AU2020290015A1

AU2020290015A1 - Oil or gas production facility, corresponding method and renovation method for obtaining such a facility

Info

Publication number: AU2020290015A1
Application number: AU2020290015A
Authority: AU
Inventors: Marc Cahay; Guilhem DELLINGER; Luc HEME DE-LACOTTE; Nicolas TECHERNIGUIN
Original assignee: Technip Energies France SAS
Current assignee: Technip Energies France SAS
Priority date: 2019-06-12
Filing date: 2020-06-12
Publication date: 2022-02-03
Also published as: FR3097311A1; EP3983665A1; FR3097311B1; EP3983665B1; WO2020249780A1

Abstract

Oil or gas production facility (10), comprising: - a treatment unit (14), - a water pick-up unit (18) for picking up water (20) from an expanse of water (12) and delivering a stream (22) of cooling water to the treatment unit, - a pressure-regulating unit (24) receiving a stream (26) of cooling water at a first pressure coming from the treatment unit, and supplying at least one stream (28) of cooling water at a second pressure lower than the first pressure, and - a control member (38). The pressure-regulating unit comprises a turbine (34) configured to receive at least part of the stream of cooling water coming from the treatment unit and to produce mechanical energy. The control member is designed to perform feedback control of the turbine in order to regulate the first pressure.

Description

Oil or gas production facility, corresponding method, and renovation method for obtaining such a facility

The present invention relates to an oil or gas production facility, for example for the production of liquefied natural gas (LNG). The invention also relates to a corresponding production method, as well as to a method for renovating such a facility. Such a facility comprises one or more treatment units cooled by cooling water drawn from a body of water. The facility is a fixed facility located on or near the body of water, or a floating facility on the body of water, such as a platform or barge. For example, platforms carrying a natural gas liquefaction unit are referred to as Floating Liquefied Natural Gas (FLNG), Floating Production Storage and Offloading (FPSO), or Single Point Anchor Reservoir (SPAR). These facilities are designed, among other things, to produce natural gas, liquefy the natural gas produced, and then store and/or transfer the liquefied natural gas to an LNG carrier or other transport barge. This simplifies the transport of gas to the point of consumption, reducing the volume transported. In addition, locating the facilities at sea removes the risks associated with these facilities from inhabited areas and reduces the impact on the environment. In order to carry out an oil or gas process economically, process units release a large amount of heat into the surrounding environment, in practice into the air or water. The advantage of a facility located on the surface or near a body of water is that it has an inherently large, low-temperature source of cooling water. Therefore, it is known to circulate water taken from the body of water to cool equipment in the treatment unit, either directly or via a fresh water loop. Current facilities use one or more pressure control valves (or pressure relief valves) in the cooling water circuit to maintain its stability. Such technology is satisfactory from the point of view of cooling the equipment in the treatment unit. However, it consumes energy to circulate the cooling water. This consumption has an impact on the overall energy efficiency of the facility. One aim of the invention is therefore to improve the overall energy efficiency of the facility without reducing its productivity. To this end, an object of the invention is an oil or gas production facility comprising: - at least one treatment unit, - at least one water pick-up unit adapted to pick up water from a body of water and to deliver at least one stream of cooling water to the treatment unit,

- a pressure-regulating unit adapted to receive a stream of cooling water at a first pressure from the treatment unit, and to provide at least one stream of cooling water at a second pressure lower than the first pressure, - at least one discharge system adapted to receive at least part of the stream of cooling water at the second pressure, and - at least one control member adapted to measure the first pressure, the pressure-regulating unit comprising at least one turbine configured to receive at least part of the stream of cooling water from the treatment unit and to generate mechanical power, the control member being designed to perform feedback control of the turbine to regulate the first pressure to a setpoint value. According to particular embodiments, the facility comprises one or more of the following features taken in isolation or in any combination that is technically possible: - furthermore at least one alternator configured to convert the mechanical energy produced by the turbine into electrical energy; - the turbine is configured to deliver the stream of cooling water at the second pressure; - the pressure-regulating unit further comprises at least one pressure relief valve mounted in parallel with the turbine and adapted to selectively receive at least part of the stream of cooling water from the treatment unit; - the control member is designed to perform feedback control of the pressure relief valve to regulate the first pressure to the setpoint value; - the control member is further adapted to measure the second pressure to regulate the first pressure to a setpoint value; - the facility is configured so that the first pressure is between 3 and 6 bar absolute; - the facility is configured so that the second pressure is between 1 and 1.5 bar absolute; - the pressure-regulating unit further comprises a pipe for conducting at least part of the stream of cooling water from the treatment unit to the turbine, the pipe having a hydraulic diameter of between 0.5 and 1 m; - the facility is a facility for the production of liquefied natural gas from natural gas, - the treatment unit is a natural gas liquefaction unit, and - the facility is located on the surface of the body of water. The invention further relates to a method for producing oil or gas, comprising the following steps: - treatment in at least one treatment unit;

