Hydro-fracturing

The Ogachi hot dry rock (HDR) field is situated at the northeast Japan and has been studied to produce geothermal electricity by Central Research Institute of the Electric Power Industry for 20 years. There are two injection/production wells (OGC-1 and -2) and an observation one (OGC-3). Two major feed zones were formed by hydro fracturing at depth of 700m and 1100m, where their temperatures are 170 and 210°C, respectively. 

The Child general type (Type ID) of solution mining is represented by deep deposits below the water table and below approximately 500 ft in depth. The ore body is shattered, hydro fractured, or chemically penetrated, Again, the hydrology of the region must be well known for proper containment of so lotions. This represents a unique situation in that the hydrostatic head will increase the oxygen solubility to the point that the direct oxygen oxidation of sulfide minerals bscomes possible. 

Hydro fracture initiation near injection point... 

Hydro fracture extends along the sample (except near outflow)... 

One result which was analyzed in a hydro-fracturing test is shown in Fig. 8.10. Eight AE events are analyzed and plotted in the elevation view. AE events are plotted at their locations from the location analysis. Then, cracks are classified based on the shear ratio. Tensile crack are indicated by arrow s3Tnbols, of which directions are determined from the direction el. Shear cracks are represented by cross symbols, of which two directions correspond to the two vectors 1 and n. Only the event No. 14 was classified into the mixed-mode cracking, and both orientations of the tensile and the shear are indicated. Results are so successful that AE events are located along the dip plane presumed from the dip angle. Remarkably, the directions of crack opening of the tensile cracks are vertical to, and the orientations of the shear cracks seem parallel to the dip plane. 

Fig. 8,10. Results of SiGMA analysis in a hydro-fracturing test.

The development of polymerizable microemulsions consisting of only three basic components (except a water component) for producing transparent solid polymers with nanostructure is a recent achievement [87]. For example. Fig. 5 shows the SEM micrograph of the fractured polymer prepared by the UV-initiated polymerization of a bicontinuous microemulsion consisting of 35 wt% water, 35 wt% AUDMAA and 30 wt% MMA. This micrograph reveals randomly distributed bicontinuous nanostructures of water channels and polymer domains. The widths of the bicontinuous nanostructures were about 40-60 nm. The sizes of the nanostructures can be readily reduced by adding 2-hydro-... 

The movement of groundwaters within crystalline environments and the numerous hydro-geologic parameters associated with these environments should have multiple controls. As discussed above, fracture generation and fracture sealing by secondary mineral phases could be a multi-phased process in the life of a crystalline... 

Figure 6. Coralline porous ceramic used for conversion to carbonated apadte by hydro-thermal processing as viewed (a) from the surface, (b) in cross-section and (c) a fractured strut showing crystallite orientation.

Stephansson, O., L. Jing and C.-F. Tsang. 1996. Coupled Thermo-Hydro-Mechanical Processes of Fractured Media—Mathematical... 

Models and methods for coupled thermo-hydro-mechanical processes of fractured rocks, in saturated conditions using crack-tensor approach (Liu et al., 2002), the equivalent continuum approach and FEM solution technique with consideration for two-phase flow of water/vapour due to phase change by evaporation for fully or partially saturated cases (Li et al., 2000). 

Damage mechanics principles have been applied extensively for well stability problems, especially for hard, brittle and fractured shale rocks. Constitutive models using damage concept, coupled with hydro-chemical swelling models, have been developed based on experimental results, and applied for design of drilling fluid density, combined with FEM methods (Liu, 1995). 

A Comprehensive understanding of the fracture distribution and hydro-geomechanical processes occurring during hydraulic stimulation is essential in both conventional and Hot Dry Rock (HDR)/ Hot Wet Rock (HWR) geothermal development. Some of this information can be obtained from well logs such as flow, temperature, pressure, BHTV, FMI, etc. However, they only provide restricted information near the well. 

Nguyen, T.S., Borgesson, L., Chijimatsu, M., Rutqvist, J., Fujita, T., Hemelind, J., Kobayashi, A., Onishi, Y., Tanaka, M. and Jing, L. IQOi.Hydro-mechanical response of a fractured granitic rock mass to excavation of a test pit-the Karnaishi Mine experiment in Japan. Int. J. Rock Mech. Min. Sci., 38(1) pp 79-94. 

Fujita T., Kobayashi A. and Borgesson L. 1996. Experimental investigation and mathematical simulation on coupled T-H-M processes of the engineered buffer materials, the TC3 problem. In Stephansson O, Jing L, Tsang C-F editors. Coupled thermo-hydro-mechanical processes of fractured media. Developments in Geotechnical Engineering, No.79, Amsterdam Elsevier, pp.369-392. 

The two-phase integrated finite difference flow code TOUGH2 was selected to perform the hydro-logical calculations for this I BEX analysis. TOUGH2 is a general-purpose program for the simulation of multi-dimensional, multiphase fluid flow in porous and fractured media. Fluid advec-tion is calculated by a multiphase extension of Darcy s law, and diffusion is included. Local thermodynamic equilibrium is assumed in all... 

Tijani, S.M. 1996. Short description of VIPLEF code. Coupled thermo-hydro-mechanical processes of fractured media. Developments in Geotechnical Engineering, 79 507 - 511. 

NUMERICAL SIMULATION OF VARIABLY COUPLED THERMO-HYDRO-MECHANICAL PROCESSES IN FRACTURED POROUS MEDIA... 

Ohnishi, Y. and Kobayashi, A. 1996. THAMES. In Stephansson, O., Jing, L., and Tsang, C.-F. editors. Coupled Thermo-hydro-mechanical Processes of Fractured Media. Developments in Geotechnical Engineering, Elsevier, 79 pp. 545-549. 

Abstract A methodology for quantifying the contributions of hydro-mechanical processes to fractured rock hydraulic property distributions has been developed and tested. Simulations have been carried out on discrete fracture networks to study the sensitivity of hydraulic properties to mechanical properties, stress changes with depth, mechanical boundary conditions, initial mechanical apertures and fracture network geometry. The results indicate that the most important (and uncertain) parameters for modelling HM processes in fractured rock are fracture density and rock/fracture mechanical properties. Aperture variation with depth below ground surface is found to be of second order importance. 

Stress conditions for this study are selected in two ways, based on the above conceptual mechanisms of hydro-mechanical coupling in fractured rock. 

HYDRO-MECHANICAL UPSCALING OF A FRACTURED ROCKMASS USING A 3D NUMERICAL APPROACH... 

A new upscaling method has been proposed by INERIS to determine the equivalent hydro mechanical properties of a fractured rock-mass. This method is based on the 3D numerical simulations of the behaviour of a "sample" of fractured rock-mass submitted to different hydromechanical boundary conditions. The simulations are defined in order to determine the equivalent permeability, stiffness and Biot tensor of a fractured rock-mass. 

Two numerical tools are used RESOBLOK (Heliot, 1988] to generate the 3D fracture network 3DEC [Itasca Consulting Group, 1994 Damjanac, 1994] to make the hydro-mechanical computations. 

Vuillot, E. 1995. Modelisation thermo-hydro-micanique de massifs rocheux fractures. Application au stockage de dichets radioactifs. These de Doctoral de I lNPL, Nancy, France. 

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