Quantitative 3D analysis for natural micro- fracture in woodford shale, southern Oklahoma, using Non-destructive micro computer tomography technique
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While the distribution of fractures in outcrops and the subsurface has been intensively studied, the nature, distribution and orientation of microfractures (< 1 mm aperture) is poorly constrained. Yet, microfractures likely contribute significantly to the secondary porosity and permeability of a reservoir. This research will utilize microtomography tomography analysis of oriented samples of brittle deformed sedimentary rocks for the following goals: 1) establishing methods to utilize microtomography imaging to detect the orientation and distribution of natural fractures within mudstones; 2) evaluate the distribution and the density of microfractures within a single bed; 3) evaluate how the orientation and distribution of natural microfractures varies with the mineralogical composition of the host rock; 4) calculate natural fracture porosities of the samples using microtomography; and 5) evaluate the roughness of natural fractures internal surface using SEM and computer tomography. Computer tomography techniques provide an unparalleled opportunity to non-destructively study the internal structure of a material by measuring the attenuation of X-rays though the sample. The advantage of using the CT technique in evaluating natural fractures lies in the ability to render the 3D orientation of anisotropic fabrics in a rock volume. Therefore, it is possible to measure the distribution, orientation and interconnectivity of fracture porosity in a rock. Evaluating microfractures within different lithologies along the same structure will provide 3D information on the nature of fracture development, localization, and connectivity. The result shows that McAlister Shale Pit has four sets of fracture, two of prominent fracture sets are nearly perpendicular to bedding and the second set is discontinuous and generally obtuse against the first planner set. Triple XRD analysis using same sample but different location shows the challenges of inconsistencies in the XRD data collection and interpretation. Therefore, the reproducibility and imprecision in the XRD analysis, and it is scatter is far larger than smaller scale heterogeneities. The data shows that the fracture densities increases within thinner bed and vise versa. The fractures are mainly mode I fracture due to high surface roughness and the propagation direction of the fractures. Finally, the research shows that Microtomography is an excellent non-destructive technique that could be used as quantitative 3D analysis technique for the internal structure of naturally fractured mudstones.