Investigation of in-situ combustion kinetics using the isoconversional principle [electronic resource]
Keywords: Energy Resources Engineering

In-situ combustion (ISC) is the most energy efficient thermal enhanced oil recovery (EOR) method implemented in crude-oil reservoirs. The worldwide implementation of ISC in commercial field projects reached a maximum of 19 during the period of 1970's to 1990's, but it has declined to 4 active operations nowadays. Many failed projects are due to incorrect operations. Understanding the complicated combustion kinetics during the ISC process is essential and significantly important to optimize field operation. The combination of the experimental tool, ramped temperature oxidation (RTO), and the measured data interpretation method, isoconversional principle, provides a workflow to unlock the complicated characteristics of ISC kinetics. Conducting reliable or repeatable RTO experiments for isoconversional interpretation is the baseline for the workflow. Simulations coupled with a synthetic reaction model in an in-house virtual kinetic cell (VKC) simulator show that reducing temperature deviation caused by exothermic reactions is critical to carry out consistent RTO experiments. The argument is supported by a series of RTO experiments of the same crude-oil mixture, but different working conditions with respect to the kinetic cell design, the volumetric flow rate of air injection and the size of the sample mixture. Furthermore, the consistent RTO experimental results prove the model-free nature of the isoconversional principle and its applicability in the investigation of ISC kinetics. An attempt to combine the isoconversional principle and the conventional interpretation method is proposed to interpret kinetic parameters including apparent activation energy, pre-exponential factor and reaction orders for both fuel and oxygen partial pressure. Simulations in the VKC were carried out to test the proposed method for a unit and a non-unit reaction order case. The result showed good matches in the kinetic parameters between the interpretation and the simulations. A three-reaction scheme is proposed for two crude-oil mixtures, Alaska crude-oil and Karamay crude-oil, based on the observation and analysis of the activation energy fingerprints and the effluent data. The stoichiometry and the kinetic parameters for the reaction model are interpreted by the proposed method. The combustion models are verified in the commercial reservoir simulator CMG-STARS regarding the temperature histories, the effluent data from RTO experiments, and the isoconversional fingerprints. Further application of the isoconversional principle to analyze the crude-oil combustion includes investigating the sand and clay surface effect on the reaction paths together with X-ray photoelectron spectroscopy (XPS) to study the coke formation characteristics and their reaction kinetics. Screening the ISC candidates with respect to different crude-oil/sand-matrix pairs is also discussed. Lastly, the development of a microwave heating system is discussed to replace the conventional electric furnace system to carry out RTO experiments. Three generations of the microwave heating system are developed and discussed.