traditional surface-set bit or impregnated
alone or combined.
Case study: L2 Drilling
The challenge
While performing surface coring
exploration for coal in the Galilee Basin, in
Queensland, Australia, L2 Drilling was in
need of a diamond core bit that would
reduce cost, as well as increase bit life and
penetration rates without losing core
recovery.
Ground conditions in the Galilee Basin
presented the greatest challenge for L2
Drilling. The unconsolidated ground
formations caused severe stress on the
equipment and caused the surface set bits
to wear quickly. L2 Drilling was using
HQ3 sized surface set bits with 10 to 15
stones per carat (SPC) and impregnated
core bits (rock group: 6 – 8) on both high
and low torque rigs.
Boreholes would have to be reamed
multiple times, because the
unconsolidated ground would crumble
in. When the bit needed to be switched
out, the borehole would have to be
reamed to the bottom before starting to
drill again.
L2 estimated that this caused the hole
to be reamed four times greater than the
metres actually drilled. This process
reduced the productivity of all the bits, but
was particularly hard on the surface set
bits as they were exposed to excess wear
through the increased reaming
requirements.
The varying ground formations
consisted of fractured and broken
sedimentary formations, swelling clay and
shale, porous sandstone that crumbles,
conglomerates, gravel and bands of quartz
up to 3 m thick. These difficult ground
conditions can cause hydraulic locking,
differential sticking and/or loss of
circulation in the equipment while drilling.
This leads to more stress on the bit.
The solution
L2 Drilling was able to overcome the
difficult ground conditions in the
Galilee Basin with the SSUMX diamond
core bit. The SSUMX bit works through
various ground conditions, reducing the
amount of times the drill string has to be
tripped out to change bits. With the
previous bits used, L2 Drilling had to
frequently change bits to cope with
varying hardness in the ground.
Very little outside diameter (OD) wear
was discovered on the SSUMX when
compared to the amount of reaming that
was done. The SSUMX also held up well
when ground conditions demanded less
than optimumwater flows.
SSUMX bits with 12 mm crown
heights were used to achieve an 80%
gain in bit life, while increasing bit
penetration rate per minute by 187%.
Other advantages were seen through a
44% reduction in per bit cost and a
consistent core recovery rate of 97.5%.
These benefits resulted in a significant
reduction in operating costs for
L2 Drilling.
“With the SSUMX, we experienced a
faster penetration rate and a longer bit life
with no tradeoff on the recovery rate,”
said Trevor Edwards, Manager of L2
Drilling. “We now require fewer bits to
cover more ground conditions, reducing
our cost of inventory.”
“The SSUMX is so versatile, we
changed our drilling methods instead of
switching out the bit through various
ground conditions,” added Edwards.
“Some of our drillers, that were loyal to
surface set bits, have converted to the
SSUMX.”
