caa a22 4500 469064439 CHVBK 20180323132903.0 cr unu---uuuuu 170328e19920101xx s 000 0 eng 10.1007/BF00890085 doi (NATIONALLICENCE)springer-10.1007/BF00890085 Lerche I. Department of Geological Sciences, University of South Carolina, 29208, Columbia, South Carolina aut Thermal focusing in complex stratigraphic regions: Lithology and porosity effects, and equivalent vertical and horizontal thermal conductivities [Elektronische Daten] [I. Lerche] Thermal focusing or defocusing by spatial variations in thermal conductivity caused by lithology and porosity fluctuations impacts the mean vertical geothermal gradient, localized fluctuations in temperature, and lateral bending of heat flow lines. Using mean field renormalization techniques, in which spatial fluctuations are treated as being randomly distributed around slowly varying mean values, estimates are given of the relative importance of lithologic and porosity variations in influencing thermal focusing. It is shown that, except for massive halite and/or evaporate variations, nearly all other geological situations can be viewed as having only a slowly varying mean lithology: fluctuations in porosity dominate thermal focusing. The mean vertical geothermal gradient is shown to be decreased by roughly 5-10% (with a maximum possible decrease of 25%) by the presence of porosity variations, relative to the mean gradient that exists in the same average medium but without fluctuations in porosity. The equivalent mean vertical thermal conductivity is shown to be increased by a maximum of about 12% relative to the non-fluctuating medium case. Root mean square temperature fluctuations vary in the typical range of 3-30°C depending on the correlation length scale of the porosity fluctuations. A correlation length of 1 km produces temperature fluctuations of around 3°C. Lateral bending of heat flux lines is implied by the thermal focusing; estimates suggest a root mean square bending angle of around 8-10°, with a corresponding mean equivalent lateral thermal conductivity of around 14% of the equivalent vertical thermal conductivity. These values are sufficiently large to suggest that fluctuations in stratigraphic sequences can lead to compartmentalized domains of juxtaposed hotter and cooler sedimentary volumes, thereby impacting the regimes of hydrocarbon generation. A simple estimate suggests that the depth of the top of the oil window may be increased by up to 0.5 km by such considerations. Effects due to anisotropic thermal conductivities, temperature dependence of thermal conductivity, and anisotropic correlated behavior of porosity and lithology fluctuations, need to be investigated to assess their significance. International Association for Mathematical Geology, 1992 thermal conductivity nationallicence heat flow nationallicence stratigraphic focusing nationallicence Mathematical Geology Kluwer Academic Publishers-Plenum Publishers 24/1(1992-01-01), 1-25 0882-8121 24:1<1 1992 24 11004 https://doi.org/10.1007/BF00890085 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00890085 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Lerche I. Department of Geological Sciences, University of South Carolina, 29208, Columbia, South Carolina aut NATIONALLICENCE 773 0- Mathematical Geology Kluwer Academic Publishers-Plenum Publishers 24/1(1992-01-01), 1-25 0882-8121 24:1<1 1992 24 11004 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer