The present invention relates to a wellhead boosting apparatus, particularly but not necessarily exclusively for increasing productivity of low energy or idle oil and gas wellheads. The invention may also be suitable to boost or make more practical weak potential wells that do not necessarily require gas lift. The invention further relates to a wellhead boosting system comprising a plurality of wellhead boosting apparatuses.

In the petroleum industry, oil wells which have insufficient reservoir pressure must be artificially boosted in order to produce. There are two main methods of boosting production.

The first method is achieved by reducing the back pressure to the wellhead to allow it to flow to a three-phase separator operating at a significantly lower pressure than compared to the export pipe network and using single-phase pumps and compressor to raise in pressure and therefore pump the oil water and gas phases separately so that the well can once again produce and export hydrocarbon fluids.

The second method is of boosting production from the well is by use of a multistage reciprocating compressor, which increases gas pressure both for export and to be used as a continuous supply of hot gas lift local to the wellhead. The generation of hot gas lift allows the well to be artificially stimulated to allow further production all year round. This is achieved by the use of gas lift, in which gas is injected into the wellhead to aerate the fluid in the well to reduce its density. The formation pressure is then able to lift the oil column to force the fluid out of the wellbore.

To generate gas lift, a gas lift facility is provided having a large compressor in a central location, and gas can be pumped to the relevant wellheads from the gas lift facility. This produces the necessary gas lift. However, this requires a large amount of infrastructure and corresponding investment, and therefore is often prohibitively expensive for regions with few wells or otherwise relatively low yields.

There are other issues with the gas lift facility. The centralised compressor is a potential single point of failure; if the compressor fails, the entire boosted wellhead network will go offline, creating significant production outages.

The above-ground pipe network between the gas lift facility and the wellheads themselves are also potential points of failure. In particular, gas lift valves are prone to freezing in cold temperatures, in which natural gas hydrates, being ice-link solids which form when water and natural gas combine at high pressure and low temperature, clog the valves. This freezing mitigates some of the benefits of providing a centralised compressor facility, since although the compressor can be maintained at a central location, to identify blockages in the pipe network, maintenance must be performed over a wide geographical area.

The present invention seeks to provide a solution to the above-referenced issues which is cost- effective for low energy or idle wellheads.

According to a first aspect of the invention, there is provided a wellhead boosting apparatus comprising: a multi-phase separator module having a separator module support and a multi phase separator, the multi-phase separator including a separator fluid inlet comprising a wellhead connector configured to engage with a wellhead, and a separator gas outlet for extracting separated gas; and a compressor module having a compressor module support and a compressor, the compressor including a compressor gas inlet which is communicable with the separator gas outlet and a compressor gas outlet which is communicable with the wellhead to provide gas lift thereto using the separated gas.

In existing system, there is a centralised facility form which lift gas is compressed and distributed to wellheads to provide gas lift. This requires significant investment to be cost- effective, and also is prone to failure, particularly in cold conditions. By providing an apparatus which is directly engagable locally at the wellhead, gas lift can be generated in situ. Not only does this significantly reduce infrastructure costs, since the apparatus is only required for a given wellhead to be boosted, but also the problem of the formation of hydrates is significantly reduced due to the proximity of the apparatus to the wellhead, meaning that there is minimal cooling of the lift gas. Furthermore, where problems do arise, identification of any issues is much simplified due to the more constrained geography of the entire system.

Preferably, the separator module support and compressor module support may be formed as container units, and more preferably as twenty- or forty-foot container units.

The ability to ship the apparatus modules to a location in a convenient unit size is one of the significant advantages of the present system, and improves the ability for the apparatus to be used on a case-by-case basis.

Optionally, the separator liquid inlet may be positioned at or adjacent to an upper portion of the multi-phase separator.

In a preferable embodiment, the multi-phase separator may be a three-phase separator. The use of a three-phase separator ensures that the water and oil can be separated and pumped as individual phases, and therefore do not form an emulsion. This will improve the quality of the oil extracted and returned to the central processing facility.

The multi-phase separator may include a separator water outlet and a separator oil outlet, and furthermore the separator water outlet and/or separator oil outlet may include a vertical standpipe, preferably for inhibiting sand ingress.

