Numerical simulation of 3D fracture propagation in wellbore strengthening conditions

The principle of damage mechanics was adopted in order to solve the lost circulation problem when drilled low bearing capacity formation. According to quadratic nominal stress criterion and B-K criterion, cohesive element with zero thickness was inserted into fracture to simulate fracture initiation and propagation. A 3D fluid-solid coupling finite element model was established to analyze circumferential stress distribution of wellbore, hoop stress distribution of crack and geometry of fracture. Results show that closed fracture surface is still in the stage of complete fracture under the action of crustal stress and crack tip reopens after plugging particle failed. The fracture is difficult to widen for filling more plugging materials in a short time while the lost circulation rate and permeability are low. The wellbore strengthening treatment will makes the fracture become short and narrow under a larger filtration coefficient, but mud cake quality has an insignificant influence on fracture geometry when filtration coefficient increases to a certain value. The simulation results were supported by providing some cases of real wellbore condition.