COMPRESSED NATURAL GAS ARTIFICIAL GAS LIFT

Abstract

A gas lift capable oil well is artificially gas lifted by transferring compressed natural gas (CNG) from a compressed natural gas vessel of a mobile CNG storage system to a tubing-casing annulus of the gas lift capable well via a pathway. The CNG transfer occurs without the use of a compressor. A mobile unloader monitors and controls the flow of CNG from the vessel to the annulus.

Description

CROSS REFERENCE

This application claims the benefit of priority from U.S. Provisional Application No. 62/279,388, filed Jan. 15, 2016, titled “Compressed Natural Gas Artificial Gas Lift,” the entire contents of which are hereby incorporated by reference herein.

BACKGROUND

1. Field of the Invention

Various embodiments relate generally to the use of natural gas to artificially gas lift a gas lift capable or plunger-lift enabled oil well, or a packerless completion gas well for dewatering.

2. Background

Oil and gas production wells collect oil and gas from natural underground reservoirs. When a pressure within such a reservoir is insufficient to push oil (or other liquid) to the surface of a well (e.g., the wellhead) or the reservoir pressure provides an undesirably low production flow rate, well operators can use a variety of artificial lift techniques to start or increase the upward flow of liquid (e.g., oil) from the reservoir to the wellhead and production equipment. One such artificial lift technique is called artificial gas lift.

In gas lift capable wells, gas (e.g., nitrogen or natural gas) is forced downhole through a tubing-casing annulus disposed between a tubing and a casing of the well. The gas then enters the tubing (e.g., via gas lift valves (or non-valved conduits) that connect the tubing and tubing-casing annuls), which decreases a density of liquid in the tubing and causes the liquid and gas to flow upwardly from the reservoir to the wellhead for production.

SUMMARY

One or more non-limiting embodiments provide a method for gas lifting a gas lift capable well. The method includes transferring compressed natural gas from a compressed natural gas vessel of a mobile compressed natural gas storage system to a tubing-casing annulus of the gas lift capable well via a first pathway, wherein said transferring occurs without the use of a compressor. According to various non-limiting embodiments, avoiding the use of a compressor may provide a simpler, more cost effective gas lift operation.

According to one or more embodiments, during said transferring, a pressure of compressed natural gas within the vessel is higher than a pressure of compressed natural gas received by the tubing-casing annulus from the vessel.

According to one or more embodiments, a pressure of compressed natural gas received by the tubing-casing annulus from the vessel during the transferring is greater than 500 psig.

According to one or more embodiments, the method also includes: disposing an unloader in the first pathway, and using the unloader to control a pressure of the compressed natural gas being provided to the tubing-casing annulus during the transferring.

According to one or more embodiments, the unloader comprises: a high-pressure outlet configured to provide compressed natural gas to the tubing-casing annulus without the use of a compressor, the high-pressure outlet being disposed in the first pathway; and a low-pressure outlet configured to provide compressed natural gas to a gas lift compressor of the gas-lift well.

According to one or more embodiments, the high-pressure outlet is configured to provide compressed natural gas at a pressure of over 500 psig, and the low-pressure outlet is configured to provide compressed natural gas at a pressure of under 500 psig.

According to one or more embodiments, the method also includes using the unloader to control a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus during the transferring.

According to one or more embodiments, the method also includes, during the transferring, actively controlling a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus through the first pathway.

According to one or more embodiments, the method also includes monitoring, via computer, operational conditions relating to the transferring.

According to one or more embodiments, the method also includes automatically controlling, via the computer, specific parameters of the transferring based on information collected during the monitoring.

According to one or more embodiments, the transferring causes an upward flow of downhole fluid within a tubing of the well.

According to one or more embodiments, the transferring increases an upward flow of downhole liquid within a tubing of the well.

According to one or more embodiments, the transferred compressed natural gas flows down the tubing-casing annulus, enters a tubing of the gas lift capable well, and flows upwardly within the tubing.

According to one or more embodiments, the mobile compressed natural gas storage system comprises a wheeled frame that supports the vessel. According to one or more embodiments, the method further includes delivering the mobile compressed natural gas storage system to a site of the well before said transferring.

According to one or more embodiments, the method also includes transferring compressed natural gas from the vessel to the tubing-casing annulus by way of a compressor via a second fluid pathway.

According to one or more embodiments, the transferring via the second fluid pathway occurs after the transferring via the first fluid pathway.

According to one or more embodiments, the compressor receives recycle natural gas from production equipment of the well, compresses the recycle gas along with natural gas received from the vessel, and forces both recycle natural gas and natural gas received from the vessel into and down the tubing-casing annulus.

One or more non-limiting embodiments provide a compressed natural gas artificial gas lift system comprising: a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame, the compressed natural gas vessel containing compressed natural gas at a supply pressure; a gas lift capable well comprising a tubing and a tubing-casing annulus; and a first fluid pathway that connects the vessel to the tubing-casing annulus, wherein there is not a compressor disposed in the fluid passageway, and wherein the system is configured to transfer compressed natural gas from the vessel to the tubing-casing annulus via the first fluid pathway.

One or more non-limiting embodiments provide a compressed natural gas artificial gas lift system comprising: a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame; and an unloader configured to transfer compressed natural gas from the vessel to a tubing-casing annulus of a gas lift capable well via a first fluid pathway that does not include a compressor. According to various embodiments, the unloader comprises an adjustable flow rate regulator disposed in the first fluid pathway.