- picking up of water from a body of water by at least one water pick-up unit, and delivery of at least one stream of cooling water to the treatment unit by the water pick-up unit; - receiving a stream of cooling water at a first pressure from the treatment unit in a pressure-regulating unit, and providing, by the pressure-regulating unit, at least one stream of cooling water at a second pressure lower than the first pressure, the pressure-regulating unit comprising at least one turbine receiving at least part of the stream of cooling water from the treatment unit and producing mechanical energy, - receiving at least part of the stream of cooling water at the second pressure in at least one discharge system, - measuring the first pressure by at least one control device, and - feedback from the control member to the turbine to regulate the first pressure to a setpoint value. Finally, the invention relates to a renovation method for obtaining a facility as described above, comprising the replacement of at least one pressure relief valve present in the pressure-regulating unit prior to the renovation and configured to receive at least part of the stream of cooling water from the treatment unit, said pressure relief valve being replaced by the turbine. The invention will be better understood upon reading the following description, given only as an example, and with reference to the attached drawings, in which Figure 1 is a schematic view of a facility according to the invention. In all that follows, the terms "upstream" and "downstream" are used in relation to the normal direction of a stream in a pipe. With reference to Figure 1, an oil or gas production facility 10 according to the invention is described. In the example shown, the facility 10 is a liquefied natural gas production facility 11. In alternative embodiments not shown, the facility 10 is another type of oil or gas facility. The facility 10 is for example arranged on the surface of a body of water 12. The body of water 12 is for example a sea, a lake or an ocean. The depth of the body of water 12 at the facility 10 is for example between 15 m and 3,000 m. In a particular embodiment (not shown), the facility 10 is a land-based facility, located near a body of water, such as a lake or river. "Near" means at a distance compatible with drawing cooling water from this body of water and delivering it to the equipment to be cooled.

The facility 10 is suitable for collecting natural gas from an underground reservoir (not shown). The natural gas is advantageously produced directly at the facility 10. Alternatively (not shown), the natural gas is produced on another production unit on the water surface 12, or on an onshore production unit and is conveyed to the facility 10 by a transport line. The facility 10 is a fixed or floating facility, for example an FLNG, FPSO or SPAR. In the example shown in Figure 1, the facility 10 is a floating natural gas liquefaction unit or "FLNG". The facility 10 comprises a treatment unit 14, which in the example is a liquefaction unit adapted to receive natural gas 16 and produce liquefied natural gas 11. The facility 10 comprises a unit 18 adapted to pick up water 20 from the body of water 12 and to deliver a stream 22 of cooling water to the treatment unit. The facility 10 further comprises a pressure-regulating unit 24 adapted to receive a stream 26 of cooling water at a first pressure from the treatment unit 14, and to provide at least one stream 28 of cooling water at a second pressure lower than the first pressure. The facility 10 comprises a discharge system 30 adapted to receive the stream 28 and discharge it into or towards the body of water 12. "Treatment unit" here means any unit contributing to oil or gas production, comprising equipment to be cooled by cooling water. Optionally, the facility 10 further comprises an alternator 32. In variants not shown, the facility 10 comprises multiple water pick-up units and/or delivers multiple streams of cooling waters to the treatment unit 14. Where natural gas 16 is being produced on-site, the facility 10 comprises units not shown for purifying the natural gas by removing water, heavy compounds (e.g. C6+ compounds) and sulphur compounds generally present in the raw gas extracted from the underground reservoir. The treatment unit 14 is adapted to cool the natural gas 16 or even to sub-cool it to obtain liquefied natural gas 11. The treatment unit 14 is adapted to bring the natural gas 16 to be cooled into a contactless heat exchange relationship with the stream of cooling water 22 and to produce the stream 26 which is therefore hotter than the stream 22. The water pick-up unit 18 has one or more pumps not shown for picking up water and circulating it through the treatment unit 14. For example, the unit 18 has filters (not shown). The stream of cooling water through the treatment unit 14 is, for example, between 0.1 and 5 m 3 /s or even between 0.7 and 2.5m 3/s.

