The Arrow Geothermal approach provides a dramatically more efficient energy transfer from a hot resource to the surface with very high formation contact and mass flow rate. Our technology combines several proven technologies from various energy recovery industries.
Hot Dry Rock - Abundant Energy That Is Different From Hydrothermal Energy
Hot Dry Rock (HDR) is an abundant source of geothermal energy available for use. A vast store of thermal energy is contained within hot – but essentially dry and impervious crystalline basement rocks found almost everywhere deep beneath the Earth's surface. The hot-dry-rock concept grew from ideas conceived in 1970 by a group of scientists and engineers at the Los Alamos National Laboratory. It was proposed as a method for exploiting the heat contained in those vast regions of the earth’s crust that contain no fluids in place—by far more widespread than natural geothermal resources (HDR represents over 99% of the total U. S. geothermal resource).
Although often confused with the small, already mostly commercialized traditional hydrothermal resource, HDR geothermal energy is completely different from hydrothermal energy. This geothermal gradient, which is the principal HDR resource variable, ranges from less than 50 °C/km to over 120+ °C/km, depending upon location. The US Department of Energy put out a study on Geothermal in the US entitled GeoVision. The conclusion Geovision estimates hot dry rock in the US could produce 5,157 GW of electricity capacity which is 5X current power consumption.
Arrow Geothermal recognizes the enormous potential for HDR. Water and permeability / porosity are not required and the resource is found around the world. For every traditional geothermal resource, there are between 10X – 100X the number of sites that have HDR. There are no technologies that are commercially available to economically exploit the energy in HDR.
Arrow Geothermal has the technology to become the first company to commercially deploy Enhanced Geothermal Systems (EGS) in HDR.
The Multiple-Transverse-Fracture Horizontal Well Concept
The vast amount of heat available for sustainable extraction from the Earth's crust requires an effective and efficient system of heat transfer from hot rock to the surface. To that end, the basic concept of heat transfer by circulating a working fluid through the rock using hydraulically connected injection and production wells was clearly articulated years ago but has not made an appreciable impact to date.
The multiple-transverse-fracture horizontal well (MTFHW) has been the subject of academic studies since the 1970s. The MTFHW has enabled commercial tight oil and shale gas production from very low permeability rock. Applying this concept to Geothermal would require up to 4km or more long horizontal well drilling in low-permeability rock at temperatures higher than the current limits which are roughly 175 °C. Continuous fluid flow through the injection production network contributes to the production of hot fluid at the surface.
The MTFHW well concept, offering a large and reliable heat exchange area, has the potential to commercially extract energy from HDR.
If successful, the proposed approach will transform geothermal energy from a niche offering to a carbon-neutral, scalable, time-responsive, geographically distributed, and economically appealing solution to sustainable electric power generation.
Oil and Gas Industry Co-Production
There are many hydrocarbon fields around the world that have high temperatures that are suitable for geothermal development.
The Haynesville Shale project has temperatures in the 150°C – 200°C range. There are also fields in the Middle East with high temperatures. The goal of the project would be to extract heat from the hydrocarbon being produced. Geothermal wells could be drilled deeper and hotter in HDR to provide more energy and additional economies of scale. The wells would be a shared expense reducing the costs of the project for both parties.
There is a potential to increase extraction of the resource by using an established 'waterflood' technique to produce the field. Waterflood has been extensively used in the oil and gas sector as an Enhanced Recovery Method. Water production is viewed as a negative for oil and gas wells. In this case, the water would be the 'working fluid' that would absorb heat and power the turbine. By running the 'waterflood' and separating the oil and gas over a period of 30 years the total amount of hydrocarbon recovered would increase significantly. Some shale fields will yield as little as 5% of the total resource in place.
HDR wells could also be drilled in regions below the hydrocarbon formation and operated to complement the geothermal energy production.