Geothermal And Electric Power Analysis Of Horizontal Well Fields
Economics constraining power generation from producing oil field fluids depend on the amount of energy generated, infrastructure costs, and power grid factors. Key factors in geothermal energy production are temperature and fluid volume, and finding the optimal combination of these factors is critical for sedimentary basin geothermal development. Sedimentary basin temperatures, typically 90 ºC to 150 ºC, require binary power conversion systems, the efficiencies of which are low, typically 6%, but recent advances in technology have led to the development of systems with efficiencies approaching 14%. Concepts for oil-field geothermal development have emphasized the use of existing infrastructure and have focused on water available in co-production or through conversion of marginally economic oil and gas wells to water production. Though technologically feasible, both concepts face limitations in delivering adequate fluid volume and, for that reason, there has been minimal progress. However, two developments, horizontal infill drilling on multi-well pads and the capability of binary systems to use the total oil and water flow, can overcome this limitation. To test the concept, we analyzed the potential for power production from two low-volume and two high-volume Bakken fields in the Williston Basin. The Bakken is a tight formation will low production rates for water and oil per well. For comparison, we also analyzed two fields in a high-volume carbonate formation. Average total production for 2017-2018 for the low-volume Clear Creek Bakken field was 7.28e5 liters/ day oil and 3.04e5 liters/day water. Production in the Baker Bakken field averaged 5.15e5 liters/day oil and 1.01e6 liters/day water. The high-volume Heart Butte Bakken field averaged 3.16e6 liters/day oil and 3.83e6 liters/day water. The Parshall Bakken field averaged 6.27e6 liters/day oil and 5.5de6 liters/day water. Bakken temperatures are approximately 120 ºC. We calculated the thermal energy production for each field based on a single pass ORC with a ΔT of 30 ºC and a cascaded ORC system with a total ΔT of 50 ºC using, where ρ is fluid density, cv is heat capacity, and V is volume. The total thermal energy for oil and water combined ranges from 5.18 e9 J for the Clear Creek field to the 1.0 e11 J for the Parshall field. Converting the numbers to electrical power with the two different ΔT values gives a range of 100 kWh to 4.11 MWh for the fields. The lower rate is for a ΔT of 30 ºC and an ORC efficiency of 6 percent. The higher rate is for a ΔT of 50 ºC and an ORC efficiency of 14 percent. A concept for future geothermal development as Bakken production declines would be to repurpose existing infrastructure by re-entering the vertical well and drilling a long lateral into the overlying water-bearing Lodgepole formation. Water production per well determined from 5 horizontal wells in the Lodgepole formation operated by Continental Resources averages 2e6 liters/day. Average production per well for the fields in our analysis of co-produced fluids averages 0.28 liters/ day. Thus, repurposing existing infrastructure in the fields to electrical power could result in a million-fold increase in energy production. Assuming the re-drilling cost in Bakken/Three Forks is $2 million per well and 4.97e5 liters oil production per well in 24 months, a Net Profit Value (NPV) of $1.75 million would be obtained with $50 per barrel at least, if one ignores the other operation costs and production decline. The South Red River B and North Red River B fields produce from mile-long horizontal wells in a dolomite/limestone formation. Well density rarely exceeds 10 per square mile, but the volume of fluid produced in the two fields provides a good comparison with the averages of our Bakken wells. The SRR-B field produces 4.28e3 liters/day total fluid and the NRR-B produces 1.39e3 liters/day. The resulting energy estimates of 1.46 e11 J and 4.62e10 J predict energy production of 6.66 MWh and 1.8 MWh respectively. This encouraging analysis of energy from co- produced fluids raises the question of who will take the lead in development.
AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019