Summary
Rapid loss of fracture conductivity after hydraulic fracture stimulation has
often been attributed to the migration of formation fines into the proppant
pack or the generation of fines derived from proppant crushing. Generation of
crystalline and amorphous porosity-filling minerals can occur within the
proppant pack because of chemical compositional differences between the
proppant and the formation, and the compaction of the proppant bed because of
proppant pressure solution reactions. Findings presented in this paper suggest
that diagenesis-type reactions that can occur between proppant and freshly
fractured rock surfaces can lead to rapid loss of proppant-pack porosity and
loss of conductivity.
Introduction
Lehman et al. (2003) reported that the use of surface-modification agents
(SMA) to coat proppants used in propping hydraulic fractures resulted in
sustained and more uniform production from wells. Fig. 1, taken from that
publication, shows the production decline curves from some of their data, and
it does appear to show a significant change in decline rate compared to the use
of untreated proppant. This SMA was described as a nonhardening resin that is
insoluble in water and oil. It is supplied in a solvent that is quickly
extracted once it is introduced to aqueous-based frac fluids, leaving a tacky,
hydrophobic coating on the proppant.
Initial use of this type of SMA treatment (Dewprashad et al. 1999; Nguyen et
al. 1998a, b) was promoted as a method to increase the conductivity of proppant
owing to its capability to prevent close packing of the proppant, which can
result in increased porosity and permeability of the pack, by rendering the
proppant surface tacky. Subsequent studies indicated that its use provided
proppant-pack protection from fines infiltration and migration. This mechanism
has been employed to explain the observations that sustained production results
from the use of SMA on proppants. This is further substantiated by long-term
results obtained in a single field study known for fines production problems.
That both mechanisms are active has been well established through laboratory
studies, but they alone do not completely explain the reduction in production
decline rate as reported.
A field study of SMA-treated proppant was reported to the Arkansas Oil and
Gas Commission 2004 CBM Workshop that disclosed long-term results on gas
production. These were CBM wells in the San Juan basin that typically required
refracturing each year to produce at an economical rate. With the SMA-treated
proppant, no refracs have been required, and as shown in Fig. 2, production has
remained essentially constant for 5 to 6 years. This longevity was initially
attributed to prevention of fines invasion into the proppant pack; however, it
is possible that there are additional mechanisms operational.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 October 2005
- Meeting paper published:
15 February 2006
- Revised manuscript received:
16 January 2007
- Manuscript approved:
7 July 2007
- Version of record:
20 September 2007
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