Early kick detection and well control decision-making are more challenging when drilling with nonaqueous drilling fluids, largely due to the poor understanding of mass transfer kinetics of formation gas in and out of nonaqueous drilling fluids during these events. In this study, a laboratory-scale experimental apparatus was developed and used to experimentally investigate the desorption kinetics of methane in diesel and internal olefin, which are among the most commonly used base fluids for oil-based muds and synthetic-based muds, respectively. Continuous measurements of discharge flow rates and totalized discharge volumes yield extent of desorption over time during each test. A model with a lumped mass transfer coefficient K L a was adopted for describing the desorption process in this study. Experimental methodologies with and without blanket gas were compared and the one without blanket gas was adopted due to its enhanced accuracy and repeatability. Time-marching analysis was conducted to evaluate the instantaneous desorption coefficient during the entire bubble desorption process, while the maximum instantaneous desorption coefficient was used to characterize each desorption process. The effects of initial saturation pressure and base oil type on the resulting desorption coefficients were studied. According to the experimental results, the maximum instantaneous desorption coefficient is larger in diesel compared to the ones in internal olefins with the same initial saturation pressures. In addition, the maximum instantaneous desorption coefficient increases with initial saturation pressure for both fluids within the range of pressures that were considered in this study. C

This paper presents an experimental investigation of the time-dependent desorption of methane from non-aqueous base fluids, for a better understanding of mass transfer processes involved in riser gas events. A laboratory-scale experimental apparatus was developed and used to experimentally evaluate the rate of desorption of methane from Internal Olefin (IO) and Internal Olefin emulsions, which are commonly used as base fluids for offshore drilling in the Gulf of Mexico. The main test column of this apparatus consists of multiple sections that can be accessed separately. Methane was injected from the bottom of the test section to saturate the fluids at given starting pressures. Upon reaching complete saturation, the pressure was rapidly reduced and the methane that liberated out of solution was measured to determine the rate of degassing over time. The experimental tests were performed under various starting pressures and with different Oil/Water (O/W) ratios of Internal Olefin emulsions. Experimental results are discussed to comprehend how pressure and base fluids affect the desorption processes in the test column. This study discloses how methane evolves out of base drilling fluids commonly used in offshore drilling. The results can be used to improve well control simulators and help to better determine riser gas equilibrium through enhanced modeling of time-dependent degassing.

Synthetic-oil based drilling mud is currently the most commonly used type of drilling fluid for offshore drilling in the Gulf of Mexico, due to the environmental regulation in the area, as well as the numerous operational benefits they provide. However, early kick detection and well control decision-making are more challenging due to the solubility of formation gas in synthetic-based fluids. This partially contributes to the poor understanding of the mass transfer kinetics of formation gas in and out of synthetic fluids during these well control events. The objective of this work was to better understand the mass transfer of gas from a solution by evaluating the influence of viscosifier concentration on the desorption kinetics of methane from pure internal olefin and internal olefin-viscosifier mixture. The desorption coefficients were determined from a custom-built mass transfer apparatus. Different suspentone concentrations ranging from 0 to 5wt% by volume of liquid were used to investigate the influence of viscosifier concentration on the desorption coefficient. It was observed that the presence of suspension agents in the liquid phase decreased the mass transfer coefficient. This decrease could be due to an increase in the resistance to the flow of gas bubbles evolving from the liquid phase.

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