METHODS FOR PRODUCING FLUID INVASION RESISTANT
CEMENT SLURRIES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to provisional application number
61/720,662 filed on October 31, 2012 and titled "Methods for Producing Fluid
Invasion Resistant Cement Slurries."
BACKGROUND
[0002] The embodiments herein relate to methods for producing
cement slurries that are resistant to fluid invasion when placed into a wellbore.
[0003] Subterranean formation operations (e.g., stimulation operations,
sand control operations, completion operations, etc.) often involve placing a
cement column around a casing or liner string in a wellbore. The cement column
is formed by pumping a cement slurry downhole through the casing and upwards
through the annular space between the outer casing wall and the formation face
of the wellbore. After placement, the cement slurry develops into a gel and then
cures in the annular space, thereby forming a column of hardened cement that,
inter alia, supports and positions the casing in the wellbore and bonds the
exterior surface of the casing to the subterranean formation. Among other
things, the cement column may keep fresh water zones from becoming
contaminated with produced fluids from within the wellbore. As used herein, the
term "fluid" refers to liquid phase and gas phase materials. The cement column
may also prevent unstable formations from caving in, thereby reducing the
chance of a casing collapse or a stuck drill pipe. Finally, the cement column
forms a solid barrier to prevent fluid loss to the formation, contamination of
production zones, or undesirable fluid invasion into the well. Therefore, the
degree of success of a subterranean formation operation depends, at least in
part, upon the successful cementing of the wellbore casing.
[0004] Fluid invasion into a cement column is a known problem
encountered in primary cementing operations. As used herein, the term
"primary cementing" refers to the process of placing a cement column around a
casing or liner string. Fluid invasion may occur before the cement slurry is
cured, which may be particularly damaging, or after the cement slurry is cured.
The trigger mechanism for fluid invasion may be the presence of an
underbalanced pressure (e.g., the pressure of a given depth inside the cement
column may be smaller than the formation pressure at that depth or nearby
depths). A number of other factors may also influence fluid invasion including,
but not limited to, properties of the subterranean formation and properties of the
cement slurry (e.g., rheological properties). As used herein, the term "fluid
invasion potential" is used to describe the tendency of fluid to invade a cement
slurry or column by any mechanism. When combined with buoyancy effects,
fluid invasion may result in the formation of channels within the cement column.
As used herein, the term "channel" refers to a defect in the quality of cement,
where the cement does not fully occupy the annulus between the casing and the
formation face. The channels may result in loss of integrity of the cement
column, failure of zonal isolation, and/or wellbore structural failure.
[0005] Because of the damaging effects of fluid invasion into a cement
column, a number of evaluation methods have been proposed to evaluate the
potential of fluid invasion, especially during the time in which the cement slurry
has not yet cured. These methods, however, may be oversimplified and not
properly capture multiple factors that may influence fluid invasion. As a result,
the predictive capabilities of such methods may be limited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The following figures are included to illustrate certain aspects of
the embodiments, and should not be viewed as exclusive embodiments. The
subject matter disclosed is capable of considerable modifications, alterations,
combinations, and equivalents in form and function, as will occur to those skilled
in the art and having the benefit of this disclosure.
[0007] FIG. 1 depicts an embodiment of a system configured for
delivering the fluid invasion resistant cement slurries of the embodiments
described herein to a downhole location.
DETAILED DESCRIPTION
[0008] The embodiments herein relate to methods for producing
cement slurries that are resistant to fluid invasion when placed into a wellbore.
Specifically, the embodiments herein relate to compatibility studies used to
predict fluid invasion potential at any particular point in time and at any
particular depth in a wellbore after cement placement in order to produce fluid
invasion resistant cement slurries.
[0009] The embodiments herein may be used to predict fluid invasion
into a cement column after primary well cementing using a normalized pressure
to determine the likelihood of fluid invasion of formation fluid into a cement
slurry column in a wellbore in a subterranean formation. As used herein, the
term "normalized pressure" refers to the ratio between the cement slurry
pressure inside the annulus and the subterranean formation pressure. Once the
normalized pressure is determined for a specific slurry, that cement slurry can
be manipulated to correct for fluid invasion potential. The embodiments
described herein may take into account one or more properties of the
subterranean formation itself and the cement slurry itself. Depending on the
particular application, some properties may be more instructive to determine the
potential for fluid invasion after primary cementing than other properties. One
of ordinary skill in the art, with the benefit of this disclosure, will recognize what
factors to consider for a particular application.
