Fibrous Cleanout Fluids in Horizontal and Inclined Wells

Abstract

AbstractThis paper presents the results of experimental and theoretical studies conducted to investigate the hole cleaning performance of fibrous fluids in horizontal and inclined wells. Coiled tubing is commonly applied in the wellbore cleanout operations of highly deviated and horizontal wells. Accumulation of proppant and other solid debris in the wellbore remarkably impedes field operations and oil and gas production. Fibrous fluids have shown great potential for cleaning solids that are difficult to remove with conventional fluid systems. The addition of fiber substantially reduces the settling velocity of particles in fluids due to the formation of a fiber network. This study is aimed to investigate wellbore cleanout and hydraulics of fibrous fracturing fluid in horizontal and inclined wells.Cleanout experiments were carried out using Xanthan gum suspensions with and without fiber (i.e. monofilament synthetic fiber). Extensive flow loop tests were performed varying fiber concentration and inclination while measuring the equilibrium bed height at different flow rates. A 22-ft long annular test section was utilized to perform the cleanout (erosion) experiments. To better explain the results, rheological and hydraulic characteristics of the test fluids were examined using the pipe viscometer and the annular test section. A model has been developed to calculate the critical velocity and flow rate needed to initiate the movement of bed particles during hole cleaning operation. The model is formulated to account for the presence of fiber through a fiber drag coefficient.Results show a noticeable reduction in critical velocity or equilibrium bed height owing to the addition of a small amount (0.04% by wt.) of fiber. Fibrous fluid demonstrated better cleanout performance than the non-fibrous fluid (base fluid). The addition of fiber to the base fluid, significantly enhanced hole cleanout, resulting in a drastic reduction of equilibrium bed height. At 70 gpm, fibrous fluid cleaned the test section 50% better than the base fluid. One possible explanation for this observation could be the development of a fiber network in the fluid that provides additional drag to agitate bed particles and initiate their movement. Results of rheology and hydraulic tests show that the addition of fiber (0 to 0.08%) had very little effect on the rheology and hydraulics of fibrous fluid. Fibrous fluid displayed slightly lower pressure loss as compared to the base fluid, which indicates minor friction reduction due to the fiber.The accuracy of the hydraulic model developed in the study has been assessed using flow loop measurements. Results show good agreement between predictions and measurements. The new model can be employed in the field to optimize the wellbore cleanout operation with fibrous fluid without increasing bottom hole pressure.