C ABOT
SP E C I A LT Y
F L U I D S
F O RM ATE
TECH N ICAL
M AN UAL
C OMPATIBILITIE S AN D IN T E R ACT IO N S
Section B12
Solubility of Minerals
and Salts in Formate Brines
B12.1Introduction.............................................................................................2
B12.2 Solubility of alkaline earth metal sulfates in formate brines...................2
B12.2.1 Effect of brine type...........................................................................2
B12.2.2 Effect of temperature.......................................................................2
B12.2.3 Effect of formate concentration.......................................................2
B12.2.4 Effect of exposure time....................................................................3
B12.2.5 Effect of pH......................................................................................3
B12.2.6 Effect of precipitation reactions........................................................3
B12.2.7 Practical significance of increased alkaline earth metal sulfate
solubility in formate brines................................................................3
B12.3 Solubility of salts in formate brines......................................................... 7
B12.3.1 Solubility of potassium sulfate in potassium formate brine.............. 7
B12.3.2 Solubility of sodium chloride (NaCl) in potassium formate brine...... 7
B12.3.3 Solubility of magnesium chloride (MgCl2) in formate brines............. 7
B12.4 Solubility of clays in formate brines....................................................... 11
B12.5 Solubility of silicates in formate brines.................................................. 11
B12.6 Solubility of galena, hematite, and ilmenate in formate brines............. 11
B12.7 Solubility of calcium carbonate in formate brines................................. 11
References............................................................................................ 12
The Formate Technical Manual is continually updated.
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SECTION B12
PAGE 1
C ABO T
S PE C I A LT Y
F L U I D S
B12.1 Introduction
Oil and gas wells are drilled through thousands of
meters of various minerals to access hydrocarbonbearing reservoirs. While being drilled and completed,
well construction fluids circulating in the wellbore
are in contact with these minerals under conditions
of high temperature and pressure. Therefore, it is
important to have a detailed knowledge of how
drilling and completion fluids interact with minerals
under down-hole conditions. In wells where it is
necessary to drill extended sections through thick
layers of salt and anhydrite, it is particularly important
to know if fluids solubilize these minerals.
Oilfield brines (completion fluids and filtrates of
reservoir drilling fluids) are also in contact with
reservoir fluids. Formation waters contain a lot of
different ions, which are often divalent and can
easily form insoluble scales when in contact with
other divalent ions. This is why it is important to
know how various formation waters react when in
contact with oilfield brines.
Well completion brines with high electrolyte content
are known to increase solubility of alkaline earthmetal sulfate minerals, like calcium sulfate (gypsum
and anhydrite) and barium sulfate, which have low
solubility in water.
For example, Templeton shows that aqueous
solutions of chloride brines can dissolve barium
from barite [1]. This is supported by Monnin [2] who
shows that at atmospheric pressure saturated
sodium chloride brine solubilizes 50 – 100 mg/L
of barium from barite at 50 – 100°C / 122 – 212°F.
At higher temperatures and pressures, barium
solubility levels can increase to 200 – 400 mg/L.
The same author demonstrates that barite is even
more soluble in calcium chloride brine, another
common well completion fluid.
This section of the Formate Technical Manual looks
at what is known about the solubility of minerals
and salts in formate brines. Data have been
collected from various known and unknown sources
and full descriptions of measuring methods are
not always available. Considering the difficulties
associated with performing good solubility
measurements in brines, the data reported here
should only be used as a rough guide.
FORMAT E
T EC HNI C AL
MANUA L
B12.2 Solubility of alkaline earth
metal sulfates in formate
brines
Shell Research has measured solubility of some
alkaline earth metal sulfates in a variety of concentrated
brines [3]. The solubility measurements were made
after exposure of solid samples of alkaline earth
metal sulfate to the brines. The following factors
were varied to study their effect: brine type, brine
concentration, temperature, exposure time, and pH.
Shell’s procedure was to mix the brines with solid
samples of alkaline earth metal sulfates, heat at
the given temperature for the desired time in a
rotating oven and quickly filter the warm fluid.
The concentration of dissolved cations in the clear
filtrate was determined by atomic absorption
spectroscopy (AAS).
Since Shell carried out these tests, it has been
shown that some precipitation of alkali metal
sulfates takes place when alkaline earth metal
sulfates dissolve in concentrated formate brines.
