Saturation fractured rock permeability

Even in the absence of fractures and thief zones, the volumetric sweep efficiency of injected fluids can be quite low. The poor volumetric sweep efficiency exhibited in waterfloods is related to the mobility ratio, M. This is defined as the mobility of the injected water in the highly flooded (watered-out) low oil saturation zone, m, divided by the mobility of the oil in oil-bearing portions of the reservoir, m, (253,254). The mobility ratio is related to the rock permeability to oil and injected water and to the viscosity of these fluids by the following formula ... 

Even where it is not occluded, the mineral surface may not be reactive. In the va-dose zone, the surface may not be fully in contact with water or may contact water only intermittently. In the saturated zone, a mineral may touch virtually immobile water within isolated portions of the sediment s pore structure. Fluid chemistry in such microenvironments may bear little relationship to the bulk chemistry of the pore water. Since groundwater flow tends to be channeled through the most permeable portions of the subsurface, furthermore, fluids may bypass many or most of the mineral grains in a sediment or rock. The latter phenomenon is especially pronounced in fractured rocks, where only the mineral surfaces lining the fracture may be reactive. 

Figure 6 shows the evolution of gas pressure at the injection point and the gas flow rate at the outflow point. It can be observed that after a period of gas pressure increase corresponding to the desaturation of the injection layer, gas starts to penetrate in the medium. Figure 7 shows degree of saturation for both the fracture and the rock matrix. Gas flow takes place through the fracture because permeability is higher than in the matrix and because desaturation is easier than in the matrix. Due to fracture aperture, permeability increases and the air entry pressure decreases. 

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... 

Aquifers are regions of saturated material that are at least moderately conductive to water and may be tapped via wells for potable, industrial, or agricultural purposes. Although many aquifers are made of coarse, unconsolidated material such as gravel, the water-bearing material also can be a porous rock such as sandstone, or even a relatively nonporous but fractured rock such as granite. Beneath an aquifer maybe a nearly impermeable layer aquiclude) or low-permeability layer (aquitard). Sometimes the aquiclude or aquitard is thin and has unsaturated material beneath it. 

The jointed rock is treated as a hydraulically discontinuous mass. According to this model the rock matrix is not permeable and the seepage flow is limited in fractures. Taking into account the contribution of water saturation and seepage pressure, the total strain and constitutive equations of the rock mass was obtained. 

The evolution of the chemical regime in the unsaturated zone surrounding a heat source is closely related to the spatial distribution of temperature and the transport of water and vapor. An important aspect of the unsaturated fractured tuff at Yucca Mountain is that the highly permeable fractures are nearly dry, whereas the low permeability and porosity rock matrix has a water saturation of about 90 percent. Thus, heating of the rock induces boiling of the matrix pore water, transport of water vapor into fractures, and condensation along fracture walls. 

Permeability, which characterizes the ability of rocks to allow the movement of fluids contained in their pores, is one of the most important parameters describing the porous media. Normally, in order to measure the permeability, the sample must have a simple geometric shape (e.g. cylinder or cube) and certain dimensions. On the other hand, measurements of porosity, pore-size distribution, and specific surface area do not require special geometric dimensions. The correlations among permeability and other easier-to-measure parameters, therefore, have been studied theoretically and experimentally. In practice, the most often reported correlation is that between the permeability and porosity The coefficient of correlation for porosity-permeability relationship varies from sample to sample, with a better correlation if the porosity used in the calculation is measured when a core contains the irreducible fluid. Porosity does not reflect the number and width of fractures, the pore sizes and topological structure, whereas the specific surface area does. Thus, it appears advisable to relate permeability simultaneously to porosity, specific surface area, irreducible water/oil saturation, grain size/pore size/throat size distribution, tortuosity, etc. 

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