Technical Field

The present disclosure relates to methods and apparatus for pressure testing wellbores in a downhole environment, and establishing fluid communication between a location inside a wellbore and one or more other locations after pressure testing is complete.

Background

Once a wellbore has been drilled, it is necessary to conduct a cementing operation to cement a casing/liner in place around the wellbore. This is commonly done by pumping cement down a centre of the casing and back up through anulus between the wellbore and the casing. In some applications, this anulus may be between two different casings. To move cement far enough downhole it is pumped downhole using a displacement fluid. To help keep the displacement fluid separate from the cement, a cementing dart (also called a cementing plug) may be used. A displacement fluid is present uphole of the cementing dart, and pumping the displacement fluid forces the cement downhole.

In order to comply with regulations, wellbores must be pressure tested after the cementing operation has taken place. It is also necessary to (eventually) establish a first fluid path between the inside of the wellbore and the formation (outside of the wellbore) in order that further pieces of equipment can be pumped downhole. Before a first fluid communication path is established between the borehole and the formation, equipment cannot be pumped downhole (a cheap method of getting equipment in position downhole), it must instead be put in position using, for example, drill pipe or coil tubing, both of which are far more expensive.

One method of obtaining a fluid path to the formation is to provide a toe sleeve system that includes a fluid flow path to the formation downhole before the cementing operation takes place. One problem with this is that any fluid flow path that is downhole during the cementing operation is likely to get permanently clogged with cement during the cementing operation.

As an attempted improvement to this problem, parties have considered using toe sleeves containing both a fluid path, and burst discs to block the entrance to the fluid path during the cementing operation. In theory, the burst discs prevent cement from entering the fluid path during the cementing operation, and then after the cementing operation, the burst discs can be burst (which opens the fluid path) by applying pressure from a displacement fluid, for example, during the required regulatory tests. One significant problem with the use of burst discs with this aim is that they have an extremely high failure rate. It is common for only up to 70% of burst discs to function as they were intended, with the rest either bursting too soon, or failing to burst at all. To slightly mitigate this problem, multiple burst discs can be built in, to give redundancy. However, due to costs and other concerns, it is common for only two burst discs to be provided, meaning that there is still a reasonably high chance that neither will function as intended, necessitating the use of drill pipe or coil tubing, at significantly increased cost

Additionally, because any burst discs that have not become clogged/broken will burst during regulatory testing, there is no choice but to have the functioning burst discs rupturing at that time.

The present invention results from Applicant’s work in developing a more reliable method for establishing a fluid path downhole after cementing operations are complete, and additionally, Applicant’s method and apparatus allows a user to customise when their fluid path opens after testing is carried out.

Summary

According to a first aspect there is provided a method for pressure testing a wellbore casing and establishing fluid communication between a first location inside a wellbore and a second location and/or a third location, the method comprising: providing a pressure testable toe sleeve for use in a wellbore, the pressure testable toe sleeve comprising: a port allowing fluid communication of a displacement fluid between the first location inside the wellbore and a chamber, via a first valve configured to open at or below the required test pressure, and the port being pluggable by a plug; the plug being configured to prevent ingress of cement into the port during a cementing operation, and the first valve being configured to allow fluid communication between the first location and the chamber when the first valve is open; the method further comprising: conducting a cementing operation while the plug is plugging the port, the cementing operation comprising using a cementing dart to separate the cement from a displacement fluid; testing the casing at the required test pressure, opening the first valve, and removing the plug, allowing the displacement fluid to flow from the first location in the wellbore to the chamber, and the displacement fluid to flow to the second location and/or the third location.

According to a second aspect there is further provided a pressure testable toe sleeve for use in a wellbore, the pressure testable toe sleeve comprising: a port allowing fluid communication of a displacement fluid between the first location inside the wellbore and a chamber, via a first valve configured to open at or below the required test pressure, and the port being pluggable by a plug; the plug being configured to prevent ingress of cement into the port during a cementing operation, and the first valve being configured to allow fluid communication between the first location and the chamber when the first valve is open.

The following optional features may be found in either the first or second aspects of the present invention.

Optionally, the plug is degradable when in contact with the displacement fluid. Optionally, there are a plurality of plugs.

Optionally, the material and/or the shape, and/or the dimensions of the degradable plug are chosen to provide a desired degradation time.

Optionally, the degradation time of the degradable plug is between 10 hours and 100 hours, preferably between 20 hours and 30 hours

Optionally, the first valve is a first piston held in position by one or more shear pins.

Optionally, the first valve and/or the second valve is rubber coated.

This helps to prevent cement from bonding to the valve

Optionally, the rubber coating is a swellable rubber.

Optionally, the chamber comprises a second valve, the second valve preventing fluid connection between the chamber and the second location when the second valve is closed, and allowing fluid connection between the chamber and the second location when the second valve is open.

