Anti-syphon device and chemical injection mandrel

Abstract

An anti-syphon device and chemical injection mandrel thereof prevents syphoning even as formation pressures decline. While conventional chemical injection mandrels rely solely on production tubing pressure to prevent syphoning, the anti-syphon device includes a sealing chamber for stem engagement, a power section chamber for a power spring, and an isolation chamber that transmits annular pressure, without fluid communication, to the stem to assist the power section. As formation pressures decline, conventional chemical injection mandrels fail when the hydrostatic head pressure exceeds the tubing pressure, resulting in syphoning. The anti-syphon device counters this by using annular pressure communicated via the isolation chamber without fluid communication to provide an assist that drives the axial translation of the stem upward onto its seat, preventing syphoning. Advantageously, this robust mechanism prevents syphoning even as formation pressures decline and increases the operational reliability and longevity of the anti-syphon device and chemical injection mandrel thereof.

Description

ANTI-SYPHON DEVICE AND CHEMICAL INJECTION MANDRELBACKGROUND OF THE INVENTION

[0001] In offshore oil production, the subsurface environment presents unique challenges, including high pressures, elevated temperatures, corrosive fluids, and the potential for formation damage, all of which can compromise well integrity and reduce hydrocarbon recovery rates. Chemical injection through downhole chemical injection mandrels addresses these issues by enabling the targeted delivery of specialized chemicals directly into the wellbore or reservoir. For instance, corrosion inhibitors arc injected to form protective films on metal surfaces, preventing degradation from acidic gases like carbon dioxide and hydrogen sulfide that are often present in produced fluids; this is crucial in offshore wells where tubing and casings are exposed to seawater ingress or reservoir brines, potentially extending equipment life and averting costly failures. Similarly, scale inhibitors work by disrupting the crystallization of minerals such as calcium carbonate or barium sulfate, which can precipitate due to pressure drops or temperature changes during production, thereby maintaining open flow paths and avoiding blockages that could necessitate expensive workovers or acid treatments.

[0002] Beyond corrosion and scaling, chemical injection serves to combat other production impediments common in offshore scenarios, such as paraffin wax deposition and gas hydrate formation. Paraffin inhibitors or pour-point depressants are deployed to modify the wax crystal structure, ensuring that hydrocarbons remain fluid even in cooler subsea conditions, which is particularly vital in deepwater operations where temperatures can drop rapidly along flowlines. Hydrate inhibitors, like methanol or monoethylene glycol, are injected to lower the freezing point of water in the produced fluids, preventing the formation of ice-like hydrates that can plug pipelines and cause operational shutdowns — events that are especially risky in remote offshore locations due to limited access for interventions. By integrating chemical injection mandrels into the production tubing, operators achieve precise dosing at optimal depths, controlled from the surface via capillary lines, which not only enhances treatment efficacy but also minimizes chemical usage, reduces environmental impact from overboard discharges, and optimizes overall production economics in high-stakes offshore environments.

[0003] Furthermore, in mature offshore fields, chemical injection plays a pivotal role in enhanced oil recovery techniques, such as polymer or surfactant flooding, where mandrels facilitate the introduction of viscosifying agents or interfacial tension reducers to mobilize trapped oil. This targeted approach improves sweep efficiency in heterogeneous reservoirs, boosting recovery factors that might otherwise plateau. The purpose extends to safety and regulatory compliance, as effective chemical management helps prevent uncontrolledreleases or equipment breaches that could lead to environmental hazards in sensitive marine ecosystems. Overall, downhole chemical injection via chemical injection mandrels represents a proactive strategy in offshore well management, balancing operational reliability, cost efficiency, and sustainability while adapting to the dynamic conditions of deepwater production.SUMMARY OF THE INVENTION

[0004] According to one aspect of one or more embodiments of the present invention, an anti-syphon device for a chemical injection mandrel includes a sealing chamber having an inlet port disposed on a top distal end of the sealing chamber that fluidly connects the sealing chamber to a connection port, a communication port disposed on a side of the sealing chamber that fluidly connects the sealing chamber to a double check valve of the mandrel via a communication path, and a first translation port disposed on a bottom distal end of the sealing chamber that permits axial translation of an engagement portion of a stem, a sealing section disposed below the sealing chamber having a plurality’ of seals disposed about the sealing section that permits axial translation of the engagement portion of the stem, and a second translation port disposed on a bottom distal end of the sealing section that permits axial translation of the engagement portion of the stem, a power section chamber disposed below the sealing section having a fluidly isolated power spring disposed about a spring interface portion of the stem, and a third translation port disposed on a bottom distal end of the power section that permits axial translation of the spring interface portion of the stem, and an isolation chamber disposed below the power section chamber having a membrane in fluid communication with an annular fluids port that is fluidly connected to an annulus surrounding the mandrel, wherein the membrane communicates annular pressure to a bottom distal end of the stem, without fluid communication, to the power section.

[0005] According to one aspect of one or more embodiments of the present invention, a chemical injection mandrel with an anti-syphon device includes A chemical injection mandrel includes a mandrel having a central lumen extending therethrough, a housing coupled to the mandrel, a connection port coupled to the housing that fluidly connects a control line to the chemical injection mandrel, where the control line controllably communicates chemicals under total injection pressure, an antisyphon device disposed within the housing having a sealing chamber having an inletport disposed on a top distal end of the sealing chamber that fluidly connects the sealing chamber to a connection port, a communication port disposed on a side of the sealing chamber that fluidly connects the sealing chamber to a double check valve of the mandrel via a communication path, and a first translation port disposed on a bottom distal end of the sealing chamber that permits axial translation of an engagement portion of a stem, a sealing section disposed below the sealing chamber having a plurality of seals disposed about the sealing section that permits axial translation of the engagement portion of the stem, and a second translation port disposed on a bottom distal end of the sealing section that permits axial translation of the engagement portion of the stem, a power section chamber disposed below the sealing section having a fluidly isolated power spring disposed about a spring interface portion of the stem, and a third translation port disposed on a bottom distal end of the power section that permits axial translation of the spring interface portion of the stem, and an isolation chamber disposed below the power section chamber having a membrane in fluid communication with an annular fluids port that is fluidly connected to an annulus surrounding the mandrel, wherein the membrane communicates annular pressure to a bottom distal end of the stem, without fluid communication, to the power section, and the double check valves disposed within the housing below the anti-syphon device having a plurality of check valves that fluidly connect the sealing chamber to an interior of the central lumen of the mandrel when opened.

[0006] Other aspects of the present invention will be apparent from the following description and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1A shows a conventional chemical injection mandrel deployed in an offshore producing well.

