CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/399,726, filed September 26, 2016, which is incorporated herein by reference.

BACKGROUND

[0002] The present disclosure relates subsea riser systems. More particularly, in certain embodiments, the present disclosure relates to subsea riser systems comprising risers, eductors, and chemical injectors and associated methods.

[0003] In recent years the search for oil and natural gas has extended into deep waters overlying the continental shelves. In deep waters it is common practice to conduct drilling operations from floating vessels or from tall bottom-supported platforms. The floating vessel or platform is stationed over a well site and is equipped with a drill rig and associated equipment. To conduct drilling operations from a floating vessel or platform a large diameter riser pipe is employed which extends from the surface down to a subsea wellhead on the ocean floor. The drill string extends through the riser into blowout preventers positioned atop the wellhead. The riser pipe serves to guide the drill string and to provide a return conduit for circulating drilling fluids. A separate riser may be used between the production wells and the host to deliver hydrocarbon from the seabed to the processing facilities on the host.

[0004] In order to control pressure and/or enhance production, gas may be injected into the riser in a technique called "gas lift." Examples of conventional gas lift operations are described in U.S. Patent Nos. 9,181,786, 7,363,983, 4,091,881, and 4,099,583, the entireties of which are hereby incorporated by reference. However, many of these gas lift systems suffer from poor performance.

[0005] It has recently been proposed that the cause of poor performance of traditional gas lift systems might be that the gas is poorly distributed as it enters the subsea riser. Specifically, it is thought that the gas enters the riser in a continuous stream forming large gas bubbles which move fast as compared to the liquid velocity, thus failing to contribute effectively to the reduction in average fluid gradient. U.S. Patent Application Serial Number 62/270,761, the entirety of which is hereby incorporated by reference, describes a system that utilizes an eductor downstream of the wellhead to may allow for improved gas distribution through the subsea riser and lower riser base pressure, enhancing the overall rate of production. However, such a system may still allow gas to slip past the liquid phase rather than displacing it.

[0006] It is desirable to develop an improved gas lift system for subsea risers.

SUMMARY

[0007] The present disclosure relates subsea riser systems. More particularly, in certain embodiments, the present disclosure relates to subsea riser systems comprising risers, eductors, and chemical injectors and associated methods.

[0008] In one embodiment the present disclosure provides a subsea system comprising: a riser; an eductor, wherein the eductor is fluidly connected to the riser by a suction line and a mixed fluid line; and a chemical injector, wherein the chemical injector is fluidly connected to the riser.

[0009] In another embodiment, the present disclosure provides a method comprising: providing a subsea system, wherein the subsea system comprises a riser, an eductor, and a chemical injector; and injecting a chemical into the subsea system through the chemical injector.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.

[0011] Figure 1 is a prior art cross sectional side view of a subsea system in accordance with certain embodiments of the present disclosure.

[0012] The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the disclosure.

DETAILED DESCRIPTION

[0013] The description that follows includes exemplary apparatuses, methods, techniques, and/or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

[0014] The present disclosure relates subsea riser systems. More particularly, in certain embodiments, the present disclosure relates to subsea riser systems comprising risers, eductors, and chemical injectors and associated methods.

[0015] Some desirable attributes of the systems and methods described herein are that they may overcome the short comings of poor gas discretion in eductor gas lift systems. In certain embodiments, the systems and methods described herein may be capable of generating an optimum bubble size that allows the buoyant forces to drive the bubble velocity at approximately the same speed as the liquid. In certain embodiments, the system and methods described herein may allow an operator to generate a sufficient amount of gas lift in a riser based system while minimizing the concentration of the chemical required.

[0016] In certain embodiments, the present disclosure describes a gas lift system. Referring now to Figure 1, Figure 1 illustrates gas lift system 100. In certain embodiments, gas lift system 100 may comprise riser 110, eductor 120, and chemical injector 130. In certain embodiments, eductor 120 may comprise any eductor described in U.S. Patent Application Serial Number 62/270,761. In certain embodiments, riser 110 may comprise any riser described in U.S. Patent Application Serial Number 62/270,761.

[0017] In certain embodiments, riser 110 may comprise any type of subsea riser. In certain embodiments, not illustrated in Figure 1, riser 110 may be connected to a subsea well head. In certain embodiments, not illustrated in Figure 1, riser 110 may be connected to a vessel. In certain embodiments, not illustrated in Figure 1, riser 110 may be connected to an offshore platform.

[0018] In certain embodiments, production fluid from a subsea well (not illustrated in Figure 1) may flow through riser 110 to a floating vessel or other host facilities for further processing, treatment, or transport. In other embodiments, return fluid be return fluid from drilling or other subsea operations where lightening of such fluid is desirable to assist movement up an alternate conduit to production riser 110. In certain embodiments, fluid stream 6 may flow up through riser 110.

[0019] In certain embodiments, eductor 120 may comprise chamber 123, nozzle 121, and diffuser 122. In certain embodiments, diffuser 122 may be a venturi diffuser.

