CA2773339A1 - Casing integrity pressure test system - Google Patents
Casing integrity pressure test system Download PDFInfo
- Publication number
- CA2773339A1 CA2773339A1 CA2773339A CA2773339A CA2773339A1 CA 2773339 A1 CA2773339 A1 CA 2773339A1 CA 2773339 A CA2773339 A CA 2773339A CA 2773339 A CA2773339 A CA 2773339A CA 2773339 A1 CA2773339 A1 CA 2773339A1
- Authority
- CA
- Canada
- Prior art keywords
- casing
- water
- plug
- wellbore
- column
- 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.)
- Abandoned
Links
- 238000012360 testing method Methods 0.000 title claims abstract description 21
- 239000011833 salt mixture Substances 0.000 claims abstract description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- 230000005496 eutectics Effects 0.000 claims abstract description 13
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 6
- 239000010959 steel Substances 0.000 claims abstract description 6
- 239000007787 solid Substances 0.000 claims abstract description 4
- 150000003839 salts Chemical class 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- 238000007789 sealing Methods 0.000 claims description 2
- 238000004090 dissolution Methods 0.000 claims 2
- 238000004519 manufacturing process Methods 0.000 abstract description 8
- 239000000203 mixture Substances 0.000 abstract description 2
- 239000010426 asphalt Substances 0.000 description 3
- 239000000295 fuel oil Substances 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 239000003921 oil Substances 0.000 description 3
- 238000010794 Cyclic Steam Stimulation Methods 0.000 description 2
- 239000004568 cement Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000001010 compromised effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 239000004317 sodium nitrate Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK 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
- E21B33/12—Packers; Plugs
- E21B33/1208—Packers; Plugs characterised by the construction of the sealing or packing means
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/10—Locating fluid leaks, intrusions or movements
- E21B47/117—Detecting leaks, e.g. from tubing, by pressure testing
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geophysics (AREA)
- Earth Drilling (AREA)
Abstract
Oilfield wells lined with tubular steel casing are periodically filled with water and pressure tested to assess whether the casing is leaking. The present invention involves landing a charge of water-soluble, molten eutectic salt mixture at a predetermined depth where it will solidify due to temperature reduction. The mixture expands as it cools and seals against the casing. It forms a solid plug bridging across the casing bore. The plug may be used in connection with pressure testing the casing above it. The plug will eventually dissolve in water to allow regular production to resume.
Description
Casing Integrity Pressure Test System Technical Field The present application relates to the field of plugs which may be temporarily and removably provided downhole in a cased well to close off the annulus. It further relates to a method for running a casing integrity pressure test using the plug.
Background The invention was specifically developed in connection with providing a system which could be used to pressure test casing in cyclic steam stimulation wells.
It is contemplated that it may find application in other contexts as well, where there is a need for and use of a temporary removable plug.
Cyclic steam stimulation is a known technique used to thermally treat subterranean reservoirs containing viscous heavy oil or bitumen. The technique typically involves:
= injecting steam down the annulus of the cased well and into the reservoir for a period of time, perhaps sixty days, thereby heating the oil or bitumen to reduce its viscosity and improve its mobility;
= terminating injection and allowing the reservoir to "soak" for a period of perhaps 15 days;
= producing heated oil or bitumen from the reservoir through the well tubing string, usually by a combination of initially flowing and subsequently pumping the well, until the rate of production diminishes significantly; and = then repeating the cycle.
Due to the cyclic heating and cooling that the well's steel casing string undergoes, its integrity may eventually be compromised and leakage may begin, typically at one or more of the threaded couplings joining the joints of casing. These leaks usually first occur in the upper reaches of the casing string, where temperature changes are most pronounced.
=
As a consequence, periodic pressure testing of the upper section of the casing string is usually carried out. For example, in wells in the Lloydminster region of Alberta, such tests are carried out on a yearly basis.
A conventional casing pressure test typically involves:
= moving a service rig onto the well site and pulling the tubing and rod strings;
= filling the wellbore with water;
= running an inflatable mechanical packer into the wellbore on the tubing string;
= expanding the packer by pressurizing it internally, so that it seals against the casing;
= pressurizing the water in the annulus above the packer, perhaps to 2500 psi for 10 minutes, and monitoring whether the pressure drops off, indicating a leak;
= collapsing the packer and removing it and the tubing string from the wellbore;
= replacing the tubing string in the well; and = moving the rig from the site.
The conventional test just described is expensive to carry out and can reduce the time available for normal production operation.
There has thus long existed a need for a less expensive and quicker technique.
