Stimulation
ViCon NF ™ Fracturing Fluid Breaker
Improved Fracture Fluid Cleanup Capability Provides Virtually 100% Retained
Permeability with Mid-to-High-Temperature Fracturing Gel Systems
B
•
90
80
40 lb guar, 1 lb/ft2
manmade proppant,
4,000 psi, 180˚ F
70
60
50
40
30
20
0
AP Breaker
No Breaker
ViCon NF
Figure 1 - Tests conducted through the Stim-Lab Completion Consortia verify the performance
of ViCon NF breaker. Note that there is no discernible difference between the baseline
permeability and the retained permeability achieved with ViCon NF breaker.
Can be run at high concentrations
without harming short-term fluid
rheology and proppant transport.
Unique chemistry and high temperature of activation
enable the use of ViCon NF breaker at higher concentrations than typical oxidizer type breakers for highly
effective cleanup (Figure 2).
High Temperature Breaker Performance
Thermagel at 275˚ F
1400
ViCon NF
0 gal/Mgal
5 gal/Mgal
8 gal/Mgal
10 gal/Mgal
Reservoir minerals have little effect on its capacity to
decompose polymer gels (unlike all other conventional
breakers).
•
The water soluble breaker stays with the fluid during
leakoff and flowback.
•
•
Removes gel filter cake for higher retained permeability.
•
•
Remains reactive days after persulfates and enzymes
are spent.
Apparent Viscosity (cp at 40/s)
1200
•
Baseline
This data is for StimLab consortium members only and cannot be used externally until August 25, 2005
HAL17771
10
1000
800
600
400
200
0
0
Secondary catalyst can be used to lower the activation
temperatures to provide the same advantages at lower
temperature ranges.
Can be run throughout the entire treatment.
180
360
540
720
900
1080
Time (minutes)
Figure 2 - Viscosity can be easily controlled by adjusting the
concentration of ViCon NF breaker to provide the desired break profile.
Specifications
Because ViCon NF breaker is a water-based solution
containing no insoluble material, it maintains its activity in
the fluid during leak off. It is useful with all fracturing fluids
with a pH range from 6 to 12. It may be added throughout
the treatment—from pad to flush. The breaker is highly
effective in both low and high permeability formations. In
high permeability formations, it can help increase production
where a soluble breaker is needed.
HALLIBURTON
HAL17772
ViCon NF breaker offers major
advantages over conventional breakers
for fracturing treatments in 150 to
350° F conditions:
100
Percent Retained Perm
etter fracturing fluid cleanup can
translate into improved production.
Recent third party testing has shown
that ViCon NF™ breaker provides
unsurpassed cleanup and retained
permeability (Figure 1). It is effective
in breaking both fracturing fluid and
filter cake.
Dry
Sg=85%
K/Ko No Breaker
K/Ko No Vicon w/Cat
K/Ko No AP Breaker
0.1
0.01
100
1,000
10,000
MSCF/D at 1000 psi BHFP
HAL17773
Regained Perm Fraction
1
Figure 3 - The above plot describes the observed cleanup behavior of a typical 35 lb/Mgal crosslinked fracturing
fluid at 180˚ F with a typical loading of AP breaker and the recommended loading for ViCon NF breaker.
ViCon NF Breaker Improves Fracture
Cleanup From 45% To Nearly 100%
In laboratory testing, no other commercially used breaker
has shown cleanup reliability comparable to ViCon NF
breaker. In Figure 3, the blue and magenta lines are the
expected clean-permeability lines for a dry pack and one at
15% Sw (this is the typical residual water saturation after
flowing gas through a water-saturated pack). The arrows
show the direction of change in flow rate for the lab test.
The green points show the cleanup profile of the fluid with
no breaker. As gas rate increases from 200 MSCF/D to 1
MMSCF/D the apparent perm actually drops slightly. Once
the rate exceeds 1 MMSCF/D the perm begins to increase.
The gas rate was increased to almost 3 MMSCF/D then
decreased. During the declining rate period the data parallels
the wet-pack curve. This means that permeability is being
controlled by non-Darcy flow, but that the base permeability
of the pack is constant. The gel-damaged pack cleans up to
about 25-30% of the flow capacity of the wet pack.
The blue data points show the same cleanup profile for a
typical persulfate breaker loading. Using any more than this
amount leads to fluid instabilities, poor proppant transport,
and early screenouts. With a “normal” amount of breaker the
gel cleanup doesn’t start until gas rate exceeds 1 MMSCF/D.
Ultimate cleanup is 40-50% of the pack permeability at
15% Sw. Adding more of this breaker is not an option
because of loss of fluid stability.
