ABSTRACT
The object of drilling is formation rock. The rate of
penetration is not only related to drilling measure
(drilling parameters, etc.), but also to matching of bit
and rock, which is well known as bit selection opti-
mization. An essential bit selection optimization pa-
rameter is rock drillability. Laboratory test is popu-
larly used as an evaluation to determine drillability
nowadays, but lab test environment differs from the
downhole environment, therefore the test result
could seldom be applied to drilling field. Drillability
was evaluated by ROP (Rate of Penetration). It re-
veals the comprehensive influence of various factors
such as formation rock, drilling technology, etc. The
result could be applied to practical drilling, but the
ROP is restricted by many factors such as drilling
parameters, drilling tools properties, hydraulics,
drilling equipment, etc, therefore it has limitation to
represent drillability with ROP (Li & Yan 2002,
Zhang & Xue 1999, Xiu & Yang 2001).
