Published: 06/17/2011
Published: 06/17/2011
Total E&P needed to conduct a VSP survey for a well in Block 17, offshore Angola, to obtain velocity information as well as image below the well path. This information would be used to refine the velocity model for future wells.
However, the cased well was a challenging acquisition environment, at 85° deviation in 650 m [2,100 ft] of water. Another critical consideration was the high rig cost, at more than USD 1 million per day.
The VSI imager survey was conducted from 2,440 to 1,250 m [8,005 to 4,101 ft] with four shuttles at 10-m [33-ft] spacing. A G. GUN cluster of three 150-in3 airguns was used, controlled with the TRISOR acoustic source control. Navigation was accurately recorded with the SWINGS seismic navigation and positioning system.
It took only 17 h to acquire the VSI imager survey in 10 3/4-in casing. Drillpipe logging had been estimated to take in excess of 60 h. Thanks to MaxTRAC tractor conveyance, the cost savings realized on the rig rate was USD 650,000.
Subsequent processing by Schlumberger petrotechnical experts found very good correlation of the VSP 2D image with the surface seismic survey, with a maximum correlation of 88% between the corridor stack extracted from the 2D image and the surface seismic survey.
"Sorry for the short notice, but this job is critical."
Elemele Ogu, Total Operation Geophysicist
Challenge: Conduct a vertical seismic profile (VSP) survey in a highly deviated cased well offshore Angola to obtain velocity information and image below the well path
Solution: Convey the VSI vertical seismic imager using the versatile MaxTRAC downhole wireline tractor system, which is engineered for deviated and high-angle wells
Results: Obtained excellent-quality borehole seismic data in only 17 h, instead of the 60 h estimated for drillpipe conveyance
