A semi-analytical model to simulate the behavior of a gas kick in an annulus was developed utilizing various concepts, including gas solubility in oil-based drilling fluids. This simulator examines critical kick indicators such as Pit Gain and Wellhead Pressure with time. It models the gas behavior using a drift-flux approach with bubble rise velocity appropriate for flow through an annulus. It also uses the Peng-Robison equation of state, van der Waals mixing rules, along with binary interaction coefficients appropriate for drilling fluids, to account for gas solubility in oil-based mud. The simulation results predict that a five-barrel (bbl) gas kick, would reach the wellhead of a 10,000 ft deep, non-circulating, vertical well in approximately 78 minutes. But it would only take 35 minutes to traverse the same well, if the well is circulating at 702 gallons per minute. The simulations also predict that if there is a constant kick influx of 1 scf/sec, the first gas bubbles would reach the wellhead of the same, non-circulating well in 4.45 hours. But only take 52 minutes when it is circulating. Incorporating gas solubility into these simulations revealed that the choice of drilling fluid volume factor (Bo) correlation affects the results significantly. It also showed that some of the existing Bo correlations fail, for drilling fluid swelling calculations, at higher pressures and temperatures. Finally, the results indicate that a gas kick would take longer to reach the wellhead when it is soluble in the mud than when it is not, regardless of the choice of Bo correlation. Most of the existing kick simulators either partially or entirely overlook the effects of solubility on gas migration. This model accounts for the gas kick's solubility in Oil-based drilling fluids, an issue that is critical for off-shore drilling. Applicability of empirical two-phase flow correlations developed for flow in cylindrical conduits, to a gas kick situation is questionable. This simulator addresses this issue by using a semi-analytical approach for modeling two-phase flow in an annulus.

Gas kick is an ever-present hazard whose importance is magnified for offshore drilling situations. Modeling gas kick is a complex problem that requires an understanding of the relevant fluid dynamics as well as the solubility of natural gas in oil-based muds (OBM). Drilling fluid swelling due to natural gas solubility in OBM significantly affects the extent of pit gain — one of the primary indicators of a kick in progress. This paper specifically addresses the issue of drilling fluid swelling from gas dissolution in OBM. Drilling fluid swelling due to gas dissolution is generally expressed the same way as oil swelling due to dissolved gas, by the volume factor, Bo. Many correlations for estimating Bo as a function of temperatures and pressures are available. We have developed a rigorous thermodynamic approach for estimating Bo. Our approach uses the Peng-Robison (1976) equation of state (EOS), van der Waals mixing rules, and binary interaction coefficients appropriate for drilling fluids to account for gas solubility. Solving the cubic form of the Peng-Robinson EOS yields a z-factor for the liquid phase of the mixture. The model uses this z-factor to estimate the liquid-phase volume of dissolved methane and, consequently, Bo. This paper validates the results of estimated Bo from this method with volume factor calculations obtained from Aspen HYSYS. Finally, this paper also presents a section where the methane mole fraction data at different P&T conditions, obtained from HYSYS simulations, is used to validate the solubility model previously developed by Manikonda et al. (2019).

Offshore well costs and risks have proven the need for research in deep water drilling and well control. This paper presents the experimental research that is ongoing at the Dual Gradient Drilling Laboratory to understand the physics involved in gas migration. A scaled prototype of an offshore well was built to mimic the Controlled Mud Level (CML) Drilling method. Instrumentation and cameras were used to monitor flow rate and gas liquid ratio. Set rates for the mud outflow and inflow were determined and tested at constant gas influx, by increasing the mud inflow in narrow increments. The prototype was successfully tested and removed a large amount of gas from the system before the gas migrated into the voided section. The results of these tests show that using high mud inflow rates can eliminate the single bubble system, leading to a dispersed bubble system. With dispersed gas bubbles the removal of the gas is a process of determining an optimal outflow rate that would also accommodate the fluid level requirement. Also, it was observed that the geometry of the outflow line have a major effect on the gas flow behavior. With the reduced outlet diameter, a Bernoulli flow was observed which increased bubble dispersion. This paper provides information regarding the research on gas behavior and migration in a scaled riser system during circulation. These experiments can be used to study the effects of flow rates on gas dispersion and elimination from the CML Drilling method.

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