Improving Borehole Quality and Drilling Efficiency with a New Suite of Drilling Tools

Abstract

Abstract In an ideal world, a borehole would be a perfect cylinder with a smooth, frictionless interior and would retain the original diameter of the drill bit. However, in the real world, a perfectly cylindrical borehole can never be achieved. A number of factors contribute toward this less-than-perfect borehole, such as formation instability and interactions between the drilling and formation fluids. Another major contributor is the actual mechanics of the drilling process and the resulting effect most types of drilling have on the borehole geometry. This less-than-perfect borehole manifests itself in a number of ways, all adversely affecting the efficiency of the drilling process and all increasing costs. These problems include reduced drift, increased torque and drag, poor hole cleaning, slower drilling rates, and increased downhole tool failures. The phenomenon of borehole spiralling is being increasingly recognised to be a result of the inefficiencies of conventional drilling assemblies. Short-pitch micro-tortuosity and the mechanisms that cause it are responsible for many of the problems described above. It has been found that borehole spiralling can largely be eliminated with a new suite of drilling tools. This suite of tools has adopted a new drilling assembly design utilising a long gauge bit and the ‘point-the-bit’ concept of directional control. The application of this suite of tools can have a significant effect on drilling operations, especially in the field of horizontal and extended-reach drilling where the improvement in hole quality can impact well design and economics.