[0010] Some embodiments described herein provide methods of
cementing a subterranean wellbore. The methods comprise providing a wellbore
in a subterranean formation and providing a proposed cement slurry
formulation. Next, the normalized pressure of the proposed cement slurry
formulation is determined at a point along the wellbore length. If the normalized
pressure is in a range in which fluid invasion potential exists, the proposed
cement slurry formulation is manipulated, and one or more revised normalized
pressure is determined. The cement slurry may be manipulated and the
corresponding normalized pressure recalculated as many times as necessary
until an acceptable cement slurry formulation, herein referred to as "fluid
invasion resistant cement slurry," is found. Next, the fluid invasion resistant
cement slurry is introduced into the wellbore in the subterranean formation and
the cement is allowed to cure and form a cement sheath within the subterranean
formation. One of skill in the art will recognize that manipulation of the cement
slurry can take many forms. By way of non-limiting example, the amount of
cement retarder, accelerator, cementitious material, pozzolanic material, or
water may be changed.
I . Cement Slurry and Fluid Invasion Resistant Cement Slurry
[0011] In some embodiments, the cement slurry may comprise a base
fluid and a cementitious material. Any aqueous base fluid suitable for use in a
subterranean operation (e.g., drilling or completion operations) may be used in
the cement slurry described in some embodiments herein. Suitable base fluids
for use in the embodiments described herein may include, but are not limited to,
freshwater, saltwater (e.g., water containing one or more salts dissolved
therein), brine (e.g., saturated saltwater), seawater, and any combination
thereof. Generally, the base fluid may be from any source, provided, for
example, that it does not contain an excess of compounds that may undesirably
affect other components in the salt-tolerant cement slurry. In some
embodiments, the base fluid may be included in an amount sufficient to form a
pumpable slurry. In some embodiments, the base fluid in the cement slurry
may be foamed. In some embodiments, the base fluid may be included in the
cement slurry in an amount of about 40% to about 200% by weight of ("w/w")
the dry cementitious material. In other embodiments, the base fluid may be
included in an amount of about 30% to about 150% w/w of the dry cementitious
material.
[0012] The cementitious material may be any cementitious material
suitable for use in subterranean operations. In preferred embodiments, the
cementitious material is a hydraulic cement. Hydraulic cements harden by the
process of hydration due to chemical reactions to produce insoluble hydrates
(e.g., calcium hydroxide) that occur independent of the cement's water content
(i.e., hydraulic cements can harden even under constantly damp conditions).
Thus, hydraulic cements are preferred because they are capable of hardening
regardless of the water content of a particular subterranean formation. Suitable
hydraulic cements include, but are not limited to Portland cement; Portland
cement blends (e.g., Portland blast-furnace slag cement and/or expansive
cement); non-Portland hydraulic cement (e.g., super-sulfated cement, calcium
aluminate cement, and/or high magnesium-content cement); and any
combination thereof. In some embodiments, the cementitious material is
present in an amount of about 20% to about 70% w/w of the salt-tolerant
cement slurry.
[0013] In some embodiments, the cement slurry may additionally
comprise a pozzolanic material. Pozzolanic materials may aid in increasing the
density and strength of the cementitious material. As used herein, the term
"pozzolanic material" refers to a siliceous material that, while not being
cementitious, is capable of reacting with calcium hydroxide (which may be
produced during hydration of the cementitious material). Because calcium
hydroxide accounts for a sizable portion of most hydrated hydraulic cements and
because calcium hydroxide does not contribute to the cement's properties, the
combination of cementitious and pozzolanic materials may synergistically
enhance the strength and quality of the cement. Any pozzolanic material that is
reactive with the cementitious material may be used in the embodiments
described herein. Suitable pozzolanic materials may include, but are not limited
to silica fume; metakaolin; fly ash; diatomaceous earth; calcined or uncalcined
diatomite; calcined fullers earth; pozzolanic clays; calcined or uncalcined
volcanic ash; bagasse ash; pumice; pumicite; rice hull ash; natural and synthetic
zeolites; slag; vitreous calcium aluminosilicate; and any combinations thereof.