One or more of these and/or other aspects of various embodiments of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. In one embodiment, the structural components illustrated herein are drawn to scale. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. In addition, it should be appreciated that structural features shown or described in any one embodiment herein can be used in other embodiments as well. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

All closed-ended (e.g., between A and B) and open-ended (greater than C) ranges of values disclosed herein explicitly include all ranges that fall within or nest within such ranges. For example, a disclosed range of 1-10 is understood as also disclosing, among other ranged, 2-10, 1-9, 3-9, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of various embodiments as well as other objects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

FIG. 1 is a diagrammatic side view of a high-pressure mode of a compressed natural gas artificial gas lift system according to various embodiments;

FIG. 2 is a diagrammatic side view of a mobile compressed natural gas (CNG) unloader according to various embodiments of the system illustrated in FIG. 1; and

FIGS. 3-4 are diagrammatic side views of optional low-pressure, high-pressure, and mixed low/high-pressure modes of CNG artificial gas lift systems according to various embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a CNG artificial gas lift system 10 according to one or more embodiments. The system 10 includes a gas lift capable well 20, production equipment 150, a mobile CNG storage system 250, and a Mobile CNG unloader 400.

Gas Lift Capable Well 20

As shown in FIG. 1, the gas lift capable well 20 includes a hollow casing 30 that extends from a wellhead 35 of the well 20 at a ground surface 40 down to an underground liquid reservoir 50 (e.g., containing natural deposit of oil, water, and/or natural gas). The well 20 also includes a tubing 60 that is disposed within the casing 30 and extends downhole from the wellhead 35. A tubing-casing annulus 70 (also called a “backside”) is formed between the tubing 60 and an interior wall of the casing 30. Depending on the well configuration, a packer system 90 may be disposed at the downhole end of the annulus 70 to seal the annulus 70 from the production side, which may include both the inside of the tubing 60 and the entire casing interior below the packing 90.

According to various embodiments, the tubing 60 may comprise one or more (e.g., at least 1, at least 2, at least 3) parallel tubing strings, all of which are disposed inside the passageway in the casing 30. According to various embodiments, packing 90 is used to seal the bottom of one, some, or all such tubing strings from the annulus 70. The bottom of one or more other tubing strings can fluidly connected to the bottom of the annulus 70 (i.e., without packing). For example, the well may comprise a dual gas lift configuration (e.g., two tubing strings disposed in a single casing of a single well), as is known in the art. According to various embodiments, when multiple tubing strings are used, different ones of the tubing strings can extend to different depths.

The well 20 may comprise any type of gas lift capable well 20. In the illustrated embodiment, the tubing 60 includes a plurality of vertically-spaced gas lift valves 80 that extend between the interior of the tubing 60 and the tubing-casing annulus 70. As is known in the art, the valves 80 are configured to selectively open so as to cause gas flow from the tubing-casing annulus 70 into the tubing 60 (e.g., based on pressures in the tubing-casing annulus 70).

According to various embodiments, the interior of the tubing 60 and the tubing-casing annulus 70 are additionally and/or alternatively fluidly connected to each other at the bottom 60a of the tubing 60.

According to various alternative embodiments, the well 20 comprises a plunger-lift system or a U-tube configuration that omit packing or include unsealed packing.

Production Equipment 150

At the wellhead 35, the tubing 60 connects to production equipment 150 via a conduit 160 to facilitate transfer of produced fluids (e.g., oil, water, and/or gas, etc.) from the well 20 to the production equipment 150.

As is known in the art, such production equipment 150 may comprise a separator 180 that separates liquids and gases. In the embodiment illustrated in FIG. 1, the separated gas flows through a conduit 190 to be flared off or for further processing, collection, distribution, refining, etc. The separated liquid flows out through liquid conduit 200 for further processing, collection, distribution, refining, etc.

CNG Mobile Storage System 250

As shown in FIG. 1, the CNG mobile storage system 250 comprises a CNG vessel 260 supported by a mobile frame 270. The vessel 260 may be removably or permanently mounted to the mobile frame 270. In the illustrated embodiment, the mobile frame 270 comprises a wheeled frame 270, in particular, a road-transportable trailer 270. However, according to alternative embodiments, the mobile frame 270 may comprise other road-transportable wheeled vehicles (e.g., truck). According to alternative embodiments, the mobile frame 270 may comprise a rail-transportable vehicle (e.g., railroad car). According to alternative embodiments of the CNG mobile storage system 250, the mobile frame 270 may comprise a water-transportable mobile frame (e.g., a barge, boat, etc.). According to various alternative embodiments, the mobile frame 270 may comprise a skid that is transportable via a flat-bed truck or trailer.

According to various embodiments, the vessel 260 may comprise one or more CNG storage tanks. For example, as illustrated in FIG. 4, the vessel 260 comprises a plurality of CNG storage modules 280 that are loaded onto and removably (or permanently) supported by a 40 foot trailer 270 being pulled by a tractor 290. Each module 280 may comprise a plurality of CNG storage tanks.

