Full-scale Experimental Study for Improved Understanding of Transient Phenomena in Underbalanced Drilling Operations

A dynamic computer simulator for underbalanced drilling can contribute significantly for designing an UBD operation and defining the most appropriate operational procedures. Timing for flow stabilization, pressure peaks in the returns and pressure variations at the bottom of the well are some of the aspects involved in determining the adequate injection flow rates, separation system and drilling procedures.A full-scale experimental investigation was planned and executed to provide data for the evaluation and improvement of transient underbalanced drilling computer simulators. The tests were performed in a 1278 m vertical well in a research facility in Brazil. The experiments involved the injection of liquid and gas through a 3 1/2