An example of a suitable commercially-available pozzolanic material is
POZMIX®-A available from Halliburton Energy Services, Inc. of Houston, TX. In
some embodiments, the pozzolanic material may be present in an amount of
about 5% to about 60% w/w of the dry cementitious material. In preferred
embodiments, the pozzolanic material is present in an amount of about 5% to
about 30% w/w of the dry cementitious material.
[0014] In some embodiments, the cement slurry may further comprise
any cement additive capable of use in a subterranean operation. Cement
additives may be added to the cement slurry to modify the characteristics of the
slurry or cured cement. Such additives include, but are not limited to, a cement
accelerator; a cement retarder; a fluid-loss additive; a cement dispersant; a
cement extender; a weighting agent; a lost circulation additive; and any
combinations thereof. The cement additives may be in any form, including
powder form or liquid form.
[0015] In some embodiments, cement slurry may comprise a base fluid,
a cementitious material, and any of one, more than one, or all of a pozzolanic
material and a cement additive. The properties of the cement slurry and the
properties of the subterranean formation into which the cement slurry is to cure
are used to determine the normalized pressure as described herein. Based on
the value of the normalized pressure, the cement slurry is then manipulated
either by adding, removing or adjusting the presence or absence or amount of
the base fluid, cementitious material, pozzolanic material, if present, or cement
additive, if present, to produce a fluid invasion resistant cement slurry particular
to the formation at issue. As used herein, the term "fluid invasion resistant
cement" refers to a cement slurry made in accordance with the teachings of the
present disclosure that has a normalized pressure greater than 1 along the
entire well depth before the cement slurry is cured. I n some embodiments, a
safety margin may be recommended and the normalized pressure may be
greater than 1 plus the safety margin. The safety margin may vary depending
on the properties of the proposed cement slurry, on the properties of the
formation, and on the geometry of the well, and may, in some embodiments
range from a lower limit of about 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35 to an upper
limit of about 0.6, 0.55, 0.5, 0.45, 0.4, and 0.35. I n some embodiments, it may
be preferred that the pressure in the cement column be compared to the
pressure in the formation. I n some embodiments, the components of the
cement slurry may be adjusted, removed, and/or added to produce the fluid
invasion resistant cement slurry.
II. Normalized Pressure
[0016] I n some embodiments, a normalized pressure may be
determined for predicting the potential of fluid invasion into a cement column
after primary well cementing. The normalized pressure describes the potential
of fluid invasion into a cement column after placement of the cement slurry into
a subterranean formation at any particular point in time and depth of the
formation. The normalized pressure is a function of time after cement
placement and depth of the wellbore and may be expressed at a point along the
wellbore. Use of the term "at a point" may represent either a particular wellbore
depth location, the entire wellbore depth, or any set of points in the wellbore at
any instance of time after placement of the proposed cement slurry or the fluid
invasion resistant cement slurry, as described herein. The normalized pressure
is determined based on one or more normalized pressure parameters of the
proposed cement slurry or the fluid invasion resistant cement slurry and the
pressure of the subterranean formation into which the slurries are to be placed.
Generally, the normalized pressure accounts for the interaction of the formation
and the cement slurry, which may contribute to fluid invasion. The normalized
pressure may vary depending on the depth of the well, the conditions in the
well, the conditions of the cement slurry, the conditions of the formation, and
the like.
[0017] Inclusion of a normalized pressure may advantageously provide
for, in some embodiments, (1) invariant parameters for fluid invasion, (2) the
same parameters and variant parameters for fluid invasion, and/or (3) inclusion
of transient elasto-viscoplastic effects.
[0018] Suitable normalized pressure parameters for use in determining
the normalized pressure may include, but are not limited to, those listed in Table
1.
TABLE 1

[0019] One skilled in the art with the benefit of this disclosure will
understand the relationship between the various nonlimiting normalized pressure
parameters in order to determine the normalized pressure of the cement slurry.
The normalized pressure takes into account properties of the cement slurry and
the subterranean formation to determine the potential of fluid invasion. The
cement slurry pressure inside the annulus is determined using the mass balance,
momentum balance, compressibility, shrinkage, shear rate, and rheological
properties of the cement. The compressibility of the cement slurry is determined
using the slightly compressible material hypothesis, known to those of ordinary
skill in the art. The chemical shrinkage of the cement slurry, known to those of
ordinary skill in the art, can also be used in the embodiments described herein.
