|Fig. 1: A solar enhanced oil recovery site in Oman. (Source: Wikimedia Commons)|
One of the significant challenges that oil companies face during oil production is the low recovery factor (RF) of mature oilfields. A mature oilfield is one where production has reached its peak and has started to decline. The average RF from mature oilfields around the world is between 20% and 40%.  Due to this reason, oilfield operators have attempted several enhanced oil recovery (EOR) techniques that offer prospects for ultimately improving the recovery factor and accelerating oil production.
Thermal recovery is an EOR technique that has been commercially successful. Conventionally, thermal EOR usually involves burning natural gas to produce steam which is injected into the reservoir to heat heavy oil to reduce its viscosity. On the other hand, solar-generated steam in EOR involves the use of concentrating solar power technology to produce this steam. Mirrors are used to reflect and concentrate sunlight onto receivers that collect solar energy and convert it to heat. This heat is then used to produce steam from water. One of the principal benefits of using solar energy for thermal EOR is the reduced energy costs and carbon footprint of the crude oil produced. Thermal energy has already been deployed in places like Oman (Fig. 1), Kuwait, and some fields in California.
As explained above, the main aim of TEOR is to use energy from steam to heat up the oil in the subsurface. This allows the oil to flow more easily due to the impact of various recovery mechanisms. Some of the mechanisms that have been shown to provide major contributions during TEOR include crude-oil viscosity reduction, thermal expansion, and crude-oil vaporization.
Solar thermal EOR faces some challenges that affect its implementation. Cyclic fluctuations in steam injection rate associated with sunlight hours and seasonal variations challenge this technology from becoming a standalone solution. [2,3] It is required to be supplemented with conventional thermal EOR to supply a continuous injection of steam. Another problem for thermal EOR is the reservoir temperature control in the oilfield as oil production wells quickly attain very high temperatures. Some other techniques, like cyclic steam injection, are being applied in order to help curtail these problems.
© Kofi Owusu-Agyeman. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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.
 A. Muggeridge et al., "Recovery Rates, Enhanced Oil Recovery and Technological Limits," Philos. Trans. R. Soc. A 372, 20120320 (2014).
 J. Sandler et al., "Solar-Generated Steam for Oil Recovery: Reservoir Simulation, Economic Analysis, and Life Cycle Assessment," Energy Convers. Manage. 77, 721 (2014).
 R. Riog, A. Argawal and A. Kovscek, "Sensitivity Analysis for Solar-Generated Steam for Enhanced Oil Recovery," One Petro SPE-190075-MS, 22 Apr 18.