The invention relates to the abandonment of hydrocarbon producing wells, and in particular to the placement of a plug in a well.

Background

Methods for abandoning wells involve placing a plug across the entire cross section of the well. Any cables or tubulars inside the well are usually removed in the area of the plug such that there are no obstructions and the plug can extend continuously from one formation wall to the opposite formation wall. Alternatively, tubulars are left in place and a plug is placed across one or more annuli and tubulars provided within the well. The plug prevents hydrocarbons from leaking out of the well after abandonment.

Statement of invention

According to a first aspect of the invention there is provided a method of treating a well, wherein the well comprises a tubular, an annulus arranged around the tubular, and a production packer arranged within the annulus; the method comprising providing first, second and third openings in the tubular wall to provide a path for fluid communication between the annulus and the tubular interior at the first, second, and third openings; wherein the first and second openings are below the production packer and wherein the third opening is above the production packer; providing a bypass portion within the tubular across the second and third openings, wherein the bypass portion provides a fluid path around the packer.

The bypass portion may divide the tubular interior into a first and a second section, wherein the fluid path around the packer passes through the first section which is isolated by the bypass portion from the second section. Optionally, the method further comprises cleaning a portion of the annulus and tubular interior by pumping fluid downwards through the tubular interior, through the first opening into the annulus, upwards though the annulus and around the packer via the second and third holes. The method may further comprise providing a base below the first opening across the tubular interior for supporting fluids or cement provided above the base, and optionally the base is provided prior to said fluids to cement being pumped into the tubular.

The method may further comprise providing a base in the annulus for supporting fluids or cement provided above the base in the annulus. The base may be a liner hanger within the annulus.

The method may further comprise providing a cement packer above the first opening and placing a first seal on the cement packer, and optionally the first seal is a dart-drift with a burst mechanism. The method may further comprise increasing fluid pressure above the dart-drift to burst the seal.

The method may further comprise pumping cement downwards through the tubular interior, and the pumping may be carried out using a cement train comprising an upper seal and a lower seal which enclose the cement within the tubular. By way of example, the upper seal and/or lower seal is a wiper plug or a dart.

The pumping of cement may take place at a rate of 1000 to 1500 litres per minute. Subsequently, the lower seal may be landed on the first seal. The pressure may then be increased and the lower seal can be burst.

Finally, the cement may be pumped into the annulus through the first opening and the pumping stops after the upper seal is landed onto the bypass portion.

According to a second aspect of the invention, there is provided a wellbore assembly for treating a well, comprising: a tubular provided within a well, an annulus between the tubular and a well casing, a production packer placed within the annulus; first, second and third openings in the tubular, wherein the first and second openings are provided below the packer and wherein the third opening is provided above the packer, a bypass portion provided within the tubular across the second and third openings, wherein the bypass portion provides a fluid path around the packer. The bypass portion may divide the tubular interior into a first and a second section, wherein the fluid path around the packer passes through the first section which is isolated by the bypass portion from the second section.

The assembly may further comprise a base below the first hole across the tubular interior, and a base within the annulus. The assembly may further comprise a cement packer arranged above the first opening and a first seal arranged on the cement packer. The first seal may be a dart-drift with a burst mechanism. The assembly may further comprise a cement train comprising an upper seal and a lower seal which enclose the cement within the tubular.

Figures

Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross section of a well;

Figure 2 is a schematic cross section of a well;

Figure 3 is a schematic cross section of a well;

Figure 4 is a schematic cross section of a well;

Figure 5 is a schematic cross section of a well;

Figure 6 is a schematic cross section of a well;

Figure 7 is a schematic cross section of a well;

Figure 8 is a schematic cross section of a well;

Figure 9 is a schematic cross section of a well;

Figure 10 is a schematic cross section of a well;

Figure 1 1 is a schematic cross section of a well;

Figure 12 is a schematic cross section of a well;

Figure 13 is a schematic cross section of a well;

Figure 14 is a schematic cross section of a well; and

Figure 15 is a flow diagram illustrating a method.