[0020] In certain embodiments, eductor 120 may be connected to riser 110 by suction line 101 and/or mixed fluid line 102. In certain embodiments eductor 120 may be connected to a compressor 125 by motive fluid line 103. In certain embodiments, motive fluid stream 12 may flow through motive fluid line 103.

[0021] In certain embodiments, suction line 101 may have an inner diameter smaller than the inner diameter of riser 110. In certain embodiments, the inner diameter of suction line 101 may be from 35% to 65% percent the size of the inner diameter of riser 110. In certain embodiments, slip stream 9 may flow through suction line 101.

[0022] In certain embodiments, mixed fluid line 102 may have an inner diameter smaller than the inner diameter of riser 110. In certain embodiments, the inner diameter of mixed fluid line 102 may be from 35% to 65% percent the size of the inner diameter of riser 110. In certain embodiments, mixed fluid stream 13 may flow through mixed fluid line 102.

[0023] In certain embodiments, valve 104 may be capable of regulating the flow of fluid through suction line 101. In certain embodiments, valve 105 may be capable of regulating the flow through mixed fluid line 102.

[0024] In certain embodiments, eductor 120 may be capable of drawing a slip stream 9 from fluid stream 6 thereby forming slip stream 9 and mainstream 10. In certain embodiments, compressor 125 may be capable of supplying a motive fluid stream 12 to eductor 120. In certain embodiments, compressor 125 may comprise any compressor described in U.S. Patent Application Serial Number 62/270,761. In certain embodiments, compressor 125 may be a subsea compressor. In other embodiments, compressor 125 may be located on a subsea platform or a vessel.

[0025] In certain embodiments, motive fluid stream 12 may comprise a high pressure stream of gas. In certain embodiments, the gas may be an inert gas or a produced gas. In other embodiments, motive fluid stream 12 may comprise a multiphase liquid and gas combination.

[0026] In certain embodiments, the supply of motive fluid stream 12 may be capable of creating suction to draw slip stream 9 into eductor 120. In certain embodiments, slip stream 9 may be combined with motive fluid stream 12 at vena contracta 129.

[0027] In certain embodiments, the pressure in motive fluid stream 12 may be at least 2.5 times the pressure in fluid stream 6. In certain embodiments, the pressure in motive fluid stream 12 may be from 2.5 to 5 times the pressure in fluid stream 6. In other embodiments, the pressure in motive fluid stream 12 may be at least 5 times the pressure in fluid stream 6.

[0028] In certain embodiments, the mass flow ratio of slip stream 9 to motive fluid stream 12 may be in the range of from 0.25: 1 to 2: 1. In certain embodiments, the mass flow ratio of slip stream 9 to motive fluid stream 12 may be in the range of from 0.5: 1 to 1.5: 1.

[0029] In certain embodiments, the mass flow ratio of fluid stream 6 to slip stream 9 may be in the range of from 0.05: 1 to 0.2: 1. In certain embodiments, the mass flow ratio of fluid stream 6 to slip stream 9 may be in the range of from 0.1: 1 to 0.15:1.

[0030] In certain embodiments, motive fluid stream 12 may pass through nozzle 121 of eductor 120. In certain embodiments, motive fluid stream 12 may then be combined with slip stream 9 to form the mixed fluid stream 13 at vena contracta 129. In certain embodiments, mixed fluid stream 13 may pass through diffuser 122.

[0031] In certain embodiments, the pressure in mixed fluid stream 13 may be at least 5% greater than the pressure in slip stream 9. In certain embodiments, the pressure in mixed fluid stream 13 may be at least 10% greater than the pressure in slip stream 9. In certain embodiments, the pressure in mixed fluid stream 13 may be from 5% to 100% greater than the pressure in slip stream 9. In certain embodiments, the pressure in mixed fluid stream 13 may be from 10% to 50% greater than the pressure in slip stream 9.

[0032] In certain embodiments, eductor 120 may be capable of mixing slip stream 9 and motive fluid stream 12 to form mixed fluid stream 13.

[0033] In certain embodiments, the mixed fluid stream 13 may be combined with main stream 10 in riser thereby forming a lightened stream 17. In certain embodiments, main stream 10 may flow through riser 110. In certain embodiments, lightened stream 17 may exhibit an improved effectiveness of gas lift bubble size.

[0034] In certain embodiments, chemical injector 130 may be in fluid communication with riser 110 and/or motive fluid line 103. In certain embodiments, chemical injector 130 may be fluidly connected to riser 110 and/or motive fluid line 103 by chemical injection line 132. In certain embodiments, chemical injector 130 may be capable of injecting a chemical into gas lift system 100 at chemical injection site 131. In certain embodiments, not illustrated in Figure 1, chemical injection site 131 may be located on riser 110 below suction line 103. In other embodiments, not illustrated in Figure 1, chemical injection site 131 may be located on riser 110 above mixed fluid line 104. In other embodiments, not illustrated in Figure 1, chemical injection site 131 may be located on riser 110 above suction line 103 and below mixed fluid line 104. In certain embodiments, as illustrated in Figure 1, chemical injection site 131 may be located on motive fluid line 103.

