NO20180438A1

NO20180438A1 - A method and system for assessing pressure integrity in a well

Info

Publication number: NO20180438A1
Application number: NO20180438A
Authority: NO
Inventors: Morten Myhre; Arne Gunnar Larsen; Arnold Østvold
Original assignee: Hydra Systems As
Priority date: 2018-03-27
Filing date: 2018-03-27
Publication date: 2019-09-30
Also published as: NO344741B1

Description

A METHOD AND SYSTEM FOR ASSESSING PRESSURE INTEGRITY IN A WELL

Technical field

The invention concerns a method and a system for assessing pressure integrity of a confined plugging material in a subterranean well, for example in a vertical or deviated production well, injection well, water well or hydrothermal well. As such, the invention may be used to assess and potentially verify the pressure integrity of one or more barriers of plugging material in a well, for example in context of plugging and abandoning (P&A) a well permanently or temporarily. The invention may also be suitable for other plugging purposes, such as zone isolation, sidetracking or remedial repairs in a well. Further, the invention is suitable for rig-less applications and may therefore be particularly advantageous in offshore settings where operational costs are especially high.

Technical background

A positive and/or negative pressure test is typically performed in a well in order to assess and verify the pressure integrity of one or more fluid-sealing plugs (or barriers) therein. Such a plug (e.g. cement plug) may be present within a pipe body (e.g. casing or liner) and/or within a surrounding annulus in the well.

When performing a positive pressure test, the hydrostatic pressure above the plug is increased and observed for a period of time to assess the pressure-sealing capacity of the plug and the associated pipe body/bodies. If the plug holds the pressure, the plug is verified as a pressure-sealing barrier in the well. During the positive test procedure, the net differential pressure direction is typically opposite to pressure direction of pressurized formation fluids (e.g. oil and/or gas) in the well.

When performing a negative pressure test, however, the hydrostatic pressure above the plug is reduced and observed for a period of time to assess the pressure-sealing capacity of the plug and associated pipe body/bodies. In order to reduce the pressure above the plug, a lighter fluid (e.g. water or gas) is typically introduced in a column of liquid (e.g. mud) above the plug. During the negative test procedure, the net differential pressure direction typically coincides with the pressure direction of pressurized formation fluids (e.g. oil and/or gas) in the weii. The negative pressure test therefore simulates a situation in which pressurized formation fluids act against the piug. By so doing, the plug and associated pipe body/bodies are tested in a situation resembling a realistic well pressure setting. For this reason, the negative pressure test is generally the preferred and most representative pressure verification test (i.e. over the positive pressure test). A negative pressure test is typically performed at the end of a well, e.g. before disconnecting a blowout preventer (BOP) or similar, to verify and thus assure that one or more plugs (or barriers) in the well are capable of withstanding formation pressures and thus preventing fluid leakages or a blowout from the well.

Although the preferred pressure test, the negative pressure test is disadvantageous in that it requires introduction of a lighter fluid in the hydrostatic column of liquid (e.g. mud) above the plug so as to reduce the hydrostatic pressure in the column, This operation requires manipulation and exchange of fluids both before and after the test, also requiring various equipment and handling to do so. The operation is therefore time consuming and costly to perform.

It would therefore be advantageous could such a negative pressure test be performed without having to manipulate and exchange the fluids in the well in order to provide the required pressure drop. It would also prove beneficial to be able to perform both a negative and a positive pressure test of a plug/barrier element during the same downhole operation in a well.

Accordingly, there appears to be a need in the industry, e.g. the petroleum industry, for simpler and more cost-efficient solutions for assessing and verifying the pressure integrity of one or more fluid-sealing plugs/barriers in a subterranean well.

Summary

The primary object of the present invention is to remedy or reduce at least one disadvantage of prior art methods of assessing the pressure integrity of a confined plugging material (i.e. one or more fluid-sealing plugs or barriers) in a well, or at least to provide a useful alternative to the prior art methods.

A further object is to provide new and/or improved solutions for making assessment and verification of said confined plugging material more expedient and cost-efficient than that currently afforded by prior art pressure testing methods.

Another object is to provide solutions suitable for rig-less applications, which may be particularly advantageous in offshore settings.

As will become clear in the following, the present invention and various embodiments thereof serve to meet these objects of the invention, hence serve to provide expedient and cost-efficient pressure testing solutions.

The objects are achieved by virtue of steps and features disclosed in the following description and subsequent claims.

In a first aspect, the present invention comprises a method for assessing pressure integrity of a section of confined plugging material in a well comprising at least one pipe body, including an innermost pipe body containing liquid, and at least one corresponding annulus located between the innermost pipe body and a surrounding wellbore wall, the method comprising:

(B) at a select location in the well, establishing a confined region of fixed volume within the innermost pipe body, the confined region containing liquid and in isolated liquid communication with the section of confined plugging material;

(C) with a selectively operable pressure altering tool in isolated liquid communication with the confined region, inducing a simultaneous pressure and volumetric change in the liquid of the confined region whilst displacing, relative to the fixed volume of the confined region, a volume of liquid corresponding to said volumetric change;

(D) measuring the pressure in the confined region over a period of time to establish a pressure development history in response to said pressure change therein; and (E) based on the pressure development history, assessing the pressure integrity of the section of confined plugging material in isolated liquid communication with the

The present invention is based on the fact that liquids are compressible to some degree and therefore have a measurable compressibility, which is a function of liquid pressure and temperature. Further, compressibility generally decreases somewhat with increasing pressure. Compressibility is defined as the fractional change in volume per unit increase in pressure. This implies that liquids will experience a measurable reduction in volume when pressurized sufficiently or, vice versa, that liquids will experience a measurable increase in volume in response to a sufficient pressure reduction therein. Water, for example, has a compressibility of 4.6 x 10<'10>Pa<-1>at room temperature and atmospheric pressure. As such, water will increase in volume by approximately 0.9 % upon reducing the water pressure by approximately 200 bars, which corresponds to a water column being 2000 metres long. Similarly, water will increase in volume by approximately 1.8 % upon reducing the water pressure by approximately 400 bars, which is the equivalent of a water column being 4000 metres long.

