Oa. Esipko et al., Physical properties of the rocks of the Tyumenskaya superdeep borehole from geophysical evidence, GEOL GEOFIZ, 41(6), 2000, pp. 905-919
Geophysical data obtained from the Tyumenskaya superdeep borehole, which ha
ve first exposed the most complete section of the Jurassic and Triassic dep
osits in the West-Siberian petroliferous province, are interpreted.
Investigation of the regularities of depth changes in physical properties o
f rocks reveals a tendency for changes in factors important for porosity an
d permeability. To a depth of 3-4 km, the key role is played by factors dir
ectly related to the depth and lithostatic consolidation. Most important ar
e factors either favoring preservation of capacity-filtration properties (o
verpressure, HC presence, and favorable sedimentation conditions) or improv
ing them (factors and processes giving rise to induced - cavernose or cleft
- porosity). Depth exerts virtually no effect on the capacity-filtration p
roperties of rocks; therefore, reservoir rocks can be present at depths exc
eeding 5 km. The obtained data allow prediction of physical properties of r
ocks and the most probable reservoir types In deep deposits not drilled yet
.
A model is proposed for the formation of a volcanosedimentary rock mass und
er irregular distribution of geostatic tension in the ranges of occurrence
of elastic and plastic rocks. This distribution gives rise to zones of tens
ion relief, favoring the preservation of high capacity-filtration propertie
s in rocks. The model permits substantiation of test ranges and explains th
e observed depth variation in physical properties and filtration-capacity p
roperties of rocks.