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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Petrophysical Properties of Seals
By
Seals are defined as generally ductile rocks with a very
high capillary entry pressure which can dam up hydrocarbons.
Petrophysical and petrographic studies of conventional
and sidewall cores from known seal
-reservoir couplets
of hydrocarbon-producing reservoirs provide a basis to
quantify the
capacity
of a
rock
to trap a hydrocarbon
column. The most important property of a
seal
is its pore size distribution as measured in thin section, scanning
electron microscope and very high pressure (up to 50,000
psi) air-mercury capillary pressure curves determined
across bedding surfaces in vertical plugs.
Seal
quality or
capacity
is determined by pore-size
distribution and interconnection, and ductility. Using the
density difference of normal saline water and 35° API gravity
oil as a standard, an arbitrary scale of
seal
types
is defined:
SEAL
TYPES
35° API Oil Column Held
METERS | FEET | ||
---|---|---|---|
TYPE A |
>300 |
>1000 |
|
|
>150 <300 | >500 <1000 | |
|
>30 <150 | >100 <500 | |
|
>15 <30 | >50 <100 | |
|
<15 |
<50 |
|
|
WASTE ZONE ROCKS |
Comparators of known seal
types
composed of samples
of the
rock
type, SEM photographs and capillary
pressure curve are used to estimate
seal
type under a
binocular microscope at 50X magnification. A catalogue of
petrophysical properties and photomicrographs allows one
to make reliable estimates of
seal
capacity
of unknown
samples in cores and cuttings with a binocular microscope.
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