Water-Base Systems MI

Water-Base Systems
Water-Base Systems 10.1 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
10
Many different types of water-base drilling
fluid systems (muds) are used in
drilling operations. Basic drilling fluid
systems are usually converted to more
complex systems as a well is deepened
and the wellbore temperature and/or
pressure increases. It is typical for several
types of drilling fluid systems to be used
in each well. Several key factors affect
the selection of drilling fluid system(s)
for a specific well. The most cost-effective
drilling fluid for a well or interval should
be based on the following criteria:
Application
• Surface interval.
• Intermediate interval.
• Production interval.
• Completion method.
• Production type.
Geology
• Shale type.
• Sand type.
• Permeability.
• Other formation types.
Makeup water
• Type of water.
• Chloride concentration.
• Hardness concentration.
Potential problems
• Shale problems.
• Bit/Bottom-Hole Assembly
(BHA) balling.
• Stuck pipe.
• Lost circulation.
• Depleted sands.
Rig/drilling equipment
• Remote location.
• Limited surface capacity.
• Mixing capabilities.
• Mud pumps.
• Solids-control equipment.
Contamination
• Solids.
• Cement.
• Salt.
• Anhydrite/gyp.
• Acid gases (CO2, H2S).
Drilling data
• Water depth.
• Hole size.
• Hole angle.
• Torque/drag.
• Drilling rate.
• Mud weight.
• Maximum temperature.
Water-base drilling fluids can usually
be placed into one of the following
classifications:
• Unweighted clay-water systems.
• Deflocculated, weighted clay-water
systems.
• Calcium-treated, weighted,
deflocculated clay-water systems.
• Saltwater systems.
• Inhibitive potassium systems.
• High-Temperature, High-Pressure
(HTHP) deflocculated systems.
• HTHP polymer systems.
• Encapsulating polymer systems.
• Cationic polymer systems.
• Extended or flocculated clay-based
systems.
• Polyglycol enhanced systems.
• Inhibitive silicate systems.
Introduction
It is typical
for several
types of
drilling fluid
systems to
be used in
each well.
Water-Base Systems
CHAPTER
10
Water-Base Systems 10.2 Revision No: A-0 / Revision Date: 03·31·98
This basic system is essentially
M-I GELT (Wyoming bentonite) and
water. Usually, this system is used to
spud a well. As drilling continues, formation
solids are incorporated into the
drilling fluid. Solids-removal equipment
is used to remove as much of the formation
solids (drill solids) as possible. Some
of the native formation solids may be
bentonitic in nature and increase the
viscosity of the drilling fluid. Therefore,
this system is often referred to as a
“native mud.” Advantages of this system
are low cost and high Rate of
Penetration (ROP). This system is
often extremely shear-thinning.
Unweighted, clay-water systems usually
are converted to another system
prior to reaching any critical part of
the well. Therefore, the solids content
should be maintained at low values to
facilitate this conversion.
Since this system is not weighted, it
has a low buoyancy effect on cuttings.
Therefore, hole-cleaning depends on viscosity
and flow rate. The plastic viscosity
should be low, if the solids content of
the system is low, so the carrying capacity
must be achieved with higher yield
points. Chemical deflocculants reduce
the yield point and viscosity dramatically.
This can result in inadequate hole
cleaning. Therefore, the use of chemical
deflocculants in this system should be
strictly limited. If a low fluid loss is
required, it should be controlled with
additions of M-I GEL (prehydrated if
used in seawater) and an appropriate
Fluid-Loss-Control Additive (FLCA).
The FLCA may be MY-LO-JELE, POLY-SALE,
THERMPACT UL, CMC or POLYPAC.T
Unweighted Clay-Water Systems
Typical Properties
Density (lb/gal) 8.5 - 10
Funnel viscosity (sec/qt) 36 - 55
Plastic viscosity (cP)* 5 - 9
Yield point (lb/100 ft2)* 12 - 25
Initial gel (lb/100 ft2) 5 - 10
10-min gel (lb/100 ft2) 10 - 20
pH 8.5 - 10.5
Pm (cm3 0.02N H2SO4) 0.1 - 1.5
Pf (cm3 0.02N H2SO4) 0.1- 1.0
Calcium (mg/l) 40 - 240
Chlorides (mg/l)
(freshwater) 0 - 5,000
Fluid loss (cm3/30 min) As needed
Low-gravity solids (%) 3 - 10
MBT (lb/bbl) See Figure 1
*See Figure 1.
