CA1326437C - Method for stimulating oil recovery from an underground reservoir - Google Patents
Method for stimulating oil recovery from an underground reservoirInfo
- Publication number
- CA1326437C CA1326437C CA000611050A CA611050A CA1326437C CA 1326437 C CA1326437 C CA 1326437C CA 000611050 A CA000611050 A CA 000611050A CA 611050 A CA611050 A CA 611050A CA 1326437 C CA1326437 C CA 1326437C
- Authority
- CA
- Canada
- Prior art keywords
- stage
- reservoir
- velocity
- flooding medium
- displacement
- 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
Links
Classifications
-
- 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
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/166—Injecting a gaseous medium; Injecting a gaseous medium and a liquid medium
- E21B43/168—Injecting a gaseous medium
-
- 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
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/164—Injecting CO2 or carbonated water
Abstract
A B S T R A C T
METHOD FOR STIMULATING OIL RECOVERY FROM AN UNDERGROUND RESERVOIR
Oil recovery from an underground reservoir is stimulated by injecting during a first stage of a fluid injection process a miscible flooding medium at a supercritical velocity through the reservoir until the flooding medium has travelled more than 90% of the distance from the injection well to a production well, whereupon the injection rate of the flooding medium is reduced to produce during a second stage of the process a displacement velocity in the reservoir less than the critical velocity at which fingering of the flooding medium through the displaced oil occurs.
METHOD FOR STIMULATING OIL RECOVERY FROM AN UNDERGROUND RESERVOIR
Oil recovery from an underground reservoir is stimulated by injecting during a first stage of a fluid injection process a miscible flooding medium at a supercritical velocity through the reservoir until the flooding medium has travelled more than 90% of the distance from the injection well to a production well, whereupon the injection rate of the flooding medium is reduced to produce during a second stage of the process a displacement velocity in the reservoir less than the critical velocity at which fingering of the flooding medium through the displaced oil occurs.
Description
3264~7 METHOD FOR STIMULATING OIL RECOVERY FROM AN UNDERGROUND RESERVOIR
The invention relates to a method for stimulating oil recovery from an underground reservoir by injecting a miscible flooding medium into the reservoir.
It is known from US patent No. 4,593,761 that oil production from an underground reservoir can be accelerated by controlling the injection rate of a miscible flooding medium such that during a first stage of the drive the displacement velocity in the reservoir is above the critical velocity for stable displacement whereas during the second stage of the drive the displacement velocity is below the critical velocity. Dùring said first stage, when the displacement velocity is above the critical velocity, density and viscosity differences between the flooding medium and the oil are such that velocity forces become greater than gravitational forces thereby causing the flooding medium to finger through the oil in an erratic manner. During the second stage reduction of the velocity to below the critical velocity allows the solubility of the flooding medium and buoyant forces to reduce or heal the fingering which has already occurred and allow the establishment of an oil bank.
In accordance with the teachings of the prior art method the flooding medium is in~ected during the first stage at a rate to produce a flow velocity of about 2 to 15 times the critical velocity until the flooding medium has travelled about 60 to 90~ of the distance from the in~ection system to the production system, whereupon the second stage is started.
A difficulty encountered with the known technique is that in practice the moment of transition from the first stage to the second stage is difficult to determine. Thus there is a need to remedy this drawback of the prior art method.
-- ~32~37 It is a further object of the present invention to increase the production rate from a reservoir without decreasing the sweep efficiency.
In accordance with the invention there is provided a method for stimulating oil recovery from an underground reservoir which is penetrated by an injection and a production well, the method comprising injecting during a first stage of a fluid in~ection process a miscible flooding medium into the injection well, at a rate to produce a displacement velocity in the.reservoir beyond a critical velocity for stable displacement, and subsequently decreasing the injection rate of the miscible flooding medium to produce during a second stage of the fluid injection process a displacement velocity in the reservoir less than the cri~ical velocity when the flooding medium has travelled more than 90~ of the distance from the in~ection well to the production well.
