Fractures permeability

In general, hydraulic fracturing with sand propping provided adequate void space for emplacement of the NG1 in these explosive-fracturing tests in the oil shale. Explosive fracturing caused significant increases in fracture permeability when a sufficient NG1 charge was detonated. 

Fig. 9. Permeability versus capillary entry pressure. Entry pressure increases with decreasing permeability. The regression line drawn through the data was derived for a range of lithologies by Ibrahim et al. (1970) (Watts, 1987 Antonellini and Aydin, 1995). The relationship appears to hold for the cataclastic faults as well. Some of the deviations from the regression are due to uncertainties in the thickness of the deformation bands and slip planes, which lead to overestimated fracture permeabilities of up to one order of magnitude.

Fig. 7. Fracture permeability versus shear displacement CSFT result.

Some preliminary work has been completed to explain the origin of the permeability of the sandstone units. In the Bow Island Formation, an attempt was made to correlate conductivity values from drill-stem tests with the estimated true formation resistivity determined from electric logs. The lack of correlation, however, suggests that fracture permeability may be prevalent. 

The fracture permeability is vastly larger than the intact shale, more rapidly exposing shale away from the borehole wall to the new cation. 

SOME THMC CONTROLS ON THE EVOLUTION OF FRACTURE PERMEABILITY... 

Importantly, fracture permeabilities may either reduce or increase, in surprising ways, depending on the paths of stress or chemical potential. We illustrate this behaviour through observations during flow-through tests on samples of varied rock types. These include a fractured porous medium (Berea sandstone), and fractures in both silicic (Arkansas novaculite) [Polak et al., 2003 Yasuhara et al., 2004] and carbonate rocks (Bellefonte Limestone) [Polak et al., 2(X)4]. 

The current model for converting fracture deformation behavior to changes in fracture permeability utilizes only the normal deformation component. The fracture permeability is calculated using the predicted fracture apertures with the cubic law ... 

Figure 6 Changes in fracture permeabilities in DST boreholes 57-61 during heating...

The data in Figure 6 represent the measured permeability at a specific segment of a Hydrology hole at a particular time during the heating phase expressed as a ratio of the baseline permeability at that segment measured before the start of heating. Fracture permeabilities evolve due to complex... 

Olivella, S., A. Gens and C. Gonzalez, 2003. Coupled THM Modeling in a Fractured Permeable Rock. Proceedings (to be published), GeoProc2003, Stockholm, Sweden, October 2003. 

Tsang, Y.W., K. Huang, and G. S. Bodvarsson. Estimation of the Heterogeneity of Fracture Permeability by Simultaneous Modeling of Multiple Air-Infection Tests in Partially Saturated Fractured Tuff. Dynamics of Fluids in Fractured Rock. Geophysical Monograph 122, American Geophysical Union. 2000... 

The periodic air-permeability measurements provide an excellent opportunity to study the evolution of TM-induced changes in fracture permeability, and TH-induced changes in fracture moisture content, throughout the four-year heating period and the subsequent cooling period. 

Fracture closure/opening caused by changes in normal stress across fractures is the dominating mechanisms for TM-induced changes in fracture permeability, whereas fracture shear dilation does not appear to be significant at the DST. 

Although mechanical processes were certainly active during the DST, measured changes in air permeability were typically less than one order of magnitude (BSC, 2002), Permeability reductions could also be attributed to increases in fracture liquid saturation in the condensation zones. In addition, variations in fracture permeability are at least a few orders of magnitude around the DST and therefore smaller mechanical effects would not have a major effect on changes in water and gas chemistry resulting from coupled THC processes. 

EFFECT OF THERMAL DEFORMATION ON FRACTURE PERMEABILITY IN STRESSED ROCK MASSES... 

Abstract We analyse the effect of thermal contraction of rock on fracture permeability. The analysis is carried out by using a 2D FEM code which can treat the coupled problem of fluid flow in fractures, elastic and thermal deformation of rock and heat transfer. In the analysis, we assume high-temperature rock with a uniformly-distributed fracture network. The rock is subjected to in-situ confining stresses. Under the conditions, low-temperature fluid is injected into the fracture network. Our results show that even under confining environment, the considerable increase in fracture permeability appears due to thermal deformation of rock, which is caused by the difference in temperature of rock and injected fluid. However, for the increase of fracture permeability, the temperature difference is necessary to be larger than a critical value, STc, which is given as a function of in-situ stresses, pore pressure and elastic properties of rock. 

Thus if the temperature difference AT becomes larger than AT, defined by Equation (8), the fracture permeability will increase drastically. AT, is referred to the critical temperature difference. Note that AT is independent of the size of the cooled region, i.e. d. 

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