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Geothermal Innovations, Part 1: Redesigning Reservoir Design from the Subsurface Up

Large-scale projects for the production of geothermal energy begin, essentially, with a detailed study of rocks. As AltaRock Energy's President/Chief Technology Officer Susan Petty told GEA by email, technology improvements "are no substitute for a thorough understanding of geology." The process of gathering and analyzing data on geologic layers of Earth is a complicated dance buoyed in recent years by a focus on innovative research and development from industry experts and aided in part by federal incentives and loans.

A distinguishing characteristic of exploring a geothermal system is that it requires drilling.  “Drilling is the only definitive method available to identify and delineate heat, permeability, and fluid supply,” according to the prepared presentation by AltaRock Energy for the National Geothermal Summit, a Geothermal Energy Association (GEA) event in Sacramento this past August. Joe Lovenitti, VP of resource, contributed to a panel of drilling innovation experts.

Representatives from AltaRock were also at the event in another capacity; the geothermal industry presented their company a GEA Honors Special Recognition award for the renewable energy company’s efforts in commercialization of Enhanced Geothermal Systems (EGS) technology for power generation.  The project, located outside Oregon’s Newberry National Volcanic Monument, targets improvements in stimulation methods that could benefit the entire geothermal industry.   

While the award recognized the successful work of dozens of individuals or more, the panel discussion reflected the industry’s urgent need to overcome significant drilling risks to effectively bring down costs. Iovenitti’s statement on drilling came with a caveat; “Any improvement in drill site selection through enhanced geoscience data understanding and integration, as well as breakthrough methodologies, will reduce risk,” he said.  Exploratory and drilling techniques essential for the success of the industry are costly and are largely ignored by incentive programs.  Many industry experts hope that together the industry and investors, including government, can form solutions before time and/or money runs out.  

Echoing this was James Faulds, director of the Nevada Bureau of Mines, University of Nevada, Reno - a panelist with Iovenitti at the Summit.  A combination of government- and industry-sponsored efforts, Faulds noted in his presentation, is needed to reduce drilling risks in the geothermal industry.

"Geothermal exploration and wellfield development are expensive and risky propositions," says Karl Gawell, executive director of the GEA.  "Government incentive policies and research efforts need to help address this problem for geothermal power production to really see dramatic expansion."

The message is clear: While some geothermal power plant technologies may be maturing as the industry grows, there is much to be done.  The reduction of risks and costs, particularly of subsurface work, is key for future technology development.  The options are being examined right now by scientific and industry professionals as well as by representatives in the federal government and Congress.      

Developers hope the message will spread to other representatives and investors soon enough to defy one of the looming threats they face: the end to production tax credits.  Tax credits for geothermal are an important driver to the industry, but are set to expire at the end of 2013 if not acted upon by Congress.

EGS Scientists Are Solving Practical Problems

The EGS technology concept differs from conventional geothermal development, as EGS allows energy extraction from geothermal resources where the naturally occurring combination of heat, water, and rock permeability is not sufficient for commercial development on its own but could be enhanced or created through methods of stimulation.  

“Companies like AltaRock are focusing on some very practical problems, like how to stimulate multiple zones in a well,” Ann Robertson-Tait said in a conversation with GEA on innovative technologies and enhanced geothermal systems (EGS).  Robertson-Tait, senior geologist and business development manager for GeothermEx, a long-established geothermal consultancy, chaired the August panel that seated Faulds, Iovenitti, and others: Hildigunnur Thorsteinsson, team lead at the U.S. Department of Energy (DOE); Bruce Kohrn, a manager at Lockheed Martin interested in the geothermal space; and Patrick Walsh, chief geologist with Ormat Technologies.

AltaRock along with Davenport Newberry were awarded a $21.4 million matching DOE grant to create and test the EGS reservoir.  The partnership is using AltaRock’s hydroshearing technology at a well drilled by Davenport in 2008.  According to the project’s Web site, their goal is “to bring the price of EGS in line with existing utility rates to demonstrate that EGS at Newberry can be an economically viable source of baseload renewable energy.”  The project has garnered much attention from press as scientists explain the nature of using drilling and stimulation technology to learn more about the geology outside the Newberry National Volcanic Monument. 

A main component of the project is to add diverters – granular materials – into the water injection line to temporarily plug-up existing fractures, thus diverting the water to form other fractures, as described on AltaRock’s website.  The materials dissolve away with time and heat.

The ability to isolate multiple zones in a reservoir “is a critically important element of stimulating EGS wells,” Robertson-Tait explains.  “Stimulating multiple zones is important because in low-permeability rock, we need to exploit as many small fractures as possible to maximize the productivity or injectivity of each well.  AltaRock and other companies are seeking other robust solutions to accomplish this goal,” she says. 

