Geology Reference
In-Depth Information
section and over the area. They differ in their origin mechanism, preserva-
tion and relaxation conditions. Their relationship to lithology, diapirism,
mud volcanism and oil and gas occurrences also differs.
Despite numerous publications on the problem, its many facets (includ-
ing the connection of AHPP and AHFP with geo-fluidal dynamics and oil
and gas occurrences) remain even now the subjects of a discussion, which
unfortunately not always facilitates the objective interpretation of observed
facts.
The present situation makes it difficult to select optimum exploration
plays and to minimize technical (in drilling) and economical risks. This
study attempts to improve the understanding of complex issues regarding
the problem.
3.1
Abnormally High Pore and Formation Pressures:
Their Nature, Types, Identification and
Diagnostics
The issue of the abnormally-high pore pressure forecast, identification,
origins, typization and diagnostics in the impermeable or low-permeabil-
ity intervals and the formation pressure in reservoirs is critical for plan-
ning and conducting exploration operations, drilling, well testing and oil
and gas production. The operational experience in the world oil and gas
basins shows a clear correlation between the extent of pressure abnor-
mality and hydrocarbons position in the regions, their phase state and
resources (Durmishyan, Muradian and Rachinsky, 1972; Durmishyan,
Muradian and Rachinsky, 1973; Durmishyan, Muradian and Rachinsky,
1976; Durmishyan, Muradian and Sporadic; Powers, 1976; Fertl, 1976;
Perry, 1969). The values of the expected pore pressure and hydraulic frac-
ture pressure are the basis of the efficient well drilling with optimum pro-
gram of drilling mud, selection of technically substantiated casing design
and natural reservoir drilling and testing procedure.
The forecast and identification of abnormal pressure areas and intervals
is no longer a difficult problem. The reason is that it became possible to use
for this purpose field geophysical data (seismic, gravity, magnetic, elec-
tric and acoustic surveys), observations in the process of drilling (drilling
speed, drill rotation torque, hook load rating, cuttings and drilling mud
parameters and mud circulation speed) and the petrophysical survey data
(electric and sonic logging, well gravimetry, nuclear-magnetic resonance).
On the other hand, their origin, typization, identification and diagnostics
remain to a substantial extent the matter of discussions.
