CA1149732A - Method of cementing wells - Google Patents
Method of cementing wellsInfo
- Publication number
- CA1149732A CA1149732A CA000362573A CA362573A CA1149732A CA 1149732 A CA1149732 A CA 1149732A CA 000362573 A CA000362573 A CA 000362573A CA 362573 A CA362573 A CA 362573A CA 1149732 A CA1149732 A CA 1149732A
- Authority
- CA
- Canada
- Prior art keywords
- cement
- column
- slurry
- annulus
- gas
- 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
Links
Classifications
-
- 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
- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/007—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof characterised by the pore distribution, e.g. inhomogeneous distribution of pores
-
- 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
- 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
- C09K8/467—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 containing additives for specific purposes
- C09K8/473—Density reducing additives, e.g. for obtaining foamed cement compositions
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices, or the like
- E21B33/14—Methods or devices for cementing, for plugging holes, crevices, or the like for cementing casings into boreholes
Abstract
A B S T R A C T
METHOD OF CEMENTING WELLS
To cement the annulus around a casing string in a well penetrating an underground formation, a column of a gas-con-taining foam cement slurry is placed in the annulus, whereafter the column of cement slurry is allowed to set.
The hydrostatic pressure at the bottom of the cement slurry column prior to setting thereof is less than the fracturing pressure of the formation at the level of the bottom of the slurry column. The amount of gas contained in the slurry and the set cement is such that the density of the cement column in the annulus in the lower region of the column is higher than the density of the cement column in the higher region thereof.
METHOD OF CEMENTING WELLS
To cement the annulus around a casing string in a well penetrating an underground formation, a column of a gas-con-taining foam cement slurry is placed in the annulus, whereafter the column of cement slurry is allowed to set.
The hydrostatic pressure at the bottom of the cement slurry column prior to setting thereof is less than the fracturing pressure of the formation at the level of the bottom of the slurry column. The amount of gas contained in the slurry and the set cement is such that the density of the cement column in the annulus in the lower region of the column is higher than the density of the cement column in the higher region thereof.
Description
973~
~THOD OF C~ENTING WELLS
The present invention ~elates to a method of cementing wells, such as oil wells, gas wells or water wells penetrating undergrour.d formations. To exclude fluids from the annular space around a casing string placed in the well, a cement slurry is placed in the annular space and the cement, after setting thereof, will seal the passage through the annulus and bond the casing string to the wall of the well. The cement slurry may be pumped directly into the annulus, or may ~irst be passed downwards through the casing string (or through a special cementing tube suspended in the string) and subsequently upwards through the annular space around the casing string.
During the cementing operations, care should be taken that the pressure at each level of the annulus is less than the fracturing pressure at the relevant level, since the formation will otherwise be fractured and the cement slurry will pass into the formation rather than filling up the annulus around the casing. To obviate this problem, which is in particular present when cementing wells that penetrate underground formations located below a body of water, such as a sea or ocean, so-called lightweight cements have been developed. The cement slurries of the lightweight type have a density that is considerably lower than the density of the normal cement slurries, such as in the range of 900 - 1900 kg/m , whereas the density of a normal cement slurry is about 1920 kg/m3.
The density decrease of cements is often obtained by adding granular material of low density to a pumpable cement slurry.
Such material may be bentonite, coal, asphalt, fired clay and void-containing particles that cannot be wetted by water (such as hollow sealed ceramic spheres). Care should then be taken that the compressive strength of the cement after setting is not decreased to ar undesirable extent.
Another attractive manner of reducing the density o~ a cement slurry is by adding gas (such as air and nitrogen) to the ~973Z
cement slurry in a manner such that the gas forms a fine dispersion in the slurry, which dispersion may be stabilized by means of suitable foaming agents.
The foaming agents must be active in the highly alkaline environment of the cement and show resistance to bivalent organic cations if seawater is used as make up water for the cement slurry. Anionic surfactants with the general formula ~- CnHm - S03~ and CnHm - 0 - S03 with alkali ions as counter ions, n and m being in the range of 12-40, have been found to be particularly suitable. An example of a surfactant with very - good performance is sodium lauryl sulphonate sold under the trade name Elfan OS 46 by AKZ0.
~` When reducing the density of a cement slurry by means of a gas, such gas may be entrained with the slurry when the latter is injected into the well. In an alternative manner, gas generating chemicals may be added to the slurry, which chemicals start the generation of gas during the introduction of the slurry into the well. The amounts of chemicals and the reaction rates are chosen such that the amounts of gas present in the slurry when the slurry is in the annulus are sufficient to reduce the density of the slurry to an extent required to obviate fracturing of the formations surrounding the well.
Because of the compressibility of gas, the amount of gas - measured under standard conditions (that is 1 bar and 273.15 K) - varies along the length of the set column of cement in the annulus of a well, the variation being such that the density of the set cement is substantially constant over the height of the cement column in the well.
