WO2017007523A1

WO2017007523A1 - Modular configurable compression systems and methods

Info

Publication number: WO2017007523A1
Application number: PCT/US2016/027521
Authority: WO
Inventors: Dag O. CALAFELL
Original assignee: Exxonmobil Upstream Research Company
Priority date: 2015-07-08
Filing date: 2016-04-14
Publication date: 2017-01-12
Also published as: US20170009774A1; EP3320214A1

Abstract

Systems, methods and apparatuses for matching an operation range to a reservoir depletion condition are disclosed herein. An embodiment provides a modular compression system for matching an operation range to a reservoir depletion condition. The modular compression system includes a compressor arranged to compress a gas, a motor or other driver coupled to the compressor and configured to provide power to the compressor, and a pressure casing surrounding the compressor and the motor. The modular compression system further includes a modular motor assembly configured to be selectively attachable and mechanically coupled to the compressor and the pressure casing. The modular motor assembly is arranged to provide supplemental power to the compressor to change the capacity of the modular compression system to compress the gas.

Description

MODULAR CONFIGURABLE COMPRESSION SYSTEMS AND METHODS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of United States Patent Application 62/190,095 filed July 8, 2015 entitled MODULAR CONFIGURABLE COMPRESSION SYSTEMS AND METHODS, the entirety of which is incorporated by reference herein.

FIELD OF THE INVENTION

[0002] This disclosure relates to compression systems and methods for processing gas or liquid streams. More particularly, this disclosure relates to configuring and reconfiguring compression systems using modular components, such as modular motor assemblies and modular compression assemblies, to adjust compression systems to process gas streams as compression requirements change, for example, in oil and gas production as hydrocarbon reservoirs are depleted and gas pressure decreases, or injection requirements change. Compression systems may further include modular turbines. This disclosure similarly relates to configuring and reconfiguring pumps using modular components.

BACKGROUND

[0003] This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

[0004] Centrifugal compressors are applied in oil and gas production to compress wellhead gases for transportation or treatment. Compressors increase gas pressure from a low suction condition to a higher discharge pressure. Some conventional compressors include one or more centrifugal impellers attached to a shaft. The impellers and shaft are rotated by a driver that provides power to compress the gas and overcome thermodynamic and mechanical inefficiencies. Conventional compressor design and staging typically results in fixed geometries that create a restricted flow range and a limited pressure rise.

[0005] Staging includes selection of various compressor parameters, such as the impeller geometry (e.g., the number and shape of the passages), the number of impellers, gas diffusion passages after each impeller, the speed of shaft rotation, and any cooling requirements. Staging options can be constrained by mechanical and dynamic considerations, including, as examples, forces exerted on the impeller, shaft, bearings, and seals that are produced by the gas compression process or static and dynamic forces.

[0006] Conventional staging selection results in a specific stable operating range of pressures in which gas will flow from inlet to outlet. In many scenarios, as the flow decreases the pressure rise increases. However, if flow rate is too low the gas will stop flowing. On the other hand, if flow rate is too high the gas will not be compressed sufficiently and the high mass flow rate may overload the compressor mechanical design or driver capabilities. These issues can limit the inlet conditions that any given unit or specific design can process.

[0007] This characteristic in centrifugal machinery converts high dynamic forces (impeller rotation combined with impeller outside diameter) to higher pressures. In some conventional embodiments, this conversion is performed by imparting energy to the gas (manifested by the high velocity gas exiting the outside diameter of the impeller) and then converting it to higher pressures by reducing the gas velocity through a gas diffusion process.

[0008] A narrow operating flow range is insufficient to meet the variations in a typical oil and gas production over the entire oil field life as the oil field matures and declines. Thus, at some point, if it is desired to keep harvesting a field, changes should be made to the compressor to accommodate changing field conditions so the gas can still be produced. Those changes can affect, as examples, the number of impellers, size of the impellers, physical size of the compressor casing, and the horsepower requirements from the installed driver.

