Parent-Child Fracture Interference: Explanation and Mitigation of Child Well Underperformance

Abstract

Abstract In the last few years, several operators in unconventional plays have seen fracture interference between existing production wells (parent wells) and newly fractured infill wells (child wells). This interference usually has a negative impact on the production from both the parent and child wells. In this work, a mechanistic explanation of the parent-child interaction is provided using results from poro-elastic simulations. Child well underperformance is studied in detail and mitigation strategies are discussed. Results shown in this work quantify the impact of depletion and refracturing on child well fracturing. In this work, a 3D reservoir-scale poro-elastic geomechanics software (Multi-Frac) was used to model the depletion of the parent well region and calculate its impact on pressure, total stress and effective stress. Refracturing simulations of the parent well were conducted to showcase the importance of a good refracturing operation in reducing the probability of fracture hits from the child well to the parent well. The poro-elastic capabilities of Multi-Frac help in analyzing the stress changes in the reservoir induced by depletion and re-fracturing. These stress changes explain the observed fracture hits from child wells. The stress changes and the depletion patterns also explain the underperformance of the child well fractures. Implications of depletion on both total stress and effective stress are analyzed. Decrease in the total stress near the parent well creates a zone of attraction for the child well fracture, thus, causing the child well fracture to be created in a region of extensive depletion. Depletion induced increase in the effective stress was observed from the simulation. This increase in the effective stress makes fracture network creation harder and thus reduces the productivity of the child well fractures. Re-fracturing of the parent well showed an increase in the stress in the reservoir and can help avoid fracture hits from neighboring child wells. Thus, re-fracturing a parent well and subsequently fracturing a child well can be a possible strategy to mitigate the impact of fracture hits and thereby improve the EUR of the pad. The three main factors that induce interference between parent wells and child wells are reservoir depletion, reservoir total stress changes and reservoir effective stress changes. All of these factors have been studied and quantified in this work. Modifications to parent well fracturing treatment design, refracturing treatment design and child well fracturing treatment design are suggested to improve productivity.