Pre-loading parent wells with surfactant-based treatment fluids for frac hit mitigation has been applied extensively in liquids-rich shale plays, where infill drilling and tighter well spacing are prerequisites for improved production and economic return. Pre-loads can provide a significant and temporary increase in fracture network pressure if done properly and are most effective with a surfactant and solvent package. However, it remains elusive why specific chemical packages help improve the parent well production, although the notion of capillary force resistance reduction for further treatment fluid leakoff into fractures and rock wettability alteration by surfactant has been proposed previously. Recent residual surfactant analysis in produced water from both parent and child wells indicates that there is indeed hydraulic communication after frac hits, and field trials in the Wolfcamp suggest that adding the same surfactant package in primary frac fluids in child wells can migrate to parent wells, thereby potentially activating various secondary oil recovery mechanisms.
Astrategy for properly selecting a surfactant solvent package is presented for parent wells. Most conventional surfactant tests do not provide much insight in the absence of formation rock. Instead, a rock-on-a-chip microfluidic device is used to illustrate the interactions between parent and child wells when frac hits occur. Spontaneous imbibitions of primary frac and secondary treatment fluids into formation rocks are performed along with computed tomography (CT) imaging to understand the surfactant efficacy for enhancing leakoff into secondary fractures.
Oil recovery and associated water saturation in the microfluidic-based device with or without surfactant are quantified and reveal that the oil recovery is enhanced with surfactant, and water saturation in the parent well could be reduced thereby mitigating water blocks from primary frac fluid invasion from child wells. Spontaneous imbibition results provide insight into a surfactant's effectiveness to leakoff into secondary fractures within a matter of several days, which coincides with a typical short time window for the offset frac to begin to achieve maximum pressure support.