Gas-Rise Velocities During Kicks

Abstract

Summary Experiments to examine gas migration rates in drilling muds were performed in a 15-m [49-ft] -long, 200-mm [7.8-in.] -ID inclinable flow loop where air injection simulates gas entry during a kick. These tests were conducted using a xanthan gum (a common polymer used in drilling fluids) solution to simulate drilling muds as the liquid phase and air as the gas phase. This work represents a significant extension of existing correlations for gas/liquid flows in large pipe diameters with non-Newtonian fluids. Bubbles rise faster in drilling muds than in water despite in the increased viscosity. This surprising result is caused by the change in the flow regime, with large slug-type bubbles forming at lower void fractions. The gas velocity is independent of void fraction, thus simplifying flow modeling. Results show that a gas influx will rise faster in a well than previously believed. This has major implica tions for kick simulation, with gas arriving at the surface earlier than would be expected and the gas outflow rate being higher than would have been predicted. A model of the two-phase gas flow in drilling mud, including the results of this work, has been incorporated into the joint Schlum berger Cambridge Research (SCR)/BP Intl. kick model partly funded by the U.K. Dept. of Energy.