Assesing the joint potential of CO2 enhanced oil recovery and CO2 plume geothermal energy extraction
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Many currently producing oil fields are depleting in the near future, leading to abandonment. In the meantime, the demand for oil is still projected to rise. Oil companies are searching for new ways to produce more oil from existing fields. To achieve the 2050 climate goals, the IEA allocates 14 percent of the projected global emission abatements to CCS, making it a potentially huge market in the near future. Using CO2 as a working fluid, geothermal energy extraction from medium temperature, naturally porous reservoirs becomes feasible while CO2 is stored in the formation. Mature CO2-EOR fields may be transformed into efficient CPG fields in a mutually beneficial way, leading to extended EOR time and reduced start-up time for CPG energy production. If this transition is viable, oil reservoirs could be transformed to CPG reservoirs that store CO2 and produce sustainable energy and heat while making smart use of energy market fluctuations. This research focusses on the technical feasibility of the transition from CO2-EOR to CPG and the parameters that affect the reservoir suitability for both technologies. The parameters that affect both techniques are discussed from literature and an uncertainty analysis was performed for the most relevant parameters. The most important benefits and pitfalls were discussed for three different configurations in which CO2-EOR and CPG might be combined. Based on the literature research, parameters were chosen for a fictional reservoir where both miscible CO2-EOR and CPG would be technically feasible. A model was created in Matlab to calculate the potential of both technologies in a case reservoir, and calculate the costs of the entire operation. The same reservoirs that can be used for CO2-enhanced oil recovery could be used for CO2plume geothermal. For deeper and hotter reservoirs, enough pressure difference can be generated to successfully operate a direct supercritical CO2 turbine. Based on the model, assuming a closed system with minimal mixing in the reservoir, a 99% dry stream of supercritical CO2 can be achieved in a relatively short period of time. Additional research is required on the effect of the presence of heavy oil fractions on CPG operation in a reservoir. The power generated by a CPG system was found to maximize at low depths or depths of 4 – 4.5 km For the reference case, an injection rate of 140 kg s-1 was found to have the best performance. At higher flow rates, the additional friction in the wellbore will reduce the efficiency of the system. Due to the high mobility of supercritical CO2 these injection rates would not lead to high pressure drops (<10MPa), as long as there is single phase flow, even at very low permeability (10-15 m2). However, if the multi-phase flow is taken into account, injection rates, may have to be reduced. The transition from miscible CO2-EOR to CPG appears to be feasible for a range of reservoir parameters. Although without the use of the heat the electricity price is not competitive with large scale electricity generation methods, additional power produced from the heat and income generated from storing CO2, may make the technology economically viable. In the future, if taxation on CO2 emissions become more rigorous, this technology provides a cost effective way of storing CO2.