Fracture flow models of core samples by X-ray CT under pressure and numerical simulation

Ito, Hisao; Kato, Kazumasa; Ochi, Yutaka; Hosokawa, Naofumi; Watanabe, Noriaki; Mino, Yasuyuki; Tsuchiya, Yushihiro

doi:10.1190/segj112013-098

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“…Ideally, both methods should be combined to diminish affectations of both possible noise sources. However, PEEK core holder technology was only successfully applied for maximum confining pressure between 36 and 50 MPa at room temperatures (23 • C; Ito et al, 2013;Watanabe et al, 2013) and, thus, is a useful option for experiments focussing on similar conditions. Typically, the strength of PEEK strongly depends on temperature (Searle and Pfeiffer, 1985) and the chemical composition of the fluid used for the experiment (Pritchard, 1994) and, thus, appears to be challenging for experiments that simulate reservoir conditions or processes in the deeper Earth's crust.…”

Section: Comparisonmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

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Abstract. Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier-Stokes-Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading-unloading cycle (0.7 to 22.1 MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray CT scanner with a voxel dimension of 0.5 × 0.5 × 1.0 mm 3 . Fracture geometries were obtained by CT images based on a modification of the simplified missing attenuation (MSMA) approach. Simulation results revealed both qualitative plausibility and a quantitative approximation of the experimentally derived permeabilities. The qualitative results indicate flow channeling along several preferential flow paths with less pronounced tortuosity. Significant changes in permeability can be assigned to temporal and permanent changes within the fracture due to applied stresses. The deviations of the quantitative results appear to be mainly caused by both local underestimation of hydraulic properties due to compositional matrix heterogeneities and the low CT resolution affecting the accurate capturing of sub-grid-scale features. Both affect the proper reproduction of the actual connectivity and therefore also the depiction of the expected permeability hysteresis. Furthermore, the threshold value CT mat (1862.6 HU) depicting the matrix material represents the most sensitive input parameter of the simulations. Small variations of CT mat can cause enormous changes in simulated permeability by up to a factor of 2.6 ± 0.1 and, thus, have to be defined with caution. Nevertheless, comparison with further CT-based flow simulations indicates that the proposed method represents a valuable method to approximate actual permeabilities, particularly for smooth fractures (< 35 µm). However, further systematic investigations concerning the applicability of the method are essential for future studies. Thus, some recommendations are compiled by also including suggestions of comparable studies.

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Section: Comparisonmentioning

confidence: 99%