Experimental Study of Polymer-Free and Polymer-Added Foams for Underbalanced Drilling: Are Two Foam-Flow Regimes Still There?

The foam-assisted underbalanced-drilling technique is more advantageous than the traditional overbalanced drilling near the productive water-sensitive formations because of its reduced formation damage, improved rate of penetration, higher cuttings-transport capacity, and lower circulation losses. However, the complicated nature of foam rheology has been a major impediment to the optimal design of field applications. Earlier studies with surfactant foams without oils and polymers show that foam flow in pipe can be represented by two different flow regimes: the low-quality regime showing either plug-flow or segregated-flow pattern, and the high-quality regime showing slug-flow pattern. The objective of this study is to investigate foam-flow characteristics in horizontal pipes at different injection conditions, with or without oils, by using polymer-free and polymer-added surfactant foams. The results of this study were presented in two different ways-by steady-state pressure drops (or,