Preferably said first stage is only terminated after a breakthrough of flooding medium from the in~ection well to the production well has occurred. Experiments revealed that the first stage may even be continued for a while after a breakthrough has occurred. It is surprising that in spite of the late reduction of the displacement velocity to a subcritical value still an oil bank is formed in front of the flooding medium during the second stage of the method according to the invention so that cumulative oil production from the reservoir is not impaired.
In the method according to the invention any suitable miscible flooding medium can be used. Preferably the flooding medium is predominantly composed of a gas selected from the group consisting of carbon dioxide, nitrogen, methane and ethane.
It i9 furthermore preferred that during the first stage of the method according to the invention the displacement velocity in the reservoir is more than lS times the critical velocity.
As is well known to those skilled in the art the critical velocity at which fingering of the flooding medium begins can be calculated by the relationship k g Qp sin~
U --c ,; .. . : . . , wherein ~c is the critical displacement velocity in m s l, k is the permeability in m , is the fractional mobile fluid porosity of the reservoir ~ is the dip angle of the reservoir ~p is the density difference between displaced fluid and the flooding medium in kg m 3, and is the viscosity difference between displaced fluid and the flooding medium in kg m ls l.
In many slightly dipping reservoirs it is preferred to select during the first stage of the process according to the invention a displacement velocity U (in m s l) which is larger than lO/sina.
The invention will now be explained in more detail with reference to the accompanying draw~.ngs, in which:
Fig. l shows a diagram where along the horizontal axis in;ection (expressed in pore volume - pv) is plotted and along the vertical axis production (pv) is plotted and in which recovery curves are given of a prior art drive (curve H), a conventional stable drive (curve S) and the method according to the invention (curve K), and Fig. 2 is a production (pv) versus (dimensionless) time (tU/L + O.Ol) diagram of a prior art drlve (curve H), a conventional stable drive (curve S) and the method according to the in~ention (curve K).
In demonstrating the invention experiments were performed in a 68 cm long and lO cm wide transparent model. The model had a dip angle of 10 relative to a horizontal plane and it was filled with glass beads to create a porous medium. The model was used to represent a vertical cross-section of a dipping reseroir. The ratio of the gravity and viscous forces, the dispersion of the porous medium and the density ratio were all properly scaled.
In the experlments a comparison was made between the prior art method disclosed in US patent 4,593,761 (see curves H), the method according to the lnvention (see curves K) and a fully stable displacement (see curves S) in which the displacement velocity of 132~A~7 the flooding medium was subcritical throughout the drive. Three process parameters of the prior art method disclosed in US p~tent 4,593,761 had to be set in the experiments: I) the displacement rate in the first stage somewhere between 2 and 15 times the critical rate, II) the distance travelled by the flooding medium at which the injecti~n rate is decreased, which should be somewhere between 0.6 and 0.9 L, and III) the subcritical injection rate in the second stage. It was decided to choose the process parameters close to their maximum value since that would be favourable to the performance of the prior art method. (Visual inspection of the fingering pattern during the experiments revealed a positive correlation between the injection rate and the number of fingers;
and that the production rate is equal to the in;ection rate in the first stage.) The displacement rate in the first stage of the prior art method was chosen at 13 times the critical rate (Uc ~ 2.25 .
s in experiment), the distance travelled at 0.8 L and the displacement rate in the second stage at 0.8 times the critical rate.
