Evaluation of working fluids for geothermal power generation from abandoned oil wells

Geothermal energy from abandoned oil and gas wells using water in combination with a closed wellbore

“…The study by Cheng et al [18] involving circulation of binary fluid in the wellbore itself produced a net power output of 239 kW with a wellbore depth of 6000 m. A similar net power output (~217 kW) was obtained in this study using a wellbore depth of 4900 m. Increasing wellbore depth to 6000 m enabled a net power output of ~429 kW to be obtained. Despite the similarity of net power outputs obtained the use of alternative wellbore fluids in each approach represents a significant difference.…”

“…Consequentially, the lower the mass flow rate, the higher the obtainable downhole fluid temperature that can be achieved for any given well depth. These results can be compared with those by Cheng et al [18] in their study using a process whereby the binary fluid itself was directly circulated in the wellbore. In their work a minimum wellbore depth of 3000 m was identified, however several key points should be noted when undertaking comparison:…”

“…A cross section of a wellbore showing construction and sub surface fluid flows for this process can be seen inFigure 2. Cross-section of wellbore showing construction and fluid flow (arrows), with the wellbore used as a heat exchanger for geothermal power generation A similar process was outlined by Davis and Michaelides[17] and further evaluated by Cheng et al[18] with one significant difference. Their approaches involved the circulation of the working fluid from the binary plant down the wellbore itself.…”

Coupling of energy conversion systems and wellbore heat exchanger in a depleted oil well

“…Several studies have proposed the use of the borehole exchangers to convert the abandoned oil wells into geothermal ones (Kujawa et al 2006;Zhang et al 2008;Wang et al 2009;Davis and Michaelides 2009;Bu et al 2012;Cheng et al 2013;Templeton et al 2014;Cheng et al 2014). Considering the drilling costs almost 25 % of the total costs of the power plant (Hance 2005), and the high costs of closure of the oil fields, the use of the WBHX could be an economic advantage both for oil companies and for geothermal companies.…”

“…Among them are the geothermal gradient, the bottomhole temperature, the depth of the well, the properties and the flow rate of the selected working fluid, the thermal insulation between the two pipes that compose the heat exchanger (Kujawa et al 2006;Davis and Michaelides 2009;Bu et al 2012;Cheng et al 2013Cheng et al , 2014.…”