by Emil Morhardt
Fracking isn’t just for natural gas and conventional oil; it also increases the production of heavy oil in low permeability reservoirs, but if the oil is heavy enough and the cracks don’t penetrate very far, the flow rates decay rapidly and not much oil is recovered. [Heavy oil, not defined in this paper, is usually a term used for oil just a little less viscous than bitumen, the “extra heavy oil” found in the highly contested Canadian tar sands—more or less like asphalt.] One possibility is to heat up the rock surrounding the well to make the oil less viscous. A technique that works in conventional oil wells is to inject steam, but with heavy oil in low permeability reservoirs steam doesn’t work very well. The approach discussed in this paper by Davletbaev et al. (2014) is to use microwave radiation (also known as radio-frequency electromagnetic radiation) of the sort used in your kitchen microwave oven. Of course it is impossible to bring the oil-shale to the oven—the oven has to go to it in the form of downhole electrodes. Another difference is the amount of energy required. A “powerful” home microwave oven consumes about 1,000 Watts (1 kW) provided by a standard kitchen electrical circuit. The heating of well bores simulated in this paper used 10–30 times that much electricity, but experimental studies have shown that after a day-and-a-half of heating, temperatures in the well can exceed 300°C (572°F) and can raise the temperature of the shale (and oil) to over the boiling point of water a few meters away.
This paper is about an operational strategy to maximize the flow of heavy oil using a combination of fracking and microwave heating, while minimizing the amount of electricity required. The idea is to frack first and let as much oil out as will come, then to heat for a while, stopping when the oil starts flowing, and reheating as many times as it takes to get as much of the oil as economically possible. The study compared the simulated oil production from a “cold” fracked well with that from a heated one for 550 days, assuming that the microwave device cost $100,000 and the oil sold for $100 per barrel. The authors concluded that the multi-stage heating could increase oil production by 87% in a well with low permeability “short” fractures, the type of well most suitable for this technique. Depending on the permeability of the fractures, the oil production rate, the amount of electricity used, and few other variables, payback times for the microwave heating ranged from 420 days to five-and-a-half years; somewhat less than the 550 days the simulations were run to four times that. The authors don’t comment on what this says about the feasibility of using microwaves to increase heavy oil production, but from my calculations, it doesn’t look like a very good option for most of the cases they tested.
Davletbaev, A., Kovaleva, L.A., Babadagli, T., 2014. Heavy Oil Production by Electromagnetic Heating in Hydraulically Fractured Wells. Energy & Fuels. Just Accepted Manuscript DOI: 10.1021/ef5014264. Abstract at: http://bit.ly/1xuHbrS