Calibrating Fracture Gradients—An Example Demonstrating Possibilities and Limitations

The fracture gradient is the upper boundary for the annular mud pressure while drilling and is one important parameter for<br>wellbore integrity. Its calibration using reliable data such as Leak-off-Tests (LOT) and events such as mud losses is essential<br>and can save the operators large amounts of money. Mud losses are often encountered when the annular pressure exceeds the<br>fracture gradient. Such an event can thus be useful to re-calibrate the fracture gradient in real-time in order to circumvent<br>additional losses while continuing drilling. However, analysis of causes for losses and the resulting delivery of proper<br>calibration data have rarely been reported in the past. In most cases, losses were analyzed after drilling, and the information<br>gained from this analysis has been used to plan future wells.