ABSTRACT
This final chapter is designed to act as a cross-discipline reference point between rock mechanics and engineering geological behaviour in the ‘static’ world of slow-andmacro deformation processes, and the geophysicists ‘dynamic’ world of fast-and-micro deformation and attenuation processes. That there are important links between the two in terms of joint or fracture compliance and its inversion: stiffness, and in terms of rock quality, deformation modulus, and seismic quality, has been established in various contexts in the chapters of Part II. In particular, this last chapter attempts to extend current thinking regarding fractured reservoirs, ‘open’ joints, and assumed H max parallelism, to also embrace the possibility, even probability, that multiple-joint-sets and shear-dilationconductivity coupling are needed, due to the inevitable tendency for joints in less competent rocks to close at reservoir depths, even when under the influence of ‘only’ h min. Shear wave splitting and polarization from two sets of conjugate (or H max straddling) joints can also appear to satisfy ‘open joints were parallel to H max’ assumptions. The important improvement would be that rock mechanics theory is not violated, when assuming that unsheared joints in weaker reservoir rocks can be conductors, when actually under high levels of effective stress. Shearing to great depth has been verified in other areas of the earthsciences, and the need for adoption in the geophysical interpretation of petroleum reservoirs is discussed, with simple joint-model illustrations. The ‘critical shearing crust’ is interpreted here in terms of the non-linear BartonBandis shear strength and coupled behaviour constitutive model. An evaluation of the importance of joint roughness at several scales, and the need for dilation-corrected stress transformation in the earth sciences is also treated.