[0009] There are various options to respond to the changing field requirements. Some common conventional options are as follows: (1) restage the compressor rotor within the compressor casing dimensional capacity and within the existing driver power requirements; (2) upgrade the driver horsepower capabilities within the driver casing capabilities; and/or (3) consider new compressor or driver sizes and types. Upgrades to the compressor or to the driver may not be available or sufficient to meet the changed compression duty. In order to modify or install new compressor and/or drivers, a substantial amount of production can be lost due to system downtime. This potential loss enters into decisions whether to modify, replace, or do- nothing to the compression system. In some circumstances, the economics of oil and gas production may preclude any opportunity to rerate, restage, repower, and/or replace the compression system. In that case, oil and gas production may cease before a reservoir is fully depleted due to the limitations of the installed compression equipment. [0010] Fig. 1 illustrates various representative examples of field flow rate declines experienced by a given gas reservoir or field. The x-axis is in units of months, and the y-axis is in units of thousands of barrels per day (a flow rate). According to Fig. 1, a given field declines in a gradual manner. The various curves are examples of flow rate decreases over time, and are intended to be illustrative and not exhaustive. For example, curve 110 represents a linear decrease in flow rate, and curves 120, 130, and 140 represent an exponential decrease. Furthermore, flow rate on the y-axis is a proxy for reservoir pressure. Therefore, the reservoir pressure typically declines in a like manner.

[0011] As explained above, conventional compression systems are fixed and can accommodate only small variations in inlet pressure and discharge pressure. As a result, conventional compression systems may be sized to accommodate a limited range of pressures exhibited by a field. Because of the capital costs and lost production associated with compressor restaging and/or rerates, in some embodiments, the depletion curve is conventionally divided into two or more specific pressure regions where compressor restaging is likely to occur.

[0012] Within each pressure region, the compressor inlet pressure is typically set at a value lower than the reservoir pressure (otherwise the gas would not flow from the reservoir to the compressor), which implies that excess pressure energy of the reservoir is being throttled at each well. Thus, a compressor replaces that energy while compressing the gas to an original design discharge pressure required for the processing or transporting the gas. A substitution of the existing reservoir drive pressure with mechanical compression energy is a large operating cost and a loss of the resource (because the energy typically comes from consuming a portion of the resource). Thus, there is a need for compression systems that are able to match reservoir depletion curves in a more efficient and cost-effective manner.

SUMMARY

[0013] Modular pressure casings can be interconnected. These casings can be fitted internally with either a driver, e.g., an electric motor, or a driven piece of machinery, e.g., compressor or pump. These internal components can be connected through various means to deliver power from one or more drivers to one or more driven machinery elements. External or internal features of these casings can ensure that the required machinery alignment is achieved without relying on multiple external support members. Example configurations consistent with this principle allow for extending the length of the machinery train via a cantilever arrangement on both ends of the interconnected modular pressure casings. Gas passages to convey fluid between/among the modular casings can be incorporated in the casing. Separation elements, e.g., in-line or cyclonic separators, and cooling elements can also form part of the casing in a standardized arrangement. Rerating the compressor or pump service may be performed in a straightforward manner by combining the appropriate modular, interchangeable pressure casings with driver and driven elements.

[0014] An embodiment provides a modular compression system that includes a compressor arranged to compress a gas, a driving element coupled to the compressor and configured to provide power to the compressor, and a pressure casing that surrounds the compressor and the driving element. The modular compression system further includes a modular motor assembly configured to be selectively attachable and coupled to the compressor mechanically or by other means such as fluid or magnetically, and the pressure casing. The modular motor assembly is arranged to provide supplemental power to the compressor to change the capacity of the modular compression system to compress the gas.

[0015] Another embodiment provides a method for processing a gas stream using a modular compression system. The modular compression system includes a driving element mechanically coupled to a compressor by at least one shaft. The modular compression system further includes a pressure casing surrounding the driving element and the compressor. The method includes removing a portion of the pressure casing to allow a modular motor assembly to couple to the compression system, and connecting the modular motor to the compression system to boost drive power supplied to the compressor.

[0016] Another embodiment provides a modular apparatus. The modular apparatus includes a modular motor assembly configured to selectively attach to and provide supplemental power to a compression system, wherein the compression system includes a first motor. The modular motor assembly includes a shaft configured to couple to the compression system, a second motor coupled the shaft and configured to provide the supplemental power, and an interface structure configured to be selectively affixed to the compression system to attach the modular motor assembly to the compression system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The advantages of the present techniques are better understood by referring to the following detailed description and the attached drawings, in which:

[0018] Fig. 1 illustrates various representative examples of field declines a given gas reservoir or field may experience;

[0019] Figs. 2A and 2B are different perspective views of an exemplary embodiment of a conventional system 200 for compressing hydrocarbon gas;

[0020] Fig. 3 illustrates an exemplary embodiment of a compression system for compressing hydrocarbon gas;

[0021] Fig. 4 illustrates an exemplary embodiment of a modular motor assembly;

