Experimental investigation of solids transport in horizontal concentric annuli using water and drag reducing polymer-based fluids

- Conducted solids transport experiments in horizontal annuli using water and polymer based drag reducing fluids.
- Investigated effects of drilling rate, fluid flow rate, fluid rheological characteristics on cuttings transport efficiency.
- Observed that drag reducing fluid can transport cuttings effectively.

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 cuttings 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 = 0.074 m, Inner Pipe OD = 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 industrial 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.