An investigation of the porosity of clays of the productive series of Middle Pliocene and Miocene-Paleogene deposits of the northwest flank of the South Caspian depression shows that the rate and degree of compaction of the argillaceous rocks vary extensively under different geological conditions, and often differ markedly from the known laws of compaction of clay deposits. In the accumulation of thick argillaceous strata, when some clay bands are overlain by others, great depth of burial of the beds is a necessary but insufficient condition of consolidation of clay rocks. Such sedimentation conditions, characterized by isolation of the clays from the region of relaxation, cause the withdrawal of pore water from the clay deposits being compacted to lag markedly behind the rate and depth of their burial. Normal consolidation of clay sediments occurs when the clay rocks are in contanct with regionally developed sand beds, which can serve as a region of relaxation for the clays undergoing compaction. Retarded withdrawal of pore water from clay rocks during submersion to present-day depths causes intense compression of the fluids to virtually geostatic pressures, which leads to abnormally high formation pressures (AHFP) in the argillaceous strata (in the given case abnormally high intrapore pressure). The following important fact is noteworthy: at the same depth, the porosity of clays in alternating arenaceous and argillaceous strata is much less than in thick clay deposits. However, the porosity of clays in zones of culminating manifestation of AHFP was much higher than in intervals with more or less normal formational pressures. Data were presented in two tables; table 1 compared actual porosity of clays with the mean porosity (according to / Vassoyevich and Weller) and table 2 presented the variations in porosity of the productive series clays from laboratory data. The new data shed light on the enormous energy reserves of young, intensely sinking, regionally thick, predominantly argillaceous strata, to which are related the basic mechanisms of primary and secondary (including Recent) migration of hydrocarbons from their regions of origin to the region of accumulation.

  • Corporate Authors:

    American Geological Institute

    5205 Leesburg Pike
    Falls Church, VA  United States  22041
  • Authors:
    • Durmishyan, A G
  • Publication Date: 1974-6

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  • Accession Number: 00261461
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 30 1974 12:00AM