Technical Committee Production Engineering

Geothermal Heat Production from abandoned Oil and Gas Wells

The engagement to reduce the COZ-emission by 20 %until 2020 by the European Council leads to an increased energy political interest on energy efficiency and profitability of renewable energy on the heat market. In respect to geothermal heat production, especially the high drilling costs for deep boreholes (ca. 500-1000 €/m) negatively influence both profitability and energy efficiency. For this reason the re-use of abandoned or non-rich deep boreholes was investigated. Only the use of borehole heat exchangers (BHEs) co-working with heat pumps was considered in this study.

Simulations of geothermal heat production were performed for 10 different scenarios in each case at 4 deep boreholes by the program ModEW (ModellErdwärme). For this a technologically effective length of 0-800 m, different heat transport fluids (ammonia, propane, ethane, carbon dioxide and water) and various working schemes (permanent, heating typical and heating typical plus air conditioning) were assumed. On the base of the results conclusions were made in respect to the energy efficiency of the simulated BHE technologies, to the requirements for a profitable re-use, to technical specifications of the borehole and the BHE, to the dimension of the geothermal heat plant and to the environmental impact of the working plant.

The simulated heat power varies caused by the geological site conditions and the variants of utilisation. A maximal geothermal heat power of about 163 kW (in winter) or a total heat power of ca. 218 kW results for an electro drive or ca. 336 kW for a gas motor drive (depending on the kind of the heat pump drive) were proven for a BHE working by direct evaporation of ammonia over a period of 20 years. The corresponding cold power of such a BHE reached about 16 KW to 69 kW assuming a stopped heat pump during the summer month.

Finally, advises for the geothermal re-use of deep boreholes were concluded by investigations to the geothermal re-use of deep borehole sites from oil and gas industry and to the permission of BHEs in Germany in the sense of mining law.