Therefore, if subjecting water in a confined space having a fixed volume of e.g. 20 litres to a relatively large pressure drop of e.g. 200 bars, the water will increase in volume by approximately 2 decilitres. The excess volume of water thus generated (i.e.

2 decilitres) must be evacuated from the confined space in order to maintain the lowered pressure therein. On the contrary, if subjecting water in the fixed volume of 20 litres to a corresponding pressure increase, the water will decrease in volume and thus require a corresponding volume of water to be supplied to the confined space in order to maintain the elevated pressure therein. This also implies that it is possible to induce a significant pressure change in the confined space of fixed volume by simply inducing a small volumetric change in the water therein. Importantly, the volume of the confined space remains fixed during manipulation of the pressure and volume of the water therein.

Insofar as liquids used in a well typically contain water and/or some other type of liquid, hence exhibit similar compressibility values and volumetric changes in response to pressure changes, the above principle of manipulating the pressure and volume of such a liquid may also be used in a confined region (i.e. space) of a well. This is therefore the underlying principle of the present invention (i.e. method and system) when used to generate a significant pressure change in the confined region thereof.

Further, the well may comprise only the innermost pipe body and an outwardly surrounding annulus.

Alternatively, the well may comprise two or more progressively larger pipe bodies arranged in a pipe-in-pipe constellation, and two or more outwardly surrounding and corresponding annuli.

Typically, some type of drilling mud or completion liquid (also termed "completion fluid") may be present as said liquid in the at least one pipe body, and commonly also in the at least one outwardly surrounding annulus.

The pressure altering tool may comprise at least one pressure sensor configured and operable to measure, in step (D), the pressure in the confined region.

Further, the pressure altering tool may comprise at least one sonic sensor configured and operable to acquire, in step (D), acoustic signals related to potential leakage of liquid relative to the confined region. Leaks that may influence the pressure measurements in the confined region, and which may take place in seals and/or packers associated with the pressure altering tool, may thus be detected and accounted for.

Yet further, the pressure altering tool may comprise a selectively operable closing valve configured and operable to close, in step (C), the tool to communication with ambient liquid. This ambient liquid could be present externally in the innermost pipe body and/or in a tubular string connected to the pressure altering tool. The closing valve may comprise, for example, at least one flapper valve.

In a first embodiment of the method, the pressure altering tool comprises a selectively operable pressure reduction tool; and

- wherein step (C) comprises operating the pressure reduction tool and thus simultaneously reducing the liquid pressure of the confined region to a first pressure whilst evacuating, from the fixed volume of the confined region, a first volume of liquid corresponding to a volumetric increase therein due to said pressure reduction, thereby performing a negative pressure test of the section of confined plugging material.

In context of this first embodiment, a first pressure relief valve may be positioned in communication with the confined region and also in communication with ambient liquid, the first pressure relief valve set to open at the first pressure upon operating the pressure reduction tool and thus reducing the pressure in the confined region. This prevents a further pressure drop therein in the event of continued operation of the pressure reduction tool. The first pressure relief valve may be included in the pressure reduction tool.

Further, the pressure reduction tool may comprise a suction device.

More particularly, the suction device may comprise a first piston and cylinder assembly configured and operable to generate said pressure reduction in step (C). In one embodiment, the first piston and cylinder assembly is operably connected to a tubular string for providing, in step (C), a mechanical actuation force to the first piston and cylinder assembly. In another embodiment, the first piston and cylinder assembly is operably connected to a second piston and cylinder assembly for providing, in step (C), a hydraulic actuation force to the first piston and cylinder assembly, the second piston and cylinder assembly operably connected to a tubular string containing a liquid for allowing selective pressurization thereof and operation of the second piston and cylinder assembly.

In a second embodiment of the method, which is additional or alternative to the first embodiment of the method, the pressure altering tool comprises a selectively operable pressure increase tool; and

- wherein step (C) comprises operating the pressure increase tool and thus simultaneously increasing the liquid pressure of the confined region to a second pressure whilst supplying, to the fixed volume of the confined region, a second volume of liquid corresponding to a volumetric decrease therein due to said pressure increase, thereby performing a positive pressure test of the section of confined plugging material.

In context of this second embodiment, a second pressure relief valve may be positioned in communication with the confined region and also in communication with ambient liquid, the second pressure relief valve set to open at the second pressure upon operating the pressure increase tool and thus increasing the pressure in the confined region. This prevents further pressure increase therein in the event of continued operation of the pressure increase tool. The second pressure relief valve may be included in the pressure increase tool.

Further, the pressure increase tool may comprise a pump device.

More particularly, the pump device may comprise a first piston and cylinder assembly configured and operable to generate said pressure increase in step (C). In one embodiment, the first piston and cylinder assembly is operably connected to a tubular string for providing, in step (C), a mechanical actuation force to the first piston and cylinder assembly. In another embodiment, the first piston and cylinder assembly is operably connected to a second piston and cylinder assembly for providing, in step (C), a hydraulic actuation force to the first piston and cylinder assembly, the second piston and cylinder assembly operably connected to a tubular string containing a liquid for allowing selective pressurization thereof and operation of the second piston and cylinder assembly.

In a third embodiment of the method, the section of confined plugging material comprises plugging material located within the innermost pipe body and below the confined region.

The plugging material may comprise cementitious material, such as cement commonly used in wells.

In context of this third embodiment, the confined region may be defined between the section of plugging material within the innermost pipe body, and a sealing element configured for fluid-sealing engagement with an inner wall of the innermost pipe body.

Further, the sealing element may comprise a packer element.

More particularly, the packer element may comprise a selectively operable and radially expandable packer. The radially expandable packer may also be selectively retractable to allow the packer to be set and unset one or more times during a downhole operation in the well.

