Method of using cementing composition having improved flow properties

Methods of using aqueous hydraulic cement compositions containing polyamido-sulfonic compounds as flow-property-improving and turbulence-inducing additives are disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an aqueous hydraulic cement slurry 
composition especially suitable for use in cementing operations. 
More particularly, the present invention concerns polyamido-sulfonic 
additives for hydraulic cements used in cementing operations which improve 
the flow properties of the cement slurry, especially facilitating high 
flow rates and turbulent flow of the cement slurry when it is being pumped 
to its desired location during the cementing operation. 
Most particularly, the present invention concerns cementing of gas and oil 
wells employing aqueous hydraulic cement slurries containing 
polyamido-sulfonic additives which improve the flow properties of the 
cement slurry. 
"Polyamido-sulfonic", as used herein, refers to water-soluble polymers of 
N-sulfohydrocarbon-substituted acrylamides. 
As used herein, the terms "improve the flow properties" or 
"flow-property-improving" are intended to describe the manner in which the 
polyamido-sulfonic additive compositions of the present invention 
facilitate or render more efficient the pumping of cement slurries, 
particularly the pumping of well cement slurries during primary cementing 
operations. This action is apparently due primarily to a reduction in the 
frictional drag experienced by the cement slurry while it is being pumped 
or moved through a confining passageway, but it is not intended to limit 
the described action to such a friction reducing effect, since other 
effects may also play a role. 
The term "turbulence-inducing" is intended to describe the effect of the 
polyamido-sulfonic additive compositions of the present invention in 
promoting the departure of a moving cement slurry from laminar flow to 
turbulent flow. The slurry in such a state of flow no longer moves in 
laminae aligned along the confining conduit, but experiences a 
disorganized flow characterized by eddies and disturbances. The 
flow-property-improving and turbulence-inducing additives of the present 
invention reduce the apparent viscosity of a cement slurry, which in turn 
reduces the flow rate required to cause turbulent flow. Thus, the 
promotion of turbulent flow may take place simply as a reduction in the 
amount of pumping pressure or volume necessary to induce a state of 
turbulent flow for a particular cement slurry under specific pumping 
conditions, below that which would be required if the turbulence-inducing 
additive were omitted from the cement slurry composition. 
In addition, since the polyamido-sulfonic flow-property-improving additives 
of the present invention reduce the apparent viscosity of a cement slurry 
to which they are added, it is possible to reduce the total aqueous 
content of the slurry, thus often obtaining greater compressive strengths 
in the monolithic solid resulting from setting of the cement; or, 
concomitantly, it is possible to increase the total solids content of the 
aqueous cement slurry while still maintaining the original apparent 
viscosity thereof. This latter possibility is of importance where 
increased total solids handling or throughput in a cement slurry 
transporting operation is especially desired. 
The term "aqueous hydraulic cement slurry" as employed herein is also 
intended to include aqueous suspensions or slurries of solids constituting 
raw materials, precursors, or intermediate materials used in the 
preparation or manufacture of hydraulic cements as hereinafter defined. 
Thus, the present invention includes improving the flow properties of 
aqueous slurries of materials transported or handled during conventional 
wet processing of cement. This improvement allows suspension or greater 
quantities of solids in the water being used as a vehicle to transport and 
intermix the solids during wet processing. The result is an improved 
efficiency of operation in the form of an increased throughput of total 
solids being processed. Moreover, the effectively reduced total water 
content results in improved efficiency during the step of kiln heating or 
calcining of the cement precursor solids, since less energy is consumed to 
remove the reduced water content during the step of heating. 
Thus, most industrial processes, especially in the construction industry, 
which entail the handling or transport of aqueous hydraulic cement 
slurries, are susceptible to improvement by the method of the present 
invention, which comprises addition to such aqueous hydraulic cement 
slurries of a polyamido-sulfonic compound as hereinafter described, 
whereby the flow properties of the slurry are improved. This flow property 
improvement may take the form of an increased solids content of the slurry 
capable of being handled at a given expenditure of pumping energy, or may 
take the form of an increased throughput of total slurry at a given 
expenditure of pumping energy. 
Techniques for drilling and completing wells, particularly gas and oil 
wells, are well-established. Of chief concern here are those wells which 
are drilled from the surface of the earth to some subterranean formation 
containing a fluid mineral which it is desired to recover. After the 
fluid-containing geologic formation is located by investigation, a 
bore-hole is drilled through the overlying layers of the earth's crust to 
the fluid-containing geologic formation in order to permit recovery of the 
fluid mineral contained therein. A casing is then secured in position 
within the bore-hole to insure permanence of the bore-hole and to prevent 
entry into the well of a fluid from a formation other than the formation 
which is being tapped. This well casing is usually cemented in place by 
pumping a cement slurry downwardly through the well bore-hole, which is 
usually accomplished by means of conducting tubing within the well casing. 