Optionally, the second valve is controlled by a degradable stop, the degradable stop being degradable when in contact with the displacement fluid.

Optionally, the second valve comprises a second piston held in position by the degradable stop in the chamber after valve 1 has been opened and until the degradable stop has degraded.

Optionally, the material and/or the shape, and/or the dimensions of the degradable stop are chosen to provide a desired degradation time. Optionally, the degradation time of the degradable stop is between 30 minutes and 48 hours, preferably between 1 hours and 12 hours

Optionally, the second location is outside the wellbore.

Optionally, the blockade holder comprises a degradable blockade holder that is removed by degrading in contact with the displacement fluid.

Optionally, displacement fluid in the chamber is in contact with the degradable blockade holder, thereby removing it.

Optionally, the third location is inside the wellbore, downhole of the second position of the cementing dart.

Optionally, a chemical or other substance could be present in the chamber, the substance increasing the degrading effect of the displacement fluid.

Optionally, the substance could be a salt, or an acid powder some other ones could be acid powders.

The following optional features may be found in the first aspect of the present invention.

Optionally, the step of removing the plug comprises waiting for the plug to degrade, the degradation of the plug occurring after the cementing operation, but before the pressure testing of the wellbore casing.

Optionally, the step of opening the first valve comprises the pressure of the testing shearing the shear pins, allowing the first piston to be moved by the displacement fluid.

Optionally, the step of opening the second valve comprises waiting for the degradable stop to degrade. Optionally, the step of opening the second valve further comprises the second piston being moved by the displacement fluid after the degradable stop has degraded.

Optionally, the cementing operation further comprises the cementing dart impacting a blockade, the blockade allowing cement to pass through the blockade, but not allowing the cement dart to pass the blockade, and the blockade being held in position by a removable blockade holder.

Optionally, the method further comprises: waiting for the removable blockade holder to be removed; the removal of the removable blockade holder allowing the displacement fluid to force the cementing dart to a second position downhole of the initial position of the cementing dart.

Optionally, the method further comprises: the movement of the cementing dart to a second position allowing the displacement fluid to flow from the first location to the third location.

Optionally, the test pressure is higher than the pressure in the wellbore after testing.

Further features and advantages of the first and second aspects of the present disclosure will become apparent from the claims and the following description.

Brief Description of Drawings

Embodiments of the present disclosure will now be described by way of example only, with reference to the following diagrams, in which: -

Fig. 1 is a cross sectional view through a pressure testable toe sleeve, shown before a cementing operation has occurred, and before any of its degradable parts (the degradable plugs, the degradable stop, and the degradable blockade holder) have degraded;

Fig. 2 is a close up view of the left hand side of Fig. 1; Fig. 3 is a cross sectional view through the pressure testable toe sleeve of Fig. 1, shown after the cementing operation has occurred, but before any of its degradable parts (the degradable plugs, the degradable stop, and the degradable blockade holder) have degraded;

Fig. 4 is a cross sectional view through the pressure testable toe sleeve of Fig. 1, shown after the cementing operation has occurred, and after the degradable plugs have degraded (the degradable stop, and the degradable blockade holder are still in place);

Fig. 5 is a cross sectional view through the pressure testable toe sleeve of Fig. 1, shown after a test at test pressure has occurred (the degradable stop, and the degradable blockade holder are still in place);

Fig. 6 is a cross sectional view through the pressure testable toe sleeve of Fig. 1, shown after the degradable stop, and the degradable blockade holder have degraded;

Fig. 7 is a close up view of the left hand side of Fig. 6; and

Fig. 8 is a close up view of the right hand side of Fig. 6.

Detailed Description

Figs. 1 and 2 show a cross sectional view through a pressure testable toe sleeve 1, shown before a cementing operation has occurred, and before any of its degradable parts (the degradable plugs 3, the degradable stop 5, and the degradable blockade holder 7) have degraded. Each plug 3 plugs a port 9 (best seen in Figs. 4-6). Ports 9 allow a displacement fluid, which is often water, sometimes with additives such as sugar, to pass from a first location 11 in the wellbore, through the ports 9 and into contact with a valve, annular piston 13. Annular piston 13 is held in place by shear pins 15, and annular piston 13 is a valve that prevents the displacement fluid from entering chamber 17 from a first location 11 in the wellbore via the ports 9 while piston 13 is in the position shown in Figs. 1-4. Shear pins 15 are configured to shear at or below the desired test pressure of the wellbore, allowing valve

13 to open. When valve 13 is open, the displacement fluid can enter chamber 17.