[0008] FIG. IB shows a cross-section of the wellbore showing the chemical injection line for the conventional chemical injection mandrel in the annulus formed between the production tubing and the wellbore.

[0009] FIG. 2A shows a top-facing perspective view of a chemical injection mandrel with an anti-syphon device in accordance with one or more embodiments of the present invention.

[0010] FIG. 2B shows a left side elevation view of the chemical injection mandrel with the anti-syphon device in accordance with one or more embodiments of the present invention.

[0011] FIG. 2C shows a right side elevation view of the chemical injection mandrel with the anti-syphon device in accordance with one or more embodiments of the present invention.

[0012] FIG. 2D shows a top plan view of the chemical injection mandrel with the antisyphon device in accordance with one or more embodiments of the present invention.

[0013] FIG. 2E shows a bottom plan view of the chemical injection mandrel with the anti-syphon device in accordance with one or more embodiments of the present invention.

[0014] FIG. 3A shows a half-sectional view of a chemical injection mandrel with an anti-syphon device and double check valves in a nominal injecting state of operation in accordance with one or more embodiments of the present invention.

[0015] FIG. 3B shows a detailed half-sectional view of the chemical injection mandrel with the anti-syphon device and double check valves in the nominal injecting state of operation in accordance with one or more embodiments of the present invention.

[0016] FIG. 3C shows a detailed cross-sectional view of the anti-syphon device in the nominal injecting state of operation permitting chemical injection in accordance with one or more embodiments of the present invention.

[0017] FIG. 3D shows a cross-sectional view of the double check valves in the nominal injecting state of operation with balls off seat permitting chemical injection in accordance with one or more embodiments of the present invention.

[0018] FIG. 4A shows a half-sectional view of a chemical injection mandrel with an anti-syphon device and double check valves in a nominal non-injecting state of operation in accordance with one or more embodiments of the present invention.

[0019] FIG. 4B shows a detailed half-sectional view of the chemical injection mandrel with the anti-syphon device and double check valves in the nominal non-injecting state of operation in accordance with one or more embodiments of the present invention.

[0020] FIG. 4C shows a detailed cross-sectional view of the anti-syphon device in the nominal non-injecting state of operation preventing chemical injection in accordance with one or more embodiments of the present invention.

[0021] FIG. 4D shows a detailed cross-sectional view of double check valves in the nominal non-injecting state of operation with balls on seat preventing chemical injection in accordance with one or more embodiments of the present invention.

[0022] FIG. 5A shows a half-sectional view of a chemical injection mandrel with an anti-syphon device and double check valves in a failsafe non-injecting state of operation despite the fact that the balls of the double check valves are off seat due to reduced wellbore pressure, relying on the anti-syphon device to prevent syphoning chemicals in accordance with one or more embodiments of the present invention.

[0023] FIG. 5B shows a detailed half-sectional view of the chemical injection mandrel with the anti-syphon device and double check valves in a failsafe non-injecting state of operation in accordance with one or more embodiments of the present invention.

[0024] FIG. 5C shows a detailed cross-sectional view of the anti-syphon device in the failsafe non-injecting injecting state of operation preventing chemical injection in accordance with one or more embodiments of the present invention.

[0025] FIG. 5D shows a detailed cross-sectional view of the double check valves in the failsafe non-injecting state of operation with balls off seat due to reduced wellbore pressure, relying on the anti-syphon device to prevent syphoning chemicals in accordance with one or more embodiments of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0026] One or more embodiments of the present invention are described in detail with reference to the accompanying figures. For consistency, like elements in the various figures are denoted by like reference numerals. In the following detailed description of the present invention, specific details are described to provide a thorough understanding of the present invention. In other instances, aspects that are well- known to those of ordinary skill in the art are not described to avoid obscuring the description of the present invention. For the purposes of this disclosure, upper or uphole refer to portions of apparatus that are disposed above, or closer to the surface, than lower or downhole portions of the same or other apparatus.

[0027] FIG. 1A shows a conventional chemical injection mandrel deployed in an offshore producing well, as described in U.S. Patent 10,309,201. During deepwater operations, Floating Production Storage and Offloading (“FPSO”) vessel 102 may be disposed on the surface of the water 104. Umbilical 106 may fluidly connect the fluid system (not independently illustrated) disposed on FPSO 102 to header 108. Header108 may connect umbilical 106 to subsea umbilical 110 that is connected to subsea wellhead 162, disposed at a depth of, for example, 5,000 feet or more. Subsea umbilical 110 may include chemical injection line 112 that is directed into wellbore 118 drilled into the subsea surface 114.

[0028] In deepwater and ultra-deepwater wells, wellbore 118 may be very' deep having a measured depth in excess of 15,000 feet and perhaps as much as 30,000 feet or more. A portion of wellbore 118 may be cased 122 up to a certain depth, ty pically shallower than the measured depth of the well. Chemical injection line 112 is disposed in annulus 130 formed between production tubing 126 and casing 122. At a certain depth, one or more packers 134 may be disposed in annulus 130 between production tubing 126 and casing 122 to isolate and seal off certain sections of wellbore 118, creating an annular seal in annulus 130. Feed-through port 138 allows chemical injection line 112 to bypass packer 134 while maintaining the annular seal in annulus 130. The conditions at the bottom of wellbore 118 vary' from well to well, but are often extremely harsh, and especially in cases of deepwater and ultra-deepwater wells. In challenging applications, temperatures may exceed 400°F and pressures may exceed 25,000 Pounds per Square Inch (‘'PSI”). Wells with pressures greater than 15,000 PSI or temperatures greater than 400°F are sometimes referred to as High Pressure / High Temperature (“HPHT”) wells.

[0029] Conventional chemical injection mandrel 200 is installed at a distal or near- distal end of production tubing 126 to deliver chemicals (not independently illustrated), such as corrosion or scale inhibitors, to mitigate flow assurance issues including formation of scale or asphaltenes, prevent corrosion of well components, or provide some other benefit, all of which are intended to prolong or enhance well productivity. Chemical injection line 112, typically extending thousands of feet from a surface facility (e.g, FPSO 102) to chemical injection mandrel 200 in annulus 130, conveys these chemicals. The length of chemical injection line 112 as well as the specific gravity of the chemicals used generates significant hydrostatic head pressure in chemical injection line 112 due to the weight of the fluid column above a given point. This hydrostatic head pressure corresponds to a pressure head 142 that corresponds to the equivalent height of the fluid column producing that pressure. However, as formation 146 pressure declines over time, the high hydrostatic head pressure in chemical injection line 112 can exceed production tubing 126 pressure,risking uncommanded and uncontrollable syphoning, as discussed in more detail herein.

