LOOKING AHEAD OF THE BIT WHILE DRILLING: FROM VISION TO REALITY
by Monica Vik Constable, Statoil
was presented on Wednesday the 7th of December, 2016.
Abstract
A vision in the oil industry for decades is
becoming a reality - we can now finally drill and
react pro-actively to formation resistivity
properties identified several meters ahead of the
drill-bit, instead of drilling reactively on resistivity
measurements at or behind the bit. Through a
technology collaboration with Schlumberger,
Statoil supported a targeted technology
development for measuring resistivity contrasts
ahead of the bit in real-time to reduce cost and risk
during drilling operations.
Two Electro-Magnetic Look Ahead (EMLA)
prototypes have been developed for 12.25” to 14”
borehole diameter. The EMLA tool is modular and
consists of a low frequency EM-transmitter
inserted in the rotary steerable drilling tool about
1.8 m behind the bit. The transmitter induces
currents at multiple frequencies around and ahead
of the bit and the resulting induced magnetic field
is recorded with 2 to 3 receivers spaced out in the
drillstring. The formation structure ahead of the hit
is interpreted by inversion of the bulk signals to
differentiate sensitivity around the tool from
effects ahead of the bit. The look ahead capability
of the EMLA tool is dependent on the transmitter
receiver spacings, frequencies, resistivity around
the tool, thickness of the target, and the resistivity
contrast ahead of the bit.
The EMLA tool provides a step change with
regards to the precision we now can detect
changes in rock properties ahead of bit, enabling
the well placement teams to “see” several meters
ahead of the bit and to react before drilling into
potential hazardous situations, even in near
vertical wells. One key use of the EMLA
technology on the Norwegian Continental Shelf is
to drill and set casing for the 12.25” section much
closer to top reservoir than we do today. This can
reduce the risk of collapse in the overburden,
especially for depleted reservoirs which require a
significantly lower mud weight for drilling the
reservoir than the optimal weight for stabilizing
the overburden. The technology can also be used
to pick the coring point more precisely and prior to
drilling into the zone of interest This will enable
coring of the transition between overburden and
reservoir which is often missed when using near
bit measurements and also prevent costly coring of
thin sand stringers mistaken as the main zone of
interest.
Statoil has recently tested the tool in a sub salt
play in the Gulf of Mexico with great success. One
of the main objectives was to detect bottom salt
before drilling through it. The highly resistive salt
formation offers a very favorable environment for
EM applications. The bottom salt was detected 30
m ahead of bit, which gave the drillers an early
warning of the salt exit and potential drilling
challenges.
In the near future, with the technology already
there, simultaneous look around and look ahead
(LALA) while drilling will be available.
Interpretation of measurements in 2D and 3D
environment is the main challenge to overcome to
make LALA happen. To do so, a tight
integration between inversions and geological
scenarios will be a necessity.
Monica Vik Constable, CV
Monica Vik Constable started working in the oil industry in 1997 as a wireline field engineer for Schlumberger. She joined Statoil in 2005 as a Petrophysicist, and was a Leading Advisor in Petrophysics in Statoil from 2009 – 2014. She is now a Specialist in Petrophysics in the Advanced Petrophysics group and coordinates the Logging Technology Group in Statoil. She has been overseeing the implementation of look ahead and look around resistivity measurements in Statoil.