Fracture Opening/Propagation Behavior and their Significance on Pressure-Time Records during Hydraulic Fracturing

In this study, in order to extract the information on fracture opening, fracture propagation and permeability of the fracture from pressure-time records during hydraulic fracturing, fracturing process is numerically simulated paying attention to the relations between the form of pressure-time curve, fracture opening/propagation behavior and fluid flow in the fracture. Hydraulic fracturing with constant water injection is modelled numerically for a rectangular longitudinal fracture in an impermeable rock mass and intersecting a borehole. Analysis of rock deformation is based on the theory of linear elasticity and also on linear fracture mechanics. Fluid flow is analyzed as laminar flow, and permeability of the mechanically closed fracture is taken into account as one of parameters in the simulations. Then the rock deformation and the fluid flow in the fracture are coupled in the modelling. The results show that both the permeability of the fracture and water injection rate significantly influence the form of pressure-time relations on early stage of fracture opening. When the permeability is sufficiently high, there is no peak in the pressure-time relations. When the permeability is low, on the other hand, the pressure-time relations have a peak, whose value becomes higher with the water injection rate. Furthermore the simulations show that the behavior of borehole presusre with fracture propagation are affected by the pre-existing fracture length.