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Case Study: 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

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.

Result:

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

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.

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.


Download: Real-Time Seismic Waveforms Guide Key Exploration Drilling Decisions in East Asia (1.05 MB PDF)

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