Ultradeep Drilling Pushes Drillstring Technology Innovations

Abstract

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.

The Effect of Combined Tensile‐Torsional Loading Path on the Stress/Strain States of Thin‐Walled Circular Tubes

“…With the development of oil drilling technology, land and deep-sea oil and gas resources have successively entered the exploration and development stage, which also puts forward higher requirements for the strength of drill pipes [33,34]. At present, the highest strength of the API series drill pipe is the S135 grade drill pipe, but as the drilling depth increases, it can no longer meet the drilling requirements of some ultra-deep wells.…”

Subsea blowout preventer (BOP): Design, reliability, testing, deployment, and operation and maintenance challenges

“…However, as drilling advances into UD waters, drill pipe properties such as material strength, toughness and ductility are continuously improved to reduce drill pipe failure and increase life span, which result in increased shearing force requirements. Studies attribute failure-to-shear to material composition [119] and other increasing exogenous parameters include drilling fluid density and shut-in pressure. Inability to cut through drill collars, drill bits, tool joints, connectors and other drill pipe attachments are not uncommon.…”

Enhancement of the rheological properties of bentonite mud using natural polymers

“…Temperature and pressure increase dramatically with the depth of the well. Oil and gas fields with temperatures and pressures above 230°C (440°F) and 160 MPa (23 000psi), respectively, have been reported [3,4]. Although there is not a universal definition, the term high pressure-high temperature (HPHT) is used by operators to indicate downhole temperatures in excess of 150°C (approximately 300°F) and pressures above 103 MPa (15000 psi) are referred to as ultra-or extreme-HPHT (xHHT or X-HPHT) wells [5].…”