In cementing wells that pass through formations with low fracturing pressures, or in marine wells situated below rela-` tively deep water, a foam cement slurry of extremely low density should be applied to obviate fracturing. It has been experienced, however, that the foam cements withextremely low density have - after setting thereof - insufficient strength for meeting the requirements that are to be fulfilled at the lower end of the cemented tubing or casing. Low strength foam .
,~
' :~ ~
' cement at this level will be cracked when the drilling proceeds through the cemented tubing or casing to deeper levels. Further, the properties of such low-density foam cements are also insufficient to meet the requirements that are to be fulfilled at the lower end of a casing at the level of a pay zone, that is the interval over which fluids are to be recovered from an underground formation. In this interval, various well completion procedures are often to be carried out to increase the productivity of the formation, such as perfor-ating the casing and the cement layer around the casingJ acidizing treatments, and fracturing procedures, and foam cements with extremely low density are found to be insufficiently strong to withstand such procedures.
The object of the invention is a method of cementing a well in a formation that is prone to fracturing, by means of a lightweight foam cement slurry, whereby an optimal strength of the set cement column will be obtained.
According to one aspect of the invention, there is provided a method of cementing the annulus around a casing string in a well penetrating an underground formation, including the steps of flowing a volume of a settable cement slurry into the annulus and continuously adding gas to the slurry so as to form a foam cement slurry. The gas is added at a pressure sufficient to enter the slurry flow. The ratio between the flow rate of the gas and the flow rate of the cement slurry is substantially constant, such that the density of the column of cement in the annulus gradually increases in downward direction.
The foam cement slurry is allowed to solidify in the annulus.
According to a second aspect of the invention, the method includes the steps of flowing a volume of settable cement slurry into the well. Gas-generating chemicals are added to the flow of settable cement at a rate such that the ratio between the flow rate of the slurry, and the rate at which the chemicals are added thereto, is substantially constant, thereby forming a foam ~ -3-., ?-., '373~
cement s~urry which, when present in the annulusJ forms a cement column with a density gradually increasing from the top of the column to the bottom thereof The cement in the column is then allowed to set.
The cement column that is obtained by application of the present inven-tion will have sufficient strength in the lower region thereof so as to meet theconditions existing at the lower end of the casing, and at the same time give an adequate support to the casing string at a fracture gradient that is sufficiently low to obviate formation fracturing.
The invention will hereinafter be described by way of example in more detail with reference to the drawing, wherein Figure 1 shows schematically a vertical section over a marine platform and a hole that has been drilled from the platform, and Figure 2 shows diagrams of the hydrostati.c pressure of various fluids in the hole of Figure 1 in relationship to the depth below the sea level.Figure 1 shows a structure 1 supported on the sea bottom 2. The structure 1 supports a platform 3 at some distance above the sea level 4. A
drilling rig 5 is carried by the platform 3, and a hole 6 has been drilled in the formations 7A, 7B and 7C below the sea bottom 2. This hole has been drilled by drilling equipment (not shown) such as a drill string with a drill bit attached thereto which is lowered into the formations 7 via the conductor string 8 that is supported from the platform 3.
After the hole 6 has reached a desired depth, the drilling equipment is lifted from the hole 6 and a casing string 9 is lo~ered into the hole and suspended from the platform 3. Details of the suspension of the casine string 9 are not shown since such suspensions are known per se.
The inlet to the casing string 9 is subsequently brought into communication with a cement pump 11 via a conduit 10. The pump can draw cement slurry from a (not shown) suitable source of cement slurry.
High pressure vessels 12 containing nitrogen under pressure are in communication with the conduit 10 by means of a pipe 13 provided with a valve 14. If the vessels contain liquid nitrogen, suitable vaporisation units are installed between the vessels and the entry of the pipe 13 to the conduit 10.
A cement slurry of a suitable composition is then forced by the pump 11 into the casing string 9 via the conduit 10. Simul-taneously therewith, nitrogen gas is supplied to the flow ofcement slurry in the conduit 10 at a pressure sufficient to enter the cement slurry flow in the conduit 10. If required, suitable mixing means may be installed and suitable foaming agents may be added to promote the formation of a homogeneous gas-containing foam cement slurry, that passes down the casing 9.
The nitrogen gas supply to the conduit 10 is controlled by the valve 14 in the pipe 13 in a manner such that the ratio between the flow rate of the cement slurry leaving the pump 11 and the flow rate of the nitrogen gas passing through the pipe 13 is kept substantially constant.