Typical Products Primary Function
M-I GEL Viscosity and
fluid-loss control
Caustic soda Increase pH and Pf
TANNATHINT Thinner
SAPP Thinner
POLYPAC Viscosity and
fluid-loss control
THERMPAC UL Fluid-loss control
MY-LO-JEL Fluid-loss control
POLY-SAL Fluid-loss control
POLY-PLUST Bentonite extender
CMC Viscosity and
fluid-loss control
Concentration
Material (lb/bbl)
M-I GEL 20 - 35
Caustic soda 0.1 - 0.5
FLCA As needed
SAPP 0.125 - 0.5
Usually,
this system
is used to
spud a well.
…the use
of chemical
deflocculants
in this system
should
be strictly
limited.
Water-Base Systems
Water-Base Systems 10.3 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
10
Figure 1: Plastic viscosity, yield point and Methylene Blue Test (MBT) ranges for water-base muds.
50
45
40
35
30
25
20
15
10
5
0
9 10 11 12 13 14 15 16 17 18 19 20
Mud weight (lb/gal)
PV (cP), YP (lb/100 ft2) and MBT (lb/bbl)
PV
MBT
YP
Figure 2: Solids range for barite water-base muds.
50
45
40
35
30
25
20
15
10
5
0
9 10 11 12 13 14 15 16 17 18 19
Mud weight (lb/gal)
Solids (% vol)
Maximum
9% LGS
6% LGS
3% LGS
Minimum
Water-Base Systems
CHAPTER
10
Water-Base Systems 10.4 Revision No: A-0 / Revision Date: 03·31·98
The SPERSENEE deflocculated system
is one of the most common drilling
fluid systems used in the industry.
The primary thinner in the system is
SPERSENE (or SPERSENE CF) lignosulfonate.
Lignosulfonates are organic acids that
supply anions (negative ions) to the
fluid. These anions reduce the yield
point and gel strengths by neutralizing
the cations (positive ions) on the clay
particles, thus deflocculating the clay
slurry causing clay particles to repel one
another. SPERSENE is very versatile due to
its high degree of solubility in both
freshwater and saltwater environments.
Since it is acidic, SPERSENE requires an
alkaline environment in which to solubilize.
Therefore, hydroxyl ions are
added usually in the form of caustic
soda (sodium hydroxide) and lime (calcium
hydroxide) to increase the pH.
This system can be treated to have a
high degree of tolerance for both solids
and chemical contamination by simply
increasing the concentration of SPERSENE
and TANNATHIN (lignite) or XP-20T (causticized
chrome lignite). Lignite is an
organic acid that also supplies anions to
the fluid, thus causing clay particles to
repel one another. In most cases, a
ratio of two SPERSENE to one TANNATHIN,
or XP-20, is a very effective combination
for treatments, but the ratio can
be varied.
Materials like SPERSENE, TANNATHIN and
XP-20 are deflocculants, but are also
referred to as dispersants and thinners,
because they allow discrete clay particles
to disperse, and they reduce the
yield point, gel strength and “n” value
of the drilling fluid.
SPERSENE systems are usually converted
from unweighted, clay-water
suspensions or “spud muds.” A typical
treatment to convert to a lightly
treated SPERSENE system would be
SPERSENE System
The SPERSENE
deflocculated
system is one
of the most
common
drilling fluid
systems
used in the
industry.
Figure 3: Solids range for hematite water-base muds.
50
45
40
35
30
25
20
15
10
5
0
9 10 11 12 13 14 15 16 17 18 19 20 21 22
Mud weight (lb/gal)
Solids (% vol)
Maximum
Minimum
9% LGS
6% LGS
3% LGS
Water-Base Systems
Water-Base Systems 10.5 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
10
(SPERSENE SYSTEM CONTINUED)
about 4 lb/bbl M-I GEL, 2 lb/bbl
SPERSENE, 1 lb/bbl of either TANNATHIN
or XP-20 and 1 lb/bbl caustic soda.
