AU2021204052B2

AU2021204052B2 - Liquid removal system

Info

Publication number: AU2021204052B2
Application number: AU2021204052A
Authority: AU
Inventors: Peter James Tait
Original assignee: Practical Pty Ltd
Current assignee: Practical Pty Ltd
Priority date: 2021-06-17
Filing date: 2021-06-17
Publication date: 2023-09-07
Anticipated expiration: 2041-06-17
Also published as: AU2021204052A1; AU2021105038A4; AU2021105038A6

Abstract

LIQUID REMOVAL SYSTEM ABSTRACT Disclosed herein is a liquid removal system comprising: a first reservoir having a first port in fluid connection with a sump and a second port; a second reservoir having a first port and a fluid discharge outlet; pump means in fluid communication with sump via the second port of the first reservoir and in fluid communication with the second reservoir via the first port of the second reservoir; a control system to control operation of the pump means, the control system configured to operate the pump means in a first mode or a second mode; wherein in the first mode, the pump means is configured to draw liquid from the sump, through the first reservoir, and transfer the liquid via the pump means to the second reservoir; wherein in the second mode, the pump means is configured to transfer liquid from the second reservoir in a volume sufficient to displace gas from the first reservoir to the sump, and restore liquid connection between the sump and the pump means. 3/6 -Ji Li, Figure 2

Description

3/6

-Ji

Li,

Figure 2

LIQUID REMOVAL SYSTEM

Field

[0001] The invention relates to a liquid removal system and related apparatus and methods, such as for use in removing liquid from an above ground source or below ground low point drain which may be associated with a coal seam gas or natural gas field.

Background

[0002] Gas production and gas transfer industries typically require the handling of gas which is prone to the drop-out of liquid (e.g. water). This liquid drop-out may be due to entrained liquid in a gas stream settling out of the gas stream, or due to a temperature drop of saturated gas resulting in condensation. These liquids have a propensity to accumulate at low points along a piping network. These low points may correspond to areas where piping follows natural variation in land level (such as crossing a gully or creek), may result from deliberately created low points (by locally burying pipe deeper to create a low point in otherwise flat land) or may result from undulation of the pipe level.

[0003] This is particularly problematic in the coal seam gas industry. Coal seam gas is generally saturated with water vapour. During production, gas is transported from a well to the surface. The temperature of the gas in the well is generally higher than the ambient temperature at the surface. Given this, once the gas is flowing in pipes in the ground (typically polyethylene), the gas cools which leads to the formation of liquid water by condensation. In addition, it is possible that carried-over production water drops out of the gas. This water can then accumulate at low points due to migration of the water through the system, typically in the form of water slugs.

[0004] The combination of incomplete separation of produced water from the gas local to the wellhead and the installation of low numbers of automated drains can lead to the production and accumulation of widely varying quantities of water within the gas production system. This occurs due to the combination of irregular build-up of water within the system with subsequent migration as water slugs and also due to wells transitioning through periods of significant water carry-over as they transition to more uniform gas production.

[0005] Within the Coal Seam Gas industry, there is a desire to use as simple a process as possible to drain low points to save cost. A key to lower cost is to use a simple geometry and avoid the need for instrumentation of the low point. This is because there are a vast number of low point drains and only a subset of them need to be routinely emptied for adequate operations.

[0006] Australian innovation patent 2015101693 (the entire disclosure of which is herein incorporated by reference) describes a means of extracting water from simple low point drain geometries which significantly lessens the requirements of manually draining low points that usually involve the use of water removal trucks and manual intervention field operations.

[0007] There are ever-increasing pressures to reduce fugitive greenhouse gas emissions and methane is a powerful greenhouse gas with an impact many times that of the carbon dioxide it would form once fully oxidised. Methane that is released to the atmosphere is slowly broken down to carbon dioxide over many years. Methane is generally considered to have a Greenhouse Warming Potential of 28-36 times that of Carbon Dioxide (on a weight basis) over a 100-year period, though it is more damaging if short time frames are considered as the average life of CH 4 in the atmosphere is estimated at 10 years. As such, it is important to minimise fugitive emissions from coal seam gas or natural gas fields.

[0008] With respect to the methane emissions from low point draining operations, the device outlined in Australian innovation patent 2015101693 and now sold commercially as the LPD MAX range of equipment has very substantially reduced the methane emissions compared to manual low point draining. This is because the LPD-MAX system avoids the need for an operator to (i) manually drain each low point, which involves the operator draining the system until observing gas break-through (which releases methane to the atmosphere) to evidence that drainage operations should be ceased, and (ii) drive between each low point to check the low point and/or drain the low point.

[0010] Small quantities of methane would normally be released along with extracted water during the operation of prior art equipment in accordance with Innovation Patent 2015101693, into the water piping system (or other water accepting system) proximal to the gas piping system. Most water piping systems incorporate self-acting gas venting valves at high points along the water pipeline and then ultimately the water discharges to open ponds. There are no known installations in Australia recovering methane from the water piping and so methane lost to the water piping system is ultimately lost to atmosphere.

[0011] There are however installations where the inlet piping from the in-ground low point to the liquid extraction means is perhaps a long and tortuous path that leads to the potential for accumulation of significant gas in the low point drainage pipeline with commensurate difficulties in establishing pump priming for pumping operations. This adds to the volume of gas that must be drawn through prior art systems in order to establish a pump prime and determine if there is actually water at the low point requiring emptying. Difficult inlet geometries therefore lead to higher gas losses compared to simpler inlet geometries when using the prior art systems.

[0012] To address the issue of pump priming, a priming vessel can be installed upstream of a pump such that once initially filled with water and providing there is no leakage, it can serve to provide for pump priming. Such a system will continue to operate successfully provided the source of the water is not allowed to go low and allow gas into the inlet piping system. Such systems would normally rely upon a level switch in the water source (for example a sump) such that the prime is retained, and the system will work when called upon to do so.