According to various embodiments, the vessel 260 contains CNG at a pressure that is (1) at least 500, 1000, 1200, 1500, 2000, 2500, 3000, 3500, 4000, and/or 4500 psig (2) less than 5000, 4500, 4000, 3700, 3600, 3000, 2500, 2000, and/or 1500 psig and/or (3) within any range within such upper and lower values (e.g., between 500 and 5000 psig, between 1000 and 3600 psig). According to various embodiment, CNG is transferred into the vessel 260 at a location that is geographically separated from the wellhead 35 by at least 0.1, 0.5, 1, 2, 3, 4, 5, 7.5, 10, 15, 20, 30, 40, 50, 75, 100, 150, 200, 250, 300, 400, and/or 500 miles. The CNG mobile storage system 250 is then transported (e.g., via road, rail, water) to the site of the well 20.

According to various embodiments, the CNG mobile storage system 250 may comprise any of the mobile transport systems disclosed in WO2014/031999 A2, the entirety of which is incorporated herein by reference.

According to various embodiments, the CNG mobile storage system 250 complies with regulations for road transportation of CNG (e.g., DOT 49 CFR, DOT SP 15136, ASME B31.3, and/or API RP 500/505).

According to various embodiments, the CNG mobile storage system 250 is 40 feet long.

Mobile CNG Unloader 400

As shown in FIGS. 1 and 2, a CNG Unloader connects the vessel 260 to the well 20 to control the flow of CNG from the vessel 260 to the well 20.

The unloader 400 comprises a mobile frame 410 and unloader equipment 420. The mobile frame 410 may be similar to or identical to any of the mobile frames 270 discussed above with respect to the CNG mobile storage system 250 (e.g., a trailer, skid, rail car, barge, boat etc.). As illustrated in FIG. 4, the mobile frame 410 may comprise a road-transportable, wheeled trailer that is 20 feet long or less according to various embodiments. According to various embodiments, the CNG Unloader 400 complies with ASME B31.3 and/or API RP 500/505.

According to various embodiments, the unloader's mobile frame 410 is eliminated altogether, and the unloader equipment 420 is supported by (removably or permanently) the CNG mobile storage system's mobile frame 270 so that the vessel 260 and unloader equipment 420 are transportable together as a unit to and from the well 20 site. User accommodations, discussed in greater detail below, may also be provided on the mobile frame 270.

As shown in FIG. 2, the unloader equipment 420 comprises an inlet conduit 430 (e.g., a flexible hose, a series of rigid pipes, etc.) and inlet connector 440 configured to detachably connect the unloader equipment 420 to the vessel 260 to receive CNG from the vessel 260. The unloader equipment 420 comprises a high pressure outlet conduit 450 (e.g., a flexible hose, a series of rigid pipes, etc.) and outlet connector 460 configured to connect the unloader equipment 420 to the tubing-casing annulus 70. As shown in FIG. 1, the connector 460 releasably mates with a tubing-casing inlet connector/port 470 at the wellhead 35. According to various embodiments, the port 470 taps into the blowoff preventer at the wellhead 35 and fluidly connects to the tubing-casing annulus 70. CNG flowing from the inlet conduit 430 to the outlet conduit 450 passes sequentially through various components of the unloader equipment 420.

According to various embodiments, the unloader equipment 420 includes a pressure regulator 480 that controls and reduces the pressure of CNG received from the vessel 260 so as to provide CNG to the tubing-casing annulus 70 at a pressure that is lower than a pressure within the vessel 260. According to various embodiments, the pressure regulator 480 is manually adjustable by a user so that the user can select the pressure at which CNG is provided to the tubing-casing annulus 70.

According to alternative embodiments, the pressure regulator 480 is automated (e.g., via mechanical and/or electronic automation). For example, the pressure regulator may be computer controlled (e.g., via the below-discussed computer 580).

According to various embodiments, the unloader equipment 420 includes a CNG meter 490 to meter the amount (e.g., in terms of mass and/or volume) of CNG that is transferred from the vessel 260 to the tubing-casing annulus 70. The meter 490 may comprise any suitable meter (e.g., an orifice plate meter).

According to various embodiments, the unloader equipment 420 includes flow rate control equipment 500 (e.g., a manual or automatic flow rate control valve, a manual or automated choke valve, a manual or automatic adjustable orifice plate). According to various embodiments, the flow control equipment 500 is manually adjustable by a user so that the user can select the flow rate (e.g., in terms of mass and/or volumetric rate) at which CNG is provided from the vessel 260 to the tubing-casing annulus 70. According to alternative embodiments, the flow rate control equipment 500 is automatically controlled (e.g., by the below-discussed computer 580).

The flow control equipment 500 may be configured to stop CNG flow entirely. However, additional shut-off valve(s) may also be positioned anywhere along the flow path between the vessel 260 and the tubing-casing annulus 70 (e.g., at the outlet port of the vessel 260, at the inlet connector 470 of the wellhead, in or at the end(s) of the conduits 430, 450).

According to various embodiments, the unloader equipment 420 includes a heater 510. According to various embodiments, the heater 510 is powered by natural gas that is supplied from the vessel 260. The heater 510 may include a user-selectable temperature input, and may automatically heat the CNG so as to deliver the CNG to the tubing-casing annulus 70 at a desired temperature or within a desired temperature range. The heater 510 may be useful in situations where a large pressure drop from the high-pressure vessel 260 would otherwise cause excessive Joule-Thompson cooling of the CNG. For example, the heater 510 may prevent cryogenic conditions along the flow path of the CNG.

