An operator in Southeast Asia drilling an offshore vertical exploration well wanted to avoid accidental penetration of the carbonate reservoir near the 12¼-in hole section because it could lead to a kick and possible loss of the well. Successful completion of the well required setting the 9⅝-in casing within 20 m of the top of the carbonate formation—and there was a ±50-m uncertainty about its depth, despite the availability of a 3D prestack depth migration and offset well data.
SLB used seismicVISION™ seismic-while-drilling service to update depth prediction at every connection, accurately geostopped 12¼ in hole section, and set 9⅝ in casing as planned.
The seismicVISION service was selected to acquire real-time checkshots and images for updating the predicted depth of the formation top. Because the checkshots were acquired during connections for best acoustics, a minimal amount of rig time was required.
After the seismic level had been acquired at a connection, windowed real-time waveforms were transmitted uphole using mud pulse telemetry. The checkshots were then processed from the waveforms at the wellsite, and real-time depth updates were calculated while drilling continued. A real-time corridor stack processed from the real-time waveforms showed the seismic position. Extrapolating a depth projection to the formation top from the look-ahead (reflectivity) information enabled the drilling team to geostop the 12¼-in section before it penetrated the carbonate formation.
Using seismicVISION service to revise the depth prediction in real time at every connection, the drilling team resolved the ±50-m uncertainty about the depth of the carbonate reservoir and geostopped the 12¼-in section before it penetrated the formation top. The 9⅝-in casing was set within 20 m of the formation top, as was required for successful completion of the well.