The provision of standpipes within the main chamber is an excellent way of keeping the liquid outflows free from particulate matter which could otherwise clog the oil and water suction lines to the pumps with solids, which in turn could damage the oil and water export pumps.

Optionally, the multi-phase separator may include a vertical mesh pad for the purposes of allowing a higher liquid level in the separator and therefore increasing the overall liquid residence time.

Improving the residence time of the oil and water phases inside the separator improves the ability for the oil and water phases to be separated efficiently. It may also provide a buffer capacity for slugging on start-up of the wellhead boosting apparatus, that is, where there is a rapid rise of liquid inflow.

The wellhead boosting apparatus may further comprise a wireless communications module.

Since there will be several apparatuses at different locations across a wellhead network, it is preferred that there is some ready means of communicating with each apparatus. The lack of a central compressor facility exacerbates this issue, and therefore the provision of a wireless communications module is highly desirable. It may also permit local fault detection to be sent to a remote location.

Preferably, the wireless communications module may include has a SIM-card-based data transmission or a satellite-based data transmission.

Many wellheads may be located in remote locations with limited options for communications. A SIM-card- or satellite-based data transmission protocol is most likely to remain operational in, for example, desert conditions. This may also reduce the need for any sort of manual intervention, effectively making each apparatus largely autonomous.

The wellhead boosting apparatus may comprise at least one operational sensor. The at least one operational sensor may comprise any or all of: a temperature sensor; a pressure sensor; and/or flow sensor. Furthermore, each of an oil flow sensor, a water flow sensor, and a gas flow sensor may be provided in order to provide multi-phase metering capability.

Providing a plurality of sensor types may allow for fault-detection capabilities within the wellhead boosting apparatus which can in turn reduce downtime and failure rates of the system. Having sensor for each phase also allows for the generation of a highly accurate multi-phase metering system.

At least one instrument of the wellhead boosting apparatus may be a pneumatic instrument operable by the separated gas from the multi-phase separator.

Since there is a gas output from the multi-phase separator, it is possible that the instrumentation of the apparatus can be pneumatically powered, which eliminates the need for a separate instrument air system, greatly simplifying the set up and installation of the wellhead boosting system.

Preferably, at least one pump may be provided associated with the multi-phase separator module, and a single-phase oil and/or water pump may be provided as said pump. Optionally, each pump may comprise one or more progressive cavity pumps.

The use of progressive cavity pumps, preferably low-shear progressive cavity pumps, as opposed to traditional screw-type multi-phase pumping systems, which reduces the likelihood of the formation of oil-water emulsions in the downstream export pipework as the oil and water phases are pumped separately. The use of progressive cavity pumps, particularly in single phase mode, can also reduce the total energy consumption of the modules, allowing for a smaller engine or generator to be provided. Pumps themselves can also assist with the low- production wellheads overcoming the pressure barrier on the main pipeline back to the central processing facility.

Preferably, the compressor module may comprise a gas engine which utilises separated gas as fuel. The wellhead boosting apparatus may include a self-sustaining power supply which utilises separated gas as fuel, for example, the gas engine may drive a generator of the compressor module via an auxiliary drive shaft. The wellhead boosting apparatus may additionally or alternatively comprise an onboard power supply to be operable independently of a power grid.

The present apparatus can be made to be self-sustaining by utilising the gas extracted onsite. This is a significant advantage, since no external power or fuel supply may be required for the apparatus in such a scenario.

The wellhead boosting apparatus may further comprise a sample quill device for injection of corrosion inhibitor into a gas export line.

It is preferred that additional equipment be provided with the apparatus which allows for additional operations to be performed which may improve the reliability of the system.

In one preferable embodiment, the apparatus may be configurable between a gas-lift mode of operation and a multi-phase export mode of operation.

Whilst the present invention is highly suited towards providing gas lift to low-energy wells, it is possible to utilise the apparatus solely in a multi-phase export mode, which vastly increases the potential utility of the present invention.

