Geology Reference
In-Depth Information
Establishment of epigenetic nature of AHPP in clay seals is among the
most efficient techniques to forecast the accumulations in the undrilled
portion of the sediment cover. It enables the forecast not only of the pres-
ence but on a number of occasions also the type of anticipated hydrocarbon
accumulations. It opens an opportunity to recommend a number of mea-
sures facilitating improvement in the efficiency of exploration and develop-
ment. In particular, when establishing the epigenetic nature of AHPP in
seals, it is recommended to restrain from drilling wells directly in the crestal
zones (AHPP there are at their maximum and for this reason drilling condi-
tions are difficult). It is recommended to drill wells in more subsided areas
of local structures where AHPP manifestations are relatively moderate and
drilling conditions are more favorable. Besides, this recommendation takes
into account the probability of negative results in the crestal wells due to
possible show of crestal waters, reservoir pinch-out zones, etc.
In evaluating AHFP role in the formation of oil and gas accumulations
in chemical deposits the following should be used as guidance:
t
The possibility of oil and gas generation in predominantly
chemical sequences and the adjacent intervals.
t
Numerous occasions when hydrocarbon accumulations are
associated with the areas of salt deposits.
t
The presence of substantial super-high pressure gradi-
ents often exceeding abnormal pressure values in clastic
sequences; they are directed into reservoir intervals adjacent
with the halogen sequences.
The presence of a salt-bearing sequence with AHFP plays an impor-
tant role in the hydrocarbon migration and formation of the oil and gas
accumulations even in cases when oil and gas generation is associated with
different stratigraphic
intervals. The salt
sequences in such a case play the
role of injectors, facilitating the longevity and efficiency of the migration
processes. It maintains pressure gradients needed for the migration, the
gradients directed into the hydrocarbon accumulation zones.
If AHFP in the salt-bearing sequence has epigenetic nature, the most
probable cause is the presence of hydrocarbon accumulations in the under-
lying section. That is why in such cases, the same as in clastic deposits,
epigenetic AHFP is an important exploration attribute indicating the pos-
sibility of hydrocarbon accumulations in the undrilled section.
There may be certain possibility for the forecast of oil and gas occur-
rences based on nature, extent and intensity of AHPP and AHFP