[0013] Inlet priming vessels can be fitted with a vacuum pump or other gas removal means to draw liquid up from the source and extract sufficient gas from the priming vessel that the pump can then operate. This would allow the pump prime to be achieved even if there had been an ingress of gas into the system (for example after gas had broken through to the inlet piping system due to a lack of level sensor at the liquid source). For the coal seam gas industry though, such previously known priming techniques are undesirable as they involve additional equipment and operating complexity. They also lead to loss of gas to atmosphere unless there is an additional connection to the gas piping to allow the gas extracted to achieve pump priming to be reinjected into the gas line. Such additional connections are not presently available in the piping networks and would represent a prohibitive cost if they were to be retrofitted.

[0014] Further, there exist many different geometries of pipework leading from the low point (typically underground) to the surface. In the absence of other design considerations, this pipework may be routed relatively directly to surface and thus provides a low volume and short, straight (largely vertical) pipe run. In other locations however, there may be a need to take the pipework along a long path from the in-ground low point to the surface such as in the situation where the low point is under a gully and it is desired to locate the riser that comes out of the ground some significant distance away (for example 50m away) to have this location out of a flood zone and away from potential flood-borne debris. Further, the installation depth of this pipe may rise and fall leading to multiple pockets where gas can accumulate. Broadly then there 9210AUP03 [EFILE-SAF.FID13432354]is a range of piping geometries from the low point to the surface that lend themselves well or poorly to the requirements of pump priming.

It is an object of the invention to address at least one shortcoming of the prior art and/or provide a useful alternative.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of Invention

[0017] In a first aspect of the invention, there is provided a liquid removal system comprising: a first reservoir comprising a first port in fluid connection with a sump and a second port; a second reservoir comprising a first port and a fluid discharge outlet; pump means in fluid communication with the sump via the second port of the first reservoir and in fluid communication with the second reservoir via the first port of the second reservoir; a control system to control operation of the pump means, the control system configured to operate the pump means in a first mode or a second mode; wherein in the first mode, the pump means is configured to draw liquid from the sump into the first reservoir, transfer liquid from the first reservoir to the second reservoir and optionally discharge a portion of the liquid from the fluid discharge outlet; wherein in the second mode, the pump means is configured to transfer liquid from the second reservoir to the first reservoir to displace gas from the first reservoir to the sump and to provide the first reservoir with an operating volume of liquid; wherein the operating volume of liquid is sufficient that the pump means is operable in the first mode to draw liquid from the sump into the first reservoir and transfer liquid from the first reservoir to the second reservoir.

[0018] In one of more forms, the present invention provides a system for positively priming a pump such that it can extract liquid (typically water) from a sump (that may be non instrumented) to the extent where gas is withdrawn from the sump and retained in the first reservoir whilst ensuring no gas enters into or passes through the pump means since this would undesirably lead to a release of gas to the environment. The system is able to do this in a repetitive manner by storing an operating volume of liquid in the second reservoir, which can be transferred to the first reservoir to restore pump prime for subsequent sump drainage operations in the first mode.

[0019] The sump may be an above ground or a below ground sump. For example, the sump may be a low point or low point drain associated with underground piping, a low point or low point drain associated with above ground piping, or an above ground or below ground gas-liquid storage or separation vessel.

[0020] In an embodiment, the first reservoir is hermetically sealed. The second reservoir may be an open reservoir or a hermetically sealed reservoir. In one example, the first and/or second reservoirs are first and/or second hermetically sealed gas-liquid separation vessels.

[0021] In an embodiment, the first reservoir has a liquid storage volume arranged between at least the first port and the second port thereof, sized to store at least the operating volume. Preferably, the operating volume is greater than an internal volume of a piping system connecting the first reservoir to the sump. More preferably, the system comprises piping connecting the first reservoir to the sump.

[0022] In an embodiment, the second reservoir has a liquid storage volume arranged between at least the first port and the fluid discharge outlet thereof, the storage volume being sized to store at least the operating volume.

[0023] In an embodiment, the controller is configured to initiate operation of the liquid removal system in the second mode.

[0024] In an embodiment, the controller is configured to cease operation in the second mode and switch operation to the first mode on determination that the operating volume of liquid has been transferred.

[0025] In one form of the above embodiment, the controller is configured to determine that a sufficient volume of liquid has been transferred based on one or more of: a level switch in the first reservoir or second reservoir, a level transmitter in the first reservoir or second reservoir, an integrating flow switch or transmitter on a fluid line connecting the first reservoir or the second reservoir and the pump means, a load cell in the first reservoir or second reservoir, or from pump means operation data (e.g. duration of pump operation in the second mode, number of pump revolutions during operation in the second mode etc.)

[0026] In an embodiment, the control system is configured to cease operation in the first mode on determination of a low liquid volume in thefirst reservoir and/or impending gas break through to the pump means.

[0027] In one form of the above embodiment, the first reservoir comprises gas break-through detection means in communication with the control system. Preferably, on detection of gas break-through, the gas break-through detection means provides the control system with a signal indicative of impending gas break-through to the pump means.

[0028] By impending gas break-through to the pump means, it is meant that continued operation of the pump means would lead to gas break-through to the pump means, that is liquid being transferred by the pump means is replaced with a two-phase gas/liquid flow or gas flow. Gas break-through detection means may be in the form of a sensor in the first reservoir or on flow line between the first reservoir and the pump means. Suitable sensors include: a level switch, a level transmitter, a density switch, a density transmitter, a conductivity switch, a conductivity transmitter, a refractive index switch, or a refractive index transmitter.

[0029] In an embodiment, the control system is configured to: initiate operation in the second mode; cease operation in the second mode on determination that the operating volume of liquid has been transferred; switch operation to the first mode; initiate operation in the second mode; cease operation in the first mode on gas break-through detection.

[0030] In an embodiment, the control system is configured to initiate operation based on a schedule and/or a manual input and/or detection of liquid in the sump.

[0031] In one such example, the control system is configured to: initiate operation in the second mode at a scheduled time; cease operation in the second mode on determination that the operating volume of liquid has been transferred; switch operation to the first mode; initiate operation in the first mode; cease operation in the first mode on gas break-through detection; and resume operation in the second mode after a wait time or at a next scheduled time.

