Abstract
This paper describes the use of a numerical simulator for study of productivity improvement by application and proper performance of UBD in wells, which are faced with near-wellbore damage. Minimizing formation damage in the near- wellbore region and thus ensuring proper well performance for enhanced productivity of the well also results in increased recovery factor. Formation damage caused by conventional overbalanced drilling (OBD) can be reduced or eliminated through UBD, which may ensure the original formation productivity is maintained. A single horizontal well numerical model has been built that simulates the UBD and OBD processes and their impacts on production of hydrocarbon under a variety of reservoir conditions. The paper describes study methodology, models, simulation results and analysis results. It also summarises the formation criteria for successful UBD operations. For the purpose of expressing rate versus time, the production rate as a series of steady state production with increasing radius of drainage is considered. This dimensionless analysis of productivity (PID) provides a simple way to describe the productivity trend with different reservoir and fluid properties and well geometry. Several hundred cases have been numerically simulated for different reservoirs and drilling operations. Dry gas, gas condensate reservoir, dead oil reservoir and black oil reservoir have been considered. Several sensitivity analyses such as impact of OBP pressure and OBP time and effect of horizontal well length have been simulated. The results clearly show that proper candidate selection is the key to success of UBD projects. This clearly demonstrates that UBD operation is good choice for some reservoirs but not for all. The results of this study provide a set of reservoir criteria that can be used as guidelines to evaluate potential UBD candidates.
