CA2378541C - Using of stokes law cement slurries for improved well cementation - Google Patents
Using of stokes law cement slurries for improved well cementation Download PDFInfo
- Publication number
- CA2378541C CA2378541C CA2378541A CA2378541A CA2378541C CA 2378541 C CA2378541 C CA 2378541C CA 2378541 A CA2378541 A CA 2378541A CA 2378541 A CA2378541 A CA 2378541A CA 2378541 C CA2378541 C CA 2378541C
- Authority
- CA
- Canada
- Prior art keywords
- cement
- density
- slurry
- slurries
- well
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/42—Compositions for cementing, e.g. for cementing casings into boreholes; Compositions for plugging, e.g. for killing wells
- C09K8/46—Compositions for cementing, e.g. for cementing casings into boreholes; Compositions for plugging, e.g. for killing wells containing inorganic binders, e.g. Portland cement
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
- C04B40/0028—Aspects relating to the mixing step of the mortar preparation
- C04B40/006—Aspects relating to the mixing step of the mortar preparation involving the elimination of excess water from the mixture
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/00034—Physico-chemical characteristics of the mixtures
- C04B2111/00068—Mortar or concrete mixtures with an unusual water/cement ratio
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/10—Compositions or ingredients thereof characterised by the absence or the very low content of a specific material
Abstract
A method for providing lower than normal API Class cement slurries for use in oil well cementing is disclosed. Rather than the use of any conventional density extenders for hydraulic cement, such as bentonite, only plain water is added to the selected normal API Class slurry to extend its density. The use of cement retarders, cement accelerators, or friction reducers for these purposes, but not for density extension, is contemplated also.
Description
USING OF STOKES LAW CEMENT SLURRIES FOR IMPROVED WELL
CEMENTATION
Background of the Invention In the operation of rotary drilling an oil or gas well, drilling fluid having a prescribed density is used during the drilling operation for several purposes including to balance the formation pressure which increases as the depth of the hole increases. Such drilling fluid or "mud" is pumped down the drill string, through the bit, and returned to the surface in the annulus between the drill pipe and the borehole wall. This process is known as "circulation" of the drilling fluid. If the density of the drilling fluid is excessive this can result in "breaking down" the formations encountered by the bit with the resultant loss of fluid into such broken down formations. This sort of condition results in the loss of the fluid communication path and a formation pressure overbalance, and is known as "lost circulation". Lost circulation can result in extensive well damage and is, altogether, an undesirable and possibly dangerous condition which must be avoided.
This condition may generally be avoided by appropriate selection of the density of the drilling fluid used. The fluid density of the drilling fluid or mud is usually controlled by the addition of heavy earth materials, such as barite, in known ratio to the fluid volume to produce a controlled, known density, mud.
When the well has "bottomed out" and is to be completed for production, it is necessary to set steel casing into the borehole to line the walls thereof in order to prevent caving in of the sidewalls. The steel casing, of course, must fit inside the hole diameter. This leaves an annulus between the outer surface of the casing and the borehole wall. This annulus is filled with oil well cement, having certain desired properties, in order to prevent fluid communication along the casing/borehole annulus. Such undesired fluid communication can result in well damage and loss of commercial production potential. The oil well cement is placed in the annulus between the casing and borehole wall by pumping a highly fluid cement slurry down a string of production tubing and out, either the casing bottom, or perforations in the casing and into the casing/borehole annulus. The volume of cement necessary to fill the annulus may be calculated since the outer diameter of the casing and the borehole diameter are known. Again, however, the density of such cement fluid slurries cannot exceed certain limits or the "lost circulation" condition will be encountered. Thus it is necessary to be able to control the density of the oil well cement used in cementing operations, just as for the drilling fluid during the drilling operation.
Mixtures of certain proportions of water with well cements are called "normal density" slurries, where the slurry and the set cement have about optimum properties for pumping into wells. For example, the normal density of American Petroleum Institute (API) Class H cement slurry is 16.4 pounds per gallon (ppg). Normal density of Class G slurry 15.8 ppg and Class C slurry is 14.8 ppg. It is often necessary to use "extended slurries" of cement having lower density than "normal" in order to prevent lost circulation due to excessive hydrostatic pressure when the slurry is pumped into the well. Extended slurries having densities of 12 ppg, or less, are routinely used. In fact most cement slurries used in the industry are extended slurries.
Most common low density, or extended, slurries are made by mixing excess water, compared to the amount for normal density slurries and additives, such as bentonite. The bentonite, a form of ground up high [surface area] clay, is used to prevent settling of the cement particles unduly, before the cement sets, or solidifies.
Cement settling prior to setting is usually evaluated in the laboratory by the API free water test. In this test, the volume of free water which accumulates on the top of the cement slurry in a specified diameter 250 cubic centimeter (cc) graduated cylinder after setting for 2 hours at room temperature is determined. Current practice is to require that the free water be below some maximum amount, for example 5 cubic centimeter (cc).