[0032] In another such example, the control system is configured to: initiate operation in the second mode based on detection of liquid in the sump; cease operation in the second mode on determination that the operating volume of liquid has been transferred; switch operation to the first mode; initiate operation in the first mode; cease operation in the first mode on gas break-through detection; and resume operation in the second mode on detection of liquid in the sump.

[0033] The skilled person will appreciate that there may be a time delay between ceasing operation in the first or second mode and commencing a subsequent operation in the other of the first or second mode.

[0034] In an embodiment, the first reservoir and/or the second reservoir are un-instrumented, and a volume of liquid stored in thefirst storage reservoir and/or the second storage reservoir is determined based on pump operation data. Preferably, the liquid removal system is un instrumented.

[0035] In an embodiment, the system further comprises a separator fluidically interposed between the first reservoir and the pump means, the separator comprising gas-break-through detection means in communication with the controller, the controller configured to cease operation of the pump means in the first mode and switch operation of the pump means to the second mode on receiving a gas break-through detection signal from the gas-break-through detection means. Operation in the second mode may commence immediately, after a wait time, or at a scheduled time.

[0036] In an embodiment, pump means comprises: at least one reversible pump operable in the first mode and the second mode, or a first pump operable in the first mode and a second pump operable in the second mode, the first pump having an inlet in fluid communication with the first reservoir and an outlet in fluid communication with the second reservoir, and the second pump having an inlet in fluid communication with second reservoir and an outlet in fluid communication with the first reservoir, or at least one pump having an inlet side, an outlet side, and controllable valve means operable to selectively connect the inlet side to the first reservoir and the outlet side to the second reservoir when operated in the first mode and to selectively connect the inlet side to the second reservoir and the outlet side to the first reservoir when operated in the second mode.

[0037] In one form of the above an embodiment, the pump means is at least one reversible pump, and the at least one reversible pump is a helical rotor pump.

[0038] In an embodiment, the liquid removal system further comprises solar panels and/or is solar powered.

[0039] In an embodiment, the liquid removal system is surface locatable. Preferably the liquid removal system is located above-ground.

[0040] In an embodiment, liquid removal system comprises a large flow rate pump connected to the first reservoir, and configured to draw liquid from the sump, through the first reservoir, and transfer the liquid to the second reservoir; wherein the control system is configured to activate the large flow rate pump when the pump means is operated in the first mode, and cease operation of the large flow rate pump when operation of the pump means in the first mode is ceased.

[0041] In a second aspect of the invention, there is provided a skid for use, or when used, in the liquid removal system according to the first aspect or embodiments thereof, the skid comprising at least the control system and the pump.

[0042] In a third aspect of the invention, there is provided a skid comprising: pump means having first connection means configured for fluid connection with a sump via a first reservoir and second connection means configured for fluid connection with a second reservoir; a control system to control operation of the pump means, the control system configured to operate the pump means in a first mode or a second mode; wherein in the first mode, the pump means is operated to draw liquid via the first connection means and discharge liquid via the second connection means, the control system being configured to cease operation of the pump means in the first mode on receipt of a signal indicative of low level or impending gas break-through; and wherein in the second mode, the pump means is operated to draw liquid via the second connection means and transfer an operating volume of liquid via the first connection means to displace gas from the first reservoir to the sump; wherein the control system is programmed with a value corresponding to an operating volume of liquid, wherein the control system is configured to operate the pump means in the second mode to transfer at least the operating volume of liquid.

[0043] In an embodiment of the second or third aspects, the skid further comprises a separator in fluid connection with the first connection means and having a port configured for fluid connection with the first reservoir upstream of the pump means, the separator comprising gas break-through detection means in communication with the controller, the controller configured to cease operation of the pump means in thefirst mode and switch operation of the pump means to the second mode on receiving a gas break-through signal from the gas break-through detection means. Operation in the second mode may commence immediately, after a wait time, or at a scheduled time.

[0044] In an embodiment of the second or third aspects, the pump means comprises: at least one reversible pump operable in the first mode and the second mode, or a first pump operable in the first mode and configured to draw liquid via the first connection means and discharge liquid via the second connection means, and a second pump operable in the second mode and configured to draw liquid via the second connection means and discharge liquid via the first connection means, or at least one pump having an inlet side, an outlet side, and controllable valve means, the controller configured to operate the controllable valve means to connect the inlet side to the first connection means and the outlet side to the second connection means in the first mode, and connect the inlet side to the second connection means and the outlet side to the first connection means in the second mode.

[0045] In one form of the above embodiment of the second or third aspects, the pump means is a reversible pump, and the reversible pump is a helical rotor pump.

[0046] In an embodiment of the second or third aspects, skid further comprises solar panels and/or is solar powered.

[0047] In an embodiment of the second or third aspects, the skid is surface locatable. Preferably the liquid removal system is located above-ground.

[0048] In a fourth aspect of the invention there is provided the installation or use of a liquid removal system according to the first aspect of the invention and/or embodiments thereof, or the skid according to the second or third aspects of the invention and/or embodiments thereof in a gas production field.

[0049] In a fifth aspect of the invention, there is provided a gas production field comprising one or more liquid removal systems according to the first aspect of the invention and/or embodiments thereof, or skids according to the second or third aspects of the invention and/or embodiments thereof, wherein the reservoir is above ground or below ground.

[0050] In a sixth aspect of the invention, there is provided a method of removing liquid from a sump with a liquid removal system comprising at least: a first reservoir, a second reservoir, and a pump means having a first connection in fluid communication with the first reservoir and a second connection in fluid communication with the second reservoir, the method comprising:

10a

operating the pump means to transfer an operating volume of liquid from the second reservoir to the first reservoir and to displace gas from the first reservoir to the sump, and ceasing operation of the pump means; wherein the operating volume of liquid is sufficient the pump means is operable in the first mode to draw liquid from the sump into the first reservoir and transfer liquid from the first reservoir to the second reservoir.

switching operation of the pump means such that the pump is operable to draw liquid from the sump, through the first reservoir, and transfer the liquid via the pump means to the second reservoir; operating the pump means to draw liquid from the sump, through the first reservoir, and transfer the liquid via the pump means to the second reservoir; detecting a low liquid level in the first reservoir and/or impending gas break-through to the pump and ceasing operation of the pump means; wherein the method further comprises: storing at least the operating volume of liquid in the second reservoir, and optionally discharging at least a portion of any excess liquid from the second reservoir via a discharge outlet of the second reservoir.

