Optimization of Managed Drawdown for a Well With Stress-Sensitive Conductivity Fractures: Workflow and Case Study

Abstract

The effect of bottomhole-pressure (BHP) drawdown schedule on the well performance is generally attributed to the stress sensitivity in propped finite-conductivity fractures. The purpose of this work is to develop a detailed workflow of optimizing BHP drawdown schedule to improve long-term performance by finding a tradeoff between delaying conductivity degradation and maintaining drawdown. First, according to experimental data of propped fracture, an alternative relationship between conductivity and pressure drawdown is developed to mimic the change of fracture conductivity with effective stress. Second, based on the dimension-transformation technique, the coupled fracture-reservoir model is semi-analytically solved and seamlessly generates the time-dependent equation (i.e., transient inflow performance relationship (IPR)) which provides the production rate response to any BHP variation. Next, the value of BHP on the reversal behavior of rate is defined as the optimum BHP on the specified time-dependent IPR, and then the optimum profile of BHP drawdown over time is achieved. Finally, we corroborate the effectiveness of this workflow with a field case from Zhaotong shale in China. Field case substantiates that (1) the well with restricted drawdown has more advantage of improving the performance than that with unrestricted drawdown and (2) after inputting the optimum BHP drawdown into the history-unrestricted case, the long-term cumulative gas production could indeed be increased.