Page 340 - Geology and Geochemistry of Oil and Gas

GLOSSARY 301
sedimentary rock composed of more that 50% (by wt)
of carbonate minerals.
Carbonates Group of minerals found mostly in limestones and
dolomites. Calcite (CaCO 3 ) is the most abundant and
most important. Aragonite has the same formula as
calcite but it is less stable; and dolomite contains
magnesium, CaMg(CO 3 ) 2 . Often used as syn. for
carbonate rocks.
Carbon dioxide injection Compressed CO 2 is injected into the formation to
supply energy to push the oil toward the producing
wells and also to improve recovery by mixing with
both the oil and water.
Casing Pipe used to keep the wellbore walls from collapsing
and to seal the borehole to prevent fluids outside the
well from moving from one portion of the well to
another (i.e., crossflow).
Catagenesis Term applied to changes in existing sediments,
or most commonly, rocks during deep burial at
elevated temperatures and pressures short of
metamorphism. Adj: Catagenetic. Syn: Mesogenesis,
Epigenesis.
Catalysis Process in which the chemical reaction rate is affected
by the introduction of another substance (catalyst).
Cation-exchange capacity The total amount of exchangeable cations that a
(CEC) particular substance can adsorb at a given pH.
Exchangeable cations are held mainly on the surface
of clay minerals, and are measured in milligram-
equivalents per 100 g of the substance.
Caustic injection Adding caustic to the water being injected to improve
oil recovery by forming oil–water emulsions that help
plug-off the larger pore channels, giving a more even
push to oil in moving it toward the producing wells.
Also reduces interfacial tension and increases the
relative permeability to oil.
Caustobiolith A combustible organic rock, usually of plant origin.
Cellar Area dug out beneath the drilling platform to allow
room for installation of blowout preventer (BOP).
Cement Naturally occurring (biogenic or abiogenic)
precipitate of mineral material, usually calcite,
aragonite, or dolomite in sedimentary rocks, that
binds particles together into a lithified framework.
Cementation Process by which sedimentary rock particles or
fragments are cemented together after deposition.
Partial syn: Consolidation.