EGS technologies can function as baseload resources that produce power 24 hours a day. Unlike hydrothermal, EGS may be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a 3–5 kilometres (1.9–3.1 mi) layer of insulating sediments that slow heat loss. At this depth, what's the typical reservoir conditions (temperature and pressure) of enhanced geothermal systems?
FYI:
The geothermal gradient (temperature rise with depth) of HDR resource typically ranges between 10 and 100 °C/km. In the continental US within the depth of 10 km, more than 99% of the geothermal energy is contained in hot rocks. Aiming at HDR resource to the depths of 10 km, the geofluid temperatures are 100–800 °C, thus having a very high power generation potential that increases with depth.
cited from 2014 Comparative Analysis of Power Plant Options for Enhanced Geothermal Systems (EGS)
Soultz is a multiple well fracture system in granite and one of the most important European research sites on EGS, where research and measurements have been conducted over the
past 20 years. Two reservoirs have been created in granite, at 3.5km and 5km vertical depths. The successful long term circulation test of the reservoir at 3.5km was followed by drilling a deeper reservoir at 5km. The reservoir at 5km has temperature around 200℃ and consists of three wells, one production well and two injection wells. Temperatures at 5km have been calculated based on conditions at 800m deep boreholes, see fig.1 (2011 Engineered Geothermal Systems.jpg). The majority of the sites were in the range of 100 to 200 ℃, which can be classified as medium temperature fields.
Cited from 2011 Engineered Geothermal Systems
Figure 2 (Physical data from six EGS reservoirs) may also be useful.
cited from Fluid-rock interaction studies on an enhanced geothermal system in the cooper basin, south Australia
Hi,
The general formula to calculate the temperature in geothermal environment is Q=K(ΔT/ΔZ) and according the calculations, in average the geothermal gradient is 30 ˚C in 1 Km. So 150 ˚C is possible for your case.
In case of Pressure we must consider several factors. The lithology and the density of rocks in the stratigraphic column is important. The role of reservoir fluids and gas content of reservoir should be noted. Of course the tectonic setting of EGS is important. According P-T diagrams we can imagine at least 170 MPa pressure for 3-5 Km depth.
Cheers,
Are you looking at Australia or in general on existing EGS reservoirs?
This really depends on heat flow. In areas with very low heat flow (for example in cratons - which may be a problem over a large portion of Australia), you have gradients of 20°C/km or even less, so you would have to drill to 10 km and I can't see how this could be feasible for electricity generation, even if there is high heat productivity in the basement.
For conditions in current EGS - now that's a good question! This changes every year with technological advances, so I would look at some most recent review papers (here is one from 2016 Article Enhanced geothermal systems (EGS): A review
) and go through abstracts of the World Geothermal Congress 2015 Melbourne or Stanford Geothermal Workshop 2017 for the most up-to date information.- Badges
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- Thermodynamics
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