Summary
Drilling ultradeep (UD) wells places significant requirements on the
drillstring. Lengthy drillstrings lead to high tensile loads, which can lead to
slip crushing of the drillstring; hoisting capacity issues; and drillpipe
collapse capacity concerns at the blowout preventer (BOP). BOP shear rams may
also have difficulty shearing today’s high-strength, high-toughness drillpipe.
Bottomhole assembly (BHA) connection failures pose greater risk and cost at UD
well depths.
This paper analyzes the many challenges associated with drillstring designs
specifically for UD drilling (UDD). It presents emerging drillstring
technologies that are solutions expected to increase depth capability for the
industry’s continued advancement of deep-drilling operations.
Trend of Deep Total Vertical Depth (TVD) Drilling
Deep-drilling trends in the United States and throughout the world are
increasing. Since 1995, the number of US wells drilled greater than a TVD of
15,000 ft has more than doubled (see Fig. 1). The number of annual, active U.S.
rigs drilling greater than 15,000 ft TVD has nearly tripled (see Fig. 2)
(Spears & Associates 2006). The number of high-pressure/ high-temperature
(HP/HT) completions in the U.S. has nearly tripled since 2000 (Mayerhofer et
al. 2005). US gas production from "deep" formations is also expected to
double from 7% in 1999 to 14% by 2010 (Schlumberger Data 2005).
During late 2005, the Knotty Head well in Green Canyon Block 512 was drilled
to a total depth (TD) of 34,189 ft, the Gulf of Mexico's (GOM) deepest well
ever drilled (Discoverer Spirit). The 14 3/4-in.-hole section was drilled to
24,085 ft, and more than 4 million ft or approximately 775 miles (1,250 km) of
drillpipe was tripped throughout the course of the well. The previous record
well in the GOM was drilled earlier in the year to a TD of 32,727 ft
(Discoverer Spirit 2005).
Many rig contractors are presently upgrading or building new jackup,
semisubmersible, and dynamically-positioned drillship rigs capable of drilling
to 35,000 ft (TD). One rig contractor recently contracted the manufacture of a
USD 650 million dynamically-positioned drillship capable of drilling in 12,000
ft of water to well depths of 40,000 ft (Transocean 2006). Wells to these
depths will require substantial investment and the advancement of facilitating
technologies for UDD.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
18 October 2006
- Meeting paper published:
1 November 2007
- Revised manuscript received:
15 January 2008
- Manuscript approved:
11 January 2008
- Version of record:
20 June 2008
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