Page 245 - Drilling Technology in Nontechnical Language

236 Drilling Technology in Nontechnical Language Second Edition

Some of the routinely available coring systems include the following:
▫ Sleeve coring. An outer steel barrel supports the core
system. Inside this is an inner sleeve, which may be made of
fiberglass, aluminium, or rubber. The inner sleeve supports

loose, fractured, or unconsolidated formations. Once at
the surface, the core may be kept in the inner sleeve for
transporting to the laboratory for analysis. Fiberglass or
aluminium sleeves are often sawn into convenient lengths
(still with the core inside), with end caps installed to seal the
ends, and then are boxed up for transport to the laboratory
for analysis.
▫ Sponge coring. An aluminium inner sleeve has a sponge
sleeve inside the aluminium tube. The core sits inside the
sponge sleeve. When the core is recovered to the surface, any
formation fluids that bleed out of the core are absorbed by the

sponge where they can be later analyzed.
▫ Orientated coring. A knife blade creates a scratch mark
along the core, showing orientation downhole. This can
be very important if permeability is highly directional or
if the bedding plane directions and inclinations need to be
accurately measured.
▫ Pressure coring. After cutting the core, the core barrel is
sealed down hole so that when the core reaches the surface,
it is still kept at the pressure of its downhole environment.
Of course, as the core barrel cools down during recovery, the
internal pressures will reduce somewhat, which cannot be
avoided. However, if the core contains dissolved gases or very
light hydrocarbons, these are kept in solution during recovery.
Pressure coring is very expensive. The system is sent to the
wellsite inside a standard 40 ft oceangoing container.

Successful coring requires a lot of planning and coordination. The

drilling fluid may have to have special physical or chemical attributes to
help to avoid contamination of the core and to preserve it as it is pulled
out of the well. Surface handling, preservation, and storage are extremely
important to ensure that the core is in good condition by the time it arrives
at the core analysis laboratory and to recognize and document important
information with the core on the rig.

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