Comparing the drilling fluid properties
at the flow line with those in the
pits indicates the degree to which wellbore
contaminants are affecting the
drilling fluid properties. This is also a
reflection of the stability of the system.
In most cases, a significant difference
in the properties between the flow line
and the pits indicates an unstable fluid.
The stability of a SPERSENE system can
be increased by increasing the concentration
of SPERSENE and TANNATHIN (or
XP-20). Lightly treated SPERSENE systems
contain 2 to 6 lb/bbl SPERSENE and 1 to
3 lb/bbl of TANNATHIN (or XP-20), while
a fully inhibitive SPERSENE system may
contain 8 to 12 lb/bbl SPERSENE and 4 to
6 lb/bbl of TANNATHIN or (XP-20).
Maintenance of a SPERSENE system
(and other drilling fluids systems) while
drilling means maintaining the properties
at predetermined, near-constant
values. These values are controlled by
the concentration of materials in the
drilling fluid. As water is added to the
drilling fluid to maintain an acceptable
drilled solids concentration, products
must be added to maintain the desired
concentration of additives. Therefore,
the volume of dilution water should be
measured or estimated to use as a basis
for product additions. The amount of
dilution required depends on the hole
size, rate of penetration, type of formation,
solids-control equipment and the
optimum concentration of drill solids
in the drilling fluid.
The temperature limitation of this
system is approximately 320°F (160°C)
due to the increased rate of thermal
degradation of lignosulfonate above
this temperature. The temperature limit
of this system can be increased significantly
by increasing the concentration
of lignite and reducing the concentration
of lignosulfonate. Lignite has
a temperature limitation of about
450°F (232°C).
NOTE: SPERSENE and XP-20 contain
chrome and may not be allowed under
some environmental regulations. When
chrome is not permitted, SPERSENE CF and
TANNATHIN should be used.
Typical Properties
Density (lb/gal) 10 - 18
Funnel viscosity (sec/qt) ± (3.5 x mud weight)
Plastic viscosity (cP) See Figure 1
Yield point (lb/100 ft2) See Figure 1
Initial gel (lb/100 ft2) 2 - 8
10-min gel (lb/100 ft2) 2 - 14
pH 9.5 - 11.5
Pm (cm3 0.02N H2SO4) 2.0 - 5.0
Pf (cm3 0.02N H2SO4) 0.5 - 1.5
Calcium (mg/l) 40 - 240
Chlorides (mg/l) 0 - 20,000
Fluid loss (cm3/30 min) As needed
Low-gravity solids (%)* 5 - 7
MBT (lb/bbl) See Figure 1
*See Figures 2 and 3.
Typical Products Primary Function
M-I BAR Increase density
M-I GEL Viscosity and
fluid-loss control
Caustic soda Increase pH and Pf
Lime Increase Pm and
treat out CO3
Gyp Treat out CO3
SPERSENE (CF) Thinner
TANNATHIN Fluid loss and thinner
XP-20 HT thinner and
fluid-loss control
POLYPAC API fluid-loss control
and viscosity
RESINEXT HTHP fluid-loss control
DUO-VIST Increase low-shear
viscosity
Concentration
Material (lb/bbl)
M-I BAR or FER-OX 0 - 550
M-I GEL 5 - 30
Caustic soda 0.3 - 2
Lime 0 - 1
SPERSENE (CF) 2 - 12
XP-20 or TANNATHIN 1 - 12
POLYPAC 0.50 - 2
RESINEX 2 - 6
DUO-VIS 0.25 - 0.50
Lignite has a
temperature
limitation
of about
450°F…
The concentration
of
reactive
solids in
the drilling
fluid
determines
the viscosity
increase
encountered
when calcium
is added to
the system.
