WO2011088517A1

WO2011088517A1 - Networked infield compression

Info

Publication number: WO2011088517A1
Application number: PCT/AU2011/000067
Authority: WO
Inventors: Guy Hamilton Hodgson
Original assignee: Energy Process Services Pty Ltd
Priority date: 2010-01-21
Filing date: 2011-01-21
Publication date: 2011-07-28
Also published as: AU2011207117A1

Abstract

The invention provides a networked distribution system for the gathering and compression of coal seam gas. The networked distribution system is characterised by an array of wells arranged in spaced apart relation, with each well being connected to a field compression station and in turn to a booster compression station. Low pressure gas is initially passed from the wells to the field compression station with nominal pressure loss and then compressed before being reticulated to the booster compression station, where the pressure is again increased.

Description

"Networked Infield Compression"

Field of the Invention

The present invention relates to a coal seam gas field networked distribution system. More particularly, the coal seam gas field networked distribution system of the present invention is intended for use in the gathering and distribution of gas in coal seam gas fields.

Background Art

Coal seam gas ("CSG") that is presently of commercial interest is formed within coal seams that are typically saturated with water and comprises methane in large part. The static water pressure within the coal seam acts to retain the methane within the coal. This water is pumped out after wells are drilled into the coal seams, which causes the CSG to be desorbed and released. The CSG is released at low pressure which requires compression to reticulate the gas for final energy consumption. Infield screw type compressors are typically used to compress the produced gas at fairly low pressures (1 ,000 kPag to 1 ,600 kPag) to a central processing facility where the CSG is further compressed by reciprocating or centrifugal compressors to a higher pressure (9,800 kPag to 10,200 kPag) then dehydrated and reticulated into a transmission pipeline.

Large scale CSG field developments are presently being driven by the liquefied natural gas ("LNG") feed gas volume demand. These CSG field developments have, to date, been developed around large centralised compressor stations designed and constructed on conventional gas project guidelines. Such conventional guidelines typically require large scale, inflexible, expensive centralised gas compression and processing systems. Traditional gas gathering and transmission methods suffer from a number of particular problems and disadvantages.

These include: an inability to retrieve total (maximum) gas from depleting wells, for example; those with flowing head pressures less than 100kPa; they require significant installed compression power to overcome pipeline pressure losses and require low point drains for saturated gas; they require low point drains to remove water than would otherwise congest the gas pipe network system; these central compression facilities cannot be easily re-located as wells and fields deplete; they require future in-field or wellhead compression and therefore increased future capital expenditure; Initial compression is based at a source and subject to the depleting gas pressure conditions at the inlet to the compressors; each well-head requires regular inspection and maintenance necessitating good quality road access. The process of the present invention has as one object thereof to overcome the abovementioned problems associated with the prior art, or to at least provide a useful alternative thereto.

The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

In accordance with the present invention there is provided a networked distribution system for the gathering and compression of coal seam gas, the networked distribution system characterised by an array of wells arranged in spaced apart relation, each well being connected to a field compression station and in turn to a booster compression station, wherein low pressure gas is initially passed from the wells to the field compression station with nominal pressure loss and then compressed before being reticulated to the booster compression station at which the pressure is again increased. Initially, the low pressure gas obtained from the wells is regulated at between 250 kPag to 450 kPag. The flowing wellhead pressure may finally drop to as low as 0 kPag.

The compression field stations may compress the gas to between about 3,500 kPag to 4,750 kPag. The booster compression station may compress the gas to between about 9,800 kPag to 10,200 kPag, for entry into a transmission pipeline. In conventional wellhead designs, each well typically has its own two- phase separator to separate the gas and the water, and the gas is then able to be reticulated from the well to the initial compression station by using the pressure in the separator as a prime moving force. The networked gathering system of the current invention does not have a separator at each well but uses a single water knockout vessel at the initial field compressor.

