiled all the existing information and has prepared a geothermal conceptual model for the site. Gaea plans to complete the previous investigations by drilling one to two more core holes and one to two deep production-size holes to confirm and test the productivity of the reservoir. Back to Top2. Geology and resource summaryHigh-temperature geothermal resources around the world are associated with quaternary volcanoes where high-level magma chambers under the volcanoes provide heat to the rock to create and maintain steam and hot water reservoirs. The Mount Meager volcanic complex lies near the northern end of geologically recent (quaternary) volcanoes called "the Garibaldi Volcanic Belt" in Canada and "the Cascade Volcanic Belt" in the United States. The "Pebble Creek (North Reservoir)" and the "South Meager Creek" geothermal prospects are located on opposite flanks of the Mount Meager volcanic belt. Vocanological dating studies in the Meager Creek Complex shows that the volcanoes become younger going from south towards the north, with the youngest volcano being located in the Pebble Creek (Gaea) Prospect. This means that the Pebble Creek area is less cooled and therefore hosts the main heat source in the Meager Creek area. This is further evidenced by surface manifestations of an active hydrogen sulphide gas vent in the headwaters of Job Creek and Sodium-bicarbonate hot springs (Pebble Creek hot springs in the Lillooet River Valley). Hydro-geochemical data from the Pebble Creek hot springs and exploration wells suggest the presence of steam-heated water reservoirs at relatively shallow depth - phenomena occurring in high-temperate geothermal fields. Down-hole temperature surveys (Figs. 2 , 3, 4, and 5) indicate presence of a relatively shallower geothermal reservoir, resulting from an upflow of geothermal fluids in permeable zones. This is especially evidenced by a remarkably high convective geothermal gradient of about 210 C/km observed in the hole L1 (Fig. 3). A conservative, yet consistent, geothermal gradient, which can be depicted from all temperature gradient holes (Figs. 2, and 3), is 80 C/km (i.e. 47 F/1000 ft). This means that, in the worse case scenario, a commercially viable reservoir (for single flash power generation) of 230 C can be intersected at depth 2900m (9400 ft). Adjacent high-country of the Meager Complex (some 2400 m relief; Figs. 1,2 and 5) provides for a powerful hydraulic head on the ground water, which in turn will pressure the underlying geothermal system towards the valleys (Meager Creek in the South and Lillooet River Valley in the Pebble Creek area). This is manifested in the Meager Creek and Pebble Creek hot springs ( Fig. 4). In summary, based on existing data, a geothermal reservoir in the Pebble Creek area should be located at depth less than 2900 m (most likely less than 2500 m). In the Pebble Creek area, highly fractured rocks (in connection with brittle Miocene stocks and brecciated volcanic vents) are expected to provide enough permeability to sustain fluid into the geothermal production wells. Pebble Creek Geothermal Prospect compares well with many successfully developed geothermal prospects around the world. Coso geothermal development in California (with 300 MW electric power capacity) is one example with geological, geochemical and geophysical features similar to Pebble Creek.. Back to Top3. Description of works completedPast works include 9 "slim holes" to a maximum depth of 1280 m (4,200 ft), geological
mapping, several geophysical surveys (heat flow, temperature gradient, electrical resistivity, self potential
and refraction seismic), major ions and stable isotope geochemistry. The data support presence of a significant high-temperature geothermal reservoir in the Pebble Creek area. A model constructed based on the field information (Figs. 4 and 5) indicate that the core of the Meager Creek geothermal system is in the
