Understanding Refracturing

This case study focuses on a typical Eagle Ford well re-fractured three years after initial treatment. The refracturing treatment intended to “infill” between the initial frac stages. We studied the effect of depletion on fracture fluid flow, re-fracture geometry and microseismic response looking at:

  • Pore pressure changes
  • Stress changes
  • Stress shadowing
  • Diversion
The pore pressure is higher but the stress is lower in the undepleted zone. In the case of poor diversion (all old perforations are open), the old fractures initially take all the fluid (pressure is below breakdown pressure in refractured area). After two minutes  breakdown occurs and the new stage takes up to 90% of the fluid. The old fractures experiencing “negative net pressure” (the flow is limited by propped width). After four minutes, the fluid flow into the old fractures increases as they reopen (pressure in wellbore high than the minimum horizontal stress). After six minutes the net pressure breaks over because the old fractures are all opening (positive net pressure). And after forty minutes the  stress shadowing dominates the flow and the old fractures take most of the fluid.