Schlumberger

Industry Article: Using Seismic-While-Drilling Technology to Reduce Uncertainty

Offshore - Jan 2011
Publication: Offshore
Publication Date: 01/01/2011

The Well-1 was drilled through the flanks of, and then beneath, a salt dome in a deepwater area of the southeast region of the GoM. Analysis of a 3D seismic dataset indicated shallow drilling hazards in the area, which constrained the options for the well location at the surface. Other drilling challenges included the possible presence of a salt tongue at about 1,800 m (5,905 ft) related to the main salt body, and stresses related to salt tectonics. A geomechanical study was performed to determine how stresses could affect wellbore stability in the section close to the salt flank. A rapid increase in pore pressure was suspected to exist in sediments beneath a fault plane at 2,200 m (7,217), so it was considered important to set the 16-in. casing just below the fault. PEMEX decided to use the seismicVISION seismic-while-drilling service to deliver real-time check-shot and interval velocity measurements, plus data for look-ahead vertical seismic profile (VSP) processing.

Seismic-while-drilling technology provides borehole seismic data while the well is being drilled—without disrupting operation—even in challenging subsalt regimes. A PEMEX well drilled through the flanks of and beneath a salt dome in the southeast Gulf of Mexico benefited from this technology. The service reduced drilling uncertainty in an area of complex geology related to the presence of salt bodies. Real-time VSP imaging confirmed that the well trajectory would pass through a clastic sediment sequence rather than a salt tongue. The results also were used to recalibrate subsurface models, reducing uncertainty about pore pressure.




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