Evaluating Hole Cleaning Capability of Biodegradable Fiber-Containing Drilling Fluids in Riserless Tophole Drilling

Abstract

Abstract Fiber-containing drilling fluid enhances hole cleaning or cuttings transport efficiency without significantly affecting the rheological properties of the base fluid. Objective of this study is to evaluate the hole cleaning capability of a novel seawater-biodegradable polymer fiber-containing drilling fluid for use in riserless tophole drilling through large-scale cuttings transport experiments. The Poly(3-HydroxyButyrate-co-3-Hydroxyhexanoate) (PHBH) is 100% bio-based and biodegradable yet resistant to heat and hydrolysis. Dispersibility of the PHBH polymer fiber in base fluids and rheological properties of the fiber-containing fluids were examined in the laboratory. Cuttings transport experiments were then conducted using the large-scale cuttings transport flow loop apparatus for several selected combinations of base fluids and fibers based on the lab test. Cuttings transport behaviors were recorded on a digital video for further image analyses. The fibers showed good dispersibilities in base fluids with various concentrations of polyanionic cellulose (PAC) polymer and even in water. Adding fibers to base fluids increased viscosities at low shear rate ranges corresponding to 3, 6 and 100 rpm measurements of Fann Model 35 rotational viscometer without significant changes in overall rheological properties, which is expected to considerably improve cuttings transport efficiency. In addition, this positive tendency to cuttings transport efficiency was more significant in relatively low concentrations of PAC. To the video images recorded during the cuttings transport experiments, the particle image velocimetry (PIV) technique was applied to determine the cuttings transport velocities and cuttings concentrations accumulated in the annulus. Adding fibers increased cuttings transport velocities by up to about 1.5 times in vertical annulus. In near-vertical (hole inclination angles up to 30°) annulus, the cuttings were observed to flow as dunes or fluidized beds in which the cuttings re-entrainment from dunes was confirmed to be enhanced particularly at lower fluid flowrates.