The cement slurry flows out of the open lower end of the casing at the 
well bottom and then upwardly around the casing in the annular space 
between the outer wall of the casing and the wall of the well bore-hole. 
The drilling process which produces the bore-hole will usually leave 
behind on the wall of the bore-hole produced, a drilling fluid filter cake 
of mud-like material. This material is a barrier to the formation of 
proper bonding by any cement composition employed to produce an 
impermeable bond between the casing and the well wall. As a result, 
cementing operations have often proven inadequate, permitting fluids from 
other formations to migrate into the producing formation, and vice versa. 
Prior art solutions to this problem have included washing away the filter 
cake from the well wall prior to the cementing operation. However, the 
washing liquids themselves have introduced new problems, including reduced 
permeability of the producing formation. 
Nevertheless, an effective cementing operation requires that the drilling 
fluid filter cake be removed from the well bore wall and replaced by the 
cement slurry in order to permit the formation of a solid layer of 
hardened and cured cement between the casing and the geologic formations 
through which the well bore-hole passes. It has been recognized in the art 
that removal of the drilling fluid filter cake may be accomplished by a 
sufficiently high flow rate for the cement slurry during its injection 
into the well bore-hole. Such a high flow rate will usually occur as 
turbulent flow. 
The flow properties of cement slurries are also important during primary 
well cementing operations in other respects. The pressure drop in the 
annulus being cemented which results from friction will increase both the 
hydraulic horsepower required to move the cement slurry into place in a 
given time period, as well as the hydrostatic pressure exerted on the 
producing formation. Moreover, some investigators have felt that obtaining 
actual turbulent flow of the cement slurry is not necessary to remove the 
drilling fluid filter cake, and that high flow rates are sufficient where 
the drilling fluid has low gel strength and there is good centralization 
(concentric placement of the well casing within the well bore-hole). 
Consequently, the present invention is directed to use of cementing 
compositions having improved flow properties, including, but not limited 
to, adaptability to turbulent, especially high turbulent flow. 
Prior to the discovery of flow-property-improving, especially 
turbulence-inducing additives for well cement compositions, achieving high 
flow rate and turbulent flow for conventional cement slurries presented a 
number of problems not normally encountered with less viscous fluids. 
Inducing turbulence by control of flow rate alone has required a certain 
minimum velocity, which in turn is dependent upon maintaining a certain 
minimum pressure. Particularly, where the turbulence induced is sufficient 
to assure removal of drilling fluid filter cake, additional pumping 
capacity and very high pressure levels are required. Producing high flow 
rates has, of course, required the same measures. These required pressure 
levels, especially for deep walls, have often exceeded the pressure at 
which many subterranean formations break down, thus giving rise to a 
problem of lost circulation. It also may happen that the required pressure 
level exceeds the capacity of the pumping equipment or the endurance of 
the well drilling and associated apparatus. 
The present invention facilitates pumping of cement slurries at high flow 
rates and permits pumping of cement slurries in turbulent flow at 
significantly lower flow rates than would be possible using conventional 
cement slurry compositions, by adding to the said cement slurries a 
flow-property-improving and turbulence-inducing agent. The lower flow 
rates required for turbulence result in a corresponding reduction in the 
pump pressures required to force the cement slurry into place in the 
desired manner. Correspondingly, higher flow rates may be achieved with a 
reduced amount of required pressure and pumping capacity. 
The present invention also permits increased use of fluid-loss control 
agents which have a viscosity-increasing effect on cement slurries with 
which they are employed. This thickening tendency otherwise requires use 
of only small amounts of fluid-loss control agents to avoid problems in 
pumping of an overly viscous cement slurry. Use of the 
flow-property-improving and turbulence-inducing additives of the present 
invention in conjunction with fluid-loss control agents produces a cement 
slurry having desirable flow properties, yet containing adequate 
quantities of the fluid-loss control agent. 
2. Description of the Prior Art 
U.S. Pat. No. 3,359,225 discloses an additive for Portland-type cements 
comprising polyvinylpyrrolidone and the sodium salt of naphthalene 
sulfonate condensed with formaldehyde. The additive reduces the friction 
encountered as the cement is flowed or pumped into place, and also permits 
the utilization of decreased quantities of water in the cement mixture. 