[0051] In an embodiment, the method is manually initiated, or automatically initiated based on one or more of a schedule or detection of liquid in the sump.

[0052] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

[0053] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief Description of Drawings

[0054] Figure 1A is an illustration of system with simple low point geometry with low prospect for formation of gas pockets between the low point and the surface-located riser from which the liquid is extracted.

[0055] Figure 1B is an illustration of system with more complicated low point geometry than that of Figure 1A and with higher prospect for formation of gas pockets between the low point and the surface-located riser from which the liquid is extracted.

[0056] Figure 2 is an illustration of a water drainage system in accordance with an aspect of the invention.

[0057] Figure 3 is an illustration of another water drainage system in accordance with an embodiment of the invention.

[0058] Figure 4 is an illustration of still another water drainage system in accordance with an embodiment of the invention.

[0059] Figure 5 is an illustration of yet another water drainage system in accordance with an embodiment of the invention.

Description of Embodiments

[0060] The invention broadly relates to a liquid removal system and method that is able to drain liquid from a sump or other low point, such as of a gas production system, whilst minimising fugitive gas emissions (particularly methane gas). The liquid removal system comprises first and second reservoirs (which may be in the form of separation vessels), pump means, and a control system to control the pump means. The first reservoir is in fluid communication with the sump and at least a first connection means of the pump means, and the second reservoir is in fluid communication with a fluid discharge outlet and at least a second connection means of the pump means.

[0061] The control system is configured to operate the pump means in two modes.

[0062] In the first mode, the control system operates the pump means such that the pump means draws liquid from the sump to the first reservoir, and to transfer liquid from the first reservoir to the second reservoir. In the first mode of operation, the pump means drains liquid from the sump. It will be appreciated that the first reservoir is a hermetically sealed reservoir such that the pump means is operable to draw liquid from the sump via thefirst reservoir. The second reservoir receives liquid from the first reservoir, thus increasing the volume of liquid in the second reservoir. The second reservoir has a storage volume for retaining a volume of the liquid, with water in excess of this storage volume being discharged from the second reservoir via the fluid discharge outlet (e.g. to a water piping system for treatment and/or removal). In this way, liquid drained from the sump is discharged from the system. The second reservoir may be open but is preferably hermetically sealed.

[0063] During operation in the first mode, gas such as methane may accumulate within headspace of the first reservoir. This may be due to entrained or dissolved gases being released from the liquid in the first reservoir, or from gas break-through from the sump during drainage. Retention of gas is another reason the first reservoir is hermetically sealed. At some stage, sufficient gas accumulates in the head space of the first reservoir to trigger an impending gas break-through detection, at which point the control system ceases operation of the pump means in the first mode and switches operation of the pump means to the second mode. Operation in the second mode may commence immediately, after a wait time, or at a scheduled time.

[0064] As noted above, the second reservoir has a storage volume for retaining a volume of liquid. The purpose of this storage volume is to enable sufficient water to be transferred back to the first reservoir during operation of the pump means in the second mode to displace gas accumulated in the first reservoir back into the gas production system via the sump and to provide the first reservoir with an operating volume of liquid. The operating volume of liquid is sufficient that the pump means is subsequently operable in the first mode to draw liquid from the sump into the first reservoir and transfer liquid from the first reservoir to the second reservoir. This is also referred to herein as reinstating the priming potential of thefirst reservoir.

[0065] Once the operating volume of liquid has been transferred to the first reservoir (i.e. to reinstate the priming potential of the first reservoir), the control system ceases operation of the pump means in the second mode and switches operation of the pump means to the first mode for subsequent operation at a future time. The control system may actuate the pump means to operate in the first mode once sufficient water has accumulated in the sump. This actuation may be based on detection of sufficient fluid in the sump or based on a timer (e.g. in consideration of a liquid accumulation rate in the sump). On actuation, the pump means is primed and able to draw water from the sump via the first reservoir.

[0066] In one example, the system comprises piping connecting the first reservoir with the sump, e.g. 50m of 63mm hdpe between the sump and the inlet to the first vessel. The ID is 51mm. Thus, the internal volume of the inlet piping is 102 litres. In this example, the first reservoir and the second reservoir are in the form of 200 litre vessels. The control system is configured to pump back 150 litres during the second mode of operations. This is more than sufficient to fully prime the hdpe piping system even if it was all gas as it would be on start-up on day 1. When the system is operated in the second mode, gas is displaced from the headspace of the first reservoir into the pipework - however not all of the gas will necessarily be displaced from the hdpe pipework into the sump because complicated (rising and falling) pipework traps gas pockets. However, provided that the first reservoir is filled with a sufficient operating volume it can act as a priming vessel. Because the first reservoir is sized correctly for the inlet pipework system, water will be drawn from the sump into the first reservoir before the first reservoir runs empty (or gets down to a level where low level or impending gas breakthrough sensor is detected which would trigger the pump means to cease operation in the first mode). By this means, when low level or gas break through is detected, the inference is that the sump has run out of liquid (e.g. has been drained). The operating volume is thus large enough to suit the inlet piping system from the sump to the first reservoir; and the second reservoir large enough to reinstate the operating volume to the first reservoir.

[0067] The system thus provides a means for reducing fugitive gas emissions since gas that breaks through from the sump is captured in the first reservoir and is subsequently returned to the gas production system via the sump when the pump means is operated in the second mode.

[0068] The general operation cycle of the liquid removal system is broadly outlined below. It will be appreciated that the order of the steps may vary depending on the particular system and process requirements.