Therefore in potassium formate brine, precipitation
of potassium sulfate occurs and in cesium formate
brine some cesium sulfate precipitation takes
place. This precipitation is not considered in the
Shell solubility data as only soluble alkali earth metal
ion levels were measured (Ba2+, Sr2+, Ca2+).
B12.2.1 Effect of brine type
Solubilities of sulfate minerals in the different brines
are listed in Table 1 and shown graphically in Figure 1.
These tests were performed after 16-hour exposure
at 85°C / 185°F. All fluids were tested at pH = 9.5
(measured in undiluted brines).
Concentrated potassium and cesium formate
brines dissolve significantly higher levels of alkaline
earth metal sulfates than any other tested brines.
Potassium formate brine dissolves more barium
sulfate than cesium formate brine, whilst cesium
formate brine dissolves more strontium sulfate.
Concentrated sodium formate brine generally
dissolves more alkaline earth metal sulfates than
concentrated halide brines, but significantly less
than potassium and cesium formate brines.
B12.2.2 Effect of temperature
The temperature dependence of barium and
strontium sulfate solubility in concentrated potassium
formate brine has been measured and reported by
Shell [3]. See Figure 2. Solubility increases significantly
with rising temperature.
B12.2.3 Effect of formate concentration
Shell also measured the influence of formate
concentration on barium and strontium sulfate
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SECTION B: COMPATIBILITIES AND INTERACTIONS
solubility in concentrated potassium formate brine [3].
See Figure 3. Solubility increases with greater formate
concentration.
B12.2.4 Effect of exposure time
Shell measured influence of contact time on barium
and strontium sulfate solubility in concentrated
potassium formate brine. See Figure 4. The results
show that strontium sulfate dissolves significantly
faster than barium sulfate. At 85°C / 185°F, 90% of
strontium sulfate dissolved after about three hours
and 100% after around 12 hours. Ninety percent of
the barium sulfate dissolved after about 13 hours
and 100% after around 19 hours.
B12.2.5 Effect of pH
Shell measured the influence of pH on barium and
strontium sulfate solubility in concentrated potassium
formate brine. See Figure 5. In the pH range tested
(pH = 7 – 13, measured in undiluted brine), no significant
pH effect was observed.
B12.2.6 Effect of precipitation reactions
Testing has been carried out to evaluate the extent
other precipitation mechanisms take place when
alkali metal earth sulfates dissolve in formate brines.
Tests were completed by measuring both cation
(Ca2+) and anion (SO42-) concentrations in the brine.
For anhydrite (CaSO4), it was found that this mineral
dissolved quite readily in high-concentration potassium
formate brine (71%wt = 1.53 g/cm3 / 12.8 lb/gal).
However, some dissolved sulfate precipitated out
as K2SO4, resulting in a correspondingly low sulfur
concentration in the liquid phase. At lower concentration
potassium formate (30%wt = 1.19 g/cm3 / 9.9 lb/gal),
formation of syngenite, K2Ca(SO4)2·H2O, was observed
in addition to K2SO4. The sulfur concentrations in
solution were similar to those measured when
dissolving K2SO4 in the brine (see B12.3).
For barium sulfate (BaSO4) with lower concentrations
of potassium formate, i.e. 10%wt = 1.06 g/cm3 /
8.8 lb/gal and 30%wt = 1.19 g/cm3 / 9.9 lb/gal, the
sulfate concentration in solution matched K2SO4
solubility (see B12.3), indicating that precipitation had
not taken place. For higher formate concentration
(71%w = 1.53 g/cm3 / 12.8 lb/gal), solubility (calculated
on sulfur determination) was significantly lower than
corresponding BaSO4 solubilities measured by Shell
and determined by analysis of barium content in the
liquid phase, which indicates that some precipitation
of K2SO4 takes place.
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CABO T
S P ECIALTY
FLUIDS
B12.2.7 Practical significance of
increased alkaline earth metal
sulfate solubility in formate brines
The increased solubility of alkaline earth sulfate
minerals (‘scales’) in concentrated formate brines
has certain implications and consequences in well
construction operations. Concentrated formate
brines dissolve some barium and strontium from
common oilfield scales and barite at high temperatures
and pressures. This may cause some simultaneous
precipitation of alkali metal sulfates in concentrated
formate brines after contact with sulfate scales or
barite. These precipitated products, such as
potassium sulfate, are not scales. They easily
dissolve as soon as the formate concentration
lowers or temperature increases, and therefore are
of no significant threat to well productivity.