Harrison - U.S. Pat. No. 3,409,080 discloses an aqueous hydraulic cement 
slurry containing an O,O-alkylene-O', O'-alkylene pyrophosphate-urea 
pyrolysis product and a water-soluble, water-dispersible polymeric 
material. The cement composition has improved properties whereby it may be 
injected in a state of turbulence without the expenditure of the amount of 
additional energy usually required to attain such a state. Kucera -- U.S. 
Pat. No. 3,465,824 discloses an aqueous hydraulic cement slurry containing 
a bisulfite-modified phenol-formaldehyde condensation product which serves 
as a turbulence-inducer to the slurry while being moved in a confined 
passageway. Hook et al. -- U.S. Pat. No. 3,465,825 discloses an aqueous 
cement slurry containing a turbulence-inducing agent comprising the 
lithium salt of the condensation product of mononaphthalene sulfonic acid 
and formaldehyde. Scott et al. -- U.S. Pat. No. 3,511,314 discloses an 
aqueous hydraulic cement slurry containing a turbulence-inducing, 
fluid-loss control agent consisting of the reaction product of (1) an 
amino compound selected from the group consisting of 
polyalkylenepolyamines, polyalkylenimines, and their mixtures, and (2) an 
acidic compound selected from the group consisting of carboxylic acids, 
sulfonic acids, polymers having a carboxyl substituent, and polymers 
having a sulfonate substituent. Messenger -- U.S. Pat. No. 3,558,335 
discloses cement compositions comprising hydraulic cement in admixture 
with a turbulence-inducer and silica or diatomaceous earth particles. A 
number of known turbulence-inducers are set out, any of which may be 
employed in the compositions disclosed. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there are provided methods of 
cementing, particularly well cementing, and of cement handling, which 
employ or are applied to cementing compositions comprising hydraulic 
cement, water, and from about 0.01 to about 5.0% by weight of the cement 
of a flow-property-improving and turbulence-inducing additive comprising a 
polyamido-sulfonic compound. Preferably, this composition contains from 
about 0.1 to about 2.0% by weight (based on dry weight of cement) of the 
polyamido-sulfonic compound additive. 
The polyamido-sulfonic compounds employed as flow-property-improving and 
turbulence-inducing additives for cement compositions employed in cement 
operations and subject to cement handling methods of the present invention 
may be represented by the following formula 
##STR1## 
wherein R.sub.1 is hydrogen or methyl; R.sub.2, R.sub.3, R.sub.4, and 
R.sub.5 are each independently selected from the group consisting of 
hydrogen, phenyl, straight or branched alkyl of from one to twelve carbon 
atoms, and cycloalkyl of up to six carbon atoms; R.sub.6 is straight or 
branched alkyl of from one to twelve carbon atoms, cycloalkyl of up to six 
carbon atoms, phenyl, or is absent; A is hydrogen, alkali metal ion, or 
ammonium; and n is an integer of from 2 to about 100, such that the weight 
average molecular weight of the polyamido-sulfonic compound is from about 
200 to about 10,000, and preferably from about 200 to about 1,500. 
A particularly preferred polyamido-sulfonic compound for use in the present 
invention is polymeric 2-acrylamido-2-methylpropane sulfonic acid 
comprising recurring units of the following formula: 
##STR2## 
The polyamido-sulfonic compounds used in the present invention may be 
prepared by way of a number of conventional polymerization routes, and 
consequently any such method giving satisfactory yields of acceptably pure 
product will be suitable. 
The methods of the present invention may employ or be applied to any type 
of hydraulic cement. Hydraulic cement is defined as any cement which will 
set or cure under the action of water, and is intended to include all 
mixtures of lime, silica and alumina, or of lime and magnesia, silica, and 
alumina and iron oxide. Hydraulic cements include hydraulic limes, 
grappier cements, pozzolan cements, natural cements, and portland cements. 
Pozzolan cements include slag cements made from slaked lime and granulated 
blast furnace slag. Among these hydraulic cements, the portland cements 
are preferred, chiefly because of their superior strength characteristics. 
The term portland cement is intended to include any cement regarded in the 
cementing art as a portland cement, usually as defined by standard 
reference works. The precise composition of any one particular portland 
cement will vary from another, but generally portland cements are produced 
by mixing and grinding together a calcareous and an argillaceous material, 
kiln heating the mixture (1350.degree. to 1800.degree. C.) until 
vitrification begins, pulverizing the clinker thus produced and mixing the 
same with a small amount of gypsum. The portland cements may be ground to 
any desired particle size, and grading of portland cements is on the basis 
of the specific surface of the cement, which will range between 1200 and 
2600 square centimeters per gram. Grading is also based on the amount of 
cement particles retained on a No. 325 Screen, U.S. Sieve Series. Thus, 
preferred oil well cements have a specific surface of about 1480 square 
centimeters per gram and about 85% by weight passes through a No. 325 
Screen. 