Water-Base Systems
CHAPTER
10
Water-Base Systems 10.6 Revision No: A-0 / Revision Date: 03·31·98
When calcium is added to a clay-water
slurry, a base exchange occurs as the calcium
(Ca2+) cation, which has higher
bonding energy, replaces the sodium
(Na+) cation on the clays, converting
them to calcium-base clays. Figure 4
shows the amount of calcium adsorbed
by Wyoming bentonite and native
clays. This cation exchange results in
partial dehydration of the hydrated clay
particles, reducing the size of the water
envelope around the clay particles (see
Figure 5). The reduction in the size
of the water envelope allows the clay
particles to come into contact with
one another, resulting in flocculation.
Flocculation causes an increase in the
yield point and gel strengths. If a deflocculant
is not used, the size of the flocs
of clay eventually will increase and may
precipitate out, resulting in a gradual
decrease in the plastic viscosity.
If a deflocculant is used, then the
clays will still have the reduced water
envelope, but the flocs of clay will
be dispersed.
This phenomenon occurs when calcium
contamination occurs while drilling
then is subsequently treated, or
when a fluid is converted (“broken
over”) to a calcium-base drilling fluid
such as a SPERSENE/gyp or a SPERSENE/
lime system.
The concentration of reactive solids in
the drilling fluid determines the viscosity
increase (viscosity hump) encountered
when calcium is added to the
system (see Figure 6). Therefore, prior to
converting to a calcium-base system, or
before drilling into formations that contain
calcium (such as anhydrite), the
reactive solids content of the drilling
fluid should be reduced by dilution
while the viscosity is maintained with
additions of polymers.
Calcium systems provide soluble
and reserve calcium in a drilling fluid.
Soluble calcium performs several functions.
It provides wellbore inhibition
by minimizing the hydration of drill
solids and exposed shales through
base exchange into calcium-based
clays. It makes a drilling fluid compatible
with formations that contain high
Calcium-Treated Drilling Fluids
Figure 4: Adsorption of calcium by clays.
16
14
12
10
8
6
4
2
0
0 500 1,000 1,500 2,000
Filtrate calcium (mg/l)
Calcium adsorbed (mg/g)
Wyoming
bentonite
Native clay
Figure 5: Reduction in water of hydration for sodium
clay during base exchange with calcium.
Na+
Na+
Na+
Ca2+
Water of hydration
(envelope of water)
+ Ca2+
Flocculation
causes an
increase in
the yield
point and gel
strengths.
Ca2+
Figure 6: Effect of solids concentration
on viscosity with calcium additions.
100
80
60
40
20
0
0 100 200 300 400 500 600 700 800
Filtrate calcium (mg/l)
Viscosity (cP)
High solids
Low solids
Water-Base Systems
Water-Base Systems 10.7 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
10
(CALCIUM-TREATED DRILLING
FLUIDS CONTINUED)
concentrations of calcium, such as
anhydrite. It precipitates carbonate
ions (CO3
2–) which result from carbon
dioxide (CO2) contamination.
The solubility of calcium is inversely
proportional to the pH of the drilling
fluid. It is nearly insoluble at a pH above
12.5, but is very soluble at a low pH.
This is illustrated in Figure 7 where, on
Line A (when only lime is added), the
pH does not increase above 12.5, but
on Line B (with added caustic), the pH
increases above 12.5 and the soluble
calcium decreases rapidly. Therefore,
calcium as lime (Ca(OH)2) helps to
buffer the pH when acid gases such
as CO2 or hydrogen sulfide (H2S)
are encountered.
Calcium solubility is also directly
related to salinity or chloride (Cl–) concentration.
The soluble calcium in seawater
is often around 1,200 mg/l and
will increase as the salinity is increased,
as shown in Figure 8. Figure 8 shows
the soluble calcium from gyp added
to increasing concentrations of salt.
SPERSENE/GYP SYSTEM
The SPERSENE/gyp (gypsum) system is
designed to drill anhydrite (CaSO4)
and/or provide inhibition while drilling
water-sensitive shales by using gypsum
(CaSO4•2H2O) as the source of calcium.
To maintain a sufficient amount of soluble
calcium, the pH of the SPERSENE/gyp
system should be kept low (9 to 10.5).
The normal concentration of soluble
calcium in this system is in the 600 to
1,200 mg/l range. Since the solubility
of calcium is affected by pH and salinity,
the actual level will depend on
these properties.