According to a second aspect of the invention, there is provided a wellhead boosting system comprising: a plurality of wellheads at different locations; a plurality of wellhead boosting apparatuses in accordance with the first aspect of the invention, each of the wellhead boosting apparatuses being associated with a corresponding wellhead to provide gas lift thereto.

The wellhead boosting system may preferably further comprise a central processing facility which is in communication with each of the plurality of wellhead boosting apparatuses.

A system which comprises a plurality of wellhead boosting apparatuses directly engaged at the respective wellheads eliminates the need for a centralised gas lift facility, which reduces the likelihood of hydrate formation within the pipe network, and can improve the efficiency of wells which would otherwise be unprofitable. Additionally, the remote communication capabilities of each individual apparatus may advantageously provide improved monitoring capabilities.

In a preferable embodiment, no central gas lift facility is provided. The omission of a central gas lift facility is one of the advantages of the present system, since the system can be utilised with a few, otherwise unproductive, wellheads. This may allow for unproductive wellheads to be utilised without significant capital outlay.

According to a third aspect of the invention, there is provided a method of providing gas lift to a wellhead, the method comprising the steps of: a] using a multi-phase separator, extracting gas from a wellbore fluid of the wellhead; b] using a compressor, compressing the gas extracted from the separator; and c] injecting the compressed gas directly into the wellhead; wherein the multi-phase separator and compressor are each provided at or adjacent to the wellhead.

The use of a cyclical gas extraction and injection methodology at or adjacent to the wellhead allows for gas lift to be provided on an ad-hoc basis for wellheads which are otherwise unproductive.

According to a fourth aspect of the invention, there is provided a wellhead boosting apparatus comprising: a multi-phase separator, the multi-phase separator including a separator fluid inlet comprising a wellhead connector configured to engage with a wellhead, and a separator gas outlet for extracting separated gas, and at least one further fluid phase outlet connectable to one or more export lines; and a compressor including a compressor gas inlet which is communicable with the separator gas outlet and a compressor gas outlet; wherein the compressor gas outlet is selectably operable between a gas-lift condition in which separated gas is diverted to the wellhead to provide gas lift thereto, and a multi-phase export condition in which the separated gas is diverted to the or each export line to boost the pressure thereof.

The provision of an apparatus which can be selectively configured between a multi-phase gas export mode and a gas lift mode is highly useful since the present apparatus can then be used for not only standard export conditions, but also in a boosting condition in which low-producing wells can be maintained for a longer period of time.

According to a fifth aspect of the invention, there is provided a three-phase separator module comprising: a separator module support; a three-phase separator, the three-phase separator including a separator fluid inlet comprising a wellhead connector configured to engage with a wellhead, a separator gas outlet for extracting separated gas, a separator water outlet, and a separator oil outlet; a single-phase water pump communicable with the separator water outlet; and a single-phase oil pump communicable with the separator oil outlet.

Optionally, at least one of the single-phase water pump and single-phase oil pump is provided as a progressive cavity pump. The provision of a separator module which has single-phase pumping capability following separation of the multi-phase well output can advantageously reduce the energy consumption thereof. This not only results in pumping efficiency improvements, but also means that the separator module can be created in a compact package, particularly where slim progressive cavity pumps are used. This is an important aspect for providing a suitably portable separator module.

According to a sixth aspect of the invention, there is provided a satellite wellhead boosting system comprising: a plurality of wellhead boosting apparatuses, each of the wellhead boosting apparatuses comprising: a multi-phase separator module having a separator module support and a multi-phase separator, the multi-phase separator including a separator fluid inlet and a separator gas outlet for extracting separated gas; and a compressor module having a compressor module support and a compressor, the compressor including a compressor gas inlet which is communicable with the separator gas outlet and a compressor gas outlet; wherein each of the plurality of multi-phase separator modules and compressor modules are selectably interchangeable and/or interconnectable to ensure redundancy in the event of failure.