Yet further, the sealing element may comprise a selectively operable and radially expandable gripping element configured for gripping engagement with the inner wall of the innermost pipe body. The radially expandable gripping element may also be selectively retractable to allow the gripping element to be set and unset one or more times during a downhole operation in the well. The gripping element may be in the form of a gripping dog or similar provided with gripping teeth for gripping engagement with said pipe body.

The sealing element may also comprise a resinous body, which provides a tight and flexible seal against the inner wall of the innermost pipe body.

Further, the sealing element may be operably connected to the pressure altering tool for allowing fluid-sealing engagement with the inner wall of the innermost pipe body.

In a fourth embodiment of the method, the section of confined plugging material comprises annular plugging material located within the at least one annulus and in vicinity of the select location.

In one variant of this fourth embodiment, step (B) of the method comprises bringing the confined region in isolated liquid communication with at least one hole previously formed (hence already existing) in the at least one pipe body at the select location, the at least one hole already in communication with said annular plugging material.

In another variant of this fourth embodiment, the method also comprises the following steps before step (B):

(A1) positioning a perforation tool in the innermost pipe body at the select location;

(A2) with the perforation tool, forming at least one hole in the at least one pipe body at the select location; and

- wherein step (B) also comprises bringing the confined region in isolated liquid communication with the at least one hole formed in step (A2), thereby establishing communication with said annular plugging material.

The annular plugging material may comprise cementitious material, such as cement commonly used in wells. Additionally or alternatively, the annular plugging material may comprise formation material from the surrounding wellbore wall, such as formation material having collapsed or moved inwards from the surrounding wellbore wall. Preferably, such formation material has low permeability.

Further in context of this fourth embodiment, the select location may be a location above the section of confined annular plugging material, thereby establishing, in step (B), communication with an annular region located above the section of confined annular plugging material.

Alternatively, the select location may be a location below the section of confined annular plugging material, thereby establishing, in step (B), communication with an annular region located below the section of confined annular plugging material.

Yet alternatively, the select location may be a location vis-å-vis the section of confined annular plugging material, thereby establishing, in step (B), communication with an interior region of the section of confined annular plugging material.

Yet further in context of this fourth embodiment, the confined region may be defined between a first sealing element and a second sealing element, both sealing elements configured for fluid-sealing engagement with an inner wall of the innermost pipe body.

As such, at least one of the first sealing element and the second sealing element may comprise a packer element.

Further, at least one of the first sealing element and the second sealing element may comprise a selectively operable and radially expandable gripping element configured for gripping engagement with the inner wall of the innermost pipe body. The radially expandable gripping element may also be selectively retractable to allow the gripping element to be set and unset one or more times during a downhole operation in the well.

Additionally or alternatively, at least one of the first sealing element and the second sealing element may comprise a resinous body, which provides a tight and flexible seal against the inner wall of the innermost pipe body.

The method according to any one of claims 39-45, wherein at least one of the first sealing element and the second sealing element is operably connected to the pressure altering tool for allowing fluid-sealing engagement with the inner wall of the innermost pipe body, which provides a tight and flexible seal against the inner wall of the innermost pipe body.

In a fifth embodiment, the method also comprises the following steps before step (B): (A1) positioning a perforation tool in the innermost pipe body;

(A2) with the perforation tool, forming a series of spaced apart holes in the at least one pipe body along a longitudinal section of the well, an uppermost hole and a lowermost hole thereof defining the extent of the longitudinal section;

(A5) placing a fluidized plugging material within the innermost pipe body and along at least the longitudinal section, also allowing the fluidized plugging material to enter the at least one annulus via said holes in the at least one pipe body so as to form a substantially cross-sectional plug along the longitudinal section;

(A6) removing an upper part of the plug from within the innermost pipe body so as to expose holes therein along the removed upper part of the plug, thereby retaining a lower part of the plug within the innermost pipe body and also an annular part of the plug along the entire longitudinal section, said retained plug material constituting the section of confined plugging material in the well;

- wherein the confined region is defined between said lower part of the plug and a sealing element in fluid-sealing engagement with an inner wall of the innermost pipe body; and

- wherein step (B) also comprises bringing the confined region in isolated liquid communication with at least one hole exposed in step (A6), thereby establishing communication with said lower part of the plug and also with an interior region of the annular part of the plug.

Step (A2) may include spacing the holes substantially evenly along the longitudinal section.

The method may also comprise the following steps between steps (A2) and (A5): (A3) positioning a washing tool in the innermost pipe body at the longitudinal section;

(A4) displacing a washing liquid out of the washing tool and directing the washing liquid out into the at least one annulus via holes formed along the longitudinal section in step (A2), thereby removing any debris therein and cleaning both the innermost pipe body and the at least one annulus before placing the fluidized plugging material therein in step (A5).

Such debris may comprise various particles, deposits and/or well fluids, for example filter cake, formation particles, drill cuttings, drilling additives, e.g. barite, cement particles and/or residues and old drilling mud (or similar), that have settled out or remain in the annulus from previous well operations.

Step (A4) may comprise pumping the washing liquid from surface and down to the washing tool via a tubular string.

The annular plugging material may comprise cementitious material, such as cement commonly used in wells. Additionally or alternatively, the fluidized plugging material may comprise resinous material.

Further, the sealing element may comprise a packer element.

More particularly, the packer element may comprise a selectively operable and radially expandable packer. The radially expandable packer may also be selectively retractable to allow the packer to be set and unset. The packer may also be configured to longitudinally span several of the holes exposed in step (A6) of the method. This may prevent liquids from potentially bypassing the packer via the annulus when in fluidsealing engagement with the innermost pipe body and operating the pressure altering tool.

Yet further, the sealing element may comprise a selectively operable and radially expandable gripping element configured for gripping engagement with the inner wall of the innermost pipe body. The radially expandable gripping element may also be selectively retractable to allow the gripping element to be set and unset.

Additionally or alternatively, the sealing element may comprise a resinous body, which provides a tight and flexible seal against the inner wall of the innermost pipe body. The resinous body may also be configured to longitudinally span several of the holes exposed in step (A6) of the method. This may also prevent liquids from potentially bypassing the packer via the annulus when in fluid-sealing engagement with the innermost pipe body and operating the pressure altering tool.

