Turning water into wine has reportedly been accomplished—just not in current times, as far as I know. Turning water into oil would have obvious benefits, but turning oil into water would not be as desirable for obvious reasons. It really does not make sense.
However, what can make sense is turning oil (and gas) wells into geothermal wells—those wells that are inactive that could still produce hot water with heat sufficient to provide energy for electricity generation or for power applications. The repurposing of oil and gas wells for geothermal is a topic that is not so new, but it hasn’t gotten far despite the attention it has been given in recent years. The question is, how realistic or practical can it be?
Challenges. We know the benefits of geothermal energy as an abundant global resource—including in the U.S. alone. It is also a clean, environmentally favorable energy source. However, only a small amount of the resource has been developed, despite its desirability. With the total number of oil and gas plus geothermal wells currently drilled annually, geothermal wells roughly represent only about 2% of that total.
There are numerous challenges for geothermal projects, such as long permitting timelines. Tapping into hot water sources below the surface of the earth with new wells faces the same obstacles as in oil and gas exploitation. While drilling and completion technologies continue to advance, geothermal wells are typically quite deep, so that they can source water temperatures of 400° to 500° F and greater. So, for drilling, completion and well hardware that will withstand high temperature conditions, costs are substantial.
Geothermal brines can be corrosive and subject to downhole (and surface) scaling and salt deposition. Geothermal resources are often located in remote areas around the world, which can result in significant logistical costs for well construction and operations. Also, geothermal wells, which typically produce from very tight or naturally fractured volcanic rocks, are often in need of well stimulation upon completion, as well as during well life.
Another challenge or limitation is that repurposed oil and gas wells will not produce volumes of hot water at rates comparable to newly drilled geothermal wells. Also, heat from hot water is not easily transportable, depending on the necessary distance. There also must be a geographical demand, which is met by the geothermal source temperature and produced volume. However, there is such a substantial number of inactive wells, so those that meet necessary criteria for applicable geothermal energy usage may still be numerous.
Wells of opportunity. Inactive and active oil and gas wells that could be reasonably converted or repurposed as geothermal wells are referred to as “wells of opportunity,” by the U.S. Department of Energy. The utilization of active wells that produce sufficient volumes of water along with oil and/or gas is referred to as co-production. Just as with geothermal wells, water can be reinjected and allowed to heat up in the formation, then produced again and used for energy generation.
Utilizing inactive wells has the advantage of avoiding or at least significantly delaying the high costs associated with well abandonment. Of course, the integrity of an inactive well must be intact or, at least, not requiring prohibitively expensive repair. However, if such wells need repair or rework for safe production operations, that can be weighed relative to abandonment requirements and costs otherwise. There are many inactive wells throughout the world that are no longer used (or useful) for economic production or injection, but they can produce sufficient volumes of water, naturally combined with reinjection/recycling, and are, or can be, in good enough shape to provide viable geothermal energy.
With co-production, there are wells—although not very numerous—that produce water at sufficiently high temperatures that the heat can be captured and used to generate electricity. Again, water produced can be reinjected where logistically possible and reused for energy capture. An issue with that, in both repurposed inactive wells, and with co-production, is how long reinjected water must reside in the formation to warm up enough to be produced back. But in high-temperature reservoirs, the time may not be so long as to become impractical. So, an efficient and sustainable recycling operation is achievable in such cases.
However, it is important to note that produced water temperatures do not have to be so high for broader energy applications. The highest temperatures are needed for electricity generation but not necessarily for industrial processes or for heating and cooling needs in buildings or other structures. Generally speaking, non-electricity applications of geothermal energy represent much greater potential for inactive or uneconomic oil and gas wells especially and, for the most part, co-production opportunities too.
What is realistic? The focus for repurposing oil and gas wells (inactive and active), should seemingly, or obviously, be primarily for low-temperature geothermal applications. Low-temperature geothermal resources are generally considered those below 300° F. Per the U.S. Department of Energy Geothermal Technology Office (GTO):1
Low-temperature geothermal uses include geothermal heat pumps (GHPs) for homes and businesses, district heating and cooling, and direct-use applications, where water from the geothermal resource is piped through heat exchangers or directly into commercial or residential buildings to meet heating and hot water demands. These resources can meet many energy needs, from heating and cooling to industrial processes like paper drying, greenhouses and even beer brewing.
The GTO is conducting the Low-Temperature and Coproduced Resources Program. As described by the GTO1:
[The program] conducts research, development, and demonstration (RD&D) activities focused on improving the efficiency of low-temperature geothermal systems and expanding their utility through additional revenue streams. The program also researches the direct use of thermal resources for energy storage, as well as process and space-heating applications, which have the potential to provide cost-effective, reliable thermal energy in large portions of the United States. Low-temperature geothermal energy resources can be used by a wide array of community customers, including urban centers, rural areas and remote communities.
Repurposing oil and gas wells—whether they are inactive, active but uneconomic, or active and producing sufficiently high volumes and rates of water—is a very interesting area that is recommended for the reader to explore further. There are many companies, organizations and academic institutions addressing its various aspects. However, it is surely the oil and gas industry that will be the one to bring this potential to reality or, at least, greater reality than where it stands now. WO
REFERENCE
https://www.energy.gov/eere/geothermal/low-temperature-coproduced-resources#:~:text=Low%2Dtemperature%20geothermal%20uses%20include,to%20meet%20heating%20and%20hot
LKALFAYAN@HESS.COM / Leonard Kalfayan has 44 years of oil, gas and geothermal experience. He has worked for Hess, BJ Services, Unocal, and as a consultant. He is an SPE Distinguished Lecturer and Distinguished Member. He has authored numerous publications, including 3 books, and also holds 13 U.S. patents.