[0030] In operative use, the fluids system (not independently illustrated) including one or more pumps (not shown) disposed on FPSO 102 seeks to controllably inject chemicals via chemical injection line 112 and chemical injection mandrel 200 into production tubing 126 for mixture with production fluids 150. The application of a predetermined amount of fluid pressure from the surface in chemical injection line 112, exceeding the pressure of production fluids 150 emanating from formation 146, causes the injection valve system (not independently illustrated) of chemical injection mandrel 200 to open, permitting the inj ection of chemicals into production tubing 126. The chemicals mix with production fluids 150 within production tubing 126 and the fluids return to the surface via subsea wellhead 162 and production flow line 166, that is directed to FPSO 102 for further processing or storage. Conversely, when the application of fluid pressure from the surface in chemical injection line 112 stops, the injection valve system (not independently illustrated) of chemical injection mandrel 200 is expected to close, preventing the injection of chemicals into production tubing 126 and with additional protection mechanisms to prevent syphoning. Conventional chemical injection mandrel 200 typically includes double check valves (not independently illustrated) disposed below the injection valve system that rely upon the upward pressure of production fluids 150 from formation 146 to close and prevent syphoning of the expensive chemicals. However, there are complicating factors that, despite best efforts, result in the uncommanded and uncontrolled syphoning of chemicals.

[0031] As formation 146 pressure declines over time, tubing pressure at the depth of, and within, chemical injection mandrel 200 decreases significantly. This creates a pressure differential where the hydrostatic head pressure in chemical injection line 112, without the application of pressure from the surface, exceeds the reduced tubing pressure at chemical injection mandrel 200. Consequently, the double check valves (not independently illustrated) of chemical injection mandrel 200 may fail to close or hold their closure, triggering an uncommanded and uncontrolled syphoning effect, sometimes referred to as the U-tube effect — where chemicals are syphoned and flow freely into wellbore 118 without active pumping from the surface 104. This syphoning leads to excessive consumption of expensive chemicals, creates potential vacuum formation in chemical injection valve 112, and risks chemical boiling orprecipitation, which can clog or damage chemical injection mandrel 200 and other equipment, as described in more detail herein.

[0032] Uncommanded syphoning of chemicals (not independently illustrated) due to a failed chemical injection mandrel 200 in a deepwater or ultra-deepwater well poses several significant risks, impacting operational efficiency, safety, and the environment. Syphoning driven by the hydrostatic head pressure in chemical injection line 112 exceeding tubing pressure leads to uncontrolled syphoning of chemicals into wellbore 118. This rapidly depletes reserves of expensive chemicals, increasing operational costs and potentially disrupting treatment schedules, which can compromise well integrity by allowing corrosion or scale buildup. As syphoning continues unchecked, a vacuum can form in chemical injection line 112, particularly in deepwater and ultra-deepwater wells with long capillary-style lines. This low- pressure environment may cause chemicals to boil or flash, altering their properties, reducing their effectiveness, or leading to vapor lock, which can stall the injection valve system of chemical injection mandrel 200 entirely.

[0033] In addition, uncontrolled syphoning can cause chemicals to precipitate solids, especially if volatile solvents evaporate under vacuum conditions or if incompatible fluids mix in the wellbore. These precipitated solids can clog the injection valve of chemical injection mandrel 200, production tubing 126, or flowlines (not shown), necessitating costly interventions like flushing or tubing replacement. While the double check valves of chemical injection mandrel 200 are designed to prevent backflow, they may erode or corrode due to prolonged exposure to high-velocity chemical flow or well fluids entering chemical injection line 112. This can exacerbate the failure, potentially damage adjacent completion components and require extensive repairs. In addition, excessive chemical injection can alter fluid chemistry, potentially leading to emulsion formation, reduced hydrocarbon flow, or reservoir damage. Conversely, if syphoning depletes inhibitors, unprotected tubing 126 may corrode, increasing risk of leaks or catastrophic failure. In extreme cases, the uncontrolled and uncommanded injection of chemicals can contribute to pressure imbalances, increasing the risk of well control issues. If syphoning leads to surface spills during interventions or if chemicals contaminate the reservoir, environmental damage and regulatory penalties may result, particularly in sensitive deepwater or ultra-deepwater ecosystems.

[0034] Continuing, FIG. IB shows a cross-section of wellbore 118 showing chemical injection line 112 for conventional chemical injection mandrel 200 in annulus 130 formed between production tubing 126 and wellbore 118.

[0035] These risks associated with a failed chemical injection mandrel (e.g., 200 of FIG. 1A) collectively elevate operations costs, requiring floating a drilling rig back onto the remote well site, pulling the entire production tubing (e.g., 126 of FIG. 1A) string, replacing the failed chemical injection mandrel (e.g., 200 of FIG. 1A), and redeploying production tubing (e.g., 126 of FIG. 1A) in what amounts to a recompletion of the well. These operations can take several months and cost tens of millions of dollars. In addition, profits derived from production are lost for the duration of such operations. As such, the impact of a failed chemical injection mandrel (e.g., 200 of FIG. 1A) in repair time, repair costs, and lost profits are substantial. The pragmatic problem with conventional chemical injection mandrels (e.g. , 200 of FIG. 1A) is that, while they may be fully functional and operational when deployed, they are a ticking timebomb of sorts. As formation (e.g, 146 of FIG. 1A) pressure declines over time (which could be months, years, or even decades), they may cease to operate in a manner that results in the uncommanded and uncontrolled syphoning of expensive chemicals downhole that are not easily replaceable in deepwater and ultra-deepwater wells.

[0036] Accordingly, in one or more embodiments, an anti-syphon device (and as part of a chemical injection mandrel thereof) prevents uncontrolled syphoning as formation pressure declines, overcoming the limitations of conventional double check valves that rely solely on production tubing pressure. The anti-syphon device comprises a sealing chamber for the stem’s engagement portion, a power section chamber housing a spring for stem actuation, and an isolation chamber that transmits annular pressure to the power section without fluid communication. Under nominal operating conditions, when the production tubing pressure exceeds the total injection pressure, defined as the sum of surface applied pressure and hydrostatic head pressure in the chemical injection line, the double check valves close, preventing syphoning. However, as formation pressures decline, when the hydrostatic head pressure alone exceeds the tubing pressure, the double check valves may fail, causing uncommanded and uncontrolled chemical syphoning downhole. The anti-syphon device of the present invention counters this by using annular pressure, typically higher due to the presence of comparably static completion fluids in the annulus, communicatedthrough the isolation chamber, without fluid communication, to provide an assist to the power section that drives the axial translation of the stem upward onto its seat, preventing syphoning. Advantageously, this robust mechanism prevents syphoning even as formation pressures decline and increases the operational reliability and longevity of the anti-syphon device and chemical injection mandrel thereof.

