Research to Increase Casing Milling Efficiency in the Oil and Gas Industry

Although the milling technique is already well advanced, it still sometimes happens that existing casings in deep boreholes have to be removed. If pulling out is not possible, it is necessary to mill the casing away. The challenge is to design a milling process, which achieves fast progress with continuous and complete chip removal. This can be difficult to be achieved in practice, because the detailed effects of the milling process have not yet been fully understood. So for example nests of chips can be formed, or because of a conical worn milling tool the casing dilates and rolls up. This leads to large sheet-like fragments. Such malfunctions can hinder a controlled milling process. On behalf of the DGMK the Institute for Drilling Engineering and Fluid Mining (IBF) of the TU Bergakademie Freiberg conducted basic research for milling casings. For this task an existing small scale drilling test stand (KKBVS) was modified and equipped with sophisticated measurement technology. A model mill, fitted with a conventional tungsten carbide insert, cuts the casing. During the tests the milling process was investigated and observed in detail. The investigation's objective was to optimize process parameters and tool geometry. The aim of this research was to find operational parameters and geometries of the cutters to provide a controlled milling process and effectively avoid building nests of chips, as well as expanding and rolling up of the casing.