Gyrostab Project : The Missing Link Azimuth and Inclination Mastered with New Principles for Standard Rotary BHAs.

Abstract Trajectory control in directional wells essentially requires control of only two parameters: well inclination and well azimuth. However, always tighter economic constraints and the increasing complexity of well trajectories keep setting higher challenges that demand purpose-designed and cost-efficient solutions. The standard rotary drilling tools first used for directional drilling gave poor trajectory control. The subsequent addition of Variable Gauge Stabilizers (VGS) addressed only one side of the problem: control of inclination. Both inclination and azimuth were then mastered with Steerable Motor technology, which rapidly gained supremacy. However, there has been discontent with Down Hole Motors (DHM) for a variety of problems ranging from Rate Of Penetration (ROP), sliding mode, friction and lost-in-hole incidents to well tortuosity and hole cleaning. Jumping to rapid conclusions, one might thus think that that motors will soon be replaced by Rotary Steerable Systems (RSS). This evolution of directional drilling techniques has led to the development of more and more sophisticated tools integrating electric and/or hydraulic power systems and loads of "embarked" electronics. The related expenditures have driven service costs to levels that are very often prohibitive for standard drilling programs and/or environments. This paper introduces an innovative technical solution that makes it possible to control both azimuth and inclination using standard rotary Bottom Hole Assemblies (BHAs). It is based on a patented concept permitting command of Bit & BHA walking tendencies through downhole friction management at the level of a "strategic" string stabilizer. On the basis of this concept, a joint industry project led by TotalFinaElf has successfully designed, built and field-tested a first prototype - the "Gyrostab". This missing link in the evolution of directional drilling announces the birth of a new generation of standard rotary drilling tools.