Transcript 2_Classification_Additives_Calculations

Well Design – Spring 2012
Well Design
PE 413
Classification – Additives – Calculation
of Drilling Cements
Prepared by: Tan Nguyen
Well Design – Spring 2012
Classification of Drilling Cements
API has defined eight standard classes and three standard types of cement for
use in wells. The eight classes specified are designated class A to class H.
Three types specified are: Ordinary O, Moderate sulfate-resistant MSR, and
high sulfate-resistant HSR.
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Well Design – Spring 2012
Classification of Drilling Cements
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Well Design – Spring 2012
Classification of Drilling Cements
Prepared by: Tan Nguyen
Well Design – Spring 2012
Classification of Drilling Cements
Prepared by: Tan Nguyen
Well Design – Spring 2012
Classification of Drilling Cements
Prepared by: Tan Nguyen
Well Design – Spring 2012
Classification of Drilling Cements
Prepared by: Tan Nguyen
Well Design – Spring 2012
Cement Additives
For the slurry:
• Thickening time (acceleration, retardation)
• Density (extenders, weight increase/reduction)
• Friction during pumping
• Fluid loss (by filtrate)
• Lost-circulation resistance (whole slurry loss)
For set cement:
• Compressive strength
• Strength retrogression (loss with time)
• Expansion/contraction
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Well Design – Spring 2012
Cement Additives
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Well Design – Spring 2012
Cement Additives
Accelerators
Cement-setting time is accelerated to reduce WOC time and to increase early
strength. This is desirable for surface pipe, in shallow (cooler) wells, and for setting
plugs. The most common accelerators are calcium chloride, sodium silicate,
sodium chloride (low concentrations), seawater, hemihydrate forms of gypsum,
and ammonium chloride.
Type: Accelerators
Calcium Chloride (CaCl2) (flake, powder)
Amount used per sack
(% by weight)
2-4
Sodium Chloride (NaCl)
3 - 10 (water)
Sodium Chloride (NaCl)
1.5 - 5 (cement)
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Well Design – Spring 2012
Cement Additives
Retarders
Cement-thickening time is slowed primarily to allow the slurry to be pumped and
displaced into position before setting.
Retarders
Amount used per sack
(% by weight)
Calcium-Sodium Lignosulfonate
0.1 - 1.0
Calcium Lignosulfonate
0.1 to 1.0
Saturated Salt Solutions
-
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Cement Additives
Temperature Effect on the Thickening Time
Thickening
time
function
of
is
a
both
temperature and pressure,
and these effects must be
predicted before additives
are selected
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Cement Additives
Density Reducing Additives - Extenders
Slurry density may be reduced with extenders such as bentonite, pozzolan,
diatomaceous earth, and anhydrous sodium metasilicate.
Low-density slurry is frequently preferred, to decrease the likelihood of breaking
down the formation and causing lost circulation. In addition, low-density slurries
cost less per cubic foot because yield per sack is increased.
Density decrease results in large part from increased water content. Extenders,
with their high surface area to "tie up" water, permit water addition without
separation. Cement strength is reduced approximately in proportion to watercontent increase. However, we shall see later that high strength is not always
required
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Well Design – Spring 2012
Cement Additives
Density Reducing Additives - Extenders
Type: Density reducers/extenders
Amount used per sack
(% by weight)
Bentonite
2 to 16
Attapulgite
1/2 to 4
Diatomaceous Earth (Diacel D)
Pozzolan, Artificial (fly ash)
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10, 20, 30 or 40
74 lb/sk
Well Design – Spring 2012
Cement Additives
Density Increasing Additives
High density cement sluries are often necessary to offset the high pressures that
are frequently encountered in deep or abnormally pressured fromations. Density
may be increased with weight material such as sand, barite, hematite or ilmenite,
and/or salt dissolved in the mix water.
Density increasers
Sand
Amount used per sack
(% by weight)
5 to 25
Barites
10 to 108
Ilmenite (iron-titanium oxide)
5 to 100
Hematite
4 to 104
Salt
5 to 16
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Well Design – Spring 2012
Cement Additives
Filtration Control Additives
Fluid loss, or the premature escape of mix water from the slurry before chemical
reaction occurs, can cause many downhole problems, including
1. Differential sticking of casing and decentralization
2. Formation damage by filtrate (if not controlled by mud cake)
3. Loss of pumpability
4. Cement bridging above gas zones and gas cutting from hydrostatic pressure
loss
5. Improper or premature dehydration during squeezing
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Well Design – Spring 2012
Cement Additives
Filtration Control Additives
Materials to reduce filtrate loss and
friction
Fluid-loss additives
Amount used per sack
(% by weight)
0.5 -1.5%
Organic polymers (cellulose)
0.5 – 1.5%
Carboxymethyl hydroxyethyl cellulose
(CMHEC)
0.3 - 1.0%
Latex additives, form films
1.0 gal/sk
Bentonite cement with dispersant
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12-16% gel
Well Design – Spring 2012
Cement Additives
Friction Reducer
Friction reducers or dispersants are commonly used to lower viscosity, yield point
and gel strength of the slurry to reduce friction in pipe, and thus allow turbulent
flow to occur at reduced pump rates. These additives also permit slurries to be
mixed at lower water/cement ratios so that higher densities may be achieved.
