Projects that will expand the Extended Reach Drilling (ERD) envelope are in the planning stages in various parts of the world. Drilling engineers are no longer wondering if 50,000 ft ERD wells can be drilled but how can this be safely and efficiently accomplished and what new technologies are required to make this a reality. It has been estimated that the last 10 percent of drilled interval can result in 50 percent of the total drilling cost. Consequently, pushing the ERD envelope can be very costly, and drill string technology is crucial to enabling these ground breaking ERD projects. This paper discusses the latest drill string technologies involving advanced materials, ultra-high torque connection designs and other design considerations that are essential to achieve the ERD targets planned for the future. It will also present emerging drill string technologies that are solutions expected to increase reach capability for the industry's continued advancement to drill longer wells.
Primary considerations include high torsional strength connections and high strength to weight ratio materials to overcome high frictional drag forces and for efficient hydraulic performance to optimize hole cleaning and penetration rates, promote good control of the well trajectory and minimize drill pipe sticking tendencies. The paper reviews the potential advantages and weaknesses of sophisticated material choices that might be useful in building high performance drill strings for ERD including: Aluminum, Titanium, carbon-fiber based Composite and Ultra-High Strength Steel (Z-140, V-150 and development of 165 ksi yield strength). Other issues of concern include casing/riser and drill pipe wear considerations and BOP shear rams that may have difficulty shearing today's high-strength, hightoughness drill pipe.
Industry publications have presented the idea of using nonsteel drill strings primarily for the reduction of torque and drag loads in ER wells. Other torque and drag reduction and management tools and techniques have proved successful, are lower cost and more practical, thus being the preferred method for meeting current ER torque and drag challenges. The competition of these alternative technologies has, appropriately, inhibited progress of developing commercially available non-steel drill pipe.1
The future industry direction toward longer departure ERD wells, however, has led to increased consideration recently for commercially available non-steel drill pipe. Any discussion of drill stem requirements for world-class ERD would be incomplete without consideration of advanced material technologies and their potential future use for enabling longer ERD objectives. Generally three advanced materials should be included in this discussion: carbon fiber based composites, Titanium and Aluminum.2 Each of these materials has been studied for use to manufacture drill pipe, and each has been employed in drill strings with varying degrees of uptake and success. Each material has both strengths and weaknesses relating to its use for drill pipe to drill ER wells and other critical applications such as ultra-deep drilling and deepwater. A discussion on the capabilities and potential for each of these material types follows.