The drive in which the method according to the invention was applied had a much higher displacement rate in the first stage:
66 times the critical rate (exp K). In our model reservoir 66 Uc is equal to 1.26 m per day. The second stage was started at the moment of gasbreakthrough because this moment can easily be detected in practice and because maximum use of the high production rate of the first stage is made. The rate in the second stage was taken as 0.8 times the critical rate as in the simulation of the prior art method. A visual comparison was made of the distribution of oil and solvent at the end of the first stage (0.19 pv in~ected). Said comparlson revealed that the method according to the invention produced a much more extended and pronounced finger pattern than the prior art method. Hence at higher displacement rates a much better mixing is obtained, as revealed from the wider transition zone between oil and gas. The production vs in~ection curve of the prior art method and the corresponding curve R of the method according to the invention in Fig. 1 differ not much (0.02 pv at 132~37 maximum), so the sweep was not affected adversely by the far more extended fingers produced by the method according to the invention thanks to the better mixing in the second stage. A fully stable displacement was also performed; Fig. l shows that the stable displacement has the same production versus in~ection characteristic (see curve S) as the drives with a period of unstable injection (curves K and H).
However, as shown in Fig. 2, the production versus time curves of the three drives differ significantly.
In Figure 2 the production in pv is given as a function of dimensionless time, defined as t UC/L. According to this definition a fully stable drive reaches l pv injection at a dimensionless time greater than l. The dependent variable in the figure is log(t UC/L
+ O.Ol~. This variable is chosen to display both the steep production rise of the first stage and the slow production increase of the second stage in one figure. Further, O.Ol is included to be able to display t - 0 on a logarithmic scale. Figure 2 shows that in the first stage of the process according to the invention (curve K) the production rate is significantly improved (without affecting the sweep of course). The difference in cumulative production between the method according to the inven~ion (curve K), the prior art method (curve H) and the subcritical displacement process (curve S) levels off in the second st.qge towards nihil at the end of the drive. The total recovery is in all cases practically lO0~. All drives were stopped when the oil fraction became lO~.
From the experiments discussed above it can be concludsd that the method according to the invention shows a higher production rate without affecting the vertical sweep compared to the prior art method. Difference in horizontal sweep between the two methods is not expected because the second stages in both methods are of equal length.
For an economic evaluation of the new method, we have calculated the present value of the purchase of each drive in pore volumes with ~he expression -` 1326~37 T
dP (1 - r)t/r dt O
where P is the cumulative production (in pore volumes), r is the interest rate per time period r, and T i9 the total duration of the drive. With a characteristic time L~'UC of the drives of 20 years and with an interest rate of 8~ per year, the present value of the fully stable drive (curve S) is 0.32 pv, the present value of the drive with the prior art method (curve H) is 0.44 pv and the present value of the method according to the invention (curve K) is O.Sl pv, so 60% higher compared to a fully stable drive.
In summary, the experiments revealed that an unstable displacement until solvent breakthrough followed by a stable displacement results in a considerable improvement in production rate without affecting the vertical sweep, particularly in reservoirs at low dip angle. The method described in US patent 4,593,761 can be improved both on prescribed injection rate as on duration of unstable displacement. The improvements are:
1. unrestricted injection velocity instead of an in~ection velocity restricted to 15 Uc 2. a start of the stable in~ection at or ~ust before solvent breakthrough instead of the moment at which the flooding medium has travelled 60 to 90 percent of the distance between the in~ection well and production well. The late start of the second stage in the method according to the invention, i.e. after the flooding medium has travelled more than 90 percent of the distance between the in~ection well and production well has the following advantages:
1) easy detection of the moment for starting the second stage viz.
using the moment of solvent breakthrough or a rapidly decreasing backpressure in the period ~ust before solvent breakthrough, II) maximum use ls made of the high production rate of the first stage.
As mentioned before any miscible flooding medium can be used as solvent in the method according to the invention. It is preferred to select the solvent from a gas selected from the group consisting of carbon dioxide, nitrogen, methane and ethane.
The invention relates to a method for stimulating oil recovery from an underground reservoir by injecting a miscible flooding medium into the reservoir.
