Offshore Geothermal Energy Production
Study on the potential of reusing oil and gas reservoirs for geothermal electricity production in the Dutch offshore
M.D. Torres Ruhe (TU Delft - Civil Engineering & Geosciences)
D.F. Bruhn – Mentor (TU Delft - Civil Engineering & Geosciences)
Alexandros Daniilidis – Mentor (TU Delft - Civil Engineering & Geosciences)
Liesbeth Jorissen – Mentor (Witteveen+Bos)
A.M.H. Pluymakers – Graduation committee member (TU Delft - Civil Engineering & Geosciences)
Raphaël van de Velde – Mentor (Witteveen+Bos)
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Abstract
Reusing oil and gas reservoirs for geothermal energy production in the Dutch offshore could be an interesting energy resource for the energy transition. The Dutch offshore contains a large number of abandoned, and producing wells that are connected to hydrocarbon reservoirs. These reservoirs have undergone significant amounts of research, and large datasets are available on them. This reduces the need for expensive and extensive research. Additionally, developed reservoirs already have the necessary infrastructure used for production built around them, such as a platform, wells and technical equipment.
In this report a portfolio of reservoirs is constructed that have the highest probability of displaying an adequate geothermal potential for producing electricity. This is done by 1): assessing the reservoir wells on the temperature in the reservoir formation and 2): plotting the wells that show an adequate temperature over an interpolated permeability map. From this map the reservoirs with the highest formation temperatures and permeabilities are selected. The geothermal electricity production potential of the selected reservoirs is then evaluated by estimating their power output with DoubletCalc. To do so, the reservoirs are assumed to be laterally homogeneous on rock type, porosity, and permeability.
Of the 325 offshore reservoirs in the Netherlands, only 6 reservoirs met the required temperatures of over 120C and an expected permeability of over 40mD. These cut-off values were introduced based on the fact that below these values the economic potential of a reservoir becomes riskful. Using the available data on NLOG an estimate of the power output could be made, which unfortunately resulted in low expected thermal power outputs (P50 < 1MW). This results from the low permeabilities in the aquifer layer, and lead to a low flow rate in the production well. As the thermal energy needs to be converted to electricity, which only returns around 14% for a Binary conversion system, the electrical power estimates are not sufficient to make such projects economically viable. The reservoirs selected in this study are thus not suitable for development of geothermal electricity production. The output is too low and the costs to realize such a project would most likely be much larger than the potential of the project.
As these reservoirs were the best case scenario reservoirs from the reservoir selection process, the conclusion can be drawn that the hydrocarbon reservoirs in the dutch offshore are not good enough to reuse, as is. Further research should therefore be done on Enhanced Geothermal Systems (EGS). Here the permeability is enhanced through methods such as 'fracking', which could potentially increase the reservoir power output due to higher flow rates.