1
background
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
2
Geothermal for Electricity – Hot Water
Resources
-
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
3
Geothermal for Electricity – Warm water resources
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
However:
-
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.
3.1
Potential use in O&G industry operating oil and gas
fields
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.
3.2
Potential use in O&G industry in abandoned wells
Alberta has around 100,000
abandoned wells as potential use due to the O&G industry. The potential
electricity generation is around 200 MW.
3.3
Potential use in O&G industry - Other potentials
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.
4
Greenhouse gas emission intensity in Alberta
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.
5
CONCLUSIONS
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.