Effects of Pipe Rotation on the Performance of Fibrous Fluids in Horizontal Well Cleanout

Abstract

The deposition of rock cuttings is a problem commonly faced during drilling, completion, and intervention operations. Using polymer-based fluids is a common technique to improve horizontal downhole cleaning. However, these fluids cannot always guarantee an efficient wellbore cleanout. One way to enhance cleanout efficiency is by rotating the drill pipe to mitigate the settling of solids and facilitate their removal. However, drill string rotation often increases equivalent circulating density (ECD). Therefore, this study explores how the impact of rotation on hole cleaning can be synergized by using fibrous fluids to perform cleanout at reduced rotational speeds with limited impact on ECD.

The flow loop utilized for this study consists of a 48-ft long eccentric annular (5" × 2.375") test section. Each experiment began by forming a stationary bed of natural sand (average diameter of 1.2 mm) in the test section. High-viscosity and low-viscosity polymer-based suspensions with and without fibers were used. Drill pipe rotation speed was varied from 0 to 150 rpm. In each experiment, the flow rate was increased from 35 to 195 gpm stepwise. The equilibrium bed perimeter was measured at every test flowrate until a complete bed cleanout was achieved. As part of the test, flow rate, pressure gradient, and equilibrium bed height were measured. Rotational viscometers were used to measure fluid rheology before and after each test.

Fiber particles improve the carrying capacity of the fluid by reducing the settling of solids and minimizing the re-deposition of particles. The results demonstrate the effectiveness of fiber in synergizing the effect of pipe rotation on hole cleanout performance in horizontal wellbores. The impact of fiber is more pronounced when used with low viscosity fluid. The cleanout performance of the low-viscosity fluid amplified significantly with rotation, almost entirely cleaning the bed at 75 gpm and a rotational speed of 50 RPM, compared to more than 195 gpm without rotation. Even more improvement could be achieved by adding a small amount of fiber (0.04% wt/wt). Furthermore, the fiber improved the cleanout performance of the high-viscosity fluid. The enhancement, however, was not as noticeable as with the low-viscosity fluid. In general, rotation combined with low-viscosity fibrous fluid exhibits the most effective sand cleaning performance. Rotating the pipe re-suspends the settled solids, which are then carried away by the fluids. Fiber particles enhance the fluid's ability to carry solids.