Mechanically Induced Permeability Damage Due to Rock Proppant Interactions

Hydraulic proppant fracturing technology is used for a wide range of problems from bypassing drilling induced near wellbore damage to increasing productivity of extreme low-permeable reservoirs. During production the placed proppant pack interacts mechanically with the rock matrix. This causes proppant embedment and grain / proppant crushing and leads to permeability damage at the fracture face. To investigate this mechanically induced fracture face skin (FFS) new laboratory equipment was used to quantify the permeability damage ratio at the fracture face and to locate the damaging events via acoustic emission (AE). High permeable Bentheim sandstone as well as low permeable Flechtingen sandstone was investigated. The tests point out that crushing and fines production starts at low stresses at the fracture face. This effects a permeability reduction at the fracture face up a factor of 67 compared to the initial rock permeability for high permeable rock. For low permeable rock the permeability reduction factor is about 7. The conducted tests give evidence that rock matrix proppant interactions induce a significant permeability reduction and leads to mechanically induced FFS.