In a second aspect, the present invention comprises a system for assessing the pressure integrity of a section of confined plugging material in a subterranean well, the system comprising:

- at least one pipe body, including an innermost pipe body containing liquid, positioned in the well;

- at least one corresponding annulus located between the innermost pipe body and a surrounding wellbore wall of the well;

- a confined region of fixed volume established within the innermost pipe body at a select location in the well, the confined region containing liquid and in isolated liquid communication with the section of confined plugging material;

- a selectively operable pressure altering tool positioned in isolated liquid communication with the confined region, the pressure altering tool configured and operable to induce a simultaneous pressure and volumetric change in the liquid of the confined region and displace, relative to the fixed volume of the confined region, a volume of liquid corresponding to said volumetric change;

- at least one pressure sensor in communication with the confined region, the at least one pressure sensor configured and operable to measure the pressure in the confined region over a period of time to establish a pressure development history in response to said pressure change; and

- a data conveyance system for conveying pressure data measured over said period of time to a surface of the well for assessing the pressure integrity of the section of confined plugging material.

From this definition of the system, it is clear that many of the features and comments provided above in relation to the claimed method, also are inherent and thus applicable to the claimed system. For the sake of expedience, such comments will not be reiterated in the following, and reference is therefore made to the comments made in relation to the method above.

The data conveyance system may also contain batteries and other control equipment necessary for operation and control thereof. Such equipment would be familiar to a person skilled in the art and is therefore not discussed herein.

The system may also comprise at least one sonic sensor configured and operable to acquire acoustic signals related to potential leakage of liquid relative to the confined region; and

- wherein the data conveyance system is configured for conveying acoustic data acquired over said period of time to the surface of the well.

Further, the data conveyance system may comprise a data transmission unit configured and operable to transmit said data to the surface of the well. Such data may be transmitted wirelessly or via a suitable cable or similar. Equipment and methods associated with such transmission would also be familiar to the person skilled in the art and is therefore not discussed herein.

Additionally or alternatively, the data conveyance device may comprise a data recording unit configured for retrieval of said data to the surface of the well. Such a data recording unit and data recorded therein may be retrieved to the surface of the well for further assessment thereof. Also such data recording units would be familiar to the person skilled in the art and is therefore not discussed herein.

Yet further, the pressure altering tool may comprise a selectively operable closing valve configured and operable to close the tool to communication with ambient liquid. This ambient liquid could be present externally in the innermost pipe body and/or in a tubular string connected to the pressure altering tool. The closing valve may comprise at least one flapper valve.

In a first embodiment of the system, the pressure altering tool comprises a selectively operable pressure reduction tool, the pressure reduction tool configured and operable to simultaneously reduce the liquid pressure of the confined region to a first pressure and evacuate, from the fixed volume of the confined region, a first volume of liquid corresponding to a volumetric increase therein due to said pressure reduction, whereby the system is configured to perform a negative pressure test of the section of confined plugging material.

Further, the pressure reduction tool may comprise a suction device.

More particularly, the suction device may comprise a first piston and cylinder assembly configured and operable to generate said pressure reduction in the confined region. In one embodiment, the first piston and cylinder assembly is operably connected to a tubular string for providing a mechanical actuation force to the first piston and cylinder assembly. In another embodiment, the first piston and cylinder assembly is operably connected to a second piston and cylinder assembly for providing a hydraulic actuation force to the first piston and cylinder assembly, the second piston and cylinder assembly operably connected to a tubular string containing a liquid for allowing selective pressurization thereof and operation of the second piston and cylinder assembly.

In a second embodiment of the system, which is additional or alternative to the first embodiment of the system, the pressure altering tool comprises a selectively operable pressure increase tool, the pressure increase tool configured and operable to simultaneously increase the liquid pressure of the confined region to a second pressure and supply, to the fixed volume of the confined region, a second volume of liquid corresponding to a volumetric decrease therein due to said pressure increase, whereby the system is configured to perform a positive pressure test of the section of confined plugging material.

In context of this second embodiment, a second pressure relief valve may be positioned in communication with the confined region and also in communication with ambient liquid, the second pressure relief valve set to open at the second pressure upon operating the pressure increase tool and thus increasing the pressure in the confined region. This prevents a further pressure increase therein in the event of continued operation of the pressure increase tool. The second pressure relief valve may be included in the pressure increase tool.

Further, the pressure increase tool may comprise a pump device.

More particularly, the pump device may comprise a first piston and cylinder assembly configured and operable to generate said pressure increase in the confined region. In one embodiment, the first piston and cylinder assembly is operably connected to a tubular string for providing a mechanical actuation force to the first piston and cylinder assembly. In another embodiment, the first piston and cylinder assembly is operably connected to a second piston and cylinder assembly for providing a hydraulic actuation force to the first piston and cylinder assembly, the second piston and cylinder assembly operably connected to a tubular string containing a liquid for allowing selective pressurization thereof and operation of the second piston and cylinder assembly.

In a third embodiment of the system, the section of confined plugging material comprises plugging material located within the innermost pipe body and below the confined region; and

- wherein the confined region is defined between the plugging material within the innermost pipe body and a sealing element in fluid-sealing engagement with an inner wall of the innermost pipe body above said plugging material.

In a fourth embodiment of the system, the section of confined plugging material comprises annular plugging material located within the at least one annulus and in vicinity of the select location;

- wherein the confined region is defined between a first sealing element and a second sealing element, both sealing elements in fluid-sealing engagement with an inner wall of the innermost pipe body; and

- wherein the confined region is in isolated liquid communication with at least one hole formed in the at least one pipe body at the select location, the at least one hole in communication with said annular plugging material.

