Abstract

We discuss the emerging Engineered Geothermal Systems (EGS) industry, highlight its significant relationship with the oil and gas drilling industry, and describe overlapping opportunities available for the two industries. EGS refers both to the creation of geothermal reservoirs in deep hot rocks and sedimentary basins, as well as to the unconventional use of co-produced hot water from oil and gas production. It has the potential for transforming geothermal energy from a relatively minor source of baseload electricity production into a resource capable of providing 10 percent or more of domestic US energy needs within a few decades. Traditionally, geothermal has been tied to places with the relatively rare combination of plentiful hot water that is shallow. EGS reservoirs exploit the natural increase of temperature with depth nearly everywhere on Earth. The recovery of just 2 percent of the thermal energy between 3 and 10 km depth in the United States represents about 2,800 times the current domestic energy usage. A modest drilling program of 150 wells per year would provide annual increments of 1,000 to 2,000 MWe. EGS power generation is a readily available domestic source of energy that is reliable, steady, and environmentally friendly. Not only does it emit no greenhouse gases, but there is the potential for CO2 sequestration by mining the geothermal heat with CO2, rather than with water. EGS power plants would require minimal footprints, and waste hot-water from the plant can be exploited for direct-use applications such as manufacturing processes and heating buildings and greenhouses. Drilling rigs, casing, tools, and other typical oil field services have been used to drill geothermal wells. This paper will discuss the level of these services needed for EGS growth, and describe new technologies that must be developed, primarily for the creation of EGS reservoirs.

Introduction

The future looks promising for renewable energy development because it can help achieve the major societal goals of energy independence, greenhouse gas emission reduction, and meeting an ever increasing electrical load growth that will likely include electrical vechicles in the near future. Renewable sources useful for generating electricity include wind, solar, biomass, hydroelectric, and geothermal. Absent some scalable form of energy storage, however, wind and solar will continue to be intermittent sources with transmission-grid integration issues. Biomass—the conversion of grown matter to useful energy—is at best considered carbon neutral, and until cellulosic methods are realized, trades off with demands for food. Hydroelectric generation, while a mighty economic engine in the last century, is now deemed a limited resource because of potential harmful environmental effects.

From among all these, geothermal emerges as the most widespread baseload renewable energy resource, capable of providing a steady amount of electricity on a 24/7 basis. Everywhere you go on Earth, it gets hotter with depth, so it becomes a matter of being able to mine this heat in an economic manner. The geothermal industry is well on its way toward exploiting this heat in an expanding variety of locations. Currently, most cost-competitive geothermal developments are hydrothermal, which involves the combination of plentiful hot water and open fractures, and most of these are no deeper than 3 km. However, these are relatively rare resources. Unlocking geothermal's wider potential is the goal of Engineered (or Enhanced) Geothermal System (EGS) efforts.

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