Additionally and/or alternatively, the unloader equipment 420 may comprise additional and/or alternative components 520, for example, any of the unloader components described in WO2014/031999 A2, the entirety of which is incorporated herein by reference.

According to various embodiments, the unloader equipment 420 includes a manually-actuatable distribution control valve 530 that can be manually controlled by a user of the unloader 400 to selectively and alternatively deliver CNG to:

• • i) the high-pressure conduit 450 and connector 460 (e.g., providing outlet pressures above 500 psig),
  • ii) a low-pressure conduit 1070 and connector 1080, which is discussed in greater detail below (e.g., providing outlet pressures of under 200 psig), and/or
  • iii) a medium-pressure conduit 1075 and connector 1085, which is discussed in greater detail below (e.g., providing outlet pressures of 200-500 psig).

According to various embodiments, the valve 530 is a switching valve 530 that enables only one of the conduits 450, 1070, 1075 and pressure modes to be used at any given time.

According to alternative embodiments, the valve 530 comprises a plurality of shut-off valves, one for each conduit 450, 1070, 1075 and pressure mode. The individual shut-off valves are connected to appropriate points within the CNG flow path(s) in the unloader 400. Separate pressure regulators 480, flow control equipment 500, and other unloader equipment 420 may be provided for each of the low, medium, and/or high pressure conduits 450, 1070, 1075 and pressure modes so as to facilitate simultaneous transferring of CNG from the vessel 260 to the well 20 via the unloader 400 at different pressures via parallel conduits 450, 1070, 1075 and connectors 460, 1080, 1085.

According to various embodiments, the unloader 400 may be configured to unload at only one of the pressure ranges (e.g., high, medium, low), in which case the valve 530 may be omitted, and all conduits may be configured for the designed outlet pressure range for the unloader.

According to various embodiments, the unloader equipment 420 includes a variety of pressure sensors 540 and temperature sensors 550 that measure CNG conditions at various points in the system 10 (e.g., the CNG being received by the unloader 400, the CNG being delivered at the wellhead 35 to the tubing-casing annulus 70). In FIG. 2, the sensors 540,550 are illustrated as being disposed at the connectors 440, 460. However, the sensors 540, 550 may alternatively be disposed at any other suitable point along the flow path of the CNG from the vessel 260 to the tubing-casing annulus 70.

As shown in FIG. 1, according to various embodiments, the unloader 400 includes a check valve 560 in the conduit 450 (or otherwise disposed along the flow path between the vessel 260, unloader 400, and tubing-casing annulus 70) to prevent backflow from the tubing-casing annulus 70 toward or into the unloader 400 and/or vessel 260.

According to various embodiments, the unloader equipment 420 includes a computer 580 (e.g., a PC, laptop, tablet, programmable controller, or other computer) that is operatively connected to the sensors 540, 550, other equipment 420 (e.g., pressure regulator 480, CNG meter 490, flow control equipment 500, heater 510), and/or other sensors in the system 10 (e.g., flow rate and/or pressure sensors of the production equipment 150; pressure sensors in the well 20 that measure uphole, downhole, and/or midhole pressures in the tubing 60 and/or the tubing-casing annulus 70; flow rate sensors in the well 20 that measure uphole, downhole, and/or midhole flow rates in the tubing 60 and/or the tubing-casing annulus 70) to track and record the operational characteristics of the system 10 during gas lift operation. The computer 580 may connect to a data transmission system (e.g., internet, WIFI, SCADA, LAN, WAN, Ethernet, digital or analog connection, phone connection, cellular network) to provide (1) a live feed of such operational characteristics of the gas lift system 10 and/or (2) provide historical data for such operational characteristics for past operation of the gas lift system 10.

According to various embodiments, the computer 580 may calculate optimal pressure and flow rate using appropriate user inputs (tubing 60 size, casing 30 size, packer 90 depth, tubing 60 depth, etc.). Such user inputs may additionally or alternatively include well-type-specific information: (e.g., gas lift valves size and depth for gas lift wells 20, information particular to a u-tube configuration well 20, information particular to a plunger lift well 20). According to various embodiments, this reduces the setup and interaction needed by the customer and may improve production while the lift process is occurring.

While the individual components of unloader equipment 480, 490, 500, 510, 520, 530 are illustrated in FIG. 2 in a particular sequential order, the components may alternatively be arranged in any other order without deviating from the scope of the invention.

While a variety of exemplary unloader equipment 420 is illustrated, any component(s) of the unloader 400 may be eliminated or altered without deviating from the scope of the invention.

User Accommodations

According to various embodiments, user accommodations (e.g., a kitchen, bed, sleeping quarters, etc.) may also be provided on the mobile frame 270 and/or 410. Such user accommodations may comprise any type of accommodations that are provided in an RV or long-haul tractor. The user accommodations facilitate the user's extended well-site stay during the use of the CNG mobile storage system 250 and unloader 400 to gas lift the well 20. According to various embodiments, initially lifting the well 20 may require anywhere from minutes to days of artificial gas lift (depending on the reservoir 50 pressure, depth, gas/liquid content or proportion, etc.), so the user accommodations facilitate the user's extended well-site stay during the operation.

