WO2015051415A1

WO2015051415A1 - A gas well casing and method

Info

Publication number: WO2015051415A1
Application number: PCT/AU2014/050276
Authority: WO
Inventors: David MATHEW; Helmet Gunar DAMBERGS
Original assignee: Wds (Oil & Gas) Pty Ltd
Priority date: 2013-10-09
Filing date: 2014-10-09
Publication date: 2015-04-16

Abstract

A gas well casing comprising at least one tubular section of softer material that is softer than the predominant material used for the gas well casing, each of the at least one tubular section of softer material positioned on the gas well casing such that in use, when the gas well casing is located within a gas well, each of the at least one tubular section of softer material is located above a respective target coal seam, wherein each of the at least one tubular section of softer material is adapted to have at least one lateral hole drilled outwardly therefrom and into the respective target coal seam.

Description

TITLE

"A GAS WELL CASING AND METHOD"

FIELD OF THE INVENTION

This invention is concerned with a gas well casing. The invention is concerned particularly, although not exclusively, with gas weli casing for coal seam gas.

BACKGROUND OF THE INVENTION

Coal seam gas (CSG) is gas trapped in underground coal seams. Similarly, unconventional gas can be trapped in shale and sandstone reservoirs and conventional gas can be trapped in sandstone reservoirs. It is desirable to utilise this gas, as gas fired power stations create less greenhouse gas emissions than coal fired power station. In some coal seams, it is also desirable to extract the gas before the seam is mined to prevent excess gas escaping to the atmosphere during the mining phase and to mitigate the risk of fire or explosion.

Typically, to extract the coal seam gas or the unconventional gas, a vertical well is drilled. A surface to inseam lateral hole is then drilled from the surface remote from the vertical weli, having a relatively large radius and then running horizontally along the coal seam for a relatively long distance (e.g. 1000m) to intersect the vertical well. Alternatively, the wells are drilled such that they are initially vertical and then turn in a large radius to run horizontally along the coal seam. These wells are typically spaced at set intervals, for example at 500m x 1000m. Gas trapped in the coal seam, shale or sandstone reservoirs then typically permeates into the lateral hole and is extracted via the vertical well.

A problem with existing wells is that the turning of the inseam lateral hole or the well from vertical to horizontal must be carefully controlled so that the horizontal section runs along the coal seam, and in the case of a surface to inseam lateral hole, that the lateral hole also intersects the vertical well.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base o were common general knowledge in the field relevant to the present invention as it existed before the priorit date of each ciaim of this application,

OBJECT OF THE INVENTION

it is an object of the invention to overcome or at least alleviate one or more of the above problems and/or provide the consumer with a useful or commercial choice.

Other preferred objects of the present invention will become apparent from the following description.

SUMMARY OF THE INVENTION

In one form, although it need not be the only or indeed the broadest form, the invention resides in a gas well casing comprising:

at least one tubular section of softer material that is softer than the predominant material used for the gas well casing, each of the at least one tubular section of softer material positioned on the gas well casing such that in use, when the gas well casing is located within a gas well, each of the at least one tubular section of softer material is located above a respective target coal seam,

wherein each of the at least one tubular section of softer material is adapted to have at least one lateral hole drilled outwardly therefrom and into the respective target coal seam.

Preferably, the gas well casing is predominantly formed of steel. Preferably the softer material is a composite material Preferably the composite material is a fibreglass composite material.

Preferably, each of the at least one portion of softer materia! is located at a predetermined location where it is desirable to form an aperture in the gas well casing. More preferably, each of the at least one portion of softer material is located at a predetermined location where it is desirable to form an aperture in the gas well casing such that at least one lateral hole can be drilled outwardly f om the gas well casing. Preferably the at least one lateral hole is drilled outwardly and into the respective target coal seam.

Preferably, each of the at least one portion of softer material is a tubular section of softer material. Preferably each of the at least one portion of softer material is disposed between sections of the gas well casing formed of steel. For example, the gas well casing may have a section formed of steef attached to a top part of a tubular section of composite material and another section formed of steel attached to the bottom part of the tubular sectio of composite material. Preferably, once the gas well casing is in position, a casing bit forms the desired number of apertures through each of the tubular sections of composite material.

Typically the casing bit is deflected into the casing by a wedge assembly.

Preferably the gas well casing is a gas well casing used in a gas well for coal seam gas. Alternatively, the gas well casing may be a gas well casing used in gas well for unconventional or conventional gas. Alternatively the gas well casing may be a gas well casing used in a gas well for sequestration of gas or liquids into suitable formations.

