Well casing/tubing disposal

Abstract

A method of clearing well casing (3) or tubing from a target region of an oil/gas well (1) borehole is provided. The clearance of the oil/gas well bore hole being achieved by employing chemical agents (9) that consume, weaken or melt the well casing/tubing. In some aspects of the method the well casing is cleared to expose the rock formation within which the well borehole is formed so that the rock formation can be accessed from within the well casing/tubing. In other aspects of the method the removal of inner tubing structures is used to facilitate the unimpaired deployment of repair tools down the well borehole.

Claims

1. A method of clearing well casing or tubing from a target region of an oil/gas well borehole, said method comprising: subjecting the target region to a rapid temperature change so as to alter a physical property of the well casing/tubing in the target region and thereby embrittle, soften or otherwise weaken the well casing/tubing without melting it; applying one or more physical or environmental stresses to the target region to clear the weakened well casing/tubing; and clearing well casing or tubing from a target region of an oil/gas well borehole to expose the rock formation within which the well borehole is formed so that the rock formation can be accessed from within the well casing/tubing.

2. The method of claim 1, wherein the temperature is rapidly cooled before said physical or environmental stress is applied.

3. The method of claim 1, wherein the temperature is first increased to a temperature not exceeding the melting point of the well casing/tubing and then rapidly cooled; and wherein the one or more physical or environmental stresses are selected from the group consisting of physical attack, sonic attack, milling, and drilling.

4. The method of claim 1, wherein the temperature changes are facilitated by delivering chemical heating and/or cooling means to the target region; and, wherein the one or more physical or environmental stresses breaks the weakened well casing/tubing.

5. The methods of any of claims 2, 3 or 4, wherein the source of the one or more physical or environmental stresses is selected from the group containing: an incendiary device; a sonic device; and a milling or drilling device.

6. The method of claim 4, further comprising: producing a plurality of perforations in the well casing/tubing before delivering the chemical heating or cooling means down the oil/gas well.

7. The method of claim 6, wherein an area adjacent to the outer surface of the well casing/tubing is cleaned out using pressure washing techniques within the well casing/tubing in the region of the perforations before the delivery step.

8. The method of claim 7, further comprising providing an insulating material in the cleaned out area adjacent the outer surface of the well casing/tubing to maximise the impact of the temperature changes produced in the well casing/tubing.

9. The method of claim 7, further comprising providing a material in the cleaned out area adjacent the outer surface of the well casing/tubing to draw the heat generated within the well casing/tubing through the walls of the well casing/tubing.

10. The method of claim 6, wherein the delivery of the chemical heating or cooling means mixture further includes squeezing the chemical heating or cooling means into the perforations in the well casing/tubing so that said means are provided on both sides of the well casing/tubing as well as within the wall of the well casing/tubing itself.

11. The methods of any of claims 1, 2, 3, or 4, wherein the temperature change is facilitated by delivering chemical heating from a chemical heating means and wherein the chemical heating means comprises thermite or thermate.

12. The methods of any of claims 1, 2 or 3 wherein the temperature change is facilitated by delivering chemical heating from a chemical heating means and wherein the chemical heating means is provided as a gel, a paste, a pseudo liquid or a solid.

13. The method of claim 1, wherein the rapid temperature change is facilitated by delivering chemical heating from a chemical heating means comprising a solid form chemical heating means and is provided as at least one solid block.

14. The method of claim 13, wherein said solid block has a central hole or conduit to allow access or egress through the solid block when such is within the well casing or tubing.

15. A method of plugging an oil/gas well bore, said method comprising: using the method of claim 1 to clear away a target region of well casing or tubing so as to expose the rock formation that surrounds the well bore hole; and forming a plug within the well bore, wherein said plug extends across the entire cross-section of the well bore.

16. The method of claim 15, wherein the plug formed within the well bore is a eutectic alloy based plug.

17. A method of repairing an oil/gas well bore, said method comprising: using the method of claim 1 to clear away a target region of well casing or tubing; and deploying a repair tool within the well bore to affect a repair of the well casing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various aspects of the present invention will now be described with reference to the drawings, wherein:

(2) FIG. 1a shows a well casing in situ within a well bore hole;

(3) FIG. 1b shows the well casing perforation stage of the method of the present invention;

(4) FIG. 1c shows the jet washing stage of the method of the present invention;

(5) FIG. 1d shows the step of the delivery of chemical heating mixture into and around the well casing;

(6) FIG. 1e shows the separate portions of the well casing following the reaction of the chemical heating mixture within the well bore hole.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(7) So that the general concept of the present invention might be better understood an exemplary process of the well casing/tubing disposal method of the present invention will be described with reference to FIGS. 1a-1e.

