After several years of production in situ, it has become clear that current THAI (Toe Heal Air Injection) methods do not work as planned. Amid steady drops in production from their THAI wells at Kerrobert, Petrobank has written down the value of their THAI patents and the reserves at the facility to zero. They have plans to experiment with a new configuration they call “multi-THAI,” involving adding more air injection wells.
It is estimated that approximately 90% of the Alberta oil sands (1.75 trillion barrels of oil bitumen in place) are too far below the surface to use open-pit mining. Several in-situ techniques have been developed. Steam assisted gravity drainage is the most successful method and THAI fireflooding was another method.
Using Petrobank’s patented THAI technology, air is injected into the reservoir through a vertical well to spark combustion of some of the oil, creating a heated chamber that warms the remaining oil and allows it to flow to the toe of a horizontal well to be produced.
Petrobank said it now believes “permeability channels” are forming in the reservoir that take the air away from the combustion zone, preventing the zone from expanding.
It has initiated water co-injection in several wells with limited results and is experimenting with “multi-THAI,” adding more air injection wells along each horizontal well to expand the combustion zone. It said it expects the first “multi-THAI” wells to begin producing in the fall.
Steam assisted gravity drainage was developed in the 1980s by the Alberta Oil Sands Technology and Research Authority and fortuitously coincided with improvements in directional drilling technology that made it quick and inexpensive to do by the mid 1990s. In SAGD, two horizontal wells are drilled in the oil sands, one at the bottom of the formation and another about 5 metres above it. These wells are typically drilled in groups off central pads and can extend for miles in all directions. In each well pair, steam is injected into the upper well, the heat melts the bitumen, which allows it to flow into the lower well, where it is pumped to the surface. SAGD has proved to be a major breakthrough in production technology since it is cheaper than CSS, allows very high oil production rates, and recovers up to 60% of the oil in place.
Several experiments use solvents, instead of steam, to separate bitumen from sand. Some solvent extraction methods may work better in in situ production and other in mining. Solvent can be beneficial if it does not require the energy needed to produce steam. Also, as opposed to water that must be impounded, solvent may be removed from the sands and re-used.
Combustion Overhead Gravity Drainage is an experimental method that employs a number of vertical air injection wells above a horizontal production well located at the base of the bitumen pay zone. An initial Steam Cycle similar to CSS is used to prepare the bitumen for ignition and mobility. Following that cycle, air is injected into the vertical wells, igniting the upper bitumen and mobilizing (through heating) the lower bitumen to flow into the production well. It is expected that COGD will result in water savings of 80% compared to SAGD
Vapor Extraction Process (VAPEX) is an in situ technology, similar to SAGD. Instead of steam, hydrocarbon solvents are injected into an upper well to dilute bitumen and enables the diluted bitumen to flow into a lower well. It has the advantage of much better energy efficiency over steam injection, and it does some partial upgrading of bitumen to oil right in the formation. It is very new, but the process has attracted much attention from oil companies, who are beginning to experiment with it.
The above three methods are not mutually exclusive. It is becoming common for wells to be put through one CSS injection-soak-production cycle to condition the formation prior to going to SAGD production, and companies are experimenting with combining VAPEX with SAGD to improve recovery rates and lower energy costs
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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