High Pressure Air Injection (HPAI) is an Improved Oil Recovery (IOR) technique in which compressed air is injected into light oil, high-pressure reservoirs. The objective of this process is the oxygen from the injected air reacts with a small fraction of the reservoir oil at an elevated temperature to produce a mixture of carbon dioxide and nitrogen. The produced gas flowing from the reaction region mobilizes the oil downstream of the reaction zone towards the production wells. Knowledge of the oil's oxidation behaviour is a key to the successful implementation of this process. However, information on oxidation behaviour of oils based on their compositions is limited, especially for light oils. An experimental study was designed to examine the oxidation behaviour of three crude oils (a light oil, a medium oil, and an Athabasca bitumen) by using the Pressurized Differential Scanning Calorimeter (PDSC) at pressures from 110 to 6,894 kPa. Pure hydrocarbon aromatics and paraffin samples were also selected for the current study. The study shows an increase of pressure results in an increase in the rate of oxidation reactions and heat released from the oxidation reactions. The PDSC heat flow curves also clearly demonstrate the effect of chemical structure of the samples on their oxidation behaviour. The extent of oxidation of hydrocarbon samples is strongly dependent on the nature of the hydrocarbon. Introduction Air injection continues to be an important oil recovery process, used to increase both the amount and the rate of oil recovered from a petroleum reservoir(1,2). When air is injected into a light oil reservoir, exothermic chemical reactions occur between the reservoir oil and the oxygen contained in the injected air. The reactions are mainly oxidation reactions resulting in heat generation and the production of carbon dioxide, carbon monoxide, and water corresponding to the consumption of oxygen. The heat of reactions results in a temperature elevation leading to vapourization of some lighter components and a decrease of viscosity of the oil, even though the heat effect is not very important for light or medium oil compared to heavy oil. Therefore, the driving gas, which can sweep the oil to production wells, is not the injected air but an in situ-generated flue gas, composed of CO, CO2, N2, and vapourized light hydrocarbon components. Air injection is a complex process involving simultaneous heat and mass transfer in a multiphase environment coupled with oxidation chemical reactions. Oxidation reactions play an important role in this process. In order to improve the efficiency of the air injection process, it is necessary to have additional knowledge of the factors influencing the process and how they affect the oxidation of oil. In recent years, the application of thermal analysis techniques, thermogravimetry (TG/DTG), and differential scanning calorimetry (DSC) have obtained wide acceptance in the study of combustion behaviour of oil. Attempts to use thermal analysis techniques to study crude oil combustion began with Tadema(3).

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This research is aimed at providing a better understanding of the oxidation behaviour of fractions of crude oil, and to then develop an approach to improve ignition for air injection processes. In this research, Thermogravimetric and Differential Thermal Analysis (TG/DTA) techniques were used to investigate oxidation behaviour using thermal fingerprinting effects on pure paraffin samples and mixtures of pure components with crude oil. The results demonstrated that each paraffin sample shows different oxidation behaviours at low temperatures and high temperatures. The fractions lighter than C16 distill before they reach a temperature where oxidation reactions are significant. Only low temperature exothermic activities are apparent for the fractions between C16 and C26. The heavier fractions show both low and high temperature exothermic activities. The lower molecular weight samples show lower onset temperatures for oxidation reactions. With increasing molecular weight, the exothermic peak temperatures both in the low and high temperature regions shift to higher temperatures and increased energy release. When low activity Oil B and the more reactive Oil C were mixed with a small amount of paraffin sample heavier than C26, both crude oils showed intensified low temperature oxidation behaviour, with a greater magnitude of heat evolution. The addition of heavier paraffins offers the potential to accelerate reactions and improve ignition. Introduction High Pressure Air Injection (HPAI) has been proven as a potential and viable process for improving oil recovery from several light oil reservoirs. When air is injected into an oil reservoir, the oxygen contained in the air can potentially react with the oil in place by various oxidation reaction schemes. Success of such a process depends mainly on the crude oil properties and rock properties, as well as operating conditions. The oxidation behaviour and the conditions typically favouring auto-ignition of crude oils are of the utmost importance for light oil air injection. However, because of the low initial temperature of many of the formations, and the poor reactivity of some crude oils, the magnitude of timedelay is often so great that spontaneous ignition is not economically attractive. Chemical ignition is one of the options to improve ignition(1, 2). Unfortunately, little research has been documented. The potential for using thermal analysis techniques to investigate oxidation behaviour of crude oils during combustion has been realized. Thermal analysis techniques include Thermogravimetric (TG) and Differential Thermal Analysis techniques (DTA) or Differential Scanning Calorimetry (DSC). In TG, a small amount of a sample of crude oil, with or without sand, is heated in the presence of flowing air and the change in weight of the sample is recorded as a function of temperature. In DTA or DSC, the difference in temperature or energy input/output during hemical or physical transitions based on the differences between the sample and a reference material is recorded as a function oftemperature or time.