[0069] Step 1: Run the water transfer in the reverse direction (i.e. second mode of operation) so water stored downstream (with respect to the forward pumping direction) of the pump means is pumped back into the first reservoir which is located upstream of the pump means (noting that upstream and downstream refers to the normal forward direction of pumping). This reverse flow of water is used to displace gas accumulated in the first reservoir into the sump (which may be in the form of a low point drainage piping system). Reverse pumping is ceased when sufficient volume has been returned to the first reservoir such that the pump is primed for use in the forward direction (i.e. first mode of operation). By 'primed' it is meant that the first reservoir has sufficient volume of liquid within it that, when subsequently operated in the forward direction it can accommodate the gas volume that will be withdrawn from the inlet piping system from the low point sump to the first reservoir and to thereafter draw water from the low point sump prior to the first reservoir running out of liquid fill.

[0070] Step 2: Run the water transfer system in the forward direction until such time as gas is detected upstream of the pump, such as in the first reservoir, at which point water transfer via the pump is ceased.

[0071] Step 3: Wait for the next scheduled water extraction operation.

[0072] This cycle can be conducted multiple times per day and can be held at any point. For example, a sequence might consist of forward pumping (step 2) followed by reverse pumping (step 1) and then awaiting the next run time (step 3). There can also be pauses between the two steps. An important aspect is that the forward operations is ceased on detecting impending gas break-through. Thereafter, the unit is operated in reverse sufficient to restore the priming capability before being operated in the forward direction again.

[0073] In the specific case of the pump being a helical rotor pump, it is most convenient to reverse the flow by reversing the direction of rotation of the pump. It is also possible to reduce the overall cost of the system by avoiding the use of instrumentation by not monitoring the reverse flow quantity of water as might be evidenced by a level switch, level transmitter or integrating flow meter, but rather by counting reverse revolutions of the pump and approximating the returned volume by this means. Further, the net production of extracted water can be estimated by the number of forward pump revolutions minus the number of reverse pump revolutions. As an alternative low-cost solution, the pump might be operated in reverse for a fixed quantity of time tailored to reinstate the priming potential of the inlet accumulator having regard for the volume of the piping from the low point to the first reservoir (which may be a priming vessel). It is also noted that whilst the first and/or second reservoirs are generally referred to as vessels, these reservoirs may also be pipework of sufficient internal volume and suitable geometry.

[0074] In another embodiment of the system, equipment as described above can be used as a pilot device that can trigger a larger capacity pump to assist with water extraction. For example, in the case where the equipment above uses a positive displacement pump that is operated forward and backwards with number of revolutions counted to infer the water transfer volume, then the net production of water can be established once the number of forward revolutions of the pump exceeds the number of reverse revolutions of the pump required to reinstate in inlet priming capability. From this point onwards, it would be possible to start a second pump that can assist with water extraction such that higher volumes of water can be transferred than if one was to rely solely upon the helical rotor pump at the core of the unit. By this means, essentially any practical water volumetric rate can be extracted from a low point by using the removal system described above as a pilot instrument that triggers on (and subsequently triggers off) supplementary pumping capacity.

[0075] Much of the description here refers to the use of a helical rotor pump, but the invention can be performed using any style of pump. Similarly, whilst within this description reversing of the pump is referred to in order to reverse flow as may apply to a positive displacement pump, such reverse flow can also be achieved through the use of control valves such that the pump operates always in a forward direction but the liquid is caused to flow forwards or backwards as described. It is also possible to use a separate pump to reinstate the priming volume so that a first pump might operate to transfer liquid in a forward direction and a second pump used to transfer liquid in a reverse direction.

[0076] The present invention offers a number of advantages of prior art systems. In particular:

• prevention of gas migration through the pump means thereby avoiding transfer of gas from the inlet of the system through to the discharge point of the system;

• the operation of the pump means solely on liquid pumping duty (specifically avoiding a phase of gas and liquid pumping as in prior art systems such as self-priming pump systems);

• the provision of a prime by providing sufficiently large priming vessel (i.e. the first reservoir) on a first side of the pump when compared to the maximum gas hold-up volume in the inlet pipework from the low point drain to the priming vessel;

• the ability to reinstate liquid in the priming vessel by having stored sufficient liquid downstream of the pump means such that it can be transferred back to the inlet side of the pump means prior to the next forward liquid drainage operation;

• the use of reverse flow of liquid into the inlet priming vessel (i.e. thefirst reservoir) to compress and discharge gas from the headspace of the inlet priming vessel and return at least a portion of the gas back into the gas line from where the liquid was sourced, this provides both return of excess gas drawn towards the pump during the liquid discharge phase and reinstates the full priming potential of the inlet priming vessel; the preservation of a large inventory of liquid to allow operations of the system for many months in the absence of any liquid available for discharge (such as may occur when installed on a new pipeline that takes a long time to accumulate water or for a pipework system subject to slugging that sees highly irregular water supply).

[0077] The invention will now be described below with reference to the Figures and in relation to preferred embodiments thereof.

[0078] Figure 1A illustrates a very simple low point geometry with a low prospect for the formation of gas pockets between the low point and the surface-located riser from which the liquid is extracted. In particular, Figure 1A shows gas piping (1) e.g. of a gas production system, incorporating a water separation means (2) having a low point and water extraction piping (3) connected to the low point and rising directly to the surface. Also shown is water reinjection piping (4) through which water extracted from the low point is injected into water gathering system pipework (5).

[0079] Figure 1B illustrates a more challenging geometry for water extraction. Gas piping (6) incorporates low point geometry (7) and water extraction piping (8) to surface mounted riser (9). Water reinjection riser (10) connects to the water gathering system (11). The low point is located below a gully (12) that is subject to flooding. A secondary gully (13) further complicates the installation with an undesirable consequence of the water extraction piping (8) incorporating a localised low point highlighted by point (14) and a lengthy piping run to a flood free location for the riser.

