In unconventional reservoirs, a "frac hit" is the infill-to-parent well communication during hydraulic fracturing. In most shale plays, production from the parent-infill well system drops below original forecasts due to production degradation after fracture hits from offset wells. This study reviews current methods to mitigate the production degradation and evaluates the effectiveness of these methods. Major challenges and opportunities are also presented.
The mitigation methods discussed in this lecture include (1) applying far-field diverter during fracturing in the infill wells, (2) reinjecting water into the parent wells and (3) refracturing parent wells. Key design considerations for each method are presented in detail. A total of 565 fracture "hit events" at 41 impacted parent wells are statistically analyzed. Long-term well performance of several hundred impacted wells are also evaluated.
Based on the comprehensive analysis, the abovementioned three mitigation methods are field-proven and effective in protecting parent wells and improving infill well stimulation efficiency. With low operational costs, pumping far-field diverters results in a P50 EUR increment by 6%, with a 20% failure rate in the parent well protection. Water reinjection in the parent wells shows successful parent well protection, but the impact on the long-term well performance is negligible. Re-stimulation of properly selected parent wells with near-wellbore diverters indicates a P50 EUR increment by 40%. Selection of parent well protection methods needs to be fit-for-purpose and is fundamentally dictated by well conditions, operational experience and economic models applicable to the area.
Take-away: "Frac hit" mitigation methods need to be fit-for-purpose and are fundamentally dictated by well conditions, operational experience and specific economic models.