It will be appreciated that the gas present in the foam cement slurry will be compressed during the travel of the slurry to the lower end of the casing 9 since the hydrostatic pressure increases in the direction of travel. On passing out of the casing and ~lowing upwards in the annulus 15 around the casing 9, the gas expands again. When the foam cement slurry is finally in place in the annulus 15, the pressure of the gas bubbles in the fo~m ce~.ent column i~creases gradually from the top of the cement column to the bottom thereof. Since the gas/cement ratio of the slurry at injection thereof into the casing 9 was kept sub-stantially constant, the density of the ce~ent column in the 73~
annulus 15 will gradually increase fromthe top of the column down to thebottom thereof. As aresult thereof,the compressive strength ofthe foam cement after settingwillincrease from the top ofthe column downto the bottom thereof. Thus, the compressive strength oftheset cement inthe region ofthe lower end ofthe column, is sufficiently high forthe purpose (such as for drilling through in atophole or intermediate string cementing job, or for comple-tion procedures when the lower end of the column is at the level of a hydrocarbon fluid producing formation), whereas the compressive strength of the cement in the upper parts of the column which is not subjected to high loads, is relatively low.
It will be appreciated that although a dense cement is present in the lower end of the column, the hydrostatic pressure in the column prior to setting of the cement has not exceeded the fracturing pressure of the formation.
In the diagram in Figure 2, curve A indicates the hydro-static pressure prevailing at the various levels in the foam cement column present in the annulus 15 prior to setting. The hydrostatic pressure P is indicated along the horizon~al axis, and the lerel L below the sealevel 4 is indicated along the vertical axis of the diagram. The density of the foam cement in the column is in the lower region thereof higher than at the levels near the top thereof. The density increases gradually from the top to the bottom of the column.
The straight line B in the diaeram of Figure 2 indicates the hydrostatic pressure in the well 6 when containin~ seawater over the full height thereof.
The straight line C indicates the pressure at which the formations 7 will fracture, whereas the straight line D indicates the hydrostatic pressure that would prerail in the cement column in the annulus if no gas would have been added to the cement. It will be clear from the diagram, that a column of seawater in the well 6 cannot fracture anyone of the formations 7A, 7B and 7C, since the hydrostatic pressure present therein is always lower than the fracturing pressure C. A cement column that has not been treated for obtaining a relatively low density (see straight 373~
line D) will fracture the formatiorl.
The cement slurry that has been treated to form a gas-containing foam slurry having a substantially constant amount of gas (measured at standard conditions) per unit volume of cement ~ill, when present in the annulus, form a cement column wherein the hydrostatic pressure varies in accordance with the curve A. At any level in the well, this pressure is lower than the pressure at wnich fracturing will occur. Moreover, the column has its maximum density, and consequently its greatest ~0 compressive strength, at the bottom part thereof. As has already been explained above, this large compressive strength at the particular lower levels of the well is advantageous in view of the treatments that are to be carried out at these levels after the cement column has set.
It will be appreciated that the method according to the invention may also be carried out by varying the amount of gas supplied per unit volume of cement that is supplied to the well.
The variations in the amount of gas are chosen such that the density of the foam cement column in the annulus decreases in downward direction, and the hydrostatic pressure at the bottom of the column is less than the fracturing pressure of the formation at that level.
Any gas other than nitrogen gas as described with reference to Figure 1 may be used for carrying out the present cementing method, such as pressurized air that is supplied to the cement conduit 10 (or to a foam generating unit that is inserted in this conduit) from a compressor unit.
Also, the gas may be generated by chemicals that are mixed with cement slurry prior to injecting the slurry into the well.
Gas-generating agents for use in forming foam cement are known per se and are therefore not described in detail. A suitable agent for this purpose is aluminium powder that may be mixed with dry cement prior to forming the cement slurry by the addition of water. It will be appreciated, however, that appli-cation of the method according to the present invention is not restricted to the use of aluminium as a gas-generating agent, ~9732 nor to any other type of gas-genera-ting agent or means.
~he rehc-tion rate o~ the gas-generating agents is controlled (if necessary by adding a react;on ra-te controller) such that the gas has been generated prior to the moment that the total cement column is present in the annulus. The amoun-ts of the gas-generating agents present per unit volume of cement slurry are controlled such that the density of the cement column at the top thereof is smaller than the density at the lower region thereof, and that the hydrostatic pressure at the lower region is lower than the fracturing pressure of the formation at the level of that region. Attractive results will be obtained by controlling the supply of chemicals to the cement in a manner such that ~e column of foam cement slurry in the annulus has a density that gradually increases from the top of the column to the bottom thereof. The amount of gas-generating agents per unit volume of cement slurry, that is present in or supplied to the slurry that is passed into the well, may either be kept substantially constant (as a result whereof the density will gradually increase in downward direction) or be varied (gradually or stepwise), provided that the variation is such that the density of the cement column increases in downward direction and tha-t the hydrostatic pressure at the lower region is lower than the fracturing pressure of the formation at the level of that reGion.
