Source rocks

Keywords plate tectonics, sedimentary basins, source rocks, maturation, migration, reservoir rocks, traps, seismic, gravity survey, magnetic survey, geochemistry, mudlogs, field studies. 

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. 

The maturation of source rocks is followed by the migration of the produced hydrocarbons from the deeper, hotter parts of the basin into suitable structures. Hydrocarbons are lighter than water and will therefore move upwards through permeable strata. 

To assess potential yield and maturity of source rocks and classify those according to their vitrinite reflectance . 

Objecfive Method Basin Source Rock Maturation Migration Rese rvoir Rock Trap Fluids oil, gas, water... 

General Rock Types 240. Historical Geology 24 1. Petroleum Geology 242. Source Rocks 243. 

These deposits would result in carbonate rock (e.g., limestone). A third source rock possibility would be evaporite rocks (e.g., salt, gypsum, anhydrite), which often contain large organic concentrations when originally deposited [26-29]. 

S. Source rock potential of shale A relation exists between the uranium-to-potassium ratio and the organic carbon content. The source rock potential of shale can thus be evaluated. 

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. 

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