Page 374 - Geology and Geochemistry of Oil and Gas

GLOSSARY 335
Sedimentary rock A layered rock originated from the compaction and/
or consolidation of sediments, including a clastic rock
such as sandstone or siltstone, a chemical rock such as
rock salt or gypsum.
Semisubmersible Marine drilling rig that can either be anchored to the
drilling rig bottom of sea or maintained at a given position.
Sensitivity analysis Statistical analysis of sensitivity (variability) of
different parameters of a process or system as the
response to some action or influence on the process or
system.
Separator Equipment for separating the crude oil from the
natural gas and water. The primary function of the
separator is to produce gas-free liquid and liquid-free
gas.
Sequence A succession of geologic events, processes, or rocks,
arranged in chronological order.
Set theory The branch of mathematics, which is concerned with
the study of sets, i.e., any collection of items
(elements) defined by specifying the elements. See also
Fuzzy set theory.
Shale-out trap A petroleum trap formed by the lateral variation or
facies change of a porous sandstone in which the clay
constituents increase and the hard mineral grains are
reduced until porosity and permeability disappear
and the bed grades to claystone or shale. Cf: Pinch-
out trap.
Shale shaker Mechanical device (vibrating screen) for separation of
drilling cuttings from the drilling fluid as it arrives at
the surface.
Shear Action or stress that results from applied forces
and that causes or tends to cause two adjoining
portions of a substance or body to slide relative to
each other in a direction parallel to their plane of
contact.
Shelf A gently sloping or near-horizontal, shallow, marine
platform. A stable cratonic area that was periodically
flooded by shallow marine waters and received a thin,
well-winnowed cover of sediments.
Shoal Area of shallow water.
Sidetracking Drilling a new section of wellbore parallel to a
previously drilled hole but blocked with junk.
Sidewall core Core generally one inch in diameter taken from the
side of the wellbore, often by wireline.
Silcrete A soil-replacive or sand and gravel-replacive deposit
composed of silica.