When converting an existing
untreated or lightly treated system
to a SPERSENE/gyp system, the MBT and
low-gravity solids content should be
reduced to minimize the “break-over
viscosity hump.” Then, about 8 lb/bbl
gyp, 8 lb/bbl SPERSENE and 2 lb/bbl caustic
soda should be added simultaneously
over one or two circulations. After the
initial conversion, properties such as
fluid loss, pH and alkalinity should be
refined by the additions of the proper
materials. Materials that have a low
hardness tolerance should not be used
in this system. Since soluble calcium
increases the hardness of the water
phase, treatments with about 2 lb/bbl
SURFAK-ME are beneficial for reducing
the surface tension of the water phase,
and improving the performance of the
chemical additives.
In addition to the maintenance
procedures previously described, the
“excess gyp” test should be used to
Figure 8: Solubility of calcium vs. chlorides.
2.0
1.6
1.2
0.8
0.4
0
0 50 100 150 200
Chlorides (mg/l x 1,000)
Soluble calcium (mg/l x 1,000)
Figure 7: Line A - soluble calcium vs. lime
concentration; Line B - Soluble calcium of 4 lb/bbl
of lime added to caustic solutions.
1,000
900
800
700
600
500
400
300
200
100
0
0 1 2 3 4 5 6
Caustic soda or lime concentration (lb/bbl)
Calcium (mg/l)
pH 12.4
Line A
pH 12.2
pH 12
pH 12.4
pH 12.9
pH 13.2
Line B
Materials
that have a
low hardness
tolerance
should not
be used in
this system.
Water-Base Systems
CHAPTER
10
Water-Base Systems 10.8 Revision No: A-0 / Revision Date: 03·31·98
(SPERSENE/GYP SYSTEM CONTINUED)
monitor the concentration of excess
gyp in the system. Mass-balance equations
cannot accurately monitor excess
gyp, because gyp is removed from the
system on drilled solids due to base
exchange.
Excess gyp procedure
The excess gyp content can be determined
by measuring the “whole mud
Versenate total hardness” (Vt) and the
total hardness of the filtrate (Vf) using
this procedure and the calculation
which follows:
Procedure to determine the gyp content
(see API RP13B-1, Appendix A.8):
1. Add 5 ml whole mud to 245 ml
distilled water.
2. Stir for 30 min at room temperature
or 15 min at 150°F.
3. Filter the solution with the API filter
press. Discard the first cloudy
portion of the filtrate. Collect the
clear filtrate.
4. Pipette 10 ml of the collected clear
filtrate into a titration dish and add
1 ml strong buffer and 4 to 6 drops
Calmagite Indicator.
5. Titrate with Standard Versenate to a
blue or blue-green end point, record
the number of ml of Standard
Versenate as Vt.
6. To 1 ml of mud filtrate from the
standard API filtrate test, add 1 ml
strong buffer and 4 to 6 drops
Calmagite Indicator, titrate with
Standard Versenate from wine-red
to blue, record the number of ml
of Standard Versenate as Vf.
Total calcium sulfate (lb/bbl) =
2.38 x Vt
Excess calcium sulfate (lb/bbl) =
2.38 x Vt - (0.48 x Vf x Fw)
Where:
Fw = Water fraction from retort
NOTE: A simplified field method
titrates 1 ml of whole mud in 150 to
350 ml distilled water in a quart jar,
using 2 to 3 ml strong buffer and 1 to
2 ml Calmagite Indicator. Record the ml
of Standard Versenate as the Vm. The
color change may be hard to see due to
Typical Properties
Density (lb/gal) 10 - 18
Funnel viscosity (sec/qt) ± (3.5 x mud weight)
Plastic viscosity (cP) See Figure 1
Yield point (lb/100 ft2) See Figure 1
Initial gel (lb/100 ft2) 1 - 5
10-min gel (lb/100 ft2) 1 - 10
pH 9.0 - 10.5
Pm (cm3 0.02N H2SO4) 0.5 - 2.5
Pf (cm3 0.02N H2SO4) 0.2 - 1.6
Calcium (mg/l) 600 - 1,200
Chlorides (mg/l) 0 - 20,000
Fluid loss (cm3/30 min) As needed
Low-gravity solids (%)* 4.5 - 7
MBT (lb/bbl) See Figure 1
Excess gyp (lb/bbl) 3 - 12
*See Figures 2 and 3.
