A Rigorous Reservoir-Wellbore Cross-Flow Equation for Predicting Liquid Inflow Rate During Underbalanced Horizontal Drilling

摘要

Underbalanced drilling (UBD) has been widely used as a means of reducing formation damage during drilling. The benefit of reduced formation damage results from the fact that the borehole pressure is intentionally maintained to be lower than formation pore pressure during drilling the pay zone. UBD operations require additional surface equipment such as separators and reserve tanks to process and store the produced reservoir fluids. Selection of separators and reserve tanks for UBD involves using a method to predict reservoir fluid inflow rate and volume. Such a method is not available in the literature for UBD horizontal wells. This study filled the gap. A rigorous reservoir-wellbore cross-flow equation was derived in this study for predicting liquid inflow rate during UBD horizontal drilling. A work procedure was developed to calculate fluid inflow rate and influx volume profiles. Application of the procedure is illustrated in solving an example problem. This paper presents drilling engineers a mathematical tool that can be used for sizing separators and reserve tanks during horizontal UBD planning.