Tetsuya Tamagawa

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)

Construction of Fracture Network Model Using Static and Dynamic Data

This study reports a new process of constructing a discrete fracture network (DFN) model, which reflects various statistical properties of fractures extracted from static data such as borehole images and dynamic data such as pressure derivative curves. A DFN model is constructed by generating a number of disc-shaped fractures based on their statistical properties. The process of constructing DFN model proposed consists of two streams. One stream is for the fractures with wide apertures, which work as main flow path of fluid. Another stream is for the fractures with narrow apertures, which work as main storage of fluid. In the each stream, a DFN model is constructed by applying fractal theory and geostatistics that define the size and spatial distribution of fractures, respectively. The overall DFN model is obtained by merging the two types of DFN models. Then, the DFN model is converted to a continuum model with equivalent permeable blocks based on cubic law and is evaluated by the fluidflow behavior. Japex has been operating the Yufutsu fractured basement gas reservoir since 1996. A total of approximately 8,000meters of electrical borehole images from eleven wells is measured to understand the fracture system. According to the proposed process, the DFN models are constructed. To evaluate the DFN models by comparing the simulated pressure derivative curves with the observed curve, flow simulations are carried out as a simulation of a single porosity type. The observed pressure derivative curve shows a concave shaped curve like a dual porosity behavior, but the curve never reaches the second flat state. Through the parameter studies of the statistical properties, which relate to the size distribution and the spatial distribution of fractures, the observed curve was successfully reproduced and the quantitative relationship between the fractures with wide apertures and the fractures with narrow apertures was found.

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.

Fractured Reservoir Characterization Incorporating Microseismic Monitoring and Pressure Analysis During Massive Hydraulic Injection

The fractured basement gas reservoir in Yufutsu field was characterized by integrating static fracture information obtained from borehole micrtyo-resistivi images and dynamic information recorded during a massive hydraulic injection operation. Yufutsu gas reservoir is so called “fractured reservoir” seated in Cretaceous granite and Eocene conglomerate formation at around 4 - 5km depth in the Southern Ishikari Plain, central Hokkaido, Japan. One of the most important issues in the development of this reservoir is how to model the fracture system which contributes to the hydrocarbon migration.

Use of a computational fault-extraction process with calibrations to characterize a fractured basement reservoir, Yufutsu, Japan

The Yufutsu oil and gas field, located in Hokkaido, northern Japan, produces hydrocarbon from a typical fracture-type reservoir composed of very tight Cretaceous granitic basement and overlying conglomerate of the Eocene. Here, delineations of faults accompanying large open fractures are essential for optimal developments. To capture fault distribution objectively, various seismic-attribute estimates ascribed to fault distributions are derived from three-dimensional seismic data by computational procedures. However, to use the estimates properly, calibrating them with independent observations other than seismic data is important. We present a calibration scheme by coupling seismic data with microseismic data and in-situ stress data to delineate active faults under a strike-slip faulting stress regime in the Yufutsu field. Active faults are interpreted to be fluid pathways formed by shear dilation. In the calibration, two kinds of parameter sets are tuned. One controls linkages of fault responses fragmented by artificial noises caused by seismic acquisition and processing to adjust spatial continuities of fault surfaces properly. Another limits extracted fault strikes with respect to Mohr-Coulomb failure criterion to highlight active faults. The calibrated seismic-attribute estimates show a qualitative consistency with the microseismic hypocenter distribution observed during a massive hydraulic stimulation. In addition, a large difference in gas productivity observed at four wells, from very high productivity to no gas flowing, is clearly related to an existence of distinct lineation with strong magnitudes of the calibrated seismic attributes. It suggests that the calibrated estimate becomes a criterion to judge an economic viability of a well.

Three Dimensional Numerical Analysis of Fluid Flow through Fractured Rock Core Using X-Ray Computed Tomography

A three dimensional numerical modeling coupled with X-ray Computed Tomography (CT) for fracture flow was applied to fractured granite core samples. One of the samples had an artificial single fracture, and the others had natural multiple fractures. A relationship between CT value and fracture aperture (fracture aperture calibration curve) was obtained by X-ray CT scanning for a fracture aperture calibration standard with varying the aperture from 0.1 to 0.5 mm. As a result, a linear relationship was obtained between CT value and fracture aperture.

Computer Simulation for Sandbox Experiments

Summary Structural deformation (e.g. folds and faults) of geological strata has been analyzed by analog modeling techniques for nearly a century. Recent knowledge suggests that sandbox experiment is the most appropriate to model brittle behavior of the upper crust. This type of physical experiments using granular materials can also be done as numerical simulation (digital modeling) on the computer with the Discrete Element Method (DEM). Two types of geological settings, the extension case and the contraction case, are investigated and compared with the sandbox experiments results. It is concluded that the DEM approach to the geological deformation study can be a powerful tool

Roles of seismic simulation in the geophysical exploration.

Seismic simulation technology has been developed for many years. Recent trend that targets of exploration have become deeper and more complicated recalls demand of the seismic simulation technology. However, it has been only used for limited study due to various technical reasons. In recent years, the seismic simulation technology is rapidly advanced with new simulation methods and parallel computers. We have developed the wave propagation methods and applied to various exploration problems. We will show some results of seismic simulation in this paper.The first example is related to the Marmousi model. This simulation result shows that the wave propagation is very complicated and is beyond our image. The second example is a virtual seismic survey related to the sub-salt play. The virtual exploration shows the problems and solutions for sub-salt seismic imaging. The third example is the difference between acoustic and elastic modeling. This result shows the problem in onshore seismic data and the future direction.Using a seismic simulation, we can recognize various pitfalls and limitation in seismic processing and seismic interpretation. Seismic simulation can be used as potential tools for virtual explorations. We can gain the knowledge and the virtual experience through the virtual explorations.