Summary of the invention In accordance with the invention, a water-soluble eutectic salt mixture, which melts at an elevated temperature and solidifies at a lesser temperature, is used. A slug of the eutectic salt mixture is melted at ground surface and then delivered into the wellbore of a cased well at a depth where the temperature is sufficiently low to cause "freezing" or solidification of the molten salt mixture. Delivery may be effected by displacing the slug to the desired depth through a string of small diameter tubing. Sufficient eutectic salt mixture is supplied to form a column extending across the annulus. As it solidifies, the salt mixture expands, presses against the steel casing and adheres to it. The solidified salt column provides a temporary, removable plug, sealed against the casing, that is operative to withstand a pressure differential thereacross, sufficient for an integrity pressure test of the casing. A casing integrity pressure test can then be carried out by pressurizing water
Background The invention was specifically developed in connection with providing a system which could be used to pressure test casing in cyclic steam stimulation wells.
It is contemplated that it may find application in other contexts as well, where there is a need for and use of a temporary removable plug.
Cyclic steam stimulation is a known technique used to thermally treat subterranean reservoirs containing viscous heavy oil or bitumen. The technique typically involves:
= injecting steam down the annulus of the cased well and into the reservoir for a period of time, perhaps sixty days, thereby heating the oil or bitumen to reduce its viscosity and improve its mobility;
= terminating injection and allowing the reservoir to "soak" for a period of perhaps 15 days;
= producing heated oil or bitumen from the reservoir through the well tubing string, usually by a combination of initially flowing and subsequently pumping the well, until the rate of production diminishes significantly; and = then repeating the cycle.
Due to the cyclic heating and cooling that the well's steel casing string undergoes, its integrity may eventually be compromised and leakage may begin, typically at one or more of the threaded couplings joining the joints of casing. These leaks usually first occur in the upper reaches of the casing string, where temperature changes are most pronounced.
=
As a consequence, periodic pressure testing of the upper section of the casing string is usually carried out. For example, in wells in the Lloydminster region of Alberta, such tests are carried out on a yearly basis.
A conventional casing pressure test typically involves:
= moving a service rig onto the well site and pulling the tubing and rod strings;
= filling the wellbore with water;
= running an inflatable mechanical packer into the wellbore on the tubing string;
= expanding the packer by pressurizing it internally, so that it seals against the casing;
= pressurizing the water in the annulus above the packer, perhaps to 2500 psi for 10 minutes, and monitoring whether the pressure drops off, indicating a leak;
= collapsing the packer and removing it and the tubing string from the wellbore;
= replacing the tubing string in the well; and = moving the rig from the site.
The conventional test just described is expensive to carry out and can reduce the time available for normal production operation.
There has thus long existed a need for a less expensive and quicker technique.
Summary of the invention In accordance with the invention, a water-soluble eutectic salt mixture, which melts at an elevated temperature and solidifies at a lesser temperature, is used. A slug of the eutectic salt mixture is melted at ground surface and then delivered into the wellbore of a cased well at a depth where the temperature is sufficiently low to cause "freezing" or solidification of the molten salt mixture. Delivery may be effected by displacing the slug to the desired depth through a string of small diameter tubing. Sufficient eutectic salt mixture is supplied to form a column extending across the annulus. As it solidifies, the salt mixture expands, presses against the steel casing and adheres to it. The solidified salt column provides a temporary, removable plug, sealed against the casing, that is operative to withstand a pressure differential thereacross, sufficient for an integrity pressure test of the casing. A casing integrity pressure test can then be carried out by pressurizing water
2 in the wellbore annulus above the plug. Upon termination of the test, the water in the annulus will dissolve and thereby remove the plug.
Description of the Drawing Figure 1 is a sectional view showing a cased well having a production tubing string and a small diameter tubing string positioned in the wellbore, and a eutectic salt mixture plug temporarily closing off the annulus.
Description of a preferred embodiment Having reference to the Figure, a well 1 is shown cased by a string 2 of steel production casing 3. A string 4 of steel production tubing 5 extends down the casing wellbore 6 from a wellhead 7 to a heavy oil reservoir 8. The casing and tubing strings 2, 4 define an annulus 9 between them (which is part of the wellbore 6). The casing string 2 is perforated at the reservoir 8, to allow heavy oil to enter the annulus 9 and tubing string bore 20 as well as to permit steam to be injected down the annulus and through the perforations 10 into the reservoir 8. A subsurface pump 21 is provided in the lower end of the tubing string bore 20, for pumping oil to ground surface.
