Geology basins

Figure 20.1 shows the number of Class I wells in the 1986 survey by state, divided into U.S. EPA regions, and also indicates the regulatory status of such wells in each state as of 1989. The map shows the heavy concentration of hazardous waste injection wells in three geologic basins Gulf Coast, Illinois Basin, and the Michigan Basin.1 3 ... 

Manning, R.A., Manhardt, P.D., Orzechowski, J.A., Cathles, L.M., Baker, A.J. 1993. A parallel 3-D geologic basin modeling code. Technical Report for the SIAM Conference on Mathematical and Computational Issues in the Geosciences, Knoxville. 

Because natural gas bums cleanly, the nation s domestic natural gas resources, and the presence of supporting infrastructure, the development of domestic shale gas reserves will be an important component of the United States energy coffer for many years. Recent successes in a variety of geologic basins have created the opportunity for shale gas to be a strategic part of the nation s energy and economic growth (IPAMS, 2008). 

Several conditions need to be satisfied for the existence of a hydrocarbon accumulation, as indicated in Figure 2.1. The first of these is an area in which a suitable sequence of rocks has accumulated over geologic time, the sedimentary basin. Within that sequence there needs to be a high content of organic matter, the source rock. Through elevated temperatures and pressures these rocks must have reached maturation, the condition at which hydrocarbons are expelled from the source rock. 

Hydrocarbons are of a lower density than formation water. Thus, if no mechanism is in place to stop their upward migration they will eventually seep to the surface. On seabed surveys in some offshore areas we can detect crater like features ( pock marks ) which also bear witness to the escape of oil and gas to the surface. It is assumed that throughout the geologic past vast quantities of hydrocarbons have been lost in this manner from sedimentary basins. 

Even if all of the elements described so far have been present within a sedimentary basin an accumulation will not necessarily be encountered. One of the crucial questions in prospect evaluation is about the timing of events. The deformation of strata into a suitable trap has to precede the maturation and migration of petroleum. The reservoir seal must have been intact throughout geologic time. If a leak occurred sometime in the past, the exploration well will only encounter small amounts of residual hydrocarbons. Conversely, a seal such as a fault may have developed early on in the field s history and prevented the migration of hydrocarbons into the structure. 

Miall, Andrew (1984) Principles of Sedimentary Basin Analysis,468p, Springer Verlag North, F. K., (1985) Petroleum Geology, 607p, Allen Unwin... 

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

Other coal sample banks are also in existence. The Penn State Sample Bank at Peimsylvania State University has the most diverse collection of samples (86). The Illinois Basin Coal Sample Program at the Illinois State Geological Survey specializes in samples from the Illinois Basin (89). The European Center for Coal Specimens has a significant collection of samples from the entire world and is located in Eygelshoven in The Netherlands (88). Each makes samples available in kilogram quantities. 

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

The fluid pressure in the rock at the bottom of a well is commonly defined as pore pressure (also called formation pressure, or reservoir pressure). Depending on the maturity of the sedimentary basin, the pore pressure will reflect geologic column overburden that may include a portion of the rock particle weight (i.e., immature basins), or a simple hydrostatic column of fluid (i.e., mature basins). The pore pressure and therefore its gradient can be obtained from well log data as wells are drilled. These pore pressure data are fundamental for the solution of engineering problems in drilling, well completions, production, and reservoir engineering. 

The constant value of 0.25 for Poisson s ratio versus depth reflects the geology and the rock mechanics of the mature sedimentary basin in the West Texas region. Since mature basins are well cemented, the rock columns of West Texas will act as compressible, brittle, elastic materials. 

Calculations for prospective areas with structures not yet tested by drilling, or assessments on the basis of the general geological setting of a basin. 

The nature of human impacts on the Great Lakes relates closely to historical development and land use in the basin which, in turn, relate closely to the geology and physiography of the watershed. The southern part of the basin consists largely of Palaeozoic sedimentary rocks. Land use consists primarily of intense... 

Table 3. Matrix for Estimating Interactive Erosional Impact of Land-use Activities with Terrain Properties of Geology Land Slope, MolaUa River Basin, Oregon ...

Watersheds, also known as drainage basins, define a natural context for the study of relationships among soils, geology, terrestrial ecosystems, and the hydrologic system because water and sediment travel downslope under the influence of gravity. This material is a continuation of some of what was presented in Chapter 6. 

Fig. 9-3 Conceptual model to describe the interaction between chemical weathering of bedrock and down-slope transport of solid erosion products. It is assumed that chemical weathering is required to generate loose solid erosion products of the bedrock. Solid curve portrays a hypothetical relationship between soil thickness and rate of chemical weathering of bedrock. Dotted lines correspond to different potential transport capacities. Low potential transport capacity is expected on a flat terrain, whereas high transport is expected on steep terrain. For moderate capacity, C and F are equilibrium points. (Modified with permission from R. F. Stallard, River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco basins. In J. I. Drever, ed. (1985), "The Chemistry of Weathering," D. Reidel Publishing Co., Dordrecht, The Netherlands.)...

Drever, J. I. and Hurcomb, D. R. (1986). Neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the North Cascade Mountains. Geology 14,221-224. 

Stallard, R. F. (1985). River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco basins. In "The Chemistry of Weathering" (J. I. Drever, ed.), pp. 293-316. D. Reidel Publishing Co., Dordrecht, Holland, NATO ASI Series C Mathematical and Physical Sciences 149. 

Evaporite deposition is a much more episodic process and thus difficult to quantify. Because seawater is significantly undersaturated with respect to common evaporitic minerals, like gypsum and halite, evaporites are only formed when restricted circulation develops in an ocean basin in which evaporation exceeds precipitation. A geologically recent example is the Mediterranean Sea of 5-6 Myr ago. At this time excess evaporation exceeded the supply of ocean water through shallow inlet(s) from the Atlantic Ocean. As salinity increased, first CaS04, then NaCl precipitated. Over time, salt deposits 2-3 km thick formed. This thickness represents about 40 desiccations of the entire... 

What are the relative contributions of these two sources Two approaches have been taken. One is to establish the geology and hydrology of a basin in great detail. This has been carried out for the Amazon (Stallard and Edmond, 1981) with the result that evaporites contribute about twice as much sulfate as sulfide oxidation. The other approach is to apply sulfur isotope geochemistry. As mentioned earlier, there are two relatively abundant stable isotopes of S, and The mean 34/32 ratio is 0.0442. However, different source rocks have different ratios, which arise from slight differences in the reactivities of the isotopes. These deviations are expressed as a difference from a standard, in the case of sulfur the standard being a meteorite found at Canyon Diablo, Arizona. 

Hedenquist, J.W. (1987) Volcanic-related hydrothermal systems in the Circum-Pacific basin and their potential for mineralization. Mining Geology, 37, 347-364 (in Japanese). 

Masuda, F. (1984) Sedimentary basins in arc-trench system as a high-sensitive recorder of oceanic plate motion. Mining Geology, 34, 1-20 (in Japanese). 

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