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of pore solutions in the sealing intervals. (The probability of invaded water
halos may be to a certain extent substantiated in the study conducted by
Sukharev and Krumbold (1962). They studied the chemistry of the pore
solutions squeezed out of the South Caspian Basin's Productive Sequence
clay and established their hydrocarbonate-sodium type in the intervals
saturated with injected alkaline waters. The following is noteworthy: we
conducted a special study of water extracts' chemical composition in clay
samples from the Kala Fm. in the same region (Zyrya prospect). The alka-
line water injection there was relatively restricted, and the study showed
their mostly hard nature - Mekhtiyev, Akhundov and Rachinsky, 1970).
Following are the diagnostic attributes of epigenetic AHFP
:
t
Development of low-density (decompacted) clays only
within the crestal zones of local highs with hydrocarbon
accumulations of great height.
t
“Contamination” of clays with gas.
t
Concentration of maximum clay porosity values within their
contact zone with productive reservoir.
t
Inverse relationship in the sections of individual struc-
tures between the depth and porosity (density) of clayey
formations.
t
Porosity and pore pressure gradient decrease within seal
intervals in the direction from structural crests toward their
flanks and plunges. Decompacted clays there demonstrate
Lower water-saturation and plasticity and higher oil-gas-
saturation. In the process of drilling epigenetic AHPP are
usually accompanied by gas shows of various intensity and
periodic blowouts of the drilling fluid, which however do
not cause uncontrolled blowouts.
Epigenetic AHFP'
s
occur in natural reservoirs most commonly as a
result of elastopulse subvertical injection (mostly from the underlying
sediments) of high-pressure fluids. The invasion uses systems of tectonic
unconformities (structural discordances), eruption vents of mud volca-
noes, contact zones of crypto-diapirs and diapirs with enclosing rocks,
areas of elevated fracturing, etc. The invasion was a result of the cross-
flow-injection in the geo-hydrodynamic system at the time of a climax in
the neotectonic processes and osmosis effects caused by the ground water
concentration differential in the contacting beds separated by semiperme-
able clay membranes. Following are the diagnostic attributes of epigenetic
AHFP's
in the former case:
