Following the gradual maturity of oil fields, engineers and geologists are expected to devise solutions to recover the remaining petroleum content in the subsurface reservoir. Prior to employing the enhanced oil recovery solutions—also known as tertiary recovery—the reservoir maintains its flow mainly due to its existing subsurface pressure—known as primary recovery. Following the dwindling reservoir pressure, pumping water or gas—known as secondary recovery—in an attempt to recover the lost pressure is also a particularly useful procedure for production engineers. The secondary recovery methods are further refined and specialised to develop tertiary recovery methods. Typically, only 40 to 50 percent content of an oil well is recoverable through primary and secondary recovery methods. This leaves a huge gap and a dire necessity for the effective formulation of tertiary oil recovery methods partly because is it more cost efficient to increase recovery than starting a new exploration and drilling operation.
Currently the most prevalent method of tertiary recover in North America is the use of an oil miscible gas—most commonly carbon dioxide—which is pumped into the reservoir under high pressure. The miscibility of carbon dioxide gas enables it to mix up and essentially swell up the oil molecules. Acquiring more volume per same weight unit, the carbon dioxide effectively reduces its viscosity and the continuous flow of carbon dioxide makes this mixture easier to flow up to the production well. One of the main purposes of any tertiary extraction operation is to reduce the viscosity of the oil. Certain properties of carbon dioxide, which include its tendency to reduce the viscosity of heavy oils when mixed, make it a very lucrative especially for heavy oil extraction. Especially as heavier oil is notoriously unyielding to conventional extraction methods.
One of the few challenges petroleum engineers face while maintaining the use of carbon dioxide for enhanced oil recovery is the accurate determination of the reservoir pressure and subsequently the pressure of carbon dioxide needed to be injected in the oil reservoir. Only at a certain pressure and temperature will the target oil and carbon dioxide be miscible in each other. Not attaining these thermodynamic conditions renders the use of carbon dioxide to be non prolific .
Economically speaking, carbon dioxide is one of the more viable methods of enhanced oil recovery. Primarily because the cost of maintaining and producing this gas is far less than the cost of using other oil miscible solvents including organic polymers and gaseous hydrocarbons. Carbon dioxide is also considered to be a environmentally prevalent compound, which further bolsters the argument for its use. Furthermore, new projects and research relating to carbon dioxide sequestration are being studied and implied at a great speed as the petroleum industry expands. The essentials of carbon dioxide sequestration involve harvesting the excess carbon dioxide in the atmosphere or the from the exhaust in combustion facilities. Such facilities include the Boundary Dam project in Southern Saskatchewan, Mississippi Powers Kempers project, and the Weyburn Midland carbon dioxide project. Two of the plants occur in Saskatchewan, Canada. The Boundary Dam project in southern Saskatchewan stands out as the pioneer of the technology of carbon sequestration, capturing one million tonnes of carbon dioxide annually, much of which it sells off a hundred kilometres norht to the Weyburn oilfield for oil recovery purposes.
Stating that such a venture could possibly hold the key to global warming crisis would be an overstatement, however the potential it holds is blatantly apparent. As the enhanced oil industry witnesses a surge of optimism and investment, the use of carbon dioxide would prove vital. Beside the recovery benefits, the dual aspect-nature of capturing carbon dioxide; which is that it can be economically viable, and environmentally promoting, makes it one of the most compelling methods of hydrocarbon recovery.
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