Real-Time Seismic Waveforms Guide Key Exploration Drilling Decisions in East Asia | SLB
Case Study
Location
Offshore
Details

Challenge: Set casing within 20 m of top of key formation in offshore exploration well despite uncertainty about formation depth

Solution: Use seismicVISION seismic-while-drilling service for casing point selection

Results:

  • Geostopped wellbore within 10 m of key formation top at a TVD of approximately 3,000 m
  • Avoided time and expense of contingency strings
Products Used

Real-Time Seismic Waveforms Guide Key Exploration Drilling Decisions in East Asia

Accurately geostopping wellbore at critical casing point near top of overpressured formation enables successful completion

Select casing point

An operator drilling an offshore exploration well in East Asia expected to encounter a key formation at about 3,000 m TVD. Because the formation was suspected of being overpressured, the operator’s objective was to set casing within 20 m of its top. That objective would have been difficult to achieve using conventional 2D surface seismic, which had a depth uncertainty of ±100 m.

Acquire seismic data while drilling

The seismicVISION seismic-while-drilling service provided checkshots that enabled drilling to be geostopped within 10 m of the formation top. Checkshots were acquired at planned levels during the acoustically quiet periods while connections were made. A standard three-air-gun cluster deployed at surface was used as a source. As the wellbore neared the formation top, checkshots also were acquired at mid-stand levels.

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The checkshots were processed from windowed real-time waveforms transmitted uphole by mud pulse telemetry, and real-time depth updates were calculated while drilling. A real-time corridor stack processed from the waveforms showed seismic position, and geostopping decisions were guided by depth projections to the key formation, which were extrapolated from look-ahead (reflectivity) information.

Save time and expense

Use of the seismicVISION service enabled the operator to geostop the wellbore less than 10 m from the top of the overpressured formation. This accurate casing point selection allowed successful construction of the well to TD—without the time and expense of contingency strings.

Graph: Real-Time Seismic Waveforms Guide Key Exploration Drilling Decisions in East Asia - Accurately geostopping wellbore at critical casing point near top of overpressured formation enables successful completion
The seismicVISION real-time checkshots were also used with Schlumberger visualization software to update a predrill model, showing the actual depth of the key formation top (red horizon) to be shallower than the pre-drill predicted depth of the formation top (yellow horizon).
The seismicVISION service enabled the operator to accurately select the casing point and avoid penetrating the overpressured formation.
Products Used

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