Each knockout pot may serve between seven to nine wells, dependant on the flowing regime of each well. In one form of the present invention the wells are arranged in rows and bays, with each intersection thereof defining a pod, wherein each pod comprises a plurality of wells connected to a field compression station by low pressure gas pipelines, the pods being connected by way of intermediate pressure gas pipelines that receive gas from each field compression station. Preferably, neighbouring pods in a bay have provided therebetween one or more low pressure gas balancing lines, thereby allowing the supply of gas between pods to be balanced. The low pressure gas balancing lines preferably extend between wells in the neighbouring pods.

Still preferably, intermediate pressure gas balancing lines are provided between the intermediate pressure gas pipelines, thereby allowing the supply of gas between bays to be balanced.

One or more pods are preferably provided with a booster compression station to which the intermediate pressure gas pipeline feeds gas. Preferably, these same . pods additionally comprise a high pressure gas pipeline that receives gas from the booster compression station.

Preferably, the low pressure gas pipelines are formed of a material that can be coiled prior to deployment by way of a spool. Still preferably, the material is a high density polyethylene.

Preferably, the intermediate pressure gas pipelines are formed of a material that can be coiled prior to deployment by way of a spool. Still preferably, the material is a reinforced high density polyethylene.

Preferably, the high pressure gas pipeline is formed of a material that can be coiled prior to deployment by way of a spool. Still preferably, the material is a high density polyethylene.

Preferably, each well has provided thereat a wellhead pressure regulator and each field compression station has provided thereat a combined wellhead stand.

Still preferably, each well is provided with individual flow metering and pressure control located at the field compressor station, obviating the need for a user to have to visit each individual well on a continual basis.

In one form of the present invention the intermediate pressure gas pipelines are paired to reduce pressure losses.

In accordance with the present invention there is further provided a method for the gathering and networked distribution of coal seam gas, the method characterised by the method steps of: i) Directing gas from a well to a field compression station in which the pressure of that gas is increased; ii) Directing gas from the field compression station to a booster compression station in which the pressure of that gas is further increased; and iii) Directing gas from the booster compression station for sale.

Preferably, step i) of the method comprises a plurality of wells arranged in an array.

The gas obtained from the wells of step i) is preferably regulated at a pressure of between about 250 kPag to 450 kPag. .

Still preferably, the compression field stations of step ii) increase the pressure of the gas to between about 3,500 kPag to 4,750 kPag. .

Still further preferably, the booster compression station of step iii) increases the pressure of gas obtained to between 9,800 kPag to 10,200 kPag. . Step i) preferably further may comprise a water knockout vessel or separator through which gas is passed from the wells to the field compression station.

Brief Description of the Drawings

The system of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:-

Figure 1 is a plan view of a networked distribution system for the gathering and networked distribution of coal seam gas in accordance with the present invention, showing an array of wells arranged into rows, bays and pods;

Figure 2 is a plan view of a single pod of the distribution system of Figure 1 ; and

Figure 3 is a plan view of a portion of a pod of the distribution system of Figure 1 , the pod portion showing a high pressure gas pipeline passing therethrough.

Figure 4 is a diagrammatic representation of a part of a distribution system using seven wells per Pod, in accordance with one aspect of the invention. Figure 5 is a diagrammatic representation of a part of a distribution system using seven wells per Pod, in accordance with one aspect of the invention.

Best Mode(s) for Carrying Out the Invention

In Figure 1 there is shown a generic coal seam gas field networked distribution system 10 in accordance with the present invention. The distribution system 10 comprises a field or array of wells 12, low pressure gas pipelines 14 and field compression stations 16. The distribution system 10 further comprises intermediate pressure gas pipelines 18, an intermediate pressure gas balancing line 20 and central or booster compression stations 22. The array of wells 12 is arranged in Rows A to H and in columns or Bays 1 to 3. The intersection of each Row and Bay defines a module or Pod. For example, the intersection of Row E with Bay 1 defines Pod 1 E. Each Pod comprises a 3 x 3 arrangement of wells 12 with an arrangement of independent low pressure gas pipelines 14 leading from each well 12 to a water gas separator 24, which in turn communicates with a field compression station 16, as is best seen in Figure 2.

