33 AUGUST 2021 WorldWide Drilling Resource® A Quiet Pivot to New Potential Compiled the Editorial Staff of WorldWide Drilling Resource® For centuries, geothermal springs have been used for bathing, heating, and cooking. But only in the early 20th century did people start to consider geothermal as a practical source of energy with huge potential. The only problem was wells were needed in geothermal installations, but they could be costly to drill. A new idea was born out of the desire for a more cost-efficient method of producing geothermal energy. Using existing oil wells, whether low-producing/abandoned or in production, for such installations can reduce costs and help promote the use of geothermal energy as a viable and sustainable means of electric and thermal power generation in various geological environments, including crystalline, sedimentary, metamorphic, and volcanic. Oil wells can either be used to coproduce oil and heat or converted solely for geothermal production. Let’s look at coproduction first. Typically, oil production declines, while water increases during the lifetime of a well. Oil produced is accompanied by a lot of hot brine, up to 194ºF (90ºC) at the surface, which is separated by gravity. Normally, the hot brine is reinjected into the reservoir to enhance production and maintain pressure. This means the calorific energy of the water is wasted. But if the heat is extracted before the brine’s reinjection, it can be used for heating or electricity production. In one field test, an Organic Rankine Cycle turbine was connected to an oil well in the Chaunoy oilfield in the Paris Basin, France, a mature oilfield producing 95% water from 32 wells. On one of the wells, the electricity turbine was installed on the flow line transporting oil, gas, and water from the wellhead to the manifold. Two flexible hoses bypassed the production flow line and allowed fluid inflow and outflow to the turbine. The produced fluid temperature was used to heat up and boil a different fluid at high pressure, called the working fluid. This vapor was depressurized to produce mechanical work, which was ultimately transformed into electricity with the help of an alternator. The produced fluid was returned to the production line at a slightly lower temperature. Conversion is the second option. Many onshore wells are suspended because they are not producing enough oil anymore, but these can still produce a lot of water. To be economical, there must be a heat demand nearby to avoid transporting heat long distances by costly insulated flow lines. The heat source must be high enough to match the demand, in temperature and flow rate. Ideally, the well should be eruptive enough so no extra energy with downhole pumps is required to lift the fluids. The well integrity must be good, with no deterioration of casing and cement. Taking the idea of the gas and oil industry and geothermal one step further, a Texas-based geothermal energy firm led by former gas and oil executives secured climate venture funding to drill the company’s Phase I demonstration well in Texas, with eyes on the potential pivot of the gas and oil sector to geothermal. With most of the news coverage on the technology transfer rather than concrete investment into development, two former gas and oil industry leaders reunited after decades to brainstorm new scalable geothermal energy concepts. Lev Ring, former Weatherford global head of R&D (research and development), and Lance Cook, former Shell chief scientist of wells, founded Sage Geosystems in 2020. They were excited about the idea of leveraging the core competencies of gas and oil to unlock this baseload and abundant form of green energy. Describing itself as a venture focused on hot, dry-rock geothermal energy development, Sage targets “heat harvesting” with a combination of a single-well closed-loop system and a novel use of stimulation with a target to create an Advanced Geothermal System/Enhanced Geothermal System - a hybrid geothermal system. Sage CEO Lev Ring said, “We intend to quickly derisk a novel approach to heat harvesting in hot sedimentary basins, unlocking terawatts of potential globally.” Lance Cook, CTO of Sage added, “If you think about how vast the gas and oil industry is globally, and what would happen if the industry engaged at scale in geothermal energy development, we could be developing a terawatt (one trillion watts) or more of geothermal energy each year. That places us in excess of world energy demand by 2050.” The company experienced a series of fast successes, including having its models validated by an international oil company, and being selected to advance in the U.S. Department of Energy Geothermal Prize Competition, a million dollar multiphase competition for geothermal innovation. They have seen every major gas and oil entity quietly forming new efforts in geothermal, and fully expect the trend will snowball over the coming months as this information is made public. Chris Anderson, Sage’s lead investor, is intrigued by the potential pivot to clean geothermal energy by major hydrocarbon industry entities, and believes “the skills and resources of the oil and gas industry can play an absolutely crucial role . . . [with its] drilling and [hydraulic fracturing] capabilities to unlock vast quantities of zero-carbon energy. This is why Sage is so exciting to us.” Photo courtesy of Helmerich & Payne, Inc. GEO
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