Simulation study on the dynamic evolution of gas bubbles in gas kick wellbore

Abstract With the exploitation of oil and gas resources, deep and ultra-deep oil and gas resources are gradually becoming the core areas for increasing oil and gas reserves and production in the future. Gas kick is easy to occur during drilling in deep and ultra-deep wells. In order to reduce the harm of gas kick, this paper uses a numerical simulation method to study the mechanism of multiphase flow in the wellbore after a gas kick. Using Ansys Fluent, selecting volume of fluid (VOF) multiphase flow model and RNG k-ε turbulence model, taking gas kick velocity and drilling fluid density as variables, three-dimensional numerical simulation of bubble formation and rise in single hole of gas kick wellbore is carried out, and the influence of gas kick velocity and drilling fluid density on bubble formation and rise velocity is studied. The results show that the radius length of the bubble major axis is positively correlated with gas kick rate, and negatively correlated with drilling fluid density. The bubble rising velocity increases with the increase of gas kick rate due to the influence of bubble generation diameter and other factors; the drilling fluid density increases and bubble rising velocity decreases due to the influence of bubble generation diameter, gas-liquid resistance and bubble breakage caused by turbulence. In addition, the bubble generation chart under different gas kick rates and drilling fluid densities is established, which is helpful to analyze the bubble generation and evolution process under different conditions.