Brief Description of the Invention The present invention results from a study of cement settling calculations based on the Stokes-Einstein equation. These calculations show that the sedimentation rate of cement particles in water is relatively slow compared to the depth of a well. For example, a sedimentation (total) of about 50 feet in 4 hours was calculated for API Class C cement particles in fresh water.
An implication drawn from this is that if a low density API Class C slurry, using no bentonite in the water extender, is pumped into the casing/borehole annulus in a vertical well, that the top surface of the cement would settle about 50 feet by the time the cement has set. This degree of settling will not cause any operational problems. Thus the present invention is to apply oil well cement having API Classes known, [or other suitable cement,] and extending the density of such mixes purely by the addition of excess water, using no bentonite, or any other extender, to achieve a desired extended density. Such mixes are called "Stokes Law" mix. The resulting oil well cement slurries have numerous advantages discussed below, compared to prior art extended density slurries employing all extender.
The invention is best understood by the following detailed description of preferred embodiment. These descriptions are intended as descriptive, not limitative of the invention.
Detailed Description of a Preferred Embodiment One form of the Stokes-Einstein equation is given here:
V = [2gr2(dp - df)] / [9u]
V = velocity, cm/sec g = gravity, 980 cm/sect r= particle radius, cm dp = fluid density, g/cm3 df = fluid density, g/cm3 u = fluid viscosity, poise Numerical solutions of this equation for different API Classes of oil well cement using plain water for the purpose of extending (lowering) the slurry density have shown that, compared to the depth of a well (i.e. the overall height of a cement annulus from casing bottom to well head) the sedimentation velocity (or rate) of cement particles in water is slow. In one specific preferred example using API class C cement particles in fresh water, a sedimentation amount in 12 hours was about 40 feet. Twelve hours represented the time required for the slurry to begin to solidify under the conditions of low density and temperature of the example.
Avoidance of the use of bentonite, as in prior art extenders has several advantages. Among these are:
1. Slurries are less expensive because of fewer components.
CEMENTATION
Background of the Invention In the operation of rotary drilling an oil or gas well, drilling fluid having a prescribed density is used during the drilling operation for several purposes including to balance the formation pressure which increases as the depth of the hole increases. Such drilling fluid or "mud" is pumped down the drill string, through the bit, and returned to the surface in the annulus between the drill pipe and the borehole wall. This process is known as "circulation" of the drilling fluid. If the density of the drilling fluid is excessive this can result in "breaking down" the formations encountered by the bit with the resultant loss of fluid into such broken down formations. This sort of condition results in the loss of the fluid communication path and a formation pressure overbalance, and is known as "lost circulation". Lost circulation can result in extensive well damage and is, altogether, an undesirable and possibly dangerous condition which must be avoided.
This condition may generally be avoided by appropriate selection of the density of the drilling fluid used. The fluid density of the drilling fluid or mud is usually controlled by the addition of heavy earth materials, such as barite, in known ratio to the fluid volume to produce a controlled, known density, mud.
When the well has "bottomed out" and is to be completed for production, it is necessary to set steel casing into the borehole to line the walls thereof in order to prevent caving in of the sidewalls. The steel casing, of course, must fit inside the hole diameter. This leaves an annulus between the outer surface of the casing and the borehole wall. This annulus is filled with oil well cement, having certain desired properties, in order to prevent fluid communication along the casing/borehole annulus. Such undesired fluid communication can result in well damage and loss of commercial production potential. The oil well cement is placed in the annulus between the casing and borehole wall by pumping a highly fluid cement slurry down a string of production tubing and out, either the casing bottom, or perforations in the casing and into the casing/borehole annulus. The volume of cement necessary to fill the annulus may be calculated since the outer diameter of the casing and the borehole diameter are known. Again, however, the density of such cement fluid slurries cannot exceed certain limits or the "lost circulation" condition will be encountered. Thus it is necessary to be able to control the density of the oil well cement used in cementing operations, just as for the drilling fluid during the drilling operation.
Mixtures of certain proportions of water with well cements are called "normal density" slurries, where the slurry and the set cement have about optimum properties for pumping into wells. For example, the normal density of American Petroleum Institute (API) Class H cement slurry is 16.4 pounds per gallon (ppg). Normal density of Class G slurry 15.8 ppg and Class C slurry is 14.8 ppg. It is often necessary to use "extended slurries" of cement having lower density than "normal" in order to prevent lost circulation due to excessive hydrostatic pressure when the slurry is pumped into the well. Extended slurries having densities of 12 ppg, or less, are routinely used. In fact most cement slurries used in the industry are extended slurries.