Subsurface Analysis without Drilling: Geothermal’s “Holy Grail”

The geothermal industry has grown at an increased pace over the last few years.  Since 2006, when the Energy Policy Act's new geothermal tax incentive and leasing provisions took effect, 14 different companies have built 28 geothermal power plants or additions in nine states with a combined power capacity of 502.7 MW. The 2006-2012 growth represents an 18% increase in total U.S. megawatts (MW) online, and during this period 33% of U.S. geothermal power plants were either built or expanded.

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By comparison, U.S. geothermal capacity grew by roughly the same amount between the six-year period 2006-2012 as it did between the 20-year period 1960-1979, which is considered to be a solid growth period for the industry, Gawell noted. 

Robertson-Tait reflects that as the industry has grown, so has the ability to interpret reservoir information.  After data is gathered, the next step is accurate integration and interpretation, a skill that takes training and experience to develop a robust conceptual model of the geothermal system and the controls on permeability and fluid flow.   She and her counterparts at GeothermEx (operating as part of Schlumberger, the global oilfield services conglomeration, since its 2010 purchase) bring this type of analysis to the table, deciphering multi-disciplinary data sets to characterize geothermal resources.  Using that experience they identify specific R&D activities that can improve the development of both EGS systems and conventional geothermal systems.

Getting accurate temperature readings at various depths, which requires drilling, is the most fundamental component of any geothermal project because they reveal much about the flow of hot fluids.  “The only way we’re currently able to measure temperature accurately is by poking holes in the ground,” said Robertson-Tait.  But this may not be the case in the future: “The geothermal ‘holy grail’ would be methods that reveal subsurface temperatures without having to drill deep, expensive wells.” 

Already, scientists measure wavelengths to create images of a geologic area; while the results of using this seismic profiling technology can improve drilling targets, it is more costly than solely using geophysical methods. Developers have to make difficult decisions on whether to de-risk the drilling by spending more money upfront.

While the cost is significant now, this could ultimately decrease costs as well as improve readings. 

“Because of the terrains that are involved [in the U.S.], I think we’re going to see a resurgence of the use of seismic techniques to better understand geothermal resources,” says Robertson-Tait. “Chevron is coming back into the geothermal game in the United States, and I would bet they’re going to be using seismic methods to gain a better understanding of subsurface structure.  They recognize the cost-benefit of this approach.”

Robertson-Tait also noted that Lockheed Martin and others have developed innovative airborne exploration methods to a new level through the use of “gravity and magnetic gradiometry” -- meaning – “the difference in gravity or magnetic field from place to place,” a method that is quick to implement and provides broad coverage of an area, yielding additional insights into the geologic variations in the subsurface, testing the geologists’ concepts of the geothermal reservoir and its surroundings. 

Geothermal Innovators Cross-fertilize with Related Industries 

Geothermal developers are pros at using existing ideas in new ways.  One such project received credit from the industry through the GEA Honors Technological Advancement award.  

Robertson-Tait was on the committee that selected it.  “Enel [Green Power North America]’s combined solar and geothermal project [is] a great example of how marrying two technologies actually yields something that’s bigger than the sum of the parts,” she said.  “When I looked at the nominees, I immediately thought that this was something that should be recognized for technical innovation.  Neither the geothermal piece nor the solar piece was “new” in terms of the technology, but putting the two together was a very clever thing.” 

Enel’s hybrid project happened in stages in the hot Nevada desert: first the binary geothermal plant, then the solar field.  In the hot summer months, the solar field will offset the use of water for cooling the geothermal plant.

Geothermal can also take some plays from the oil and gas book, such as the use of seismic surveys and utilizing some of that industry’s drilling and completion concepts.  Geothermal developers routinely gather data from old wells – particularly that precious temperature data, and there is increasing interest in utilizing the heat in co-produced geothermal waters in some oil and gas fields. 

“I like that kind of cross-fertilization, and I think it’s important for the industry to recognize that it’s happening,” said Robertson-Tait.  On the other side of it, oil and gas developers have used techniques from EGS to create big flow paths in tight gas shelves.  “Although there are important differences, there is more overlap between the two technologies than people may realize,” she said.  

New Study Shows Deep Potential in Geothermal-savvy Nevada 

“Nevada continues to make valuable contributions to the geothermal community and shows immense promise in terms of both geothermal energy and economics,” Gawell said leading up to the recent GEA Geothermal Energy Expo in Reno.

Commenting on the GEA Expo in a letter, Majority Leader of the U.S. Senate Harry Reid (D-NV), a longtime proponent of geothermal and other renewable energy sources, highlighted Nevada’s continued clean energy efforts.  “Clean energy development has already created thousands of jobs in Nevada, and continued investment will help to drive our economy forward. Clean energy innovators like those at the Expo will provide the solutions that Nevada and the rest of the country need to maintain its momentum as a leader in clean energy development,” Reid said. 

