Hole cleaning is often more difficult during drilling of inclined wells. The resulting poor removal of cuttings can lead to problems such as borehole pack-off and excessive ECD, which are both difficult and expensive to resolve. Fluid sweeps are commonly implemented when normal circulation cannot adequately remove cuttings from the borehole. Field reports have indicated that specialized fibrous-type materials enhance cleaning performance when added to fluid sweeps. Yet, understanding of the behavior of this improvement remains inexact.
This paper presents a comparative experimental investigation of the hole cleaning performances of fiber sweeps, conducted with different drill pipe rotation speeds and fiber concentrations. Experiments were carried out in an inclined flow loop apparatus with an inner rotating drill pipe. The hole cleaning performance of fiber-containing sweep fluids using different fiber concentrations (0%, 0.05%, 0.1%, and 0.2%, by weight) and varying drill pipe rotation speeds (0 to 90 rpm) was evaluated. Sweep efficiencies were compared in terms of the measurement of cuttings bed heights before and after circulating the sweep fluid.
The results indicate that significant improvement associated with higher fiber content requires a commensurate increase in drill pipe rotation speed. With lower or no pipe rotation speed, increasing fiber concentration yields less dramatic returns. Pairing high fiber content with rapid pipe rotation resulted in enhanced performance over the control sweep, which contained no fiber, but relatively low concentrations did not surpass the control.
With the increasing need in the industry to drill extended reach or otherwise inclined wells, there is greater potential to develop problems stemming from inadequate hole cleaning. This research gives insight into the specific interaction of sweep fiber and pipe rotation with the cuttings bed, and with each other. Deeper understanding of fiber sweeps would inform in-field decisions when dealing with poor hole cleaning.