Type: Friction reducer
Amount used per sack
(% by weight)
Polymer: blend
0.5 to 0.3 lb/sk
Polymer: long chain
0.5 to 1.5 lb/sk
Calcium lignosulfonate
0.5 to 1.5 lb/sk
Sodium Chloride
Organic acid
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1 to 16 lb/sk
0.1 to 0.3 lb/sk
Well Design – Spring 2012
Cement Additives
Lost Circulation Materials
"Lost circulation" or "lost returns" refers to the loss to formation voids of either
whole drilling fluid or cement slurry used during the course of drilling or completing
a well. Cement, with its larger particle size is less susceptible to loss in permeable
formations.
Types of lost-circulation additives available for cement are blocky-granular
materials (walnut shells, gilsonite, crushed coal, perlite-expanded and perlitesemiexpanded) which form bridges, and laminated materials (cellophane flakes)
which form flake-type mats.
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Well Design – Spring 2012
Cement Additives
Lost Circulation Materials
Type material Generic name
Type particle
Volumes used, typical range
Gilsonite
Graded
Perlite
Expanded
Walnut shells
Graded
1-5 lb/sk
Coal
Graded
1-10 lb/sk
Lamellated
Cellophane
Flakes
1/8-2 lb/sk
Fibrous
Nylon
Short fibers
Granular
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5-50 lb/sk
1/2-1 cu ft/sk
1/8-1/4 lb/sk
Well Design – Spring 2012
Cement Additives
Lost Circulation Materials
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Well Design – Spring 2012
Cement Additives
Compressive Strength Stabilizers
Four variables: composition,
temperature,
pressure,
and
time — affect compressive
strength. However, at high
temperatures,
compositions
cement
may
lose
strength after reaching a high
value and never attain the
strength
reached
curing temperatures
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at
lower
Well Design – Spring 2012
Cement Additives
Summary
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Calculation
Basic Calculations
When the concentration of an additive is expressed as a weight percent, the
intended meaning is usually that the weight of the additive put in the cement
mixture is computed by multiplying the weight of cement in the mixture by the
weight percent given by 100%.
Percent mix = water weight x 100/cement weight
The volume of slurry obtained per sack of cement used is called the yield of the
cement.
1 sack = 94 lbm.
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Well Design – Spring 2012
Calculation
Basic Calculations
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Well Design – Spring 2012
Calculation
Basic Calculations
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Well Design – Spring 2012
Calculation
Basic Calculations
Example 1: it is desired to mixed a slurry of class A cement containing 3%
bentonite, using the normal mixing water as specified by API. Determine the
weight of bentonite and volume of water to be mixed with one 94-lbm sack of
cement. Also compute the percent mix, yield, and density of the slurry.
Prepared by: Tan Nguyen
Well Design – Spring 2012
Calculation
Basic Calculations
The weight of bentonite to be blended with one sack of class A cement:
94(lbm)0.03 = 2.82 lbm / sag
The normal water content for class A cement is 46%. 5.3% water must be added
for each percent bentonite. Thus, the percent mix is:
46 + 5.3 x 3 = 61.9%
The weight of water to be added per sack
0.619 x 94 = 58.186 lbm / sag
The volume of water to be added for one sack
58.186(lbm) / 8.33 (lbm/gal) = 6.98 gal /sag
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Well Design – Spring 2012
Calculation
Basic Calculations
Yield = total volume of slurry in one sack
Yield = Vcement per sack + Vbentonite per sack + Vwater per sack
Yield = 94(lbm) x 0.0382(gal/lbm) + 2.82 (lbm) x 0.0453 (gal/lbm) + 6.98 (gal)
Yield = 10.69 gal/sack
Density of the slurry = total mass of slurry / total volume of slurry
Density of the slurry = 94 + 2.82 + 58.186 / 10.69 = 14.48 lbm/gal
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Well Design – Spring 2012
Calculation
Density Calculations
Example 2: It is desired to increase the density of a class H cement slurry to 17.5
lbm/gal. Compute the amount of hematite that should be blended with each sack
of cement. The water requirements are 4.5 gal/94 lbm class H cement and 0.36
gal/100 lbm hematite.
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Well Design – Spring 2012
Calculation
Density Calculations
Let x represent the mass of hematite per sack needed to bring the slurry cement
density up to 17.5 lbm/gal. The slurry includes: 94-lbm cement, x-lbm hematite,
and y-lbm water.
The volume of water needed for mixing 1 sack of cement and x-lbm of hematite:
Vwater = 4.5 + 0.36(x)/100 = 4.5 + 0.0036x (gal)
The weight of water needed for mixing 1 sack of cement and x-lbm of hematite
mwater = (4.5 + 0.0036x)8.33 (lbm)
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Well Design – Spring 2012
Calculation
Density Calculations

total m ass
total volum e
17.5 
94  x  4.5  0.0036 x 8.33
94  0.0382  x  0.0239  4.5  0.0036 x
x = 18.3 lbm hematite per 94 lbm cement.
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