Porosity fracture permeability

Carbonate rocks are more frequently fractured than sandstones. In many cases open fractures in carbonate reservoirs provide high porosity / high permeability path ways for hydrocarbon production. The fractures will be continuously re-charged from the tight (low permeable) rock matrix. During field development, wells need to be planned to intersect as many natural fractures as possible, e.g. by drilling horizontal wells. 

On the other hand, the addition of fibers may cause undesired properties of the cement [1759]. Fibers can actually increase pore and fracture systems in latex cements. The amount of fibers in a fiber seal cement influences the porosity and permeability while affecting compressive strength. During acid treatment of the formation, the fibers in the cement can be easily dislodged and extracted from the cracks, leaving pore spaces behind. 

N2 injection rapidly increases the methane production rate. The timing and magnitude depends on the distance between injection and production wells, on the natural fracture porosity and permeability, and on the sorption properties. N2 breakthrough at the production well occurs at about half the time required to reach the maximum methane production rate in this ideal case. The N2 content of the produced gas continues to increase until it becomes excessive, i.e., 50% or greater. 

Preferred fluid migration pathways are influenced by porosity and permeability, sedimentary sequences, facies architecture, and fractures. Porosity is a measure of pore space per unit volume of rock or sediment and can be divided into two types absolute porosity and effective porosity. Absolute porosity (n) is the total void space per unit volume and is defined as the percentage of the bulk volume that is not solid material. The equation for basic porosity is listed below ... 

Plants exert additional effects on weathering. The presence of forest trees tends to lower soil surface temperatures by shading the soil surface and reducing surface albedo (Kelly et al., 1998). Also, roots fracture mineral grains and increase soil porosity and permeability, which allows greater contact between soil solutions and minerals (April and Keller, 1990 Colin et al., 1992). 

The extent of surface weathering of crystalline rocks or of sedimentary rocks such as shales or carbonates, and thus rock permeability (and yield to wells), decreases rapidly with depth. Also, rock weathering is deeper under valley bottoms than on ridges or hill slopes. This reflects the fact that the weathering, which is facilitated by joints, fractures, and faults, tends to create valley bottoms in the first place. Valley bottoms continue to concentrate runoff (R is then a positive term in the infiltration equation) and so remain the locus of deeper development of secondary rock porosity and permeability and thus of enhanced groundwater storing and transmitting capacity. 

Two types of reservoirs, each with different permeability, are found within the petroliferous bed of the fields in the Krasnodar Petroliferous Region. A number of laboratory models were therefore prepared to reproduce these permeability differences. Models using sand as porous medium (porosity-type models) simulated the reservoirs of the first type. The range of permeability of this medium corresponded to that of the actual reservoirs of the same type. Models characterized by fracture-type porosity (fracture-type models), were used to represent the second type of the reservoir. Again, the permeability characteristics of the medium used in the latter type models were similar to those of the real reservoirs. 

The moisture content of both the wood and the adhesive affect the fracture behavior of adhesive bonded joints. Wood joints are especially sensitive to moisture effects as a result of the porosity and permeability of wood, which allows ready access by water to both the interior of the wood member and the adhesive layer. Irle and Bolton [57] showed that the superior durability of wood-based panels bonded with an alkaline PF adhesive compared to panels bonded with a UF adhesive was due to the ability of the phenolic adhesive to absorb and be plasticized by water. In the plasticized state, the phenolic adhesive is able to reduce stress concentrations that otherwise fracture the wood or the adhesive in urea-bonded panels. 

Fu, L., Milliken, K.L., Sharp Jr., J.M. (1994). Porosity and permeability variations in fractured and Liesegang-banded Breathitt sandstones (Middle Pennsylvanian), eastern Kentucky Diagenetic controls and implications for modeling dual porosity systems. Journal of Hydrology, 154, 351-381. 

Fractures are important for fluid flow in oil, gas, and water production and geothermal processes. In such cases, the fluids are stored mainly in the matrix porosity but produced primarily using fracture permeability. Fractures penetrating impermeable shale layers create hydraulic conductivity and can develop a reservoir. Artificial fracturing (hydrofrac) can create new fractures or magnify existing fracture. On the other hand, fractures significantly reduce mechanical rock properties. 

Fracture permeability from this model calculation is controlled by porosity and the square of the fracture dimensicm. This is comparable to the architecture of Eq. (2.53) with square of pore radius. 

The bulk of the cement is extremely porous as the fractured surface of a specimen shows (Figure 6.3c). The pores are 0-5 pm in diameter and more abundant in the depth of the cement. The porosity arises from excess unbound water which separates out as globules in the cement and is trapped by the rapid setting. Subsequent diffusion of these globules leaves the cement porous. This makes the cement permeable to dyes (Wisth, 1972). 

Hydraulic conductivity is one of the characteristic properties of a soil relating to water flow. The movement of water in soil depends on the soil structure, in particular its porosity and pore size distribution. A soil containing more void space usually has a higher permeability. Most consolidated bedrocks are low in permeability. However, rock fractures could create a path for water movement. 

The geology not only provides the chemical source for trace-element mobility but it also provides the physical framework for water-flow paths. The structural properties of the rocks, the porosity, permeable fractures, provide for water-mineral reaction and element mobility. The geomorphology contributes to water-table levels, aquifer permeability, surface-water travel times, and time periods for erosion and sediment transport. Examples of... 

Porosity that includes the voids between mineral (or soil) grains is referred to as primary porosity. When the porosity is the result of cracks, fractures, or solution channels, it is known as secondary porosity. The porosity of soft clay is often over 50%, but clay typically has low permeability because the pores are either not interconnected or are too small to permit easy passage of water. On the other extreme, nonfracture igneous rock often has a porosity of less than 0.1% but, again, low permeability. 

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