In a fifth embodiment of the system, the section of confined plugging material comprises annular plugging material located within the at least one annulus along a longitudinal section of the well, the section of confined plugging material also comprising plugging material located within the innermost pipe body along a lower portion of the longitudinal section;

- wherein the confined region is defined between a top of said plugging material within the innermost pipe body and a sealing element in fluid-sealing engagement with an inner wall of the innermost pipe body along an upper portion of the longitudinal section; and

- wherein the confined region (hence the select location) is in isolated liquid communication with at least one hole formed in the at least one pipe body along said upper portion of the longitudinal section, whereby the at least one hole is in communication with an interior region of said annular plugging material.

Brief description of the drawings

Exemplary embodiments of negative pressure tests according to the invention are now described and depicted in the accompanying drawings, where:

Figs. 1-3 show, in side view, a well provided with a pipe body having a cement plug therein, the cement plug to be pressure tested according to a first embodiment of the present invention;

Fig. 4 shows, in side view, a well provided with a pipe body and a surrounding annulus having collapsed formation material therein, the collapsed formation material to be pressure tested according to a second embodiment of the invention; and

Figs. 5-11 show, in side view, a well provided with a pipe body and a surrounding annulus, an annular part of a cement plug filling the annulus along a longitudinal section thereof, and an interior part of the cement plug filling the pipe body along a lower part of the longitudinal section, the interior and annular part of the cement plug to be pressure tested according to a third embodiment of the present invention.

The figures are schematic and merely show steps, details and equipment essential to the understanding of the invention. Further, the figures are distorted with respect to relative dimensions of elements and details shown therein. The figures are also somewhat simplified with respect to the shape and richness of detail of such elements and details. Elements not central to the understanding of the invention may also have been omitted from the figures. Further, equal, equivalent or corresponding details in the figures are given substantially the same reference numerals.

Detailed description of embodiments of the invention

Reference is made to Figures 1-3, which show a first embodiment of the present method and system.

Figure 1 shows a subterranean well 2 comprising a pipe body 4 (e.g. a casing or liner) and an annulus 6 located between the pipe body 2 and a surrounding wellbore wall 8 formed through formation material 10 (i.e. subterranean rocks). A cement plug 12 is located within a section of the pipe body 4. A negative pressure test of this cement plug 12 is to be performing according to this first embodiment of the present invention. A selectively operable pressure reduction tool 14, here in the form of a suction device, to be used for this purpose is shown positioned a short distance above a top of the cement plug 12. The pressure reduction tool 14, which is connected to a lower end of a tubular string 16 (e.g. drill string or coiled tubing), comprises a housing 18 and a selectively operable and radially expandable packer 20, which is also selectively retractable. The packer 20 may be of a type commonly used in the art and thus having a configuration and operating principle commonly known to a person skilled in the art. When lowering the pressure reduction tool 14 into the pipe body 4, the packer 20 is in a retracted position (not shown). Figure 1 shows the tool 14 at a select location in the well 2, and after having activated and expanded the packer 20 to fluid-sealing engagement with an inner wall 22 of the pipe body 4. A confined region 24 of fixed volume VF is thus defined between the top of the cement plug 12 and the packer 20 when in its set position. The confined region 24 and the interior of the pipe body 4 above the packer 20 is filled with ambient liquid 26 at hydrostatic pressure PH. In this case, the ambient liquid 26 consists of drilling mud, which is a liquid.

Figure 2 shows a partial cross section through the pressure reduction tool 14 of Figure 1, the cross section showing central elements of the tool 14. The housing 18 of the tool 14 includes a piston and cylinder assembly 28 comprising a cylinder 28a and a hollow piston 28b sealingly and slidably disposed within the cylinder 28a. The piston 28b is operably connected (not shown) to said tubular string 16 for providing a mechanical or hydraulic actuation force to the piston 28b. The hollow piston 28b includes a selectively operable closing valve 30, for example one or more flapper valves, configured and operable to close the tool 14 to communication with ambient liquid 26 in the tubular string 16. As such, the closing valve 30 remains open when lowering the tool 14 into the pipe body 4. The closing valve 30 is closed after setting of the expandable packer 20 and before operation of the piston 28b, as shown in Figure 2. The packer 20 includes a central passage 32, which is part of the fixed volume VF of the confined region 24. The packer 20 also includes a data recording unit 34 furnished with a pressure sensor (not shown) and a sonic sensor (not shown). The pressure sensor is configured and operable to measure the pressure in the confined region 24 over a period of time after activating the pressure reduction tool 14. The sonic sensor is configured and operable to acquire acoustic signals related to potential leakage of liquid 26 relative to the confined region 24 during said period of time, hence will indicate any leakage around the packer 20 or through seals (not shown) in the tool 14. The data recording unit 34 is also configured to record such pressure and acoustic data. Therefore, upon completing the negative pressure test and retrieving the pressure reduction tool 14 to the surface of the well 2, the data recording unit 34 and its data will also be retrieved to the surface for further assessment thereof. A pressure relief valve 36 is also positioned in the housing 18 below the piston 28b, whereby the pressure relief valve 36 is in communication with the confined region 24 and also in communication with ambient liquid 26 externally in the pipe body 4.

Figure 3 shows, also in partial cross section, the pressure reduction tool 14 of Figure 2 after having activated and moved the hollow piston 28b a distance upwards within the cylinder 28a whilst keeping the closing valve 30 in a closed position. This movement and distance is indicated with a bold arrow in Figure 3. The distance covered by the piston 28b defines an additional cylinder volume Vi being in contact with the fixed volume VF of the confined region 24. The suction thus produced induces a simultaneous pressure and volumetric change in the liquid 26 of the confined region 24. More particularly, the pressure of the liquid 26 in the confined region 24 is reduced to a first pressure Pi whilst the volume thereof is increased by a first volume Vi corresponding to said additional cylinder volume Vi. In this context, the pressure relief valve 36 is set to open at said first pressure Pi upon operating the pressure reduction tool 14 and thus reducing the pressure in the confined region 24. The pressure relief valve 36 therefore serves to maintain the pressure at Pi in the confined region 24 and thus prevent further pressure drop therein should the piston 28b be moved further upwards within the cylinder 28a. By operating the pressure reduction tool 14 in the above-described manner, a negative pressure test of the cement plug 12 is performed. The net pressure direction is shown with black arrows in Figure 3.