In one embodiment, the wedge assembly comprises a wedge having a deflection face adapted to deflect the casing bit.

Preferably, the deflection face of the wedge is contoured to the shape of the casing bit. Typically, when the wedge is located in the gas well casing, the wedge is adapted to deflect the casing bit into an inner surface of the gas well casing to create an opening in the casing. Preferably the deflection face is set at a predetermine angle relative to the longitudinal axis of the wedge assembly, the longitudinal axis of the wedge assembly being parallel to the longitudinal axis of the gas well casing when the wedge assembly is located in the gas well casing. Preferably the predetermined angle forms an acute angle.

Preferably the wedge is formed from a cylindrical material. More preferably, the wedge is formed from a cylindrical piece of steel. Typically the defiection face is machined into the cylindrical material. Preferably the wedge is secured to a wedge casing. More preferably the wedge is welded into a wedge casing. Preferably the wedge casing will have an opening such that the defiection face is open to the gas well casing.

Preferably, the casing bit is a casing mill bit. More preferably, the casing bit is a casing mill bit and reamer assembly.

Preferably, the wedge assembly further comprises a packer located near a lower end of the wedge. Preferably the packer is adapted to seal a space between the gas well casing and the wedge assembly to prevent drill cuttings from migrating down the gas well casing. Preferably the packer is attached to the wedge casing.

Preferably, the wedge assembly further comprises spacer operatively attached to a lower end of the wedge. Preferably the spacer is adapted to position the wedge at a predetermined location within the gas well casing. Typically, different length spacers may be utilised to position the wedge at different predetermined locations within the gas well casing.

Preferably, the wedge assembly further comprises a direction assembly adapted to set the direction of the deflection face relative to the gas well casing. Preferably the direction assembly is provided between the spacer and the wedge. More preferably, the direction assembly is provided between the spacer and the packer. Typically the direction assembly is adapted to rotatably connect the upper part of the wedge assembly with the lower part of the wedge assembly such that once a predetermined direction of the upper part of the wedge assembly is achieved relative to the lower part, the direction assembly can be releasably locked to prevent further rotation.

Preferably, an orientation assembly is adapted to orient the wedge assembly relative to the gas well easing. Preferably, in use, part of the orientation assembly is secured relative to the bottom of the gas well casing. Typically the orientation assembly will have an upper orientation sub assembly and a lower orientation subassembly. Preferably the upper and lower orientation subassemblies can be releasably secured to one another in only one orientation. Preferably in use, the upper orientation subassembly is secured to the wedge assembly and the lower orientation subassembly is secured relative to the bottom of the gas well casing.

Preferably, the wedge assembly further comprises a deployment casing adapted to lower the wedge assembly down the gas well casing. Preferably the deployment casing is hollow so that a casing bit can be lowered through the deployment casing and deflected by the deflection face of the wedge. Typically the deployment casing will also acts as a eonduit for drilling fluids. Preferably an orientation indicator is provided towards the top of the deployment casing to aid in the orientation or to check the orientation of the wedge assembly. Preferably the orientation indicator is an orientation flange attached to the top of the deployment casing. Preferably the deployment casing has a plurality of ports through which hig pressure air is injected. The high pressure air typically mingles with the drilling fluid returning to the surface to make this fluid lighter.

Preferably, the wedge assembly further comprises a plurality of centralisers adapted to centralise the wedge assembly in the gas well casing. For example, the centralisers may be attached to the deployment casing such that they are positioned between the deployment casing and the gas well casing.

Preferably, one of the upper orientation subassembly or the lower subassembly has a orientation pin and the other of the upper orientation subassembly or the lower subassembly has a slot to receive the orientation pin. More preferably the upper orientation subassembly has the orientation pin and the lower subassembly has the slot to receive the orientation pin. It will be appreciated that the orientation pin may be of any suitable shape, including rectangular, square, circular and/or the like. Preferably, one of the upper orientation subassembly or the lower subassembly has a shank from which the orientation pin extends and the other of the upper orientation subassembly or the lower subassembly has a receiving recess in which the slot is formed Alternatively, the slot may be formed on the shank and the orientation pin may be formed within the receiving recess. An advantage of having the slot formed on the shank is that the slot is easier to access for cleaning purposes. Preferably, the receiving recess is adapted to receive the shank. Preferably, the receiving recess has a tapered opening. Typically the tapered opening aids in locating the shank relative to the receiving recess.

