Pressure Sink Mitigation: Effect of Preloading Parent Wells to Better Control Infill Hydraulic Fracture Propagation

Abstract

Effective stimulation of infill (child) wells can be challenging: pressure sinks resulting from production of existing (parent) wells can impair child wells’ completions leading to a loss of production potential. Special completion techniques are required to better stimulate the new rock volume and divert the fracture energy away from the depleted zones. This study investigates pre-loading and re-fracking of parent wells as potential Pressure Sink Mitigation (PSM) techniques to minimize fracture asymmetry in child wells. The impact of these techniques on possible production uplift for both parent and child wells are also investigated. A black-oil reservoir flow simulation model was created and history matched to production from three existing parent wells in a Montney field. Three new child wells have been drilled in close proximity (100m-200m) to the parent wells and were subjected to fracture generation and subsequent production. The fracture generation of the child wells was directly modelled in the reservoir simulator with hydraulic fracture conductivity as an exponential function of pressure. The conductivity-pressure relationship of the newly created hydraulic fractures were validated quantitatively to field history data and qualitatively to a third-party fracture creation software. To limit the influence of the depleted zone, water was injected into the parent wells before the child well fractures are created. Since the child well fracture behavior is directly related to the pressure, a theoretical "reservoir pressure vs injected pre-load volume" relationship was generated. From the relationship, a series of simulation sensitivities were performed where the child well fracture creation and successive production were subjected to different pressure (pre-load) scenarios. The production uplift of each scenario over the non-preload base case was calculated to determine the efficacy of the technique and optimum injection volumes. Additionally, the time for the parent wells to return to their pre-child well production levels was quantified. A practical and robust simulation workflow to evaluate a pressure sink mitigation technique was successfully developed using an actual field case in the Montney formation. As infill drilling and high well density become standard operational practice, understanding how to limit the influence of existing depleted wells is essential for optimizing recovery from hydraulically fractured formations.