Experimental Investigation and Modeling of the Effects of Rising Gas Bubbles in a Closed Pipe

Abstract

Summary Transient multiphase flow in the wellbore causes problems in well-test interpretation when the well is shut in at surface and the pressure is measured downhole. Pressure-buildup data recorded during a test can be dominated by transient wellbore effects (i.e., phase change, flow reversal, and re-entry of the denser phase into the producing zone), making it difficult to distinguish between true reservoir features and transient wellbore artifacts (Gringarten et al. 2000). This paper is a follow-up to paper SPE 96587 (Ali et al. 2005), which presented experimental results of phase redistribution effects on pressure-buildup data. Though the results of the experiments were revealing, they are complex because they reflect the real well situation. To obtain results in which the phase redistribution in the well is studied independently of the interaction with the reservoir, a further set of experiments was carried out. In these experiments, the tube (simulating the well) was isolated at both the top and the bottom at the same time. The pressure distribution was measured during the transient following shut-in and for the steady-state final condition, in which there was a liquid-filled zone at the bottom of the test section and a gas-filled zone at the top. A substantial number of tests were conducted in the bubbly-flow region and could therefore be analyzed by a simple 1D model for bubbly flow. The results of the comparison between the model and the experimental data are presented in this paper.