The hydraulic cement may be employed alone in preparing the cementing 
composition merely being admixed with water and the 
flow-property-improving and turbulence-inducing additive, or it may have 
additionally incorporated therein any of a number of conventional cement 
additives. For example, the cement may include a minor portion, up to 
about 2.0% by weight of dry cement, of a retarder composition. Such an 
additive is preferred for oil well cements, since cementing operations are 
conducted under ambient well bottom temperatures which can exceed about 
200.degree. F. Examples of conventional retarder compositions include 
carboxymethylhydroxyethyl cellulose, borax, dehydrated borax, calcium 
lignosulfonate and ferrochrome lignosulfonate. 
Fluid-loss control agents may be employed, as previously discussed. 
Well-known fluid-loss agents include such materials as 
polystyrenesulfonate, polyvinylpyrrolidone, polyvinyl alcohol, 
polyvinylacetate, and carboxymethylhydroxyethyl cellulose. 
Weighting components comprising inert materials such as barite and ilmenite 
are often employed. Silica may be employed to retard high temperature 
strength retrogression. 
Other known additives conventionally employed with cementing compositions 
may be employed with the cementing compositions employed with the methods 
of this invention, and in amounts sufficient to produce the intended 
modification of the cementing composition characteristics for which any 
additive was selected. More than one such additive, may of course, be 
employed at the same time. 
The dry hydraulic cement component of the cementing composition is admixed 
with water to form a pumpable, settable cement slurry. The cement sets to 
form a monolithic solid. The water which is employed to form this cement 
slurry may be any naturally occurring water suitable for preparing cement 
slurries. Particularly, brines of any concentration of calcium chloride or 
sodium chloride or their mixtures are suitable. Sea water may be employed 
and is thus convenient in offshore operations. The water should be 
employed in an amount which is sufficient to produce a pumpable, settable 
slurry. Excessive amounts of water may produce a weakened finally set 
cement which is lacking in homogeneity owing to the settling of the 
aggregate portions thereof. Proper amounts of water for producing a 
suitable cement slurry are described in technical publications, such as 
the bulletins of the American Petroleum Institute (API). Increasing water 
content in a cement composition effects a lowering of the plastic 
viscosity of the cement slurry, which results in the slurry being more 
readily pumped in turbulent flow. However, the water content should not be 
in excess of the amount which will give 4.0 ml. of supernatant water for a 
250 ml. sample of cement slurry which has been allowed to stand 
undisturbed in a 250 ml. graduated cylinder for a period of two hours. The 
type of hydraulic cement composition employed will also, of course, 
determine the amount of water required. Other factors are significant as 
well. For example, where silica is added to the cement composition, and 
high temperatures are encountered in the cementing operation (above about 
250.degree. F.), additional amounts of water will be required. Generally, 
the amount of water necessary to give a settable cement composition having 
the required characteristics, which contains the flow-property-improving 
and turbulence-inducing additive of the present invention will be an 
amount of from about 25% to about 60% by weight, based on the weight of 
dry hydraulic cement. 
Water content may be varied in order to effect a change in the density of 
the cement slurry. It is customary practice to employ a cement slurry 
which has a density at least as great as that of the drilling fluid used 
in the drilling operation. Thus, densified slurries may be produced by 
diminishing the amount of water which would otherwise be employed. 
The procedure for preparing the cementing compositions employed with the 
methods of the present invention does not require any particular sequence 
of steps. The polyamido-sulfonic flow-property-improving and 
turbulence-inducing additives of the present invention may be employed in 
the water-soluble acid, alkali metal or ammonium salt form, and simply 
added to the water which is used to produce the final cement slurry 
composition. When other conventional additives are employed, they may be 
incorporated into the final cement slurry compositions in any known 
suitable manner. 
The influence of the turbulence-inducing additives of the present invention 
on the rheological properties of the total cement slurry composition is 
susceptible to mathematical characterization. Expert opinion varies as to 
the correct theoretical model, and thus the proper mathematical 
characterization of the rheological properties of cement slurries. They 
have been treated according to the principles of Bingham plastic fluids as 
well as according to the Power Law concept. The mathematical formulation 
employed herein is based on Fann Viscometer readings, as will be described 
hereinafter. 