It is known from US patent No. 4,593,761 that oil production from an underground reservoir can be accelerated by controlling the injection rate of a miscible flooding medium such that during a first stage of the drive the displacement velocity in the reservoir is above the critical velocity for stable displacement whereas during the second stage of the drive the displacement velocity is below the critical velocity. Dùring said first stage, when the displacement velocity is above the critical velocity, density and viscosity differences between the flooding medium and the oil are such that velocity forces become greater than gravitational forces thereby causing the flooding medium to finger through the oil in an erratic manner. During the second stage reduction of the velocity to below the critical velocity allows the solubility of the flooding medium and buoyant forces to reduce or heal the fingering which has already occurred and allow the establishment of an oil bank.
In accordance with the teachings of the prior art method the flooding medium is in~ected during the first stage at a rate to produce a flow velocity of about 2 to 15 times the critical velocity until the flooding medium has travelled about 60 to 90~ of the distance from the in~ection system to the production system, whereupon the second stage is started.
A difficulty encountered with the known technique is that in practice the moment of transition from the first stage to the second stage is difficult to determine. Thus there is a need to remedy this drawback of the prior art method.
-- ~32~37 It is a further object of the present invention to increase the production rate from a reservoir without decreasing the sweep efficiency.
In accordance with the invention there is provided a method for stimulating oil recovery from an underground reservoir which is penetrated by an injection and a production well, the method comprising injecting during a first stage of a fluid in~ection process a miscible flooding medium into the injection well, at a rate to produce a displacement velocity in the.reservoir beyond a critical velocity for stable displacement, and subsequently decreasing the injection rate of the miscible flooding medium to produce during a second stage of the fluid injection process a displacement velocity in the reservoir less than the cri~ical velocity when the flooding medium has travelled more than 90~ of the distance from the in~ection well to the production well.
Preferably said first stage is only terminated after a breakthrough of flooding medium from the in~ection well to the production well has occurred. Experiments revealed that the first stage may even be continued for a while after a breakthrough has occurred. It is surprising that in spite of the late reduction of the displacement velocity to a subcritical value still an oil bank is formed in front of the flooding medium during the second stage of the method according to the invention so that cumulative oil production from the reservoir is not impaired.
In the method according to the invention any suitable miscible flooding medium can be used. Preferably the flooding medium is predominantly composed of a gas selected from the group consisting of carbon dioxide, nitrogen, methane and ethane.
It i9 furthermore preferred that during the first stage of the method according to the invention the displacement velocity in the reservoir is more than lS times the critical velocity.
As is well known to those skilled in the art the critical velocity at which fingering of the flooding medium begins can be calculated by the relationship k g Qp sin~
U --c ,; .. . : . . , wherein ~c is the critical displacement velocity in m s l, k is the permeability in m , is the fractional mobile fluid porosity of the reservoir ~ is the dip angle of the reservoir ~p is the density difference between displaced fluid and the flooding medium in kg m 3, and is the viscosity difference between displaced fluid and the flooding medium in kg m ls l.
In many slightly dipping reservoirs it is preferred to select during the first stage of the process according to the invention a displacement velocity U (in m s l) which is larger than lO/sina.
The invention will now be explained in more detail with reference to the accompanying draw~.ngs, in which:
Fig. l shows a diagram where along the horizontal axis in;ection (expressed in pore volume - pv) is plotted and along the vertical axis production (pv) is plotted and in which recovery curves are given of a prior art drive (curve H), a conventional stable drive (curve S) and the method according to the invention (curve K), and Fig. 2 is a production (pv) versus (dimensionless) time (tU/L + O.Ol) diagram of a prior art drlve (curve H), a conventional stable drive (curve S) and the method according to the in~ention (curve K).
In demonstrating the invention experiments were performed in a 68 cm long and lO cm wide transparent model. The model had a dip angle of 10 relative to a horizontal plane and it was filled with glass beads to create a porous medium. The model was used to represent a vertical cross-section of a dipping reseroir. The ratio of the gravity and viscous forces, the dispersion of the porous medium and the density ratio were all properly scaled.