The pressure-regulating unit 24 comprises a turbine 34 configured to receive at least part of the stream 26 of cooling water, a pressure relief valve 36 mounted in parallel with the turbine, and a control member 38. In a particular embodiment (not shown), the unit 24 comprises a number of turbines, for example three, connected in series, or in parallel, and replacing the turbine 34. These arrangements, particularly the parallel arrangement, may have a size advantage, or be more suitable for the space available for the turbine(s). Advantageously, the pipe 40 has a hydraulic diameter of between 0.1 and 2 m, or even between 0.5 and 1 m. The turbine 34 is configured to selectively receive all or part of the stream 26 and to produce mechanical energy from the energy in the water to drive the alternator 32 and produce electrical energy. In a variant not shown, the facility 10 has no alternator and the mechanical energy of the turbine is used directly, for example to drive a compressor of the treatment unit 14 or another unit, or to drive one or more pumps of the water extraction unit 18, or any other pump. The pressure relief valve 36 is adapted to selectively receive all or part of the stream 26. The control member 38 is adapted to measure the first pressure (that of the stream 26), and advantageously the second pressure (that of the stream 28), and to perform feedback control of the turbine 34 and/or on the pressure relief valve 36 to regulate the first pressure to a setpoint value. The turbine 34 and/or the pressure relief valve 36 are adapted to provide the stream 28 of cooling water. The facility 10 is advantageously configured so that the first pressure is between 3 and 6 bar absolute. The first pressure is for example about 4 bar absolute. The second pressure is advantageously between 1 and 1.5 bar absolute, and is for example about 1 bar absolute. The pressure-regulating unit 24 comprises a pipe 40 connected to the treatment unit 14 at the upstream end and to the turbine 34 at the downstream end. The discharge system 30 comprises, for example, a discharge line 42 connected to the pressure-regulating unit 24 at the upstream end to receive the stream 28 of cooling water. The operation of the facility 10 can be deduced from its structure and will now be briefly described.

The water pick-up unit 18 picks up the water stream 20 from the body of water 12 and supplies the stream of cooling water 22 to the treatment unit 14. The treatment unit 14 cools the natural gas 16 to produce the liquefied natural gas 11 and generates a heat flow. The stream of cooling water 22, by contactless heat exchange with the natural gas 16, receives at least part of this heat stream and warms up before leaving the treatment unit as the stream 26. In a preferred mode of operation, the entire stream 26 of cooling water from the treatment unit 14 enters the turbine 34, generating the stream 28 of cooling water at the second pressure and the mechanical energy to drive the alternator 32. In another mode of operation, for example in the event of maintenance of the turbine 34, the entire stream 26 is directed to the pressure relief valve 36, and forms the stream 28 after its pressure drops. Intermediate modes of operation are possible, in which the stream 26 of cooling water is divided into a portion passing through the turbine 34 and another portion passing through the pressure relief valve 36, these two portions joining downstream of these elements to form the stream 28. The stream 28 is finally discharged into the body of water 12 via the discharge pipe 42. Thanks to the features described above, in particular the turbine 34, the energy present in the stream 26 of cooling water, due to its relatively high pressure, is recovered in the form of mechanical energy which is used either directly or to produce electrical energy. In this way, the energy required to pick up the cooling water and bring it to a suitable pressure is at least partially recovered, thus improving the overall energy efficiency of the facility 10. The electrical power supplied is equal to the product of the following quantities: - the density of water (1,000 kg/m3 ), - the acceleration of gravity (g = 9.81 m/s 2 ), - the flow rate of the stream of cooling water in the turbine (e.g. 2 m3 /s), - the static pressure difference between the first pressure and the second pressure (e.g. 25 m water column), and - the efficiency of the turbine 34 and alternator 32 assembly (e.g. 60%). In this example, an electrical power of about 300 kW is obtained. A renovation method is also described for obtaining the facility 10 from an existing liquefied natural gas production facility (not shown). The existing facility can be derived from the facility 10 shown by replacing the turbine 34 with a pressure relief valve similar to the pressure relief valve 36.