Preferably, the slot is formed such that the orientation pin is initially received in a direction parallel to a longitudinal axis of the receiving recess. Preferably the slot is formed such that the orientation pin moves in a radial direction relative to the longitudinal axis of the receiving recess to secure the upper orientation subassembly to the Sower orientation subassembly. Preferably the slot is "J" shaped, having a longitudinal component and a radial component relative to the longitudinal axis of the receiving recess.

Preferabl the upper orientation subassembly has a shear pin hole. Preferably, the lower orientation subassembly has a shear pin hole. Preferably the shear pin hole of the upper orientation subassembly aligns with the shear pin hole of the lower orientation subassembly when the upper orientation subassembly is in a predetermined orientation relative to the lower orientation subassembly. Preferably the orientation assembly further comprises a shear pin that is adapted to be inserted into the shear pin hole of the upper orientation subassembly and the shear pin hole of the lower orientation subassembly when aligned to secure the upper orientation subassembly to the lower orientation subassembly. Preferably the shear pin is adapted to shear when a predetermined force is applied to the upper orientation subassembly relative to the lower orientation subassembly. For example, the shear pin may be adapted to shear when predetermined downward force is applied to the upper orientation subassembly relative to the lower orientation subassembly.

Preferably, the upper orientation subassembly has an upper coupling adapted to be operatively attached to the wedge assembly.

Preferably, the lower subassembly has a lower coupling adapted to be operatively attached to an anchor. Preferably, the anchor is secured toward the bottom of the gas well casing.

In another form, the invention resides in a gas well comprising:

a gas well casing having at feast one tubular sectio of softer material that is softer than the predominant material used for the gas well casing, each of the at least one tubular section of softer material located above a respective target coal seam; and

at least one lateral hole drilled outwardl from each of the at least one tubular section of softer material and into the respective target coal seam.

Preferably the gas well casing is a gas well casing as described in this specification.

In yet another form, the invention resides in a method of locating a gas well casing in a gas well, the method including the steps of:

locating a gas well casing in a gas well, the gas well casing comprising at least one tubular section of softer material that is softer than the predominant material used for the gas well casing;

completing the location of the gas well casing in a gas well such that each of the at least one tubular section of softer material is located above a respective target coal seam;

forming at least one aperture through each of the at least one tubular section of softer material; and

drilling at least one lateral hole outwardly from the at least one aperture of each of the at least one tubular section of softer material and into the respective target coal seam.

Preferably the gas well casing is predominantly made of steel. Preferably the at least one tubular section of material that is softer than the predominant material used for the gas well casing is at least one tubular section of composite material. Preferably the composite material is a fibreglass composite material.

Preferably the well is a gas well for coal seam gas. Alternatively, the well may be a gas well for unconventional or conventional gas. Alternatively the well may be a gas well for sequestration of gas or liquids into suitable formations. Preferably the method further includes the step of forming at least one aperture through each of the at least one portion of softer material such that the respective at least one lateral hole can be drilled outwardly from the tubular section of softer material. Preferably the step of forming at least one aperture through each of the at least one portion of softer material involves using a wedge assembly to def lect a casing bit into each of the at least one portion of softer material. Preferably the wedge assembly has a deflection face to deflect the casing bit. Alternatively, the wedge assembly may be a wedge assembly as described in this specification.

in one embodiment, the method includes the step of forming an aperture in the gas well casing. Preferably the step further includes the steps of locating a wedge assembly within the gas well casing, providing a casing bit and deflecting the casing bit with the wedge assembly, such that the casing bit forms an aperture in the gas well casing.

Preferably the step of deflecting the casing bit with the wedge assembly, such that the casing bit forms an aperture in the gas well casing involves deflecting the casing bit such that it contacts an inner surfac of the gas well casing. Preferably the step further includes milling the gas well casing with the casing bit such that an aperture is formed from the inner surface of the gas well casing to an outer surface of the gas well casing. It will be appreciated that in this context, milling can include drilling. Preferably a deflection face of the wedge assembly deflects the casing bit.

Preferably the step of locating a wedge assembly within the gas well casing involves spacing the wedge assembly from the bottom of the gas well casing using a spacer. Preferably the step further includes releasably securing the spacer relative to the bottom of the gas well casing. Preferably the step further includes using a direction assembly to set a predetermined radial direction of the wedge assembly relative to the gas well casing.

Preferably the step of locating a wedge assembly within the gas well casing involves lowering the wedge assembly using a deployment casing.

