Simulated Field Testing of an Industry-First, Unflasked Perforating Gun for Enhanced Geothermal Systems, and Superhot Rocks
Authors: Roy Ting , BenNaceur Kamel , Simpson Wylie , Koyanagi Yoshihiko , Takahashi Mari , Shelton James , Harrison Casey , Jones Kenny , Earthman James , Mahbod Pouya , Singh Anil , Roy Indranil 
Published: November 2024

Use of geothermal energy for power generation is now attracting greater attention as one of decarbonization wedges required for a sustainable energy transition. Among the different geothermal sources, Superhot Rock (SHR) Geothermal Energy, as defined for instance by the Clean Air Task Force (CATF), is a visionary energy source deserving of investment, and yet almost entirely unrecognized in the decarbonization debate. SHR geothermal energy can be generated from dry rock that is at least 752 °F (400 °C). It exists all over the earth at depths between two and 12 miles. Projections place cost of energy production harnessing SHR to be between $20 and more than $35 per megawatt hour, which is generally competitive with what energy from natural gas plants costs today.

SHR geothermal energy production is not a reality yet. Recent innovations in drilling and completion have made it possible to harness ultra-deep HPHT wells (&gt;15,000 m), which will ultimately enable highly efficient power generation from Enhanced Geothermal Systems (EGS) with a much larger geographical scope. Currently, there are no SHR geothermal energy systems operating and delivering energy. However, geothermal energy is being used in a few places where superhot temperatures exist close to the surface of the earth. How far we must drill to get to 752 °F depends on where we are. On the edges of tectonic plate boundaries or near recent volcanic activity, for example, Salton Sea in the Western United States, it might be two miles down. In the middle of a continent, we might have to go down 12 miles to reach such environments.

Iceland is a leader in investigating SHR geothermal energy with its Iceland Deep Drilling Project. A test there suggests one well could produce 36 megawatts of energy, which is five to ten times more than that of a typical conventional geothermal well. Beyond Iceland, Italy, Japan, New Zealand, and the United States are leaders in SHR. Other areas on the edges of tectonic plates, including Central America, Indonesia, Kenya, and the Philippines, also have some development.

Many challenges to achieve this economically remain. To outline a few: first, hotter, deeper wells require for the completions alloys with high strength, creep, and corrosion resistance; second, retaining system-enthalpy in EGS needs tubing with near-zero thermal conductivity; second, such Ultra-HPHT formations need perforating systems to produce entry holes large enough to enable effective formation stimulation between an injector and the producer. As such current EGS and SHR systems employ perforated liners, rather revert to unproven reliability of perforating guns in such hostile environments.

In their recent report, "Policy Brief: Earth Energy Innovation", CATF outlined several policy solutions to barriers advancing geothermal energy. They are (1) Inability to deploy projects (2) Lack of financial incentives for project development and deployment (3) Gaps in applied research and bench-scale testing (4) Limited access to in-field testing (5) Need for an increased focus on superhot (400 °C +) geothermal resources at the agency level (6) Ineffective resources for data sharing. Some solutions were offered to spur technological innovations which will allow us to access this energy, which has the potential to meet long-term demands for zero-carbon, always-on power. To summarize, SHR geothermal energy to be commercialized and deployed broadly will require new technologies, including rapid ultra-deep drilling, heat resistant materials and tools, and ways to develop deep-heat reservoirs in hot dry rock.

To address this unmet need and bridge some of the technology gaps, here we present an economical, engineered-to-order, precipitate hardened, thermally stable, and grain-refined corrosion resistant alloy with excellent elevated-temperature mechanical-properties as a metallic-skin on a nanocomposite tube. This is the input-material for designing a perforating-gun body, enabling it to survive a 15K-psi collapse at elevated operating temperatures. The nanocomposite tubular gun-body with near-zero thermal conductivity allows the gun to operate at 750 °F, for fracturing Ultra-HPHT and hot granite formations.

The gun body, designed from a nanocomposite tube having a high-strength, thermally stable, corrosion resistant metallic skin is designed to prevent supercritical fluids and subcritical corrosive hydrothermal-brines from subjecting the gun to environmentally assisted cracking. The end of the gun is insulated with high-temperature reusable surface insulation (HRSI) materials and equivalent- seals, including metal-to-metal seals. Passive electronics, the switch, and detonator, generates little to no heat and does not affect the internal temperature of the gun, requiring no refrigeration to dissipate internal heat to cool the system.

Decades of completions experience drawn from the oil & gas industry and strategic partnerships amongst the advanced materials world, played a pivotal role in solving these challenges associated with such Ultra-HPHT environments, expected in EGS. Our patent-pending embodiment, a concept, using a specially designed nanocomposite tube with a near-zero thermal conductivity of &lt;0.02 W/m-K to design a perforating gun, completely isolating the charges, switch, detonator, and detonation chord from the external EGS environment. The tested and proven composite insulation maintains the temperature of the gun internals below 150 °F, even when the external environment is in excess of 750 °F, for days.

For the very first time, an Ultra-HPHT perforating gun rated to 750 °F, 15K-psi for fracturing superhot/granite formations to enable EGS and SAGD was conceived and designed. Key novelties of this industry-first design are (a) No required flasking of the gun: avoiding multiple steel barriers that would limit the depth of penetration, and Entry Hole Diameter (b) Ability to deploy RDX-charges in a system rated to 750 °F (c) Reliable performance at extreme temperatures (d) Ability to deploy tracers via shaped charges, field- tested and proven to survive T &gt; 750 °F, well suited for EGS (e) Unparalleled economics, not requiring the additional cost of a "Flasked- system".