The nonlimiting rheological properties are used as inputs to determine the shear
stress. Examples of nonlimiting rheological properties may include shear stress;
relaxation time; retardation time; viscosity; structural shear modulus; structural
viscosity; steady shear flow; steady-state viscosity; consistency index; power
law index; static yield stress; dynamic yield stress; steady-state viscosity of an
unstructured state; steady-state viscosity of a structured state; equilibrium
time; and any combinations thereof.
[0020] The choice of a normalized pressure parameter for determining
the normalized pressure may be dependent upon the composition of the cement
slurry, both chemical and concentration (e.g., the concentration and structure of
the various chemicals and additives in the cement slurry). One skilled in the art,
with the benefit of this disclosure should be able to identify a parameter to
include to determine the normalized pressure of a particular cement slurry. For
example, a summation of all of the parameters listed in Table 1 may be one of
the more versatile models. This may advantageously allow for taking into
account a comprehensive view of the cement properties to ensure that the
normalized pressure is highly accurate. As used herein, the "normalized
pressure" refers to the potential of fluid invasion into the cement column after
primary well cementing as determined by the equation shown in Table 2.
TABLE 2
[0021] The pressure inside the cement, P, is determined using any or all
of the normalized pressure parameters listed in Table 1. The formation pressure
is determined based on the precise subterranean formation in front of which the
cement slurry is meant to be placed. The formation properties suitable for use
in determining the normalized pressure may include, but are not limited to,
permeability, capillary pressure, swelling capacity, stress, well dimensions, and
density. The formation properties for use in determining the normalized
pressure may be obtained by any known method in the industry.
[0022] The normalized pressure is determined based on the normalized
pressure parameters for the cement slurry and the formation. If the normalized
pressure is greater than 1 along the entire well depth before the cement is
cured, the risk of fluid invasion is drastically reduced. Therefore, manipulation
of the cement slurry may not be required because the cement slurry is a fluid
invasion resistant slurry. However, in some embodiments, the cement slurry
may be manipulated to further enhance the normalized pressure, such as by a
safety margin, so that the already fluid invasion resistant cement is more
resistant to fluid invasion than the cement slurry without manipulation.
[0023] If the normalized pressure is less than 1, the potential for fluid
invasion into the cement column after primary well cementing is high.
Therefore, according to the embodiments described herein, the cement slurry is
manipulated either by the addition, removal, substitution, or concentration
adjustment of the base fluid, cementitious materials, and any additional
components such as pozzolanic material or cement additives to produce a fluid
invasion resistant cement slurry. In some embodiments, the manipulated
cement is again evaluated to determine a revised normalized pressure. If
necessary, the cement is again manipulated and another revised normalized
pressure is determined until a fluid invasion resistant cement slurry is obtained.
The process may be repeated as many times as necessary in order to obtain a
fluid resistant cement slurry.
[0024] In various embodiments, systems configured for preparing,
transporting, and delivering the fluid invasion resistant cement slurry described
herein to a downhole location are described. In various embodiments, the
systems can comprise a pump fluidly coupled to a tubular (e.g., a casing, drill
pipe, production tubing, coiled tubing, etc.) extending into a wellbore
penetrating a subterranean formation, the tubular may be configured to circulate
or otherwise convey a fluid invasion resistant cement slurry. The pump may be,
for example, a high pressure pump or a low pressure pump, which may depend
on, inter alia, the viscosity and density of the fluid invasion resistant cement
slurry, the type of the cementing operation, and the like.
[0025] I n some embodiments, the systems described herein may
further comprise a mixing tank arranged upstream of the pump and in which the
fluid invasion resistant cement slurry is formulated. I n various embodiments,
the pump (e.g., a low pressure pump, a high pressure pump, or a combination
thereof) may convey the fluid invasion resistant cement slurry from the mixing
tank or other source of the fluid invasion resistant cement slurry to the tubular.
I n other embodiments, however, the fluid invasion resistant cement slurry can
be formulated offsite and transported to a worksite, in which case the fluid
invasion resistant cement slurry may be introduced to the tubular via the pump
directly from a transport vehicle or a shipping container (e.g., a truck, a railcar,
a barge, or the like) or from a transport pipeline. I n yet other embodiments, the
cementing fluid may be formulated on the fly at the well site where components
of the cementing fluid are pumped from a transport (e.g., a vehicle or pipeline)
and mixed during introduction into the tubular. I n any case, the fluid invasion
resistant cement slurry may be drawn into the pump, elevated to an appropriate
pressure, and then introduced into the tubular for delivery downhole.
