New Methods for Caving Volume Analysis in Real Time

ABSTRACT: Caving is an important wellbore instability indicator. It is therefore essential to monitor caving volume during drilling operations to reduce costly drilling risks. Two methods based on different data sources are developed to estimate caving volume in real time. The first method measures caving volume by performing image and caliper log analysis. It is assumed that the shape of any breakout in the cross section of all wellbore intervals can be approximated by the part of an ellipse. In this way, caving volume can be calculated with only four parameters. As image and caliper logs may not be always available, the second method is developed to predict caving volume by quantifying the size of wellbore shear failure region based on geomechanical analysis. To perform the geomechanical analysis, wellbore is discretized equally into small volumes. The discretization and symmetrical character of breakouts allow a calculation efficient equation to be derived to estimate caving volume in real time. Although these two methods are based on completely different data and principles, they yield comparable results. The geomechanics-based method calibrated with the log-based method represents an optimal way to monitor caving volume in real time and helps reduce drilling risk and cost.