Typical Products Primary Function
M-I BAR Increase density
M-I GEL (prehydrated) Viscosity and
fluid-loss control
Caustic soda Increase pH and Pf
Gyp Calcium source
SPERSENE Thinner
TANNATHIN Fluid-loss control
POLYPAC API fluid-loss control
RESINEX HTHP fluid-loss control
SURFAK-ME Surface-acting agent
Concentration
Material (lb/bbl)
M-I BAR or FER-OX 0 - 550
M-I GEL 7.5 - 25
Caustic soda 0.2 - 1.5
Gyp 8 - 12
SPERSENE 5 - 15
TANNATHIN 2.5 - 10
POLYPAC 0 - 2
RESINEX 3 - 6
SURFAK-M 0 - 2
Water-Base Systems
Water-Base Systems 10.9 Revision No: A-0 / Revision Date: 03·31·98
CHAPTER
10
the dark brown color of the lignosulfonate
and lignite. This color change may appear
to be from the original color of the solution
with a red tint to only a slight green or bluegreen
tint. The rule-of-thumb calculation for
this procedure is:
Excess gyp (lb/bbl) = (Vm+Vf) ÷ 2
SPERSENE/LIME SYSTEM
Generally, SPERSENE/lime systems are
used to reduce the effects of acid
gases such as CO2 or H2S and/or to
reduce the hydration of formation
clays. SPERSENE/lime systems use lime
(Ca(OH)2) as their source of calcium.
Since lime has a high pH (12.4), the
pH of the system will be high. The
pH of the system depends on the concentration
of lime and caustic soda
(NaOH). Lime muds maintain a concentration
of excess lime which is not
in solution, since the solubility of
lime is an inverse function of pH.
Therefore, this excess (reserve) lime
goes into solution only as the pH of
the system is reduced by reactions
with acidic contaminants incorporated
into the system during drilling
operations. This results in the excess
lime having a buffering effect on the
pH, which provides greater stability to
the system.
Lime muds are subdivided into low-,
medium- and high-lime categories
according to the amount of excess
lime that they contain. This level of
excess lime is chosen based on the anticipated
severity of contamination and
on local practice. Typical alkalinities
and excess lime concentrations for
the low-, medium- and high-lime categories
are shown below. These systems
are more stable if the Pf is kept roughly
equal to the excess lime content
(lb/bbl). Lime muds generally are
not used when mud densities are
below 10 lb/gal because it is difficult to
maintain rheological properties sufficient
to clean the wellbore. Temperatures in
excess of 300°F (149°C) may cause
severe gelation or cementation of
medium- and high-lime drilling fluids.
This severe gelation, or cementation,
is caused by high alkalinity, high concentrations
of reactive solids and high
temperature which combine to form
alumino-silica cement.
When converting an existing
untreated or lightly treated system
to a SPERSENE/lime system, the MBT
and low-gravity solids content should
be reduced to minimize the “break-over
viscosity hump.” Then a treatment of 1
to 10 lb/bbl lime, 2 to 12 lb/bbl SPERSENE
and 2 lb/bbl caustic soda should be
added simultaneously during one or
two circulations. After the initial conversion,
properties such as fluid loss, pH
and alkalinity should be refined by the
additions of the proper materials.
In addition to the maintenance procedures
previously described, the “excess
lime” should be calculated as often as
required to monitor the concentration
of excess lime in the system. Massbalance
equations cannot accurately
monitor excess lime, because lime is
removed from the system on drilled
clays as the result of base exchange.
