Despite the abundance of in situ combustion models of oil oxidation, many of the effects are still beyond consideration. For example, until now, initial stages of oxidation were not considered from a position of radical chain process. This is a serious difficulty for the simulation of oil recovery process that involves air injection. To investigate the initial stages of oxidation, the paper considers the sequence of chemical reactions, including intermediate short-living compounds and radicals. We have attempted to correlate the main stages of the reaction with areas of heat release observed in the experiments. The system of differential equations based on the equations of oxidation reactions was solved. Time dependence of peroxides formation and start of heat release is analytically derived for the initial stages. We have considered the inhibition of initial oxidation stages by aromatic oil compounds and have studied the induction time in dependence on temperature. Chain ignition criteria for paraffins and crude oil in presence of core samples were obtained. The calculation results are compared with the stages of oxidation that arise by high-pressure differential scanning calorimetry. According to experimental observations we have determined which reactions are important for the process and which can be omitted or combined into one as insignificant.
Summary Application of air injection as an enhanced oil recovery method involves high risks, both economic and technological. One of the main risks of this technology is the lack of oil self-ignition during air injection and difficulties in creating a combustion front in the reservoir. In a number of fields the reservoir thermal and pressure conditions and the oil properties cause spontaneous ignition (mainly light oil fields with a high reservoir temperature), while in other fields special ignition programs are required. In the present paper three possible ways of air injection process development are shown: the method of "pushing" oil with air without combustion front appearance, in-situ combustion (ISC), and thermogas treatment, or, using the American terminology, high pressure air injection (HPAI). The field’s properties that determine which way in-situ combustion process will develop are identified. One way to determine in which of these three ways the process will develop is to study the oxidation characteristics using the pressurised differential scanning calorimetry (PDSC). For the improved study of the combustion process DSC experiments of oil samples oxidation reactivity, oil-saturated core and other actively reactive substances are performed. High precision of modern thermo-analytical PDSC equipment enables investigating the initial stages of oxidation reactions of hydrocarbons and describing the initial stages of the reaction in terms of the Arrhenius theory as well as the theory of chain reactions. This approach allows us to identify the most reactive oil components (oil paraffins), and describe the process of their oxidation in terms of the chain mechanism of birth and death of free radicals. It is shown how oil can change its reaction activity at the reservoir rock samples; the activity among others, is caused by the adsorption of asphaltenes and oxidised components on the core surface during the heating process. In addition, the unsteady type of oil (tarry light oil) has been studied, oxidation of which is accompanied by transition of resins to secondary asphaltenes, which, as it has been first shown, in the presence of core significantly increases the amount of fuel. In the case when the pressure and temperature conditions of the reservoir and oil reactivity prevent spontaneous ignition, some cases for combustion initiation have been considered. It is shown that due to PDSC experimental results a comparison of hydrocarbon and other fluids in order to find a reagent with the lowest self-ignition temperature can be achieved. It is shown that vegetable oil additions to oil can significantly reduce the temperature of the heat output, and can serve as oil ignition initiators for air injection. Technical aspects of combustion ignition are also discussed in the paper. The technology integrate heating agent and reactive hydrocarbon liquid injection, which reduces the lack of ignition risks in the oilfields with low temperature.
The paper focuses on the problem of the crude oil self-ignition in situ, which has not yet been solved in the general case and for a particular oilfield as well. To solve the problem of ignition, we approached from a theoretical point of viewapplied the theory of chain reactions to the description of the initial stages of oxidation. The obtained dependences of heat release on time should be of a general nature for experiments in which self-ignition occurred (we called them high rate experiments) and for experiments in which fuel formation was observed (low rate experiments). We first demonstrated this relationship in the experiments we conducted by high pressure rate calorimeter (PDSC). And then we analyzed the various experiments from literature sources. The novel results of the presented approach show the probabilistic nature of the ignition and the presence of a group of processes that do not lead to ignition, in which the free radicals are not sufficiently active and the heat sink exceeds the heat release. Instead of the heat balance, a new ignition criterionφ-factor for chain reaction, the difference in the rate of formation and death of free radicalsis derived. A positive value of φ-factor indicates the increase of energy in the system and the ignition by the chain mechanism, while a negative value indicates the attenuation of the reaction and the formation of oxidized compounds without ignition. The PDSC experiments with light crude oil oxidation were conducted under various heating rates in order to explore the ignition temperature–time dependence (the example of high rate experiments). The results show the same dependence of the process time on temperature predicted theoretically. The other types of high rate experiments (adiabatic experiments, combustion tube experiments) and low rate oxidation experiments from literature sources are also considered in terms of our approach. The comparison of different types of experiments with the obtained mathematical formulas gives a good agreement. The low rate oxidation dependences refer to the negative values of φ-factor, and high rate oxidation refers to positive φ-factor modes. Both types of experiments are in good consistency with the theoretically obtained dependence and show that the model of the chain reaction approach works well. Thus, the chain reaction approach to the ignition mechanism gives one a good consistency with experimental data and can be applied for the prediction of ignition time for air injection projects. The other result of our approach is the difference between heavy and light oil oxidation in low and high rate processes. In high rate processes, free radicals are active enough for igniting the oil, and light oils contain more free radicals of this type and are more reactive for ignition. Heavy oils have better affinity for fuel formation and oxygen addition reactions. So heavy oils can usually ignite at higher temperature than light oils.