When formate brine filtrate enters the reservoir the
high solubility of alkaline earth metal sulfate affects
the ability of sulfate scales to form from contact
between formation water and contaminants in the
brine. This high solubility of sulfate scale in formate
brines is not allowed for in most scale prediction
software packages used widely in the industry to
predict incompatibilities between oilfield brines and
formation waters.
The low solubility of potassium sulfate in concentrated
potassium formate can also cause some precipitation
of potassium sulfate if the formate fluid is in contact
with seawater for example. This precipitation is
likely to take place at the surface, over the shakers,
where fluid temperature is lowered. These crystals
re-dissolve at higher temperatures and dissolve
completely if the formate concentration is brought
down by contact with reservoir water for example.
A second precipitation mechanism takes place in
buffered formate brines when alkali earth metal
sulfates dissolve. This is precipitation of alkali earth
metal carbonates. Barium carbonate (BaCO3) is
insoluble in formate (under alkaline pH conditions)
and also consumes carbonate buffer added to the
formate brine. For this reason, it is important to
avoid contaminating formate brines with barite.
The occurrence of precipitation also greatly
complicates laboratory solubility testing. To gain a
full understanding of the dissolution / precipitation
process, preferably both cations and anion levels
in the liquid should be determined, the solid
phase analyzed, and a mass balance carried out.
Solubility figures also look different for buffered and
unbuffered brines.
SECTION B12
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C ABO T
S PE C I A LT Y
F L U I D S
FORMAT E
T EC HNI C AL
MANUA L
Table 1 Solubility of alkaline earth sulfates and scales after 16-hour exposure to various saturated brines at 85°C / 185°F. Some precipitation
of sodium, potassium, and cesium sulfates takes place in all of these tests, so brine sulfate levels do not correspond to levels of dissolved
alkali earth metal sulfates.
Dissolved
minerals/scales
[mg/L]
Sodium salts
Water
NaFo
(40%w)
NaCl
(26%w)
Potassium salts
NaBr
(46%w)
KFo
(75%w)
KCl
(24%w)
Cesium salts
KBr
(34%w)
CsFo
(82%w)
Cs2SO4
BaSO4
2
80
8
3
5,800
16
14
600
2
Barite
1
160
50
20
2,600
80
50
700
8
SrSO4
26
2,700
300
250
110,000
700
500
180,000
350
1,200
2,800
9,000
9,000
90,000
15,000
10,000
80,000
600
Scale (BaSO4)
nd
80
50
14
7,000
50
30
800
1
Scale (SrSO4)
nd
nd
nd
nd
600
nd
nd
nd
nd
CaSO4·2H2O
Solubilities in saturated salts
1,000,000
BaSO4
Barite
100,000
SrSO4
CaSO4·2aq
Solubility [mg/L]
10,000
1,000
100
10
1
H 2O
NaCOOH
(40%w)
NaCl
(26%w)
NaBr
(44%w)
KCOOH
(75%w)
KCl
(24%w)
KBr
(34%w)
CsCOOH
(82%w)
Cs2SO4
(60%w)
Figure 1 Solubility of alkaline earth sulfates after 16 hours at 85°C / 185°F in various saturated brine systems with pH of 9.5 (measured
on undiluted brines). The bar chart shows the amount of dissolved sulfate salt calculated from measured barium / strontium / calcium
concentrations in the brine after exposure. Some precipitation of sodium, potassium, and cesium sulfates have taken place in all of these
brines, so brine sulfate levels do not correspond to levels of dissolved alkali earth metal sulfates.
