Coiled tubing erosion during hydraulic fracturing slurry flow

The pumping of fracturing slurry through coiled tubing can cause considerable wear of tubing and is an issue of industrial concern, both from safety and economic considerations. In hydraulic fracturing operations employing coiled tubing, the tubing wall is affected by non-uniform erosion for the section of the tubing spooled on the reel. The non-uniform wall erosion is caused by the centrifugal forces when pumping slurries at high rates. In spite of the large number of fracturing jobs performed in the industry today, research in this area of investigating and evaluating erosion has been limited. A computational fluid dynamics (CFD) study is undertaken to investigate the major contributing factors affecting erosion. The mechanisms leading to the erosion process have been discussed and erosion rate has been investigated as a function of flow rate, slurry concentration, proppant (solid particles) size and density, and fluid viscosity. This study utilizes both experimental tests and CFD simulations to investigate erosion in coiled tubing. The experiments have been conducted on a full-scale test facility at the Well Construction Technology Center (WCTC), The University of Oklahoma. CFD simulations have been conducted by utilizing erosion prediction and particle tracking modules in a commercial CFD code FLUENT. It is found that erosion phenomenon in coiled tubing is highly non-uniform with tubing extrados (external radius) being more susceptible to erosion as compared to intrados (internal radius). Results from CFD simulations established slurry flow rate to be the most significant factor affecting erosion. Slurry concentration and fluid viscosity are also found to influence erosion rate greatly.