Specific description

Establishing a permanent cement plug is sometimes carried out by cementing all cross sectional cavities including the annulus. This technique involves establishing a continuous cement plug by circulating cement down central tubing and out into the annulus between the tubing and a production casing, which is referred to as the A- annulus, above the production packer. Together with the already present cement on the outside of the production casing, the cement in the A-annulus and the tubing constitute the continuous permanent cement plug. The plug is referred to as continuous to indicate that the plug seals all cavities over the entire cross section of the well. The plug is placed above the production packer. A difference between this type of permanent plug compared to the more conventional cement plugs is that the tubing is left in place when establishing the cement plug. A conventional standard method in the industry involves retrieving the tubing to the surface prior to placing cement for establishing a permanent plug.

The inventors have realised that placing an A-annulus cement plug below the production packer is particularly challenging due the obstruction of the production packer. The production packer forms a seal within the annulus between the tubular and the casing which prevents the flow of fluids such as water or cement through the annulus. In an embodiment of the invention first, second and third openings are provided in the tubular wall to provide a path for fluid communication between the annulus and the tubular interior at the first, second, and third openings. The first and second openings are below the production packer while the third opening is above the production packer. The openings may be provided in the tubular before the tubular is installed or before the abandonment process is started, or alternatively one or more of the holes may be made at the start of the process. The holes may be made with mechanical means, hydraulic means or other means such as explosives. A bypass portion is placed within the tubular across the second and third openings, such that the bypass portion provides a fluid path around the packer, while isolating the fluid path from the remaining part of the tubular interior. A bypass around the packer is thus provided and the fluid path enables the flow of both cleaning fluids and cement upwards through the annulus. A specific example of a bypass portion is a straddle, and in particular an inflatable packer or sealing element.

The straddle allows for a cleaning operation to be carried out in which cleaning fluids are circulated downwards through the interior of the tubular and back upwards through the annulus. A plug is provided below the first opening to direct the fluids into the first opening. After washing the interior of the tubular and the annulus, cement can be pumped down to fill an entire cross section of the well and allowed to set to form a plug below the production packer. An advantage of forming a plug below the production packer instead of above the production packer is the absence of control lines below the production packer, while control lines may be present above the production packer. The presence of control lines may compromise the integrity of the plug as they may cause leaks. The present method further avoids the need to remove production tubing and any attached control lines to the surface, or if possible removing the control lines with tubing left in place, before placing a plug.

Figure 1 shows a schematic cross-section of a cased wellbore 1 with productions casing 2, tubing 3, production packer 4, liner 5 and a liner hanger 6. Between the tubing 3 and the casing 2 there is an annulus 7, which may be referred to as the A- annulus. The annulus 7 is divided into two longitudinal sections 8 and 9 by the production packer 4. The lower section 8 extends longitudinally (i.e. along the length of the wellbore) between the production packer 4 and the liner hanger 6. The upper section 9 extends upwards from the production packer 4. A gauge carrier 10 is attached to the tubing.

Before the method is carried out, the cement integrity of the production casing cement is confirmed by data collected with a diagnostics tool or from data collected during cementing. Further, the amount of A-annulus available below the production packer is determined to decide whether a cement plug of sufficient length can be formed, which in practice is between 30 and 100 m.

Figure 2 shows the cased wellbore 1 in a first step of an embodiment of the invention. The figure shows production casing 2, tubing 3, production packer 4, liner 5, liner hanger 6, annulus 7, lower section of the annulus 8 and upper section of the annulus 9.

The liner hanger 6, or a liner packer or a gravel pack packer form the basis for the annulus plug, but other options may be available. If a base for the cement in the A- annulus does not exist, then this can be created for example using an epoxy plug on wireline. Figure 3 illustrates a subsequent step of the embodiment, in which the tubing 2 has been punched to create three punch intervals 20, 21 and 22 (i.e. three sections of perforated tubing). Upper and intermediate punch intervals 22 and 21 are made directly above and below the production packer 4, and the lower punch interval 20 is made directly above the liner hanger 6. A plug 23 (e.g. a bridge plug) is lowered and set in the liner 5 below the liner hanger 6. The plug 23 isolates the liner 5 below plug 23 from the tubing 3 above the plug 23.