The behavior of cement slurries may be viewed as governed by the Power Law 
concept. For a mathematical characterization of this concept, two slurry 
parameters are determined: the flow behavior index (n') and the 
consistency index (K'). A Fann Viscometer may be used to make these 
determinations. The instrument readings at 600 and 300 r.p.m. are recorded 
and the values for n' and K' are then calculated as follows: 
##EQU1## 
where N is the extension factor of the torque spring of the particular Fann 
Viscometer instrument. 
The so-called Reynolds Number for a fluid moving through a conduit is the 
critical value at which the flowing fluid will begin to flow in 
turbulence. The Reynolds Number may be calculated according to the 
following equation: 
EQU N.sub.Re = 1.86 V.sup.(2n.spsp.'.sup.) .rho./K'(96/D).sup.n.spsp.' 
where: 
N.sub.Re is the Reynolds Number (dimensionless), 
V is the velocity, feet per second, 
.rho. is the slurry density, pounds per gallon, 
n' is the flow behavior index (dimensionless), 
K' is the consistency index, pound-seconds per square foot, 
D is the inside diameter of the pipe, inches. 
The velocity (V.sub.c) at which turbulence may begin is readily calculated 
from the following equation, which is derived from the equation for the 
Reynolds Number, and assumes a Reynolds Number of 2100: 
##EQU2## 
where the different elements of the equation have the same meaning as 
indicated above for the Reynolds Number equation. Where the conduit 
through which the cement slurry passes is the annulus between the well 
casing and the well wall, D = D.sub.O - D.sub.I, where D.sub.O is the 
outer inside diameter or hole size in inches, and D.sub.I is the inner 
pipe outside diameter in inches. 
The Power Law concept equation will give higher flow rates, or lower flow 
rates required to produce turbulence, where the Fann Viscometer readings 
are reduced.

EXAMPLE 
Fann Viscometer Readings for a Cementing Composition Containing 
Poly-(2-acrylamido-2-methylpropane-1-sulfonic acid) 
Flow-Property-Improving and Turbulence-Inducing Additive 
A 38% Class H (AP1 Class H cement has a fineness in the range of 1400-1600 
sq. cm./gram, and contains, in addition to free lime and alkali, the 
following compounds in the indicated proportions: tricalcium silicate -- 
52, dicalcium silicate -- 25, tricalcium aluminate -- 5, tetracalcium 
aluminoferrite -- 12, and calcium sulfate -- 33.) cement slurry was made 
up by adding tap water (228 ml.) to a Waring blender, dissolving the 
indicated amount of poly-(2-acrylamido-2-methylpropane-1-sulfonic acid) 
turbulence-inducing additive in the water, then mixing in the cement (600 
g.) at low speed. Molecular weight of the poly 
(2-acrylamido-2-methylpropane-1-sulfonic acid) was estimated to be less 
than 1000. The resultant slurry was then mixed at high speed for 35 
seconds. The slurry was then stirred at high speed on a laboratory 
gang-stirrer for 20 minutes. The viscosity of the slurry was then 
immediately measured on a Fann Viscometer equipped with a No. 1 spring. 
The instrument readings for various speeds were recorded and are 
illustrated in the table of values below. 
______________________________________ 
% Additive 
Turbulence- (based on Fann Viscosities at 
Inducing weight of Indicated R.P.M.'s 
Additive dry cement 
600 300 200 100 
______________________________________ 
Control.sup.XX 
-- 165 105.5 
87.5 65 
Poly-(2-acrylamido- 
2-methylpropane-1- 
0.5 114.5 48.5 
34.5 18.5 
sulfonic acid) 
0.25 104 88.5 
53.5 25.5 
______________________________________ 
.sup.XX Neat Class H cement. 
The polyamido-sulfonic flow-property-improving and turbulence-inducing 
additive of the present invention is employed to prepare cementing 
compositions which are readily pumped in turbulent flow during a cementing 
operation, particularly a well cementing operation, at a satisfactorily 
low pump rate. The additive is also used to advantage to reduce the 
pumping pressure required for a given flow rate, or to obtain a higher 
flow rate at a given pumping pressure, or to increase the solids content 
of a slurry capable of being transported at a given pumping pressure. The 
cementing composition employed with the methods of this invention which 
has improved flow properties and is easily flowed in turbulence is 
employed in the conventional cementing and cement handling operations 
comprising the methods of the present invention in the same manner as 
would a cementing composition which did not contain the 
flow-property-improving and turbulence-inducing additive, but which was 
otherwise the same composition. 
Obviously, many modifications and variations of the invention as 
hereinabove set forth can be made without departing from the essence and 
scope thereof, and only such limitations should be applied as are 
indicated in the appended claims.