[0026] FIGURE 1 shows an illustrative schematic of a system that can
deliver the fluid invasion resistant cement slurries described herein, according to
one or more embodiments. I t should be noted that while FIGURE 1 generally
depicts a land-based system, it is to be recognized that like systems may be
operated in subsea locations as well. As depicted in FIGURE 1, system 1 may
include mixing tank 10, in which a fluid invasion resistant cement slurry may be
formulated. Again, in some embodiments, the mixing tank 10 may represent or
otherwise be replaced with a transport vehicle or shipping container configured
to deliver or otherwise convey the cementing fluid to the well site. The fluid
invasion resistant cement slurry may be conveyed via line 12 to wellhead 14,
where the fluid invasion resistant cement slurry enters tubular 16 (e.g., a
casing, drill pipe, production tubing, coiled tubing, etc.), tubular 16 extending
from wellhead 14 into wellbore 22 penetrating subterranean formation 18.
Upon being ejected from tubular 16, the fluid invasion resistant cement slurry
may subsequently return up the wellbore in the annulus between the tubular 16
and the wellbore 22 as indicated by flow lines 24. In other embodiments, the
cementing fluid may be reverse pumped down through the annulus and up
tubular 16 back to the surface, without departing from the scope of the
disclosure. Pump 20 may be configured to raise the pressure of the fluid
invasion resistant cement slurry to a desired degree before its introduction into
tubular 16 (or annulus). It is to be recognized that system 1 is merely
exemplary in nature and various additional components may be present that
have not necessarily been depicted in FIGURE 1 in the interest of clarity. Nonlimiting
additional components that may be present include, but are not limited
to, supply hoppers, valves, condensers, adapters, joints, gauges, sensors,
compressors, pressure controllers, pressure sensors, flow rate controllers, flow
rate sensors, temperature sensors, and the like.
[0027] One skilled in the art, with the benefit of this disclosure, should
recognize the changes to the system described in FIGURE 1 to provide for other
cementing operations (e.g., squeeze operations, reverse cementing (where the
cement is introduced into an annulus between a tubular and the wellbore and
returns to the wellhead through the tubular), and the like).
[0028] I t is also to be recognized that the disclosed fluid invasion
resistant cement slurry may also directly or indirectly affect the various
downhole equipment and tools that may come into contact with the treatment
fluids during operation. Such equipment and tools may include, but are not
limited to, wellbore casing, wellbore liner, completion string, insert strings, drill
string, coiled tubing, slickline, wireline, drill pipe, drill collars, mud motors,
downhole motors and/or pumps, surface-mounted motors and/or pumps,
centralizers, turbolizers, scratchers, floats (e.g., shoes, collars, valves, etc.),
wellbore projectiles (e.g., wipers, plugs, darts, balls, etc.), logging tools and
related telemetry equipment, actuators (e.g., electromechanical devices,
hydromechanical devices, etc.), sliding sleeves, production sleeves, plugs,
screens, filters, flow control devices (e.g., inflow control devices, autonomous
inflow control devices, outflow control devices, etc.), couplings (e.g., electrohydraulic
wet connect, dry connect, inductive coupler, etc.), control lines (e.g.,
electrical, fiber optic, hydraulic, etc.), surveillance lines, drill bits and reamers,
sensors or distributed sensors, downhole heat exchangers, valves and
corresponding actuation devices, tool seals, packers, cement plugs, bridge plugs,
and other wellbore isolation devices, or components, and the like. Any of these
components may be included in the systems generally described above and
depicted in FIGURE 1.
[0029] Embodiments disclosed herein include:
[0030] A. A method comprising: providing a wellbore in a
subterranean formation having a wellbore length; providing a proposed cement
slurry formulation; calculating a normalized pressure at a point along the
wellbore length based on properties of the proposed cement slurry formulation
and properties of the wellbore in the subterranean formation; manipulating the
proposed cement slurry formulation based on the normalized pressure so as to
produce a fluid invasion resistant cement slurry; introducing the fluid invasion
resistant cement slurry into the wellbore; and cementing the fluid invasion
resistant cement slurry in the wellbore.
