Long-term conductivity testing at realistic environment conditions has greatly improved the measurement of proppant pack permeability. However, the use of low flow rates to insure Darcy flow in such measurements has masked the total effect of failed proppant fines on proppant pack permeability. As flow rates increase, corresponding with those commonly found in the field, fines are mobilized and migrate into new positions that reduce the permeability of the proppant pack beyond that normally observed in conductivity measurements. This effect has generally been overlooked in proppant pack design.
This paper examines the extent of conductivity reduction caused by migrating proppant fines and the effect of proppant type on the extent of that reduction. The role of fines migration on the conductivity of proppant packs containing two different types of proppants, where the more capable proppant is used near the wellbore, is also evaluated.
Representative commercially available proppants, including sand, resin-coated sand, and low density ceramics are included in the study.
With the most commonly used proppants, such as sand, the generation of fine particles in the proppant pack as a result of subsurface closure stresses is well established. A method for evaluating the extent of crushing has been developed by an API committee,1 and the extent to which commonly used proppants crush has been reported in the literature.2 The detrimental effect of the presence of fines in the proppant pack has been demonstrated experimentally.3,4 While studies on fines migration have been reported,5,6 they have focused on fines native to the formation, rather than proppant fines, and the reduction in matrix permeability of the formation rather than the reduction of fracture conductivity. The current work was undertaken to evaluate the effect of fines migration, at representative field flow rates, on proppant pack permeability.