[0080] Undulations in the water extraction piping (8) encourages gas pockets to form along the length of the piping. Gas pocket formation is exacerbated by the common practice of using piping significantly larger than dictated by water flow and pressure loss. That is, whilst a 25mm diameter piping is adequate from a frictional pressure loss perspective, it is common to use mm HDPE piping primarily because (a) this provides a mechanically robust piping selection in soils that are commonly subject to expansion and contraction with variations in moisture content and (b) mitigates blockage of the water extraction piping (8) with foreign objects such as piping swarf or settled solids. The use of large diameter water extraction piping, the potential for undulations along that pipework and the use of long piping runs of water extraction pipework lead to the accumulation of significant gas pockets permanently in the water extraction piping (8). It also makes it difficult when operating water extraction means to differentiate between gas that needs to be extracted in order to then be extracting water from gas that is a result of gas break-through from the low point. As a consequence, such difficult geometries necessitate a higher discharge of gas to establish water extraction (if indeed there is water to be extracted) whether or not the low point is manually drained or by the prior art automated water extraction means.

[0081] Figure 2 illustrates a system according to one embodiment of the invention. Gas piping system (15) incorporates a low point (16) and water extraction piping (17) to a surface-mounted riser. Water is transferred from low point (16) via water extraction piping (17) and surface mounted riser to a first reservoir in the form of first separator (18). Separator (18) comprises level sensing means (which in this example comprises a high-level sensor and a low-level sensor). The system also comprises pumping means in the form of reversible positive displacement pump (20) which is connected on one side thereof to first separator (18) and on the other side thereof to a second reservoir in the form of second separator (19). Second separator (19) comprises a low-level sensor. Operation of the system is controlled by control system (21).

[0082] The first separator (18) and the second separator (19) are configured such that in afirst direction of pumping, i.e. when pumping liquid from first separator (18) to second separator (19), separator (18) takes in a fluid (comprising gas and/or liquid) from low point 16 at a high elevation with water selectively flowing from first separator (18) to pump (20). In the first direction of pumping, second separator (19) stores a sufficient volume of liquid for subsequent reverse flow operation (i.e. in a second direction of pumping, i.e. when pumping liquid from second separator (19) to first separator (18)) and discharges excess water via reinjection riser (22) to water pipework (23).

[0083] Operations comprise awaiting for a time-based initiation of the water extraction means, operating the pump in a reverse flow direction (which is generally referred to as the second direction of pumping) that will transfer water previously retained in second separator vessel (19) into the first separator (18) by operating pump (20) in the second direction. Pumping in the second direction is continued until the high-level switch in first separator (18) indicates first separator (18) has sufficient liquid fill to perform as a priming vessel for pump (20). This pumping can also be used to displace any gas that is trapped within first separator (18) backwards into the water extraction piping (17) and displacing any excess gas within the water extraction piping (17) into low point (16). As a result, this gas is reintroduced into the gas piping system which minimizes gas wastage and reduces fugitive emissions.

[0084] Upon the completion of the reverse pumping phase, pump (20) is switched to again pump in the forward direction. This causes any water accumulated in the low point to be drawn into the inlet pipework and subsequently into inlet separator (18). After extraction of all the water in the low point (16), gas break-through will occur within the inlet piping (17) that ultimately migrates to first separator (18). The time taken for gas break-through to be detected in first separator (18) is a function of the volume, shape and length of the water extraction pipework (17). This pipework can be very simple (as per Figure 2, item 17) or more complicated (e.g. as per Figure 1B, item 8 through item 14). Once the water level in first separator (18) is reduced to a low level (as detected in this example by the low-level switch in the first separator (18)), pumping in the forward direction is ceased, and the automated water extraction means goes back into a wait mode until the next low point discharge sequence is initiated.

[0085] Figure 3 provides an illustration of another embodiment of system of invention. In the system of Figure 3, neither first separator (27) nor second separator (29) are fitted with level sensing or gas break-through sensing instrumentation (and both separators may be entirely devoid of instrumentation). Gas piping (24) incorporates low point (25) where water accumulates. This water may be extracted from low point (25) to inlet separator (27) with pump (35) via water extraction pipe (26). First separator (27) is connected to water extraction skid (28) using flexible pipe (32). The discharge of the water extraction skid (28) is connected to a second separator (29) by flexible pipe (36). The headspace of second separator (29) is connected to water injection riser (30) with water ultimately discharged to water piping (31).

[0086] In this embodiment, water extraction skid (28) includes a small separator (33) fitted with a low-level switch (34) and a reversible progressing cavity pump (35) and a control system (not shown). The small on-skid separator (33) and level switch (34) can be used to detect impending gas break-through to pump (35). That is, if pumping was to continue, gas break-through to pump (35) would occur.

[0087] As discussed above, neither first separator (27) nor second separator (29) includes level sensing means. However, the control system keeps track of pump operation data and calculates the volume of liquid held in first separator (27) and second separator (29) based on this data. This data can include, for example, mode of operation of the pump, duration of operation of the pump (such as in each mode), number of revolutions of the pump etc. The control system includes programming logic to enable the control system to determine whether the pump should be operated in the first mode or the second mode.

[0088] In one example, when triggered to operate in the second mode, the water extraction system operates in reverse direction (i.e. when pump (35) transfers water from second separator (29) to first separator (27)) for a specified number of pump revolutions determined to supply sufficient liquid into first separator (27) such that subsequent pumping operation in the forward direction (i.e. when pump (35) transfers water from first separator (27) to second separator (29)) will achieve satisfactory priming of the system without exhausting the supply of water in second separator (29) during the reverse pumping phase. Once the defined number of reverse pump revolutions have occurred, pump (35) is stopped and restarted in the forward pumping direction to drain low point 25 and discharge water via line (30) to water piping (31). Forward pumping continues until such time as gas is detected in the on-skid separator (33) by level switch (34) (or any other suitable means of detecting impending gas break-through) whereupon forward pumping is ceased, and the system is switched to the reverse mode of operation and awaits the nextrun.

[0089] Automated valves are illustrated upstream and downstream of pump (35). These valves can be closed when the unit is not operational to limit any forward or reverse leakage of liquid or gas.

[0090] In this example, once again, discharge of liquids is achieved without gas reaching pump (35). Gas in first separator (27) or on-skid separator (33) can be returned to gas piping (24) via water extraction piping (26) and low point (25) when pump (35) is operated in the reverse direction (that is, in the second mode).

