New Hampshire, USA — Commissioning a geothermal project is no easy task. Of all the renewable energy technologies, it has one of the longest project lead times – it can take an average of eight years from start to finish. Due to its heavy front-end expense, developers must be as certain as possible that they are spending time and money on a viable resource. So when drilling through hot rock, imagine the developer’s surprise — and utter disappointment — when equipment suddenly melts away after hitting magma.
Though extremely rare, this exact scenario happened in 2009 at the Iceland Deep Drilling Project. Located in the Krafla volcanic caldera, which is heated by centrally located magma chamber, drilling was expected to reach 4-5,000 meters based on preexisting modeling data and nearby well depths. But at little more than 2,000 meters, after days of slow, difficult progress, drillers were met with dramatically reduced resistance as the equipment shot straight through rock and into super-hot magma.
Since this mishap, the project team decided not to close off the well, but attempt to take advantage of the super-hot resource — an accomplishment in itself. However, this case brings up a long-standing issue in the geothermal industry: resource assessment.
It Starts with Data
Resource assessment starts with information. Existing geothermal data — including heat maps, existing well locations, geological surveys — can be a project developer’s best friend. However, this information had previously been scattered, disorganized, and simply impossible to find. Enter initiatives such as the U.S. Department of Energy’s National Geothermal Data System (NGDS).
Realizing the need for organized information, the Geothermal Technologies Office designed an information network that adds data from more than 10 information hubs across the U.S., and puts them in one centralized location. NGDS is also expanding its reach abroad.
Learn from Experience
The Southern Methodist University (SMU) Geothermal Lab, already a huge asset to the NGDS, is currently looking to a more experienced industry for geothermal opportunity. At the Renewable Energy World North America Conference and Expo, Maria Richards, coordinator at the SMU Geothermal Lab, explained that the program is now culling data of all the existing abandoned oil and gas bore wells in the United States.
The geothermal industry can take advantage of these wells and either co-produce with existing oil and gas plant, or go beyond that and revitalize the wells to produce geothermal electricity. In Texas alone, there are more than 3,100 oil fields with “extractable” thermal energy. “The infrastructure already exists,” said Richards, “we might as well exploit it.”
The U.S. Department of Energy is also taking a cue from the oil and gas industry. It recently announced a $3 million fund to spur geothermal development using play fairway analysis — a resource mapping tool widely used in the oil and gas industry. This approach uses existing geologic maps and data, likely from the NGDS and elsewhere, to help identify and explore new resource development areas.
Steps to create a play fairway map. Credit: U.S. Department of Energy
Play fairway analysis helps to rapidly locate and analyze geothermal sweet spots, according to Cathy Hanks, structural geologist at the Geophysical Institute, which then creates a favorable project for investors. “It helps sell the lead to companies and investors and leverages man power and data for next place to put their best efforts. It is a robustly used analytical method,” explained Hanks.
A play fairway is an area where resource concentration is projected to occur based on its geologic characteristics. There are a number of geologic factors that contribute to a play: a source for hydrocarbons, a reservoir, a seal to keep them in place, a trap to concentrate them in one place and generation and migration. Developers must identify these areas and determine how the resource can be exploited.
The total play fairway process can be boiled down to five steps. Developers must compile existing data; integrate and interpret that data; determine the best possible play types that may occur and necessary conditions for each; construct a probability map for each geologic factor that needs to exist for each play type; merge the individual play maps into a composite probability map.
“This map should summarize the probability that a play exists given a specific set of factors so it’s a success,” said Hanks, “How competent are you that the areas exist? How big might the potential prize be?”
The program will focus on under- or unexplored regions and consider a wide range of geothermal resources, which include hydrothermal, enhanced geothermal systems (EGS), or low-temperature resources. “We would like to see proposals that apply innovative analysis methods that extract new value from existing and private data. Risk analysis is a major part of this,” said Hanks. The DOE expects to award the best proposals by the end of September.
A Model Approach
Enhanced geothermal systems (EGS) have seen continued progress and could account for 100 GW of power in the U.S. alone. These systems use fluid to stimulate hot rocks and create a flowing reservoir to capture the heat resource. Once developers find a viable site, they need reliable modeling tools to monitor the deployment of the resource.
A simulation showing how FALCON can reproduce observed behavior. Credit: Idaho National Laboratory
Previous modeling techniques simply examine one geologic characteristic at a time, such as heat transfer and chemical composition. When researchers try to put this information together, it creates information gaps, errors and incomplete data sets. How can developers avoid this flawed data? Enter: FALCON.
Developed by the Idaho National Laboratory (INL), the Fracturing and Liquid CONvection (FALCON) code combines all data sets together, which reduces risk and costs.
“Each piece of physics, such as fluid flow, heat transport, mechanics, chemistry, needs to be considered correctly,” said Robert Podgorney, who co-led FALCON development. “Previously, we had a disadvantage where we would lose information from one model to the next. FALCON solves all variables simultaneously.”
FALCON allows for a better understanding of what is going on in the geothermal reservoir. For example, it can be used to model how the injection of cold water might increase the permeability, and hence the energy production. Explained Podgorney, “It is a tool to get a better conceptual understanding of the resource. It can create predictions of what operations can be like for the future.”
However, it does have some limitations. Developers must input existing data from the site, so the returning data is “only as good as info you put in,” said Podgorney.
What the industry is essentially looking for, said Hanks, are new resource initiatives that will solidify resource probability and enhance investment. “We would like to see proposals that allow for innovative analysis methods that extract new value from existing and private data.”