Thermal enhanced oil recovery techniques
Heavy oils are rated below 22.3 API gravity and do not flow easily. Extra-heavy oil and bitumen is rated below 10 API gravity and is heavier than water. To extract this type of oil, an enhanced oil recovery (EOR) method is needed. In this case, a thermal EOR will be sufficient for extracting the hydrocarbons.
Oil and honey
Think of heavy oil as honey; slow, thick, unyielding. By putting it in tea, the viscosity decreases and that slow, thick honey becomes fluid and smooth; it’s ready to be extracted. It’s easy enough to pour some honey into tea but rather difficult to heat oil in the ground, encased in rock and perhaps located in harsh environmental conditions such as the Oil Sands in Alberta, Canada.
One of the main up-and-coming technologies Dr. Hascakir spoke about is microwave thermal extraction. Not a new technology, it was first tested in 1970s but later disbanded because of costs and the lack of success.
Microwave heating can target specific areas of the reservoir, whereas other thermal EOR methods usually heat the entire reservoir, taking more time and using more resources to heat. Imagine cooking something in a conventional oven versus a microwave. The time and energy saved greatly favors the microwave over the oven. Right now, this technology is in a pilot-testing phase with a handful of companies—one being Suncor in Canada—to see if this technology really is efficient in recovering more oil with less energy. The primary challenge to microwave heating is wavelength limitations. It cannot be amplified. To overcome this, an antenna must be inserted downhole, but then another limitation surfaces. The casing in the borehole can absorb the microwaves, especially metal casings, and in this instance the microwave is not going to heat the reservoir but rather heat the well. To remedy this, the well bore should be made from plastic or porcelain (these come with higher costs), which allows the microwaves to freely pass though the well into the reservoir. In addition, prior to using microwave heating, a water concentration must be introduced to the reservoir to absorb the waves and heat the hydrocarbons. Despite the challenges associated with this technique, however, the industry sees it as a promising technology that may be commercialized within the next five years. A major factor is the price of oil. If the price climbs up again, then there will be more viability in using this technology. Unfortunately, the current low prices equate to low profitability for producers.
Steam-assisted gravity drainage
SAGD is also an emerging technology but geared toward bitumen reservoirs. It is more effective than regular steam-flooding methods (15% recovery rate), which are inefficient because they do not permit the bitumen to be exposed long enough to the steam. SAGD, with a recovery rates as high as 70%, uses two wells: one introduces steam into the bitumen, and the other is used for extraction. The injection and production wells are in close proximity to one another and are located at the bottom of the reservoir. With this setup, the steam chamber expands above the injection well and covers a large area of the reservoir. This allows the temperature inside the steam chamber to remain constant and equal. The desired effect is that the bitumen remains hot as it flows toward the production well. This technique provides longer exposure to the steam and keeps the bitumen flowing, unlike the steam-flooding method.
In-situ combustion provides in-ground refining and separation
ISC occurs when oil is produced in the reservoir via combustion. Due to the fact that thermal cracking reactions occur at elevated temperatures (~450 C), heavy oil in place is cracked in light oil and some heavy ends such as ash or coke. Therefore, heavy metals and sulfurs are being separated from the oil and either left behind in the ground in the form of ash or produced water (acid water) or in gas form (H2S). This method could provide many advantages over other thermal recovery processes, including higher recovery rates, lower production and capital costs, minimal usage of natural gas and fresh water for extraction purposes, and a partially upgraded crude-oil product. By refining in situ, the oil requires less refining than the original oil in place, saving steps in the refining process.
-Dr. Berna Hascakir is an assistant professor at the Harold Vance Department of Petroleum Engineering at Texas A&M University. She directs research on thermal EOR at HOCAM.
-Edited by Eric R. Eissler, associate editor, Oil & Gas Engineering, CFE Media. email@example.com