Operation of the System 10 in High-Pressure Mode

Hereinafter, operation of the system 10 in a high-pressure mode is described with reference to FIG. 1. The CNG mobile storage system 250 and unloader 400 may be used to (1) initially lift the well 20 (i.e., start the flow of liquids from the reservoir 50 to the production equipment 150 via the tubing 60), and/or (2) increase the rate of production of liquids (e.g., oil) from the reservoir 50 to the production equipment 150 via the tubing 60 for ongoing artificial gas lift.

The CNG mobile storage system 250 and unloader 400 are delivered (e.g., via tractor/truck) to the well 20 site. According to various embodiments, the system 250 and unloader 400 are positioned so as to be within 600, 500, 400, 300, 200, 100, and/or 50 feet of the wellhead 35. According to various embodiments, the system 250 and/or unloader 400 is/are positioned so as to be at least 25, 50, 75, 100, 150, 200, 250, 300, 400, and/or 450 feet from the wellhead 35.

The user(s) connects the connector 440 to the vessel 260 and connects the connector 460 to the inlet connector 470 of the tubing-casing annulus 70. The valve 530 (if present) is set to provide CNG flow to the high-pressure conduit 450 and connector 460. According to various embodiments, the user may be one person or multiple people. Various actions (e.g., operating the unloader 400) may be carried out by a user affiliated with the unloader 400. Various other actions (e.g., connecting the unloader 400 to the well head 35) may be carried out by the operator of the well 20.

The user then opens any shut-off valves and controls the unloader equipment 420 so as to transfer CNG from the vessel 260 to the tubing-casing annulus 70 along a first pathway that includes: the vessel 260, the connector 440, the conduit 430, the unloader equipment 420, the valve 560, the conduit 450, the connector 460, and the inlet connector 470.

As shown in FIG. 1, this transfer from the vessel 260 to the tubing-casing annulus 70 occurs without the use of a compressor or any other driver that can forcibly move gas (e.g., a blower). According to various embodiments, the high-pressure mode of the system 10 (as illustrated in FIG. 1) is simpler, and/or less expensive than artificial gas lift systems that rely on a compressor to compress gas before transferring gas into the tubing-casing annulus.

The user monitors operational parameters of the system 10 and controls the operational parameters (e.g., flow rate, pressure, etc.) of the unloader 400 so as to cause the transferred CNG to gas lift liquid from the reservoir 50 to the production equipment 150 via the tubing 60. The user may vary the flow rate, pressure, etc. during the transfer (e.g., varying the flow rate or pressure up and down). According to various embodiments, the user manipulates the gas lift operational parameters to maximize a production flow rate of liquids from the reservoir 50 to the production equipment 150.

According to various embodiments, as illustrated in FIG. 1, the user causes the CNG mobile storage system 250 and CNG mobile unloader 400 to deliver CNG to the tubing-casing annulus 70 via the first pathway (a high pressure delivery pathway) at a delivery pressure (i.e., at the inlet into the tubing-casing annulus 70) that is (1) at least 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2250, 2500, 2750, 3000, 3500, 3600, 3750, 4000, and/or 4500 psig, (2) less than 6000, 5000, 4500, 4000, 3700, 3600, 3000, 2500, 2000, 1500, 1400, 1300, 1200, 1100, 1000, 900, 800, 700, and/or 600 psig, and/or (3) in any range within such upper and lower values (e.g., between 300 and 6000 psig, between 500 and 1500 psig). According to various embodiments, as illustrated in FIG. 1, during the transferring of CNG from the vessel 260 to the tubing-casing annulus 70, a pressure of CNG within the vessel 260 is higher than a pressure of CNG received by the tubing-casing annulus 70 from the vessel 260.

According to various embodiments, the transfer of CNG from the CNG mobile storage system 250 to the tubing-casing annulus 70 (1) starts an upward flow of downhole liquid within the tubing 60 to lift a well, (2) increases an upward production flow rate of downhole liquid within the tubing 60, (3) causes CNG received by the tubing-casing annulus during the transferring to flow down the tubing-casing annulus 70, enter the tubing 60, and flow upwardly within the tubing 60 to the production equipment 150.

According to various embodiments, CNG from the CNG mobile storage system 250 is used to initially lift the well 20. Once the well 20 begins to produce naturally, artificial gas lift using CNG from the CNG mobile storage system 250 is stopped.

Additionally and/or alternatively, CNG from the CNG mobile storage system 250 is used to provide continuous artificial lift to a producing well 20 to increase the production flow rate of liquids from the reservoir 50 to the production equipment 150.

Compressor-Equipped Gas Lift System 1010

FIG. 3 illustrates a CNG artificial gas lift system 1010, which is generally similar or identical to the above-discussed system 10, except as discussed below. Accordingly, a redundant description of identical or substantially similar features is omitted. Unless otherwise stated, the system 1010 includes all of the features of the system 10.

As shown in FIG. 3, a gas recycle conduit 1030 replaces the flare conduit 190 of the system 10, and directs separated production gas to an inlet 1040a of a compressor 1040. An outlet 1040b of the compressor connects via a conduit 1050 to the tubing-casing annulus 70. As a result, gas that is produced by the well 20 and separated in the production equipment 150 is directed through the conduit 1030 to the compressor 1040. The compressor 1040 compresses the gas and transfers it into the tubing-casing annulus 70 via the conduit 1050 to facilitate gas lifting of additional liquids.