The renovation consists of replacing this pressure relief valve with turbine 34. In the existing facility, the stream 26 of cooling water passes through either of the pressure relief valves before being discharged. In the renovated facility, i.e. facility 10, at least at certain times, all or part of the stream 26 passes through the turbine 34, thereby generating energy and improving the overall efficiency of the renovated facility. As can be seen from the above features and Figure 1, each of the turbine 34 and the pressure relief valve 36 is adapted in itself to control the first (upstream) pressure. Advantageously, the facility 10 does not have an upstream pressure regulator located upstream of the turbine 34. In one particular mode of operation, the entire stream 26 passes through the turbine 34, which then regulates the first pressure on its own. In this case, if there were no turbine 34, the first pressure would be substantially equal to the second pressure and there would be no pressure regulation in the treatment unit 14. In the embodiment in which the turbine 34 is replaced by several turbines connected in series, the stream 26 passes successively through each of said turbines. In the embodiment in which the turbine 34 is replaced by a number of turbines mounted in parallel to one another, the stream 26 divides and passes through each of said turbines and then recombines to form the stream 28. In another mode of operation, for example if the turbine 34 is undergoing maintenance, the entire stream 26 passes through the pressure relief valve 36, which then regulates the first pressure on its own. Between these two extreme situations, according to the above-mentioned intermediate operating modes, the stream 26 passes through the turbine 34 and the pressure relief valve 36, which together regulate the first pressure. Thus, as can be seen, the turbine 34 is not a passive member from the point of view of regulating the upstream pressure prevailing in the treatment unit 14, but an active member. The turbine 34 not only recovers the energy contained in the stream 26, but also regulates the first pressure, advantageously without the intervention of any other active organ.

Claims

1. An oil or gas production facility (10) comprising: - at least one treatment unit (14), - at least one water pick-up unit (18) adapted to pick up water (20) from a body of water (12) and to deliver at least one stream (22) of cooling water to the treatment unit (14), - a pressure-regulating unit (24) adapted to receive a stream (26) of cooling water at a first pressure from the treatment unit (14), and to provide at least one stream (28) of cooling water at a second pressure lower than the first pressure, - at least one discharge system (30) adapted to receive at least part of the stream (28) of cooling water at the second pressure, and - at least one control member (38) adapted to measure the first pressure, characterised in that: - the pressure-regulating unit (24) comprises at least one turbine (34) configured to receive at least part of the stream (26) of cooling water from the treatment unit (14) and to generate mechanical power, and - the control member (38) is adapted to perform feedback control of the turbine (34) to regulate the first pressure to a setpoint value.

2. The facility (10) according to claim 1, further comprising at least one alternator (32) configured to convert the mechanical energy produced by the turbine (34) into electrical energy.

3. The facility (10) according to claim 1 or 2, wherein the turbine (34) is configured to deliver the stream of cooling water (28) at the second pressure.

4. The facility (10) according to any one of the claims 1 to 3, wherein the pressure regulating unit (24) further comprises at least one pressure relief valve (36) mounted in parallel with the turbine (34) and adapted to selectively receive at least part of the stream (26) of cooling water from the treatment unit (14).

5. The facility (10) according to claim 4, wherein the control member (38) is adapted to perform feedback control of the pressure relief valve (36) to regulate the first pressure to the setpoint value.

6. The facility (10) according to any one of claims 1 to 5, wherein the control member (38) is further adapted to measure the second pressure to regulate the first pressure to the setpoint value.

7. The facility (10) according to any one of claims 1 to 6, configured so that the first pressure is between 3 and 6 bar absolute.

8. The facility (10) according to any one of claims 1 to 7, configured so that the second pressure is between 1 and 1.5 bar absolute.

9. The facility (10) according to any one of claims 1 to 8, wherein the pressure regulating unit (24) further comprises a pipe (40) for conducting at least part of the stream (26) of cooling water from the treatment unit (14) to the turbine (34), the pipe (40) having a hydraulic diameter of between 0.5 and 1 m.

10. A method for producing oil or gas, comprising the following steps: - treatment in at least one treatment unit (14), - picking up of water (20) from a body of water (12) by at least one water (20) pick up unit (18), and delivery of at least one stream (22) of cooling water to the treatment unit (14) by the water (20) pick-up unit (18), - receiving a stream (26) of cooling water at a first pressure from the treatment unit (14) in a pressure-regulating unit (24), and providing, by the pressure-regulating unit (24), at least one stream (28) of cooling water at a second pressure lower than the first pressure, the pressure-regulating unit (24) comprising at least one turbine (34) receiving at least part of the stream (26) of cooling water from the treatment unit (14) and producing mechanical energy, - receiving at least part of the stream (28) of cooling water at the second pressure in at least one discharge system (30), - measurement of the first pressure by at least one control device (38), and - feedback from the control member (38) to the turbine (34) to regulate the first pressure to a setpoint value.

11. A renovation method for obtaining a facility (10) as described by any of claims 1 to 9, comprising replacing at least one pressure relief valve (36) present in the pressure regulating unit (24) prior to renovation and configured to receive at least part of the stream

(26) of cooling water from the treatment unit (14), said pressure relief valve (36) being replaced by the turbine (34).