[0091] Figure 4 illustrates an embodiment that is based on a combination the embodiments illustrated in Figure 2 and Figure 3. In this embodiment, supplementary pump (47) which operates in a manner similar to that disclosed in relation to Figure 2, is provided for extraction of water from low point (38) at large volumetric flow rates and pump (46) which operates in a manner similar to that disclosed in relation to Figure 3, interacts with a small or on-skid separator (44) to detect gas break-through. On detection of gas break-through the control system can cease operation of the pumps in the forward direction (i.e. from first separator (40) to second separator (48)). In essence, pump (46) and associated instrumentation and controls act as a pilot instrument to determine the operation of the supplementary pump (47). This can provide a convenient means to increase the flow capacity of a system without markedly changing key components or functionality of the system.

[0092] In Figure 4 gas piping (37) incorporates a low point (38) with water extraction piping (39) connected to first separator (40) via connection port (41). In contrast with embodiments described above, first separator (40) is fitted with an upper withdrawal port (42) and a lower withdrawal port (43). The upper port (42) is connected to small separator (44) fitted with gas/liquid interface sensor (45) and pump (46) as per the example of Figure 3. The lower port (43) on inlet vessel (40) is connected to supplementary pump (47) which is generally of higher capacity than pump (46). Pump (47) whilst shown as a progressive cavity pump could also be a centrifugal pump (or other type) configured with suitable valving arrangement for proper operation of the system.

[0093] The combined liquid outputs of pump (46) and supplementary pump (47) in the first mode of operation is fed to second separator (48) and then discharged via riser (49) to water piping system (50).

[0094] In operations, pump (46) is used as a pilot to determine if there is water to be extracted from low point (38). This is achieved by operating pump (46) in the reverse flow direction for a predetermined number of revolutions known to be sufficient to achieve a prime of the inlet piping system and then subsequently operated in the forward pumping direction to transfer liquid to the outlet separator (48). Once the number of forward pumping rotations of pump (46) exceeds the initially used number of reverse rotations by a suitable margin, it can be inferred that there was indeed water in the low point that needs extraction. Then (or at a nominated time thereafter) the supplementary pump (47) can be started to assist in the extraction of water from the low point (38). The control system may monitor the operation of the pumps to determine the volume of water transferred and/or retained in second separator (48).

[0095] By virtue of the relative heights of the offtakes on first separator (40), when gas finally begins to break-through from low point (38) to separator (40) this gas will preferentially flow to the small separator (44) fitted with interface detector (45). Upon sensor (45) detecting impending gas break-through, the operation of both supplementary pump (47) and pump (46) will be ceased. Thus, pump (46) and associated controls is effectively being used as a pilot to operate supplementary pump (47) which is potentially much larger than pump (46).

[0096] Figure 5 is an embodiment illustrating the use of the system to extract water from an above ground reservoir in contrast with the previous embodiments which related to removal of water from a below ground low point.

[0097] In the embodiment of Figure 5, cased well (51) includes a perforated section through a coal seam wherefrom gas and water are extracted. Downhole pump (52) is used to extract water which is transferred via water pipe (55) to wellhead separator (56). Gas rising up the annulus of well (51) flows via the gas piping (54) to wellhead separator (56).

[0098] In the absence of the liquid removal system of the present invention, separated gas from wellhead separator (56) is transferred via valve (57) and line (58) to gas riser (59) and then to gas gathering system (60). Water from wellhead separator (56) flowed via water piping (62) to water riser (63) and then to water gathering system (64). Control valve / level controller (61) controlled flow of water from wellhead separator (56).

[0099] One issue with this arrangement is that the head pressure of wellhead separator (56) must be choked by the gas discharge valve (57) to provide sufficient pressure to be able to force the water into water gathering system (64) via level control valve arrangement (61). If operated in this manner, there can be a significant gas back-pressure applied to the well in order to have sufficient motive force to force water into the water gathering system (64). This gas back pressure can significantly reduce the production of the gas well.

[0100] This problem can be ameliorated by incorporating the liquid removal system of the present invention. In particular, dip pipe (65) is fitted into wellhead separator (56) such that the bottom of the dip pipe corresponds to the lowest desired level to which water is extracted from wellhead separator (56). Water from dip pipe (65) is directed to first separator (66) fitted with level instrumentation and then flows via pump (67) to second separator (68) where water is discharged via water discharge line (69) to water injection riser (63) and then to water gathering system (64).

[0101] With the addition of this equipment, wellhead separator (56) operations can be beneficially modified. Gas choke valve (57) can be fully opened so pressure in wellhead separator (56) falls to the pressure of gas gathering system (60). The original liquid discharge valve and level control (61) can be closed and isolated (or removed and blanked off). Water extraction from wellhead separator (56) can now be conducted via dip pipe (65), first separator (66), pump (67), second separator (68), discharge water piping (69) into water injection riser (63). The additional equipment associated with the water removal system is controlled by control system (70).

[0102] The water extraction system has the characteristics as described before where it starts according to a schedule, incorporates a reverse pumping phase and a forward pumping phase until impending gas break-through is detected by a sensor upstream of the pump (67) thereby ensuring gas does not pass the pump (67). The system as highlighted in Figure 5 avoids gas being injected into the water gathering system, provides high integrity priming, ensures pump operations solely on liquid (never 2 phase) and breaks the linkage of wellhead separator pressure from water gathering system pressure and thereby allows enhanced gas production.

[0103] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A liquid removal system comprising: a first reservoir comprising a first port in fluid connection with a sump and a second port; a second reservoir comprising a first port and a fluid discharge outlet; pump means in fluid communication with the sump via the second port of the first reservoir and in fluid communication with the second reservoir via the first port of the second reservoir; a control system to control operation of the pump means, the control system configured to operate the pump means in a first mode or a second mode; wherein in the first mode, the pump means is configured to draw liquid from the sump, into the first reservoir, transfer liquid from the first reservoir to the second reservoir, and optionally discharge a portion of liquid from the fluid discharge outlet; wherein in the second mode, the pump means is configured to transfer liquid from the second reservoir to the first reservoir to displace gas from the first reservoir to the sump and to provide the first reservoir with an operating volume of liquid; wherein the operating volume of liquid is sufficient that the pump means is operable in the first mode to draw liquid from the sump into the first reservoir and transfer liquid from the first reservoir to the second reservoir.

