Experimental Investigation of Drilled Cuttings Transport in Inclined Boreholes

Abstract

ABSTRACTThis paper describes an experimental investigation into drilled cuttings transport in inclined boreholes carried out in the Department of Petroleum Engineering at Heriot-Watt University.The paper describes how a 21 ft. borehole simulator and peripheral equipment built within the department has been used to determine the effects of various drilling parameters on the circulation rate required to ensure that the drilled cuttings in a deviated borehole are efficiently transported to surface.The procedures used to conduct the experiments are fully explained and experimental results and observations are discussed.Two distinctly different cuttings transport mechanisms were identified. The first occurs where the cuttings are transported to surface by a rolling/sliding motion along the low-side wall of the annulus and the second is where the cuttings are transported in suspension in the circulating fluid. The latter mechanism requires a higher fluid velocity than the first. Although these two mechanisms produce the same effect (to clean the hole) their response to variations in the drilling parameters investigated was significantly different.The main conclusions from the experiments carried out to date are that the annular fluid velocity required to initiate cuttings transport with either of the two different transport mechanisms is sensitive to variations in hole angle but that the relationship between the required fluid velocity and hole angle is different for each of these transport mechanisms. The effectiveness of a circulating fluid in removing drilled cuttings is not only dependant on the rheology of the fluid but also on whether the fluid is in laminar or turbulent flow. Water in turbulent flow, can be a very effective cuttings transport medium. Pipe rotation had little or no effect on the fluid velocity required to transport the cuttings when circulating water but significantly reduced the fluid velocity required to transport the cuttings when circulating medium or highly viscous fluids. It should be noted however that these experiments were conducted on a relatively small annulus. The fluid velocity required to transport the cuttings is a function of the size of the cuttings.