As shown in FIG. 3, a three-way joint 1060 (e.g., Y or T joint) is disposed in the conduit 1030 upstream from the compressor 1040. As shown in FIG. 2, the unloader equipment 420 includes a low-pressure conduit 1070 that leads from the valve 530 to a low-pressure connector 1080. As shown in FIG. 3, the connector 1080 is connected to a mating connector 1090 on one of the ends of the three-way joint 1060. As shown in FIG. 3, a check valve 560 is disposed in the conduit 1070.

According to various alternative embodiments, the check valve 560 in the conduit 450 and check valve 560 in the conduit 1070 may be combined into a single check valve that connects at its upstream end to the unloader 400 and branches out at its downstream end into the conduits 450, 1070 with appropriate valves in each downstream branch. The system can alternate between low pressure delivery to the compressor 1040 and high pressure delivery to the wellhead 35.

As shown in FIG. 2, the unloader equipment 420 includes a medium-pressure conduit 1075 that leads from the valve 530 to a medium-pressure connector 1085. The medium-pressure connector 1085 can connect to the connector 1090 on one of the ends of the three-way joint 1060.

As shown in FIG. 3, a three-way joint 1100 may optionally be disposed in the conduit 1050 downstream from the compressor (i.e., at an outlet side of the compressor). A high-pressure connector 1110 that is similar or identical to the connector 460 may connect to one of the ends of the three-way joint 1100. As shown in FIG. 3, the high-pressure connector 460 of the unloader 400 may be connected to the connector 1110.

As shown in FIG. 3, a surge conduit 1120 extends from the recycle gas conduit 1030 back to the vessel 260 of the CNG mobile storage system 250 so that the CNG mobile storage system 250 can act as a buffer vessel to absorb surge recycled gas flow in the conduit 1030. The conduit 1120 connects to the vessel 260 via suitable valves and connectors (e.g., via a branch connector off of the connector 400 (see FIG. 1).

As shown in FIG. 3, the surge conduit 1120 can also be used to collect excess natural gas (e.g., recycled lift gas and/or natural gas originating from the reservoir 50) and store it in the vessel 260 for later use (rather than flaring off such gas). For example, excess natural gas produced by the well may be collected in the vessel 260 when the gas lift functionality of the system 1010 is not being used (e.g., when sufficient flow exists without gas lift). Such excess natural gas flowing through the conduit 1120 to the vessel 260 can be dried. Additionally and/or alternatively, methanol may be injected into the natural gas flowing into the vessel 260 via the conduit 1120 so as to prevent hydrates from forming inside the vessel 260. The excess natural gas being collected in the vessel 260 can then be used to lift the well and/or power the system 1010 (e.g., the compressor 1040) as desired (e.g., when insufficient gas is flowing from the wellhead).

Operation of the System 1010 in Low-Pressure or Medium Pressure Mode

Hereinafter, operation of the system 1010 in low-pressure mode is described with reference to FIG. 3.

If the well illustrated in FIG. 3 is not flowing, or if the production flow provides insufficient recycle gas, then insufficient recycle gas may be available to gas lift the well 20. In such circumstances, the CNG mobile storage system 250 and unloader 400 may be used to provide enough supplemental natural gas to initially lift the well 20 and/or increase the rate of production of liquids from the reservoir 50.

The CNG mobile storage system 250 and unloader 400 are delivered (e.g., via tractor/truck) to the well 20 site as described above with respect to the system 10.

The user connects the connector 440 to the vessel 260 (see FIG. 1) and connects the connector 1080 to the connector 1090.

As shown in FIG. 3, the user then opens any shut-off valves and controls the unloader equipment 420 so as to transfer CNG from the vessel 260 to the tubing-casing annulus 70 along a second pathway that includes: the vessel 260, the connector 440, the conduit 430, the unloader equipment 420, the valve 530, the conduit 1070, the connector 1080, the connector 1090, the three-way joint 1060, the compressor 1040, and the conduit 1050.

The user controls the pressure 480 to provide low-pressure CNG to the inlet 1040a of the compressor 1040. According to various embodiments, CNG is provided to the compressor 1040 from the vessel 260 at a compressor 1040 inlet 1040a pressure of (1) less than 600, 500, 450, 400, 350, 300, 250, 200, 150, 100, 75, and/or 50 psig, (2) more than 5, 10, 25, 50, 75, 100, 150, 200, 250, 300 psig, and/or (2) within any range between any two such upper and lower values (e.g., between 5 and 500 psig).

If the CNG pressure provided to the compressor 1040 is under 200 psig, the mode may be considered low-pressure according to various embodiments. If the CNG pressure provided to the compressor 1040 is between 200 and 600 psig, the mode may be considered medium pressure. Different types of conduits, valving, connects, etc. may be used depending on the pressure range for the CNG provided to the compressor 1040. For example, low-pressure flexible hoses may be used for low-pressure (e.g., 5-200 psig) delivery (e.g., via conduit 1070 and connector 1080). Medium pressure equipment (e.g., conduit 1075, connector 1085) may be used for medium-pressure delivery. High pressure equipment (e.g., rigid pipes, valves, connectors, etc. configured to accommodate high CNG pressure (e.g., pressure over 600 psig)) may be used for high-pressure delivery (e.g., via conduit 450 and connector 460).

