Computer simulation technology has been widely applied in many drilling engineering areas to simulate drilling engineering problems, optimization, and to train engineers with real drilling operations and/or to handle rare applications and accidents.
One of the increasingly applied drilling operations is Under-Balanced Drilling (UBD). UBD is the drilling process in which the wellbore pressure is intentionally designed to be lower than the pressure of the formation being drilled. This results in higher rate of penetration (ROP), prevents fluid losses and related causes of formation damage.
This paper presents the design and development of a UBD simulator which is computer software that simulates and integrates the effects of:
Bottomhole pressure (BHP)
Minimum volumetric gas and liquid requirement
Required back pressure (BP) for required cutting removal to surface and controlling BHP
Kinematic energy per unit volume used in the hole cleaning considerations
Stand pipe pressure (SPP)
Rock drillability
ROP
Drilling costs per meter
The goal of the simulator is to enable the user to presimulate different scenarios of the UBD drilling operations, so that the ideal optimized combination of drill bit durability and drilling efficiency integrating all UDB operational parameter affecting the overall cost can be obtained before the fact. The UBD simulator is designed to simulate most of the basic technologies of UBD (air, aerated, and foam drilling). The goal of the UBD simulator is to design an effective UBD program by linking the BHP to rock drillability which takes into account the effect and degree of underbalance on the effective rock strength, ROP and $/m, which can be optimized for the operation. The complete UBD optimization integration is shown herein with illustrations including flowcharts.
This simulator is developed to simulate and optimize different underbalanced drilling modes including:
Using only the compressed air or other gas as the circulating fluid (air or gas drilling operations),
Using compressed air or other gas mixed with an incompressible fluid (aerated drilling operations)
Using the compressed air or other gas with an incompressible fluid and surfactant to create continuous stable foam as the circulating fluid during drilling operations
The simulator can be used in well planning to see the effect of change in operating parameters on performance and cost. The major simulation objective is to be able to experiment with different scenarios without incurring the costs of drilling an actual well. As part of obtaining the lowest UBD cost before the fact the simulator also be used to:
Generate drillability logs which can be used for the drilling ROP optimization analysis.
Simulate multiple drilling parameters to obtain optimal ROP and $/m including fluid injection rates and bit operating parameters.
Simulate different drill bit designs for optimal performance selection and for optimum bit pull depths.
The main part of this simulator is the BHP calculation routines. This part calculates BHP based on the two phase flow modeled procedures.