[0031] B. A method comprising: providing a wellbore in a
subterranean formation having a wellbore length; providing a proposed cement
slurry formulation; calculating a normalized pressure at a point along the
wellbore length based on properties of the proposed cement slurry formulation
and properties of the wellbore in the subterranean formation; manipulating the
proposed cement slurry formulation based on the normalized pressure so as to
produce a fluid invasion resistant cement slurry; wherein the properties of the
proposed cement slurry formulation used to determine the normalized pressure
are selected from the group consisting of: mass balance; momentum balance;
compressibility; shrinkage; shear rate; rheological properties; and any
combinations thereof; introducing the fluid invasion resistant cement slurry into
the wellbore in the subterranean formation; and cementing the fluid invasion
resistant cement slurry in the wellbore in the subterranean formation.
[0032] C. A method comprising: providing a wellbore in a
subterranean formation having a wellbore length; providing a proposed cement
slurry formulation; calculating a normalized pressure at a point along the
wellbore length based on properties of the proposed cement slurry formulation
and properties of the wellbore in the subterranean formation; manipulating the
proposed cement slurry formulation based on the normalized pressure so as to
produce a fluid invasion resistant cement slurry; wherein the properties of the
proposed cement slurry formulation used to determine the normalized pressure
are selected from the group consisting of: mass balance; momentum balance;
compressibility; shrinkage; shear rate; rheological properties; and any
combinations thereof; wherein the rheological properties are selected from the
group consisting of: shear stress; relaxation time; retardation time; viscosity;
structural shear modulus; structural viscosity; steady shear flow; steady-state
viscosity; consistency index; power law index; static yield stress; dynamic yield
stress; steady-state viscosity of an unstructured state; steady-state viscosity of
a structured state; equilibrium time; and any combinations thereof; introducing
the fluid invasion resistant cement slurry into the wellbore in the subterranean
formation; and cementing the fluid invasion resistant cement slurry in the
wellbore in the subterranean formation.
[0033] Each of embodiments A, B, and C may have one or more of
the following additional elements in any combination:
[0034] Element 1: Wherein the normalized pressure is determined at
multiple points along the wellbore length of the wellbore.
[0035] Element 2: Wherein the steps of: calculating a normalized
pressure at a point along the wellbore length and manipulating the proposed
cement slurry formulation based on the normalized pressure are repeated at
least once so as to produce the fluid invasion resistant cement slurry.
[0036] Element 3: Wherein the proposed cement slurry formulation
comprises a base fluid and a cementitious material.
[0037] Element 4 : Wherein the proposed cement slurry formulation
is manipulated to produce the fluid invasion resistant cement slurry by altering
an amount of the cementitious material.
[0038] Element 5: Wherein the proposed cement slurry formulation
further comprises a pozzolanic material; a cement accelerator; a cement
retarder; a fluid-loss additive; a cement dispersant; a cement extender; a
weighting agent; a lost circulation additive; or any combinations thereof.
[0039] Element 6: Wherein the pozzolanic material is selected from
the group consisting of: silica fume; metakaolin; fly ash; diatomaceous earth;
calcined or uncalcined diatomite; calcined fullers earth; pozzolanic clays;
calcined or uncalcined volcanic ash; bagasse ash; pumice; pumicite; rice hull
ash; natural and synthetic zeolites; slag; vitreous calcium aluminosilicate; and
any combinations thereof.
[0040] Element 7: Wherein the properties of the proposed cement
slurry formulation used to determine the normalized pressure are selected from
the group consisting of: mass balance; momentum balance; compressibility;
shrinkage; shear rate; rheological properties; and any combinations thereof.
[0041] Element 8: Wherein the rheological properties of the
proposed cement slurry formulation used to determine the normalized pressure
are selected from the group consisting of: shear stress; relaxation time;
retardation time; viscosity; structural shear modulus; structural viscosity;
steady shear flow; steady-state viscosity; consistency index; power law index;
static yield stress; dynamic yield stress; steady-state viscosity of an
unstructured state; steady-state viscosity of a structured state; equilibrium
time; and any combinations thereof.
