PROPAGATION VELOCITY OF A NATURAL HYDRAULIC FRACTURE IN A POROELASTICMEDIUM

The propagation rate of a natural hydraulic fracture is limited by the rate that fluid flows from the saturated rock into the void space cre ated by fracture growth. Unlike induced hydraulic fractures, natural h ydraulic fractures can not be modeled by specifying rates of fracture growth or fluid flow into the fracture as boundary conditions. Numeric al solutions of the governing equations for natural hydraulic fracture growth in a poroelastic medium indicate that growth rates are primari ly controlled by the hydraulic conductivity K, the storage S-p' and th e initial flaw length 2a(o). Computationally more efficient models whi ch partially and completely decouple material stresses from fluid pres sures give similar results. Results for several rock types indicate th at, although the rate of fracture propagation is limited by fluid flow , fracture growth still accelerates. Results are generalized in dimens ionless plots of fracture length versus time for various values of the dimensionless parameter phi = (1-v)/(GS(p)'), where G is the shear mo dulus and v is the drained Poisson's ratio.