The compressor 1040 then compresses the CNG from the vessel 260 (as well as recycle gas from the conduit 1030 if the well 20 is producing recycle gas) to gas lift pressures and delivers the compressed gas to the tubing-casing annulus 70 via the conduit 1050. The CNG mobile storage system 250 and unloader 400 thereby facilitate initial lifting and/or continuous artificial gas lift for compressor-equipped gas lift wells that have no recycle gas or recycle gas with insufficient pressure and/or flow rate.

Operation of the System 1010 in High-Pressure Mode

As shown in FIG. 3, the CNG mobile storage system 250 and unloader 400 may alternatively be used in a high-pressure mode with compressor-equipped wells. The CNG mobile storage system 250 and unloader 400 may operate in the same manner as described above in connection with the system 10. In particular, the CNG mobile storage system 250 and unloader 400 bypasses the compressor 1040 and connects the unloader's high pressure conduit 450 and connector 460 to the conduit 1050 downstream from the compressor 1040 (or to a separate wellhead port like the connector 470 illustrated in FIG. 1). According to various embodiments, this high-pressure, compressor-bypass route can be used to surge high volume, high pressure CNG into the tubing-casing annulus 70 as flow rates that are higher than is possible via the compressor 1040.

The user may switch between high-pressure direct (compressor bypass) delivery and low-pressure compressor-based delivery by actuating the valve 530 as desired and appropriately modifying the pressure regulator to provide appropriate pressure CNG (e.g., high pressure CNG for direct injection, low pressure CNG for injection into the compressor 1040). According to various embodiments, the user initially uses the CNG mobile storage system 250 and unloader 400 in the high-pressure mode (i.e., directly transferring high pressure CNG to the tubing-casing annulus 70 via the first pathway without use of the compressor), for example to initially lift the well and start production, and subsequently switches to the low-pressure mode that transfers CNG to the tubing-casing 70 via the second pathway and compressor 1040, and also relies on recycle gas from the flowing well. The low-pressure mode reduces the well system's dependence on CNG from the CNG mobile storage system 250 by taking advantage of gas produced by the well 20 (including gas that was initially provided by the CNG vessel 260 and already traversed the gas-lift path to the production equipment 150).

According to various embodiments, the CNG mobile storage system 250 and unloader 400 may be used temporarily to lift a well 20. Once liquids start to flow from the reservoir 50 to the production equipment 150 via the tubing 60, the flow may be sustainable, such that further artificial gas lift can be stopped. If so, the CNG mobile storage system 250 and unloader 400 can be removed from the well 20 site after lifting for use at a different well 20 site.

Alternatively, the CNG mobile storage system 250 and unloader 400 may be continuously used in a producing well 20 to provide extended (e.g., continuous) artificial gas lift in order to increase a liquid (e.g., oil) production rate of the well 20. Such extended (e.g., continuous) artificial gas lift is well suited for wells in which natural reservoir pressure is insufficient to provide natural lift and/or the natural lift results in an undesirably low production rate.

According to various embodiments, the CNG mobile storage system 250 and unloader 400 may be kept at the well site for extended periods of time, even when not being actively used for artificial gas lift. The onsite availability of the CNG mobile storage system 250 and unloader 400, according to various embodiments, may provide (1) cost effective and responsive unplanned lifting service, and/or (2) makeup gas when/if the recycle gas system fails (e.g., if the separator 180 slugs with fluid), thus starving the compressor 1040 of gas, regardless of gas production rates from the well 20. The available onsite gas lift service provided by the CNG mobile storage system 250 and unloader 400 may keep the compressor 1040 running and avoid trips on low suction pressure.

According to various embodiments, a single CNG mobile storage system 250 provides enough CNG to initially lift the well 20. According to alternative embodiments, multiple CNG mobile storage systems 250 are required to provide sufficient gas to initially lift a well. Where multiple CNG mobile storage systems 250 are needed to initially lift a well 20 (or where continuous artificial lift is desirable using CNG from a CNG mobile storage system 250), a fresh CNG mobile storage system 250 may be delivered to replace a depleted CNG mobile storage systems 250 as desired. The unloader 400 may include multiple inlet connectors 440 so that a fresh CNG mobile storage system 250 can be connected to the unloader 400 before a depleted CNG mobile storage system 250 is disconnected. Appropriate check valves and other shut-off valving may be included to facilitate a continuous supply of CNG to the unloader 400 during switch off between depleted and fresh CNG mobile storage systems 250. The direct swap systems disclosed in WO2014/031999 A2 may be used to facilitate swapping of the fresh and depleted CNG mobile storage systems 250.

As used herein, “depleted” means depleted to an extent, and does not require complete evacuation of all CNG within a CNG mobile storage system 250. According to various embodiments, a CNG mobile storage system 250 may be considered depleted when the vessel 260 pressure falls below a predetermined threshold (e.g., 2000, 1750, 1700, 1600, 1500, 1400, 1300, 1200, 1100, 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 75, 50, 25 psig).

According to various embodiments, the passageways, fluid paths, and other conduits described herein may comprise any suitable conduit (e.g., rigid or flexible piping, concrete enclosed passage, annular passageways between nested conduits). The various connectors may comprise any suitable connectors for the temperature, flow rate, and/or pressure designed to flow through such connectors. The unloader 400 may include a variety of adaptors to accommodate connecting the unloader 400 to CNG systems 250, vessels 260, and well 20 connectors of different types and models.

