Geology Reference
In-Depth Information
limitations (the environment of the natural fluid flow and discharge) enable
the utilization of geothermal data for the determination of the form, type
and direction of oil, gas and ground water migration.
The necessary precondition in the discussion of these issues is a review
of theoretical temperature and temperature gradient models as functions
of the status of geologic medium and realized fluid-transfer processes
accompanied by the heat exchange. A match, by the region, between the
actual data and a possible model should be interpreted as the objective
manifestation of certain migration mechanism.
In the absence (or significant restrictions) of fluid flow, the geothermal
regime of local structures is defined mostly by the conductive heat transfer
controlled by the relationship in the section of heat-transferring and heat-
insulating intervals. Strong positive temperature anomalies cannot form
under these conditions and formation temperatures must remain approxi-
mately at the background level. When lateral fluid mobility dominates, the
fluids flow updip and cover significant area. The heat-exchange between
the migrants and the enclosing rocks occurs during long times and along
the entire path.
The volumetric incompatibility between the reacting masses and the
duration of their contact provide under actual geologic environment for
smoothing out of the migrating fluids and reservoir temperature to the
regional background level stipulated by the natural unexcited temperature
field. In other words, under the lateral filtration model the heat exchange
between slow-flowing fluids and the enclosing geologic medium cannot
form and preserve in time noticeable temperature anomalies
7
. Under the
vertical flow, the contact area of the flowing fluids and enclosing rocks
is limited by the gaping-opening-conductivity of the channels, fracture
zones, mud volcano eruptions, hydrogeological “windows”, etc. The heat-
exchange between them occurs within a much smaller volume. The flow
of high-temperature fluids from the generation intervals to the accumula-
tion volumes happens much faster and (in general cases) over a shorter
path. The combination of these factors eventually results in the injection of
hot fluids into the zones of lowered (normal for the given section interval)
temperature and emergence of positive temperature anomalies.
Under the first and second models typical of tectonically quiet areas,
of buried structures and of insignificantly faulted areas, the temperature
field is practically not affected by the convective component. Variations
7
This naturally refers to the cases of low dip angles; the migration up a steep dip
should be treated as a version of the vertical fluid migration.