A satellite system provides a smaller-scale local alternative to a central processing facility, improving the ease of maintenance, since switchover between individual modules of the apparatuses can be readily achieved without complete shutdown of production.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic representation of one embodiment of a wellhead boosting system in accordance with the second aspect of the invention;

Figure 2 shows a diagrammatic representation of a first embodiment of a wellhead boosting apparatus in accordance with the first aspect of the invention;

Figure 3 shows a schematic vertical cross-section through a multi-phase separator of a third embodiment of a wellhead boosting apparatus in accordance with the first aspect of the invention;

Figure 4a shows an end representation of a multi-phase separator module of a fourth embodiment of a wellhead boosting apparatus in accordance with the first aspect of the invention; Figure 4b shows a side representation of the multi-phase separator of Figure 4a;

Figure 4c shows a perspective representation of the multi-phase separator of Figure 4a;

Figure 4d shows a plan representation of a multi-phase separator of Figure 4d;

Figure 5a shows an end representation of a compressor module of the fourth embodiment of the wellhead boosting apparatus in accordance with the first aspect of the invention;

Figure 5b shows a side representation of the compressor module of Figure 5a;

Figure 5c shows a perspective representation of the compressor module of Figure 5a;

Figure 5d shows a plan representation of the compressor module of Figure 5a;

Figure 6 shows an indicative diagrammatic representation of a low-pressure wellhead and pipeline in accordance with the state of the art;

Figure 7 shows a diagrammatic representation of the low-pressure wellhead and pipeline of Figure 6, inclusive of a second embodiment of a wellhead boosting apparatus in accordance with the first aspect of the invention;

Figure 8 shows a diagrammatic representation of second configuration of the wellhead boosting apparatus of Figure 2;

Figure 9 shows a diagrammatic representation of second configuration of the wellhead boosting apparatus of Figure 7; and

Figure 10 shows a diagrammatic representation of a satellite wellhead boosting facility in accordance with the sixth aspect of the invention.

Referring to Figure 1, there is indicated a wellhead boosting system, referenced globally at 10, which is suitable for providing gas lift to underperforming oil wellheads 12. This is achieved by providing a plurality of wellhead boosting apparatuses 14, each associated with an individual wellhead 12, which provide gas lift to the wellheads 12 and which are configured to send separated oil to the central processing facility 16.

The operation of a wellhead boosting apparatus 14 is indicated in Figure 2. In order to increase the pressure in the wellhead 12, gas is pumped into the well 18 via a compressor gas outlet 20 of a compressor 22, which is provided as a compressor module 24 having a compressor module support 26.

The pressure in the well 18 results in gas lift, which allows the oil in the well 18 to be forced into a multi-phase separator 28 as part of a separator module 30, having a separator module support 32, for the various components of the wellbore fluid from the well 18.

The multi-phase separator 28 is connectable to the wellhead 12 via a wellhead connector 34, which comprises a conduit via which fluid can be introduced into a main chamber 36 of the multi-phase separator 28. The separator fluid inlet 38 which is connected to the wellhead connector 34, is preferably positioned at or adjacent to an upper portion of the multi-phase separator 28.

The multi-phase separator 28 is here shown as a three-phase separator for separating the gas, water and oil phases. Preferably, the multi-phase separator 28 comprises one or more progressive cavity pumps. The shape of a progressive cavity pump is long and narrow, which makes it straightforward to fit alongside the multi-phase separator 28, simplifying transportation thereof. Other advantages of a progressive cavity pump include that it is good for services where flowrate is relatively low, typically below 10m ³ /hr and where differential pressure is relatively high, typically greater than 35 bar DR. Not only that, but the progressive cavity pump is robust, and has a good tolerance for solids, such as sand, whilst also being tolerant to multi phase flows.

It may be possible, however, to provide a different type of pump, such as a multi-stage centrifugal barrel-type pump, though such motors require a large motor than a progressive cavity pump, are intolerant to changes in differential head and therefore suffer from both under and over-thrust, and are intolerant to solids.

The multi-phase separator 28 therefore has a separator gas outlet 40, a separator water outlet 42, and a separator oil outlet 44, which respectively allow for the extraction of the gas, water and oil phases. This can be provided as three single-phase streams, or can be exported as a multi-phase pump, for example, via a water pump 46 or an oil pump 48.