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SECTION B: COMPATIBILITIES AND INTERACTIONS
CABO T
S P ECIALTY
FLUIDS
METRIC
Solubility in 75% potassium formate vs. temperature
100,000
Solubility [mg/L]
10,000
1,000
Dissolved BaSO4
Dissolved SrSO4
100
20
30
40
50
60
70
80
90
100
110
Temperature [°C]
FIELD
Solubility in 75% potassium formate vs. temperature
100,000
Solubility [mg/L]
10,000
1,000
Dissolved BaSO4
Dissolved SrSO4
100
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
Temperature [°F]
Figure 2 Influence of temperature on the dissolution of alkaline earth metal sulfates in a concentrated potassium formate brine (75% =
1.57 g/cm3 / 13.1 lb/gal). Contact time = 16 hours. pH = 9.5 (measured in undiluted brine). The graphs show amounts of dissolved
sulfate salt calculated from measured barium / strontium concentrations in the brine after exposure. Some precipitation of potassium
sulfate has taken place, so brine sulfate levels do not correspond to levels of dissolved barium and strontium sulfates.
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SECTION B12
PAGE 5
C ABO T
S PE C I A LT Y
F L U I D S
FORMAT E
T EC HNI C AL
MANUA L
Solubility vs. potassium formate concentration
100,000
Dissolved BaSO4
Dissolved SrSO4
Solubility [mg/L]
10,000
1,000
100
10
1
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
KFo concentration [%wt]
Figure 3 Influence of formate concentration on the dissolution of alkaline earth metal sulfates in potassium formate brine. Temperature =
85°C / 185°F. pH = 9.5 (measured on undiluted brine). Contact time = 16 hours. The graph shows the amount of dissolved sulfate salt
calculated from measured barium / strontium concentrations in the brine after exposure. Some precipitation of potassium sulfate has
taken place, so brine sulfate levels do not correspond to levels of dissolved barium and strontium sulfates.
Solubility in 75% potassium formate vs. exposure time
11,000
10,000
9,000
Solubility [mg/L]
8,000
7,000
6,000
5,000
4,000
3,000
Dissolved BaSO4
Dissolved SrSO4
2,000
1,000
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Exposure time [hours]
Figure 4 Influence of contact time on the dissolution of alkaline earth metal sulfate salts in concentrated potassium formate brine
(75% = 1.57 g/cm3 / 13.1 lb/gal). pH = 9.5 (measured on undiluted brine). Temperature = 85°C / 185°F. The graph shows the amount
of dissolved sulfate salt calculated from the measured barium / strontium concentrations in the brine after exposure. Some precipitation
of potassium sulfate has taken place, so brine sulfate levels do not correspond to levels of dissolved barium and strontium sulfates.
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CABO T
S P ECIALTY
FLUIDS
Solubility in 75% potassium formate vs. pH
Solubility [mg/L]
100,000
10,000
Dissolved BaSO4
Dissolved SrSO4
1,000
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
pH (undiluted)
Figure 5 Influence of pH on the dissolution of alkaline earth metal sulfate salts in concentrated potassium formate brine (75% = 1.57 g/cm3 /
13.1 lb/gal). Contact time = 16 hours. Temperature = 85°C / 185°F. The graph shows the amount of dissolved sulfate salt calculated
from the measured barium / strontium concentrations in the brine after exposure. Some precipitation of potassium sulfate has taken
place, so brine sulfate levels do not correspond to levels of dissolved barium and strontium sulfates.
B12.3 Solubility of salts in
formate brines
B12.3.1 Solubility of potassium sulfate
in potassium formate brine
Some data are available on the solubility of potassium
sulfate (K2SO4) in potassium formate brines [4].
Solubility is about 176 mg/L in 71%wt potassium
formate brine (1.53 g/cm3 / 12.8 lb/gal) at 25°C / 77°F,
but this increased with decreasing formate
concentration. For comparison, solubility of potassium
sulfate in fresh water is 120,000 mg/L at 25°C / 77°F.
No precipitation was observed in the formate brine.
Figure 6 shows the soluble sulfate concentration
measured in three potassium formate brines as a
function of temperature.
B12.3.2 Solubility of sodium chloride
(NaCl) in potassium formate brine
Some solubility test results are available for solubility
of sodium chloride in potassium formate brine [4].
The solubility of sodium chloride in 71%wt potassium
formate brine is about 14,000 mg/L at 25°C / 77°F,
compared with about 218,000 mg/L in fresh water.
Solubility of NaCl increases in brines with lower
potassium formate content. Additions of excess
NaCl led to precipitation of solid potassium chloride.
