Influence of proppant fragmentation on fracture conductivity - Insights from three-dimensional discrete element modeling

Proppant crushing under high closure stress is widely observed in the laboratory and the field but has rarely been simulated numerically. This paper presents 3D discrete element modeling of proppant fragmentation and its influence on the fracture conductivity. A particle breakage model was implemented to simulate proppant fragmentation. A practical procedure was developed to calibrate the parameters in the breakage model using stress-strain responses and grain size distributions from laboratory crush tests. The breakage model, along with the calibrated parameters for Jordan sand, Genoa sand, and a ceramic proppant, was used in a parametric analysis for multilayer proppant packs. The influence of proppant type, particle size, and proppant mixture on proppant fragmentation and fracture conductivity was examined. The results indicate that the proppant size needed to achieve optimal fracture conductivity is greatly affected by particle fragmentation, which in turn is sensitive to closure stress and size-dependent particle strength. A Hardin breakage ratio larger than 0.05 represents the onset of excessive proppant fragmentation that can greatly decrease fracture conductivity.