According to various embodiments, the use of the CNG mobile storage system 250 to artificially lift the well 20 may have various non-limiting benefits. According to one or more non-limiting embodiments, the use of CNG reduces or prevents detrimental oxygen introduction into the well 20. Various nitrogen lifting procedures (e.g., the use of a filter to obtain nitrogen from ambient air) result in significant oxygen being entrained with the nitrogen and causing explosion possibilities and/or corrosion of metal downhole or production equipment.

According to one or more non-limiting embodiments, the use of CNG reduces or avoids the step of purging nitrogen from the produced fluid (e.g., a mixture of gas and liquid) before commencing production, as is required for nitrogen-based gas lifting. Such purging frequently results in the waste of valuable hydrocarbons (e.g., natural gas) that are produced from the well but are flared off as part of the nitrogen purge step.

According to various embodiments, use of the CNG mobile storage system 250 to gas lift a well 20 creates little or no disruption to the operation of the well 20, and can be used to gas lift the well 20 without interruption in well 20 production (if the well 20 is already producing prior to use of the CNG mobile storage system 250 for artificial gas lift).

The foregoing illustrated embodiments are provided to illustrate the structural and functional principles of various embodiments and are not intended to be limiting. To the contrary, the principles of the present invention are intended to encompass any and all changes, alterations and/or substitutions thereof (e.g., an alterations within the spirit and scope of the following claims).

Claims

1. A method for gas lifting a gas lift capable well, the method comprising:

transferring compressed natural gas from a compressed natural gas vessel of a mobile compressed natural gas storage system to a tubing-casing annulus of the gas lift capable well via a first pathway, wherein said transferring occurs without the use of a compressor.

2. The method of claim 1, wherein, during said transferring, a pressure of compressed natural gas within the vessel is higher than a pressure of compressed natural gas received by the tubing-casing annulus from the vessel.

3. The method of claim 2, wherein a pressure of compressed natural gas received by the tubing-casing annulus from the vessel during the transferring is greater than 500 psig.

4. The method of claim 2, further comprising:

disposing an unloader in the first pathway; and

using the unloader to control a pressure of the compressed natural gas being provided to the tubing-casing annulus during the transferring.

5. The method of claim 4, wherein the unloader comprises:

a high-pressure outlet configured to provide compressed natural gas to the tubing-casing annulus without the use of a compressor, the high-pressure outlet being disposed in the first pathway, and

a low-pressure outlet configured to provide compressed natural gas to a gas lift compressor of the gas-lift well.

6. The method of claim 5, wherein the high-pressure outlet is configured to provide compressed natural gas at a pressure of over 500 psig, and the low-pressure outlet is configured to provide compressed natural gas at a pressure of under 500 psig.

7. The method of claim 4, further comprising using the unloader to control a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus during the transferring.

8. The method of claim 1, further comprising, during the transferring, actively controlling a flow rate of the compressed natural gas from the vessel to the tubing-casing annulus through the first pathway.

9. The method of claim 1, further comprising monitoring, via computer, operational conditions relating to the transferring.

10. The method of claim 9, further comprising automatically controlling via the computer specific parameters of the transferring based on information collected during the monitoring.

11. The method of claim 1, wherein the transferring causes an upward flow of downhole fluid within a tubing of the well.

12. The method of claim 1, wherein the transferring increases an upward flow of downhole liquid within a tubing of the well.

13. The method of claim 1, wherein the transferred compressed natural gas flows down the tubing-casing annulus, enters a tubing of the gas lift capable well, and flows upwardly within the tubing.

14. The method of claim 1, wherein:

the mobile compressed natural gas storage system comprises a wheeled frame that supports the vessel; and

the method further comprises delivering the mobile compressed natural gas storage system to a site of the well before said transferring.

15. The method of claim 1, further comprising:

transferring compressed natural gas from the vessel to the tubing-casing annulus by way of a compressor via a second fluid pathway.

16. The method of claim 15, wherein the transferring via the second fluid pathway occurs after the transferring via the first fluid pathway.

17. The method of claim 15, wherein the compressor receives recycle natural gas from production equipment of the well, compresses the recycle gas along with natural gas received from the vessel, and forces both recycle natural gas and natural gas received from the vessel into and down the tubing-casing annulus.

18. A compressed natural gas artificial gas lift system comprising:

a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame, the compressed natural gas vessel containing compressed natural gas at a supply pressure;

a gas lift capable well comprising a tubing and a tubing-casing annulus; and

a first fluid pathway that connects the vessel to the tubing-casing annulus,

wherein there is not a compressor disposed in the fluid passageway, and

wherein the system is configured to transfer compressed natural gas from the vessel to the tubing-casing annulus via the first fluid pathway.

19. A compressed natural gas artificial gas lift system comprising:

a mobile compressed natural gas storage system including a compressed natural gas vessel supported by a wheeled frame; and

an unloader configured to transfer compressed natural gas from the vessel to a tubing-casing annulus of a gas lift capable well via a first fluid pathway that does not include a compressor,

wherein the unloader comprises an adjustable flow rate regulator disposed in the first fluid pathway.