[0042] Element 9: Wherein the properties of the wellbore in the
subterranean formation used to determine the normalized pressure are selected
from the group consisting of: permeability; capillary pressure; swelling capacity;
stress; well dimensions; density of the formation; and any combinations thereof.
[0043] By way of non-limiting example, exemplary combinations
applicable to A, B, C include: A with 1, 5, and 7; B with 2, 8, and 9; and C with
3, 4, 5, and 6.
[0044] Therefore, the embodiments described herein are well adapted
to attain the ends and advantages mentioned as well as those that are inherent
therein. The particular embodiments disclosed above are illustrative only, as
they may be modified and practiced in different but equivalent manners
apparent to those skilled in the art having the benefit of the teachings herein.
Furthermore, no limitations are intended to the details of construction or design
herein shown, other than as described in the claims below. It is therefore
evident that the particular illustrative embodiments disclosed above may be
altered, combined, or modified and all such variations are considered within the
scope and spirit of the disclosure. The embodiments illustratively disclosed
herein suitably may be practiced in the absence of any element that is not
specifically disclosed herein and/or any optional element disclosed herein. While
compositions and methods are described in terms of "comprising," "containing,"
or "including" various components or steps, the compositions and methods can
also "consist essentially of" or "consist of" the various components and steps.
All numbers and ranges disclosed above may vary by some amount. Whenever
a numerical range with a lower limit and an upper limit is disclosed, any number
and any included range falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to about b," or,
equivalently, "from approximately a to b," or, equivalently, "from approximately
a-b") disclosed herein is to be understood to set forth every number and range
encompassed within the broader range of values. Also, the terms in the claims
have their plain, ordinary meaning unless otherwise explicitly and clearly defined
by the patentee. Moreover, the indefinite articles "a" or "an," as used in the
claims, are defined herein to mean one or more than one of the element that it
introduces. If there is any conflict in the usages of a word or term in this
specification and one or more patent or other documents that may be
incorporated herein by reference, the definitions that are consistent with this
specification should be adopted.

CLAIMS
The invention claimed is:
1. A method comprising:
providing a wellbore in a subterranean formation having a wellbore
length;
providing a proposed cement slurry formulation;
calculating a normalized pressure at a point along the wellbore length
based on properties of the proposed cement slurry formulation and properties of
the wellbore in the subterranean formation;
manipulating the proposed cement slurry formulation based on the
normalized pressure so as to produce a fluid invasion resistant cement slurry;
introducing the fluid invasion resistant cement slurry into the wellbore;
and
cementing the fluid invasion resistant cement slurry in the wellbore.
2. The method of claim 1, wherein the normalized pressure is determined at
multiple points along the wellbore length of the wellbore.
3. The method of claim 1, wherein the steps of: calculating a normalized
pressure at a point along the wellbore length and manipulating the
proposed cement slurry formulation based on the normalized pressure are
repeated at least once so as to produce the fluid invasion resistant cement
slurry.
4. The method of claim 1, wherein the proposed cement slurry formulation
comprises a base fluid and a cementitious material.
5. The method of claim 2, wherein the proposed cement slurry formulation is
manipulated to produce the fluid invasion resistant cement slurry by
altering an amount of the cementitious material.
6. The method of claim 2, wherein the proposed cement slurry formulation
further comprises a pozzolanic material; a cement accelerator; a cement
retarder; a fluid-loss additive; a cement dispersant; a cement extender; a
weighting agent; a lost circulation additive; or any combinations thereof.
7. The method of claim 6, wherein the pozzolanic material is selected from
the group consisting of: silica fume; metakaolin; fly ash; diatomaceous
earth; calcined or uncalcined diatomite; calcined fullers earth; pozzolanic
clays; calcined or uncalcined volcanic ash; bagasse ash; pumice;
pumicite; rice hull ash; natural and synthetic zeolites; slag; vitreous
calcium aluminosilicate; and any combinations thereof.
8. The method of claim 1, wherein the properties of the proposed cement
slurry formulation used to determine the normalized pressure are selected
from the group consisting of: mass balance; momentum balance;
compressibility; shrinkage; shear rate; rheological properties; and any
combinations thereof.
