Research on Bubble Migration in Pipe Under Gas-Liquid Countercurrent Flow

Abstract

Abstract Body text 1 paragraph. Deep/ultra-deep gas reservoirs generally have the characteristics of deep well depth, high temperature and high pressure (maximum temperature > 200 °C, maximum pressure > 190 MPa), multiple fractures, narrow safety density window (the narrowest window < 0.01 g·cm-3), and many layers. During drilling, it is easy to encounter abnormal high pressure formation, and the probability of overflow is high[1]. The conventional circulation killing method circulates the gas in the wellbore out of the wellbore through positive circulation killing or reverse circulation killing. The positive circulation killing fluid is pumped into the annulus by the drill pipe, and the gas in the wellbore is discharged with the killing fluid through the bottom hole, annulus and wellhead. The flow in the annulus is gas-liquid upward flow in the same direction. The reverse circulation killing well is pumped into the drill pipe by the annulus, and the gas in the wellbore is discharged through the bottom hole-drill pipe-wellhead circulation with the killing fluid[2]. Due to the complexity of the formation pressure system in deep wells, the conventional cyclic well killing operation is often used to over-pressure and over-leak, and the leakage and inrush are alternating, which even leads to the risk of blowout out of control and single well scrapping. The conventional cyclic well killing method is not applicable. The pressure-back well killing method can directly pressure the overflow gas containing hydrogen sulfide back to the formation, which is a common well killing method for dealing with the drilling overflow of such gas reservoirs. In the process of killing, the killing fluid flows downward from the wellhead annulus pump, and the invading gas in the wellbore moves upward due to buoyancy. The killing fluid and the invading gas in the wellbore flow in the opposite direction, forming a gas-liquid reverse two-phase flow in the wellbore. For the problem of bubble migration in gas-liquid two-phase flow, different scholars have carried out many studies in various aspects. Liu[3] carried out visual experiments on the movement behavior of single bubbles in distilled water, tap water and glycerol solution, and studied the rising process and velocity change of bubbles in static liquid phase. Based on experiments and numerical simulations, Xu[4] studied the rising trajectory of a single bubble in viscoelastic fluid and the interaction between two bubbles. Wang et al.[5] studied the fusion process of two coaxial bubbles, and found that the bubbles were easy to break when the surface tension was small, and the bubbles did not fuse when the surface tension was large. Azzopardi et al.[6] experimentally studied the rising law of large bubbles in high viscosity liquid, and established the corresponding velocity model.