In the experlments a comparison was made between the prior art method disclosed in US patent 4,593,761 (see curves H), the method according to the lnvention (see curves K) and a fully stable displacement (see curves S) in which the displacement velocity of 132~A~7 the flooding medium was subcritical throughout the drive. Three process parameters of the prior art method disclosed in US p~tent 4,593,761 had to be set in the experiments: I) the displacement rate in the first stage somewhere between 2 and 15 times the critical rate, II) the distance travelled by the flooding medium at which the injecti~n rate is decreased, which should be somewhere between 0.6 and 0.9 L, and III) the subcritical injection rate in the second stage. It was decided to choose the process parameters close to their maximum value since that would be favourable to the performance of the prior art method. (Visual inspection of the fingering pattern during the experiments revealed a positive correlation between the injection rate and the number of fingers;
and that the production rate is equal to the in;ection rate in the first stage.) The displacement rate in the first stage of the prior art method was chosen at 13 times the critical rate (Uc ~ 2.25 .
s in experiment), the distance travelled at 0.8 L and the displacement rate in the second stage at 0.8 times the critical rate.
The drive in which the method according to the invention was applied had a much higher displacement rate in the first stage:
66 times the critical rate (exp K). In our model reservoir 66 Uc is equal to 1.26 m per day. The second stage was started at the moment of gasbreakthrough because this moment can easily be detected in practice and because maximum use of the high production rate of the first stage is made. The rate in the second stage was taken as 0.8 times the critical rate as in the simulation of the prior art method. A visual comparison was made of the distribution of oil and solvent at the end of the first stage (0.19 pv in~ected). Said comparlson revealed that the method according to the invention produced a much more extended and pronounced finger pattern than the prior art method. Hence at higher displacement rates a much better mixing is obtained, as revealed from the wider transition zone between oil and gas. The production vs in~ection curve of the prior art method and the corresponding curve R of the method according to the invention in Fig. 1 differ not much (0.02 pv at 132~37 maximum), so the sweep was not affected adversely by the far more extended fingers produced by the method according to the invention thanks to the better mixing in the second stage. A fully stable displacement was also performed; Fig. l shows that the stable displacement has the same production versus in~ection characteristic (see curve S) as the drives with a period of unstable injection (curves K and H).
However, as shown in Fig. 2, the production versus time curves of the three drives differ significantly.
In Figure 2 the production in pv is given as a function of dimensionless time, defined as t UC/L. According to this definition a fully stable drive reaches l pv injection at a dimensionless time greater than l. The dependent variable in the figure is log(t UC/L
+ O.Ol~. This variable is chosen to display both the steep production rise of the first stage and the slow production increase of the second stage in one figure. Further, O.Ol is included to be able to display t - 0 on a logarithmic scale. Figure 2 shows that in the first stage of the process according to the invention (curve K) the production rate is significantly improved (without affecting the sweep of course). The difference in cumulative production between the method according to the inven~ion (curve K), the prior art method (curve H) and the subcritical displacement process (curve S) levels off in the second st.qge towards nihil at the end of the drive. The total recovery is in all cases practically lO0~. All drives were stopped when the oil fraction became lO~.
From the experiments discussed above it can be concludsd that the method according to the invention shows a higher production rate without affecting the vertical sweep compared to the prior art method. Difference in horizontal sweep between the two methods is not expected because the second stages in both methods are of equal length.
For an economic evaluation of the new method, we have calculated the present value of the purchase of each drive in pore volumes with ~he expression -` 1326~37 T
dP (1 - r)t/r dt O
where P is the cumulative production (in pore volumes), r is the interest rate per time period r, and T i9 the total duration of the drive. With a characteristic time L~'UC of the drives of 20 years and with an interest rate of 8~ per year, the present value of the fully stable drive (curve S) is 0.32 pv, the present value of the drive with the prior art method (curve H) is 0.44 pv and the present value of the method according to the invention (curve K) is O.Sl pv, so 60% higher compared to a fully stable drive.