An intermediate pressure gas pipeline 18 runs through each Pod and receives gas from that Pod's field compression station 16. The intermediate pressure gas balancing line 20 joins each intermediate pressure gas pipeline 18 across the array of wells 12, as shown both in Figures 1 and 2. Further, Pods in each Bay are connected by way of low pressure gas balancing lines 25.

The Pods 1 D, 2D and 3D each further comprise a central compression station 22 that receives gas from the intermediate pressure gas pipelines 18 and in turn feeds it to a high pressure gas pipeline 26 that runs through across Row D, as is best seen with reference to Figure 3. It is to be understood that the scale of coal seam gas field developments vary greatly and the specific arrangements in terms of the number of wells drilled and their respective locations is expected to vary in use. The expected performance from the gas reservoirs will also vary with individual well gas flows expected to range from 300 mscfd to 1 ,500 mscfd, or more. For the purposes of this description we assume a field gas delivery requirement of 100 TJ/d from vertical wells each producing 0.5 TJ/d. The remaining 8 TJ/d is used for power generation at the wells for wellhead pumps, and ancillary items including dehydration, offices and amenities. Due to the modular nature of the distribution system 10 of the present invention it is scalable and able to be replicated to suit any required field size. Details for the assumed 100 TJ/d example, together with estimates of lower and upper limits are provided in Table 1 below:

^* no limit There are 216 wells 12 in the distribution system 10. Each well 12 is spaced about 1000 meters apart such that each Pod is 2000 meters across and each field compression station 16 about 3000 meters apart.

The wellhead used at each of the wells 12 is divided into two sections, being gas regulation and water displacement. Unlike prior art systems, the majority of the necessary infrastructure is located at each field compression station 16. That is, the infrastructure is disseminated throughout the array. In conventional wellhead designs, each well typically has its own two-phase separator to separate the gas and the water, and the gas is then able to be reticulated from the well to the initial compression station by using the pressure in the separator as a prime moving force. The networked gathering system of the current invention does not have a separator at each well but uses a single water knockout vessel at the initial field compressor.

Each knockout pot may serve between seven to nine wells, dependant on the flowing regime of each well.

Gas regulation consists of manual valves for isolation and pressure regulation, set at the maximum operating pressure of the low pressure gas pipelines 14 (for example 450 kPag to 500 kPag). Other traditional functions such as communications, flow metering and automated pressure control, are again centralised at each field compression station 16.

There are a number of options available for water displacement depending on water volumes and operator preferences. Most power required is to dewater the well, where other well ancillaries are operated by way of gas instruments or small solar panels.

To provide electrical power generation for dewatering, the system 10 offers two methods. The first option is a low speed gas fired single piston Ajax engine with a generator driving electric submersible pumps ("ESPs") or hydraulic drives, this system is very low maintenance. The second option is a high speed gas fired conventional engine and generator providing electric power to ESPs.

Power generation is located at each well site eliminating reticulation of power.

Water pipelines (not shown) maintain a common pressure rating throughout the field, and share a common pipe trench to the compressed gas pipelines. In the described example there is approximately 238 km of 1 10 mm high-density polyelthylene ("HDPE") piping and 88 km of 200 mm & 355 mm HDPE piping operating at between 450 kPag to 500 kPag. The water lines connect to the wellhead, and are routed through the field compression station 6, and booster compression station 22. The water pipelines terminate at the edge of the array or field for an operator to select and install a preferred treatment method. The low pressure gas pipelines 14 connect from a wellhead pressure regulator (set at between 450 kPag to 500 kPag, not shown) at the well 12 to a combined wellhead stand (not shown) located at the field compression stations 16. The low pressure gas pipelines 14 can also operate at between 0 kPag to 100 kPag, based on the central wellhead stand. As such, aside from the wellhead pressure regulator, the low pressure gas pipelines 14 act as an extension of the wells 12 in order to centralise the wellhead components.

There is approximately 238 km of 110 mm HDPE low pressure gas pipelines 14. The 110 mm pipeline is supplied in coiled form and can be spool fed, or spooled from a suitable deployment apparatus, and ploughed in together with the water pipelines described hereinabove.

The low pressure gas pipelines 14 of one Pod are interconnected between respective vertical neighbours through the low pressure gas balancing lines 25, as shown in Figures 1 and 2. The desired effect is to distribute the gas across multiple field compression stations 16. An example is shown in Figures 1 and 2, wherein at Pod 1 E there is provided an additional low pressure gas balancing line 28 transfer surplus gas to the neighbouring filed compressors.

The intermediate pressure gas pipelines 18 extend between the Field Compression stations 16 and a suction header provided at the booster compression stations 22. The intermediate pressure gas pipelines operate at about 3,500 kPag to 4,750 kPag based on the field compression station 16 discharge pressure. There is approximately 88 km of intermediate pressure gas pipeline 18. The gas pipeline used for the intermediate pressure gas pipelines 18 is a flexible high pressure reinforced HDPE pipe typically less than 6" in diameter that is able to be stored in coil form. Where required, the intermediate pressure gas pipelines 18 may be paired to reduce pressure losses. The high pressure gas pipeline connects a discharge header of each booster compression station 22 to a sales gas line (not shown). There is provided about 20 km of high pressure gas pipeline operating at 10 MPag. The pipeline used is a flexible high pressure reinforced HDPE pipe similar to that from which the intermediate pressure gas pipeline 18 is formed and is deployed in substantially the same manner. Steel piping can also be used as an alternative to the high pressure line to the transmission pipeline.

There are 24 field compression stations 16 in the distribution system 10 of the present invention, and each processes approximately 4.5 TJ/d supplied by the surrounding wells 12lt is envisaged that field compression stations 16 may be positioned anywhere within a Pod to accommodate physical terrain constraints or proximity to buildings, roads, to meet landowner requirements, or in noise sensitive areas..

The facilities provided at each field compression station 16 includes engineering procurement construction ("EPC") services, site preparation, earthworks, perimeter fence, freight, instrument-electrical equipment, common wellhead valve stand, control panel, data communications incoming/outgoing, lighting, infrared fire protection, lightening protection, one Ajax integral engine/compressor, lube oil storage tank, pre-compression gas/water knock out separator, compression station valves, noise abatement, oily water separator combined with water pump and waste oil storage, steel pipe work, installation, commissioning, performance testing and warranties (not shown).

The gas enters the field compression station 16 at the valve stand from the low pressure gas pipeline 14 and is then directed to the water separator 24 that is both buried and is pre-compression. Each well 12 is provided with individual flow metering, and pressure control, enabling a user to remotely operate the wellhead pressure from 0 kPa to 500 kPa, with a nominal 450 kPag initial set point. This enables the compression capital to be minimised during the initial years of the field by decreasing the suction pressure as the wells deplete, enabling a full recovery of gas from the reservoir wellhead. The three booster compression stations 22 located in the Pods at Row D each contain two compressors of the same design as those provided at the field compression stations 16. The booster compressors compress the gas to a sales gas pressure of between 9,800 kPag to 10,200 kPag. The infrastructure scope of each of the three booster compression stations 22 is of the same scope as the field compression stations 16, but has some additional facilities (if required) at the booster compression station of Pod 1 D, including an electric generator set, an office, 2 x 50 TJ/d glycol dehydration skids and a metering station (not shown). It is envisaged that alternate well arrangements may be utilised without departing from the scope of the present invention. Such alternate arrangements may include horizontally drilled clustered wells on a common drill pad, whereby a cluster of 9 wells (in certain cases 7 wells, as discussed below) is positioned about a single compression station. Figure 4 is a diagrammatic representation of part of a networked distribution system 10 in accordance with one aspect of the invention, in which seven wells 12 are connected via low pressure gas pipelines 14 to field compression stations 16, before feeding into the remainder of the distribution system 10 in the manner described hereinbefore. Figure 5 similarly is a diagrammatic representation of part of a networked distribution system 10 in accordance with one aspect of the invention, which shows a block diagram of Pod-to-Pod connections. In the drawing, seven wells 12 in each Pod are connected to a water knock-out vessel 30 on one side, while being connected to a water header regulator 32 on the other. The gas from each water knock-out vessel 30 is directed to a field compression station 16 from where it forms part of the gas fed to a compression booster station 22 via pipeline 34, the remaining stream being delivered to the water pipeline running adjacent to compressor station 22. The oil collected in the oily water separator is stored until manually collected by trucks. This is repeated for each Pod. The distribution system 10 of the present invention presents a low capital and operating cost model that, without other considerations, is reasonably expected to result in a significantly lower net present cost over the lifecycle of a CSG field development project when compared with alternative systems of the prior art. Further advantages of the distribution system 10 of the present invention include potential savings on time and cost on any front end engineering and design ("FEED") study, potential time and cost saving on design engineering, benefits of "cookie cutter" development model for future projects, potential cost savings from limited capital outlay over shorter construction period, earlier sales gas availability, flexible low cost relocation of compression as field reservoir changes, relatively low cost of adding additional compression by banking units, high residual value of skid mounted movable compression at end of field life, and lower rehabilitation costs at end of field life.

The benefits of the distribution system 10 of the present invention over the centralised compressor station concepts of the prior art are numerous. However, it is envisaged that between 10% to 28% additional gas can be recovered. The Applicant reasonably expects that 216 wells of 1.5 Pj @ 10% and a gas price of AU$4.00 Gj, additional revenue of AU$130 million can be expected.

It is envisaged that using the distribution system of the present invention may reduce suction pressure limits of prior art arrangements, with the ability to retrieve additional gas from depleting wells with flowing head pressure of less than 5 kPag.

Still further, the distribution system of the present invention may reduce the overall installed compression power by up to about 50% relative to prior art arrangements through the reduction of pipeline pressure losses and eliminating low point drains from field compression by way of higher gas velocities. As the system of the present invention utilises low diameter piping at higher average pressures low point drains can be avoided as small "slugs" of water are passed through to the water knockout vessels provided at the field compressor locations with minimal pressure loss. The distribution system of the present invention is considered to be particularly flexible relative to the prior art through its utilisation of interconnected gas gathering networks that can be modified to accommodate depleting wells. This arrangement also provides for relatively easy relocation and/or optimisation as fields reduce in output, and ultimately can be relocated as sections of the field deplete.

The compression provided in the distribution system of the present invention is distributed on a network of pipes and acts relatively evenly across the field on a blanket of distributed interconnected compression. The flow metering, automated pressure control and communications of the distribution system of the present invention are centralised at field compression stations thereby significantly reducing the need to access the wellhead location, as compared to prior art arrangements, as it effectively extends the wellhead function to a centralised location. Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

- 14 - Claims

1. A networked distribution system for the gathering and compression of coal seam gas, the networked distribution system being characterised by an array of wells arranged in spaced apart relation, each well being connected to a field compression station and in turn to a booster compression station, wherein low pressure gas is initially passed from the wells to the field compression station with nominal pressure loss and then compressed before being reticulated to the booster compression station at which the pressure is again increased.

2. A networked distribution system according to claim 1 , wherein the low pressure gas obtained from the wells is regulated at an initial pressure of between about 450 kPag and 500 kPag.

3. A networked distribution system according to claim 1 or 2, wherein the compression field stations increase the pressure of the gas to between about 3500 kPag to 4750 kPag.

4. A networked distribution system according to any one of claims 1 to 3, wherein the booster compression station increases the pressure of gas obtained to about 10,000 kPag.

5. A networked distribution system according to any one of the preceding claims, wherein each well feeds low pressure gas to a field compression station through a water knockout vessel. .

6. A networked distribution system according to any one of the preceding claims, wherein the wells are arranged in rows and bays, with each intersection thereof defining a pod, wherein each pod comprises a plurality of wells connected to a field compression station by low pressure gas pipelines, the pods being connected by way of intermediate pressure gas pipelines that receive gas from each field compression station. - 15 -

7. A networked distribution system according to claim 6, wherein neighbouring pods in a bay have provided therebetween one or more low pressure gas balancing lines, thereby allowing the supply of gas between pods to be balanced.

8. A networked distribution system according to claim 7, wherein the low pressure gas balancing lines extend between wells in the neighbouring pods.

9. A networked distribution system according to any one of claims 6 to 8, wherein intermediate pressure gas balancing lines are provided between the intermediate pressure gas pipelines, thereby allowing the supply of gas between bays to be balanced.

10. A networked distribution system according to any one of claims 6 to 9, wherein one or more pods are provided with a booster compression station to which the intermediate pressure gas pipeline feeds gas.

11. A networked distribution system according to claim 10, wherein the pods additionally comprise a high pressure gas pipeline that receives gas from the booster compression station.

12. A networked distribution system according to any one of claims 6 to 11 , wherein the low pressure gas pipelines are formed of a material that can be coiled prior to deployment by way of a spool.

13. A networked distribution system according to any one of claims 6 to 12, wherein the intermediate pressure gas pipelines are formed of a material that can be coiled prior to deployment by way of a spool.

14. A networked distribution system according to any one of claims 6 to 13, wherein the high pressure gas pipeline is formed of a material that can be coiled prior to deployment by way of a spool.

15. A networked distribution system according to any one of claims 12 to 14, wherein the material is a high density polyethylene. - 16 -

16. A networked distribution system according to any one of the preceding claims, wherein each well has provided thereat a wellhead pressure regulator and each field compression station has provided thereat a combined wellhead stand.

17. A networked distribution system according to any one of the preceding claims, wherein each well is provided with individual flow metering and pressure control, thereby enabling a user to remotely operate the wellhead pressure.

18. A networked distribution system according to any one of claims 6 to 17, wherein the intermediate pressure gas pipelines are paired to reduce pressure losses.

19. A method for the collection and distribution of coal seam gas, the method characterised by the method steps of: i) Directing gas from a well to a field compression station in which the pressure of that gas is increased; ii) Directing gas from the field compression station to a booster compression station in which the pressure of that gas is further increased; and iii) Directing gas from the booster compression station for sale.

20. A method according to claim 19, wherein step i) comprises a plurality of wells arranged in an array.

21. A method according to claim 20, wherein the gas obtained from the wells of step i) is regulated at a pressure of between 450 kPag to 500 kPag.

22. A method according to any one of claims 19 to 21 , wherein the compression field stations of step ii) increase the pressure of the gas to between about 3500 kPag to 4,750 kPag. - 17 -

23. A method according to any one of claims 19 to 22, wherein the booster compression station of step iii) increases the pressure of gas obtained to about 10MPa.

24. A method according to any one of claims 19 to 23, wherein step i) further comprises a water knockout vessel through which gas is passed from the well to the field compression station.

25. A method according to any one of claims 19 to 24, wherein gas is fed from wells arranged in rows and bays, with each intersection thereof defining a pod, wherein each pod comprises a plurality of wells connected to a field compression station by low pressure gas pipelines, the pods being connected by way of intermediate pressure gas pipelines that receive gas from each field compression station.

26. A method according to claim 25, wherein the supply of gas between neighbouring pods in a bay is balanced through one or more low pressure gas balancing lines provided therebetween.

27. A method according to claim 26, wherein the low pressure gas balancing lines extend between wells in the neighbouring pods.

28. A method according to any one of claims 25 to 27, wherein the supply of gas between bays is balanced through intermediate pressure gas balancing lines provided between the intermediate pressure gas pipelines.

29. A networked distribution system for the collection and distribution of coal seam gas substantially as hereinbefore described with reference to Figures 1 to 3.

30. A method for the collection and distribution of coal seam gas, the method being substantially as hereinbefore described with reference to Figures 1 to 3.