[0037] FIG. 2A shows top-facing perspective view of a chemical injection mandrel 300 with an anti-syphon device (not independently illustrated) in accordance with one or more embodiments of the present invention.

[0038] Chemical injection mandrel 300 may include a mandrel 320 having an upper connection end 310, a lower connection end 320, and a central lumen 350 that extends from end to end. Upper connection end 310 and lower connection end 320 may be any type or kind of threaded connections, well known in the art, that permit a secure and pressure tight seal with standard tubulars of a production tubing string (e.g, 126 of FIG. 1A). Housing 330 may be integrally made with or coupled to mandrel 320. Housing 330 may house the anti-syphon device (e.g, 400) and the double check valves (e.g, 500) as well as provide a connection port 360 for the removable attachment of a chemical injection line (e.g, 112) in the annulus (e.g, 130 of FIG. 1A) between production tubing (e.g., 126 of FIG. 1A) and the casing (e.g, 122 of FIG. 1A) of a given well, when disposed downhole. Housing 330 may include an annular fluids port 370 that is used to communicate annular pressure as described in more detail herein.

[0039] Continuing, FIG. 2B shows a left side elevation view7of chemical injection mandrel 300 with the anti-syphon device (e.g., 400) in accordance with one or more embodiments of the present invention. Continuing, FIG. 2C shows a right side elevation view of the chemical injection mandrel 300 with the anti-syphon device (e.g, 400) in accordance with one or more embodiments of the present invention. Continuing, FIG. 2D shows a top plan view7of the chemical injection mandrel 300 with the anti-syphon device (e.g., 400) in accordance with one or more embodiments of the present invention. In this plan view, central lumen 350 is shown as well as connection port 360 for connection to a chemical injection line (e.g, 112 of FIG. 1A). Continuing, FIG. 2E shows a bottom plan view7of the chemical injection mandrel 300 with the anti-syphon device (e.g., 400) in accordance with one or more embodiments of the present invention. One of ordinary skill in the art. having the benefit of this disclosure, will recognize that the size, shape, and configuration of chemical injectionmandrel 300 may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0040] In the description that follows, FIGs. 3A-3D show chemical injection mandrel 300 with anti-syphon device 400 in a nominal injecting state of operation where the total injection pressure is greater than the tubing pressure, FIGs. 4A-4D show chemical injection mandrel 300 with anti-syphon device 400 in a nominal noninjecting state of operation where the total injection pressure is less than tubing pressure, and FIGs. 5A-5D show chemical injection mandrel 300 with anti-syphon device 400 in a failsafe non-injecting state of operation where the hydrostatic head pressure exceeds the tubing pressure, where because of declining formation pressure or other failure of double check valves 500, anti-syphon device 400 is automatically engaged by annular pressure that assists closure to prevent the syphoning of chemicals.

[0041] FIG. 3A shows a half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valves 500 in a nominal injecting state of operation in accordance with one or more embodiments of the present invention.

[0042] For purposes of illustration, chemical injection mandrel 300 may be disposed downhole at the distal or near-distal end of the production tubing (e.g., 126 of FIG. 1A) of the wellbore (e.g., 118 of FIG. 1A). Chemical injection line 112 may fluidly connect to connection port 360 of chemical inj ection mandrel 300 in the annulus (e.g. , 130 of FIG. 1A) formed between the production tubing (e.g., 126 of FIG. 1A) and the casing (e.g., 122 of FIG. 1A) of the wellbore (e.g., 118 of FIG. 1A). For purposes of illustration, production fluids 150 may flow from the producing formation (e.g., 146 of FIG. 1A) upward through central lumen 350 of chemical injection mandrel 300 toward the surface in the production tubing (e.g., 126 of FIG. 1A). The pressure associated with the production fluids 150 within the production tubing (e.g., 126 of FIG. 1A) is ty pically referred to as tubing pressure. In this nominal injecting state of operation, the total injection pressure in chemical injection line 112 includes pressure applied from the surface plus the hydrostatic head pressure in line 112, that taken together causes anti-syphon device 400 and double check valves 500 to open and permit the injection of chemicals 111 into mandrel 320. While the opening aperture of double check valves 500 are shown in an exaggerated manner to facilitate understanding, one of ordinary skill in the art will recognize that they open to a lesser extent than shown and at least permit flow. Chemicals 111 mix with production fluids150 in mandrel 320 as they travel upwards through the production tubing (e.g., 126 of FIG. 1A) towards the surface.

[0043] Continuing, FIG. 3B shows a detailed half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valves 500 in the nominal injecting state of operation in accordance with one or more embodiments of the present invention. In this figure, the flow path of chemicals 111 through anti-syphon device 400 and double check valves 500 for mixture with production fluids 150 is shown. Chemicals 111 in chemical injection line 112 are fluidly communicated to chemical injection mandrel 300 via connection port 360. Chemical injection line 112 is typically a small-diameter capillary tube that is typically fitted with a Ferrule-type male fitting that mates with a female threaded connection port 360. Notwithstanding, one of ordinary skill in the art will recognize that there are many different types or kinds of connection mechanisms that are well known in the art that may be used in accordance with one or more embodiments of the present invention. The total injection pressure in chemical injection line 112 causes stem 490 to translate axially downward off its seat formed by the distal end of inlet port 403 creating a fluid communication path for chemicals 111 through anti-syphon device 400 and causes balls 590a, 590b to translate axially dow nw ard off their respective seats formed by the distal ends of check valve inlets 510a, 510b creating a fluid communication path for chemicals 111 through double check valves 500, permitting chemicals 111 to be injected into central lumen 350 of mandrel 320 for mixture with production fluids 150, as they travel toward the surface.

[0044] Continuing, FIG. 3C shows a detailed cross-sectional view' of anti-syphon device 400 in the nominal injecting state of operation permitting chemical 111 injection in accordance with one or more embodiments of the present invention. Antisyphon device 400 may include sealing chamber 401, power section chamber 421, isolation chamber 431, and stem 490 having stem tip 493 on a top distal end of engagement portion 495 and spring interface portion 497. Engagement portion 495 may have a larger diameter than spring interface portion 497. Stem 490 axially translates without fluid communication betw een chambers 401, 421, and 431. Sealing chamber 401 may include inlet port 403 disposed on a top distal end of sealing chamber 401 that fluidly connects sealing chamber 401 to connection port 360. Communication port 405 may be disposed on a side of sealing chamber 401 that fluidly connects sealing chamber 401 to double check valves 500 via communicationpath 406. First translation port 407 may be disposed on a bottom distal end of sealing chamber 401 that permits axial translation of engagement portion 495 of stem 490.