[0035] In certain embodiments, chemical injector 130 may be capable of injecting a foamer into motive fluid line 103 and/or riser 100. In certain embodiments, the foamer may comprise any conventional foamers. Examples of conventional foamers are described in U.S. Patent Nos. 7,565,933, 8,579,035, 7,624,804, 8,746,341, 8,950,494, and 8,551,925, the entireties of which are hereby incorporated by reference.

[0036] In certain embodiments, the foamer may be injected into motive fluid line 103 and/or riser 110 at a rate in the range of from 0.5 liters per hour to 50 liters per hour. In other embodiments, the foamer may be injected into motive fluid line 103 and/or riser 110 at a rate in the range of from 1 liter per hour to 20 liters per hour.

[0037] In certain embodiments, the present disclosure provides a method comprising: providing a subsea system, wherein the subsea system comprises a riser, an eductor, and a chemical injector; and injecting a chemical into the subsea system.

[0038] In certain embodiments, the subsea system may comprise any combination of features discussed above with respect to subsea system 100. In certain embodiments, the riser may comprise any combination of features discussed above with respect to riser 110. In certain embodiments, the eductor may comprise any combination of features discussed above with respect to eductor 120. In certain embodiments, the chemical injector may comprise any combination of features discussed above with respect to chemical injector 130.

[0039] In certain embodiments, the riser may be connected to the eductor by a suction line. In certain embodiments, the suction line may comprise any combination of features discussed above with respect to suction line 101. In certain embodiments, the eductor may be connected to a compressor by a motive fluid line. In certain embodiments, the compressor may comprise any combination of features discussed above with respect to compressor 125. In certain embodiments, the motive fluid line may comprise any combination of features discussed above with respect to motive fluid line 103.

[0040] In certain embodiments, the method may further comprise flowing a fluid stream through riser 110. In certain embodiments the fluid stream may comprise any combination of features discussed above with respect to fluid stream 6.

[0041] In certain embodiments, the method may further comprise separating a slip stream from the fluid stream. In certain embodiments, the slip stream may comprise any combination of features discussed above with respect to slip stream 9. In certain embodiments, the slip stream may be separated from the fluid stream by supplying a motive fluid stream to the eductor. In certain embodiments, the motive fluid stream may comprise any combination of features discussed above with respect to motive fluid stream 12.

[0042] In certain embodiments, the motive fluid stream may flow through the motive fluid line into the eductor. In certain embodiments, the motive fluid stream may flow through a nozzle in the eductor. In certain embodiments, the nozzle may comprise any combination of features discussed above with respect to nozzle 121. In certain embodiments, the slip stream may flow through the suction line into the eductor. In certain embodiments, a mainstream may be formed when the slip stream is separated from the fluid stream. In certain embodiments, the mainstream may comprise any combination of features discussed above with respect to mainstream 10. In certain embodiments, the mainstream may flow up through the riser.

[0043] In certain embodiments, the method may further comprise mixing the slip stream and the motive fluid stream in the eductor. In certain embodiments, the method may further comprise forming a mixed stream by mixing the motive fluid stream and the slip stream. In certain embodiments, the mixed stream may comprise any combination of features discussed above with respect to mixed fluid stream 13. In certain embodiments, the slip stream and motive fluid stream may be mixed at a vena contracta. In certain embodiments, the vena contract may comprise any combination of features discussed above with respect to vena contracta 129.

[0044] In certain embodiments, the method may further comprise flowing the mixed fluid stream through the eductor. In certain embodiments, flowing the mixed fluid stream through the eductor may comprise flowing the mixed fluid stream through a diffuser in the eductor. In certain embodiments, the diffuser may comprise any combination of features discussed above with respect to diffuser 122. In certain embodiments, the method may further comprise flowing the mixed fluid stream to the riser through the mixed fluid line.

[0045] In certain embodiments, the method may further comprise mixing the mixed fluid stream and the main stream to form a lightened stream. In certain embodiments, the lightened stream may comprise any combination of features discussed above with respect to lightened stream 17. In certain embodiments, lightened stream 17 may flow up through the riser.

[0046] In certain embodiment, injecting the chemical into the subsea system may comprise injecting a foamer into the riser and/or motive fluid line. In certain embodiments, the foamer may comprise any foamer discussed above. In certain embodiments, injecting the chemical into the subsea system may comprise injecting a foamer into the subsea system at a chemical injection site. In certain embodiments, the chemical injection site may comprise any combination of features discussed above with respect to chemical injection site 131.

[0047] In certain embodiments, the foamer may be injected into the subsea system at a rate in the range of from 0.5 liters per hour to 50 liters per hour. In other embodiments, the foamer may be injected into the subsea system at a rate in the range of from 1 liter per hour to 20 liters per hour.

[0048] While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.

[0049] Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.