Published: 01/27/2023
Published: 01/27/2023
A major North Sea operator was drilling an appraisal well with a jackup rig in 236 ft [72 m] of water to a 10,000-ft [3,050-m] TD, with a significant ~32° deviation trajectory over the last 7,000 ft [2,134 m]. As part of the appraisal, the operator needed to accurately measure interval velocities and the reflectivity response of the rocks drilled in and away from the well, to achieve a robust well-to-seismic tie.
Traditional vertical seismic profiles (VSPs) using geophones can take more than 12 hours to complete. In this case, the operator used a faster and more effective alternative: the Optiq TuffLINE conveyance system, a fiber-optic technology mounted on a torque balanced, high-performance cable that can collect VSP data in minutes instead of hours. Fiber-optic cables use distributed sensing technology to provide continuous, real-time measurements along the entire length of the wellbore. For VSPs, the shorter survey time translates directly into lower costs and reduced environmental impact.
To optimize VSP density and efficiency, the Optiq TuffLINE wireline conveyance was used to transport the Sonic Scanner acoustic scanning platform and PressureXpress* reservoir pressure-while-logging service, operating in tandem. The Optiq TuffLINE system delivered high-quality distributed acoustic sensing (DAS) data in both the openand cased-hole sections of the deviated well, accurately measuring interval velocities and the reflectivity response of rocks drilled, along with those away from the well.
The high-density DAS data, with VSP traces output every 16.7 ft [5.1 m], enabled optimal sampling of both P and S wavefields, with a bandwidth of 4 to 64 Hz at the target level around 9,000-ft [2,743-m] TVD. A triple G-SOURCE was deployed at 16-ft [5-m] depth from the rig crane and autotuned using the TRISOR* acoustic source control system to ensure perfect synchronization of all three guns within 0.5 ms. The DAS laser interrogator box parameters were optimized to improve the signal-to-noise ratio across the seismic bandwidth.
After deploying the toolstring to the well TD at 11,000-ft [3,352-m] MD, the cable was slacked off by three different amounts and five shots were stacked. A slack of 5 ft [1.5 m] enabled optimal coupling with the formation in the 30° deviated open hole and cased hole, and 30 shots were stacked in 10 min. Remote real-time monitoring confirmed the excellent data quality. As a result, the operator decided to cancel the contingent VSP that would have been run with conventional geophone array tools.
The Optiq TuffLINE conveyance system recorded dynamic strain DAS VSP data with gauge length of 98 ft [30 m], pulse frequency rate of 10 kHz, and a laser resolution of 21.7 ft [6.6 m]. The raw optical phase data was also recorded, and additional enhancements, such as gauge-length optimization, are possible in the optical domain.
This was the first time the new logging technology, with improved optical specifications and a safe working load (SWL) of 80,000 N [18,000 lbf], was deployed in this geographical area. The novel logging technology enabled borehole seismic acquisition with a reduced number of shots and without a dedicated run, which helped minimize the impact to marine biodiversity that is often associated with seismic surveys. The operation not only demonstrated the abilities of the Optiq TuffLINE conveyance system to record accurate DAS VSP data in near-real time but to minimize the environmental impact. The reduced GHG emissions were estimated at 33 metric tons.
Our customer and its partners are gratefully acknowledged for permission to reproduce the data.
Optiq TuffLINE™ torque-balanced fiber-optic wireline conveyance reduced the cost of a seismic acquisition by eliminating the need for a dedicated run. Logging a 10,000-ft vertical seismic profile in 30 min vs. 13 h using traditional methods, Optiq TuffLINE conveyance achieved a faster acquisition time, minimizing impact to marine biodiversity.
