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The Leading Edge; July 2002; v. 21; no. 7; p. 660-668; DOI: 10.1190/1.1497320
© 2002 Society of Exploration Geophysicists
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Dealing with shallow-water flow in the deepwater Gulf of Mexico

R. M. Ostermeier, J. H. Pelletier, C. D. Winker, J. W. Nicholson, F. H. Rambow and K. M. Cowan

Shell International E&P, Inc., Houston, Texas, U.S.

Corresponding author: rmo@shell.com

Editor's note: The material in this paper was presented at the 2000 Offshore Technology Conference. A more extensive version is included in the 2000 OTC Proceedings.

The first 20% of the full text of this article appears below.

Shallow-water flow (SWF) may occur while drilling shallow overpressured formations at deepwater sites. It is a high-profile problem in the Gulf of Mexico, although it does occur elsewhere and will likely be encountered in other deepwater regions (Figure 1).


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  		Figure 1. Known and potential SWF regions.

 
Drilling shallow overpressured sands may cause large and long-lasting uncontrolled flows, well damage and foundation failure, formation compaction, damaged casing, and reentry and control problems. Most spectacularly, eruptions from overpressured sands may result in seafloor craters, mounds, and cracks (Figure 2).


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  		Figure 2. Fissures and cracks resulting from SWF.

 
The problem is compounded by the difficulty in seismically imaging these sands because of the relatively low sand/shale contrast in acoustic impedance. The impact of this problem on well site selection and well design is significant and makes drilling in SWF areas particularly challenging.

This complexity of the problem and the major financial impact it can have on projects caused Shell to create a multidisciplinary team of specialists in geology, geophysics, petrophysics, drilling, and civil engineering to analyze the various issues. The team developed several methodologies to deal with various aspects of the problem. These include regional trends and databases, shallow seismic interpretation and sand prediction, well site and casing point selection, geotechnical well design and data interpretation, logging program design and interpretation, cementing design and fluids formulation, and methods for remediation and mitigation of lost circulation.

This team has taken advantage of Shell's extensive deepwater GOM drilling experience to develop a new understanding of the problem. Examples include delineation of trends in shallow-water flow occurrence and severity, trends and departures in PP/FG, and rock properties pertaining to seismic identification of sands. New knowledge has also been acquired through geotechnical wells. One example is the rapid onset/growth of overpressures below the mudline, facts not heretofore . . . [Full Text of this Article]






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