2. The liquid removal system of claim 1, wherein the first reservoir is hermetically sealed.

3. The liquid removal system of claim 1 or 2, wherein the first reservoir has a liquid storage volume arranged between at least the first port and the second port thereof, the liquid storage volume sized to store at least the operating volume, and wherein the liquid storage volume is greater than an internal volume of a piping system connecting the first reservoir to the sump.

4. The liquid removal system of any one of the preceding claims, wherein the second reservoir has a liquid storage volume arranged between at least the first port and the fluid discharge outlet thereof, the storage volume sized to store at least the operating volume.

5. The liquid removal system of any one of the preceding claims, wherein the controller is configured to cease operation in the second mode and switch operation to the first mode on determination that the operating volume of liquid has been transferred.

6. The liquid removal system of any one of the preceding claims, wherein, the control system is configured to cease operation in the first mode on determination of a low liquid volume in the first reservoir and/or impending gas break-through to the pump means.

7. The liquid removal system of any one of the preceding claims, wherein the control system is configured to initiate operation of the liquid removal system in the second mode.

8. The liquid removal system of any one of the preceding claims, wherein the control system is configured to: initiate operation in the second mode; cease operation in the second mode subsequent on determination that the operating volume of liquid has been transferred; switch operation to the first mode; initiate operation in the first mode; and cease operation in the first mode on gas break-through detection.

9. The liquid removal system of any one of the preceding claims, wherein the system further comprises a separator fluidically interposed between the first reservoir and the pump means, the separator comprising gas-break-through detection means in communication with the controller, the controller configured to cease operation of the pump means in the first mode and switch operation of the pump means to the second mode on receiving a gas break-through detection signal from the gas-break-through detection means.

10. The liquid removal system of any one of the preceding claims, wherein the pump means comprises: at least one reversible pump operable in the first mode and the second mode, or a first pump operable in the first mode and a second pump operable in the second mode, the first pump having an inlet in fluid communication with the first reservoir and an outlet in fluid communication with the second reservoir, and the second pump having an inlet in fluid communication with second reservoir and an outlet in fluid communication with the first reservoir, or at least one pump having an inlet side, an outlet side, and controllable valve means operable to selectively connect the inlet side to the first reservoir and the outlet side to the second reservoir when operated in the first mode and to selectively connect the inlet side to the second reservoir and the outlet side to thefirst reservoir when operated in the second mode.

11. A skid for use, to be used, or when used, in the liquid removal system of any one of claims 1 to 10, the skid comprising at least the control system and the pump means.

12. A skid comprising: pump means having first connection means configured for fluid connection with a sump via a first reservoir and second connection means configured for fluid connection with a second reservoir; a control system to control operation of the pump means, the control system configured to operate the pump means in a first mode or a second mode; wherein in the first mode, the pump means is operated to draw liquid via the first connection means and discharge liquid via the second connection means, the control system being configured to cease operation of the pump means in the first mode on receipt of a signal indicative of low level or impending gas break-through; and wherein in the second mode, the pump means is operated to draw liquid via the second connection means and transfer an operating volume of liquid via the first connection means to displace gas from the first reservoir to the sump; wherein the control system is programmed with a value corresponding to an operating volume of liquid, wherein the control system is configured to operate the pump means in the second mode to transfer at least the operating volume of liquid.

13. The skid of claim 12, wherein the skid further comprises a separator in fluid connection with the first connection means and having a port configured for fluid connection with the first reservoir upstream of the pump means, the separator comprising gas-break-through detection means in communication with the controller, the controller configured to cease operation of the pump means in the first mode and switch operation of the pump means to the second mode on receiving a gas break-through signal from the gas break-through detection means.

14. The skid of claim 12 or 13, wherein the pump means comprises: at least one reversible pump operable in the first mode and the second mode, or a first pump operable in the first mode and configured to draw liquid via the first connection means and discharge liquid via the second connection means, and a second pump operable in the second mode and configured to draw liquid via the second connection means and discharge liquid via the first connection means, or at least one pump having an inlet side, an outlet side, and controllable valve means, the controller configured to operate the controllable valve means to connect the inlet side to the first connection means and the outlet side to the second connection means in the first mode, and connect the inlet side to the second connection means and the outlet side to the first connection means in the second mode.

15. The liquid removal system of claim 10 or the skid of claim 14, wherein the pump means is a reversible pump, and the reversible pump is a helical rotor pump.

16. The liquid removal system of any one of claims 1 to 10 or the skid of any one of claims 11 to 15, wherein the liquid removal system and/or skid are solar powered.

17. Installation or use of a liquid removal system of any one of claims 1 to 10 or 15 to 16 or the skid of any one of claims 11 to 16 in a gas production field.

18. A gas production field comprising one or more liquid removal systems of any one of claims I to 10 or 15 to 16 or skid of any one of claims 11 to 16.

19. A method of removing liquid from a sump with a liquid removal system comprising at least: a first reservoir, a second reservoir, and a pump means having a first connection in fluid communication with the first reservoir and a second connection in fluid communication with the second reservoir, the method comprising: operating the pump means to transfer an operating volume of liquid from the second reservoir to the first reservoir and to displace gas from the first reservoir to the sump, and ceasing operation of the pump means; wherein the operating volume of liquid is sufficient the pump means is operable in the first mode to draw liquid from the sump into the first reservoir and transfer liquid from the first reservoir to the second reservoir. switching operation of the pump means such that the pump is operable to draw liquid from the sump, through the first reservoir, and transfer the liquid via the pump means to the second reservoir; operating the pump means to draw liquid from the sump, through the first reservoir, and transfer the liquid via the pump means to the second reservoir; detecting a low liquid level in the first reservoir and/or impending gas break-through to the pump and ceasing operation of the pump means; wherein the method further comprises: storing at least the operating volume of liquid in the second reservoir, and optionally discharging at least a portion of any excess liquid from the second reservoir via a discharge outlet of the second reservoir.

Practical Pty Ltd Patent Attorneys for the Applicant SPRUSON & FERGUSON