In fact, four of the seven geothermal plants that came online in the past year are located in Nevada, including Tuscarora and McGinness Hills by Ormat Technologies; San Emidio by U.S. Geothermal; and Beowawe 2 by Terra-Gen and TAS Energy.  In the most recent industry-wide survey on geothermal projects in development, conducted this past April by the GEA, developers confirmed that 59 of a total 147 geothermal projects-in-development in the U.S. are located in Nevada.  These 59 have the combined potential to account for more than 2,000 MW of geothermal capacity.  

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Furthermore, says Robertson-Tait, “there is ignored geothermal potential deep beneath the Great Basin.”  Deep underneath eastern Nevada and western Utah, underlying limestone-and-dolomite formations “represent a significant geothermal target,” she said; they are susceptible to the kind of permeability needed for a successful geothermal reservoir, and there is a significant body of knowledge related to permeability enhancement.  Additionally, oil and gas drilling in the area means that there are already wells for gathering data. 

This concept of high-temperature geothermal resources beneath young sedimentary basins was the topic of a project and a 2012 Geothermal Resources Council paper by Rick Allis of the Utah Geological Survey and several co-authors: “Stratigraphic Reservoirs in the Great Basin – The Bridge to Development of Enhanced Geothermal Systems.”  

Conventional Hydrothermal Projects Continue to Lead Geothermal Development 

Technology innovations complement the addition of geothermal MW to the grid in recent years, mostly via conventional hydrothermal facilities.  The GEA’s springtime survey of projects-under-development showed that of the 147 projects surveyed, 116 projects (about 80%) were developing conventional hydrothermal resources in areas where the geothermal resource had not previously been developed for power generation; 18 were developing conventional projects in areas already proven for production; and five were expansions to existing conventional plants. 

There were also five coproduction and three EGS projects.  These are both rather different than conventional hydrothermal, and are exciting, relatively new technology developments that are bringing geothermal energy to more regions of the U.S. than ever before. Efforts in Nevada, California, and throughout the West are undoubtedly an inspiring example, particularly as state leaders and communities across the U.S. are becoming more aware of geothermal technology as a reliable and renewable resource. 

While a 2006 estimate by the Western Governors Association (WGA) considered 13,000 MW could be developed by 2025 in Western states, there was no equivalent study in the Eastern states.  Four years later, Southern Methodist University (SMU) brought to light 18,890 MW of geothermal power potential in West Virginia – a discovery representing the largest known geothermal reserve in the Eastern U.S.  The future successful production of EGS technologies, many of which are being tested now, could ultimately mean geothermal energy in parts of the U.S. where it hasn’t previously been viable.

EGS a Substantial Resource that Merits Further R&D 

The data from the SMU study supports estimates that EGS could widen geothermal potential across the U.S. to 2,980,295 MW -- a near 40-fold increase compared to traditional geothermal technology potential.  It is considerable both in terms of the potential, and in the work that still needs to be done.  

“How can we stimulate large volumes of rock and create these heat exchangers? What conditions are best for that? What stress conditions, what rock types?  Is it realistic to think we can do this in the Eastern U.S. at depths of 15,000 or 20,000 feet?” said Robertson-Tait, laying out the kinds of problems EGS scientists are dealing with.

Still, in order to get to something like 10% of the U.S. electricity supply – considered realistic by many experts – it “will probably require an EGS component,” she reasons.  

A report from the Massachusetts Institute of Technology (MIT) conducted in 2006, the same year as the WGA estimate, concluded over 100,000 MWe could feasibly be reached in the next 50 years with a reasonable, sustained investment in R&D.  “As the MIT report showed very well, [EGS] is a substantial resource.  As a long-term strategic resource that is still not viable, it merits research.”  

The U.S. DOE helps the industry do just that through its Geothermal Technologies Program of the Office of Energy Efficiency and Renewable Energy.  Their work to demonstrate the technical feasibility of EGS includes seven demonstration projects in five Western states.  Seventeen other currently-funded projects comprise a mix of coproduction, geopressure, and low-temperature projects. 

“A DOE program to fund exploratory drilling would be very successful, as was done in the late 1970s with a U.S. industry drilling program which drilled many wells across the West,” Robertson-Tait said.  Iovenitti, Faulds, and others noted the industry’s need for improvements in drilling and data analysis; DOE has also recognized this.

DOE has set targets to reduce the levelized cost of electricity from EGS to 6 cents/kWh by 2030 and the LCOE from coproduction, geopressure, and low-temperature technologies to 6 cents/kWh by 2020.  GEA’s next feature article, “Geothermal Innovations, Part 2” will follow up with a look at DOE’s hand in some of the most creative geothermal innovations happening today.

Lead image: Lightbulb via Shutterstock

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