The equation for calculating excess
lime is:
Excess lime (lb/bbl) = 0.26 (Pm - PfFw)
Generally,
SPERSENE/lime
systems are
used to
reduce the
effects of
acid gases…
Alkalinities
Low-lime Pf (cm3 0.02N H2SO4) 0.5 - 1
Pm (cm3 0.02N H2SO4) 2.4 - 4.8
Excess lime (lb/bbl) 0.5 - 1
Medium-lime Pf (cm3 0.02N H2SO4) 1 - 4
Pm (cm3 0.02N H2SO4) 4.8 - 19
Excess lime (lb/bbl) 1 - 4
High-lime Pf (cm3 0.02N H2SO4) 4 - 10
Pm (cm3 0.02N H2SO4) 19 - 46
Excess lime (lb/bbl) 4 - 9.4
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Water-Base Systems
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Water-Base Systems 10.10 Revision No: A-0 / Revision Date: 03·31·98
Typical Properties
Density (lb/gal) 10 - 16
Funnel viscosity (sec/qt) ± (3.5 mud weight)
Plastic viscosity (cP) See Figure 1
Yield point (lb/100 ft2) See Figure 1
Initial gel (lb/100 ft2) 1 - 5
10-min gel (lb/100 ft2) 1 - 10
pH 11.5 - 13.5
Calcium (mg/l) 40 - 200
Chlorides (mg/l)
(freshwater) 0 - 5,000
Chlorides (mg/l)
(seawater) 20,000
Low-gravity solids (%)* 4.5 - 7
MBT (lb/bbl) See Figure 1
Excess lime (lb/bbl) 1 - 10
*See Figures 2 and 3.
Typical Products Primary Function
M-I BAR Increase density
M-I GEL (prehydrated) Viscosity and
fluid-loss control
Caustic soda Increase Pf
Lime Excess lime and
increase Pm
SPERSENE Fluid loss and thinner
TANNATHIN Fluid-loss control
XP-20 HTHP thinner and
fluid-loss control
POLYPAC Viscosity and
API fluid-loss control
MY-LO-JEL Fluid-loss control
POLY-SAL Fluid-loss control
RESINEX HTHP fluid-loss control
Concentration
Material (lb/bbl)
M-I BAR or FER-OX 0 - 550
M-I GEL 15 - 30
Caustic soda 0.5 - 1.5
Lime 0.5 - 10
SPERSENE 2 - 15
XP-20 or TANNATHIN 3 - 8
RESINEX 0 - 6
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(SPERSENE/LIME SYSTEM CONTINUED)
Water-Base Systems
Water-Base Systems 10.11 Revision No: A-1 / Revision Date: 07·17·98
CHAPTER
10
Seawater and brackish-water systems
are used in offshore and coastal drilling
operations due to the endless supply of
that type of water at the drillsite. Other
benefits derived from using sea or
brackish water in drilling fluids include
a lesser degree of hydration of drilled
clays than when using freshwater.
An understanding of seawater drilling
fluids requires an understanding of seawater,
and how mud components react
in it. The pH of seawater is buffered
against changes by a solubility equilibrium
with atmospheric CO2 and sedimentary
calcium carbonate. This means
that as the pH of seawater is increased
through the addition of alkaline materials,
atmospheric CO2 will be absorbed
into the seawater in an effort to buffer
the pH. Since the buildup of these carbonates
is detrimental to drilling fluid
properties, an excess concentration of
lime (which is not in solution) is maintained
in the system. The lime prevents
the build-up of carbonates and buffers
the pH in the desired range. So, a seawater
mud should be run as a “low-lime
system” (see lime muds).
The cost-effectiveness of XP-20 and
TANNATHIN in seawater is minimized
due to their reduced solubility; therefore,
in environments where chlorides
exceed 15,000 mg/l, the use of lignites
should be minimized and the use of
SPERSENE increased.
The temperature limitation of this system
is approximately 320°F (160°C). If
bottom-hole temperatures greater than
320°F (160°C) are anticipated, freshwater
should be added to reduce the chlorides
to less than 15,000 mg/l so that XP-20
will be more soluble. Or, displace with a
synthetic- or oil-base system.
Since this system is similar to a
SPERSENE/low-lime system, conversion
and maintenance are the same as with
a SPERSENE/low-lime system.
SPERSENE/XP-20 Seawater System
…a seawater
mud should
be run as a
“low-lime
system”.
Typical Properties
Density (lb/gal) 10 - 18
Funnel viscosity (sec/qt) ± (3.5 x mud weight)
Plastic viscosity (cP) See Figure 1
Yield point (lb/100 ft2) See Figure 1

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