| World petroleum resource will continue to face a shortage stage in the next decade for the high demand of fossil fuel. Various enhanced oil recovery (EOR) methods will play a key role for the contribution of world oil production. Currently, the conventional gas injection EOR method cannot be widely implemented in China compared to Europe and North American. While, the low-cost air can be easily obtained and High-Pressure Air Injection (HPAI) has been accepted as an effective EOR method. Besides, for high-temperature and high salinity reservoirs, many chemical EOR methods cannot be directly implemented; hence it can also provide a good opportunity for using HPAI. HPAI has received considerable attention as an effective improved oil recovery (IOR) process in light oil reservoirs. However, there are still a lot of misunderstandings and blanks in the aspect of fundamental theory and application research, among which crude oil oxidation mechanism, thermal effect and gas channeling prevention are the highlights in this study. HAPI application in onshore fields in China initiated later compared to abroad, it is urgent to promote research because the lack of accumulative research work in the aspect of relevant theory and assistant techniques.In the first chapter, it provides a comprehensive literature review on the research progress, research methodology and the main results of HPAI. We established a reservoir screen criterion for HPAI application and made an in-depth analysis on the weak links of basic theories and application aspects of HPAI, and also discussed how these weak links will affect HPAI performance, which gives clear research ideas for the subsequent chapters.TG/DTG/DTA thermal analysis tools as well as the classical theory of the oxidation thermokinetics of crude oil were conducted to study the influence of rock composition on the oxidation and thermal behavior of crude oil. How and why the discrepancy of oil oxidation behavior working and which rock minerals having catalyzing ability/and or inert were primarily figured out, and then different clay mineral types on oxidation kinetics of crude oil were investigated. It can give a reference for HPAI project design. On the basis of experimental results, it revealed the catalyzing contribution of different types of clays. Results showed that smectite is ranked first, illite is ranked second followed by chlorite and kaolinite in the aspect of catalytic ability for crude oil oxidation. Kaolinite is not the best catalytic agent for crude oil oxidation, which provides new insights through this research.The kinetics parameters of crude oil, oil composition and reservoir characteristics etc. are used as analogy analysis approach to preliminary estimate the feasibility of light-oil autoignition during the HPAI process at reservoir conditions. On that basis, we developed a thermal effect monitoring device, which is similar to the isothermal oxidation tube, and we have detected the obvious exothermic phenomenon of K reservoir crude oil (Tarim basin, China) in porous media in the isothermal aging test at reservoir conditions. The apparent hydrogen/carbon (H/C) ratio calculated from the effluent gas composition is used to analyze the exothermic degree of crude oil during the oxidation process in porous media. It demonstrates that the analysis approach is reasonable and also provide a convenient, economical and speedily laboratory analysis method to understand the thermal effect phenomenon. To clarify the influences of thermal effect on oil production, we derived a mathematical model for calculating oil flow rate, which is based on the heat conduction property in porous media from the combustion tube experiment. This model can perfectly simulate the influence of thermal effect on oil flow characteristic, accordingly, it proposes some methods to achieve high cumulative oil production contributed by thermal effect. On the basis of experimental results and theory calculation, it will give people a profound awareness in the aspect of thermal effect phenomenon.Sensitivity studies on the LTO behavior of crude oil in porous media have been addressed and the influences of factors such as pressure, oxidation time, water saturation (Sw), and clays on the oxidation behavior of crude oil in porous media are investigated by oxidation tube experiments. We made an in-depth analysis on the LTO reaction mechanism of light crude oil through the varied characteristics of system pressure, effluent gas and crude oil composition and established a new cracking reaction model of middle components in light crude oil. Some key factors affecting the oxygen uptake rate and oxygen consumption are discussed according to the two-step process LTO model (oxygen addition reaction and carbon-carbon bond stripping reaction). In the last part of this chapter, the influence of different gases in HPAI process on oil recovery efficiency is studied by experimental investigation.The software used for the HPAI simulations is STARS model embedded in reservoir simulation software CMG. K reservoir characteristic and geological conditions are used as research references. Simulation targets include reservoir temperature distribution, gas override, gas breakthrough time, and oil recovery efficiency. Some key factors to affect HPAI performance are discussed. Based on the understanding of the current situation of polymer gel widely used in the aspect of mobility control in gas flooding, water/and or gas shutoff, simulation results strengthen the importance for studying various polymer gel techniques during HPAI implementation. Hence, it provides an avenue in the next chapter for the study of polymer gel and gas channeling prevention mechanism when application of polymer gel assisted HPAI technique.For the fracture/and or strong heterogeneity reservoirs, it gives a study on the polymer gel techniques to enhance HPAI performance when facing such issues as gas channeling and high GOR. Developing a novel secondary cross-linking gel system and investigating into the gelation kinetics of polyethyleneimine (PEI) cross-linking gel system are addressed as the representative researches in the aspect of polymer gel assisted HPAI. It put emphasis up on the gelation performance of both two gel systems affected by porous media shearing and water salinity, and also discusses the gas channeling prevention mechanism through the experiments of gas compressing polymer gel in porous media. According to the experimental results, it not only can play a guidance to develop series of new generation of polymer gel systems based on the two gel systems, but also can guide field application. The two gel systems can act as efficient tools for assisting HPAI application.This dissertation has achieved a lot of research progresses in the aspect of crude oil oxidation mechanism and gas channeling prevention technologies in HPAI process, which present favourable reference for related work and field application. |
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