Effects of Particle Density on Hole Cleanout Operation in Horizontal and Inclined Wellbores

Abstract

Abstract Coiled Tubing (CT) is widely used in wellbore cleanout operations to remove solid particles such as drilled solids or residual proppant from the hydraulic fracturing treatments. The cleanout operation is often associated with inefficiency and substantially increases the operational cost. This study is aimed at developing a model to predict the required fluid circulation rate and time to efficiently remove solids from the wellbore and optimize cleanout operation. To study the hole cleaning mechanism, solids bed erosion experiments were conducted using a flow loop that has a 10.4 m long annular (127 mm × 60 mm) test section. The effects of solid density, flow rate, inclination angle and fluid type on cleanout operation were investigated by measuring bed erosion and hole cleaning efficiency. A stable bed was initially formed in the annular test section of the flow loop. Once the setup was positioned at the desired inclination, the bed was eroded for 30 minutes at a constant flow rate. The amount of solids removed during each test was weighed to determine cleanout efficiency. A traveling camera system was utilized to measured bed height at different locations in the test section. The measurements resulted in the generation of bed erosion curve (average bed height versus circulation time plot) for each test. The trends are consistent with previously reported measurements; however, certain discrepancies were found when examining the trends. This study indicates that solid density has a slight to moderate effect on hole cleanout operation. For a given flow rate, high-density solids make hole cleaning much more challenging, especially in near horizontal well sections. The critical angle of inclination that is defined as the angle at which cleaning is the most difficult was not significantly affected by the density of the solids. Irrespective of the density of solids, the effective cleanout fluid to be used in wellbore cleaning operation at all inclinations remained the same. The outcomes of this investigation can be applied in the field to optimize cleanout operations in horizontal and deviated wells. The bed characteristics recorded during the investigation give more insight into the mechanisms of solids transport in inclined wellbores and can be used as the basis for further investigation.