PREDICTING LIQUID GRADIENT IN A PUMPING-WELL ANNULUS.
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This work proposes a hydrodynamic model for estimating gas void fraction, f//g, in the bubbly and slug flow regimes. The model is developed from experimental work, involving an air/water system, and from theoretical arguments. The proposed model suggests that prediction of f//g, and hence the bottomhole pressure (BHP), is dependent on such variables as tubing-to-casing-diameter ratio, densities of gas and liquid, and surface tension. Available correlations do not include these variables as flexible inputs for a given system. Computation on a field example indicates that slug flow is the most dominant flow mechanism near the top of liquid column at the earliest times of a buildup test. As buildup progresses, transition from slug to bubbly flow occurs in the entire liquid column.