Enhanced oil recovery (also known as tertiary recovery or EOR) means the implementation of a range of techniques in order to increase the amount of crude oil which can be extracted from the oil field. The main three techniques, according to the US Department of Energy, are chemical injection, gas injection, and thermal recovery. Gas injection uses natural gas, carbon dioxide, or nitrogen, the technique accounting for close to 60% of United States’ production of EOR. Chemical injection can involve polymers in order to increase the effectiveness of the waterfloods, the technique accounting for approximately 1% of the country’s EOR production. Today, thermal enhanced oil recovery accounts for about 40% of the EOR production in the nation, the technique involving the introduction of heat.
There are currently being developed new technologies to extract heavy oil. Dr. Berna Hascakir works at the HOCAM center at the Texas A&M University, and talked about microwave heating, in-situ combustion, and gravity drainage which is steam-assisted. Heavy oil is below 22.3 API gravity, which means they don’t flow easily. Additionally, bitumen and extra-heavy oil is rated below 10 API gravity, making it even heavier than water. In order to extract this type of oil, thermal EOR is necessary.
Microwave thermal extraction is an up-and-coming technology that Dr. Hascakir talked about. Despite being considered up-and-coming, the technology was first tested back during the 1970s, but it was disbanded as a result of costs and its lack of success. Microwave heating, compared to other thermal EOR techniques that generally heat the whole reservoir, is able to target specific areas – making it more time efficient and using fewer resources to heat. The technology is still in the pilot-testing phase with a number of companies, in order to see how efficient, the technology is and if it can recover more oil using less energy.
A main challenge that microwave heating is facing is the wavelength limitation which cannot be amplified. In order to overcome this hurdle, an antenna needs to be inserted downhole, but this raises a different problem. The borehole casing is able to absorb the microwaves, which means the microwave will not be able to heat the reservoir and it will end up heating the well. In order to fix the issue, bore needs to be made from either porcelain or plastic, which will allow microwaves to pass through the well and into the reservoir – but the cost of plastic or porcelain is higher.
Additionally, before using microwave heating, there needs to be introduced to the reservoir a water concentration in order to absorb the waves and to heat the hydrocarbons. Despite the fact that the technique needs to overcome some hurdles, the industry sees potential in it. SAGD or steam-assisted gravity drainage is another emerging technology, but it is geared more towards bitumen reservoirs. The technology is considered more effective than the regular methods which involve steam-flooding, which do not allow bitumen to be exposed to steam long enough. The technology’s recovery rates go as high as 70%.