Some traces of sodium formate solid were also
precipitated at the lowest temperature in the 71%wt
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potassium formate brine. Figure 7 shows the
concentration of soluble chloride in the liquid phase
as a function of temperature and formate
concentration. Increasing temperature did not have
a significant effect on solubility of NaCl.
B12.3.3 Solubility of magnesium
chloride (MgCl2) in formate brines
Magnesium chloride has very low solubility in
high-density potassium formate brine and
saturated sodium chloride brine. A low MgCl2
solubility is important when drilling through salt
formations containing magnesium chloride, such as
Zechstein bischofite.
Shell [1] measured solubility of magnesium chloride
(MgCl2·6H2O) in saturated brines of potassium
formate, sodium formate, potassium chloride, and
sodium chloride as a function of temperature.
Testing also included an oversaturated magnesium
chloride brine, which was previously used as a
drilling fluid when drilling through Zechstein
bischofite sections. The results, shown in Figure 8,
indicate a very low solubility of magnesium chloride
in potassium formate and sodium chloride compared
with the other brines.
SECTION B12
PAGE 7
C ABO T
S PE C I A LT Y
F L U I D S
FORMAT E
T EC HNI C AL
MANUA L
METRIC
Solubility of potassium sulphate in potassium formate
1,000,000
SO4- solubility [g/mL]
100,000
10,000
1,000
KFo 1.54 g/cm3
KFo 1.19 g/cm3
KFo 1.06 g/cm3
Water (Wikipedia)
100
10
20
30
40
50
60
70
80
90
Temperature [°C]
FIELD
Solubility of potassium sulphate in potassium formate
1,000,000
SO4- solubility [g/mL]
100,000
10,000
1,000
KFo 1.54 g/cm3
KFo 1.19 g/cm3
KFo 1.06 g/cm3
Water (Wikipedia)
100
10
70
80
90
100
110
120
130
140
150
160
170
180
Temperature [°F]
Figure 6 Dissolution of potassium sulfate in three concentrations of potassium formate brine. The figures show measured concentration
of sulfate in liquid. Open symbols represent dissolution type experiments; closed symbols represent precipitation type experiments.
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SECTION B: COMPATIBILITIES AND INTERACTIONS
CABO T
S P ECIALTY
FLUIDS
METRIC
Dissolution of sodium chloride in potassium formate
250,000
Cl- solubility [mg/L]
200,000
150,000
100,000
Water (Wikipedia)
KFo 1.06 g/cm3
KFo 1.20 g/cm3
KFo 1.54 g/cm3
50,000
0
20
30
40
50
60
70
80
90
Temperature [°C]
FIELD
Dissolution of sodium chloride in potassium formate
250,000
Cl- solubility [mg/L]
200,000
150,000
100,000
Water (Wikipedia)
KFo 1.06 g/cm3
KFo 1.20 g/cm3
KFo 1.54 g/cm3
50,000
0
70
80
90
100
110
120
130
140
150
160
170
180
190
Temperature [°F]
Figure 7 Dissolution of NaCl in three potassium formate brines. The figures show the amount of Cl - in liquid phase as a function of
temperature and formate concentration.
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SECTION B12
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C ABO T
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F L U I D S
FORMAT E
T EC HNI C AL
MANUA L
METRIC
Solubility of MgCl2· 6H2O in concentrated brines
800
KFo concentrated
KCl concentrated
NaCl concentrated
Heated MgCl2 (sat at 60°C)
Solubility MgCl2·6H2O [g/L]
700
600
500
400
300
200
100
0
20
30
40
50
60
70
80
90
100
110
120
Temperature [°C]
FIELD
Solubility of MgCl2· 6H2O in concentrated brines
800
KFo concentrated
KCl concentrated
NaCl concentrated
Heated MgCl2 (sat at 60°C)
Solubility MgCl2·6H2O [g/L]
700
600
500
400
300
200
100
0
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
Temperature [°F]
Figure 8 Solubility of MgCl2·6H2O in various saturated brine systems.
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Saturated sodium formate brine also reduced
solubility of magnesium chloride significantly, but
precipitation problems made measurements
difficult. There is no information about how these
measurements were completed and a possibility
that some precipitation could also have taken place
in the other brine systems.