The foam cement slurry when in place in the annulus is kept stationary until solidification of the cement has taken place.
The solidified cement column in the annulus has a dens;ty that is relatively high near the bottom of the column and relatively low near the top thereof. The compressive strength of the column is largest in the re~rrion of tile lower parts thereof.
~lthough the invention has been described with reference to a well drilled from a marine p]atform, the use of the invention is not restricted hereto. If desired, the invention may also be applied in a land-based well or borehole, in particular in a well or borehole that has been drilled through formations or a formation of low fracturing pressure.
~THOD OF C~ENTING WELLS
The present invention ~elates to a method of cementing wells, such as oil wells, gas wells or water wells penetrating undergrour.d formations. To exclude fluids from the annular space around a casing string placed in the well, a cement slurry is placed in the annular space and the cement, after setting thereof, will seal the passage through the annulus and bond the casing string to the wall of the well. The cement slurry may be pumped directly into the annulus, or may ~irst be passed downwards through the casing string (or through a special cementing tube suspended in the string) and subsequently upwards through the annular space around the casing string.
During the cementing operations, care should be taken that the pressure at each level of the annulus is less than the fracturing pressure at the relevant level, since the formation will otherwise be fractured and the cement slurry will pass into the formation rather than filling up the annulus around the casing. To obviate this problem, which is in particular present when cementing wells that penetrate underground formations located below a body of water, such as a sea or ocean, so-called lightweight cements have been developed. The cement slurries of the lightweight type have a density that is considerably lower than the density of the normal cement slurries, such as in the range of 900 - 1900 kg/m , whereas the density of a normal cement slurry is about 1920 kg/m3.
The density decrease of cements is often obtained by adding granular material of low density to a pumpable cement slurry.
Such material may be bentonite, coal, asphalt, fired clay and void-containing particles that cannot be wetted by water (such as hollow sealed ceramic spheres). Care should then be taken that the compressive strength of the cement after setting is not decreased to ar undesirable extent.
Another attractive manner of reducing the density o~ a cement slurry is by adding gas (such as air and nitrogen) to the ~973Z
cement slurry in a manner such that the gas forms a fine dispersion in the slurry, which dispersion may be stabilized by means of suitable foaming agents.
The foaming agents must be active in the highly alkaline environment of the cement and show resistance to bivalent organic cations if seawater is used as make up water for the cement slurry. Anionic surfactants with the general formula ~- CnHm - S03~ and CnHm - 0 - S03 with alkali ions as counter ions, n and m being in the range of 12-40, have been found to be particularly suitable. An example of a surfactant with very - good performance is sodium lauryl sulphonate sold under the trade name Elfan OS 46 by AKZ0.
~` When reducing the density of a cement slurry by means of a gas, such gas may be entrained with the slurry when the latter is injected into the well. In an alternative manner, gas generating chemicals may be added to the slurry, which chemicals start the generation of gas during the introduction of the slurry into the well. The amounts of chemicals and the reaction rates are chosen such that the amounts of gas present in the slurry when the slurry is in the annulus are sufficient to reduce the density of the slurry to an extent required to obviate fracturing of the formations surrounding the well.
Because of the compressibility of gas, the amount of gas - measured under standard conditions (that is 1 bar and 273.15 K) - varies along the length of the set column of cement in the annulus of a well, the variation being such that the density of the set cement is substantially constant over the height of the cement column in the well.
In cementing wells that pass through formations with low fracturing pressures, or in marine wells situated below rela-` tively deep water, a foam cement slurry of extremely low density should be applied to obviate fracturing. It has been experienced, however, that the foam cements withextremely low density have - after setting thereof - insufficient strength for meeting the requirements that are to be fulfilled at the lower end of the cemented tubing or casing. Low strength foam .
,~
' :~ ~
' cement at this level will be cracked when the drilling proceeds through the cemented tubing or casing to deeper levels. Further, the properties of such low-density foam cements are also insufficient to meet the requirements that are to be fulfilled at the lower end of a casing at the level of a pay zone, that is the interval over which fluids are to be recovered from an underground formation. In this interval, various well completion procedures are often to be carried out to increase the productivity of the formation, such as perfor-ating the casing and the cement layer around the casingJ acidizing treatments, and fracturing procedures, and foam cements with extremely low density are found to be insufficiently strong to withstand such procedures.
The object of the invention is a method of cementing a well in a formation that is prone to fracturing, by means of a lightweight foam cement slurry, whereby an optimal strength of the set cement column will be obtained.
According to one aspect of the invention, there is provided a method of cementing the annulus around a casing string in a well penetrating an underground formation, including the steps of flowing a volume of a settable cement slurry into the annulus and continuously adding gas to the slurry so as to form a foam cement slurry. The gas is added at a pressure sufficient to enter the slurry flow. The ratio between the flow rate of the gas and the flow rate of the cement slurry is substantially constant, such that the density of the column of cement in the annulus gradually increases in downward direction.
