Model research of full hole two-phase flow inunderbalanced horizontal well drilling

In order to provide engineering design considerations for the UBD horizontal well technique, according to the evaluation on the application of the two-phase flow research method to the UBD drilling, using the mechanical research results of two-phase flow in annulus lines, a full hole two-phase flow model is established. The numerical method is used to find the solution to the model. The predicting results of the model are verified using the field measurement data and experimental data. The model can be used to simulate the whole process of the UBD horizontal well drilling and predict the bottomhole pressure variation rule. It is shown that the accuracy of the model is about 5% in predicting the casing pressure and the pressure in string, and it can meet the requirement of the engineering design of UBD drilling. The two-phase flow model provides theoretical basis for the prediction and control of the borehole pressure and guarantee the successful operation of UBD drilling.