Rock structure

One of the major effects of acidic deposition is felt by aquatic ecosystems in mountainous terrain, where considerable precipitation occurs due to orographic lifting. The maximum effect is felt where there is little buffering of the acid by soil or rock structures and where steep lakeshore slopes allow little time for precipitation to remain on the ground surface before entering the lake. Maximum fish kills occur in the early spring due to the "acid shock" of the first meltwater, which releases the pollution accumulated in the winter snowpack. This first melt may be 5-10 times more acidic than rainfall. 

The structures seen in the ALH84001 meteorite could easily have formed from molten material solidifying rapidly or even by precipitation of minerals from saturated solutions. Neither explanation is as romantic as Martian nanobacteria. Similar sized features have been seen following electron microscopy analysis of basalt rock structures found in riverbeds, such as from the Columbia river (Figure 6.15). 

All samples plot in the basalt to alkaline basalt fields of the Zr/Ti02 vs. NbA diagram of Pearce (1996) (Fig. 3). The NbA ratios define two distinct groups (1) tholeiitic metavolcanic rocks structurally underlying VMS mineralisation and (2) more alkaline ultramafic cumulates and metavolcanic rocks above VMS... 

Fig. 4. Representative primitive mantle normalised trace element patterns of metavolcanic rocks structurally above and below VMS mineralisation. Normalising values are from Sun and McDonough (1989).

The abrasiveness test results by Mackensen s method for selected cubes of known abrasiveness on Bohme s disc, given in Table 4.5.4, show very clearly a way of detecting inhomogeneities in rock hardness, induced by structural and textural differences. By this method we can observe the influence of pockets, laminae or veins occurring in a rock, which have a different composition from the typical rock structure, and also the influence of cracks and weathering of rock on its overall hardness (abrasiveness). In the tests with cubes (previously used for Bohme tests), some 24 measurements were taken in each case (four on each face) by the Mackensen method. This is sufficient to give a comprehensive characterization of rock hardness, not possible in the same time with any other method (a single... 

Another kind of underground storage reservoir is called an aquifer. An aquifer is an underground rock structure holding large quantities of water. The. iindergiound lock is poious and penneable The. pole, spaces aie filled with w ater, and impermeable rock covers the porous rock. Wells are drilled into such formations, and gas is forced into the pores under pressure. As [he gas pressure increases, the gas pushes the water farther down into the porous rock, making room for the gas. 

Fig. 8. Onshore seismic field operation, using the shot hole energy method. Energy from a controlled explosion is directed toward underlying rock structures and is reflected to indicate shape of formation below—in this case an anticline. Geophones placed on the ground surface by the surveying crew measure and record the reflected acoustic energy. With the survey truck safely away from the shot hole, the explosives are detonated by an assigned radio frequency from tile truck...

Decker, D.L., Tyler, S.W., Papelis, C. and Simunek, J. (1999) A reactive transport model for arsenic in unsaturated gold mine heap and waste rock structures. Abstracts with Programs-Geological Society of America, 31(7), 70. 

Pressure solution can cause major alterations in carbonate rock structures on megascopic to microscopic scales. Numerous papers and reviews deal with this topic (e.g., Bathurst, 1975 Choquette and James, 1987). We feel that one of the best attempts to bring an orderly picture out of the many complex features that are observed was that by Wanless (1979), who also emphasized the importance of pressure solution for subsurface dolomitization (see next section). Figure 8.12 presents his general model for the characteristics and controls on pressure solution types in limestones. The primary variables that Wanless considered were the clay content of the limestone, the concentration of structurally resistant elements, and variations between different units or beds. Temperature, pressure and fluid composition are also likely to play an important role in determining the timing and extent of pressure solution. 

Emery, K.O., and Uchupi, E. (1972) Western Atlantic Ocean Topography, Rocks, Structure, Water, Life, and Sediments. American Association of Petroleum Geology Memoires 17, Washington, DC. 

On a time series of Quaternary marine terraces in northern California, Brimhall et al. (1992) conducted the first mass balance analysis of soil formation over geologic time spans. This analysis provided quantitative data on well-known qualitative observations of soil formation (i) the earliest stages of soil formation (on timescales of 10 -10 yr) are visually characterized by loss of sedimentary/rock structure, the accumulation of roots and organic matter, and the reduction of bulk density and (ii) the later stages of soil development (>10 yr) are characterized by the accumulation of weathering products (iron oxides, silicate clays, and carbonates) and the loss of many products of weathering. 

Figure 8.2 Calculated hydrocarbon column heights below hypothetical cap rock structure at different times before present (from Lehner et al., 1987. Reprinted by permission of Editions Technip).

In 1959, Wagner and Leach (11) suggested that increased oil recovery could be obtained by changing wettability of rock material from oil-wet to water-wet. Melrose and Bradner (7) and Morrow (12) also suggested that for optimal recovery of residual oil by a low interfacial tension flood, the rock structure should be water-wet. Previous investigators (13,14) have used sodium hydroxide to make the reservoir rock water-wet. Slattery and Oh (15) have shown that intermediate wettability may be less desirable than either oil-wet or water-wet rocks. Since, chemical floods satisfy many of these conditions, they have been considered promising for enhanced recovery of oil. The mechanism of oil displacement in porous media has been reviewed by Bansal and Shah (16) and more recently by Taber (17). 

When a surfactant-water or surfactant-brine mixture is carefully contacted with oil in the absence of flow, bulk diffusion and, in some cases, adsorption-desorption or phase transformation kinetics dictate the way in which the equilibrium state is approached and the time required to reach it. Nonequilibrium behavior in such systems is of interest in connection with certain enhanced oil recovery processes where surfactant-brine mixtures are injected into underground formations to diplace globules of oil trapped in the porous rock structure. Indications exist that recovery efficiency can be affected by the extent of equilibration between phases and by the type of nonequilibrium phenomena which occur (J ). In detergency also, the rate and manner of oily soil removal by solubilization and "complexing" or "emulsification" mechanisms are controlled by diffusion and phase transformation kinetics (2-2). 

As the water flows across the land surface and into the soil and rock structures some soluble salts will be dissolved. The pH of the water will influence the solubilisation process. The final composition of the resulting solution will depend to a large extent on the geology of the area through which the water flows. Water that tends to remain on the land surface is generally referred to as "surface water" whereas the water that penetrates deeper into the soil and rock surfaces is generally termed "ground water". 

Shales are fine grained, clay-like rock structures that cleave readily into thin layers. Many shales are coloured black on account of the bitumen that they contain. There are also gas shales in which considerable quantities of natural... 

Stress field inside a solid or rock structure with combined mechanical and thermal loadings has been successfully reconstructed by the inverse boundary element technique. 

The main emphases in oil and gas production are how to explore sites and how to operate resources for optimal flow, and long term resource management. The rock structure, rock stress field, primary and secondary rock permeabilities, wellbore locations and orientations, and fluid flow are all coupled and hence there are many interactions that require modelling. 

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