The foam cement slurry is allowed to solidify in the annulus.
According to a second aspect of the invention, the method includes the steps of flowing a volume of settable cement slurry into the well. Gas-generating chemicals are added to the flow of settable cement at a rate such that the ratio between the flow rate of the slurry, and the rate at which the chemicals are added thereto, is substantially constant, thereby forming a foam ~ -3-., ?-., '373~
cement s~urry which, when present in the annulusJ forms a cement column with a density gradually increasing from the top of the column to the bottom thereof The cement in the column is then allowed to set.
The cement column that is obtained by application of the present inven-tion will have sufficient strength in the lower region thereof so as to meet theconditions existing at the lower end of the casing, and at the same time give an adequate support to the casing string at a fracture gradient that is sufficiently low to obviate formation fracturing.
The invention will hereinafter be described by way of example in more detail with reference to the drawing, wherein Figure 1 shows schematically a vertical section over a marine platform and a hole that has been drilled from the platform, and Figure 2 shows diagrams of the hydrostati.c pressure of various fluids in the hole of Figure 1 in relationship to the depth below the sea level.Figure 1 shows a structure 1 supported on the sea bottom 2. The structure 1 supports a platform 3 at some distance above the sea level 4. A
drilling rig 5 is carried by the platform 3, and a hole 6 has been drilled in the formations 7A, 7B and 7C below the sea bottom 2. This hole has been drilled by drilling equipment (not shown) such as a drill string with a drill bit attached thereto which is lowered into the formations 7 via the conductor string 8 that is supported from the platform 3.
After the hole 6 has reached a desired depth, the drilling equipment is lifted from the hole 6 and a casing string 9 is lo~ered into the hole and suspended from the platform 3. Details of the suspension of the casine string 9 are not shown since such suspensions are known per se.
The inlet to the casing string 9 is subsequently brought into communication with a cement pump 11 via a conduit 10. The pump can draw cement slurry from a (not shown) suitable source of cement slurry.
High pressure vessels 12 containing nitrogen under pressure are in communication with the conduit 10 by means of a pipe 13 provided with a valve 14. If the vessels contain liquid nitrogen, suitable vaporisation units are installed between the vessels and the entry of the pipe 13 to the conduit 10.
A cement slurry of a suitable composition is then forced by the pump 11 into the casing string 9 via the conduit 10. Simul-taneously therewith, nitrogen gas is supplied to the flow ofcement slurry in the conduit 10 at a pressure sufficient to enter the cement slurry flow in the conduit 10. If required, suitable mixing means may be installed and suitable foaming agents may be added to promote the formation of a homogeneous gas-containing foam cement slurry, that passes down the casing 9.
The nitrogen gas supply to the conduit 10 is controlled by the valve 14 in the pipe 13 in a manner such that the ratio between the flow rate of the cement slurry leaving the pump 11 and the flow rate of the nitrogen gas passing through the pipe 13 is kept substantially constant.
It will be appreciated that the gas present in the foam cement slurry will be compressed during the travel of the slurry to the lower end of the casing 9 since the hydrostatic pressure increases in the direction of travel. On passing out of the casing and ~lowing upwards in the annulus 15 around the casing 9, the gas expands again. When the foam cement slurry is finally in place in the annulus 15, the pressure of the gas bubbles in the fo~m ce~.ent column i~creases gradually from the top of the cement column to the bottom thereof. Since the gas/cement ratio of the slurry at injection thereof into the casing 9 was kept sub-stantially constant, the density of the ce~ent column in the 73~
annulus 15 will gradually increase fromthe top of the column down to thebottom thereof. As aresult thereof,the compressive strength ofthe foam cement after settingwillincrease from the top ofthe column downto the bottom thereof. Thus, the compressive strength oftheset cement inthe region ofthe lower end ofthe column, is sufficiently high forthe purpose (such as for drilling through in atophole or intermediate string cementing job, or for comple-tion procedures when the lower end of the column is at the level of a hydrocarbon fluid producing formation), whereas the compressive strength of the cement in the upper parts of the column which is not subjected to high loads, is relatively low.
It will be appreciated that although a dense cement is present in the lower end of the column, the hydrostatic pressure in the column prior to setting of the cement has not exceeded the fracturing pressure of the formation.
In the diagram in Figure 2, curve A indicates the hydro-static pressure prevailing at the various levels in the foam cement column present in the annulus 15 prior to setting. The hydrostatic pressure P is indicated along the horizon~al axis, and the lerel L below the sealevel 4 is indicated along the vertical axis of the diagram. The density of the foam cement in the column is in the lower region thereof higher than at the levels near the top thereof. The density increases gradually from the top to the bottom of the column.
