Geothermal Techno-Economic Model with Flow Assurance Calculations

Texas, USA, has many untapped geothermal resources that could potentially support energy development. One promising opportunity is to use the state’s extensive network of oil and gas wells. Existing oil and gas wells connect to deeper geothermal resources, many with water as hot as 200°C (392°F). More than 12 billion barrels of water are currently produced each year from oil and gas wells in Texas. Heat from this water could be used to generate electricity using simple binary power systems.

In order to assess the technical performance and cost-competitiveness of a potential Geothermal plant, Chirality Research Inc has developed a web app which can model a plant, including the reservoir, wellbore, surface plant, economic models, scaling and corrosion. The model estimates capital and operation and maintenance costs, instantaneous and lifetime energy production, flow assurance and overall levelized cost of energy of a geothermal plant. Figure 1. shows some screenshots of the web app.

Figure 1. The Geothermal app home page and Temperature Parameters input page

The free and open-source simulators used for developing the web app are listed in Table 1.

Table 1: Open-source simulators

Some of the useful inputs are listed in Table 2 and useful outputs are listed in Table 3. The outputs are calculated for the entire lifetime of the plant which helps significantly in the design of the plant. Default values for inputs are used where not provided, making it user-friendly. The web app also has a feature of uploading a csv of inputs so multiple scenarios can be simulated and results plotted for analysis.

Table 2. Useful inputs

Table 3. Useful outputs

Using the model, some of the analyses that were done:

· The impact on net electricity production and the capital and O&M costs as input parameters like flow rate, well diameter, depth, bottom hole temperature, were varied. See Figure 2.

· CaCO3 scale deposition for the lifetime of the plant with and without inhibitor treatment. Opex vs. Capex depending upon the number of work-overs.

· Decline in water temperature and flow rate with the life of the plant as the heat content of the reservoir depletes, the geothermal arrival temperature and net electricity production for every year of the life of the plant.

· Dashboard prepared showing geographic location and electricity production of all power plant types (coal, natural gas, solar, wind, hydroelectric, nuclear, biomass) in Texas, USA.

Figure 2. Change in net electricity production (MW) and costs (M USD) with flow rate (kg/s)

Further topics researched in this project include:

· Better design: surface or downhole heat exchanger.

· Feasibility of power generation with natural gas obtained from the production wells, phase separation and temperature losses.

· Geological CO2 sequestration, whether CO2 can be reinjected into the reservoir along with the brine or will it be too corrosive.

· Land requirement for a geothermal + natural gas + CO2 sequestration facility.

· Competitive pressure from other alternatives for power generation in the target geography.

· Study of latest patents in geothermal plant design. Technologies used by all the geothermal plants in the USA.

· Comparative study on outputs given by other models, eg, the Rice University’s ScaleSoft Pitzer scale prediction model.

Conclusion:

Texas has increased its renewable portfolio standard (RPS) to now require electric utilities to generate 10,000 megawatts of power from renewable energy, including geothermal, by 2025. The U.S. Department of Energy released a groundbreaking analysis detailing how the United States as a whole can benefit from the vast potential of geothermal energy. Geothermal electricity generation could increase more than 26-fold from today — reaching 60 gigawatts (GW) of installed capacity in the United States by 2050.

Many Oil & Gas companies are now looking to tap into their geothermal resources. The Geothermal web app developed by Chirality Research Inc. is a very good starting point for assessing the potential for constructing a geothermal power plant. Chirality Research Inc. can provide analyses and dashboards, consultation and literature research for geothermal resource utilization.

References:

https://www.nrel.gov/docs/fy06osti/38242.pdf

https://doi.org/10.1186/s40517-019-0119-6

https://www.usgs.gov/software/phreeqc-version-3

https://wiki.olisystems.com/wiki/images/e/eb/Norsok_standard_M-506.pdf

https://www.energy.gov/sites/default/files/2019/06/f63/GeoVision-full-report-opt.pdf