Published: 08/19/2021
Great Oil Perfurações Brasil Ltda. wanted to obtain time vs. depth and velocity information for a vertical openhole land well in the Reconcavo Basin with a maximum deviation of 4°. At the time of logging, this exploration well was the deepest in the basin. However, executing the seismic program with a conventional borehole seismic imager tool would require two descents (intermediate and final depth) owing to constraints posed by the well’s construction. The two seismic logging runs would have a significant adverse effect on overall rig time.
Instead of deploying a conventional borehole seismic tool, Schlumberger proposed using the Optiq Seismic solution to avoid the 15 hours that would be required for the dedicated logging runs. The solution’s optical interrogator unit at surface would be connected to Optiq TuffLINE torque-balanced fiber-optic wireline conveyance to collect seismic data along the entire length of the cable used to convey other wireline tools.
No time is required for rigging up and down and conducting a separate seismic tool deployment; the seismic survey is acquired when the cable is stationary during the normal operation sequence of the other logging services, such as pressure measurement and fluid sampling stations, coring points, calibration of nuclear magnetic resonance (NMR) tools, and plug setting. Whether the objective of the survey is first-time arrivals for basic velocity calculation and sonic corrections (checkshot) or full waveforms to extract a reflectivity series for well-tie analysis (VSP), the acquisition time is essentially the same: minimal.
Dual portable airgun tanks (PATs) were used for this operation to facilitate the deployment of airguns for a land operation. Excellent Optiq Seismic solution data can be efficiently acquired with the full range of Schlumberger seismic sources, including airguns and vibroseis units.
The Great Oil logging program consisted of two runs: one for basic petrophysical logging with a quad-combo comprising resistivity, density, porosity, and sonic and a second run for NMR and pressure measurement. VSP survey was acquired with Optiq Seismic solution during both descents, earning the moniker penta-combo for the combination of a quad-combo and seismic measurement.
Data from the first logging run was of excellent quality up to 2,600 m, at which point there were fewer shots in the stack because stationary time was minimized for this run. Adding a third PAT to the cluster would have resolved this effect but was not an available option at the time. adding an additional PAT to the cluster.
The second logging run of an NMR tool and the MDT modular formation dynamics tester provided the ideal configuration to use the Optiq Seismic solution for acquiring borehole seismic data simultaneously with the 10-minute stationary calibration periods for the NMR tool or at MDT tester stations for pressure measurement.
Challenge: Efficiently obtain a vertical seismic profile (VSP) in a deep vertical and well in the Reconcavo Basin.
Solution: Deploy Optiq Seismic fiber-optic borehole seismic solution—leveraging distributed acoustic sensing (DAS) technology and Optiq TuffLINE torque-balanced fiber-optic wireline conveyance—to simultaneously record data during stationary logging operations.
Results: Acquired complete zero-offset VSP without any additional rig time with the data quality confirmed by a good match to the synthetic seismogram and well-tie analysis.
