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| Fig. 1: Abandoned gas well on refuge lands in Lower Rio Grande Valley National Wildlife Refuge. (Source: Wikimedia Commons) |
Currently, there are a reported 123,318 orphan oil and gas wells in the United States. [1] One such well is pictured in Fig 1. These wells are at the very least leaking methane, into the air and groundwater. [1] Plugging them to stop this from happening involves setting a mechanical or cement plug. But what if instead of being stationary, these plugs could move to store and release energy? Gravity-based storage methods have been touted for their efficiency. Lifted weight storage (LWS) is a form of gravity storage that uses a pulley to raise a weight when there is excess energy, and lowers it to release the stored energy.
There are depth data for 49% of the orphan wells. Their average depth is 754 meters or 2,474 feet. [1] Conventional concrete has a density of around 2,300 kg m-3. The diameter of the weights being lifted would be limited by the smallest drill bit used in the well. Assuming a smallest drill bit radius of 3 inches, and limiting the height of the weight to 50 meters, each mass would occupy a volume of
| π × (3 in / 39.4 in m-1)2 × 50 m | = | 0.91 m3 |
Gravitational potential energy is directly proportional to the mass being moved, the height it is moving, and the force is gravity. In each well, a 1 cubic meter mass of concrete would weigh 2,300 kg. Performing the calculation for the energy stored in each well:
| Energy | = | 2,300 kg m-3 × 0.91 m3 × 9.8 m sec-2 × 754 m |
| = | 1.53 × 107 J |
Summing over all of the orphan wells in the United States, 15.3 MJ from each of the 123,318 wells is approximately 1.9 TJ of energy. Given that there are 3,600 joules in 1 watt-hour, 1.9 TJ becomes 524 MWh.
The most common form of gravity storage used today is pumped hydropower storage, of which the US has an estimated 553 GWh of capacity, which accounts for 93% of utility-scale storage. [2] That is greater than the calculations for LWS in orphan wells by three orders of magnitude.
© Christopher Perez. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Boutot et al., "Documented Orphaned Oil and Gas Wells Across the United States," Environ. Sci. Techol. 56, 14228 (2022).
[2] R. Martinez et al., "U.S. Hydropower Market Report," U.S. Department of Energy, January 2021.
