Depth of burial

Table 3.7 Effect of depth of burial on the rusting of mild steel flats (BISRA)...

The depth of burial should be that which will be occupied by the structure of interest. Specimens to be compared should be buried at the same depth. Ideally, tests for structures, such as piling, that will extend through several horizons would require the use of test specimens long enough to extend to the same depth. 

The relevance of the remarks on sulfur content is that, for reasons explained above, it is usually a valid index of the salinity of the environments of deposition. It was remarked earlier that the Eastern and Interior provinces have experienced different temperature/pressure/time histories. It should be added that coals of the Rocky Mountain, Pacific and Alaskan provinces most probably experienced yet further sets of conditions of metamorphism a locally increased geothermal gradient that produced relatively high temperatures at relatively low depths of burial and hence at relatively low pressures of overburden. 

The production of significant quantities of natural gas plus a petroleum-like substance from organic material in shales apparently occurs between 60 and 120°C. This, as we have seen, could as well be a function of time as of depth given the data at hand. The reason is that all hydrocarbons above CH weight are inherently unstable in a thermodynamic sense, even at 25°C and 1 atmosphere (Thorstenson, 1970). However, if depth of burial and time elapsed since deposition can be considered as one variable (basin subsidence therefore must occur at similar rates for similar geothermal gradients) a depth-temperature plot will be useful. 

Dr. Fester The ratio of the C20 isoprenoid paraffin to the total iso-prenoid paraffins decreased with depth of burial while the ratio of each of the C15, Cie, C18, and C19 isoprenoids to the total isoprenoid paraffins tended to increase with depth of burial. These variations may be caused by a combination of several factors, one important factor being environmental conditions of the lake at the time of deposition. 

Just as a relationship exists between the various properties of petroleum with parameters such as depth of burial of the reservoir (Speight, 1999), similar relationships exist for the properties of coal (e.g., Solomon, 1981 Speight, 1994). Variations in hydrogen content with carbon content or oxygen content with carbon content and with each other have also been noted. However, it should be noted that many of the published reports cite the variation of analytical data or test results not with rank in the true sense of the word but with elemental carbon content that can only be approximately equated to rank. 

Diagenetic modification of expandable clay during burial is an important source of mixed-layer illite-montmorillonite. With increasing depth of burial and increasing temperature the proportion of contracted 10 A layers systematically increases. From about 50°C— 100°C the contracted layers are distributed randomly. At higher temperatures only a few additional layers are contracted but the interlayering becomes more ordered (Perry and Hower, 1970 Weaver and Beck, 1971a). The final product, 7 3 to 8 2, is relatively stable and persists until temperatures on the order of 200°C— 220° C are reached. 

Figure 3. GC-FID chromatograms for thiophene compound fractions from Alberta petroleums. The peak labels are as follows 1. dibenzothiophene, 2. 4-methyldibenzothiophene, 3. 2- and 3-methyldibenzothiophene and 4. 1-methyldibenzothiophene. Samples are arranged in order of their depth of burial. Note the shift toward lower molecular weight compounds and a reduction in the amount of the unresolved complex mixture with increasing depth of burial. (Reproduced from Reference 34. Copyright 1989, American Chemical Society.)...

Figure 3. Partial FID chromatograms (/z-Cg to n-C9 region) from flash pyrolysis of Monterey Fm. kerogens, Santa Barbara basin. Open and closed circles indicate w-alk-l-enes and /z-alkanes respectively. Depth of burial, Rock-Eval pyrolysis Tmax, Hydrogen Index (HI), and the thiophene ration (TR) are shown.

Figure 4. Variation in the thiophene ratio (TR) with depth for samples from four sedimentary sequences. For samples from the Paris Basin, maximum depths of burial from Mackenzie et al (23) were used.

Figure 6. Ternary plots showing the variation in relative abundances of 2,3-dimethylthiophene, n-non-l-ene and 1,2-dimethylbenzene with depth (meters) for samples from the four sedimentary sequences. Maximum depths of burial are given for samples from the Paris Basin.

Figure 11. Variation in the ratio of eCj-C alkylbenzo[fr]thiophenes (Peaks 16-18, Figs. 10 and 13) relative to eC1-C3 alkylthiophenes (Peaks 2-14, Figs. 10 and 13) with respect to depth or temperature of artificial maturation. Maximum depths of burial are used for samples from the Paris Basin. Values determined from peak height data, corrected for quadratic response of FPD. Continued on next page.

Manghnani M.H., Schlanger S.O. and Milholland P.D. (1980) Elastic properties related to depth of burial, strontium content and age, and diagenetic stage in pelagic carbonate sediments. In Bottom Interacting Ocean Acoustics (eds. W.A. Kupferman and F.D. Jensen), pp. . Plenum Press, New York. 

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