The straight line B in the diaeram of Figure 2 indicates the hydrostatic pressure in the well 6 when containin~ seawater over the full height thereof.
The straight line C indicates the pressure at which the formations 7 will fracture, whereas the straight line D indicates the hydrostatic pressure that would prerail in the cement column in the annulus if no gas would have been added to the cement. It will be clear from the diagram, that a column of seawater in the well 6 cannot fracture anyone of the formations 7A, 7B and 7C, since the hydrostatic pressure present therein is always lower than the fracturing pressure C. A cement column that has not been treated for obtaining a relatively low density (see straight 373~
line D) will fracture the formatiorl.
The cement slurry that has been treated to form a gas-containing foam slurry having a substantially constant amount of gas (measured at standard conditions) per unit volume of cement ~ill, when present in the annulus, form a cement column wherein the hydrostatic pressure varies in accordance with the curve A. At any level in the well, this pressure is lower than the pressure at wnich fracturing will occur. Moreover, the column has its maximum density, and consequently its greatest ~0 compressive strength, at the bottom part thereof. As has already been explained above, this large compressive strength at the particular lower levels of the well is advantageous in view of the treatments that are to be carried out at these levels after the cement column has set.
It will be appreciated that the method according to the invention may also be carried out by varying the amount of gas supplied per unit volume of cement that is supplied to the well.
The variations in the amount of gas are chosen such that the density of the foam cement column in the annulus decreases in downward direction, and the hydrostatic pressure at the bottom of the column is less than the fracturing pressure of the formation at that level.
Any gas other than nitrogen gas as described with reference to Figure 1 may be used for carrying out the present cementing method, such as pressurized air that is supplied to the cement conduit 10 (or to a foam generating unit that is inserted in this conduit) from a compressor unit.
Also, the gas may be generated by chemicals that are mixed with cement slurry prior to injecting the slurry into the well.
Gas-generating agents for use in forming foam cement are known per se and are therefore not described in detail. A suitable agent for this purpose is aluminium powder that may be mixed with dry cement prior to forming the cement slurry by the addition of water. It will be appreciated, however, that appli-cation of the method according to the present invention is not restricted to the use of aluminium as a gas-generating agent, ~9732 nor to any other type of gas-genera-ting agent or means.
~he rehc-tion rate o~ the gas-generating agents is controlled (if necessary by adding a react;on ra-te controller) such that the gas has been generated prior to the moment that the total cement column is present in the annulus. The amoun-ts of the gas-generating agents present per unit volume of cement slurry are controlled such that the density of the cement column at the top thereof is smaller than the density at the lower region thereof, and that the hydrostatic pressure at the lower region is lower than the fracturing pressure of the formation at the level of that region. Attractive results will be obtained by controlling the supply of chemicals to the cement in a manner such that ~e column of foam cement slurry in the annulus has a density that gradually increases from the top of the column to the bottom thereof. The amount of gas-generating agents per unit volume of cement slurry, that is present in or supplied to the slurry that is passed into the well, may either be kept substantially constant (as a result whereof the density will gradually increase in downward direction) or be varied (gradually or stepwise), provided that the variation is such that the density of the cement column increases in downward direction and tha-t the hydrostatic pressure at the lower region is lower than the fracturing pressure of the formation at the level of that reGion.
The foam cement slurry when in place in the annulus is kept stationary until solidification of the cement has taken place.
The solidified cement column in the annulus has a dens;ty that is relatively high near the bottom of the column and relatively low near the top thereof. The compressive strength of the column is largest in the re~rrion of tile lower parts thereof.
~lthough the invention has been described with reference to a well drilled from a marine p]atform, the use of the invention is not restricted hereto. If desired, the invention may also be applied in a land-based well or borehole, in particular in a well or borehole that has been drilled through formations or a formation of low fracturing pressure.
Claims (2)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of cementing the annulus around a casing string in a well penetrating an underground formation, the method including the steps of flowing a volume of a settable cement slurry into the annulus and continuously adding gas to the slurry so as to form a foam cement slurry, the gas being added at a pressure sufficient to enter the slurry flow, wherein the ratio between the flow rate of the gas and the flow rate of the cement slurry is substantially constant, such that the density of the column of cement in the annulus gradually increases in downward direction, and allowing the foam cement slurry to solidify in the annulus.
