Mr. Yongyang Sun, PhD Candidate, Exploration Geophysics, Curtin University
Title: Solid substitution: Modeling elastic properties of porous and cracked rocks saturated with liquid and solid octodecane
Held: Monday 8 October, 10AM–11AM
ABSTRACT: Quantifying the impact of pore fill on elastic properties of porous rocks, especially cracked rocks, is of ongoing interest in geophysics. Different from fluids, the finite rigidity of high viscoelastic or solid pore fill prevents the pressure equilibration within the pore space due to the coexistence of stiff and soft pores. Indeed, the variation of the shear modulus of the pore fill can produce larger change in the effective elastic properties than one may expect from the change of the shear modulus of inclusions.
Our analysis shows that the pressure dependency of elastic properties of cracked rocks is controlled by the squirt flow between stiff, compliant, and so-called intermediate pores (with an aspect ratio larger than that of compliant pores but much less than that of stiff pores). In this paper, we present a triple porosity recipe for solid substitution. Compared to ultrasonic measurements on an octodecane saturated sandstone, the model predictions reveal a reasonable fit for both bulk and shear modulus with the aspect ratio of stiff pores set to 0.22, which is much smaller than the previously assumed value 1 for spherical pores.
Computation of liner elastic properties directly from the digitised tomographic images using numerical simulation based on the finite element method (FEM) shows excellent fit to the predictions of our model, which confirms the validity and applicability of this theory.