Page 341 - Geology and Geochemistry of Oil and Gas

302 APPENDIX C

Cementing Pumping of the cement slurry down the casing and
then back up the annular space between the casing
and the borehole.
Cement slurry A mixture of cement and water in a liquid form which
is pumped behind the casing. The slurry is allowed to
set until it hardens.
Centralizer Device fitted around the outside of casing as it is
lowered down in the borehole to keep cement in the
hole, to achieve a good cement job.
Chalk Carbonate rock of low-magnesian calcite composition
consisting dominantly of the remains of coccoliths
and coccospheres.
Chlorite A group of minerals that are related in structure and
composition to the micas. They are hydrated silicates
and have general formula (Mg,Fe) 5 Al(AlSi 3 )O 10 ;
green, soft, and platy.
Choke A device that restricts the flow in flowline or through
the orifice, and causes a pressure drop or reduced flow
rate. It provides precise control of wellhead flow rates
in surface production applications involving oil and
gas and in enhanced recovery.
Christmas tree Array of valves, pipes, and fittings placed at the top of
the well, on the surface.
Circulation system Portion of the rotary drilling system, which circulates
the drilling fluid (mud).
Circumgranular Cement which completely lines the pores in a rock.
Clarke The average abundance of a chemical element in the
Earth’s crust. It is named in honor of Frank W.
Clarke (1847–1931), a Chief Chemist of the US
Geological Survey from 1884 to 1925.
Clastic Term used in reference to particles (carbonate,
siliciclastic, or other mineralogies) that commonly are
transported by fluids.
Claystone A compacted, non-fissile, fine-grained, sedimentary
rock composed predominantly of clay-sized particles.
See: Mudstone.
Cluster analysis A statistical method of classifying observations into
homogenous subsets based on their mutual
similarities and hierarchical relationships.
Coated grain Carbonate particle consisting of nuclear fragment
surrounded by a cortex of chemically precipitated
carbonate (e.g., ooids, pisoliths) or cortex composed
of organic encrustation (e.g., oncolites, rhodolites).
Coccolith A button-like plate composed of calcium carbonate,
generally about 3 mm in diameter, a number of which