Vapor-Phase Combustion in Accelerating Rate Calorimetry for Air-Injection Enhanced-Oil-Recovery Processes

Abstract

Summary The accelerating rate calorimeter (ARC) is unique for its versatility of operation and application—reliability, validity, and accuracy of results—caused by very-high adiabaticity. Accelerating rate calorimetry is one of the screening tests used to determine the suitability of a reservoir for air-injection enhanced oil recovery. The ARC is well-suited for investigating the reaction mechanisms in the low-temperature range (LTR), negative-temperature-gradient region (NTGR), and high-temperature range (HTR). The ARC provides full time–temperature, time–pressure, and self-heat rate-inverse absolute-temperature profiles. An experimental and simulation study is carried out to expand knowledge and interpretation of the data derived from high-pressure closed ARC tests. Athabasca bitumen is used for the experimental study in a closed ARC at an initial pressure of 13.8 MPag (2,000 psig) to identify the nature of the oxidation reactions occurring over the different temperature ranges. The simulation component of the study focused on the development of a numerical model that captured the elements of the ARC test. The model incorporated solubility of oxygen and diffusion to control the transfer of oxygen in the liquid-oil phase. Mass transfer is found to play an important role at low temperatures up to the temperature at which chemical interaction starts to control the distribution of oxygen within the liquid bitumen. Likewise, vaporization of oil and generation of vapor by cracking reactions are also believed to play an important role in air-injection processes. Therefore, a vapor-phase combustion reaction is integrated into the traditional Belgrave kinetic model. This modified model predicted that the combustion of vaporized oil integrated with its flammable limits and the rate of diffusion of the vaporized component in the gas phase. The results of this study indicate that, with the addition of mass transfer to the kinetic model, it is possible to predict the NTGR. The result showed that solubility and diffusion of oxygen played an important role up to a temperature of 125°C at which chemical reactions started to control the distribution of oxygen within the liquid bitumen. The results also showed that vapor-phase combustion creates a temperature gradient between the gas and bitumen phases when vaporized components became flammable (stoichiometry). This showed that the ARC could be an effective tool for understanding liquid and vapor-phase reaction and their relative importance in different temperature regimes.