A eutectic salt melter 11 is connected at ground surface with the small diameter tubing string 12, which extends down the annulus 9. The small diameter tubing string 12 is landed above the bottom of the production tubing string 4. At its bottom end, the small diameter tubing string 12 is connected with a salt distribution nozzle 13.
The melter 11 is operative to heat the eutectic salt mixture sufficiently so that it melts. A pump (not shown) is provided to pump the molten salt mixture down the string 12. The nozzle 13 is landed at a subsurface elevation which is at a temperature lower than the temperature at which the molten salt solidifies. The molten salt is discharged through the nozzle 13 into the annulus 9, where it contacts the casing string 2, cools, solidifies and forms a plug 14 comprising a solid column extending across the annulus 9 and sealing against the adjacent casing 3 and tubing 5.
The eutectic salt mixture used is selected so as to have the following characteristics:
Description of the Drawing Figure 1 is a sectional view showing a cased well having a production tubing string and a small diameter tubing string positioned in the wellbore, and a eutectic salt mixture plug temporarily closing off the annulus.
Description of a preferred embodiment Having reference to the Figure, a well 1 is shown cased by a string 2 of steel production casing 3. A string 4 of steel production tubing 5 extends down the casing wellbore 6 from a wellhead 7 to a heavy oil reservoir 8. The casing and tubing strings 2, 4 define an annulus 9 between them (which is part of the wellbore 6). The casing string 2 is perforated at the reservoir 8, to allow heavy oil to enter the annulus 9 and tubing string bore 20 as well as to permit steam to be injected down the annulus and through the perforations 10 into the reservoir 8. A subsurface pump 21 is provided in the lower end of the tubing string bore 20, for pumping oil to ground surface.
A eutectic salt melter 11 is connected at ground surface with the small diameter tubing string 12, which extends down the annulus 9. The small diameter tubing string 12 is landed above the bottom of the production tubing string 4. At its bottom end, the small diameter tubing string 12 is connected with a salt distribution nozzle 13.
The melter 11 is operative to heat the eutectic salt mixture sufficiently so that it melts. A pump (not shown) is provided to pump the molten salt mixture down the string 12. The nozzle 13 is landed at a subsurface elevation which is at a temperature lower than the temperature at which the molten salt solidifies. The molten salt is discharged through the nozzle 13 into the annulus 9, where it contacts the casing string 2, cools, solidifies and forms a plug 14 comprising a solid column extending across the annulus 9 and sealing against the adjacent casing 3 and tubing 5.
The eutectic salt mixture used is selected so as to have the following characteristics:
3 = it needs to solidify if exposed to the temperature existing at the depth where the nozzle is landed and the plug is to form;
= it needs to expand on solidifying, so as to press against the casing (and production tubing, if present) and provide a pressure tight seal; and = it needs to be sufficiently water soluble so as to dissolve if contacted over time (typically several hours) with water, for removal of the plug.
As stated, a slug or suitable volume of the molten salt mixture is pumped down the bore of the small diameter tubing string 12 and is delivered into the annulus 9 through the nozzle 13. The molten salt mixture slug forms a column in contact with the casing 3 and any other strings present in the wellbore. As the salt mixture cools upon contacting the casing, it solidifies. As the salt mixture solidifies, it expands and seals against the string(s) with which it is in contact. It thereby forms the plug 14, which adheres to the strings, so as to remain fixed in place, and seals to enable using it for a casing integrity pressure test.
Following the pressure test, the plug 14 will dissolve in the water present in the annulus 9 within a few hours.
Experimental A test was conducted to assess the strength of a selected eutectic salt mixture plug.
A 3 inch diameter column was formed of a water-soluble eutectic salt mixture of sodium nitrate and potassium nitrate. The mixture was supplied by Houghton International Inc., Valley Forge, PA 19482. The material was identified under the designation Draw Temp 430. It had a melt temperature of approximately 315 C
and a solidification temperature of approximately 260 C.
The column was subjected to end loading in an MTS load frame. Load was monitored with a load cell. The column was found to fail at a compressive load of 3660 psi.
= it needs to expand on solidifying, so as to press against the casing (and production tubing, if present) and provide a pressure tight seal; and = it needs to be sufficiently water soluble so as to dissolve if contacted over time (typically several hours) with water, for removal of the plug.