Preferably the method includes the step of using a packer to seal an upper part of the wedge assembly from the gas well casing below to prevent drill cuttings from the forming of the aperture from migrating down the gas well casing.

In another embodiment, the method includes the step of installing a gas well orientation assembly. Preferably the step of installing a gas well orientation assembly includes the steps of providing a gas well orientation assembly having an upper orientation subassembly and a lower orientation subassembly, releasably securing the upper orientation subassembly to the lower orientation subassembly and securing the lower orientation subassembly to a bottom portion of the gas well casing.

Preferably, the step of releasabl securing the upper orientation subassembly to the lower orientation subassembly involves receiving an orientation pin of one of the upper orientation subassembly or the lower subassembly into a slot of the other of the upper orientation subassembly or the lower subassembly. Preferably, the step of releasably secu ing the upper orientation subassembly to the lower orientation subassembly involves inserting a shear pin into a shear pin hole of the upper orientation subassembly and a shear pin hole of the lower orientation subassembly.

Preferably, the step of securing the lower orientation subassembly to a bottom portion of the gas well casing involves securing the lower orientation subassembly to an anchor. Preferably the step further involves securing the anchor to a bottom portion of the gas well casing. Preferably the anchor is lowered to a bottom portion of the gas well casing using the gas well orientation assembly and is secured to the gas well casing.

Preferably, the method includes the step of orienting the gas well orientation assembly in a predetermined orientation relative to the gas well casing. Preferably the anchor is secured to a bottom portion of the gas well casing once the gas well orientation assembly is oriented in a predetermined orientation relative to the gas well casing.

Preferably, the method includes the step of shearing the shear pin.

Preferably the step of shearing the shear pin Is performed after the lower orientation subassembly is secured to a bottom portion of the gas well casing.

In another embodiment, the method includes the step of forming a gas well. Preferably the step of forming the gas well includes the steps of locating the gas well casing in a well. Preferably the well is a vertical well,

Preferably the method includes the step of drilling a plurality of lateral holes outwardly from the gas well casing. Preferably the plurality of lateral holes extend outwardl from at least one aperture in the gas well casing. More preferably the method includes forming at least one aperture in the gas well casing and then drilling a plurality of lateral holes outwardly from the gas well casing, the plurality of lateral holes extending from the at least one aperture in the gas well casing.

Preferably, the method includes the step of drilling at least one branch lateral hole outwardly from at least one of the pluraiity of lateral holes. A benefit of this is that only one aperture may to be formed for a single lateral hole extending outwardly from the gas well casing and having at least one branch lateral hole extending from the laterai hole (i.e. no additional aperture needs to be formed in the gas well casing for the at least one branch lateral hole).

Preferably the plurality of lateral holes extend outwardly from the gas well casing spaced over 360° when viewed in plan view. Alternatively, the plurality of lateral hoies may extend outwardly from the gas well casing spaced over substantially 180⁰ or 90⁰ when viewed in pla view. Having the plurality of lateral holes extend outwardly from the gas well casing spaced over substantially 180° or 90° when viewed in plan view may be beneficial when the gas well casing is located near a boundary. It will be appreciated that the plurality of lateral holes may extend outwardly from the gas well casing spaced over a predetermined angle depending on other factors such as geological formations

Preferably, the step of locating the gas well casing in a well involves forming the well. Preferably the step further includes lowering the gas well casing in the well.

Preferably, the step of forming a plurality of lateral holes outwardly from the gas well casing includes the step of forming apertures in the gas well casing at predetermined locations. Preferably the step of forming apertures in the gas well casing at predetermined locations involves deflecting a casing bit into an inner surface of the gas well casing using a wedge assembly.

Preferably the step of forming a plurality of lateral holes outwardly from the gas well casing involves drilling a plurality of lateral holes such that they diverge from one another. Preferably, the step of forming a plurality of lateral holes outwardly from the gas well casing involves drilling a plurality of lateral holes such that each hole runs substantially parallel to at least one other lateral hole. More preferably, the ste of forming a plurality of lateral holes outwardly f om the gas well casing involves drilling a plurality of lateral holes such that they initially diverge from one another and then run substantially parallel to at least one other lateral hole.

