Geology Reference
In-Depth Information
Qualitatively, the criteria for regional zones will be of the same type
as for local structures: zones of
predominant gas accumulation will have
generally elevated formation water
salinity
and
lowered participation in
formation water mixes of alkaline component. (The situation will be the
opposite in zones of predominant oil accumulation.) On local commer-
cially saturated structures, the formation waters in these zones will have
high sulphate content and substantial amounts of organic acids (naph-
thene acids).
Hydrogeologically, zones of predominant gas accumulation must have
relatively stagnant hydrodynamical conditions causing low mobility of
alkaline waters in the vertical section of local structures.
he necessary
preconditions are weak rock deformations,
no faults, which would create
paths for vertical fluid discharge, and conditions for the preservation of
gas-condensate aggregations.
Confirmation of the possibility for the practical application of the stated
criteria in the Productive Sequence is as follows: It is growth down its
regional dip in formation water salinity, decrease in their alkalinity and
increase in soluble salts of organic (naphthene) acids and
SO
−
ion con-
tents, which matches the main pattern (increase in gas-saturation causing
the transition in the same direction from oil accumulations to gas-oil and
farther on to gas-condensate).
Thus, we reviewed the hydrochemical criteria,
enabling forecast of
hydrocarbon accumulations and
types of accumulations.
Based on our
studies, we believe it is expedient to recommend for introduction into
exploration operations and the complex of hydrogeological (hydrody-
namical)
attributes
providing the opportunity for quantitative
estimate of
hydrocarbon volumes (reserves) accumulated in the structural traps. Such
estimates may be based on correlations (described in Chapter 6) between
hydrocarbon reserve density, structural attributes
d
i
, K
ин
and ground
water mobility parameters (indicators of the extent of alkaline water inva-
sion into the local structure sections -
h
a
,
Г
, K
ан
), etc. (Figures 8.4, 8.7,
8.9). These parameters determined from first appraisal wells may give (in
consideration of geophysical data about the structure size) an idea of the
hydrocarbon amounts concentrated in them.
The complex of hydrogeological and hydrochemical hydrocarbon
satura-
tion
in the Productive/Red-Bed Sequence of the South Caspian Depression
is listed further in Table 11.3.
Currently no commercial aggregations of natural gas are discovered
in the Paleogene-Miocene and Mesozoic complexes. That is why it is
impossible to define with accuracy the specifics of ground waters in con-
tact with accumulations of this type. For this reason hydrogeological and
