High pressure accelerating rate calorimetry (ARC) tests have been performed on three different crude oils, at their respective reservoirs pressures. The experiments on medium heavy Clair oil and heavy Wolf Lake oil used clean silica sand, incorporating 3% kaolinite, to represent the reservoir matrix, whereas Athabasca Tar Sand was used in its preserved, virgin state. The Clair oil and Wolf Lake oil tests involved high initial water saturations, representative of either, a post-waterflooded or a post-steam injection state, in the reservoir. A second test on Athabasca Tar Sand used a lower oil (bitumen) saturation, but without adjusting the original brine saturation. Although the medium Clair oil exhibited high exothermicity, throughout the temperature range, the temperature detected for the onset of low temperature oxidation (LTO) was much higher than that for Athabasca Tar Sand. The calculated activation energies also indicate that Athabasca Tar Sand is very reactive in the LTO region. Furthermore, the overall continuity exhibited by the measured exotherms, indicates that all three oils are potentially good candidates for in situ combustion, as an oil recovery method.
The most important factor governing the selection, ultimately, of any improved oil recovery (IOR) process, is the availability of a suitable fluid to inject into the reservoir. Even when a fluid agent has been identified for application in a particular reservoir, it needs to be easily deliverable, and available in sufficiently large volumes. Otherwise, the prospect of improved oil recovery is academic. For an increasing number of reservoir situations, air injection is gaining increasing attention for both heavy and light oil recovery. Air injection, into heavy oil reservoirs, otherwise referred to as in situ combustion (ISC), or ‘fire flooding’, has been applied with varying degrees of success, over the last 40 years. The most recent heavy oil projects are in the Cambay Basin, India (1), using conventional ISC, and the first field pilot at Christina Lake, using the advanced THAI (Toe-to-Heel Air Injection) process (2). There have also been significant developments in high pressure air injection into light oil reservoirs, as evidenced by economically viable air injection projects in the Williston Basin, and project feasibility studies for Barrancas, Argentina (3), and Cantun, Mexico (4). In the latter case, air injection is seen as a possible replacement for more expensive nitrogen injection. The future IOR prospect in the latter case is huge, some 56 billion barrels of accessible resource.
There are many economic and technical benefits deriving from air injection - excellent displacement efficiency, mobilization of extra oil ahead of the combustion zone, reservoir pressurization, oil swelling from produced CO2, flue gas stripping, injection gas substitution and, for high pressure, hot reservoirs, and there may be additional factors, such as spontaneous ignition and near miscibility effects.
The accelerating rate calorimeter (ARC) was first advocated as technique for screening oil reservoir candidates for air injection by Yannimaras and Tiffen (5). The technique was developed as a method for studying the reaction kinetics by following reactions adiabatically, especially at high pressure.