Most common low density, or extended, slurries are made by mixing excess water, compared to the amount for normal density slurries and additives, such as bentonite. The bentonite, a form of ground up high [surface area] clay, is used to prevent settling of the cement particles unduly, before the cement sets, or solidifies.
Cement settling prior to setting is usually evaluated in the laboratory by the API free water test. In this test, the volume of free water which accumulates on the top of the cement slurry in a specified diameter 250 cubic centimeter (cc) graduated cylinder after setting for 2 hours at room temperature is determined. Current practice is to require that the free water be below some maximum amount, for example 5 cubic centimeter (cc).
Brief Description of the Invention The present invention results from a study of cement settling calculations based on the Stokes-Einstein equation. These calculations show that the sedimentation rate of cement particles in water is relatively slow compared to the depth of a well. For example, a sedimentation (total) of about 50 feet in 4 hours was calculated for API Class C cement particles in fresh water.
An implication drawn from this is that if a low density API Class C slurry, using no bentonite in the water extender, is pumped into the casing/borehole annulus in a vertical well, that the top surface of the cement would settle about 50 feet by the time the cement has set. This degree of settling will not cause any operational problems. Thus the present invention is to apply oil well cement having API Classes known, [or other suitable cement,] and extending the density of such mixes purely by the addition of excess water, using no bentonite, or any other extender, to achieve a desired extended density. Such mixes are called "Stokes Law" mix. The resulting oil well cement slurries have numerous advantages discussed below, compared to prior art extended density slurries employing all extender.
The invention is best understood by the following detailed description of preferred embodiment. These descriptions are intended as descriptive, not limitative of the invention.
Detailed Description of a Preferred Embodiment One form of the Stokes-Einstein equation is given here:
V = [2gr2(dp - df)] / [9u]
V = velocity, cm/sec g = gravity, 980 cm/sect r= particle radius, cm dp = fluid density, g/cm3 df = fluid density, g/cm3 u = fluid viscosity, poise Numerical solutions of this equation for different API Classes of oil well cement using plain water for the purpose of extending (lowering) the slurry density have shown that, compared to the depth of a well (i.e. the overall height of a cement annulus from casing bottom to well head) the sedimentation velocity (or rate) of cement particles in water is slow. In one specific preferred example using API class C cement particles in fresh water, a sedimentation amount in 12 hours was about 40 feet. Twelve hours represented the time required for the slurry to begin to solidify under the conditions of low density and temperature of the example.
Avoidance of the use of bentonite, as in prior art extenders has several advantages. Among these are:
1. Slurries are less expensive because of fewer components.
2. Slurries have predictable properties resulting in less pilot testing and quality control requirements.
3. The set cement has improved properties. For example, bentonite reduces the ability of cement to protect casing from corrosion.
4. The reduction or absence of gel strength development, combined with the settling motion of the cement particles maintains hydrostatic pressure after the cement is pumped, as it transitions from liquid slurry to a solid. This provides a better seal through producing zones.
3. The set cement has improved properties. For example, bentonite reduces the ability of cement to protect casing from corrosion.
4. The reduction or absence of gel strength development, combined with the settling motion of the cement particles maintains hydrostatic pressure after the cement is pumped, as it transitions from liquid slurry to a solid. This provides a better seal through producing zones.
5. Cement logs are improved.
6. Slurries have a more nearly Newtonian rheology (as compared to the extended slurries currently used which generally exhibit a Bingham Plastic rheology). Such slurries go into turbulent flow at lower pumping rates and improve the displacement of drilling fluid (in the casing/borehole annulus) by the cement slurry.
Example of Use in Field Well It was proposed to cement a string of seismic detectors into an unused, existing well in a commercial field. The well was relatively shallow (about 800 feet).
Unknown to the cementing contractor until his arrival at the weilsite was the fact that a lost circulation problem had been encountered when the well was drilled. The contractor arrived with normal API Class C oil well cement having a mix density of about 14.8 ppg. No liquid or solid extenders were available at the wellsite.
Based on the previous calculations it was advised to the contractor to extend the normal slurry density of 14.8 ppg using a mixture of plain water. An initial plain water mix of the class C slurry to 11 ppg was started. This was gradually increased during the pumping operation to 14 ppg for the final section of the job. No lost circulation was encountered and the borehole was filled to the surface level with slurry. Several days later (after cement set) the distance from the surface, though clear water, to the cement top was measured to be 40 feet, (by one system) and feet by another system.
Conclusion While the invention comprises extending and using cement slurries solely by the use of plain water to form Stokes Law slurries, it does not exclude the use of other types of cement additives. For example, the use of cement accelerators, retarders, friction reducers, etc, that are not related to the art of preventing free water by inhibiting or preventing particle settling are within the scope of the invention.
