Abstract
In this article, we propose and investigate a methodology for subsurface energy storage as part of a subsurface injection-production process, e.g., hydrocarbon production. To reduce the carbon emissions from offshore operations, gas turbines need to be replaced with cleaner energy. With an increasing share of renewable energy in the energy mix, the energy supply is more intermittent, resulting in fluctuating prices or availability. This situation increases the need for energy storage. Production processes, injecting into and producing fluids from the subsurface, require vast amounts of energy for the pumping of fluids. Energy use can be balanced by a varying injection rate; however, this will rapidly affect production through the change in pressures at the producer wells. This article suggests storing energy in the subsurface by injection into an adjacent reservoir. For example, the injection well is drilled deeper than the target, entering a lower-laying reservoir where the surplus energy can be stored by compressing fluids into the porous medium. This stored energy is released during low energy supply, alternatively, during periods with high energy prices, by cross-flow in the well from the lower-laying reservoir into the main producing reservoir. This concept stores energy from periods with high availability to periods with low availability, which provides a more continuous and balanced injection into the producing reservoir, and thereby improves the drainage process. Wind-powered water injection into an oil producing reservoir is used as a case study for our proposed energy storage method. In this case study, we compare wind-powered water injection with and without subsurface energy storage towards a base case where the injection is supported by a stable energy source such as a gas turbine. The results show that the use of a storage reservoir can sustain the water-injection during the low wind period and thereby sustain the oil production. There is a trade-off between storage capacity and efficiency, depending on the size and petrophysical properties of the storage reservoir. Efficiency is reduced by leakage between the storage reservoir and the producing reservoir.