[0045] Sealing section 411 may be disposed below sealing chamber 401 and may include a plurality of seals 413 disposed about sealing section 411 that fluidly isolates sealing chamber 401 from sealing section 411, power section chamber 421, and isolation chamber 431. The plurality of seals 413 may be disposed about an interior passageway of sealing section 411 and permit axial translation of stem 490 without fluid communication. The plurality of seals 413 may be static, O-ring shaped, metal- on-metal seals and in certain embodiments may be composed of tungsten carbide. Second translation port 415 may be disposed on a bottom distal end of sealing section 411 and permits axial translation of engagement portion 495 of stem 490. Power section chamber 431 may be disposed below sealing section 411 and may include a fluidly isolated power spring 423 disposed about spring interface portion 497 of stem 490. Third translation port 425 may be disposed on a bottom distal end of power section chamber 421 and permits axial translation of spring interface portion 497 of stem 490.

[0046] Isolation chamber 431 may be disposed below power section chamber 431 and may include a membrane 433 in fluid communication with annular fluids port 370 that is fluidly connected to an annulus (e.g, 130 of FIG. 1A) surrounding mandrel 300, where membrane 433 communicates annular pressure, without fluid communication, to a bottom distal end 498 of spring interface portion 497 of stem 490. In this way, sealing chamber 401 may be fluidly isolated from sealing section 411, sealing section 411 may be fluidly isolated from power section chamber 421, and power section chamber 421 may be fluidly isolated from isolation chamber 431. Notwithstanding, isolation chamber 431 transits annular pressure that provides an assist to power spring 423. In certain embodiments, membrane 433 may be an edge welded bellows. In other embodiments, membrane 433 may be a piston. In still other embodiments, membrane 433 may be composed of flexible barrier. One of ordinary skill in the art will, having the benefit of this disclosure, will recognize that membrane 433 may be anything that permits the communication of pressure without fluid communication.

[0047] In nominal operating conditions, when an operator on the surface wishes to inject chemicals 111 downhole, they apply pressure from the surface via one or more pump systems (not shown). The total injection pressure in chemical injection line 112includes the surface applied pressure as well as the hydrostatic head pressure. When the total injection pressure exceeds the tubing pressure, power spring 423 may be compressed, stem 490 may axially translate downward such that stem tip 493 is moved off the seat formed by inlet port 403, thereby permitting chemicals 111 to flow into sealing chamber 401 and toward double check valves 500 for injection into the central lumen 350 of the mandrel (e.g, 320 of FIG. 3B) for mixing with production fluids 150.

[0048] Specifically, the total injection pressure pushes chemicals 111 through connection port 360 and into inlet port 403 of sealing chamber 401, where chemicals 111 make contact with, and push, stem tip 493 of engagement portion 495 of stem 490 downwards off the seat formed by inlet port 403. The downward force on stem tip 493 causes stem 490 to axially translate downward against the opposing force of power spring 423 in power section chamber 421 and tubing pressure. It is important to note that engagement portion 495 of stem 490 axially translates downward without fluid communication between sealing chamber 401 and sealing section 411. As previously discussed, sealing section 411 includes a plurality of seals 413 disposed about sealing section 411 that prevent fluid communication between sealing chamber 401 and sealing section 411. Because the application of total injection pressure prevents chemicals 411 from flowing back into chemical injection line 112 and sealing section 411 prevents communication of chemicals 411 to sealing section 411 and power section chamber 421, chemicals 411 are directed through communication port 405 to communication path 406 that fluidly connects to double check valves 500, which are kept on seat by tubing pressure from production fluids (e g, 150).

[0049] From a pressure standpoint, total injection pressure is communicated via chemical injection line 112, annular pressure is communicated by annular fluids 600 via annular fluids port 370, where membrane 433 transmits annular pressure without fluid communication to a bottom distal end 498 of spring interface portion 497 of stem 490. Just prior to the application of pressure from the surface, power spring 423 with the assistance of annular pressure communicated through isolation chamber 431, keeps step tip 493 on the seat formed by inlet port 403 and prevents chemicals 111 from entering mandrel 300. When the operator on the surface desires to inject chemicals 111 downhole, pressure is applied from the surface, and the total injection pressure exceeds tubing pressure and overcomes the opposing force of power spring 423 and the assist it receives from annular pressure communicated from isolationchamber 431, moving stem 490 off seat and permitting the flow of chemicals 111 as shown towards double check valves 500.

[0050] Continuing, FIG. 3D shows a cross-sectional view of double check valves 500 in the nominal injecting state of operation with balls 590a, 590b off their respective seats formed by check valve inlets 510a, 510b permitting chemical 111 injection in accordance with one or more embodiments of the present invention. Prior to the application of pressure from the surface, production fluids 150 in the production tubing (e.g, 126 of FIG. 1A) apply tubing pressure that keeps balls 590a, 590b on their respective seats formed by check valve inlets 510a, 510b (not shown), such that there is no fluid communication through double check valves 500. However, when stem 490 is moved off seat and translates axially downward as shown in FIG. 3C, chemicals 111 under total injection pressure are fluidly communicated by the antisyphon device (e.g., 400 of FIG. 3C) through communication path 406 and are incident on the top side of balls 590a, 590b, causing them to open against the closing force of power springs 520a, 520b and the assist they receive from tubing pressure communicated by production fluids 150. While the opening aperture of double check valves 500 are show i in an exaggerated manner to facilitate understanding, one of ordinary7skill in the art will recognize that they open to a lesser extent than shown and at least permit flow. Chemicals 111 exit via mandrel port 540 and mix with production fluids 150 in mandrel 320, as the travel upwards tow ard the surface.

[0051] FIG. 4A shows a half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valve 500 in a nominal non-injecting state of operation in accordance with one or more embodiments of the present invention. In this nominal non-injecting state of operation, there is no application of pressure from the surface such that the total injection pressure consists only of the hydrostatic head pressure in chemical injection line 112. The stem (e.g, 490) of anti-syphon device 400 should close and remain closed with the force provided by its pow er spring (e.g, 423) and the assist it receives from annular pressure as discussed with reference to FIG. 4C. So long as the tubing pressure exceeds the hydrostatic head pressure, double check valves 500 should close and remain closed, preventing the syphoning of chemicals 111. In this way, production fluids 150 provide an upward force that assists the power springs (e.g., 520) of double check valves 500 to move their respective balls (e.g. 590) back on seat, preventing the syphoning of chemicals 111 as discussed with reference to FIG. 4D.