As stated, a slug or suitable volume of the molten salt mixture is pumped down the bore of the small diameter tubing string 12 and is delivered into the annulus 9 through the nozzle 13. The molten salt mixture slug forms a column in contact with the casing 3 and any other strings present in the wellbore. As the salt mixture cools upon contacting the casing, it solidifies. As the salt mixture solidifies, it expands and seals against the string(s) with which it is in contact. It thereby forms the plug 14, which adheres to the strings, so as to remain fixed in place, and seals to enable using it for a casing integrity pressure test.
Following the pressure test, the plug 14 will dissolve in the water present in the annulus 9 within a few hours.
Experimental A test was conducted to assess the strength of a selected eutectic salt mixture plug.
A 3 inch diameter column was formed of a water-soluble eutectic salt mixture of sodium nitrate and potassium nitrate. The mixture was supplied by Houghton International Inc., Valley Forge, PA 19482. The material was identified under the designation Draw Temp 430. It had a melt temperature of approximately 315 C
and a solidification temperature of approximately 260 C.
The column was subjected to end loading in an MTS load frame. Load was monitored with a load cell. The column was found to fail at a compressive load of 3660 psi.
4 1 i The test indicated that the load rating of the eutectic salt mixture column was comparable to that of Glass G cement, which is commonly used to cement well casing into the geological formation.
, 1
, 1
Claims (2)
1. A temporary, removable plug, positioned downhole in a wellbore formed by a string of casing in a well, comprising:
a column of solid eutectic salt mixture extending across the wellbore and adhering to the inner surface of the casing;
said salt column being sufficiently soluble in water to enable its removal by dissolution in water and operative to seal against the casing to withstand a pressure differential, across the column, which is sufficient to allow a casing integrity pressure test to be performed.
a column of solid eutectic salt mixture extending across the wellbore and adhering to the inner surface of the casing;
said salt column being sufficiently soluble in water to enable its removal by dissolution in water and operative to seal against the casing to withstand a pressure differential, across the column, which is sufficient to allow a casing integrity pressure test to be performed.
2. A method for pressure testing a section of steel casing in a well comprising:
delivering a slug of molten eutectic salt mixture downhole into the wellbore of the casing to a point, at the base of the section of casing to be tested, where the slug cools and solidifies to form a solid column extending across the wellbore, said column adhering to and sealing against the inner surface of the casing to form a temporary removable plug operative to withstand a pressure differential sufficient to allow a casing integrity pressure test to be performed;
said salt mixture being sufficiently soluble in water to enable its removal by dissolution in water after pressure testing;
pressurizing the section of the wellbore above the plug with water for sufficient time to test the integrity of the casing section; and dissolving the plug in water in the wellbore above the plug to remove the plug.
delivering a slug of molten eutectic salt mixture downhole into the wellbore of the casing to a point, at the base of the section of casing to be tested, where the slug cools and solidifies to form a solid column extending across the wellbore, said column adhering to and sealing against the inner surface of the casing to form a temporary removable plug operative to withstand a pressure differential sufficient to allow a casing integrity pressure test to be performed;
said salt mixture being sufficiently soluble in water to enable its removal by dissolution in water after pressure testing;
pressurizing the section of the wellbore above the plug with water for sufficient time to test the integrity of the casing section; and dissolving the plug in water in the wellbore above the plug to remove the plug.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2773339A CA2773339A1 (en) | 2012-04-02 | 2012-04-02 | Casing integrity pressure test system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2773339A CA2773339A1 (en) | 2012-04-02 | 2012-04-02 | Casing integrity pressure test system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2773339A1 true CA2773339A1 (en) | 2013-10-02 |
Family
ID=49289825
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2773339A Abandoned CA2773339A1 (en) | 2012-04-02 | 2012-04-02 | Casing integrity pressure test system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2773339A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105089654A (en) * | 2014-05-14 | 2015-11-25 | 中国石油天然气股份有限公司 | Evaporite bed casing determining method considering interlayer characteristics |
| CN109252856A (en) * | 2018-10-25 | 2019-01-22 | 中冶集团武汉勘察研究院有限公司 | The vertical packer permeability test water-stopping method to intercept water with lateral water blockoff is carried out by boring aperture variation |
-
2012
- 2012-04-02 CA CA2773339A patent/CA2773339A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105089654A (en) * | 2014-05-14 | 2015-11-25 | 中国石油天然气股份有限公司 | Evaporite bed casing determining method considering interlayer characteristics |
| CN109252856A (en) * | 2018-10-25 | 2019-01-22 | 中冶集团武汉勘察研究院有限公司 | The vertical packer permeability test water-stopping method to intercept water with lateral water blockoff is carried out by boring aperture variation |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |
Effective date: 20170404 |