One of the famous methods of enhancing the recovery factor of the crude oil reservoirs is steam injection. Steam injection is an especially effective method for the reservoirs that contain heavy crude oil. The heat provided by steam decreases the viscosity of the crude oil, thus allowing it to flow. An important limitation of steam recovery is the cost of the fuel used by the steam generators relative to the value of the crude oil recovered. The rate of steam injection is also very important, for it's essential to keep the steam front moving smoothly. Steam injection in the areas with abundant sunshine can use the solar energy instead of fuel burning to produce steam.
Solar energy is a clean and environmental friendly way to produce energy, but using the energy efficiently is difficult. The energy is only available during the day when there is a sunshine. The amount also changes with seasons.
An efficient way to save the solar energy is to transform it to steam. A company called GlassPoint has designed such a generator that uses reflectors to focus sunlight to create steam. [1] They call it Solar-Steam. GlassPoint claims that its system can produce steam at roughly half the cost per barrel of steam produced by burning natural gas.
Solar-steam has the potential to be used in the steam injection process as an enhanced oil recovery method. Many crude oil reservoirs in the US are located in areas with abundant sunshine. Solar-steam might be an especially good option in those areas.
The rate at which steam should be generated is calculated first by means of Thermal Reservoir Simulator (e.g. STARS). Simulation of the reservoir enables engineers to calculate the amount of steam needed to keep the steam front moving through the reservoir and maintain a constant oil production rate. Some part of the steam is will be lost by heat transfer to the adjacent layers of the reservoir. There is also heat loss to the reservoir rock itself. Simulation studies determine these heat losses and then work backward to determine the amount of steam required for injection. Once the steam injection rate is known, the Solar-Steam design parameters can be assessed. Analysis by Stanford University professor Dr. Anthony R. Kovscek shows that 20% Solar-Steam generation can economically increase production by 5% to 7% and reserves by approximately 12%, for the same operating costs as gas-fired steam. [1]
A concern about using the Solar-Steam is the changing heat flux from the sun over day and also during the year. A simple solution to this problem is to use the gas-fired system to compensate the gap when the Solar-Steam rate falls below the desired level. Another approach is to use reservoir simulation to see how continuous steam injection that cycles up and down in rate over a day performs. Reservoir simulation can nicely predict this effect. It is highly dependent on the type of the reservoir. For example, in carbonate reservoirs, which are usually fractured, the impact of daily cycles can be ignored. [1] But seasonal change of the steam rate causes the cycle in oil production both for fractured and non-fractured reservoir. [1]
Solar energy is a good option for providing steam for injection purposes to the crude oil reservoirs. The steam improves the recovery of the reservoir and also is an efficient way to use the continuous energy of sun. For fractured reservoirs, the daily cycle of steam does not affect the production. Seasonal cycles have an effect in all cases. For areas with less seasonal change of sunlight, such as middle eastern countries, where the reservoirs are mostly fractured, the steam-solar system works perfectly. In other cases, gas-fired burners would be needed to fill the gaps and maintain a constant steam rate.
© Mohammad Bazargan. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] A. P. G. van Heel, "The Impact of Daily and Seasonal Cycles in Solar-Generated Steam on Oil Recovery," Society of Petroleum Engineers, 129225-MS, April 2010.