[0052] Continuing, FIG. 4B shows a detailed half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valves 500 in the nominal non-injecting state of operation in accordance with one or more embodiments of the present invention. In this figure, the flow path, or lack thereof, of chemicals 111 is shown. Chemicals 111 in chemical injection line 112 are fluidly communicated to chemical injection mandrel 300 via connection port 360. Because there is no application of pressure from the surface, the total injection pressure in chemical injection line 112 consists of hydrostatic head pressure of chemicals 111. In this case the total injection pressure is not sufficient to move stem 490 off seat against the force of its power spring (e.g., 423) and stem 490 remains on seat preventing the fluid communication of chemicals 111. as discussed with reference to FIG. 4C. Double check valves 500 close or remain closed as the tubing pressure resulting from production fluids 150 in the production tubing (e.g., 126 of FIG. 1A), provides an assist to their respective power springs 520a, 520b, as discussed with reference 4D. As such, both anti-syphon device 400 and double check valves 500 prevent the syphoning of chemicals 111.

[0053] Continuing, FIG. 4C shows a detailed cross-sectional view of anti-syphon device 400 in the nominal non-injecting state of operation preventing chemical injection in accordance w ith one or more embodiments of the present invention.

[0054] In nominal operating conditions, when an operator on the surface wishes to stop the injection of chemicals 111 downhole, they stop applying pressure from the surface via the one or more pump systems (not shown). The total injection pressure in chemical injection line 112 consists of the hydrostatic head pressure in chemical injection line 112. Because the total injection pressure is not sufficient to compress power spring 423 against annular pressure communicated via isolation chamber 431, step 490 stays on the seat formed by inlet port 403, preventing the communication of chemicals 111 into anti-syphon device 400, and by extension double check valves 500. Specifically, the total injection pressure is presented at connection port 360, however power spring 423 and the assist it receives from annular pressure communicated by isolation chamber 431 keeps step 490 on the seat formed by inlet port 403, such that chemicals 111 are kept at bay and do not enter anti-syphon device 400, and by extension, double check valves 500. From a pressure standpoint, total injection pressure is communicated via chemical injection line 112. annular pressure is communicated by annular fluids 600 via annular fluids port 370, where membrane433 transmits annular pressure without fluid communication to a bottom distal end 498 of spring interface portion 497 of stem 490. Power spring 423 with the assistance of annular pressure communicated through isolation chamber 431, keeps step tip 493 on the seat formed by inlet port 403 and prevents chemicals 111 from entering antisyphon device 400.

[0055] Continuing, FIG. 4D shows a detailed cross-sectional view of double check valves 500 in the nominal non-injecting state of operation with balls 590a, 590b on the seats formed by check valve inlets 510a, 510b preventing chemical injection and syphoning in accordance with one or more embodiments of the present invention. Production fluids 150 apply tubing pressure that, with the assistance of power springs 520a. 520b keeps balls 590a, 590b on their respective seats formed by check valve inlets 510a, 510b, such that there is no fluid communication through double check valves 500.

[0056] Taken together, FIGs. 3A-3D show the nominal injection mode of operation where FIGs. 4A-4D show the nominal non-inj ection mode of operation. In FIGs. 5A- 5D that follow, anti-syphon device 400 is engaged to prevent syphoning in a situation that would constitute a failure mode of conventional chemical injection mandrels (e.g., 200 of FIG. 1A) that result in the uncommanded and uncontrolled syphoning of chemicals 111.

[0057] FIG. 5A shows a half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valves 500 in a failsafe non-injecting state of operation despite the fact that balls (e.g, 590) of double check valves 500 permit flow due to reduced wellbore pressure, relying on anti-syphon device 400 to prevent the syphoning chemicals in accordance with one or more embodiments of the present invention. While the opening aperture of double check valves 500 are shown in an exaggerated manner to facilitate understanding, one of ordinary skill in the art will recognize that they open to a lesser extent than shown, such that they at least permit unintended fluid communication which would result in syphoning in conventional chemical injection mandrels. In this figure, there is no application of pressure from the surface such that the total injection pressure consists only of the hydrostatic head pressure in chemical injection line 112. As the formation pressure declines, or double check valves 500 fails, the total injection pressure may exceed the production tubing pressure such that the net pressure differential moves the balls (e.g., 590) of double check valves 500 off of their seat and remain at least partially open. In conventionalchemical injection mandrels (e.g., 200 of FIG. 1A), this would represent a critical failure mode that would result in the uncommanded and uncontrolled syphoning of chemicals downhole. However, in this instance, anti-syphon device 400 is engaged in to prevent syphoning. As discussed in more detail herein, annular pressure provides an assist to the power section of anti-syphon device 400 that moves the stem (e.g, 490) onto its seat and thereby prevents syphoning despite the failure of double check valves 500.

[0058] Continuing, FIG. 5B shows a detailed half-sectional view of chemical injection mandrel 300 with anti-syphon device 400 and double check valves 500 in a failsafe non-injecting state of operation in accordance with one or more embodiments of the present invention. In this failsafe non-injecting mode of operation, the operator does not wish to inject chemicals 111 downhole and is not applying pressure from the surface. Notwithstanding, the total injection pressure consists of the hydrostatic head pressure in chemical injection line 112 that is incident on anti-syphon device 400. With respect to double check valves 500, the net pressure differential on the bottom side of double check valves 500 corresponds to tubing pressure from production fluids 150 in the production tubing (e.g., 126 of FIG. 1A), which, during early phase of the wells life should be sufficient to close double check valves 500 and prevent weeping or syphoning of chemicals 111. Over time, as formation pressure declines, tubing pressure declines. When that tubing pressure declines to the point that the net pressure differential moves the balls (e.g., 590) off seat as described with reference to FIG. 5D, double check valves 500 has essentially failed and chemicals would be syphoned in the case of a conventional chemical injection mandrel (e.g., 200 of FIG. 1A). However, here, anti-syphon device 400 is engaged, preventing the syphoning of chemicals 111, as described with reference to FIG. 5C.

