Summary
The primary purpose of surfactants used in stimulating sandstone reservoirs
is to reduce surface tension and contact angle and provide leakoff control.
However, many of these chemicals adsorb rapidly within the first few inches of
the sandstone formations, reducing their effectiveness in deeper penetration.
This phenomenon causes surfactants to adsorb or plate-out, reducing their
effectiveness in post-fracturing fluid recovery.
This study describes experimental and field-case studies of various
surfactants used in the oilfield. Several different surfactants, including a
nonionic ethoxylated linear alcohol, a nonyl phenol ethoxylate, an amphoteric,
a cationic, and a microemulsion system were investigated to determine their
adsorption properties when injected into a laboratory sandpacked column. A
laboratory-simulated comparison study of commonly used surfactants and
microemulsion was used to identify their leakoff and water-recovery properties
from gas wells.
Field data collected from Bradford, Balltown, and Speechley sandstone
formations confirmed experimental sandpacked column and core-flow
investigations. Reservoirs treated with microemulsion fluids demonstrate
exceptional water recoveries when compared with conventional surfactant
treatments. Wellhead pressures, flowing pressures, and production data were
collected and evaluated using a production simulator to show effective fracture
lengths, damage surrounding the fractures, and drainage areas with various
fluid systems. These investigations and presented case studies can be used to
minimize formation damage.
Introduction
Surfactants or surface-active agents are predominantly used in hydraulic
fracturing fluids to reduce emulsion tendencies between reservoir oil and
treatment fluids. This problem is normally addressed by incorporating a
nonemulsifier within fracturing fluids. However, when gas wells are stimulated
with water-based fracturing fluids, fluid retention and a reduction in
interfacial tension between the rock and the injected fluid are the key driving
forces worthy of consideration for well cleanup. One of the continuing
challenges in Appalachian Basin gas wells is post-fracturing fluid recovery
caused by low-pressure reservoirs. This could be caused by the water-based
fluid, creating fluid retention, interfacial tension between the injected fluid
and the reservoir rock, or capillary end effect on and around the vicinity of
the face of the fractured rock (Penny and Pursley 2005). To reduce these
problems, commonly available surfactants are incorporated within the fracturing
fluid to reduce surface tension. However, surfactants alone do not provide
adequate water recovery properties for the reservoirs in the Appalachian Basin.
Low temperature, pressure, and permeability of these reservoirs may be some of
the major reasons that less than 50% of the treatment fluids can be recovered
from gas wells through conventional methods (Penny and Pursley 2005). As
illustrated in Fig. 1, it is possible that large quantities of injected
fracturing fluids could be trapped in the area near the fractured proppant
pack.
When this condition occurs, higher water saturation adversely impacts the
relative permeability, resulting in gas being trapped and thus significantly
impairing gas production into the fractured face and ultimately into the
wellbore. This condition along with capillary end effects eventually leads to
longer swabbing times, well cleanups, and poor well productivity.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
28 February 2006
- Meeting paper published:
15 May 2006
- Revised manuscript received:
8 September 2006
- Manuscript approved:
18 April 2007
- Version of record:
20 August 2007
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