Bubble Size Effect on the Gas-lift Technique

Bubble Size Effect on the Gas-lift Technique

Guet, S.C.L.

Ooms, G. (promotor)
Oliemans, R.V.A. (promotor)

Applied Sciences

2004-05-11

The gas-lift technique uses gas injection in vertical oil wells to decrease the gravitational pressure drop. The decreased pressure in the production pipe results in an increase of the pressure drop from the reservoir to the oil well and enhances the oil production. In this thesis we investigated the influence of the bubble size and initial concentration distribution on the gas-lift technique efficiency. A vertical upward bubbly pipe flow of air and water is used, with a height of 18m and a diameter of 72mm. The flow velocity conditions investigated in the experiments were representative of practical gas-lift circumstances. Different bubble injectors were tested in order to vary the size and initial concentration distribution of the bubbles. The influence of the initial concentration distribution was limited. The effect of bubble size, on the contrary, was significant. It was due to three contributions: the effect of the bubble size on the flow pattern changes, on the radial distribution (of void fraction and of gas and liquid velocity) and on the relative velocity between the gas and the liquid. To study separately these different contributions associated with bubble size changes we developed and used local measurement techniques. We investigated the possibility of Laser-Doppler Anemometry (LDA) measurements in bubbly flows. These tests were conducted in two different experimental configurations, corresponding to a stirred vessel and a pipe flow. To determine the size and the velocity of the bubbles a four-point optical fibre probe was validated and used. We also developed a method for estimating the bubble shape and orientation based on the time series provided by the four-point optical fibre probe. This method was first validated and then applied to our multiple bubbles pipe flow conditions. We then studied the effects of bubble size and concentration distribution on the gas-lift technique. In general it can be concluded that a decreasing bubble size increases the efficiency of the gas-lift technique. This is, among others, caused by the fact that the initial bubble size significantly affected the flow pattern transition from bubbly flow to slug flow. This effect could be described by using a bubble size dependent critical void fraction relation for the transition from bubbly flow to slug flow. With decreasing bubble size the transition shifts to larger values of the void fraction. Measurements were conducted to measure the influence of the bubble size on the velocity profile of gas and liquid and on the bubble concentration profile. For this purpose the four-point probe optical fibre probe and the LDA measurement technique were used. The velocity and concentration profiles were strongly influenced by the bubble size. Also the parameters C0 and Udrift of the drift-flux model are therefore bubble-size dependent. Based on the measurements, mathematical relations have been developed to describe these bubble size effects on the drift-flux parameters. We also developed a numerical model based on the Euler-Euler modelling approach for predicting the radial profiles of the void fraction and velocity as a function of the relevant parameters, such as bubble size. The predictions were in reasonable agreement with experimental data.

gas-lift
bubbly flow
bubble size

http://resolver.tudelft.nl/uuid:78f84bbf-85bd-42d0-83cc-6f6a217f1d11

DUP Science

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Institutional Repository

doctoral thesis

(c) 2004 S.C.L. Guet