[0059] using the communication of annular pressure to assist its power section

[0060] Continuing, FIG. 5C shows a detailed cross-sectional view of anti-syphon device 400 in the failsafe non-injecting injecting state of operation preventing chemical injection in accordance with one or more embodiments of the present invention. In this failsafe mode of operation, the operator on the surface wishes to stop the injection of chemicals 111 downhole and stops applying pressure from the surface via the one or more pump systems (not shown). The total injection pressure in chemical injection line 112 consists of the hydrostatic head pressure in chemical injection line 112. However, as formation pressures decline, the tubing pressureincident on the bottom distal end of double check valves (e.g., 500 of FIG. 5D) declines and at a certain point it will not be sufficient to keep the balls (e.g., 590) on their respective seats and prevent fluid communication, such that the double check valves (e.g., 500 of FIG. 5D) are weeping or open, and production fluids 150 may be communicated via communication path 406 to sealing chamber 401. While net pressure differential may cause the stem (not shown) of a conventional chemical injection mandrel (e.g., 200 of FIG. 1A) to axially translate downward, thereby permitting the syphoning of chemicals, anti-syphon device 400 is automatically engaged to prevent syphoning.

[0061] However, here, annular fluids 600 may be communicated via annular fluids inlet370 to membrane 433 of isolation chamber 431. Membrane 433 may communicate the annular pressure of annular fluids 600, without communication of annular fluids 600, to a bottom distal end 498 of stem 490 that provides an upward force to assist power spring 423 to cause stem 490 to axially translate upwards and close on its seat formed by inlet portion 403. From a pressure standpoint, total injection pressure is communicated via chemical injection line 112, annular pressure is communicated by annular fluids 600 via annular fluids port 370, where membrane 433 transmits annular pressure without fluid communication to a bottom distal end 498 of spring interface portion 497 of stem 490. Power spring 423 with the assistance of annular pressure communicated through isolation chamber 431, keeps step tip 493 on the seat formed by inlet port 403 and prevents chemicals 111 from entering anti-syphon device 400. Advantageously, a chemical injection mandrel (e.g., 300) may be design and deployed in a producing well and, over time, as the formation pressure declines, the anti-syphon device (e.g. , 400) prevents syphoning even when the double check valves (e.g., 500) fail to close or remain closed. From a force

[0062] Continuing, FIG. 5D shows a detailed cross-sectional view of double check valves 500 in the failsafe non-injecting state of operation with balls 590a, 590b off their respective seats formed by check valve inlets 510a, 510b due to reduced tubing pressure wellbore, relying on the anti-syphon device of FIG. 5C to prevent syphoning chemicals in accordance with one or more embodiments of the present invention. As previously discussed, over the producing life of a well, the formation pressure declines. While chemical injection mandrels 300 are typically designed and selected for their anticipated application, which may include the measured formation pressure at the time of completion, that formation pressure may decline after months, years, ordecades of production. Here, as the formation pressure declines, the tubing pressure declines such that the tubing pressure presented at the bottom distal end of each ball 590a, 590b, is not sufficient such that the net pressure differential on each ball 590a, 590b cause balls 590a, 590b to axially translate downwards off their respective seats formed by check valve inlets 510a, 510b, such that they are weeping or even fully opened. In the case of conventional chemical injection mandrels (e.g. 200 of FIG. 1A), this would result in the syphoning of chemicals 111. However, here, because of the action of anti-syphon device 400 as shown and described with reference to FIG. 5C, syphoning has been prevented. Advantageously, the increases the reliability of chemical injection mandrel 300, reduces operational costs, and prolongs productivity.

[0063] The design of a chemical injection mandrel and the sizing of the components thereof may vary based on an application or design. Prior to deployment, an engineer will undertake an analysis that includes defining the functional requirements, analyzing operating conditions, analyzing the pressure profile of the wellbore, determining a desired setting depth for the chemical injection mandrel, determining the types and kinds of chemicals that may be used, determining their specific gravity, estimating the hydrostatic head pressure in the control line at the setting depth of the chemical injection mandrel, calculating forces needed to actuate chemical injection mandrel, calculating forces needed to de-actuate chemical injection mandrel, determining the appropriate type. kind, and size of power springs, and careful analysis of fatigue and lifecycle analysis. As such, one of ordinary skill in the art, having the benefit of this disclosure, will recognize the size, shape, disposition, and configuration of the components of a chemical injection mandrel with an anti-syphon device may vary’ in accordance with one or more embodiments of the present invention, but function in an identical manner so long as the net pressure differentials are as described herein.

[0064] Advantageously, the anti-syphon device and chemical injection mandrel thereof works in a wide range of conditions including in HPHT wells including wells exceeding 25,000 PSI. Because all seals are static metal-to-metal seals, the antisyphon device remains very clean which promotes longevity and reliability.

[0065] While the present invention has been described with respect to the above-noted embodiments, those skilled in the art, having the benefit of this disclosure, will recognize that other embodiments may be devised that are within the scope of theinvention as disclosed herein. Accordingly, the scope of the invention should only be limited by the appended claims.

Claims

CLAIMS1. An anti-syphon device for a chemical injection mandrel comprising: a sealing chamber comprising: an inlet port disposed on a top distal end of the sealing chamber that fluidly connects the sealing chamber to a connection port, a communication port disposed on a side of the sealing chamber that fluidly connects the sealing chamber to a double check valve of the mandrel via a communication path, and a first translation port disposed on a bottom distal end of the sealing chamber that permits axial translation of an engagement portion of a stem; a sealing section disposed below the sealing chamber comprising: a plurality of seals disposed about the sealing section that permits axial translation of the engagement portion of the stem, and a second translation port disposed on a bottom distal end of the sealing section that permits axial translation of the engagement portion of the stem; a power section chamber disposed below the sealing section comprising: a fluidly isolated power spring disposed about a spring interface portion of the stem, and a third translation port disposed on a bottom distal end of the power section that permits axial translation of the spring interface portion of the stem; andan isolation chamber disposed below the power section chamber comprising a membrane in fluid communication with an annular fluids port that is fluidly connected to an annulus surrounding the mandrel, wherein the membrane communicates annular pressure to a bottom distal end of the stem, without fluid communication, to the power section.

2. The anti-syphon device of claim 1 , wherein the sealing chamber is fluidly isolated from the sealing section.

3. The anti-syphon device of claim 1, wherein the sealing section is fluidly isolated from the power section chamber.

4. The anti-syphon device of claim 1, wherein the power section chamber is fluidly isolated from the isolation chamber.

5. The anti-syphon device of claim 1 , wherein when the total injection pressure consists only of hydrostatic head pressure and a tubing pressure is not sufficient to cause the double check valves of the mandrel to close, communicated annular pressure provides an assist to the power spring of the power section chamber to overcome the hydrostatic head pressure and cause the stem to axially translate upward until a stem tip is on seat, thereby preventing a syphoning of chemicals.

6. The anti-syphon device of claim 1, wherein under normal operating conditions when the total injection pressure exceeds a tubing pressure, a positive pressure differential causes the stem to axially translate downward such that a stem tip is moved off seat,thereby permitting chemicals to flow through the sealing chamber to the double check valves and into an interior of a central lumen of the chemical injection mandrel.