Preferably the step of forming a plurality of lateral holes outwardly from the gas well casing involves drilling a plurality of lateral holes initially in a downwards direction relative to the gas well casing and then transitioning to a direction that is transverse to the gas well casing. Preferably the transverse direction is substantially orthogonal to the gas well casing. Preferably the transition has a radius in the range of 20 to 40 meters. More preferably the transition has a radius in the range of 25 to 35 meters. Even more preferably, the transition has a radius of approximately 30 meters.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to th accompanying drawings, wherein :

FIG 1 shows a schematic sectioned view of a wedge assembly located in a gas well casing;

FIG 2 shows a schematic cross sectional view of part of a wedge assembly;

FIG 3 shows a schematic cross sectional view of a wedge assembly located in a gas well casing;

FIG 4 shows a schematic perspective view of a gas well according to an embodiment of the invention;

FIG 5 shows a schematic cross sectional view of a gas well;

FIG 8 shows a schematic cross sectional view of an orientation assembly;

FIG 7 shows a plan view of prior art vertical well spacing for gas extraction;

FIG 8 shows a schematic plan view of vertical well spacing for gas extraction according to an embodiment of the invention;

FIG 9 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 10 shows a plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 1 1 shows a schematic plan view of a well design for mine degassing according to an embodiment of the invention;

FIG 12 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 13 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 14 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 15 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention;

FIG 16 shows a schematic plan view of a well design for gas extraction according to an embodiment of the invention; and

FIG 17 shows a schematic plan view of a lateral hole having branched lateral holes according to an embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic sectioned view of a wedge assembly 100 located in a gas well casing 200. it will be appreciated that the gas well casing 200 is lowered into a gas well before the wedge assembly 100 is located in the gas well casing 200. The wedge assembly 100 has a wedge 102 having a deflection face 104, The deflection face 1 4 is adapted to deflect a casing bit (not shown) such that the casing bit can form an aperture 224 in the gas well casing 200. The gas well casing 200 has a 7" (approx. 178mm) external diameter.

The wedge assembly 100 has a packer 1 12 located near a lower end of the wedge 102. The packer 1 12 isolates and seals the upper part of the wedge assembly 100 from the gas well casing 200 below to prevent drill cuttings (not shown) from the forming of the aperture 224 from migrating down the gas well casing 200.

The wedge assembly 100 has a direction assembly 1 14 that can set the direction of the deflection face 104 relative to a spacer. The direction of the deflection face 104 is set by rotating part of the direction assembly 1 14 relative to a spacer 1 16 and locking the direction assembly 14 in position once the deflection face 104 is facing the desired direction. It will be appreciated that changing the direction of the deflection face 104 will change the radial location of where the casing bit (not shown) would form an aperture in the gas well casing 200. The spacer 1 16 is connected to a lower part of the direction assembly 114. The length of the spacer 116 determines the vertical location of the deflection face 104 in the gas well casing, as the spacer 1 16 is releasably secured relative to the bottom of the gas well casing 200. It will be appreciated that using different length spacers will change the vertical location of where the casing bit (not shown) would form an aperture in the gas well casing 200. The spacer 1 16 is made from one or more lengths of 5.5" (approx 140mm) diameter casing. It will also be appreciated that in an alternative embodiment (not shown), the spacer may also be drill pipe or drill collars.

The spacer 1 6 is radially oriented and releasably secured relative to the bottom of the gas well casing 200 by an orientation assembly 400. The orientation assembly 400 has an upper orientation subassembly 420 attached to the spacer 116 and a lower orientation subassembl 440 attached to a mechanical set anchor 260 near the bottom of the gas well casing 200. The orientation assembly 400 will be explained in more detail below with reference to figure 6.

The wedge assembly 100 has a deployment casing 1 18 extending from the top end of the wedge 102 to the surface 310 when the wedge assembly 100 is located in the gas well casing 200. The deployment casing 118 is used to lower the wedge assembly 100 into the gas well casing 200. The deployment casing 118 is hollow so that a casing bit (not shown) can be lowered through the deployment casing 118 and deflected by the deflection face 104 of the wedge 102. The deployment casing 1 18 also acts as a conduit for drilling fluids (not shown) used in drilling lateral holes such as lateral hole 240. It will be appreciated that a different length deployment casing 18 may be used if the length of the spacer 116 is changed. The deployment casing 118 is made from one or more lengths of 5.5" (approx 140mm) diameter casing that has an interna! diameter of 5" (approx. 127mm).

The deployment casing 1 18 has ports 120 located at a predetermined depths. High pressure air is injected through these ports120 to mingle with the drilling fluid that is returning to the surface to make this fluid lighter and to control the hydrostatic pressure. The hydrostatic pressure can also be adjusted by the number, size and location (e.g. depth) of ports 120.

