Abstract
This case study reviews Noble Energy's completion design, execution, and results of an Eagle Ford infill well B3 and the refracturing (refrac) treatments pumped on the direct offsets referred to in this paper as wells A1 and A2. The refrac stimulations were planned to serve the joint purpose of frac hit protection of the existing parent wells' reserves and re-pressurization of depleted zones to improve the performance of the infill child well. Both chemical diversion and mechanical diversion pods were utilized on the bullhead style refrac to optimize lateral placement of fracturing fluid and proppant.
The A1 refrac was pumped first with a larger job size of proppant, water, and diversion material. The A2 refrac, pumped second, was half the size of the A1. Instantaneous shut-in pressure (ISIP) and diversion pressure response data was captured at each stage for both wells. Infill well B3 was completed last with normal plug-and-perf operations and the optimum job size of the time. The child well B3 production will be compared to offset wells with no depletion risk as well as to a 2014 vintage infill (Y3) well that was completed with no refrac on the direct offsets (X1 and X2).
The A1 refrac data showed a gradual trend of increasing ISIP and treating pressure throughout the job indicating a more uniform stimulation of the lateral. There is a sustained production uplift resulting in a 36% improvement in estimated ultimate recovery (EUR). The A2 refrac data showed anomalous ISIP and pressure spikes mid-way through the job indicating the stimulation was not accessing the entire lateral. This blockage downhole was caused by being too aggressive with the concentration of pods pumped per stage. Since the A2 was not effectively re-pressurized, there was negligible change to EUR when the well was returned to production. In comparing the two refracs, we concluded that a larger job (increased proppant, fluid, and diversion) with less concentrated but more frequent diversion drops will increase lateral coverage and more effectively protect the parent well reserves.
The surface treating pressures of the infill B3 indicate new rock was stimulated and initial production results trend with offset well production of the area showing no impact from depletion. Contrasting this with the prior infill Y3 completed with no refracs on parent wells, the Y3 has lower initial production (IP) rates and EUR when compared to its offset wells showing an obvious impact from depletion. Additionally, the refrac'd parent well A1 saw an improvement in EUR while the non-refrac'd parent X1 saw EUR degradation. In conclusion, pumping optimized refracs on the offset parent wells will both protect parent well reserves and improve the performance of the child well.