2. A method of cementing the annulus around a casing string in a well penetrating an underground formation, the method including the steps of flowing a volume of settable cement slurry into the well, wherein gas-generating chemi-cals are added to the flow of settable cement at a rate such that the ratio between the flow rate of the slurry and the rate at which the chemicals are added thereto is substantially constant, thereby forming a foam cement slurry which when present in the annulus forms a cement column with a density gradually increasing from the top of the column to the bottom thereof, and allowing the cement in the column to set.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7941635 | 1979-12-03 | ||
| GB7941635A GB2063962B (en) | 1979-12-03 | 1979-12-03 | Method of cementing wells |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1149732A true CA1149732A (en) | 1983-07-12 |
Family
ID=10509574
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000362573A Expired CA1149732A (en) | 1979-12-03 | 1980-10-16 | Method of cementing wells |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4300633A (en) |
| AU (1) | AU538586B2 (en) |
| CA (1) | CA1149732A (en) |
| DK (1) | DK510280A (en) |
| GB (1) | GB2063962B (en) |
| MY (1) | MY8500918A (en) |
| NO (1) | NO803618L (en) |
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|---|---|---|---|---|
| US4466833A (en) * | 1982-04-30 | 1984-08-21 | The Dow Chemical Company | Lightweight cement slurry and method of use |
| US4797003A (en) * | 1987-04-22 | 1989-01-10 | Dowell Schlumberger Incorporated | Foamed slurry generator |
| US5020594A (en) * | 1990-06-28 | 1991-06-04 | Sans. Gas. Inc. | Method to prevent gas intrusion into wellbores during setting of cements |
| US5133409A (en) * | 1990-12-12 | 1992-07-28 | Halliburton Company | Foamed well cementing compositions and methods |
| US5213161A (en) * | 1992-02-19 | 1993-05-25 | Halliburton Company | Well cementing method using acid removable low density well cement compositions |
| US5220960A (en) * | 1992-02-19 | 1993-06-22 | Halliburton Company | Retarded acid soluble well cement compositions and methods |
| US5281270A (en) * | 1992-02-19 | 1994-01-25 | Halliburton Company | Retarded acid soluble well cement compositions and methods |
| JPH11500477A (en) * | 1995-02-14 | 1999-01-12 | アライド フォーム テック コーポレイション | Stable and water-resistant aqueous foam composition |
| US6145591A (en) * | 1997-12-12 | 2000-11-14 | Bj Services Company | Method and compositions for use in cementing |
| US6230804B1 (en) | 1997-12-19 | 2001-05-15 | Bj Services Company | Stress resistant cement compositions and methods for using same |
| CA2316059A1 (en) | 1999-08-24 | 2001-02-24 | Virgilio C. Go Boncan | Methods and compositions for use in cementing in cold environments |
| CA2318703A1 (en) | 1999-09-16 | 2001-03-16 | Bj Services Company | Compositions and methods for cementing using elastic particles |
| US6729405B2 (en) * | 2001-02-15 | 2004-05-04 | Bj Services Company | High temperature flexible cementing compositions and methods for using same |
| US6920929B2 (en) * | 2003-03-12 | 2005-07-26 | Halliburton Energy Services, Inc. | Reverse circulation cementing system and method |
| US7096943B2 (en) * | 2003-07-07 | 2006-08-29 | Hill Gilman A | Method for growth of a hydraulic fracture along a well bore annulus and creating a permeable well bore annulus |
| US6899177B2 (en) * | 2003-10-10 | 2005-05-31 | Halliburton Energy Services, Inc. | Methods of cementing subterranean zones with cement compositions having enhanced compressive strengths |
| US7073584B2 (en) * | 2003-11-12 | 2006-07-11 | Halliburton Energy Services, Inc. | Processes for incorporating inert gas in a cement composition containing spherical beads |
| US6981491B2 (en) * | 2004-01-30 | 2006-01-03 | Siemens Vdo Automotive Corporation | Coupling valve structure for fuel supply module |
| US7290611B2 (en) * | 2004-07-22 | 2007-11-06 | Halliburton Energy Services, Inc. | Methods and systems for cementing wells that lack surface casing |
| US7252147B2 (en) * | 2004-07-22 | 2007-08-07 | Halliburton Energy Services, Inc. | Cementing methods and systems for initiating fluid flow with reduced pumping pressure |
| US7290612B2 (en) * | 2004-12-16 | 2007-11-06 | Halliburton Energy Services, Inc. | Apparatus and method for reverse circulation cementing a casing in an open-hole wellbore |
| US7322412B2 (en) | 2004-08-30 | 2008-01-29 | Halliburton Energy Services, Inc. | Casing shoes and methods of reverse-circulation cementing of casing |