Separation of the gas, oil and water occurs with the multi-phase separator 28. The gas can be directed from the separator gas outlet 40 into the compressor gas inlet 49 of the compressor 22 via a gas return line 50; thus, the separated gas can be reused for gas lift, creating a virtuous circle. The separated gas can also advantageously be used in a gas engine 68, which can then run a generator 69 via, for example, an auxiliary shaft, to provide power to the separator module 30 and/or compressor module 24. The separated oil and water can then be pumped away from the multi-phase separator 28 back to a central processing facility.

The wellhead boosting apparatus 14 can also serve as a multi-phase metering system, by the provision of sensors on each of the gas, oil, and water output lines. Here, there are respectively a gas flow meter 51a, a water flow meter 51b, and an oil flow meter 51c. This allows the flow of each of the gas, water and oil output lines to be monitored, which may be extremely useful for metering purposes. Additionally, one or more flow meters 51 d may be provided on the gas return line 50.

Figure 3 better illustrates the internal configuration of the main chamber 36 or pressure vessel of the multi-phase separator 28. The normal water and condensate levels in the main chamber are indicated at lines W-W and C-C respectively. For extraction purposes, a vertical standpipe 52 is provided for the separator oil outlet 44, which positions the opening of the vertical standpipe 52 within the oil phase in the main chamber 36. The separator water outlet 42 preferably includes a vertical standpipe 54 which extends into the water phase of the main chamber 36, and provides some prevention from sand ingress into the opening of the vertical standpipe 54, which will otherwise collect at the base of the main chamber 36.

The multi-phase separator 28 includes a primary separation section 56 which precedes a baffle 58, which leads into a gravity settling section 60, with a further mist extractor, here in the form of a mesh pad 62 positioned in an upper portion of the main chamber 36. The liquid, that is the water and oil, is able to settle in a liquid settling section 64 of the main chamber 36.

Each of the vertical standpipes 52, 54 will preferably include a vortex breaker in order to eliminate vortices when draining the relevant liquid, which might otherwise entrain vapour and/or solid particles in the liquid stream. The standpipe 54 associated with the water phase may only be activated to drain the water outlet 42 once the water has reached a predetermined level, to avoid draining the oil erroneously, and therefore a water level sensor may be provided.

The multi-phase separator 28 operates on the principle that the three phases have different densities, which permits stratification of the gas, oil and water respectively. Solid materials, in particular sand, will also settle within the main chamber 36.

The multi-phase separator 28 also includes at least one instrument, which may include one or more sensors 66 to indicate a status of the multi-phase separator 28. This could be a temperature sensor, a pressure sensor, and/or flow sensor. In particular, there may be a plurality of single-phase flow meters which can be used in individually the oil, water and gas streams to provide a highly efficient multi-phase wellhead flow measurement. This allows for multi-phase metering and data transmission for the wellhead boosting system 10, with information being relayed from a wireless communications module of each wellhead boosting apparatus 14, preferably a SIM-card- or satellite-based data transmission. Other communication means could be considered, such as WiMAX-type communication, or indeed any communications protocol already set-up at the site.

Figures 4a to 4d shows the whole separator module 30, indicating the separator module support 32. As will be apparent, the separator module 30 which is designed to be contained within or formed as part of container unit, in particular a twenty- or forty-foot container unit, though any appropriately ISO sized container would be viable. If the container dimensions are any larger, then transportation costs are increased and packing speed decreased, thereby resulting in shipment delays to site. Additionally, the package must be shipped breakbulk, which is far more expensive. The separator module 30 has the wellhead connector 34 which extends towards the edge of the separator module support 32 to permit connection to the wellhead 12. The equipment of the separator module 30, and/or indeed the compressor module 24, could be skidded to permit easier movement.

Figures 5a to 5d show the compressor module 24, which may not only include the compressor 22, but may also include a gas engine 68 for providing power to the wellhead boosting apparatus 14. The gas engine 68 drives the compressor 22, and may include an auxiliary shaft to run a generator 69 for providing electrical power to oil and water export pumps associated with the multi-phase separator 28. It will be appreciated, however, that other types of power supply could be provided in order to make the apparatus self-sustaining without connection to an external power grid. For example, a diesel, hybrid, or electric engine could be provided.

