| This dissertation investigates the mechanical control on spacing and aperture of equally-spaced fractures in layered materials using the Finite Element Method, based on the theories of elasticity and linear fracture mechanics. It also investigates the effects of fracture spacing and aperture on fluid flow through the equally-spaced fractures. The results show that under a remote extension in the direction perpendicular to the fractures the normal stress acting in this direction between adjacent fractures changes from tensile to compressive as the fracture spacing to layer thickness ratio changes from greater than to less than a critical value. This stress transition precludes further infilling of fractures unless they are driven by mechanisms other than an extension, or there are significant flaws between the fractures. Hence, it defines the condition of saturation for fractures formed under extension in flawless layered materials. When flaws are present, further infilling of fractures is possible depending upon the size and locations of the flaws. The aspect ratio of equally-spaced fractures is linearly related to the average strain, the overburden stress, and the internal fluid pressure. The aspect ratio increases nonlinearly with increasing fracture spacing to layer thickness ratio because of the mechanical interaction between adjacent fractures. The interaction becomes insignificant when the spacing to layer thickness ratio is greater than about 6.0. The aspect ratio also depends on the ratio of Young's modulus of the fractured layer to that of the neighboring layers. This dependence is significant when the fracture spacing to layer thickness ratio is less than 1.3, otherwise it is negligibe. The aspect ratio is insensitive to variations in Poisson's ratios. Fluid flow rate through equally-spaced fractures does not always increases with increasing fracture density, i.e., with decreasing spacing to layer thickness ratio. There is an optimum value for the ratio of fracture spacing to layer thickness that yields the maximum flow rate. |
