With an official start on June 12th, it has been 3 months now since we launched the first geothermal electricity production pilot for MEET. Let‘s recall why we do this, how we do it and also take a look at the initial results.
A lot of hot brine is produced together with oil production in mature oil field. After separation by gravity at surface, the water is simply reinjected in the oil field by dedicated injector wells. Vermilion holds a portfolio of 300 wells in onshore oil fields in France, with more than 40 of them initially screened as potential candidate because of fluid flow of more than 10 m3/h and surface temperature above 70°C.
Electricity is an important part of the cost of operating an oil well because electrical subsurface pumps are installed downhole (2 to 3 km deep) to lift fluids from the depleted oil reservoir up the well. It is important to investigate how much electricity can be generated on site to save operating costs. It is worth noting that in France there is currently no economic incentive to sell the electricity to the grid, therefore self-consumption is the best option.
The well chosen for the pilot is CNY40: 500 m3/d of fluid (490 m3/d of brine and 10 m3/d of oil) at 92°C. ENOGIA’s electricity turbine (figure 1) is quite easily installed on the flowline that transport oil, gas and water from the wellhead to the manifold. Two flexible hoses bypass the production flowline and allow fluid inflow and outflow to the turbine. Surface work is necessary to update the safety barriers of the production system, for instance safety valves are installed in case of pressure changes related to the turbine. Since oil, gas and water go through the turbine, a leak would turn into an oil spill on the ground.
The principle is the one of a thermodynamic motor cycle: The produced fluid temperature is used to heat up and boil a different fluid at high pressure, called the working fluid. This vapor is depressurized to produce mechanical work, which is ultimately transformed into electricity thanks to an alternator. The produced fluid is returned to the production line at a slightly lower temperature.
Figure 1: Enogia’s ORC module installed in Chaunoy oil field (Vermilion’s site), Paris basin (France)
The Figure 2 displays the gross power produced by the turbine (left axis, in kW) from June 12th to end of June.
Figure 2: Gross power produced by the turbine (in kW) in June 2020 on CNY40
Several interesting observations can be made from the chart:
- Power output is cyclical because it depends on the cold source temperature, i.e the ambient air temperature, colder at night than during day time
- Turbine optimization at end of June consisted in removing some of the “working” fluid; it resulted if better performance
The Figure 3 displays the last week of data recorded in early September: an average gross power output of 15 kW and average net power output of 7 kW were recorded. Note that the “net” considers the electrical consumption of the ORC turbine like the compressor pump, not the oil well electrical consumption.
Figure 3: Power turbine result for a full week early September: gross daily average power output (blue dots), net daily average power output (grey dots) and average outside temperature (orange dots)