In summary, the experiments revealed that an unstable displacement until solvent breakthrough followed by a stable displacement results in a considerable improvement in production rate without affecting the vertical sweep, particularly in reservoirs at low dip angle. The method described in US patent 4,593,761 can be improved both on prescribed injection rate as on duration of unstable displacement. The improvements are:
1. unrestricted injection velocity instead of an in~ection velocity restricted to 15 Uc 2. a start of the stable in~ection at or ~ust before solvent breakthrough instead of the moment at which the flooding medium has travelled 60 to 90 percent of the distance between the in~ection well and production well. The late start of the second stage in the method according to the invention, i.e. after the flooding medium has travelled more than 90 percent of the distance between the in~ection well and production well has the following advantages:
1) easy detection of the moment for starting the second stage viz.
using the moment of solvent breakthrough or a rapidly decreasing backpressure in the period ~ust before solvent breakthrough, II) maximum use ls made of the high production rate of the first stage.
As mentioned before any miscible flooding medium can be used as solvent in the method according to the invention. It is preferred to select the solvent from a gas selected from the group consisting of carbon dioxide, nitrogen, methane and ethane.
Claims (7)
1. A method for stimulating oil recovery from an underground reservoir which is penetrated by an injection and a production well, the method comprising injecting during a first stage of a fluid injection process a miscible flooding medium into the injection well, at a rate to produce a displacement velocity in the reservoir beyond a critical velocity for stable displacement, and subsequently decreasing the injection rate of the miscible flooding medium to produce during a second stage of the fluid injection process a displacement velocity in the reservoir less than the critical velocity when the flooding medium has travelled more than 90% of the distance from the injection well to the production well.
2. The method of claim 1, comprising injecting into said injection well a miscible flooding medium predominantly composed of a gas selected from the group consisting of carbon dioxide, nitrogen, methane and ethane.
3. The method of claim 1 wherein during the first stage the miscible flooding medium is injected at such a rate that the displacement velocity in the reservoir is beyond 15 times said critical velocity.
4. The method of claim 3 wherein during said first stage the displacement velocity in the reservoir is more than 50 times the critical velocity.
5. The method of claim 1 or 2 wherein during said first stage the displacement velocity U in the reservoir is more than 10/sin.alpha., .alpha.
being the dip angle of the reservoir.
being the dip angle of the reservoir.
6. The method of claim 1 wherein the first stage is terminated and the injection rate of the flooding medium is reduced to produce a displacement velocity in the reservoir less than the critical velocity when a breakthrough of flooding medium has occurred.
7. The method of claim 1 wherein the first stage of the fluid injection process is continued for a while after a breakthrough of flooding medium has occurred.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8822915A GB2224055A (en) | 1988-09-29 | 1988-09-29 | Method for stimulating oil recovery from an underground reservoir |
| GB8822915 | 1988-09-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1326437C true CA1326437C (en) | 1994-01-25 |
Family
ID=10644479
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000611050A Expired - Lifetime CA1326437C (en) | 1988-09-29 | 1989-09-12 | Method for stimulating oil recovery from an underground reservoir |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1326437C (en) |
| GB (1) | GB2224055A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106321055A (en) * | 2016-08-26 | 2017-01-11 | 新疆克拉玛依市采丰实业有限责任公司 | Acidization method for oil well with pump |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106383220B (en) * | 2016-10-09 | 2018-08-24 | 东北石油大学 | The determination method and system of laboratory experiment non-newtonian fluid injection rate |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4593761A (en) * | 1984-07-20 | 1986-06-10 | Texaco Inc. | Miscible oil flooding at controlled velocities |
-
1988
- 1988-09-29 GB GB8822915A patent/GB2224055A/en not_active Withdrawn
-
1989
- 1989-09-12 CA CA000611050A patent/CA1326437C/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106321055A (en) * | 2016-08-26 | 2017-01-11 | 新疆克拉玛依市采丰实业有限责任公司 | Acidization method for oil well with pump |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8822915D0 (en) | 1988-11-02 |
| GB2224055A (en) | 1990-04-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKEC | Expiry (correction) |
Effective date: 20121205 |