LOOKING AHEAD OF THE BIT WHILE DRILLING: FROM VISION TO REALITY
by Monica Vik Constable, Statoil
was presented on Wednesday the 7 th of December, 2016.
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.