Porosity of rock

The first super-deep drilling to 12.8 km in the Kola peninsula of Russia verified the effect of de-consolidation (the reverse of consolidation) in rocks at a depth >5 km (Dortman, 1992). This effect results from the increase of fracture content and porosity of rocks at depth. 

This formula contains the porosity of rocks. So far as we discern the porosity of transport pores and the porosity of interlayer films of water, then it is clear that n = m + m. So using n = /3-0( -ff) = we see that if we want to... 

The input parameters of the model are stated in the Chapter 2 (the definition of the area geometry, hydraulic conductivity and porosity of rocks and fissures zones, fissures openings, substances sorption parameters, diffusion coefficient, released volumes of substances in time). These parameters are analyzed (in the view of the model sensitivity and supposing the same calculated mesh but different input parameters—e.g. those of hydraulic conductivity or porosity) in the Chapter 4. 

Very clean sands are rare and normally variable amounts of c/ay will be contained in the reservoir pore system, the clays being the weathering products of rock constituents such as feldspars. The quantity of clay and its distribution within the reservoir exerts a major control on permeability and porosity. Figure 5.2 shows several types of clay distribution. 

The formation density log is the main tool for measuring porosity. It measures the bulk density of a small volume of formation in front of the logging tool, which is a mixture of minerals and fluids. Providing the rock matrix and fluid densities are known the relative proportion of rock and fluid (and hence porosity) can be determined. 

Absolute porosity—. oH porosity of a rock, regardless of whether or not the individual voids are connected. 

The various volumes of rock matrix, shale, porosity, overpressure porosity and hydrocarbons are used to compute the various tool responses according to a model. The responses are compared to the measured values and a volume optimization is made to minimize the errors grouped in an incoherence function. The value of the incoherence function for the best fit determines the quality of the answer. Figure 4-335 is an example of formation pressure calculation as well as formation evaluation for lithology and fluid content. 

The porosity of a reservoir rock is the ratio of the pore volume to the total volume of the rock and is expressed either as a percentage or as a fraction. 

Results and Discussion on Dynamic Adsorption Measurements. Baker dolomite was used to study the dynamic adsorption experiment. The computed porosity of the rock was 24%. One concentration below the CMC of AEGS, one at CMC, and two concentrations above CMC were chosen to measure the adsorption of this surfactant with Baker dolomite. The mass of surfactant adsorbed per gram of rock is plotted as a function of flow rate in a semi-log plot in Figure 9. 

Injecting acid in such an interval produces wormholes in the nearwellbore region, which is damaged, so that the acid flow only takes place in the clean primary porosity of the rock. This superposes to the original step function of the permeability profile a second, similar function, stating that the acidized profile now includes in the vicinity of the wellbore, from rw up to re, a zone of infinite conductivity... 

A packed bed is composed of crushed rock with a density of 175 lbm/ft3 of such a size and shape that the average ratio of surface area to volume for the particles is 50 in.2/in.3. The bed is 6 ft deep, has a porosity of 0.3, and is covered by a 2 ft deep layer of water that drains by gravity through the bed. Calculate the flow rate of water through the bed in gpm/ft2, assuming it exits at 1 atm pressure. 

We then pick up the fluid from the previous step as a reactant and define a system representing the limestone and its pore fluid. We specify that the rock contains 3000 cm3 of calcite, implying a porosity of about 25% since the extent of the system is 1 kg (about 1 liter) of fluid. The pore fluid is similar to the reactant fluid, except that it contains less magnesium. The procedure is... 

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 ... 

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. 

In fractured rock aquifers in which the porosity of the solid mass between fractures is insignificant. Freeze and Cherry (1974) report the retardation equation as ... 

Carbonate rocks consist mostly of calcite and dolomite with minor amounts of clay. The porosity of carbonate rocks ranges from 20 to 50%, but in contrast to sandstone, it tends to decrease with depth. Often, carbonate rocks are fractured, providing a permeability that is much greater than the primary one. In some cases, initial small-scale fractures in calcite and dolomite are enlarged by dissolution during groundwater flow, leading to an increase in rock permeability with time. 

One approach to quantitatively relate changes in porosity to changes in specific surface area is to assume that the porous medium is composed of spherical grains. The resulting specific surface area per unit volume of rock, J, is related to the porosity, [Pg.236]

Therefore, in the first model, the specific surface area increases with decreasing porosity, while in the second, the opposite relationship is specified. While some attempts have been made to experimentally verify these models in individual rock types (Kieffer et al. 1999 Jove Colon et al. 2004), the data concerning a wide range of rocks and precipitation-dissolution reactions remain limited. 

---