The gas engine 68 may be provided with an exhaust muffler cooling system which keeps surfaces cool, as well as an air cooler 70 which may be used to keep the various fluid conduits in the compressor module 24 cool. The compressor module 24, or indeed the separator module 30, may also be provided with flammable gas detectors which can detect a gas cloud and shutdown the entire wellhead boosting apparatus 14. The compressor module 24 may also be provided with a flame detector, which may be capable of shutting down the entire wellhead boosting apparatus 14 in the event of fire. Suction, discharge and fuel-gas fire-rated emergency shutdown valves may also be provided, which may actuate to protect the modules 24, 30 in the case of overpressure or fire. The wellhead boosting apparatus 14 may also be equipped with a blowdown valve which will automatically vent the package in case of a fire. The wellhead boosting apparatus 14 may be operated in a pumped mode or a bypass mode configuration. This would bypass the oil and water pumps if sufficient pressure is available, in which a bypass line is provided for automatic by-pass of the package to divert the well fluids directly into the export lines. The oil and water lines may be equipped with modulating control valves to control the levels in the multi-phase separator 28 during a floating operation mode.

Furthermore, the wellhead boosting apparatus 14 may be equipped with a sample quill system for injection of corrosion inhibitor into the gas export line for downstream pipe network protection.

The oil and water pumps are controlled by variable frequency drive to maintain the levels in the multi-phase separator 28. This allows for accurate level control and secondary computation of the export flow via a programmable logic controller and variable frequency drive system.

The variable frequency drive and any other non-hazardous area components are design to be movable to a suitable location outside of the hazardous area and may be connected using retractable, preferably pigtail, wiring, with quick-connect plug-in to the main package. The programmable logic controller is preferably the main controller for the wellhead boosting apparatus 14.

The wellhead boosting apparatus 14 is preferably configured so that a diesel generator can be plugged into the variable frequency drive, should there be insufficient gas to run the gas engine 68. This means that the separator module 30 and pumps can be run independently of the compressor 22 and power module. This may be very useful for the initial start-up of the wellhead boosting apparatus 14.

The operation of the wellhead boosting apparatus 14 is indicated in Figures 6 and 7. In Figure 6, the local well pressure of the wellhead 12 is indicated at p ^LW , whilst the main pipe pressure is indicated at p ^MP . The local well pressure p ^LW is insufficient to flow into the main pipe 72.

In Figure 7, the wellhead boosting apparatus 14 has been connected to the wellhead 12. The compressor module 24 provides the hot, high-pressure lift gas, injected via gas return line 50 at pressure p ^GR , to the wellhead 12, with the lift fluid being input into the separator module 30. This yields a multiphase output, that is oil, gas and water, pressure p ^MO which is greater than the main pipe pressure p ^MP and thus improves the output from the well.

Additionally, since the gas produced from the well 18 is relatively hot - the gas is kept hot through the heat of compression and due to the limited volumes, it does not have time to cool - there is limited opportunity for hydrate freezing within the wellhead boosting apparatus 10. It is expected that the wellhead boosting system 10 be quick to install. Each wellhead boosting apparatus 14 preferably takes no more than three to five days to rig up, particularly where existing wellhead connections are utilised.

It will be appreciated that although the present context of the use of the wellhead boosting apparatuses 14 is in land-based oil wells, it will be appreciated that this technology could well be applied in the field of offshore wells.

A second configuration of the wellhead boosting apparatus 14 is shown in Figure 8. Identical or similar features of the invention will be referenced using identical or similar reference numerals, and further detailed description is omitted for brevity.

In this configuration, the compressor module 24 has not been set up to provide gas lift to the wellhead 12. This may either be via non-connection of the compressor 22 to the wellhead 12, as illustrated, or by closing a valve to an existing gas return line.

Instead, the multi-phase separator 28 separates the gas, oil and water phases, though it will be appreciated that the following will be applicable for a two-phase separator pumping an oil/water emulsion.

The separated gas is diverted into the compressor 22, which is then in turn exported through a further gas conduit 74 into a multi-phase export line 76. Each of the water and oil pumps 46, 48 also then export their respective phases into the multi-phase export line 76. This allows the present wellhead boosting apparatus 14 to be configured for use with existing multi-phase export lines back to the central processing facility 16.