Figure 4 illustrates a subsequent step wherein the upper section 9 of the annulus 7 has been washed with treated sea water 30 or brine 30. In general, a“washtrain” 30 comprising a suitable set of chemicals to ensure clean conditions may be used. Other wellbore fluids 31 may flow down below production packer 4. Since the production packer separates the upper and lower sections 8 and 9 of the annulus 7, the washing fluid 30 cannot be circulated below production packer. The upper punch interval 22, above the production packer 4, enables circulation of the washing fluid 30 above the production packer 4. That is, fluid 30 flows down the inner tubing 3, through the perforations 22 in the tubing 3, and returns up the annulus 7.

Figure 5 illustrates a subsequent step in which a cement packer 40 has been installed in the tubing 3 below the production packer 4 and directly above the lower punch interval 20. The function of the cement packer is providing a landing point for a lower dart of a cement train at a subsequent step which is described below.

In Figure 6, a straddle 50 or pipe with swell packers 50 has been installed to isolate the interior of tubing 3 from the upper and intermediate punch intervals 21 and 22 adjacent to the production packer 4. The interior of tubing 3 is in fluid communication with the annulus 7 only via the lower punch interval 20. The lower and upper section 8 and 9 of the annulus 7 are in fluid communication via the straddle 50.

Figure 7 illustrates a subsequent step, in which the tubing 3 and annulus 7 have been cleaned below the production packer 4, by circulating fluid through the lower punch interval 20. Returns can flow up the annulus 7 from the lower section 8 to the upper section 9 through the straddle 50. In Figure 8, a dart-drift 60 (or calliper dart 60) has been pumped down the tubing 3 and set in the cement packer 40. The dart 60 has a built in burst mechanism (e.g. including a membrane or shearing pins). After setting the dart 60, further pressurising the well 1 causes the dart 60 to open/burst, due to the burst mechanism.

Figure 9 shows a subsequent step of the embodiment, in which cement 70 has been pumped down the tubing 3, between a lower dart 71 and an upper dart 72. The column of wet cement 70 between the two darts 71 and 72 may be referred to as a“cement train” 70. The lower dart 71 pushes fluid 30 in front of it so that the fluid 30 cannot mix with the wet cement 70, thereby ensuring the integrity of the cement train 70.

In Figure 10, the cement 70 has been pumped down below the production packer 4. The lower dart 71 has landed on top of the open dart-drift 60 in the cement packer 40.

The cement train can be pumped down at a high rate such as 1000 to 1500 litres per minute, but the rate is subsequently reduced to a lower rate after landing the dart, such as 100-150 litres per minute for the next step of pumping cement into the A-annulus described below.

In Figure 1 1 , the pressure is increased until the lower dart 71 opens/bursts, to allow cement 70 to pass through the two open darts 60 and 71 and past the cement packer 40 down the tubing 3.

Figure 12 shows how the upper dart 72 and the cement 70 are further pumped down the tubing 3. Cement 70 flows through the perforations of the lower punch interval 20 and into the annulus 7 in the lower section 8.

In Figure 13, the upper dart 72 has been pumped down to the straddle 50, where it sets. The cement 70 has been circulated up the annulus 7 from the lower section 8 to the upper section 9 through the straddle 50.

Figure 14 illustrates the final plug 80 in the well 1 after the cement 70 has set. The plug 80 comprises of a continuous length of cement 70 in the tubing 3 and the surrounding annulus 7 below the production packer 4. In practice, the length of the plug below the production packer can be between 30 and 50m such in order to comply with safety requirements.

After placing the plug, the integrity of the plug can be tested and measured with various existing techniques.

Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.