Additionally or alternatively, the above pressure reduction tool 14 can be readily adapted to perform a positive pressure test, thereby functioning as a pressure increase tool. This can be done by operating the piston 28b in the opposite direction, thereby increasing the pressure of the liquid 26 in the confined region 24 to a second pressure P2 whilst decreasing the volume thereof by a second volume V2(not shown), simultaneously supplying a volume of liquid 26 corresponding to the second volume V2. In this context, a corresponding pressure relief valve (not shown) is set to open at said second pressure P2 upon operating the piston 28b in the opposite direction and thus increasing the pressure in the confined region 24. This adaptation is applicable to all embodiments described herein.

Reference is now made to Figure 4, which shows a second embodiment of the present method and system. In this second embodiment, the same pressure reduction tool 14 (and operation thereof) is employed to perform a negative pressure test of a section of annular plugging material 10<'>located in the annulus 6 of the well 2. The annular plugging material 10<'>comprises formation material 10 having collapsed or moved inward from the surrounding wellbore wall 8. The annular plugging material 10<'>is expected to have low permeability and therefore may have pressure-sealing capacity in the annulus 6. Such collapsed formation material is commonly referred to as "creeping shale" in the industry. Figure 4 also shows several holes 38 formed in the pipe body 4 at a select location vis-å-vis the annular plugging material 10<'>, thereby establishing communication with an interior region of the annular plugging material 10<'>. A suitable perforation or cutting tool (not shown) may be used to form the holes 38. A sealing element, here in the form of a mechanical plug 40 (e.g. a bridge plug or similar), is also shown positioned a short distance below the holes 38 and in fluidsealing engagement with the inner wall 22 of the pipe body 4. The expandable packer 20 of the pressure reduction tool 14 is shown positioned a short distance above the holes 38, and in fluid-sealing engagement with the inner wall 22 of the pipe body 4. The confined region 24 of fixed volume VF is thus defined between the packer 20 and the mechanical plug 40, the confined region 24 thus being in isolated liquid communication with the interior region of the annular plugging material 38 via said holes 38. Figure 4 shows the pressure reduction tool 14 activated and in the process of performing a negative pressure test of the section of annular plugging material 10<'>, where the net pressure direction is shown with black arrows in the figure.

Reference is made to Figures 5-11, which show a third embodiment of the present method and system. In this third embodiment, the same pressure reduction tool 14 (and operation thereof) is employed to perform a negative pressure test of a cement plug 58<'>formed within the pipe body 4 and also in the surrounding annulus 6 along a longitudinal section L of the well 2. This cement plug is formed using the so-called Perf-Wash-Cement - PWC® - method, as shown in Figures 5-9. Various variants of the PWC-method have been disclosed in e.g. WO 2012/096580 Al, WO 2013/133719 A1 and WO 2016/200269 Al.

Figure 5 shows a perforation tool, here in the form of a perforation gun 42, positioned in the pipe body 4 along the longitudinal section L of the well 2. The perforation gun 42 is connected to the lower end of said tubular string 16 (e.g. drill string or coiled tubing) and includes a series of explosive charges 44 spaced apart and aligned in a select pattern along the gun 42. These explosive charges 44 are pressure-activated in this particular embodiment, as is common in the art. It is to be understood that the same tubular string 16 or some other tubular string or lengthy connection element (e.g. wireline or cable) could be used to convey and/or operate the perforation tool within the well 2.

Figure 6 shows the well 2 after having activated the explosive charges 44 in the perforation gun 42 and thus having formed a series of spaced apart holes 46 through the pipe body 4 along the longitudinal section L. The perforation gun 42 has also been removed from the pipe body 4. An uppermost hole 46a and a lowermost hole 46b defines the extent of the longitudinal section L. The holes 46 are also spaced substantially evenly along the longitudinal section L. Other types of perforation or cutting tools (not shown) may also be used to form these holes 46, for example a jetting tool employing jets of abrasive liquid to cut holes 46 through the pipe body 4.

Figure 7 shows a washing tool 48 positioned in the pipe body 4 at the longitudinal section L of the well 2. The washing tool 48 is connected to a lower end of said tubular string 16 for operation thereof and supply of a suitable washing liquid 50 (e.g. drilling mud). The figure also shows jets of washing liquid 50 being displaced out of variously angled nozzles 52 in the washing tool 48. The angled jets are directed out into the annulus 6 via the holes 46 formed in the pipe body 4. The washing tool 48 is also moved during washing so as to remove debris 54 in the annulus 6 and thus clean both the pipe body 4 and the annulus 6 along the longitudinal section L. The debris 54 are entrained in washing liquid 50 being circulated from the annulus 6 and into the pipe body 4 and further up through the pipe body 4 to the surface of the well 2. The circulatory pattern is indicated with black arrows in Figure 7. The washing tool 48 is removed from the pipe body 4 upon completion of the washing operation. It is to be understood that the same tubular string 16 or some other tubular string or lengthy connection element could be used to convey and/or operate the washing tool 48 within the well 2.

Figure 8 shows an open ended tubular string 16 inserted into the pipe body 4 to the longitudinal section L, and after having set a mechanical plug 56 in the pipe body 4 below the longitudinal section L. The figure also shows cement slurry 58 being pumped down the tubular string 16 and out of the open end thereof so as to fill cement slurry 58 upwards from the mechanical plug 56, simultaneously moving the tubular string 16 slowly upwards along the longitudinal section L. By so doing, cement slurry 58 is placed within the pipe body 4 along at least the longitudinal section L, also allowing cement slurry 58 to enter the annulus 6 via said holes 46 in the pipe body 4.

Figure 9 shows the well 2 after having removed the tubular string 16 from the pipe body 4, and after allowing the cement slurry 58 to set so as to form a substantially cross-sectional cement plug 58<'>along the longitudinal section L of the well 2.