An orientation flange 122 is located at the top of the deployment casing 118 to orientate or check the orientation of the deflection face 104.

The wedge assembly 100 has centralisers 124 located above and below the wedge 102 to ensure that the wedge assembly 100 is held rigidly and centrally within the gas well casing 200.

The gas well casing 200 has a steel casing 210 and a section of composite casing in the form of a ftbreglass casing 220 in the area where the aperture 224 is to be formed. An advantage of this is that a casing bit (not shown) does not have to drill through the steel casing 210. The fiberglass casing is located above the coal seam 320. Figure 1 schematically shows the fibreglass casing 220, it will be appreciated that the fibreglass casing 220 can be flush with the outside surface of the steel casing 210. it will also be appreciated that the section of composite casing can be a tubular section disposed between two sections of steel casing. The gas well casing 200 has perforations 230 that are positioned adjacent the coal seam 320 to assist in the extraction of gas from the coal seam 320. It will be appreciated that in an alternate embodiment (not shown) the perforations 230 may be omitted, to for example prevent possible ingress of coal fines from a coal seam.

Once the aperture 224 has been formed, a lateral hole 240 is drilled that follows the coal seam 320.

With reference to figure 2, there is shown part of the wedge assembly 100 in more detail. The wedge 102 is made from a piece of steel having an external diameter of 5" (approx. 127mm). The wedge 102 is welded into a wedge casing 106. The wedge casing 106 is made from a length of 5.5" (approx 140mm) diameter casing that has an internal diameter of 5" (approx. 1 7 mm}.

The wedge casing 106 has an opening formed that corresponds to the deflection face 104 of the wedge 102. The deflection face 104 has a concave shape (not shown) to suit a casing bit having a 4.75" (approx. 1 1 mm) externa! diameter.

An upper coupling 108 is located at the upper end of the wedge casing 106. The upper coupling 108 is a 5.5" BTC Coupling. The upper coupling 108 connects the wedge casing 106 to the deployment casing (1 18 as seen in figure 1 ). A lower coupling 1 10 is located at the lower end of the wedge casing 106. The lower coupling 1 10 connects the wedge casing 106 to the packer (112 as seen in figure 1).

Figure 3 shows a schematic cross sectional view of part of a wedge assembly 100 located in a gas well casing 200. The spacer 116 is of a predetermined length and the direction assembly 114 is set to a predetermined angle such that the deflection face 104 of the wedge 102 is orientated to deflect a casing bit {not shown) into the top right aperture 224 and lateral hole 240. The Packer 1 12 prevents excess drill cuttings from migrating to the gas well casing 200 below.

As can be seen in figure 3, the upper apertures 224 and lateral holes 240 are staggered to avoid excess weakening of the gas well casing 200.

With reference to figures 4 and 5, there is show schematic views of a gas well 10 according to an embodiment of the invention, Figure 4 shows a schematic perspective view and Figure 5 shows a schematic cross sectional view. The gas well 10 has a well head 1 attached to the to of th gas well casing 200 near the surface 310. Lateral drill holes 240 are drilled outwards from apertures 224 in the gas well casing 200. The lateral drill holes 240 initially have a "short" radius of approximately 30 meters and then follow the coal seams 320. A production string 14 is located in the gas well casing 200 and a progressive cavity pump 18 is located at the bottom of the production string.

With reference to figure 6, there is shown a schematic cross sectional view of an orientation assembly 400. The orientation assembly 400 has an upper orientation subassembly 420 that can be releasabiy secured to a lower orientation subassembly 440.

The upper orientation subassembly 420 has an upper coupling 424 that connects to a spacer {116 as seen in figure 1). The upper orientation subassembly 420 has a shank 426 that can be received by a receiving recess 442 of the lower orientation subassembly 440. The shank 426 has a shear pin hole 428 to receive a shear pin (not shown) which can secure the upper orientation subassembly 420 to the tower orientation subassembly 440, The shank 426 also has an orientation pin 422, which can be received into a "J" slot 444 in the receiving recess 442 of the lower orientation subassembly 440. The orientation pin 422 and the slot 444 ensure that the upper orientation subassembly 420 can only be received by the lower orientation subassembly 440 in a predetermined orientation.

