Sedimentary Geothermal Resources Offer a Bright Future for Geothermal Energy

Next-generation, or “next-gen,” geothermal resources have the potential to increase geothermal power generation in the U.S. by twenty-fold by 2050. Next-gen geothermal concepts use technologies developed by the oil and gas industry to engineer reservoirs for geothermal energy generation, vastly expanding the available resource base.

Typically, the term next-gen geothermal refers to enhanced geothermal systems (EGS) or advanced closed-loop systems (AGS), which have been getting a lot of attention due to the success of high-profile government and private pilot projects. However, there is another, largely overlooked next-gen geothermal approach with a lower technology risk than EGS and AGS: sedimentary geothermal systems.

Until recently, sedimentary geothermal resources were considered too niche, too expensive, or just lumped into the EGS bucket. Thanks to recent technological advances, cost reductions, and market demand, sedimentary geothermal resources are being viewed as a new market-ready path to clean geothermal energy.

What Are Sedimentary Geothermal Resources?

To produce economic geothermal resources, two major characteristics in the subsurface need to be present: sufficient heat and permeability. Conventional geothermal systems (often termed “hydrothermal” resources), which power the vast majority of the 30-plus geothermal power plants in the U.S., rely on finding natural fractures in reservoirs to provide permeability (Figure 1). These natural fractures and fracture networks need to be very big, because geothermal wells need significant flow rates relative to oil and gas wells in order to be economic. Due to the constraints of this unique geology, there has been limited geothermal power deployment in the U.S. equivalent to less than 4 GW of generation.

1. Enhanced geothermal system (EGS) developments sidestep the constraint of finding natural fracture permeability and instead drill into hot, un-fractured rock and stimulate hydraulic fractures—creating their own fracture permeability. While EGS pilot projects have been occurring for decades, the recent applications of horizontal drilling and multi-stage hydraulic fracturing developed in the oil and gas industry have opened up new possibilities for EGS developments. Courtesy: Projeo

Sedimentary geothermal resources offer a middle course approach between conventional geothermal and EGS developments by targeting sedimentary rock reservoirs with high natural porosity and permeability in hot sedimentary basins (Figure 1). The use of horizontal wells completed within the reservoir can increase the flow rates of production wells and improve project economics. Many of the areas being considered for sedimentary geothermal development are data-rich traditional oil gas basins, which decreases exploration costs and project risk. A prominent example is the Gulf Coast of Texas, where multiple companies have been exploring for and developing geothermal power projects.