Child/Parent Well Interactions; Study the Solutions to Prevent Frac-Hits

Abstract

Maximizing the hydrocarbon recovery for a given unconventional asset often clashes well spacing considerations against completion design. This can result in complex child/parent well interactions that can include frac-hits and reserve reallocation. In planning for a successful field development within the vicinity of producing assets, the risk of frac-hits must be evaluated carefully to minimize any damage and potential profit loss. Multiple factors such as depletion, well spacing, rock properties, and completion design all contribute to the risk of a frac-hit. Understanding the probable cause of a frac-hit allows for appropriate mitigation operations such as parent well pre-loading, re-fracturing, increased offset spacing, and revised completion design to be considered. To evaluate each remedial operation, several unconventional Permian oil wells were studied with Rate Transient Analysis (RTA) to identify well and reservoir characteristics. Based on these results multi-phase/multi-well numerical modeling was performed to evaluate how effective each operation would be to minimize the risk of future frac-hits. Simulation results regarding pressure and production performance of parent/child wells will be presented applying different frac-hit mitigation methods. Pressure build-ups around the wellbore were determined considering parent well shut-in; gas injection and water injection (pre-loading). Water injection resulted in the highest pressure build-ups in the vicinity of the wellbore (which reduces the risk of a frac-hit); however, it takes several months to unload the injected water. Production uplift due to a re-fracturing operation was evaluated with numerical modeling assuming different fracture designs that include the extension of current hydraulic fractures and adding new fractures. The performance of child and parent wells were then investigated by changing the well spacing and completion. Optimum combinations of well spacing and completion designs were determined to maximize child/parent well production and minimize the risk of frac-hits. Finally, the impact of parent well depletion on the productivity of the child well is determined. This work presents a replicable and accessible workflow to assess the impact of multiple frac-hit mitigation methods on reservoir performance.