Ultra-Extended-Reach Drilling (u-ERD: Tunnel in the Earth)—A New Well-Path Design

Abstract

Abstract Drilling ultra-extended-reach wells and extending their reach to greater depths requires both improved models and comprehensive analysis. Wellbore friction is an important factor in drilling ultra-long wells and optimizing the well-path design is an effective means for reducing torque and drag. This paper describes a new well-path design that will allow extending the reach of a well to a greater depth. Usually, well trajectories are designed with constant curvature with well-defined arcs connecting the transition between the tangent sections. Even though the transition between the tangent and build sections or tangent and drop sections appears to be smooth there will be some discontinuity that will place a lot of stress on the tubulars, increase torque and drag, and result in poor hole cleaning and other problems. To avoid curvature and torsion discontinuities between sections, curvature-bridge curves, or transition curves called clothoid spirals can be used. This paper presents a new mathematical formulation for well-path designs using curvature bridges. Results show that the essential elements in planning a proposed well path are determining the shape and position of the bridged section, the characteristic parameter describing its shape, and its position in the well profile. To provide a quantitative means for measuring the complexity of well-path designs, a coupled analytical criterion based on the minimum energy of the curve is proposed. The proposed approach is a superior method and a more effective tool for describing and comparing the minimum energies used in well-path designs. This paper compares simulated well-path designs created with the new method with actual conventional well-path designs and describes the accuracy and applicability of the new well-path model. The results of this study demonstrate that well-path designs using curvature bridges are superior to the existing well-path designs used for drilling ERD and u-ERD wells.