9. The method of claim 8, wherein the rheological properties of the proposed
cement slurry formulation used to determine the normalized pressure are
selected from the group consisting of: shear stress; relaxation time;
retardation time; viscosity; structural shear modulus; structural viscosity;
steady shear flow; steady-state viscosity; consistency index; power law
index; static yield stress; dynamic yield stress; steady-state viscosity of
an unstructured state; steady-state viscosity of a structured state;
equilibrium time; and any combinations thereof.
10. The method of claim 1, wherein the properties of the wellbore in the
subterranean formation used to determine the normalized pressure are
selected from the group consisting of: permeability; capillary pressure;
swelling capacity; stress; well dimensions; density of the formation; and
any combinations thereof.
11. A method comprising:
providing a wellbore in a subterranean formation having a wellbore
length;
providing a proposed cement slurry formulation;
calculating a normalized pressure at a point along the wellbore length
based on properties of the proposed cement slurry formulation and properties of
the wellbore in the subterranean formation;
manipulating the proposed cement slurry formulation based on the
normalized pressure so as to produce a fluid invasion resistant cement slurry;
wherein the properties of the proposed cement slurry formulation
used to determine the normalized pressure are selected from the group
consisting of: mass balance; momentum balance; compressibility; shrinkage;
shear rate; rheological properties; and any combinations thereof;
introducing the fluid invasion resistant cement slurry into the wellbore in
the subterranean formation; and
cementing the fluid invasion resistant cement slurry in the wellbore in the
subterranean formation.
12. The method of claim 11, wherein the proposed cement slurry formulation
comprises a base fluid and a cementitious material.
13. The method of claim 12, wherein the proposed cement slurry formulation
is manipulated to produce the fluid invasion resistant cement slurry by
altering an amount of the cementitious material.
14. The method of claim 12, wherein the proposed cement slurry formulation
further comprises a pozzolanic material; a cement accelerator; a cement
retarder; a fluid-loss additive; a cement dispersant; a cement extender; a
weighting agent; a lost circulation additive; or any combinations thereof.
15. The method of claim 11, wherein the rheological properties of the cement
slurry used to determine the normalized pressure are selected from the
group consisting of: shear stress; relaxation time; retardation time;
viscosity; structural shear modulus; structural viscosity; steady shear
flow; steady-state viscosity; consistency index; power law index; static
yield stress; dynamic yield stress; steady-state viscosity of an
unstructured state; steady-state viscosity of a structured state;
equilibrium time; and any combinations thereof.
16. The method of claim 11, wherein the properties of the wellbore in the
subterranean formation used to determine the normalized pressure are
selected from the group consisting of: permeability; capillary pressure;
swelling capacity; stress; well dimensions; density of the formation; and
any combinations thereof.
17. A method comprising:
providing a wellbore in a subterranean formation having a wellbore
length;
providing a proposed cement slurry formulation;
calculating a normalized pressure at a point along the wellbore length
based on properties of the proposed cement slurry formulation and properties of
the wellbore in the subterranean formation;
manipulating the proposed cement slurry formulation based on the
normalized pressure so as to produce a fluid invasion resistant cement slurry;
wherein the properties of the proposed cement slurry formulation
used to determine the normalized pressure are selected from the group
consisting of: mass balance; momentum balance; compressibility; shrinkage;
shear rate; rheological properties; and any combinations thereof;
wherein the rheological properties are selected from the group
consisting of: shear stress; relaxation time; retardation time; viscosity;
structural shear modulus; structural viscosity; steady shear flow; steady-state
viscosity; consistency index; power law index; static yield stress; dynamic yield
stress; steady-state viscosity of an unstructured state; steady-state viscosity of
a structured state; equilibrium time; and any combinations thereof;
introducing the fluid invasion resistant cement slurry into the wellbore in
the subterranean formation; and
cementing the fluid invasion resistant cement slurry in the wellbore in the
subterranean formation.
18. The method of claim 17, wherein the proposed cement slurry formulation
comprises a base fluid and a cementitious material.
19. The method of claim 18, wherein the proposed cement slurry formulation
further comprises a pozzolanic material; a cement accelerator; a cement
retarder; a fluid-loss additive; a cement dispersant; a cement extender; a
weighting agent; a lost circulation additive; or any combinations thereof.
20. The method of claim 17, wherein the properties of the wellbore in the
subterranean formation used to determine the normalized pressure are
selected from the group consisting of: permeability; capillary pressure;
swelling capacity; stress; well dimensions; density of the formation; and
any combinations thereof.