The ViCon NF breaker cleanup profile is shown by the red
points. Even at rates as low as 300-400 MSCF/D the pack
cleans up and permeability increases almost to the
15% Sw line. The permeability follows the clean-pack trend
for increasing rate and then retraces its path as rate is
decreased. Visual examination of the pack after the test
confirmed that all visible gel residue and even the wall filter
cake were removed.
So What Does This Mean In Terms Of
Production?
Understanding Breakers
To help with this, the following evaluation was conducted
using Predict-K* ver. 6.0. For simplicity, an average well will
be used to determine differences in production based on
well productivity for different permeabilities over a threeyear period. The average well parameters are as follows;
Water-based fracturing fluids are usually made
viscous by the addition of 20 to 70 lb of guar or
derivatized guar polymer per 1000 gallons of water.
Guar polymer is derived from the beans of a guar
plant. A mixture of guar dissolved in water forms a
base gel, and suitable crosslinking agents are added
to form a much more viscous fluid called a
crosslinked fluid. The viscosity of base gel is typically
20 to 50 cp and when crosslinked increases by 2 to
100 times depending on the temperature, test
method, and type of crosslinker used.
Drainage Area – 40 acres
Formation Height – 100 ft
Initial Pressure – 6,000 psi
Depth – 12,000 ft
Condensate Production – 5 bbl/mmscf
Producing Pressure – 300 psi
After the proppant is placed in the fracture and
pumping stops, the fracture closes on the proppant
bed. The pores of the proppant bed are still filled
with the fracturing fluid and must be cleaned out
to maximize conductivity of the proppant-filled
fracture. Breakers reduce the molecular weight of
guar polymer in the fracturing fluid by cutting the
long polymer chain. As the polymer chain is cut,
the fluid’s viscosity is reduced to near that of water.
This process can occur independent of crosslinking
bonds existing between polymer chains. The waterthin fluid can then be flowed from the fracture.
Unfortunately, another complicating factor exists.
Figure 4 shows the difference with and without ViCon NF
breaker in cumulative production for various formation
permeabilities. For a 0.1 md permeability formation the
difference for a propped fracture halflength of 600 feet is over
275,000 MSCF per 100 ft and 400,000 MSCF per 100 ft in 3
years for a 1,200 ft propped fracture.
400
350
300
Reservoir Permeability
0.1 md
0.05 md
0.01 md
0.001 md
250
The Filter Cake Challenge
200
As the hydraulic fracture is being formed and
propagated, fluid leaks from the fracture into the
formation matrix. As this process occurs, a filter
cake of concentrated guar polymer is formed while
the water, KCl, and breakers pass into the
formation. The filter can be a semi-elastic,
rubber-like membrane and can severely damage
the permeability of the proppant bed. In general,
higher breaker levels are required to remove filter
cake than to break fracturing fluids. Breakers must
be selected to effectively break the fracturing fluid
and remove filter cake.
150
100
50
0
200
400
600
800
1,000
1,200
Propped Fracture Half-Length, ft
Figure 4 - The ViCon NF breaker difference: In practical terms,
improved fracturing fluid cleanup and higher retained permeability
can translate into better production and profitability. Note that the
effect is even more pronounced in high permeability reservoirs.
* Predict-K is a trademark of Core Laboratories
HAL17774
3-Year Incremental Gas, MMSCF
450
Field Results
Gulf of Mexico - Halliburton’s Delta Frac® fluid system with
ViCon NF breaker achieved 0 skins, a significant improvement over the 5-7 skins typical of widely used borate gels
with the typical SP breaker used for Gulf of Mexico frac
packs. ViCon NF breaker was ramped so that the pad fluid
was broken 15 minutes prior to completion of the treatment
with break being defined as water thin! (SPE 39897)
Australia - A major integrated reservoir study for a production
company found through neural network analyses that the
use of ViCon NF breaker along with reduced polymer
concentration resulted in a 67% improvement in
12-month NPV.
ViCon NF Breaker Summary
•
•
Liquid Breaker – Goes with the fracturing fluid.
•
Reactivity – Remains reactive days after
persulfates and enzymes are spent.
•
Filter-Cake – Removes the gel filter cake resulting
in higher regained permeability.
Slowly Soluble – Can be run at high
concentrations.
South Texas - Operator was performing linear and
crosslinked CO2 fracturing treatments at BHTs between 140
to 165˚ F using a conventional breaker package. Production
was averaging 200,000 scf/d. Operator wanted more conductivity and longer effective fracture length. After switching to
ViCon NF breaker with Cat-OS 1™ catalyst, initial results
were very promising. Average production from two typical
wells increased to 300,000 scf/d.
For more information on the ViCon NF ™ Fracturing Fluid Breaker, please contact your
local Halliburton representative or email us at [email protected].
www.halliburton.com
Produced by Halliburton Communications
H05000 6/06
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