Advanced Study on Stability of Modern Drilling Foams
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Drilling low-pressure and depleted formations using conventional methods is very challenging and uneconomical because of common drilling problems such as lost circulation in severe formation damage. Underbalanced drilling is preferably to drill low-pressure and depleted formations. Due to its good hole cleaning capacity and low liquid volume requirement, foam is very commonly used in underbalanced drilling applications. Even though drilling foam provides many benefits, its applications very limited. The industry is still reluctant to drill with foam because of inherent instability, which affects its flow behavior and other critical properties. There is strong need for better understanding of the relationship between foam stability and borehole parameters such as temperature, pressure and contaminant concentration. In order to function as drilling fluid, foam must have good stability under high-pressure high-temperature (HPHT) downhole condition. Unstable foam does not have sufficient viscosity to transport cuttings to the surface. This study is aimed to: i) improve our understanding of foam stability under HPHT condition; ii) develop foam stability models; iii) provide experimental data on foam stability; iv) investigate effects of contaminants on foam stability; v) develop reliable HPHT foam stability measuring techniques; vi) expand economic use of foam drilling; and vii) simplify well planning procedures of foam drilling projects. Although the industry is using foam drilling fluid, very limited studies have been conducted to evaluate the effects of downhole parameters on its stability. Stability of foams under ambient conditions has been investigated. Some studies were conducted at intermediate temperature and pressure to explore the effects of increased temperature and pressure on aqueous foam stability. Results show noticeable distinction in stability of foam under elevated temperature and pressure conditions. Foam degradation involves different mechanisms that are very sensitive to temperature, pressure, foam quality, contaminants and level shear rate. More investigation is needed to better understand the various mechanisms involved in the degradation processes and the impacts of temperature and pressure. Results and experimental observations from this study would provide the necessary information to: i) better understand how the temperature, pressure and foam quality affects degradation of foam; ii) establish theoretical models that predict the impact of temperature and pressure; and iii) develop new drilling foam formulations with good stability and resistant against contaminants. The established models will be used to predict stability of foams under downhole conditions. The intellectual merit of the proposed research project lies in the fact that it incorporates the effects of high-temperature, high-pressure, contaminants and shear rate in the analysis. Successful completion of the project will provide the ability to accurately describe downhole stability of drilling foams. The research methodology includes theoretical analysis, mathematical modeling and experimental studies. First degradation process of foam will be theoretically studied to better understand physical phenomena responsible for destabilizing the fluid. Based on outcomes of the theoretical analysis, mathematical models will be formulated to describe degradation process of foams. In parallel with theoretical and modeling studies, experimental investigations will be carried out to examine effects of temperature, pressure and contaminants on stability of foams..........