An Enhanced Geothermal System Uses Oil And Gas Technology To Mine Low-Carbon Energy. Part 2.

An Enhanced Geothermal System Uses Oil And Gas Technology To Mine Low-Carbon Energy. Part 2.

  • Technology
  • May 19, 2022
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  • 7 minutes read


The U.S. Department of Energy (DOE) has funded a project called FORGE where hot granite rock will be drilled and fractionated with the best oil and gas technology. A general goal is to see if the water pumped by a well can circulate through the granite and heat it before pumping it through a second well to drive turbines that generate electricity.

John McLennan, of the Department of Chemical Engineering at the University of Utah, is the lead co-researcher on this DOE project. A webinar on this topic was sponsored by NSI on April 6, 2022: Frontier Observatory for Research in Geothermal Energy (FORGE): An Update and Lookahead

Part 1 addressed these questions to John McLennan:

Q1. Can you provide a brief history of geothermal energy?

P2. What are improved geothermal systems and where is fracking applied?

P3. Tell us about the FORGE project site in Utah and why it was selected.

This article is part 2, which addresses three additional questions below:

P4. What is the basic design of injection and production wells?

So far six wells have been drilled. Five of these wells are vertically drilled monitoring wells, which is consistent with the strategy of being a field laboratory. Fiber optic cables and monitoring well geophones can map the chronological growth of hydraulic fractures that interconnect an injection well, which has been drilled, and a nearby production well.

The injection well was drilled to a measured depth of 10,987 feet (a true vertical depth of 8520 feet ± below ground level). This involved drilling vertically and then building a curved section at 5 ° / 100 feet drilled, and finally keeping one side at 65 ° vertically, for about 4,300 feet in an azimuth just southeast (N105E). This direction favors the subsequent hydraulic fractures to be orthogonal to the well.

After drilling, all of the bottom 200 feet of the well were covered (a larger 7-inch diameter casing was used to move significant amounts of water with limited friction and parasitic pumping losses) and cemented to the well. surface (to hydraulically insulate the annular space).

P5. Could you summarize the three fracture treatments in the injection well and their results?

In April 2022, three hydraulic fractures were pumped near the lower extremities (toe) of the injection well. Three-well geophones, surface instrumentation, and background fiber optic sensors provide insight into evolving fracture geometries during pumping. From the interpretation of these fracture geometries, the production well will then be drilled in order to cut these microsismicity clouds.

Three stages of fracture were pumped consecutively. The first pointed to the full length of the open hole in the well (the lower 200 feet that had not been covered). That treatment was slickwater (reduced friction water). 4,261 bbl (~ 179,000 gal) were pumped at speeds of up to 50 bpm (2100 gpm). After closing briefly, the well flowed again at temperatures of about 220 ° F.

The next stage involved pumping plain water at speeds of up to 35 bpm through a 20-foot-long carcass section that had been drilled with 120 shaped loads to provide access to the formation through the carcass and the cement sheath. 2,777 bbl of stained water were pumped; and then the well flowed again.

The final stage involved 3,016 bbl of crosslinked (viscous) fluid pumped through the perforated casing at speeds of up to 35 bpm. The microproponant was pumped. In the future, assessments will be made to assess the need for and feasibility of the supported fractures to ensure the conductivity of the fractures created.

Preliminary processing of the third stage suggests a pseudo-radial fracture growth, around the well in the center. This favors a separation between the existing injector and the future producer of the order of 300 feet. A business scenario may require greater compensation than this; however, this experimental program must first establish the ability to interconnect two adjacent wells with hydraulic fracturing.

P6. What is the potential for commercial application?

In a commercial environment, a multiplicity of hydraulic fractures would be created to interconnect wells. At the FORGE field laboratory, the length of the side will be dedicated to testing new technologies. These include methods for determining reservoir characteristics, hydraulic fracturing and drilling techniques, compliance: nominally equal flow through each hydraulic fracture, and the characteristics of the flow through these fracture networks and the speed at which experiences thermal exhaustion. Research contracts are awarded to other parties (universities, national laboratories, industrial organizations) to develop these technologies and test them at FORGE.

In a commercial EGS environment, cold water would be injected and pass through the series of hydraulically created fractures, acquiring heat in the process. Hot water would be produced on the surface through the production well. On the surface, the standard geothermal technology for power generation would be implemented (a Rankine organic cycle plant (ORC), which uses a secondary organic working fluid that is invaded by steam to drive a turbine / generator). or a direct steam flash). The water produced, after removing the heat, is recirculated.

The FORGE site will not be an energy producer. It is intended to be used to test and develop technologies that promote the commercialization of this type of geothermal energy. Success focuses on technological development. Significant progress has already been made in promoting the application of compact polycrystalline diamond (PDC) bits that allow for dramatic increases in penetration rates. Subsoil measurement evaluation protocols and the training of all site staff on the platform have improved the drilling economy of this geothermal project.

It seems that hydraulic fracturing can be carried out effectively, but the real test lies in the efficiency of circulation and heat recovery after drilling the production well.

The success of EGS here can be applied elsewhere. Consider the use of hydraulic fracturing for hybrid EGS applications where conventional applications have found the geothermal equivalent of a dry hole: no natural fractures were found during drilling, but they could be cut by fracture.

Success at FORGE means testing technologies that would not otherwise be considered, passing viable technologies to private industry and encouraging geothermal development in general.



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