Geothermal for Electricity Generation in Alberta
The heat energy contained in the upper 10 km of the earth's crust has been conservatively estimated to be 292 times greater that the energy contained all of the world's fossil fuel resources combined.
The heat energy present in the Western Canada Sedimentary Basin (WCSB) was estimated to be 3 orders of magnitude larger that the energy contained in Canada's conventional oil and gas (O&G) reserves.
Geothermal (GT) systems can be classified in:
Hot Dry Rock - Hot dry rock
refers to solid rock at a very high temperature. Hot Dry Rock reservoirs have not
yet been found in
Dry Steam Resources - These
reservoirs consist of steam contained under pressure in porous rock formations.
Dry steam reservoirs have not yet been found in
- Hot Water Resources - Water in these reservoirs is generally above 180° C, and in the surface, the water to evaporate into steam.
- Warm Water Resources - Warm water reservoirs range from 50° C to approximately 180° C. The most extensive warm water reservoirs are located in large sedimentary basins such as the WCSB.
- Low Temperature Resources - At shallow depth, saline aquifers and fresh ground water between 10 and 50°C can be used by ground heat pumps for space heating and cooling.
In AB, the overall GT gradients
were found to be similar to values found in other parts of the world, the world
average being 26°C per kilometre of depth. High gradient areas were determined
in four general locations: the Hinton and Edson region, the
- The source has enough heat for use as steam to impulse a turbine to produce electricity.
- The potential use in Alberta is around the Rocky Mountain, but this mountain range is a very old geological formation and they don't have enough heat in the rocks.
- There is some hot spring born of a more recent geological formation but they don’t have enough enthalpy and temperature for electricity generation.
- On the south of BC there is a potential use; the estimation cost reported for the Canadian Geothermal Energy Association (CanGEA) are:
§ Capital Cost around 3,000 $/kW
§ COE: around 12 c$/kWh
The best GT reservoirs in Alberta are toward the west where the sedimentary basin thickens buried between 2 and 3.5 km below the surface. In these formations water temperature is expected to be between 70° C and 150° C. The temperature gradient was estimated at to be 36°C per km. Energy production estimates calculated for 5 wells provided the following range of values:
- Average heat extraction rate: from 16 kW to 22 kW
- Maximum heat extraction rate: from 1.8 MW to 18.6 MW
- The source doesn't have enough heat for use it as steam; a heat exchanger it is necessary to produce steam taking the heat of the source.
- The process is expensive to produce electricity due to the huge capital cost for well perforation.
- The system efficiency to produce electricity is low, between 5% and 15%
Alberta has a potential use, economically and technically possible because it is possible to avoid the capital cost associated with well perforation, in at least two areas:
- With the O&G industry operating O&G fields.
- With the O&G industry in abandoned O&G wells.
In the WCSB, over 200,000 wells have already been drilled for the purpose of exploiting its O&G resources. A significant number of these wells already produce undesired but warm water; then, the well and gathering pipeline infrastructure required for GT exploitation already exists in the WCSB.
Water production from oil pools in Alberta is approximately 1,500,000 m3/day. The temperature range is from 21° C to 113° C, however to produce water with temperatures less than 40° C is assumed having a little useful value. Therefore, 496 Alberta oil pools currently produce to the surface water with an estimated temperature above 40° C and, in total, account for 68,800 GJ per day of potentially useful GT energy; this is from 40 to 120 MW of electricity generation capacity.
GT energy can be converted to electrical energy using typical binary skid mounted plants over in production oil wells. The requirements are temperature and water rate of 80° C and 5,000 m3 per day respectively. Each 5,000 m3 of water at 150 ºC can produce 1.5 MW of electricity, but at 100 ºC can produce 0.5 MW. Eight oil pools exhibit a potential for electrical energy, with a 27 MW of electrical power generation. The top oil pools with GT potential are located northwest of Edmonton in a region that includes cities such as Grande Prairie, Valleyview and Swan Hills.
Alberta has around 100,000 abandoned wells as potential use due to the O&G industry. The potential electricity generation is around 200 MW.
There are several alternatives to produce power associated with the O&G industry, such as:
- Downhole Separation with GT Energy Recovery: Steamed Assisted Gravity Drainage and Cyclic Steam Stimulation involve the injection of high temperature steam into in situ reservoirs in order to heat the bitumen and reduce its viscosity. These methods use hot water which could also be used to produce electricity using conventional GT technology. The electricity production is around 0.00013 MW per day per oil bitumen barrel.
- GT with CO2 Sequestration: the O&G reservoirs have a strong potential for CO2 disposal. The combination between CO2 storage, recovery oil enhanced and power generation extend the reservoir exploitation.
- Associated with abandoned wells:
§ Eliminate Energy Input to Pressurize Binary Fluid: as a geothermal for housing but with huge transport of energy in association with producer wells.
§ Transferring the GT Source Fluid: idem but with abandoned wells and without secondary fluid pressurisation.
The GHG emission intensity in Alberta is today around 846 gCO2e/kWh. With each 100 MW of Geothermal Power Plant added to the Alberta Electricity system, this intensity could be reduced in around 1.2% or 0.72 tCO2e/y.
Generally, moderate temperature GT projects are not economical because of the high costs associated with drilling of the wells required to source and dispose of GT waters. However, in the WCSB, over 200,000 wells have already been drilled for the purpose of exploiting its O&G resources. A significant number of these wells already produce undesired but warm produced water and the wells and gathering pipeline infrastructure required for GT exploitation already exists in the WCSB.
GT opportunities from warm produced water that is already flowing to the surface as a result of existing O&G operations exist in the area northwest of Edmonton between Swan Hills and Grande Prairie. This is a regional opportunity for the development of renewable energy using existing infrastructure.
The total capacity of Power Generation in AB by GT
associated to O&G industry in under study and estimation. If
- 230 MW associated with bitumen.
- 120 MW associated with secondary oil production.
- From 100 to 250 MW associated with abandoned wells.
The potential GHG emission reduction evolves of 846 to 784 grCO2/kWh of intensity or 7.3%. In absolute value means 4.3 tCO2e/y.
There is still not cost electricity evaluation, however the first two options appears as very competitive because of the low capital cost needed and the low business risk associated to the projects.
- “An Exploratory Study – Low Carbon Futures”, March 2007, Petroleum Technology Alliance Canada (PTAC)
- Personal Communication with Mr. Bruce Peachey, who share the redaction of the before report.
- “High Enthalpy Geothermal Resources Potential”, December 2007, 2nd National GeoExchange Business & Policy Forum, Craig Dunn, CanGEA.