Enhanced geothermal systems or engineered geothermal systems (EGS) offer significant opportunities to take advantage of geothermal energy. EGS are different from conventional geothermal wells. They are located significantly deeper and require fracturing rock to create the artificial circulation system. Lessons learned from unconventional well development in the petroleum industry are benefitting the development of EGS.
To create an efficient enhanced geothermal system, engineers need to improve the natural permeability of rock via fracturing. Done correctly, water is injected into the fracture network, heated by contact with the rock, then returned to the surface via a production well in the form of steam and used to generate electricity.
Like any development of subsurface resources, enhanced geothermal systems involve risk. However, with the aid of software that enables geologists, geophysicists, and reservoir engineers to analyze geothermal resources, development teams can reduce the risk and fully realize the potential of enhanced geothermal systems. The software integrates, visualizes, and analyzes diverse spatial and temporal datasets to aid in the evaluation of geothermal resources, well planning, drilling, fracturing, and monitoring production.
Evaluate a Field for EGS Potential
Geoscientists are looking for subsurface regions with significant volumes of hot, dry rock that can be fractured. Seismic surveys and core samples provide insight into the geology, depth of the active formation, and its petrophysical properties. From this data, exploration teams can create 3D structural models that depict the extent of the active area, reveal regional faults, and show stress distributions. Rock data can provide guidance regarding natural fractures that have sealed up since originally formed. Ideally, exploration teams are looking for crystalline basement rock that doesn’t require proppants for fracturing and doesn’t present any overpressure issues.
In addition to the geological 3D model, fluid modelling can be done using the thermal model of the geothermal reservoir in preparation for determining the optimum locations of the injector well and the producing well. Geologic models also guide wellbore design with the intent to avoid subsurface conditions that increase drilling risk or cost or jeopardize long term wellbore stability.
Integrating temperature models with seismic, microseismic, and well log data allow for better-informed decisions on EGS well placement. Data source: Utah FORGE, Geothermal Data Repository (GDR), U.S. Department of Energy Geothermal Technologies Office (DOE GTO)
Software that integrates the various data into a single 3D visualization environment for collaborative evaluation benefits enhanced geothermal system development by:
- Reducing the time needed to properly assess the geothermal potential of the reservoir
- Allowing individual team members to evaluate their data in the context of other, relevant, discipline-specific data to better correlate data that influence geothermal performance
- Increasing team confidence in estimating the geothermal potential of the reservoir and designing the EGS to maximize its potential
When complex data is easy to access and analyze, development teams spend less time searching for data and can focus time and skills on analysis.
Determine Optimum Injection Well Location
The versatile software that integrates seismic data, core data, and temperature models can also aid in well planning and drilling. Integrated well-planning capabilities help determine the best location for the injection well based on surface infrastructure, geothermal “pay zone,” and geology. Well designers can evaluate the cost and risk of various trajectories before determining the best plan. Detailed annotations regarding casing methods and completion strategies can be added along the planned trajectory. Core data provides guidance regarding petrophysical properties at measured depth and helps determine drilling equipment and techniques.
When the drilling process commences, near-real-time data obtained from the BHA and delivered to a WITSML server can be incorporated into the 3D model. Azimuth, inclination, and depth data allow drilling engineers to compare planned trajectory against the actual and proactively modify the direction if needed. Temperature data can be used to update the simulation model to provide a more accurate model of geothermal dynamics.
Monitor the Critical Fracturing Process
With a more detailed and accurate 3D model of the geothermal reservoir obtained through the integration and addition of data during the drilling phase, completion engineers can then tailor the frac treatment, taking advantage of stress regimes.
Visualize the development of the fracture network to assess the effectiveness of simulation methods.
Injection rates need to be calculated to achieve the required fracture network that optimizes thermal exchange while limiting seismic risk. That can be achieved by monitoring the fracturing stage using microseismic data that pinpoints where rocks are slipping along pre-existing fractures. By incorporating microseismic data into the geothermal reservoir model, completion engineers can show the development and extent of the fracture network.
Determine Optimum Production Well Location
A geothermal reservoir model that incorporates microseismic data clearly indicates the location and extent of the fracture network. With this level of detail, geologists and drilling engineers are better informed in determining the best location for the production well to optimize thermal transfer as water moves from injector well to production well.
Monitor Enhanced Geothermal System Performance
Sustaining efficient operations of an enhanced geothermal system requires careful monitoring. Opened fractures may close if the proper injection pressure is not maintained or unexpected geological changes take place in the reservoir. Injection metrics can be compared to production metrics and this information can be correlated with changing subsurface conditions obtained from subsequent seismic surveys to identify subsurface conditions that may be affecting EGS performance.
CoViz 4D: Data, Visualization, and Analysis to Minimize EGS Risk
EGS development teams can benefit from the powerful capabilities of CoViz 4D that provide a common environment for visualizing information from many subsurface disciplines. Data integration via a registry, rich 3D and 4D (time step) visualization, and an expansive set of analytics tools and algorithms enhance decision making throughout the entire enhanced geothermal system development and operation cycle. CoViz 4D can significantly reduce decision risk by giving every team member access to relevant information such as seismic attributes, structures and properties, simulation models, well logs, and production data that characterize EGS resources. For EGS development teams challenged to maximize the potential of geothermal resources, CoViz 4D can be an essential tool.
Lead image courtesy of Shutterstock