Stimulation of the natural fracture system by graded proppant injection

Graded proppant injection i.e. the injection of particles of increasing size and decreasing concentration, is proposed as a method for stimulating natural fractures. Compared to the injection of mono-sized proppant, graded proppant injection would facilitate deeper percolation of proppant into the fracture system and enhanced well productivity. A mathematical model is developed which describes the injection stage and the capture kinetics of proppant particles in the natural fracture system. Based on the mathematical model, an injection schedule is developed which would result in the optimal placement of proppant in the fracture system. A case study is conducted to estimate the change in well productivity index due to the application of the graded particle injection method. (C) 2013 Elsevier B.V. All rights reserved.