An Analytical Description of Liquid Slug Flow In Small-Diameter Vertical Conduits

A wide range of intermittent gas-lift tests was conducted in a 1,500-ft experimental well through 1-1/4 in. and 1-1/2 in. nominal size tubing. For each tubing size, tests were conducted varying the slug length, gas volume injected and liquid viscosity and surface tension. From these tests, an empirical ''fallback'' or liquid loss correlation has been developed. A conceptual model has been developed which combines the fallback correlation with equations which govern liquid slug flow. A mathematical simulation of the model in the form of a digital computer program is used to calculate total recovery, gas volume used and clearance time for a given test. Tubing pressures at the gas-lift valve and at the gas-slug interface are calculated as a function of time. Tubing pressures at the surface during slug clearance are also calculated. The results compare favorably with the test data and verify the conceptual model. (21 refs.)