The selection of candidate wells for refracturing is often very difficult based on the information available at the surface. We propose a systematic methodology to allow a field engineer to evaluate a well's potential for refracturing from an analysis of field production data and other reservoir data that is commonly available. We successfully confronted our method to a case study in the Wattenberg field using data from 300 Codell tight gas wells.

The performance of refracturing treatments has been observed to be highly variable in the Wattenberg field (Colorado) with some wells underperforming while others are restored to initial or even higher production rates. Historically, multiple approaches have been taken to select the best candidate wells, including heuristic guidelines, field correlations, and neural networks.

After identifying the physical phenomena that are thought to impact the performance of refracturing operations, we developed five dimensionless groups to quantify them. By choosing a dimensionless approach, we establish refracturing criteria that may be applied to any oil or gas field. One potential motivation for refracturing is the stress reorientation occurring around a fractured well causing the refracture to propagate orthogonally to the initial fracture in under-depleted sections of the reservoir. Numerical simulations of the areal extent of the stress reversal region as well as tiltmeter measurements confirmed the existence of refracture reorientation in the Codell formation. Guidelines for the selection of refracturing candidates were expressed in terms of the potential for stress reorientation, the quality of the initial completion, the initial production decline and the reservoir depletion around the well of interest. Two groups of wells showed the most promise for refracturing: (a) ineffective initial completions with a small initial production decline and (b) long initial fractures in under-depleted reservoirs. The dimensionless groups help us identify such wells and provide quantitative criteria for selection of wells that may be good candidates for refracturing.