A general method for the selection of an optimum choke management strategy
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Different choke management strategies have been adopted by operators in the field. However, no general method exists for systematically selecting an optimum choke management strategy. In this study, we propose a general method for the selection of bean-up duration and bean-up strategy (choke management), that will maximize well productivity by minimizing formation damage, reducing sand production and reducing the impact of multiphase flow effects. Strategies of stepwise bottom-hole pressure (BHP) adjustments are compared using the principle of superposition and the analytical solution of the diffusivity equation for vertical wells operating under different choke settings. The optimum choke management strategy is based on the anticipated formation damage mechanisms. For example, if fines migration and sand production are a concern, then minimizing the near wellbore pressure gradients is the primary criterion for the selection of the optimum choke management strategy. Results indicate that the selection of the optimum strategy (sequence of choke settings) is independent of the drawdown and depends primarily on the duration of the ramp-up period. Among the 251 strategies evaluated, three of them consistently appear to be the optimum. We further refine strategies using a single parameter, incorporated in a dimensionless expression of BHP as a function of time. From simulation results, we conclude that for relatively short bean-up durations (i.e., infinite acting behavior), the pressure gradient reduction at the wellbore varies logarithmically with time. Choke management strategies appear to have similar performance as far as no more than 70% of the drawdown is applied during the initial 20% of the overall bean-up duration. For longer durations (i.e., when the presence of the no-flow boundary is felt), the optimum strategy depends on both reservoir properties and radial extent. For the case of square drainage area, a plot suggesting the optimum strategy with respect to dimensionless duration is presented. Positive skin and multiphase flow near the wellbore, negatively affect the performance of bean-up strategies. For vertical wells producing from multiple layers, bean-up strategies should be selected with respect to the effective horizontal permeability, ultimately yielding the greatest pressure gradient reduction in the low permeability zones. The proposed method enables engineers to select the optimum choke management strategy with respect to bean-up duration and formation properties. The duration of the bean-up process is drawdown dependent thus further research is encouraged in determining the maximum allowable pressure gradient in order to curtail sand production.