Experimental investigation of solids transport in horizontal concentric annuli using water and drag reducing polymer-based fluids * Payam Allahvirdizadeh a , Ergun Kuru b, * , Mahmut Parlaktuna a a METU Department of Petroleum and Natural Gas Engineering, Turkey b University of Alberta, Canada article info Article history: Received 5 May 2016 Received in revised form 16 September 2016 Accepted 17 September 2016 Available online 19 September 2016 Keywords: Cuttings transport Horizontal wells Drag reduction abstract When drilling long horizontal wells, drilled solids tend to settle down on the low side of the wellbore and form a stationary bed. Presence of stationary cuttings bed causes operational difficulties such as pack-off, excessive torque and drag, slow drilling rate, and in severe cases, stuck pipe, lost circulation, and even loss of the well control. Despite significant progress made in drilling fluids, tools, and field practices, along with more than 50 years of university and industry research, field experience indicates that cut- tings transport is still a major problem in most horizontal wells. There are many variables affecting the efficiency of cuttings transport (e.g. drilling fluid type, density, flow rate and rheological properties, hole inclination angle, drill pipe rotation speed and eccentricity). Among these variables, the drilling fluid flow rate and rheological properties are the most critical ones as they have strong influence on cuttings transport while at the same time, field control of these variables can be managed conveniently. An experimental study was, therefore, designed and conducted to simulate solids transport in the horizontal annuli under controlled conditions of solids feed rate, fluid flow rate and fluid rheological properties. Cuttings transport experiments were carried out using a 6.5 m long horizontal flow loop with concentric annular geometry (Outer Pipe ID ¼ 0.074 m, Inner Pipe OD ¼ 0.047 m). Water and high molecular weight partially-hydrolyzed polyacrylamide (PHPA) polymer solutions with various degrees of drag reduction capability were used as carrier fluids. Solids were made out of in- dustrial sand with median (D50) diameter of 0.00275 m. Effects of drilling rate (i.e. solids feed rate), drilling fluid flow rate and polymer concentration (i.e. drag reduction effect) on the cuttings transport efficiency and pressure losses were investigated. Maximum drag reduction was observed (i.e., 38% reduction in frictional pressure drop) when optimum polymer concentration of 0.07% W/W was used. The polymer fluid yielding the maximum drag reduction also resulted in the most efficient cuttings transport, which was observed as the lowest cuttings bed deposit height in the annulus. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The problem of cutting transport in highly inclined and hori- zontal wellbores has been investigated since 1980's. Comprehen- sive reviews of the past work could be found in papers written by Pilehvari et al. (1999) and more recently by Li and Luft (2014a, 2014b). Generally, parameters affecting cutting transport could be categorized under three groups (Bilgesu et al., 2007): fluid char- acteristics, cuttings related factors and operational variables. Effect of fluid rheological properties on transportation of drilled cuttings has been widely studied in the literature. Williams and Bruce (1950) reported that low viscosity and low gel drilling fluids are better in removing the cuttings. Tomren et al. (1986) reported that effect of viscosity depends on the flow regime; when the flow regime is laminar, it is better to use high viscosity fluids; while in turbulent flow there is no significant effect of vis- cosity. Azar and Sanchez (1997) reported that high fluid viscosity * This paper was presented at the 20th International Petroleum and Natural Gas Congress and Exhibition of Turkey held in Sheraton Hotel and Convention Center, Ankara, Turkey, May 27e29, 2015 and manuscript was revised for peer reviewed publication. * Corresponding author. E-mail address: ekuru@ualberta.ca (E. Kuru). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2016.09.052 1875-5100/© 2016 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 35 (2016) 1070e1078