Pressure testable toe sleeve 1 can be used as follows. Pressure testable toe sleeve 1 has an uphole end 19 and a downhole end 21. When toe sleeve 1 is fitted in a downhole environment, each port 9 is plugged by a degradable plug 3, as shown in Figs. 1-3. A cementing operation is carried out. This includes pumping cement down the wellbore in a downhole direction, through first location 11, through toe sleeve 1, through a blockade 23, and through a baffle 25. The displacement fluid forces the cementing dart 27 downhole, which pushes the cement downhole, until the cementing dart 27 hits a blockage. In this embodiment, the cementing dart 27 is received by blockade 23. Blockade 23 is held in position by degradable blockade holder 7 (until blockade holder 7 degrades). Plugs 3 prevent cement from entering ports 9 during the cementing operation.

Immediately after the cementing operation, the toe sleeve 1 will look as shown in Fig. 3. The cementing dart and the cement are downhole of ports 9, and degradable plugs 3, and first location 11. First location 11 is filled with displacement fluid. Plugs 3 now degrade as a result of contact with the displacement fluid.

In preferred embodiments, Applicant prefers the degradation time of the degradable plug to be between 10 hours and 100 hours, and preferably between 20 hours and 30 hours.

Applicant has found that standard magnesium alloys that degrade (otherwise known as dissolving or corroding) in aqueous chloride environments are suitable materials for use as the degradable plug(s) and or the degradable stop and/or the degradable blockade holder when the displacement fluid will be saline. Applicant has had particularly good results with SoluMag 1100 available from Luxfer Mel Technologies.

Applicant has found that standard magnesium alloys that degrade (otherwise known as dissolving or corroding) in low chloride environments are suitable materials for use as the degradable plug(s) and or the degradable stop and/or the degradable blockade holder when the displacement fluid will be a low chloride fluid. Applicant has had particularly good results with SoluMag FW available from Luxfer Mel Technologies.

Once the displacement fluid is known, the shape, thickness, surface ridging etc of each degradable part can be adjusted to alter its approximate degradation time under the conditions it will be operating under.

Once sufficient time has passed for plugs 3 to have degraded, the pressure test can be conducted. During the pressure test, the pressure of the displacement fluid is increased to test pressure. Shear pins 15 are configured to shear at or below test pressure. Therefore, during testing, shear pins 15 shear, allowing first piston 13 to move, allowing fluid connection between the first location 11 and the chamber 17. Chamber 17 therefore fills with displacement fluid. Figure 5 shows the toe sleeve 1 immediately after the first piston 13 has moved. In this embodiment, there is a piston stop 19.

As soon as chamber 17 is filled with displacement fluid, the displacement fluid is in contact with both the degradable stop 5, and the degradable blockade holder 7, and they begin to degrade. Applicant has found that materials that are suitable for use as degradable plugs are also suitable for use as the degradable stop 5, and/or the degradable blockade holder 7. However, it will also be appreciated that the materials used for the or each of the degradable plugs 3, degradable stop 5, and/or the degradable blockade holder 7 do not need to be identical to each other.

In the present embodiment, the chamber 17 has a second valve comprising degradable stop 5 and second piston 29. Annular second piston 29 is biased in an uphole direction due to hydrostatic pressure, because void 31 is at atmospheric pressure, but is prevented from moving in the uphole direction by degradable stop 5 (until stop 5 degrades).

Figs. 5 and 6 and 7 show the toe sleeve 1 after stop 5 and degradable blockade holder 7 have degraded. As a result of stop 5 degrading, nothing is preventing second annular piston 29 from moving in an uphole direction. Once second annular piston 29 has moved (valve open), the displacement fluid can flow from chamber 17 through second ports 33 to the second location, which in this embodiment is the formation outside the wellbore. It will be appreciated that ports 33 could be provided with a plug or valve or some sort, including, but not limited to, a degradable plug.

As shown in Fig. 4, the displacement fluid biases the cement dart in a downhole direction, and the cement dart pushes the blockade in a downhole direction, and the blockade is held in position by degradable blockade holder 7 (until degradable blockade holder 7 degrades). Once degradable blockade holder 7 has degraded, the displacement fluid , the cement dart, and the blockade all move in a downhole direction. In the present embodiment there is a baffle 25 which stops the movement of the cementing dart and the blockade in a predetermined location. The predetermined location has a bypass fluid path allowing the displacement fluid to leave the inside of the wellbore through holes 35, bypass the cementing dart through annular channel 37, and rejoin the inside of the wellbore at a position downhole of the cementing dart through holes 39. In this embodiment, this location downhole of the cement dart is the third location.

It will be appreciated that although the present embodiment has both a the fluid path leading to the second location (outside the wellbore) and another fluid path leading to a third location(downhole of the second position of the cementing dart), alternative products or methods according to the claimed invention could be provided with one or the other fluid path, or both fluid paths.

Although particular embodiments of the disclosure have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims.