RIASSUNTO
Abstract
Drilling ultra-deep (UD) wells places significant requirements on the drill string. Lengthy drill strings lead to high tensile loads which can lead to slip crushing of the drill string, hoisting capacity issues and drill pipe collapse capacity concerns at the blowout preventer (BOP). BOP shear rams may also have difficulty shearing today's high strength, high toughness drill pipe. BHA connection failures pose greater risk and cost at UD well depths.
This paper analyzes the many challenges associated with drill string designs specifically for UD drilling. It presents emerging drill string technologies that are solutions expected to increase depth capability for the industry's continued advancement of deep drilling operations.
Trend of Deep TVD Drilling
Deep drilling trends in the United States (U.S.) and throughout the world are increasing. Since 1995, the number of U.S. wells drilled greater than a total vertical depth (TVD) of 15,000 ft has more than doubled (Figure 1). The number of annual, active U.S. rigs drilling greater than 15,000 ft TVD has nearly tripled (Figure 2).[1] The number of high pressure, high temperature (HPHT) completions in the U.S. has nearly tripled since 2000.[2] U.S. gas production from ""deep?? formations is also expected to double from 7% in 1999 to 14% by 2010.[3]
During late 2005, the Knotty Head well in Green Canyon Block 512 was drilled to a total depth of 34,189 ft, the Gulf of Mexico's deepest well ever drilled. The 14-3/4 in. hole section was drilled to 24,085 ft and over 4 million ft or approximately 775 miles (approximately 1,250 kilometers) of drill pipe was tripped throughout the course of the well. The previous record well in the Gulf of Mexico was drilled earlier in the year to a total depth of 32,727 ft.[4]
Many rig contractors are presently upgrading or building new jack-up, semi-submersible and dynamically positioned drill ship rigs capable of drilling to 35,000 ft total depth (TD). One rig contractor, in particular, recently contracted the manufacture of a U.S. $650 million dynamically positioned drill ship capable of drilling in 12,000 ft of water to well depths of 40,000 ft.[5] Wells to these depths will require substantial investment and the advancement of facilitating technologies for ultra-deep drilling (UDD).
Extended Reach vs. Ultra-Deep TVD Drilling
Enabling technologies and innovative techniques have contributed significantly to the industry's current ability to reach significant well departure distances, which is evidenced throughout extended reach (ER) projects around the world. Some of these technologies include: [6], [7], [8], [9] and [10]
Use of sophisticated computer drilling simulators
Advancements in drilling fluid technologies providing increased lubricity and improved cuttings transport, wellbore stability and formation damage resistance characteristics
Drill string and casing friction reducing tools
Drill pipe high torque tool joints and high friction factor thread compounds
Intermediate drill pipe sizes such as 5-7/8 in.
Improved hole cleaning procedures
Casing floatation and liner rotation techniques
Highly variable gauge stabilizers (H-VGS) and rotary steerable systems (RSS)
Advancements in downhole measurement tool capabilities such as the introduction of pressure while drilling (PWD) tools and improved surveying and logging technology
Development and use of drill string dynamics monitoring and mitigation systems
New and improved rig and surface equipment
While these technologies have contributed successfully in pushing the ER envelope to increase recoverable reserves, significant obstacles remain when drilling UD and deep directional wells of lower reach/TVD ratios generally not characterized as ER.