Closed Chamber Testing: The Effects of Wellbore Friction and Fluids Compression

Abstract

ABSTRACT Closed chamber tests are commonly performed as back surge perforation cleaning in wells where high surface pressures are not desired. Typical of closed chamber tests are high fluid velocities in the wellbore, and a variable wellbore storage caused by the rapid gas compression as the liquid column approaches the upper surge assembly. In this paper, we examine the effects of wellbore friction and variable wellbore storage including liquid and vapor compressibilities on pressure responses on closed chamber tests. The bottom hole pressure builds up more rapidly at early time when frictional effects are present. This rapid build up is associated with high liquid velocities in the wellbore. However, at late time the liquid velocity decreases, and frictional effects diminish. Wellbore frictional effects are dampened significantly in the presence of positive wellbore skin. The effects of liquid and gas compressibilities in the wellbore on the pressure build up during a closed chamber test are significant. Allowing the liquid to expand in the wellbore causes the rapid gas compression to occur earlier, but results in a slower final build up. This delay in the final build up is caused by the additional late time wellbore storage that depends on the compressibility of the liquid and the vapor columns. The final wellbore storage is a combination of a large volume of a low compressibility liquid, and a small volume of a high compressibility gas. The closed chamber tests responses including frictional effects and wellbore fluids compression were generated by coupling a superposition reservoir model with a wellbore fluid flow model.