Research on Foam Sand-Flushing Simulation of Coiled Tubing in Shale Gas Horizontal Wells

To address the issues of easy leakage and low sand-flushing efficiency of coiled tubing working fluid in shale gas horizontal wells, this study investigates the flow behavior of foam fluid in both the coiled tubing and the annulus during foam sand-flushing operations, and optimizes operational parameters to enhance sand-flushing efficiency. Considering the dynamic variations in foam fluid properties with temperature and pressure, secondary flow effects in the spiral section, annular eccentricity, wellbore trajectory, and the solid phase in sand-carrying fluid, a one-dimensional steady-state hydraulic model incorporating flow and heat transfer is developed for the entire wellbore. This model covers the spiral, straight, jet, and annular sections of coiled tubing. Using field data from an example well, simulations yield the pressure distribution along the foam circulation path, the total circulation time, and key operational parameters. The feasibility of coiled tubing foam sand-flushing in shale gas horizontal wells is demonstrated, and the optimization of operational parameters to improve sand-flushing efficiency is analyzed. The findings provide important guidance for parameter design and equipment selection for safe and efficient sand-flushing operations in shale gas horizontal wells.