Application of mechanistic models in predicting flow behavior in deviated wells under UBD conditions

Underbalanced drilling (UBD) has increased in recent years because of the many advantages associated with it. These include increase in the rate of penetration and reduction of lost circulation and formation damage. Drilling of deviated and horizontal wells also increased since recovery can be improved from a horizontal or a deviated well. The drilling of deviated wells using UBD method will reduce several drilling related problems such as hole cleaning and formation damage. Prediction of flow and pressure profiles while drilling underbalanced in such wells will help in designing and planning of the well. The main aim of this research is to study and model the effect of well deviation on pressure and flow profile in the drillstring and the annulus under UBD conditions through the use of mechanistic two phase flow models. Specifically, a current model is modified to include effects of wellbore deviation. Simulation results are compared with data from a deviated well drilled with UBD technology

Mechanistic modeling of an underbalanced drilling operation utilizing supercritical carbon dioxide

Mechanistic modeling of an underbalanced drilling operation using carbon dioxide has been developed in this research. The use of carbon dioxide in an underbalanced drilling operation eliminates some of the operational difficulties that arises with gaseous drilling fluids, such as generating enough torque to run a downhole motor. The unique properties of CO2, both inside the drill pipe and in the annulus are shown in terms of optimizing the drilling operation by achieving a low bottomhole pressure window. Typically CO2 becomes supercritical inside the drill pipe at this high density; it will generate enough torque to run a downhole motor. As the fluid exits the drill bit it will vaporize and become a gas, hence achieving the required low density that may be required for underbalanced drilling. The latest CO2 equation of state to calculate the required thermodynamic fluid properties is used. In addition, a heat transfer model taking into account varying properties of both pressure and temperature has been developed. A marching algorithm procedure is developed to calculate the circulating fluid pressure and temperature, taking into account the varying parameters. Both single phase CO2 and a mixture of CO2 and water have been studied to show the effect of produced water on corrosion rates. The model also is capable of handling different drill pipe and annular geometries