Noriaki Watanabe

Beyond‐laboratory‐scale prediction for channeling flows through subsurface rock fractures with heterogeneous aperture distributions revealed by laboratory evaluation

The present study evaluates aperture distributions and fluid flow characteristics for variously sized laboratory-scale granite fractures under confining stress. As a significant result of the laboratory investigation, the contact area in fracture plane was found to be virtually independent of scale. By combining this characteristic with the self-affine fractal nature of fracture surfaces, a novel method for predicting fracture aperture distributions beyond laboratory scale is developed. Validity of this method is revealed through reproduction of the results of laboratory investigation and the maximum aperture-fracture length relations, which are reported in the literature, for natural fractures. The present study finally predicts conceivable scale dependencies of fluid flows through joints (fractures without shear displacement) and faults (fractures with shear displacement). Both joint and fault aperture distributions are characterized by a scale-independent contact area, a scale-dependent geometric mean, and a scale-independent geometric standard deviation of aperture. The contact areas for joints and faults are approximately 60% and 40%. Changes in the geometric means of joint and fault apertures (µm), em, joint and em, fault, with fracture length (m), l, are approximated by em, joint = 1 × 102 l0.1 and em, fault = 1 × 103 l0.7, whereas the geometric standard deviations of both joint and fault apertures are approximately 3. Fluid flows through both joints and faults are characterized by formations of preferential flow paths (i.e., channeling flows) with scale-independent flow areas of approximately 10%, whereas the joint and fault permeabilities (m2), kjoint and kfault, are scale dependent and are approximated as kjoint = 1 × 10−12 l0.2 and kfault = 1 × 10−8 l1.1.

Geologic Core Holder with a CFR PEEK Body for the X-ray CT-Based Numerical Analysis of Fracture Flow Under Confining Pressure

Variables A Cross-sectional area of the model (L) a Local aperture of the fracture (L) ai Aperture at the ith voxel (L) CTVi CT value at the ith voxel (Hounsfield unit) f Correction factor for the cubic law equation k Permeability of the model (L) L Length of the model (L) N Total number of voxels P Pressure of the fluid (MLT) DP Pressure difference (MLT) Q Total flow rate (LT) W Local width of the fracture (L)

New ν‐type relative permeability curves for two‐phase flows through subsurface fractures

Appropriate relative permeability curves for two-phase flows through subsurface fractures remain unclear. We have conducted decane-water and nitrogen-water two-phase flow experiments and simulations on real variable-aperture fractures in rocks under confining stress. Experiments have been conducted on fractures for different combinations of rock type (granite or limestone), wettability (contact angle of water: 0° or 90°), and intrinsic fracture permeability (10−11 m2 or 10−10 m2) using different combinations of shear displacement (0 or 1 mm) and effective confining stress (1 or 40 MPa). It has been demonstrated that nonwetting phase relative permeability depends on capillary pressure, except at either a higher contact angle or higher intrinsic permeability (i.e., bigger aperture), where no influence of capillarity is expected from the Young-Laplace equation. In the absence of an influence of capillarity, relations between wetting and nonwetting phase relative permeabilities agree with that of the X-type relative permeability curves. In order to determine the relative permeability curves under the influence of capillarity, the experimental results have been analyzed by two-phase flow simulations of the aperture distributions of the fractures. It has been revealed that nonwetting phase relative permeability becomes zero, even at a small wetting phase saturation of approximately 0.3, while wetting phase relative permeability exhibits Corey-type behavior, resulting in ν-shaped relative permeability curves. Similar curves have been reported in the literature, but have not been demonstrated for real fractures. It has been revealed that the new ν-type and traditional X-type relative permeability curves are appropriate for describing two-phase flows through subsurface fractures.

Fracture network created by 3‐D printer and its validation using CT images

Understanding flow mechanisms in fractured media is essential for geoscientific research and geological development industries. This study used 3-D printed fracture networks in order to control the properties of fracture distributions inside the sample. The accuracy and appropriateness of creating samples by the 3-D printer was investigated by using a X-ray CT scanner. The CT scan images suggest that the 3-D printer is able to reproduce complex three-dimensional spatial distributions of fracture networks. Use of hexane after printing was found to be an effective way to remove wax for the posttreatment. Local permeability was obtained by the cubic law and used to calculate the global mean. The experimental value of the permeability was between the arithmetic and geometric means of the numerical results, which is consistent with conventional studies. This methodology based on 3-D printed fracture networks can help validate existing flow modeling and numerical methods.

