Use Less Gas for EOR
During the day, steam produced with solar energy reduces the amount of natural gas burned to fuel the oilfield’s Enhanced Oil Recovery (EOR) operations. However, because oil is produced both day and night, solar steam generators are used in combination with fuel-fired steam generators to produce steam on a 24-hour basis. A number of different integration strategies are possible:
During the day, solar steam is produced, and at night, gas is burned to produce steam. The fuel-fired and solar steam generators both run from the same feed water and produce the same temperature, pressure and quality of steam. Automatic control systems vary the firing-rate of the fuel-fired steam generator to maintain a constant rate of steam injection both day and night.
Most fuel-fired steam generators have a minimum firing rate of around 30%, which means that during daytime solar can provide at most 70% of the steam required. At night, when there is no solar steam, the fuel-fired steam generators provide 100% of the steam required. The net result is that solar can reduce fuel consumption by around 25% on an annual basis.
In this configuration, the same amount of steam is injected as in the Constant Rate case, but more is steam generated during the day, and less at night. This variable-rate steam strategy allows solar to provide a larger percentage of the overall steam requirement. To achieve this, the fuel-fired generators are configured to run at a constant “base rate” both day and night. However, during the day, solar generated steam is produced in addition to the base rate of fuel-fired steam, so that more steam is generated by day (base rate + solar) than at night (base rate alone). The maximum reduction in gas use depends on the exact characteristics of the reservoir, but in most cases fuel consumption can be reduced by up to 80% using this technique.
It has been shown that oil production is not affected by variable rate steam injection. Because of the huge thermal mass of the oil formation, the amount of oil produced depends solely on the total amount of steam injected, not the hours in which it is injected. Download Full Paper
The GlassPoint solar field can also be deployed to pre-heat the water fed into conventional fuel-fired steam generators. Because the feed water is warmer, less fuel is needed to convert the water into steam.
With this technique, the feed water heated by solar energy during the day can be stored in an insulated tank and fed into the fuel-fired generator at a later time, enabling solar energy to contribute to steam generation both day and night.
The amount of energy required to raise the temperature of water is much smaller than the amount of energy required to convert it to steam, so the maximum amount of fuel that can be displaced is around 10%. However, this configuration is the easiest to add to an existing oil field and can be a useful first step towards one of the other configurations.