Reservoirs as Batteries for Wind- and Solar-power: Feasibility and Stability

Research Project, 2018 –

One of the most significant obstacles in the attempt to decarbonize energy systems has been the intermittent availability of energy coming from renewable resources, such as wind and sun, which
depend strongly on the weather and are not correlated to energy demand. An obvious solution is to store the energy produced for later in an environmentally friendly manner and with as high efficiencies as possible. An option capable of storage of large amounts of energy is the storage of gas under pressure
in depleted reservoirs or caverns. Depending on the depth of the reservoir, geothermal heat may be extracted as well when depressurizing the reservoir, thus increasing efficiency [1]. The gas is transferred to the reservoir through boreholes.

The whole procedure is linked necessarily to fluctuations in pressure over time, as pressures in the borehole and in the pores of the adjoining rock increase when gas is injected and decrease when it is
produced. These fluctuations, combined to pressure gradients, created due to the flow of the compressible gas within the reservoir, pose a challenge for the stability of the boreholes. The aim of the
suggested project is to establish a method for predicting the range of pressures and production rates at which such a reservoir may be operated with safety. This knowledge is necessary, since loss of borehole stability is linked to very high costs, reaching 10nths of millions SEK. The information is also significant to determine the viability of the approach, as the upper and lower pressure at which such a reservoir may be operated determine also the efficiency of approach for energy storage.