1. Effect of pH and Ionic Strength (Salinity) on Geochemical Water-Rock Interactions During
Hydraulic Fracturing in the Frontier Formation of the Powder River Basin, Wyoming
Bratcher, Jordan1, Herz-Thyhsen, Ryan1, Kaszuba, John1,2
1) Department of Geology and Geophysics, University of Wyoming 2) School of Energy Resources, University of Wyoming
Experimental Design
Experimental Design
Completion
Report
Fluid
Additives
USGS Data
Formation
Water
Geochemical
Model
Experimental
Frac Fluid
Chemical Field Purpose Mass Fraction
Frontier Fm. Water Solvent 86.9%
Bauxite Proppant 11%
HCl Dissolves Rock 0.12%
Tetramethylammonium Chloride Clay stabilizer 0.088%
Methanol
Prevents corrosion and reduces
friction
0.07%
Sodium Erythorbate Prevents metal precipitation 0.0009%
Results
Conclusions
Future Work
Acknowledgements and References
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Conc.(mol/kg)
Time (hrs)
Neutral pH Experiment
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Time (hrs)
Low pH Experiment
SiSi
Ca
Ca
Li Li
Sr
Sr
Ab
Qtz
50 m
Cc
Qtz
50 m
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0.135
0.14
0.145
0.15
0.155
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pH
pH of Neutral
Experiment
pH of low pH
Experiment
Ionic Strength of
Neutral pH
Experiment
Ionic Strength of
Low pH
Experiment
I(molal)
Time (hrs)
Experimental pH and Ionic Strength vs. Predictive Model Model
87% Water
2% Additives
11%
Proppant
Figure 2: Percent composition of frac fluid by
volume. Water is by far the most important
component.
Background
Hornbuckle 1-11H
Herz-Thyhsen, 2014 (unpublished)
Figure 4: Hornbuckle 1-11H well located in the
southwest corner of the Powder River Basin.
Figure 3: Experimental Apparatus. Pressure vessel consists of a stainless steel
bomb housing a flexible gold bag capable of sampling during experimentation
while maintaining constant temperature and pressure.
Figure 1: Hydraulic fracturing overview. Large
volumes of fresh water are needed to fracture a
well which needs to be collected for treatment
and disposal after production.
http://imgbuddy.com/hydraulic-fracturing.asp
ii
i
Quartz
64%
Calcite
20%
Illite
10%
Albite 5% Pyrite 1%
i
iii
iii
• USGS data from the
surrounding research area
were compared to
geochemical models to
design the Frontier Fm.
water chemistry (Figure 7)
• Geochemical model allows
Frontier Fm. mineralogy
(Figure 6) to equilibrate with
water. Water chemistry
generated by model
approximates average USGS
Frontier Fm. chemistry well
(Figure 7)
Figure 6: Simplified Frontier Fm. composition.
Five minerals were chosen to represent the
Frontier Fm. for use in geochemical models
(Herz-Thyhsen, 2014 (unpublished)).
Well Data
Average
Model
ii
Figure 7: Development of Frontier Fm. water chemistry. Blue triangles represent USGS Frontier
Fm. water chemistry taken from surrounding wells. Red circle is the statistical average of blue
triangles. Green star represents formation water predicted by geochemical model.
Figure 5: Development of experimental frac fluid.
Data from several different sources were used to
develop the frac fluid composition used in
experiments.
Figure 8: Experimental frac fluid chemistry. Fluid additives were selected from the Hornbuckle
1-11H (Figure 4) completion report based on functionality, lab safety, and accessibility (Herz-
Thyhsen, 2014 (unpublished)).