Observation of the heavy crude oil dissolution behavior under supercritical condition of water

In development of on-site partial upgrading technology of the bitumen by using supercritical water as a reaction solvent, it is important to understand the role of water in the reaction field. Therefore experiments were carried out using a batch reactor system operating with varying reaction pressure at a temperature of 703 K, and reaction time of 15 min. From the results such as the viscosity and the boiling point distribution of oil product etc., it can be seen that higher density supercritical water inhibits the cracking of bitumen to lower molecular weight substance.

High Resolution Modeling Of Aperture Structure And Flow Path In Rock Fracture

In this paper, we describe a numerical method to model aperture structures and flow paths in single rock fractures based on actual fracture surface geometries and actual fracture permeability. Fracture surfaces were measured using a CCD laser displacement sensor (resolution: 10 μm) with 250 μm square mesh for 100 mm × 150 mm single tensile fractures in granite samples. Fracture permeability was also measured under 10–100 MPa confining pressure conditions. Aperture structures and flow paths were modeled numerically using the actual fracture surface geometries so that the model’s permeability consistent with actual fracture permeability. Channeling flows were clearly observed at all conditions because of heterogeneous aperture structures. The results also suggested that fracture permeability could be overestimated if based on the conventional parallel plate model using an arithmetic mean value of local apertures.

Hydraulic fracturing and permeability enhancement in granite from subcritical/brittle to supercritical/ductile conditions

Hydraulic fracturing experiments were conducted at 200–450 °C by injecting water into cylindrical granite samples containing a borehole at an initial effective confining pressure of 40 MPa. Intensive fracturing was observed at all temperatures, but the fracturing characteristics varied with temperature, perhaps due to differences in the water viscosity. At the lowest considered temperature (200 °C), fewer fractures propagated linearly from the borehole, and the breakdown pressure was twice the confining pressure. However, these characteristics disappeared with increasing temperature; the fracture pattern shifted toward the formation of a greater number of shorter fractures over the entire body of the sample, and the breakdown pressure decreased greatly. Hydraulic fracturing significantly increased the permeability at all temperatures, and this permeability enhancement was likely to form a productive geothermal reservoir even at the highest considered temperature, which exceeded both the brittle–ductile transition temperature of granite and the critical temperature of water.

Linking microearthquakes to fracture permeability change: The role of surface roughness

Despite its importance, the relation between microearthquakes (MEQs) and changes in hydraulic properties during hydraulic stimulation of a fractured reservoir has rarely been explored, and it is still not well understood. To investigate this relation, we first formulate a plausible scale dependence, where fracture length and shear displacement are variables, for channeling flow through heterogeneous aperture distributions for joints and faults. By combining this formulation with the concept of the seismic moment, we derive quantitative relations between the moment magnitude (Mw) of MEQs and the fracture permeability change in the directions orthogonal to (kfault,⊥/kjoint) and parallel to (kfault,∥/kjoint) the shear displacement, in the form kfault,⊥/kjoint=116.4×100.46Mw and kfault,///kjoint=13.1×100.46Mw. Despite the simplicity of the derivation, these relations have the potential to explain the results of field experiments on hydraulic stimulation, such as the enhanced geothermal systems at Soultz-sous-Foret and Basel.

Evaluation Of Fluid Flow Field In Single Rock Fracture During Frictional Sliding

We report on results of fluid flow in a single fracture obtained from combination technique of physical experiments and flow simulation for investigating effects of asperity degradation due to sliding of fracture on flow properties of a fracture. We conducted sliding experiments of a rock fracture using cylindrical granite specimens (60 mm in diameter, 140 mm in axial length) containing a single tensile fracture. Sliding along the fracture was made by controlling a loading piston at constant rate of 0.001 mm/s under constant confining pressure of 5 MPa. Sliding displacement was applied up to approximately 6 mm along the surfaces. During the sliding, fluid flow was made within the fracture by applying a constant fluid pressure differential of 0.1 MPa through boreholes of 3 mm diameter drilled in the specimens. Fracture permeability was evaluated at every 0.5 mm in axial displacement by measuring the pressure differentials between inlet and outlet of the fluid and mass flow at the outlet. Flow field within ...

Calcium Phosphate Porous Materials with Unique Microstructures

Three types of calcium phosphate porous materials were prepared by the applied hydrothermal method. One of them was non-stoichiometric hydroxyapatite (HA) with calcium deficient composition and the others were β-tricalcium phosphate (β-TCP) and HA/β-TCP bi-phase material. Granules with several millimeter in size of calcium deficient HA, β-TCP and HA/β-TCP could be prepared. These granules with porosity over 70 % were composed of rod-shaped particles with aspect ratio about 10. Rod-shaped particles were locked together to make sub-micro-sized pores of about 0.1 to 0.5 µm in size. These materials must be suitable for the bone graft materials and as the scaffolds of cultured bone.