Figure 10 shows a drill bit 60 connected to a lower end of said tubular string 16 after having drilled away and thus removed an upper part LI of the cement plug 58<'>, thereby exposing spaced apart holes 46 in the pipe body 4 along the removed upper part LI of the cement plug 58<'>. By so doing, a lower part L2 of the cement plug 58<'>remains within the pipe body 4 together with an annular part of the cement plug 58<'>along the entire longitudinal section L.

Figure 11 shows the pressure reduction tool 14 positioned a short distance above a top of the lower part L2 of the cement plug 58<'>. The confined region 24 of fixed volume VF is thus defined between the top of the lower part L2 of the cement plug 58<'>and the packer 20 when in its set position. At this select location, the confined region 24 is in isolated liquid communication with the lower part L2 of the cement plug 58<'>and also with several holes 46 exposed when drilling away the upper part LI of the cement plug 58<'>, thereby also establishing communication with an interior region of the annular part of the cement plug 58<'>. The figure also shows the pressure reduction tool 14 activated and in the process of performing a negative pressure test of both the annular part and the lower part L2 of the cement plug 58<'>, where the net pressure direction is shown with black arrows in the figure. Upon completion of a successful test, the packer 20 may be retracted and the pressure reduction tool 14 withdrawn from the well 2, after which cement slurry 58 may be filled into drilled out part within the pipe body 4.

Claims

C l a i m s

1. A method for assessing pressure integrity of a section of confined plugging material (12, 10<'>, 58<'>) in a subterranean well (2) comprising at least one pipe body, including an innermost pipe body (4) containing liquid (26), and at least one corresponding annulus (6) located between the innermost pipe body (4) and a surrounding wellbore wall (8), the method comprising:

(B) at a select location in the well (2), establishing a confined region (24) of fixed volume (VF) within the innermost pipe body (4), the confined region (24) containing liquid (26) and in isolated liquid communication with the section of confined plugging material (12, 10<'>, 58<'>);

(C) with a selectively operable pressure altering tool (14) in isolated liquid communication with the confined region (24), inducing a simultaneous pressure and volumetric change in the liquid (26) of the confined region (24) whilst displacing, relative to the fixed volume (VF) of the confined region (24), a volume of liquid (26) corresponding to said volumetric change;

(D) measuring the pressure in the confined region (24) over a period of time to establish a pressure development history in response to said pressure change therein; and

(E) based on the pressure development history, assessing the pressure integrity of the section of confined plugging material (12, 10<'>, 58<'>) in isolated liquid communication with the confined region (24).

2. The method according to claim 1, wherein the pressure altering tool (14) comprises a selectively operable pressure reduction tool; and

- wherein step (C) comprises operating the pressure reduction tool and thus simultaneously reducing the liquid pressure of the confined region (24) to a first pressure (Pi) whilst evacuating, from the fixed volume (VF) of the confined region (24), a first volume (Vi) of liquid (26) corresponding to a volumetric increase therein due to said pressure reduction, thereby performing a negative pressure test of the section of confined plugging material (12, 10<'>, 58<'>).

3. The method according to claim 1 or 2, wherein the pressure altering tool (14) comprises a selectively operable pressure increase tool; and

- wherein step (C) comprises operating the pressure increase tool and thus simultaneously increasing the liquid pressure of the confined region (24) to a second pressure (P2) whilst supplying, to the fixed volume (VF) of the confined region (24), a second volume (V2) of liquid (26) corresponding to a volumetric decrease therein due to said pressure increase, thereby performing a positive pressure test of the section of confined plugging material (12, 10<'>, 58<'>).

4. The method according to claim 1, 2 or 3, wherein the section of confined plugging material comprises plugging material (12) located within the innermost pipe body (4) and below the confined region (24).

5. The method according to claim 4, wherein the confined region (24) is defined between the section of plugging material (12) within the innermost pipe body (4), and a sealing element (20) configured for fluid-sealing engagement with an inner wall (22) of the innermost pipe body (4).

6. The method according to claim 5, wherein the sealing element (20) is operably connected to the pressure altering tool (14) for allowing fluid-sealing engagement with the inner wall (22) of the innermost pipe body (4).

7. The method according to claim 1, 2 or 3, wherein the section of confined plugging material comprises annular plugging material (10<'>) located within the at least one annulus (6) and in vicinity of the select location.

8. The method according to claim 7, wherein step (B) comprises bringing the confined region (24) in isolated liquid communication with at least one hole previously formed in the at least one pipe body at the select location, the at least one hole already in communication with said annular plugging material (10<'>).

9. The method according to claim 7, wherein the method, before step (B), also comprises the following steps:

(A1) positioning a perforation tool in the innermost pipe body (4) at the select location;

- wherein step (B) also comprises bringing the confined region (24) in isolated liquid communication with the at least one hole formed in step (A2), thereby establishing communication with said annular plugging material (10<'>).

10. The method according to 7,8 or 9, wherein the annular plugging material comprises formation material (10<'>) from the surrounding wellbore wall (8).

11. The method according to any one of claims 7-10, wherein the select location is a location vis-å-vis the section of confined annular plugging material (10<'>), thereby establishing, in step (B), communication with an interior region of the section of confined annular plugging material (10<'>).

12. The method according to any one of claims 7-11, wherein the confined region (24) is defined between a first sealing element (20) and a second sealing element (40), both sealing elements (20, 40) configured for fluid-sealing engagement with an inner wall (22) of the innermost pipe body (4).

13. The method according to claim 12, wherein at least one of the first sealing element (20) and the second sealing element (40) is operably connected to the pressure altering tool (14) for allowing fluid-sealing engagement with the inner wall (22) of the innermost pipe body (4).

