Summary
In mature fields, a continuous challenge for operators is to maximize
hydrocarbon recovery while minimizing associated water production. Water
production causes several problems, including scaling, fines migration or
sand-face failure, tubular corrosion, and increased hydrostatic loadings. Thus,
although water production is almost an inevitable consequence of oil
production, it is usually desirable to defer its onset, or its rise, as long as
possible.
Proper stimulation is required to prove many reservoirs commercially,
including dirty sandstones and lower-permeability layered formations in
waterdrive reservoirs and/or with nearby water zones. The focus on water
avoidance has made conformance fracturing an interesting prospect in mature
fields because it combines synergistically a relative permeability modifier
(RPM) with a fracturing fluid to enhance production and reduce water cut in one
step. However, if a water zone is below the zone being fractured, fracture
invasion may create a conductive path for water production. For example,
proppant convection and settling can result in heavier treatment stages
displacing rapidly downward from the perforations to the bottom of the
fracture. This may occur when treatments call for large pad volumes, high
proppant concentra¬tions, or stage density contrasts.
An important technique used to avoid this problem is known locally as
inverted proppant convection. It requires proppant buoyancy in the selected
fracturing fluid, as is possible when using ultralightweight proppants (ULWPs)
with specific gravities (SG) from 1.054 to 1.75. The technique involves pumping
a high-density fluid pad with SG higher than the proppant carrier fluid, which
in turn has SG slightly higher than the selected ULWP.
This paper describes the design approach, operational procedures, and
evaluation of field case histories demonstrating the synergism of conformance
fracture and inverted proppant convection as applied in northeast Brazil, with
the potential to impact field-development strategies worldwide.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
24 July 2007
- Meeting paper published:
11 November 2007
- Manuscript approved:
14 March 2008
- Published online:
2 March 2009
- Version of record:
26 February 2009
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