Summary
The selection of candidate wells for refracturing is often very difficult to
peform 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 commonly available. The well-selection method was successfully confronted
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, five dimensionless groups were
developed to quantify them. By choosing a dimensionless approach, the goal is
to establish refracturing criteria that will not limited to one specific field,
but may used in distinct oil and gas fields. 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
underdepleted 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 underdepleted reservoirs.
The dimensionless groups help us identify such wells and provide quantitative
criteria for selection of wells that may be good candidates for
refracturing.
© 2013. Society of Petroleum Engineers
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History
- Original manuscript received:
30 June 2011
- Meeting paper published:
30 October 2011
- Revised manuscript received:
6 January 2012
- Manuscript approved:
20 June 2012
- Published online:
7 February 2013
- Version of record:
27 February 2013
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