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A light oil (API 30 º) reservoir is an excellent candidate for high pressure air injection, but the oil is not believed to be capable of self-ignition at the reservoir temperature. Several chemical additives and catalysts are studied to evaluate their effectiveness of ignition improvement for this light oil sample. Pressurized Differential Scanning Calorimetry (PDSC) and Accelerating Rate Calorimetry (ARC) experiments are examined in this study. The oil sample, which is mixed with certain catalysts and chemical additives, is subjected to a controlled heating schedule under a constant flow rate of air at 4.14 MPa (600 psig) and 13.8 MPa (2,000 psig) pressure for the PDSC and ARC tests, respectively. The amount and rate of heat released by the oxidation reactions is analyzed for those tests. In the presence of a metallic catalyst and chemical initiators, oxidation behaviour of the oil tested is dramatically improved. Also observed are a significant reduction in the onset temperature of significant exotherm and an increased rate for the release of heat. Introduction Air injection has been proven as a viable process in improving oil recovery from light oil reservoirs, and as a result, it has received much interest in recent years(1, 2). The concept of recovery increment is when air is injected into a light oil reservoir and exothermic chemical reactions occur. The desired reactions result in heat generation and the production of carbon dioxide. Downstream of the reaction zone, the combustion produced gas sweeps oil toward the production wells, combining with light hydrocarbon fractions vapourized by heat released from oxidation reactions. Therefore, incremental oil production is achieved. However, air injection for a light oil reservoir is a complex process involving simultaneous heat and mass transfer in a multiphase environment coupled with oxidation chemical reactions. Ignition is the first phase of this process and a satisfactory ignition is of prime importance in initiating a successful air injection process(2). In high temperature reservoirs, the air injection process is initiated by injecting air, which may spontaneously ignite the oil-in-place(1). However, in some cases, spontaneous ignition of the reservoir oil is not likely to occur so that several artificial means have been implemented(3), including down hole electrical heaters, a gas burner or injection of steam, but it is highly desirable to avoid having to run heaters or burners when air injection is to be applied in deep, high pressure reservoirs. As a result, chemical ignition is proposed(2). The concept of chemical ignition is where a slug of chemicals with reactive oxidation characteristics is injected into an oil bearing zone prior to the injection of air from an injector. If heat released from an oxidation reaction is continually generated at a rate greater than it is dissipated, starting at the native reservoir temperature, oil can be spontaneously ignited without the application of artificial means. The reactive nature of the base oil present in the ignition zone can be enhanced or stimulated. A spontaneous ignition may occur within the formation. Bednarski(4) reported on a chemical ignition improvement experiment.

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The conventional analysis of rate decline curve has been used to determine the deliverability and to forecast the performance of gas well, but it can't estimate reservoir properties. Modern rate decline analysis can be used to interpret the transient rate-time data and estimate reservoir properties and evaluate the information of formation damages. This method doesn't require shutting well down, and induces valuable information from production data. In this paper, a mathematical model for transient rate analysis at variable flowing pressure is proposed, based on the principle of superposition. The hybrid approach combined genetic algorithm (GA) with convention nonlinear optimization is presented to estimate these parameters of the fractured well. The hybrid mechanism has unified the behavior of more effective searching and quicker convergence than the conventional method. This modern analysis of rate decline method provides a new approach to monitor reservoir behavior.