(8) The skilled person will appreciate from the following description, that certain steps shown in the drawings may be omitted without departing from the general inventive concept. Further, the skilled person will also appreciate that additional steps to those shown may also be used to achieve additional benefits.

(9) Turning now to FIGS. 1a, 1b, 1c, 1d and 1e, which show in order the steps involved in removing/disposing of a portion of a well casing/tubing so as to create an exposed region capable of receiving a well plug that can be used to form a plug across the entire cross-section of a well bore hole (i.e. from the rock formation on one side of the borehole to the rock formation on the other side of the borehole).

(10) It will be appreciated that although FIGS. 1a, 1b, 1c, 1d and 1e depict the application of the clearance method of the present invention to remove a well casing and expose the surrounding rock formation the described method can also be employed to remove tubing other than well casing.

(11) One example of alternative tubing that can be removed using the described methods is production tubing. In cases where only the production tubing is to be removed the surrounding rock formation does not necessarily need to be exposed.

(12) FIG. 1a shows a well 1 provided in a rock formation 2. The well comprises a well casing or other form of tubing 3 formed within a bore hole in the rock formation 2. In the region between the rock formation and the casing/tubing 3 is provided an annulus 4, which may be filled with cement.

(13) FIG. 1b shows the first stage of the casing/tubing removal method, wherein a plurality of perforations 6 are formed in the casing/tubing 3 by way of a perforating device 5 that is deliverable down the well 1 using existing delivery means.

(14) Preferably the perforating device 5 is capable of delivering a controlled explosion within the region of the casing that is to be perforated. The device 5 is preferably capable of perforating the casing in a 360° target region so that perforations are provided around the entire circumference of the casing.

(15) FIG. 1c shows the next stage in the method of the present invention, wherein a pressure washing or water jet washing device 7 is delivered down the well 1 to the region of the casing in which the perforations 6 were formed. Once again existing delivery means can be utilised to deliver the washing device 7 to the target region within the well (e.g. cable wire line).

(16) Once the pressure washing or water jet washing device 7 is in position the device can be focused towards the perforations 6 in the casing. In this way the washing device 7 can be used to clean out or erode the annulus material 4 adjacent to the perforated region of the well casing/tubing.

(17) The step of the clearing away a region of annulus material 4 from area surrounding the perforated casing is considered to be advantageous because it provides additional space into which the active chemical agent 9 (see FIG. 1d) can be received. In this way the level of heating applied from the outer surface of the casing is enhanced.

(18) It is envisaged that as an alternative, insulating material or a heat drawing material (such as DOWTHERM™) may be received in the space formed by clearing away the annulus material with pressure jet washing.

(19) However it is envisaged that, although beneficial, the step of washing out the region of annulus material 4 may not be essential in all circumstances; for example when the preceding perforating step itself causes the formation of space in the annulus material 4 surrounding the casing 3, which further helps to expose the surrounding rock formation.

(20) FIG. 1d shows the step of deploying the active chemical agent 9 to the perforated region of the well casing/tubing 3. The active chemical agent 9 is delivered to the target region using a delivery tool 8, which is connectable to existing delivery means; such as cable wireline.

(21) Depending on which method of the various aspects of the present invention is being employed the active chemical agent may be selected from: A chemical agent this is capable of reacting with, and thereby consuming, one or more chemical components of the well casing; A chemical heating and/or cooling means capable of rapidly changing the temperature within the target region of the well casing; A chemical heating mixture.

(22) The delivery tool 8 is capable of carrying the active chemical agent 9 down the well to the target region. Once in position the delivery tool 8 can then be operated to force the active chemical agent 9 through the perforations 6 in the casing and in to the cleared region in the annulus material 4.