Similarly, the use of foamed nitrogen, hollow glass or ceramic spheres, etc.
in combination with excess plain water to further lower or reduce density is also contemplated. The foregoing descriptions may make other alternative arrangements apparent to those of skill in the art. The aim of the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of the invention.
Example of Use in Field Well It was proposed to cement a string of seismic detectors into an unused, existing well in a commercial field. The well was relatively shallow (about 800 feet).
Unknown to the cementing contractor until his arrival at the weilsite was the fact that a lost circulation problem had been encountered when the well was drilled. The contractor arrived with normal API Class C oil well cement having a mix density of about 14.8 ppg. No liquid or solid extenders were available at the wellsite.
Based on the previous calculations it was advised to the contractor to extend the normal slurry density of 14.8 ppg using a mixture of plain water. An initial plain water mix of the class C slurry to 11 ppg was started. This was gradually increased during the pumping operation to 14 ppg for the final section of the job. No lost circulation was encountered and the borehole was filled to the surface level with slurry. Several days later (after cement set) the distance from the surface, though clear water, to the cement top was measured to be 40 feet, (by one system) and feet by another system.
Conclusion While the invention comprises extending and using cement slurries solely by the use of plain water to form Stokes Law slurries, it does not exclude the use of other types of cement additives. For example, the use of cement accelerators, retarders, friction reducers, etc, that are not related to the art of preventing free water by inhibiting or preventing particle settling are within the scope of the invention.
Similarly, the use of foamed nitrogen, hollow glass or ceramic spheres, etc.
in combination with excess plain water to further lower or reduce density is also contemplated. The foregoing descriptions may make other alternative arrangements apparent to those of skill in the art. The aim of the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of the invention.
Claims (4)
1. In the method of providing extended density slurries for oil well cementing having lower than normal API class densities, the improvement comprising the step of adding only plain water and no other density extender or particle settling inhibitor to a selected cement slurry to form a Stokes Law Slurry and to extend its density to a lower value and preventing lost circulation and maintaining lost circulation control of the cementing slurry during the well cementing process.
2. The method of claim 1, wherein the cement slurry is a normal API Class slurry.
3. The method of claim 1 or 2 further including the step of adding: cement accelerator or cement retarder not used as a particle settling inhibitor to the cement slurry.
4. The method of claim 3 wherein a friction reducer is also added.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/031,083 US6213211B1 (en) | 1998-02-26 | 1998-02-26 | Using of stokes law cement slurries for improved well cementation |
| CA2378541A CA2378541C (en) | 1998-02-26 | 2002-04-04 | Using of stokes law cement slurries for improved well cementation |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/031,083 US6213211B1 (en) | 1998-02-26 | 1998-02-26 | Using of stokes law cement slurries for improved well cementation |
| CA2378541A CA2378541C (en) | 1998-02-26 | 2002-04-04 | Using of stokes law cement slurries for improved well cementation |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2378541A1 CA2378541A1 (en) | 2003-10-04 |
| CA2378541C true CA2378541C (en) | 2013-03-19 |
Family
ID=32327253
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2378541A Expired - Lifetime CA2378541C (en) | 1998-02-26 | 2002-04-04 | Using of stokes law cement slurries for improved well cementation |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US6213211B1 (en) |
| CA (1) | CA2378541C (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6668927B1 (en) | 2003-03-21 | 2003-12-30 | Halliburton Energy Services, Inc. | Well completion foamed spacer fluids and methods |
| US7143827B2 (en) * | 2003-03-21 | 2006-12-05 | Halliburton Energy Services, Inc. | Well completion spacer fluids containing fibers and methods |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3197317A (en) * | 1963-03-20 | 1965-07-27 | Socony Mobil Oil Co Inc | Low density cement for wells |
| US3876005A (en) * | 1972-01-24 | 1975-04-08 | Halliburton Co | High temperature, low density cementing method |
| US3804058A (en) * | 1972-05-01 | 1974-04-16 | Mobil Oil Corp | Process of treating a well using a lightweight cement |
| US4415367A (en) * | 1978-09-18 | 1983-11-15 | The Dow Chemical Company | Pumpable thixotropic cement slurries for use in cementing pipes in a well |
| US4234344A (en) * | 1979-05-18 | 1980-11-18 | Halliburton Company | Lightweight cement and method of cementing therewith |
| US4370166A (en) * | 1980-09-04 | 1983-01-25 | Standard Oil Company (Indiana) | Low density cement slurry and its use |
| US5806594A (en) * | 1997-03-31 | 1998-09-15 | Schlumberger Technology Corporation | Compositions and methods for cementing a well |
-
1998
- 1998-02-26 US US09/031,083 patent/US6213211B1/en not_active Expired - Fee Related
-
2002
- 2002-04-04 CA CA2378541A patent/CA2378541C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US6213211B1 (en) | 2001-04-10 |
| CA2378541A1 (en) | 2003-10-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20220404 |