Characterization of foam flow in horizontal pipes by using two-flow-regime concept R.N. Gajbhiye, S.I. Kam n Craft and Hawkins Department of Petroleum Engineering, Louisiana State University, Baton Rouge, LA 70803, USA article info Article history: Received 9 April 2010 Received in revised form 7 December 2010 Accepted 10 December 2010 Available online 21 December 2010 Keywords: Foam Rheology Characterization Two flow regimes Underbalanced drilling Foam fracturing abstract Foam has been widely used in numerous scientific and engineering applications. Although foam has relatively low fluid density because of high gas content, it can exhibit a viscosity value enormously higher – often several orders of magnitude higher – than that of bulk gas or liquid phase. Since foam typically exists as a complex fluid system with internal gas bubbles and external liquid phase, understanding and characterizing its flow behavior is very challenging. The objective of this study is to investigate the characteristics of foam rheology in horizontal pipes in a wide range of experimental conditions—two different pipe materials (stainless steel and nylon pipes with about 0.5 in in outer diameter and 12 ft in length), three surfactant formulations (Cedepal FA-406, Stepanform-1050, and Aquet-944), and three surfactant concentrations (0.1, 0.5, and 5 wt%). The experimental data can be collected in terms of (i) pressure measurements at several positions along the pipes and (ii) visual analysis of bubble size and bubble-size distribution during the shear flow. The concept of ‘‘two foam-flow regimes’’ consisting of high-quality regime and low-quality regime is at the heart of interpreting the experimental outcome. The experimental results showed that there were two distinct high-quality and low-quality foam flow regimes which could be identified by both pressure responses and direct visual observations. The results further showed that the high-quality regime was characterized by unstable and oscillating pressure responses represented by the repetition of fine-textured foam and free gas (i.e., slug flow), while the low- quality regime was characterized by stable pressure responses represented by either the flow of fine- textured foams (i.e., plug flow) or the flow of upper-layer foams and lower-layer liquid (i.e., segregated flow). These two regimes, separated by a locus of f g n in the contour plot, were shown to have different sensitivities to the change in gas and liquid velocities: (1) foam rheology in the high-quality regime was dependent upon both gas and liquid velocities because the lengths of fine-textured-foam and free-gas sections were altered to adjust to the new flow conditions, and (2) foam rheology in the low-quality regime was primarily dependent upon gas velocity because of the development of fine-textured foams with increase in shear rates, and was relatively independent of liquid velocity because of lubricating effect and drainage effect. The implication of these experimental findings is discussed for applications such as foam-assisted underbalanced drilling processes and foam fracturing treatments in the petroleum industry. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Foam has been considered as an important and useful means in many engineering disciplines. When properly managed and designed, foam treatments can take great advantage of its high viscosity with low density, high solids-carrying capacity, and minimum filtrate and circulation losses. Many of these features are strongly desired in drilling and fracturing operations in petroleum industry, by transporting rock cuttings and proppants effectively and minimizing the formation damage with reduced amount of aqueous phase (Bonilla and Shah, 2000; Schramm, 1994; Affonso et al., 2004; Capo et al., 2006). Surfactant foams are also popular in reservoir applications, not only in small-scale near- wellbore production enhancement but also in large-scale mobility control and sweep-efficiency improvement (Patton et al., 1983; Kovscek et al., 1995; Rossen et al., 1999; Lakatos et al., 2003; Li et al., 2008; Kam, 2008). Previous foam studies show that achieving and maintaining desired foam properties such as foam texture, foam viscosity, solid-carrying capability, and so on is often quite challenging, and furthermore the results at certain test conditions may not be easily translated into different conditions when it comes to up-scaling and down-scaling issues. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2010.12.012 n Corresponding author. Tel.: + 1 225 578 5216; fax: + 1 225 578 6039. E-mail address: kam@lsu.edu (S.I. Kam). Chemical Engineering Science 66 (2011) 1536–1549