(23) In this way both the inside and the outside of the casing/tubing 3 are placed in contact with the active chemical agent 9 thereby allowing a more uniform treatment of the casing/tubing 3 to be achieved.

(24) It is envisioned that in the case of the chemical heating mixture the active chemical agent 9 might advantageously be provided in the form of paste or gel of a material such as thermite or thermate so that it can more readily be squeezed through the casing perforations 6.

(25) Once the active chemical agent 9 is suitably distributed in and around the casing/tubing 3 the chemical reaction can be initiated. Depending on the nature of the active chemical agent being used this may be done remotely or by way of timing device.

(26) As explained above, depending on the type of active chemical agent 9 used the method of the present invention might facilitate the removal/disposal of the well casing by way of: consuming one or more chemical components of the well casing; changing the physical properties of the well casing so as to embrittle it followed by targeted physical or environmental stressing; and melting the well casing in the target region.

Consumption of the Well Casing

(27) In the first aspect of the method of the present invention the well casing/tubing is broken down by using chemicals that react with materials from which the well casing is formed.

(28) In its broadest sense any chemicals that are capable of reacting with the well casing in such a way that produces material which is readily cleared from the target region (e.g. in the form of gases or powders) to expose the rock formation are considered applicable.

(29) One appropriate chemical reaction is considered to be oxidation, wherein the casing is effectively consumed or burnt (i.e. like a fuel) rather than melted (i.e. turned from a solid state to a liquid state).

(30) In situations where the well casing/tubing has a steel component it is envisaged that a process of Iron oxidisation might be employed.

Embrittlement or Softening and Subsequent Removal of the Well Casing

(31) In a second aspect of the method of the present invention the well casing/tubing is again subjected to high temperatures; whether as a consequence of the high temperatures already present in the down-hole environment or as a result of chemical heating means delivered to the target region.

(32) However unlike the melting approach adopted in the third aspect of the present invention the well casing is subjected to a rapid cooling before melting occurs.

(33) It is envisaged that the rapid cooling of the well casing (possible using cooling means such as liquid nitrogen or cold water) results in a change the structural orientation of the metal from which the casing is formed. This can make the casing more brittle and susceptible to shattering. Although in the case of well casings/tubings that are formed from alloys that have low carbon content the casing/tubing has a tendency to soften rather than embrittle. In both cases the rapid temperature changes transform the well casing/tubing and make it easier to clear/remove.

(34) Once the casing has been embrittled the target region can be subjected to mechanical stresses, such as physical attack or sonic attack. Thus the weakened casing is removed by shattering the casing in the targeted region.

(35) Alternatively, once the casing has been softened the target region can be milled/drilled out using standard milling/drilling equipment. The softened casing is much easier, and thus quicker, to remove. An added benefit is achieve by the softening of the well casing/tubing, in that the sward formed during the milling/drilling process is created in smaller more manageable pieces.

(36) It is envisioned that providing the perforations in the well casing enables the cooling medium to access both the inside and the outside of the well casing, thus providing uniform cooling.

Melting of the Well Casing

(37) In a third aspect of the method of the present invention the well casing/tubing is subjected to high temperatures which melt the target region of the casing. It is envisaged that thermite and thermate mixes would be particularly suitable to achieve the high melting temperatures of over 1800° C. that are required.

(38) Unlike in the first and second aspect of the present invention, where it is considered merely an beneficial additional step, the step of perforating the well casing/tubing is considered essential to this aspect of the invention as it allows the heat to be applied not only from within the casing but also from outside—thereby maximising the destruction of the targeted casing region by melting.

(39) In each of the above approaches a region of the casing/tubing 3 is destroyed and a cleared region 10 is created within the well bore hole. FIG. 1e shows the well hole 1 following one of the above mentioned casing removal stages (i.e. melting; embrittlement/shattering; burning).

(40) Once created within the well hole the cleared region 10, which extends to the rock formation within which the borehole is formed, facilitates a well abandonment plug to be deployed therein. The removal of the casing/tubing means that a plug can be formed which extends across the entire cross-section of the well hole (i.e. from the rock formation on one side of the borehole to the rock formation on the other side of the borehole), thus providing a substantial and effective seal.

(41) It is envisioned that the cleared region 10 provided using the method of the claimed invention would be suitable for both cement plugs and plugs formed using eutectic alloys.