JOSH WILSON AND JOE RIVAS,
SCIENTIFIC DRILLING INTERNATIONAL, INC.,
USA, EXPLAIN HOW TOOL DESIGN IS A KEY
COMPONENT IN DRILLING OPTIMISATION.
O
ptimisation is the art of compromise. In the drilling industry
this typically correlates tomodifying drilling parameters (WOB,
flowrate and rpm) in order tomaximise, or minimise, a specific
performance characteristic whilemaintaining others at amanageable
level. However, drilling optimisation is not simply an operational method
that can only be applied at the rig site; this engineering approach can also
be executed on a component level. Designing tools to better meet the
needs of the field applies optimisation from the ground‑up. By developing
more robust equipment the drilling envelope is expanded, allowing for
more efficient operationwith less remedial intervention.
Modern reservoir exploitation involves drilling directional wellbores,
often in a horizontal configuration, in order tomaximise the contact
between the oil‑bearing formation and the wellbore. A commonmethod
for steering the well is the use of a steerable downholemudmotor. This
component provides rotational power to the bit, independent of string
rotation, and deflects the well in the direction the bend of themotor is
oriented. As can be imagined, thesemudmotors are subjected to fairly
harsh downhole conditions, where temperatures can exceed 300˚F
and pressures can be on the order of 10 000 psi. Additionally themotor
is being compressed, with a large amount of force (Roughly 30 klbf for
a 6½ in. motor), in order to push the bit into the formation andmay
be rotated upwards of 100 rpm. These operations put large loads on
themotor and, if not properly accounted for in the design, can lead to
premature failure and lost time.
Recently, several incidents have led to a component optimisation
effort; this resulted in a newmotor design, which has shown significant
increases in capability, performance and reliability. The re‑design has
allowed for more torque output from themotors, higher weight‑on‑bit
(WOB) ratings, decreased non‑productive time (NPT) on the rig, and
increased the number of drilling hours possible with one bottomhole
assembly (BHA). Apart from the improvement of notable drilling
characteristics, the engineering adjustments have led to a steerablemud
motor design that can be rotated at faster speeds and in higher doglegs
than other motors on themarket. The success of thismotor design is
one example of howdrilling optimisation, from the ground‑up, has
been paramount in the pursuit of success. Ongoing optimisation efforts
continue to push the operational envelope of downhole tools and provide
clients with the best solution for the application.
Apushfor redesign
In typical directional operations, the drill string is comprised of
three distinguishable sections: the drill pipe, which connects the
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