This process might appear counter-intuitive, to separate and re-combine the three phases from the wellhead, but there are specific advantages to this process.

Firstly, the present arrangement avoids an issue known as pump slippage, where progressive cavity pumps or screw pumps do not correctly seal, and there is internal slippage of fluid within the pump. This results in high-pressure fluid migrating to low-pressure areas, reducing the efficiency of pumping. This is a much greater issue for pumping in a multi-phase mode, particularly three-phase, when compared with single-phase pumping. Typically, in three-phase mode, multi-phase pumps are only 30% hydraulically efficient, whereas a progressive cavity pump working in a single-phase more is closer to 60% hydraulic efficiency. When a reciprocating or similar compressor is also utilised, the adiabatic efficiency is of the order of 80 to 85% for the gas extraction, and therefore, there is a significant reduction in energy consumption for the present invention when compared with multi-phase pumping techniques. Typically, an engine size for pumping and compressing would be of the order of half that required for traditional multi-phase pumping.

The second benefit is illustrated in Figure 9. Even without the addition of gas line injection using the separated gas, the separator and compressor modules 30, 24 can be used in a multi-phase export mode for improving the production of low-output wellheads 12. Pumping or compression of the individual phases extracted from the wellhead and separated by the multi-phase separator 28 allows the three phases to be diverted into the multi-phase export line 76 at a higher pressure p ^MO than that in the main pipe 72, at pressure p ^MP . This is in spite of the low pressure p ^LW at the wellhead 12.

A novel arrangement of satellite wellhead boosting system 100 is indicated in Figure 10 which is suitable for use in combination with a central processing facility. Each system 100 comprises a plurality of wellhead boosting apparatuses 14 as previously described; for clarity however, each apparatus is indicated by a single diagrammatic representation, rather than showing the separate separator and compressor modules.

In this arrangement, each of the wellhead boosting apparatuses 14 is connected to the same inlet line 78, which may be connected to a plurality of different wellheads 12. The apparatuses 14 all then export to a gas export line 80 and a bi-phase export line 82 for respectively exporting gas and oil/water emulsion. It will, of course, be appreciated that single-phase export lines could be used, or a multi-phase export line as detailed in the preceding embodiments of the invention.

The advantage of having a bank of wellhead boosting apparatuses 14, rather than an individual wellhead boosting apparatus 14 for each individual wellhead, is that there is an integral redundancy within the system 100. Each of the individual separator and compressor modules can be reconfigured with respect to one another so that, in the event of failure, there is no loss of production. The remaining active wellhead boosting apparatuses 14 would still provide the necessary boost to wellhead production. This effectively provides a modular facility in which the separator and compressor modules can be swapped in or out at will, and therefore maintenance and replacement can be performed remotely from the wellhead site or satellite facility.

Overall, the process of the present invention can be summarised as being a method of providing gas lift to a wellhead which comprises the steps of: using a multi-phase separator, extracting gas from a wellbore fluid of the wellhead; using a compressor, compressing the gas extracted from the separator; and injecting the compressed gas directly into the wellhead; wherein the multi-phase separator and compressor are each provided at or adjacent to the wellhead. This allows for a cyclical use of separated gas from the wellhead, and therefore gas lift capability does not need to be provided from a distant location.

It is therefore possible to provide a wellhead boosting apparatus and system which can be installed in situ at low-pressure wellheads on an individual basis. This eliminates the need for an expensive central gas lift facility which may only be economical where a large number of wells required boosting in a small geographical location.

This arrangement is suitable for wells which are otherwise close to their end of life, and may also benefit wells with insufficient energy for the oil to arrive at a central processing facility. This is achieved through the combination of artificial gas lift and multiphase wellhead boosting.

The system also benefits wells which have intermittent production profiles where the operator has to switch the wellhead on and off in order to recover production, since continuous flow can be achieved.

In particular, the system is ideal in areas where a traditional injection network has been deemed unviable due to uncertainties, and low-energy or idle oil wells are the best candidates for the system. This requires minimal intervention to improve the output of such low-producing wells.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.