RIASSUNTO
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.