Particulate material to be removed from a wellbore can have a vast range in size and density. Typical materials are formation sand, drilling cuttings and various fracture proppants such as resin-coated sands, ceramics, Bauxite and ultra light-weight materials. The characteristic size, shape and density of the particles greatly influence their dynamic behavior in flowing media. Terminal velocity, drag and gravity forces and shear stresses are affected by particle properties and the rheology of the circulation fluid.
This paper presents the results of a solids transport study on four different density proppants with same particle size (20/40 mesh) and three different diameter particles ranging from 0.15 to 7 mm. The specific gravity of the proppants varied from 1.25 to 3.6. The tests were performed using a sophisticated flow loop. Findings indicate that particle density and size have a significant effect on the solids transport. For a given flow rate, higher density solids result in higher in-situ solids concentrations and lower wiper trip speed (the wiper trip speed is the coiled tubing pull-out-of-hole (POOH) speed) and reduced transport efficiency. The solids transport for different particle sizes is strongly influenced by wellbore deviation angle. In a near-vertical wellbore larger particles have the lower transport efficiency while in a horizontal wellbore the medium sized particles have the lowest transport efficiency.
New correlations have been developed from the experimental data to predict solids in-situ concentration, solids carrying capacity and optimum wiper trip speed for these tested solids under a given operating condition.