Evaluate the borehole condition to reduce drilling risk and avoid potential well bore damages by using image logs

Abstract

By drilling a well, i.e. removal of a cylinder of rock from the subsurface, a disturbance of the natural stress state is created. Where the horizontal stresses are strong and unequal, then the borehole will be subjected to an imbalanced horizontal stress condition. Drilling mud is weighted to create a hydrostatic pressure to balance the formation stress. However, in Iran there are high stresses then stressing anisotropy will remain. After drilling it is important that the borehole stays in good shape if it is to successfully perform its intended function, e.g. produce hydrocarbons. Borehole instability will severely compromise this function and reduce the working life of the well. An evaluation of the borehole condition and the mechanism of borehole failure by using image log tools would clearly help. The tool referred to is the Ultrasonic Borehole Imager (UBI). Currently it is a standard practice to use this tool for a comprehensive structural analysis and fracture characterization; however interpretation of borehole shape analysis needs a lot of improvement. In this study found solution regarding borehole stability by early warning of wellbore instability and improve information about the well condition by working on advanced borehole shape analysis. Image logs showed exactly where the losses are happening and allowed the remedial action to be precisely made.