Page 73 - Geology and Geochemistry of Oil and Gas

DEFORMATION OF ROCKS IN DEPTH 49

Fig. 3.8. Relationship between the clay content and permeability of quartz sand fractions:
(a) 0.35–0.50 mm and (b) 0.08–0.12 mm (after Tsvetkova, modified by Klubova, 1984). Clays:
1 – montmorillonite; 2 – polymictic; 3 – kaolinite.

also changes the chemistry of the ongoing processes because of (1) changing pH, (2)
reactions with CO 2 forming as a result of organic matter transformations, (3) direct
effect on the temperature (as a result of endothermic and exothermic processes), and
(4) pressure changes due to increase in volume after the formation of new
compounds.

3.1.3. Paleotemperature
The study of evolution of a sedimentary basin is incomplete without a sufficient
knowledge of its paleotemperature regime. The probability of occurrence of
some mineral resources in basins is to a great extent controlled by the temperature,
which determines feasibility and direction of various chemical reactions. Usually,
the products of chemical reactions are what we are looking for, i.e., mineral
resources.
The preservation and destruction of migrating mineral resources (such as oil and
gas) also depend to a great extent on the temperature evolution of a basin.
Thermodynamic boundaries for some reactions or formation of some compounds,