Page 244 - Drilling Technology in Nontechnical Language

Chapter 10 – EVALUATION 235

There are many different bottomhole coring systems available.
Choosing between them will depend on the formation being cored (whether
complete and well consolidated, unconsolidated, or fractured) and what
the hole inclination will be. It also depends on what the desired state is for
the recovered core (for instance, it can be kept under downhole pressure
if required).

Often on an exploration well, core equipment is kept ready on the rig
with an instruction to “core on shows” (stop drilling and go coring if oil is
spotted), as well as to core once the potential reservoir is reached.
Recovering a whole piece of formation allows some properties to

be measured that cannot be adequately measured by logs (fig. 10–4).

Permeability tests can be done using plugs of formation by flowing fluids
under pressure through the core plug. Magnetic resonance imaging (MRI)
can be used on the core to show the internal structure of the core. Many
other useful tests can be carried out on cores, which can justify the cost

and difficulty of coring.

Fig. 10–4. PDC core bit

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