Bullhead refracturing and mechanical diversion via liners are two common methods of horizontal refracturing. Bullhead refracturing attempts to treat the entire lateral in a single stage, while installing a liner allows for multi-stage completions in the existing lateral. Bullhead treatments are highly effective on short laterals but struggle to effectively treat longer laterals. Liners can treat longer laterals to improve incremental EUR but come with significant cost and mechanical risk. To optimize the overall value of refracs, a "hybrid" system combines the bullhead and liner approaches.
In the hybrid approach, expandable patches were installed across the two heel-most perforation clusters in the refrac well. The first refracturing stage was a bullhead-style treatment pumped past the patches in the heel. The first stage was followed by eight plug & perf stages within the patched region across the heel-side portion of the lateral. Unique gas chemical tracers were pumped in each stage to quantify individual stage production, compare bullhead to plug & perf production performance, and evaluate the hybrid approach versus traditional bullhead completions.
Plug & perf stages resulted in higher gas production rates than the bullhead stage. This difference was amplified when normalizing by stage length, showing the production benefit of the plug & perf section enabled by the Hybrid Expandable Liner System. The cost and economic performance of the hybrid system compete well with other available liner systems. Contributing factors include the shortened liner length and near-full ID available, which mitigate the common limitations on frac pump rate and artificial lift design present with some liner systems while keeping installation costs low.
The Barnett Shale of the Fort Worth Basin started the "shale revolution" from the early days of George Mitchell’s Mitchell Energy drilling and subsequent foam fracturing of the C.W. Slay #1 well in 1981. Slickwater fracture treatment designs were trialed in 1997. The tipping point of the shale revolution came after the publicity of the successful slickwater refracturing of the C.W. Slay #1 in 1998. Numerous attempts were made and studied over the next decade to determine what factors drive restimulation success (Vincent 2010). Mitchell Energy’s Barnett assets were purchased by Devon in 2002. Early hydraulic fracturing treatments, both vertical and horizontal, left substantial room for improvement which translates into significant opportunities for refracturing treatments.