Oil oxidation reactions have attracted considerable interest in terms of mechanism comprehension for thermally enhanced oil recovery applications. Many hypotheses regarding oil oxidation mechanisms appear to be disputable even now. The aim of our work was to broaden current knowledge on the crude oil oxidation chain reaction mechanism including the formation behavior of free radicals and hydroperoxides. In this context, we attempted to shed light on the main differences in the oxidation reactions between heavy and light oils. We have found a way to solve both analytically and numerically a set of differential equations for concentrations corresponding to the reaction scheme. Taken together, our findings allowed us to obtain hydroperoxide concentration dependence on time for the initial stages of oxidation. Two main time dependencies were observed, one for low-temperature oxidation (LTO) and the other for high-temperature oxidation (HTO). Both dependencies were revealed in the oxidation experiments of different types of oils and were taken for the matching procedure, which is also presented in this work. The φ-factor of branched-chain reactions, obtained as a combination of reaction rates, determines the efficiency of LTO and transition from LTO to HTO. By matching the experimental data, we were able to find that the success of self-ignition may be achieved only if the concentration ratio of saturated hydrocarbons to inhibitors in crude oil is equal to 2 or more and the temperature is more than 415 K. Under these conditions, the ignition time for heavy oil was 5–7 days, and that for light oil was 15–30 min in oxidation experiments, which were well matched by the presented chain reaction model.
Лабораторные исследования и реализация технологии инициирования горения нефти при закачке воздуха в нефтяные пласты.Валерий Андреевич Клинчев, Владислав Вячеславович Зацепин, Александра Сергеевна Ушакова, ОАО "Зарубежнефть", Сергей Владимирович Телышев, ООО "СК "Русвьетпетро" Авторское право 2014 г., Общество инженеров нефтегазовой промышленности Этот доклад был подготовлен для презентации на Российской технической нефтегазовой конференции и выставке SPE по разведке и добыче, 14 -16 октября, 2014, Москва, Россия.Данный доклад был выбран для проведения презентации Программным комитетом SPE по результатам экспертизы информации, содержащейся в представленном авторами реферате. Экспертиза содержания доклада Обществом инженеров нефтегазовой промышленности не выполнялась, и внесение исправлений и изменений является обязанностью авторов. Материал в том виде, в котором он представлен, не обязательно отражает точку зрения SPE, его должностных лиц или участников. Электронное копирование, распространение или хранение любой части данного доклада без предварительного письменного согласия SPE запрещается. Разрешение на воспроизведение в печатном виде распространяется только на реферат объемом не более 300 слов; при этом копировать иллюстрации не разрешается. Реферат должен содержать явно выраженную ссылку на авторское право SPE. РезюмеПрименение закачки воздуха в качестве метода увеличения нефтеотдачи сопряжено с высокими рисками как экономического, так и технологического характера. Одним из основных рисков данной технологии является вероятность отсутствия самовоспламенения нефти при закачке воздуха и сложность создания в пласте очага горения.Для ряда месторождений термобарические условия пласта и свойства нефти таковы, что происходит самопроизвольное воспламенение нефти (в основном месторождения легкой нефти с высокой пластовой температурой) для других месторождений требуются специальные мероприятия по инициированию горения.В данной работе показаны три возможных пути развития процесса закачки воздуха: "способ проталкивания" нефти воздухом без возникновения фронта горения, внтурипластовое горение (ВПГ) и термогазовое воздействие (ТГВ) или по американской терминологии (high pressure air injection), выявлены особенности месторождений, определяющие, по какому пути развития будет идти процесс внутрипластового горения. Один из способов определения, по какому из трех вышеперечисленных вариантов пойдет процесскинетические исследование окисления с помощью калориметров высокого давления (ДСК). Проводятся лабораторные исследования реакционной активности при контакте с воздухом образцов нефти, нефтенасыщенной породы и других реакционно-активных веществ. Высокая точность современного термоаналитического оборудования ДСК позволяет исследовать начальные стадии окислительных реакций углеводородов, описывать реакции как c помощью теории Аррениуса, так и в рамках теории цепных реакций.Такой подход позволяет выделить наиболее реакционно-активные нефтяные компоненты (нефтяные парафины) и описать процесс их окисления с точки зрения цепного механи...
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