| Abstract |
Fracture length, pressure, and the distributions of pore pressure and stresses around a fracture are of interest in hydraulic fracturing during injection/extraction operation in a geothermal reservoir and water-flooding of petroleum reservoirs. The fracture extension as well as stress and pore pressure fields around it are affected by: poro- and thermoelastic phenomena as well as by fracture opening under the combined action of applied pressure and in-situ stress. In this work we develop a model for calculating the length of a water-flood induced fracture from a single well in an infinite reservoir. Similarly to Perkins and Gonzalez (1985) and Koning (1985), the model allows the leak-off distribution in the formation to be two-dimensional with the pressure transient moving elliptically outward into the reservoir with respect to the growing fracture. The model calculates the length of a water flood fracture and the extent of the cooled and flooded zones. The thermoelastic stresses are calculated by considering a cooled region of fixed thickness and of elliptical cross section. The methodology of Perkins and Gonzalez (1985) and Koning (1985) is used to calculate the fracture length, bottomhole pressures (BHP’s), and extent of the flood front as the injection process proceeds. However, in contrast to previous works that only calculate the poroelastic changes in rock stress at the fracture face for a quasi steady-state pressure profile, we calculate the pore pressure and the stress changes at any point around the fracture caused by thermo- and poroelasticiy and fracture compression. This is useful for investigating the response of the rock mass to stress variations resulting from pore pressure and temperature changes. In particular, we calculate the failure potential around the fracture to determine the zone of tensile and shear failure. This is of interest in interpretation of micro-seismicity in hydraulic fracturing and in assessing permeability variation around a stimulation zone. The work can also be used to assess the accuracy of more complex numerical models. |