The lower orientation subassembly 440 has a tapering opening 446 to assist in guiding the shank 426 of the upper orientation subassembly 420 into the receiving recess 442. The lower orientation subassembly 440 has a shear pin hole 448_> which aligns with the shear pin hole 428 of the upper orientation subassembly 420 when the orientatio pin 422 is located in the bottom left part of the ^KJ" slot 444. The lower orientation subassembly has a lower coupling 450 that secures to a packer or a mechanical set anchor (260 as seen in figure 1 ) secured to a bottom section of the gas well casing (200 as seen in figure 1 ). The packer or mechanical set anchor (not shown) is usually secured in the bottom of the gas well casing (not shown) by rotation or a downward force.

In use, the shank 426 of the upper orientation subassembly 420 is inserted into the receiving recess 442 of the lower orientation subassembly 440 such that the orientation pin 422 slides to the bottom of the "J" slot, the upper orientation subassembly 420 is then rotated relative to the lower orientation subassembly such that the orientation pin is located at the left end of the "J" slot 444. In this position, the shear pin holes 428 and 448 align and a shear pin (not shown) can be inserted into the holes 428,448 to secure the upper orientation subassembly 420 to the lower orientation subassembly 440, The lower orientation subassembly 440 is connected to an anchor (not shown), the wedge assembly (100, see figure 1 ) is then lowered into a gas well easing (not shown). Once the wedge assembly is oriented correctly, the anchor (not shown) is set. The shear pin (not shown) can then be sheared b providing the upper orientation subassembly 420 with a downward force relative to the lower orientation subassembly 440. The upper orientation subassembly 420 can then be rotated relative to the lower orientation subassembly 440 such that the orientation pin 422 is in line with the vertical part of the "J" slot 444. The upper orientation subassembl 420 can then be removed from the lower orientation subassembly 440. The lower orientation subassembly 440 remains at the bottom of the gas well casing (not shown) to act as an orientation reference point. If a lateral hole (not shown) should fail, the lower orientation subassembly 440 can be used as a reference point to orient the wedge assembly (100, see figure 1) such that the lateral hole (not shown) can be re-drilled.

With reference to figure 7, there is shown a plan view of prior art vertical well spacing for gas extraction. The vertical wells 500 are spaced 500m apart in the Y direction and 1000m apart in the X direction. The vertical wells 500 have a horizontal component 510 that runs for approximately 1000m along a coal seam. The horizontal component 510 is either a surface to inseam lateral hole that is drilled from the surface, remote from the vertical well 500, to intersect the vertical well 500, or, alternatively, the horizontal component 500 is a single continuation of the vertical well 500 which turns a large radius to continue horizontally along the coal seam.

Figure 8 shows a schematic plan view of vertical well spacing for gas extraction according to an embodiment of the invention. The vertical portions of the gas wells 10 are spaced 500m apart in the Y direction and 1000m apart in the X direction. Lateral holes 240 are drilled outwardly from the vertical portions of the gas wells 10. As can be seen from the figure, lateral holes 240 on the left sides of the gas wells 10 diverge from each other and then run parallel to each other. Similarly, the lateral holes 240 on the right sides of the gas wells 10 diverge from each other and then run parallel to each other. Such well spacing and lateral hole drilling results in much earlier peak gas production compared to the prior art well placements with the same number of vertical drilling placements. Additionally, the direction of lateral holes (while they are being drilled) is easier to control over shorter distances (eg 500m compared to 1000m). The risk of not intersecting a vertical well, which is present when drilling a surface to inseam lateral hole that intersect the vertical well is also eliminated.

With reference to figures 9 and 10, there is shown a more detailed plan view of a well design for gas extraction according to an embodiment of the invention. The lateral holes 240 are drilled outwardly from the vertical well 10. The lateral holes 240 diverge from one another from the vertical well 10 to approximately 70-150m left or right of the vertical well. After this, the lateral holes 240 run parallel for approximately 400m. Having 4 lateral holes 240 reduces the risk of production failure if a single lateral hole 240 fails.

With reference to figure 1 , there is shown schematic plan view of a well design for mine degassing according to an embodiment of the invention, in this embodiment, vertical wells 10 are drilled down through the longwall 322 that is to be degassed, lateral holes 240 are drilled outwardly from the vertical wells 10. The lateral hales extend outwardly in an "X" shaped formation. Wit reference to figures 12 and 13 there is shown a schematic plan view of a well design for gas extraction according to an embodiment of the invention. A vertical well 10 (including a gas well casing) has lateral holes 240 extending from apertures in the gas well casing (not shown). Figure 12 shows 5 lateral holes 240 extending outwardly, spaced over 180⁰ and figure

13 shows 9 lateral holes 240 extending outwardly, spaced over 180°,

With reference to figure 14, there is shown a schematic plan view of a weil design for gas extraction according to an embodiment of the invention. A vertical well 10 (including a gas weil casing) has lateral holes 240 extending from apertures in the gas well casing (not shown). Branch lateral holes 242 extend outwardly from the lateral holes 240.

