Drilling with Rotary Steerable System Reduces Wellbore Tortuosity

Abstract

Abstract Wellbore tortuosity can be defined as any unwanted deviation from the planned well trajectory. As wells become more complex, oil companies increasingly perceive wellbore tortuosity as a concern in the process of drilling, completing and producing wells. Tortuosity is a potential source of additional torque/drag and can lead to problems while running casing, liners and completions. In specific applications, excessive tortuosity in horizontal wells can even impair productivity. Due to the conceptual difference in steering principle between conventional directional drilling systems, utilizing steerable bent housing motor technology, and rotary steerable systems, it has been claimed that rotary steerable systems produce a less tortuous wellbore. This effect has so far not been quantified, mainly due to the absence of a sufficient body of comparative data. In this paper, results of a tortuosity analysis of a number of North Sea wells drilled with rotary steerable systems, and offset wells drilled with steerable motors systems is presented. Various mathematical definitions of wellbore tortuosity and their implications are also discussed. The analysis shows that drilling with rotary steerable systems significantly reduces tortuosity. In tangent sections drilled with the rotary steerable system, superior inclination hold performance was observed and in areas of the wellbore where deviation changes were planned, more continuous curve sections were drilled. In order to illustrate potential benefits this may have with respect to drilling conditions, results from the evaluation were used to carry out torque/drag simulations. Levels of tortuosity produced by steerable motor systems and rotary steerable systems were calculated from the well data studied. These values were superimposed on a generic well profile. It was found that the torque reducing effect of the lower tortuosity delivered by the rotary steerable system is quantifiable and in some cases significant.