Geothermal Resource Development For District Heating: Providing The Consumer With The Lowest Heat Price

Abstract

Many of the sedimentary basins throughout the world contain several geothermal reservoirs that are potentially attractive for the production of low-enthalpy geothermal energy for district heating. For example, in Denmark locally there are as many as four sandstone reservoirs, which have the potential to produce geothermal energy for district heating at commercial rates. These reservoirs occur at depths ranging from 800 to greater than 3000 meters below the ground surface and have temperatures between 30 to greater than 80 oC. The big question is which reservoir to develop in order to provide the consumer with the lowest heat price? Our strategy for determining which reservoir to develop for the most cost-effective production of geothermal energy for district heating involves estimating the geothermal power production from each reservoir, defining the heat demand of the district heating network, constructing business case models for the different reservoirs and calculating the cost of geothermal energy production from each reservoir. Flow rates were simulated for 25 exploration wells from 3 different sandstone reservoirs in northern Jutland, Denmark. The flow rate estimates decrease with depth by a factor of 10 due to the reduction in porosity and permeability, whereas the reservoir temperatures increase by a factor of 3 over the same depth interval. Next, a base case flow rate versus depth curve was established, which was used along with the geothermal gradient to calculate a geothermal power production versus depth curve. Business case models were created for the geothermal power production curve and the normalized cost per megawatt hour of thermal energy produced versus depth was calculated. The results show that the lowest cost per megawatt hour of thermal energy produced is from relatively shallow reservoirs, which are characterized by having high permeability and low temperatures. In summary, for basins filled with clastic sediments, shallow reservoirs may be the optimal targets for providing the consumer with the lowest heat price by maximizing geothermal energy production while minimizing risk and cost.

AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019