| US7284608B2 (en) * | 2004-10-26 | 2007-10-23 | Halliburton Energy Services, Inc. | Casing strings and methods of using such strings in subterranean cementing operations |
| US7303008B2 (en) | 2004-10-26 | 2007-12-04 | Halliburton Energy Services, Inc. | Methods and systems for reverse-circulation cementing in subterranean formations |
| US7303014B2 (en) * | 2004-10-26 | 2007-12-04 | Halliburton Energy Services, Inc. | Casing strings and methods of using such strings in subterranean cementing operations |
| US7270183B2 (en) | 2004-11-16 | 2007-09-18 | Halliburton Energy Services, Inc. | Cementing methods using compressible cement compositions |
| US7357181B2 (en) | 2005-09-20 | 2008-04-15 | Halliburton Energy Services, Inc. | Apparatus for autofill deactivation of float equipment and method of reverse cementing |
| US20070089678A1 (en) * | 2005-10-21 | 2007-04-26 | Petstages, Inc. | Pet feeding apparatus having adjustable elevation |
| US7533729B2 (en) | 2005-11-01 | 2009-05-19 | Halliburton Energy Services, Inc. | Reverse cementing float equipment |
| US7392840B2 (en) * | 2005-12-20 | 2008-07-01 | Halliburton Energy Services, Inc. | Method and means to seal the casing-by-casing annulus at the surface for reverse circulation cement jobs |
| JP4410195B2 (en) * | 2006-01-06 | 2010-02-03 | 株式会社東芝 | Semiconductor device and manufacturing method thereof |
| US7597146B2 (en) * | 2006-10-06 | 2009-10-06 | Halliburton Energy Services, Inc. | Methods and apparatus for completion of well bores |
| US7533728B2 (en) | 2007-01-04 | 2009-05-19 | Halliburton Energy Services, Inc. | Ball operated back pressure valve |
| US7614451B2 (en) | 2007-02-16 | 2009-11-10 | Halliburton Energy Services, Inc. | Method for constructing and treating subterranean formations |
| US7654324B2 (en) | 2007-07-16 | 2010-02-02 | Halliburton Energy Services, Inc. | Reverse-circulation cementing of surface casing |
| CN103541679B (en) * | 2013-10-16 | 2016-11-23 | 中国矿业大学 | Method for sealing underground hydraulic fracture drilled hole of coal mine in combined manner |
| CN110776902B (en) * | 2019-10-31 | 2022-04-12 | 西安石油大学 | Open-cell foam cement fracturing fluid, preparation method thereof and method for constructing fracturing reservoir by using open-cell foam cement fracturing fluid |
| CN110862809B (en) * | 2019-12-03 | 2022-01-21 | 中国石油化工股份有限公司 | Solid foam profile control composition, solid foam profile control slurry, preparation method of solid foam profile control slurry and profile control method |
| CN111963150B (en) * | 2020-08-27 | 2023-08-22 | 安徽理工大学 | Coal bed gas pressure measuring device and using method |
| US11828133B1 (en) * | 2022-05-19 | 2023-11-28 | Baker Hughes Oilfield Operations Llc | Foamed cementing system including automated gas supply |
| CN117350084B (en) * | 2023-12-05 | 2024-04-05 | 青岛理工大学 | Intensity gradient well cementation safety performance evaluation method suitable for deep water shallow layer |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2236987A (en) * | 1939-01-04 | 1941-04-01 | California Portland Cement Co | Method of cementing wells |
| US2288556A (en) * | 1939-06-28 | 1942-06-30 | Gulf Research Development Co | Method of and composition for producing permeable packs in wells |
| US3098754A (en) * | 1959-01-23 | 1963-07-23 | Phillips Petroleum Co | Method for preparing cellular cement |
| GB1209462A (en) * | 1967-03-30 | 1970-10-21 | Bp Chemicals U K Ltd Formerly | An expanded magnesia cement |
| US3623330A (en) * | 1968-03-21 | 1971-11-30 | Takenaka Komuten Co | Sealing off formation having pores in civil engineering or architectural construction work |
| FR2229854B1 (en) * | 1973-05-18 | 1975-08-22 | Gaz De France | |
| US4234344A (en) * | 1979-05-18 | 1980-11-18 | Halliburton Company | Lightweight cement and method of cementing therewith |
-
1979
- 1979-12-03 GB GB7941635A patent/GB2063962B/en not_active Expired
-
1980
- 1980-06-05 US US06/156,848 patent/US4300633A/en not_active Expired - Lifetime
- 1980-10-16 CA CA000362573A patent/CA1149732A/en not_active Expired
- 1980-12-01 NO NO803618A patent/NO803618L/en unknown
- 1980-12-01 AU AU64945/80A patent/AU538586B2/en not_active Ceased
- 1980-12-01 DK DK510280A patent/DK510280A/en not_active Application Discontinuation
-
1985
- 1985-12-30 MY MY918/85A patent/MY8500918A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU6494580A (en) | 1981-06-18 |
| GB2063962B (en) | 1983-06-02 |
| DK510280A (en) | 1981-06-04 |
| NO803618L (en) | 1981-06-04 |
| GB2063962A (en) | 1981-06-10 |
| US4300633A (en) | 1981-11-17 |
| AU538586B2 (en) | 1984-08-23 |
| MY8500918A (en) | 1985-12-31 |
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