It will be appreciated that the well designs of figures 12-13 can be used near boundaries or geological formations where it may be desirable to have the lateral holes 240 and branch lateral holes 242 extend over a predetermined angle. It will also be appreciated that the well design of figure

14 will require less apertures in the gas well casing (not shown) compared to the well design of figure 13. Typically, forming apertures in a gas well casing is more expensive and time consuming than initiating a branch lateral hole 242 from a lateral hole 240.

With reference to figures 15 and 16 there is shown a schematic plan view of a well design for gas extraction according to an embodiment of the invention. A vertical well 10 (including a gas well casing) has lateral holes 240 extending from apertures in the gas well casing (not shown). The lateral holes 240 extending outwardly, spaced over 360°. Figure 15 shows branch lateral holes 242 extending outwardly from the lateral holes.

With reference to figure 17 there is shown a schematic plan view of a lateral hole 240 having branched lateral holes 242 according to an embodiment of the invention. The lateral hole 240 extends from a gas well (not shown). Each branched lateral hole 242 extends from the lateral hole 240. The branched lateral holes 242 alternately extend from opposed sides of the lateral hole 240 to form a "herringbone" pattern.

Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention. For example, individual features from one embodiment may be combined with another embodiment.

it will be appreciated that various other changes and modifications may be made to the embodiment described without departing from th spirit and scope of the invention.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements. integers or steps.

Claims

1. A gas well casing comprising:

wherein each of the at least one tubular section of softer material is adapted to have at least on lateral hole drilled outwardly therefrom and into the respective target coal seam.

2. A gas well casing as claimed in claim 1₅ wherein the gas well casing is predominantly made of steel.

3. A gas well casing as claimed in claim 1 or claim 2, wherein the at least one tubular section of softer material is at least one tubular section of composite material.

4. A gas well casing as claimed in claim 3, wherein the composite material is a fibreglass composite material.

5. A gas well casing as claimed in any one of the preceding claims, wherein each of the at least one tubular section of softer material is disposed between sections of the gas well casing formed of steel.

6. A gas well casing as claimed in any one of the preceding claims, wherein, when the gas well casing is located in a gas well, a casing bit forms a desired number of apertures through each of the at least one tubular section of softer material, from which the at least one lateral hole is adapted to be drilled outwardly and into the respective target coal seam.

7. A gas well casing as claimed in claim 6, wherein the casing bit is deflected into the gas well casing by a wedge assembly to form the desired number of apertures through each of the at least one tubular section of softer material.

8. A gas well casing as claimed in any one of the preceding claims, wherein the gas well casing is located in a coal seam gas well.

9. A method of locating a gas well casing in a gas well, the method including the steps of:

locating a gas well casing in a gas well, the gas well casing comprising at least one tubular section of softer material that is softer than the predominant material used for the gas weii casing;

completing the location of the gas well casing in a gas well such that each of the at least one tubuiar section of softer material is located above a respective target coal seam;

10. A method as claimed in claim 9, wherein the at least one tubular section of softer material is at least one tubular section of composite material.

11. A method as claimed in claim 10, wherein the composite material is a fibreglass composite material.

12. A method as claimed in claim 9, 10 or 1 1 , wherein the gas well casing is predominantly made of steel,

13. A method as claimed in any one of claims 9 to 12, wherein the step of forming at least one aperture through each of the at least one tubular section of softer material involves using a wedge assembly to deflect a casing bit into each of the at least one tubular section of softer material.

14. A method as claimed in any one of claims 9 to 13, wherein the well is a coal seam gas well.

15. A method as claimed in any one of claims 9 to 14, wherein two lateral holes are drilled outwardly from each of the at least one tubular section of softer material, and wherein the respective two lateral holes are substantially parallel to each other.

16. A method as claimed in any one of claims 9 to 1 5, wherein each of the at least one lateral hole is drilled initially in a downwards direction relative to the gas well casing and then transitioning to a direction that is transverse to the gas well casing.

17. A method as claimed in claim 16, wherein the transition has a radius in the range of 20 to 40 meters.

18. A method as claimed in claim 16, wherein the transition has a radius in the range of 25 to 35 meters.