• 4 experiments over a range of pH
and ionic strengths take place for a
month at a time each (Figure 9)
• Geochemical models are used to
predict and analyze experimental
results
• Rock samples are taken from the
Frontier Fm. interval of Hornbuckle
1-11H core (Figure 4), reacted with
frac fluid, and both liquids and solids
are analyzed
• Data from 84 wells
surrounding the Hornbuckle
1-11H were averaged and
compared to geochemical
model results (Figure 7)
• Experimental ionic
strength range
designed to represent
naturally existing ionic
strength range in
Frontier Fm. water and
extended to include
more saline flowback/
produced waters
• Make use of produced
and flowback waters
• Free up freshwater for
other uses
• Mitigate transport,
treatment, and
disposal costs
• Predict and track
downhole changes
quickly
Research Impacts
• Calcite and albite both show strong dissolution features among
experiments however calcite is much more sensitive to low pH
• Geochemical model predicts pH, ionic strength, and most major
aqueous species within reasonable accuracy
• This information forms a basis for predicting and tracing downhole
chemical changes based on frac fluid chemistry
• Understanding downhole chemistry is the first step to replacing
freshwater with produced/flowback water in hydraulic fracturing
• Compare results of
experiments 1, 2, and 3 to
better understand the
effect of ionic strength on
geochemical water-rock
interactions
Funding/ Support: UW Cretaceous Tight Oil Consortium II, School of Energy Resources
Laboratory/Technical Aid: Norbert Swoboda-Colberg, Susan Swapp, Janet Dewey, Virginia Marcon, Alexa Socianu,
Quin Miller, Jonathan Pullam, Bianca Majumder, Amber Zandanel
References
• Heier “Trace Elements in Feldspars-A Review” Norsk. Geol. Tidsskr., v. 42, 415-454
• Paquette and Reeder “Relationship Between Surface Structure, Growth Mechanism, and Trace Element
Incorporation in Calcite” Geochimica et Cosmochimica Acta, v. 59, 735-749
Experimental Design
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Conc.(mol/kg)
Time (hrs)
Neutral pH Experiment
SO4
Cl
Na
K
Mg
Ca
Si
Li
Sr
Al
Model
Initial pH = 7.3
T = 115 C
P = 350 bar
I = ~0.15 molal
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Conc.(mol/kg)
Time (hrs)
SO4
Cl
Na
K
Mg
Si
Li
Sr
Al
ModelLow pH Experiment
Initial pH = 7.3
T = 115 C
P = 350 bar
I = ~0.15 molal
Figure 9: Initial conditions of each experiment.
Subsequent figures focus on the effect of pH on
geochemical reactions (expt. 2 and 4).
• Geochemical model
adequately predicts pH
• Ionic strength predictions
within 10% difference
• Geochemical model
accurately predicts
concentrations of most
aqueous species for
experiments 2 and 4
Figure 9: SEM images of dissolving albite (left) and calcite (right) in reacted chips. While both
minerals show dissolution features, calcite shows a stronger dissolution response to low pH.
Fluid Characterization
Figure 10: Comparison of pH and ionic strength for experiments 2 and 4 to predictive model.
Model predicts pH of both low and neutral experiments well while ionic strength is still within
10% difference.
Figure 11: Comparison of aqueous species of experiment 4 to predictive model. Na, Cl, SO4,
and Si are predicted well by model while K and Ca are predicted to be lower concentrations.
Figure 12: Comparison of aqueous species from experiment 2 to predictive model. Ca and K
are still predicted at lower concentrations. Noticeable differences between experiment 2 and
4 are the elevated concentrations of Ca, Sr, and Mg.
Figure 13: Comparison of major and minor elements associated with calcite and albite
between experiments 2 and 4. Ca and Sr show the strongest response to low pH conditions
indicating an increase in dissolution of calcite. Li and Si show little response meaning albite
dissolution is relatively unaffected by changing pH on experimental time scales.
• Fresh water usage in
hydraulic fracturing is critical
(Figure 1 and 2)
• 2 - 8 million gallons
freshwater required per well
(USGS)
• Freshwater typically hauled
to drilling sites
• Wastewater is collected
during production to be
treated and disposed of
(Figure 1)
• The potential to replace
freshwater with produced
and flowback water exists
• The ability to use
geochemical analysis and
models to predict and
track downhole changes
in siliciclastic reservoirs
such as the Frontier
Formation is appealing
Results
Robert Kirkwood – background image
Seyfried et al., 1987
Gold Bag
Sample Port
Pressure Vessel