Summary
The selection of proppant to provide highly conductive pathways in
hydraulically generated fractures is typically based on the proppant crush
strength, permeability, availability, and cost. Extensive libraries of
laboratory-determined conductivity values, obtained using API standardized
methods at a variety of simulated well conditions, are available for most
proppants. However, post-fracture-stimulation well testing indicates that these
values are often one to two orders of magnitude too high. In many fields, the
productivity of fractures declines rapidly, requiring frequent restimulation
treatments to remain economically viable.
Proppant crushing and embedment, fracturing-fluid damage, and fines invasion
are proppant-pack permeability-damage mechanisms that have been used to explain
this loss of productivity. This paper reports on recent studies that have
determined that alumina-based proppant materials may promote geochemical
reactions that can occur at a surprisingly rapid rate, even at moderate
temperatures, resulting in the loss of porosity and permeability and the
creation of fines in the proppant pack.
The compatibilities of several man-made proppants, ranging from lightweight
ceramics to high-strength bauxites, with a variety of formations are presented.
These findings indicate that the formation mineralogy plays a heretofore
unrecognized role in determining proppant suitability. Most proppants were
found to lose 50–60% permeability before stabilizing, while others were shown
to lose up to 90% in only a few days.
This paper describes the specialized methods that were developed to study
these geochemical reactions and reports quantitative changes in permeability,
proppant composition, and fluid changes. Surface analysis using scanning
electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis provides
dramatic visual confirmation of this damage mechanism.
Results of this study have a great potential economic significance,
suggesting new, important fracture design parameters that need to be determined
to enable choosing the appropriate proppant for maximized stimulation
longevity.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
1 August 2008
- Meeting paper published:
11 October 2008
- Revised manuscript received:
7 April 2009
- Manuscript approved:
8 April 2009
- Published online:
5 November 2009
- Version of record:
12 March 2010
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