7. The anti-syphon device of claim 1, wherein under normal operating conditions when the total injection pressure is less than a tubing pressure, a negative pressure differential causes the double check valves of the chemical injection mandrel to close and causes the stem to axially translate upward until a stem tip is on seat, thereby preventing chemical injection.

8. The anti-syphon device of claim 1, wherein the engagement portion of the stem is at least partially disposed within the sealing chamber and the sealing section and the spring interface portion of the stem is at least partially disposed within the power section chamber and the third translation port.

9. The anti-syphon device of claim 1 , wherein the engagement portion of the stem has a larger diameter than the spring interface portion of the stem.

10. The anti-syphon device of claim 1, wherein each of the plurality of seals comprise an O-ring shaped seal.

11. The anti-syphon device of claim 1, wherein each of the plurality of seals are composed of tungsten carbide.

12. The anti-syphon device of claim 1. wherein all seals are metal-to-metal seals.

13. The anti-syphon device of claim 1, wherein all seals are static.

14. A chemical injection mandrel comprising: a mandrel comprising a central lumen extending therethrough; a housing coupled to the mandrel; a connection port coupled to the housing that fluidly connects a control line to the chemical injection mandrel, wherein the control line controllably communicates chemicals under total injection pressure; an anti-syphon device disposed within the housing comprising: a sealing chamber comprising: an inlet port disposed on a top distal end of the sealing chamber that fluidly connects the sealing chamber to the communication port disposed on a side of the sealing chamber that fluidly connects the sealing chamber to a double check valve section, and a first translation port disposed on a bottom distal end of the sealing chamber that permits axial translation of an engagement portion of a stem; a sealing section disposed below the sealing chamber comprising: a plurality of seals disposed about the sealing section that permits axial translation of the engagement portion of the stem, and a second translation port disposed on a bottom distal end of the sealing section that permits axial translation of the engagement portion of the stem; a power section chamber disposed below the sealing section comprising:a fluidly isolated power spring disposed about a spring interface portion of the stem, and a third translation port disposed on a bottom distal end of the power section that permits axial translation of the spring interface portion of the stem; and an isolation chamber disposed below the power section chamber comprising a membrane in fluid communication with an annular fluids port that is fluidly connected to an annulus surrounding the mandrel, wherein the membrane communicates annular pressure to a bottom distal end of the stem, without fluid communication, to the power section; and the double check valves disposed within the housing below the anti-syphon device comprising a plurality of check valves that fluidly connect the sealing chamber to an interior of the central lumen of the mandrel when opened.

15. The chemical injection mandrel of claim 14, wherein the sealing chamber is fluidly isolated from the sealing section.

16. The chemical injection mandrel of claim 14, wherein the sealing section is fluidly isolated from the power section.

17. The chemical injection mandrel of claim 14, wherein the power section is fluidly isolated from the isolation chamber.

18. The chemical injection mandrel of claim 14, wherein when the total injection pressure consists only of hydrostatic head pressure and a tubing pressure is not sufficient to causethe double check valves to close, communicated annular pressure provides an assist to the power spring of the power section chamber to overcome the hydrostatic head pressure and cause the stem to axially translate upward until a stem tip is on seat, thereby preventing a sy phoning of chemicals.

19. The chemical injection mandrel of claim 14, wherein undernormal operating conditions when the total injection pressure exceeds a tubing pressure, a positive pressure differential causes the stem to axially translate downward such that a stem tip is moved off seat, thereby permitting chemicals to flow through the sealing chamber to the double check valves and an the interior of the central lumen of the chemical injection mandrel.

20. The chemical injection mandrel of claim 14, wherein undernormal operating conditions when the total injection pressure is less than a tubing pressure, a negative pressure differential causes the double check valves to close and causes the stem to axially translate upward until a stem tip is on seat, thereby preventing chemical injection.

21. The chemical injection mandrel of claim 14, wherein the engagement portion of the stem is at least partially disposed within the sealing chamber and the sealing section and the spring interface portion of the stem is at least partially disposed within the power section chamber and the third translation port.

22. The chemical injection mandrel of claim 14, wherein the engagement portion of the stem has a larger diameter than the spring interface portion of the stem.

23. The chemical injection mandrel of claim 14. wherein each of the plurality of seals comprise an O-ring shaped seal.

24. The chemical injection mandrel of claim 14, wherein each of the plurality7of seals are composed of tungsten carbide.

25. The chemical injection mandrel of claim 14, wherein all seals are metal -to-metal seals.

26. The chemical injection mandrel of claim 14, wherein all seals are static.

27. A chemical injection mandrel comprising: a body connected to a well tubing, a first port in said body7that is connected to a chemical injection line inlet, a second port in said body conveying annulus pressure and annular fluid to one side of said sealing section, a third port in said body connected to a tubing outlet that allow introduction of said chemicals injected through said chemical injection line into said tubing, a stem and seat in said body operable to control flow between said first port connected to said chemical injection line inlet and said third port in said body connected to tubing outlet, a spring in said body that provides closing force to said stem, a sealing section in said body acting on said stem that provides isolation of said second port conveying annulus pressure and a chamber formed between the downstream of the stem and seat and upstream of a backcheck section,a sealing section in said body acting on said stem that provides an effective area for said annulus pressure to provide a closing force that in conjunction with said spring is adequate to maintain said chemical injection line hydrostatic pressure, thereby preventing syphoning as formation pressure decreases.

28. The injection device of claim 27, wherein the second port in said body conveying annulus pressure is isolated by a membrane constituting a second barrier between the annular fluids and the sealing section. The membrane and the sealing section form a fluid filled isolation chamber through which pressure from the annulus can be transmitted to the sealing section.

29. The injection device of claim 28, wherein the fluid filled isolation chamber formed by the membrane and the sealing section act to prevent egress of annular fluids from interacting with the sealing section.

30. The injection device of claim 27, wherein the stem and seat form a contact seal area where when the device is closed the pressure on either side of the contact seal area is applying counter forces, both opening and closing. Additionally, the injection device of claim 1 develops a sealing system effective area between a housing and a stem where the sealing section provides contact and develops a sealing section effective area that when subjected to pressures on either side is applying counter forces, both opening and closing.

1. The inj ection device of claim 30, wherein the effective areas of the stem and seat contact seal area and the sealing system effective area are intentionally and effectively the same causing the elimination of tubing pressure from consideration in the opening of the injection device. It may be noted that in conditions that differ from this specific application, the effective areas may be changed to develop a different outcome that can be specific to a particular set of conditions.

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