14. The method according to claim 1, 2 or 3, wherein the method, before step (B), also comprises the following steps:

(Al) positioning a perforation tool (42) in the innermost pipe body (4);

(A2) with the perforation tool (42), forming a series of spaced apart holes (46) in the at least one pipe body along a longitudinal section (L) of the well (2), an uppermost hole (46a) and a lowermost hole (46b) thereof defining the extent of the longitudinal section (L);

(A5) placing a fluidized plugging material (58) within the innermost pipe body (4) and along at least the longitudinal section (L), also allowing the fluidized plugging material to enter the at least one annulus (6) via said holes (46) in the at least one pipe body so as to form a substantially cross-sectional plug (58<'>) along the longitudinal section (L);

(A6) removing an upper part (LI) of the plug (58<'>) from within the innermost pipe body (4) so as to expose holes (46) therein along the removed upper part (LI) of the plug (58<'>), thereby retaining a lower part (L2) of the plug (58<'>) within the innermost pipe body (4) and also an annular part of the plug (58<'>) along the entire longitudinal section (L), said retained plug material (58<'>) constituting the section of confined plugging material in the well (2);

- wherein the confined region (24) is defined between said lower part (L2) of the plug (58<'>) and a sealing element (56) in fluid-sealing engagement with an inner wall (22) of the innermost pipe body (4); and

- wherein step (B) also comprises bringing the confined region (24) in isolated liquid communication with at least one hole (46) exposed in step (A6), thereby establishing communication with said lower part (L2) of the plug (58<'>) and also with an interior region of the annular part of the plug (58<'>).

15. The method according to claim 14, wherein the method, between steps (A2) and (A5), also comprises the following steps:

(A3) positioning a washing tool (48) in the innermost pipe body (4) at the longitudinal section (L);

(A4) displacing a washing liquid (50) out of the washing tool (48) and directing the washing liquid (50) out into the at least one annulus (6) via holes (46) formed along the longitudinal section (L) in step (A2), thereby removing any debris (54) therein and cleaning both the innermost pipe body (4) and the at least one annulus (6) before placing the fluidized plugging material (58) therein in step (A5).

16. The method according to claim 14 or 15, wherein the fluidized plugging material (58) comprises cementitious material.

17. The method according to claim 14, 15 or 16, wherein the sealing element (56) is operably connected to the pressure altering tool (14) for allowing fluid-sealing engagement with the inner wall (22) of the innermost pipe body (4).

18. A system for assessing the pressure integrity of a section of confined plugging material (12, 10<'>, 58<'>) in a subterranean well (2), the system comprising:

- at least one pipe body, including an innermost pipe body (4) containing liquid (26), positioned in the well (2);

- at least one corresponding annulus (6) located between the innermost pipe body (4) and a surrounding wellbore wall (8) of the well (2);

- a confined region (24) of fixed volume (VF) established within the innermost pipe body (4) at a select location in the well (2), the confined region (24) containing liquid (26) and in isolated liquid communication with the section of confined plugging material (12, 10<'>, 58<'>);

- a selectively operable pressure altering tool (14) positioned in isolated liquid communication with the confined region (24), the pressure altering tool (14) configured and operable to induce a simultaneous pressure and volumetric change in the liquid (26) of the confined region (24) and displace, relative to the fixed volume (VF) of the confined region (24), a volume of liquid (26) corresponding to said volumetric change;

- at least one pressure sensor in communication with the confined region (24), the at least one pressure sensor configured and operable to measure the pressure in the confined region (24) over a period of time to establish a pressure development history in response to said pressure change; and

- a data conveyance system for conveying pressure data measured over said period of time to a surface of the well (2) for assessing the pressure integrity of the section of confined plugging material (12, 10<'>, 58<'>).

19. The system according to claim 18, wherein the system also comprises at least one sonic sensor configured and operable to acquire acoustic signals related to potential leakage of liquid (26) relative to the confined region (24); and

- wherein the data conveyance system is configured for conveying acoustic data acquired over said period of time to the surface of the well (2).

20. The system according to claim 18 or 19, wherein the data conveyance system comprises a data transmission unit configured and operable to transmit said data to the surface of the well (2).

21. The system according to claim 18, 19 or 20, wherein the data conveyance device comprises a data recording unit (34) configured for retrieval of said data to the surface of the well (2).

22. The system according to any one of claims 18-21, wherein the pressure altering tool (14) comprises a selectively operable closing valve (30) configured and operable to close the tool (14) to communication with ambient liquid (26).

23. The system according to any one of claims 18-22, wherein the pressure altering tool (14) comprises a selectively operable pressure reduction tool, the pressure reduction tool configured and operable to simultaneously reduce the liquid pressure of the confined region (24) to a first pressure (Pi) and evacuate, from the fixed volume (VF) of the confined region (24), a first volume (Vi) of liquid (26) corresponding to a volumetric increase therein due to said pressure reduction, whereby the system is configured to perform a negative pressure test of the section of confined plugging material (12, 10<'>, 58<'>).

24. The system according to claim 23, wherein a first pressure relief valve (36) is positioned in communication with the confined region (24) and also in communication with ambient liquid (26), the first pressure relief valve (36) set to open at the first pressure (Pi) upon operating the pressure reduction tool and thus reducing the pressure in the confined region (24).

25. The system according to claim 23 or 24, wherein the pressure reduction tool comprises a suction device.

26. The system according to claim 25, wherein the suction device comprises a first piston and cylinder assembly (28) configured and operable to generate said pressure reduction in the confined region (24).

27. The system according to any one of claims 18-26, wherein the pressure altering tool (14) comprises a selectively operable pressure increase tool, the pressure increase tool configured and operable to simultaneously increase the liquid pressure of the confined region (24) to a second pressure (P2) and supply, to the fixed volume (VF) of the confined region (24), a second volume (V2) of liquid (26) corresponding to a volumetric decrease therein due to said pressure increase, whereby the system is configured to perform a positive pressure test of the section of confined plugging material (12, 10<'>, 58<'>).

28. The system according to claim 27, wherein a second pressure relief valve is positioned in communication with the confined region (24) and also in communication with ambient liquid (26), the second pressure relief valve set to open at the second pressure (P2) upon operating the pressure increase tool and thus increasing the pressure in the confined region (24).

29. The system according to claim 28, wherein the pressure increase tool comprises a pump device.

30. The system according to claim 29, wherein the pump device comprises a first piston and cylinder assembly (28) configured and operable to generate said pressure increase in the confined region (24).