The interaction between unconventional parent and child wells has gained a lot of attention over the past few years as infill drilling has increased. Despite numerous mitigation approaches, including pre-loading and recompletion of the parent well, de-spacing, and adjusting the completion size of the child well, the detrimental effect of parent-child interaction has proven inevitable. Understanding the physical mechanisms and controlling factors through data gathering and modeling is the key to quantifying the degree of possible interaction and to mitigate the degradation.
Given the complex nature of the interaction between parent and child wells, a coupled flow and geomechanical modeling approach has been widely applied to address stress evolution around the parent well and its impact on child well fracture geometries. This type of modeling commonly includes fracture and numerical modeling calibrations by utilizing fracture diagnostic results before and after child well completion, which is time- and capital-intensive.
In this study, the productivity of child wells was evaluated using the different approaches of Rate Transient Analysis (RTA) and numerical simulation. The RTA results showed that child wells exhibit similar or in some cases larger contacted stimulated areas than infill wells with no depletion. However, their productivity is significantly lower due to preferential fracture growth toward the depleted zones around the parent wells, where there is lower reservoir pressure and lower hydrocarbon saturation.
A simplified numerical modeling approach utilizing results of several microseismic datasets is presented to assess the effect of key factors on child well performance. The simulation results demonstrated that the most important factors in child well performance are parent cumulative production, lateral and vertical distance to the parent well, and completion size of the parent well.
Although the proposed methodology is a simplified approach representing a complex system, it can capture the actual physical phenomena occurring in parent-child interaction. More importantly, depletion degradation factors predicted through this model are consistent with observed cases in the basin.