Further investigation of magnesium chloride
solubility in potassium formate has concluded that
some precipitation takes place. MgCl2·6H2O was
added in excess to three concentrations of potassium
formate (70%, 31.6%, and 10.7%). In the highest
concentration potassium formate brine (70%),
potassium chloride mainly precipitated. Some
magnesium formate Mg(COOH)2·2H2O was
also identified in the precipitates, increasing in
concentration in brines with lower formate content.
B12.4 Solubility of clays in
formate brines
CABO T
S P ECIALTY
FLUIDS
B12.5 Solubility of silicates in
formate brines
Solubility data for quartz and amorphous silicate
(glass) in concentrated formate brines and water
are shown in Table 3. Apart from slightly elevated
levels of silicate dissolved from amorphous silica by
cesium formate there is little practical difference
between water and formate brines.
B12.6 Solubility of galena,
hematite, and ilmenate in
formate brines
Galena (PbS), ilmenate (TiO2, FeO), and hematite
(Fe2O3) are all insoluble in formate brines.
Measurements show solubilities of less than <10 ppm,
which is the detection limit of the instrument (ICP).
B12.7 Solubility of calcium
carbonate in formate
brines
Some solubility data are available for certain common
shales in concentrated sodium, potassium, and cesium
formate brines [3]. The shales tested were sodium
montmorillonite [(Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·
n(H2O)], Kaolinite [Al2Si2O5(OH)4], and Manco shale.
The extent of solubilization was estimated by
measuring levels of soluble Al and Si in the brine
phase after 16-hour contact of the brine with shale
at 85°C / 185°F. The results of the soluble Al and Si
analyses shown in Table 5 indicate that little shales
are dissolved or leached by formate brines.
Calcium carbonate is the most commonly used
bridging material in formate fluids. Its solubility in
formate brines is dependent on pH. At the alkaline
pH of commercial formate brines used in the field,
solubility of calcium carbonate is negligible. This is
particularly true of formate brines buffered with
carbonate / bicarbonate.
Table 2 Solubility of clays in concentrated formate brines. NaFo (46%wt = 1.33 g/cm3 / 11.1 lb/gal), KFo (75%wt = 1.57 g/cm3 / 13.1 lb/gal),
CsFo (82%wt = 2.26 g/cm3 / 18.9 lb/gal). T = 85°C / 185°F. Exposure time = 16 hours.
Solubility
[mg/L]
Montmorillonite
Kaolinite
Manco shale
45%w NaFo
Al3+
Si4+
45.0
45.0
7.5
8.0
4.0
7.0
75%w KFo
Al3+
82%w CsFo
Al3+
Si4+
4.0
8.5
--
Si4+
4.0
1.0
4.0
77.0
7.0
5.0
8.5
8.5
4.0
Table 3 Solubility of silicates in concentrated formate brines. NaFo (46%wt = 1.33 g/cm3 / 11.1 lb/gal), KFo (75%wt = 1.57 g/cm3 / 13.1 lb/gal),
CsFo (82%wt = 2.26 g/cm3 / 18.9 lb/gal). Temperature = 85°C / 185°F. Exposure time = 16 hours.
pH
Quartz
Amorphous silicate (glass)
V ER S IO N
1
–
05/ 1 1
Water
8
10
12
8
10
12
Solubility of SiO2 [mg/L]
NaFo
45
20
55
60
175
360
350
255
430
255
500
245
KFo
CsFo
30
55
125
940
940
930
SECTION B12
40
35
35
1,600
1,600
1,650
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C ABO T
S PE C I A LT Y
F L U I D S
FORMAT E
T EC HNI C AL
MANUA L
References
[1] Templeton, C.C.: “Solubility of barium sulphate in
sodium chloride solutions from 25°C to 95°C”,
Journal of Chemical and Engineering Data, 5
(October 1960), 514–516.
[2] Monnin, C.: “A thermodynamic model for the
solubility of barite and celestite in electrolyte
solutions and seawater to 200°C and to 1 kbar”,
Chemical Geology, 155 (1999) 187–209.
[3] Howard, S.K., Houben, R.J.H., Oort, E. van,
Francis, P.A.: “Report # SIEP 96–5091 Formate
drilling and completion fluids – technical manual”,
Shell International Exploration and Production,
August 1996.
[4] Unknown source.
PAGE 12
SECTION B12
V E R SION
1
–
0 5 / 1 1