Pressure drop models for gas-liquid two-phase flow and its application in underbalanced drilling*

Hasan-Kabir's model and modified Ansari's model were used to analyze the pressure drop of two-phase flow in underbalanced drilling (UBD). The mathematical and physical models of UBD were established and solved numerically. The effects of injection rate of gas and liquid and, back pressure on bottom-hole pressure were analyzed. The bottom-hole pressure control procedures were concluded. The computer simulations were validated with data obtained from experiment performed in a full-scale well located at Louisiana State University. The prediction accuracy of two methods was analyzed. The results showed that the error with the Hasan-Kabir model is less than 10%, however the error with the modified Ansari model is less than 5%. Ansari's model is superior to Hasan-Kabir's model in predicting pressure. This supplies theoretical support for success in UBD.