North side (i.e. at the Pebble Creek). Considering that Pebble Creek geothermal prospect had been dormant for almost a decade, the first and most imperative task carried out by Gaea Energy was data gathering and processing. Gaea has successfully prepared a comprehensive archive of Maps, reports, aerial photos, pictures, anecdotal information and published articles related to the Pebble Creek Geothermal Prospect. Gaea has also conducted recent field investigations to help with processing and modeling of the data. During the fieldwork, old geological maps were revisited, reported cartographic information was verified (or corrected when needed), and especially the location of old boreholes were inspected and plotted on new site maps. Back to Top4.1 Magneto-telluric (MT) survey Existing resistivity and borehole data suggest the presence of a relatively shallow geothermal reservoir in the area between L1 and Pebble Creek hot springs (Figs. 2, 3 and 4). Deep seeing MT is planned to be carried out in this area to cast light on the spread and extent of the anomaly. The work is expected to be carried out in the fall and winter of 2004. The cost of this survey is estimated at $100,000 to 150,000. 4.2 core drilling and well testing Preliminary plans for drilling one to two additional core holes (4.5" diameter) to a depth of 1200 m have been worked out. The wells will be spread between the existing borehole L1 and the Pebble Creek Hot springs. Final decisions on the exact location of the planned holes and the design of the wells are in progress. The wells are intended to provide: 1- Complementary temperature data needed to fine-tune the sub-surface temperature model. 2- Provide more information on the lithology of the reservoir and the nature of its hydraulic conductivity. 3- Provide hydro-geochemical data to predict the extent and chemistry of the geothermal fluids and calculate the reservoir temperature. 4 - Provide data on the reservoir productivity through injectivity tests After fine-tuning of the plan, Gaea intends to acquire a permit for a production-size drilling on site. The cost of core holes and associated engineering works are estimated at 1 to 1.5 million dollars. 4.3 Confirmatory rotary drilling Based on the temperature model acquired from processed borehole, geochemical and geophysical data, presence of a high-temperature geothermal reservoir at a depth of 1800 to 2500 m proves to be likely. Planned core holes will further cast light on the extent of the reservoir. In addition at least one or two deep confirmatory production-size rotary holes will be needed to fully confirm and evaluate the commercial value of the reservoir. The deep rotary hole(s) and related well testing serve two goals: 1- commercial evaluation of the reservoir and 2- test the production and fine-tune the power plant design The cost of the confirmatory rotary hole(s) and associated reservoir engineering work is estimated at 5 to 8 million dollars. The total costs of resource confirmation are therefore estimated at 7 to 10 million dollars. Back to Top5. Development objectives, costs and marketExisting data provide strong evidence for presence of a substantial geothermal reservoir at depth less than 2500m. The evidenced reservoir has a high likelihood to support production of several hundred megawatts of electricity, at full-scale development. By comparisons to similar geothermal sites in the same coastal range in US (e.g Coso, California), the present day cost of development will be between $1500 to 2500 per kilowatt installed (i.e.150 to 250 million dollars for 100 megawatts). Cash flow analysis, conducted for a feasibility study, show that the resource can potentially produce electricity at a cost of less than 5 cents per kilowatt-hour. This includes all costs related to capital investment (drilling, power plant and connection to the Grid), amortized over 25 years, and operating costs. Present B.C. market for electricity makes the resource a commercially viable alternative to conventional power generation schemes (e.g. hydro and gas). Green bonus further adds to the value of the resource. A wholesale power price of C$70 per megawatt-hour (equivalent to 7 cents per kWh) is representative of prices currently being offered by BC Hydro under the Renewables Certificate program. This power price is projected to escalate at the rate of inflation (2.5% per annum). Once the resource confirmed, a long-term power purchase agreement with B.C. Hydro will practically guarantee the financing of the power project. Power sales can also be negotiated with large industrial power consumers or utilities in US. For these possibilities, The generated power will be wheeled through the transmission systems of the BC Transmission Corp. (BCTC). Based on a 2003 cash flow analysis, the net benefit of the project for an initial 100 MW development can be 15 to 35 million Cdn$ per year. As for an ultimate full-scale development of 300 MW, the net benefit can reach 100 million Cds$ per year. Back to TopGaea Energy Enterprises Ltd. Dr. Mory M. Ghomshei, P.Eng., P.Geo. Director and Project Engineer July 4, 2004 |
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