[0022] Figs. 5A and 5B illustrate exemplary embodiments for coupling modular motor assembly to a compression system;

[0023] Fig. 6 illustrates an exemplary embodiment of a modular compressor assembly;

[0024] Fig. 7 illustrates an exemplary embodiment of a modular compression system;

[0025] Fig. 8 illustrates another exemplary embodiment of a modular compression system; and

[0026] Fig. 9 is a flowchart of an exemplary embodiment of a method for processing a gas stream. DETAILED DESCRIPTION OF THE DRAWINGS

[0027] In the following detailed description section, specific embodiments of the present techniques are described. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, this is intended to be for exemplary purposes only and simply provides a description of the exemplary embodiments. Accordingly, the techniques are not limited to the specific embodiments described below, but rather, include all alternatives, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0028] At the outset, for ease of reference, certain terms used in this application and their meanings as used in this context are set forth. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present techniques are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments, and terms or techniques that serve the same or a similar purpose are considered to be within the scope of the present claims.

[0029] As used herein, "compressor" may be defined a number of ways and the particular definition intended for a given context set forth herein may be selected from the following, as will be clear to those of skill in the art. One definition indicates that "compressor" refers to a device used to increase the pressure of an incoming fluid by decreasing its volume. In another definition, a "compressor" is a machine that increases the pressure of a gas by the application of work (compression). Accordingly, a low pressure gas (for example, 5 pounds per square inch gauge (psig)) may be compressed into a high-pressure gas (for example, 1000 psig) for transmission through a pipeline, or other processes. In yet another definition, a "compressor" refers to a device for compressing a working gas, including gas- vapor mixtures or exhaust gases, and includes reciprocating compressors, piston compressors, rotary vane or screw compressors, and devices and combinations capable of compressing a working gas.

[0030] As used herein, "pump" may be defined a number of ways and the particular definition intended for a given context set forth herein may be selected from the following, as will be clear to those of skill in the art. One definition indicates that "pump" refers to a device that moves fluids (liquids or gases) by mechanical action. Pumps operate by some mechanism, and consume energy to perform mechanical work by moving the fluid.

[0031] As used herein, "turbine" may be defined a number of ways and the particular definition intended for a given context set forth herein may be selected from the following, as will be clear to those of skill in the art. One definition indicates that "turbine" refers to a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work.

[0032] Fig. 2A is an embodiment of a conventional system 200 for compressing hydrocarbon gas. Fig. 2A is a cross-sectional side view of the system 200. The system comprises an electric motor 15 and a compressor 20 connected by one or more shafts 30. The electric motor 15 is an adjustable speed alternating current (AC) or direct current (DC) motor. In an embodiment, the compressor 20 and the motor 15 are in hermetically sealed compartments within a casing 25 and separated by a partition 35. Although illustrated as a single casing 25, in some embodiments casing 25 may comprise separate casings, with one casing, for example, housing the motor 15 and one casing housing the compressor 20, in which case the partition 35 represents two end walls, located adjacent one another, of the respective pressure casings. In some embodiments, the casings can be coupled via any known coupling technique. For example, the casings may be coupled via flanges (not shown) that are fitted with bolts. The compressor 20 has an associated inlet 40 for receiving gas and outlet 45 for discharging gas. Gas flows into inlet 40 and is discharged out of outlet 45. In an embodiment, the partition 35 allows for some of the gas that is processed to enter the cavity surrounding the motor 15, in which case the motor is affected by the compression process taking place in the volume around the compressor 20. In some embodiments, cooling of the motor or motor casing may be beneficial to dissipate the motor losses and the fluid frictional losses. These facilities are not shown.

[0033] The motor 15 is used to drive the compressor 20 via one or more shafts 30. As one of ordinary skill in the art would understand, the system 200 also includes a plurality of bearings (not shown), some of which are radial bearings and at least one of which is a thrust bearing. These bearings may be magnetic bearings in which case a power source and associated controls are used to control the magnetic bearings. A shaft associated with the motor 15 and a shaft associated with the compressor 20 are illustrated as one shaft 30 for simplicity, but the shafts of the motor 15 and compressor 20 may be separate shafts that are connected via any known type of coupling (not shown), such as a stiff coupling, a flexible coupling, a fluid coupling, a magnetic coupling, an elastomeric coupling, or a gear coupling. Altematively, or additionally, the shafts may be coupled using any known type of clutch or gear. In an embodiment, the system 200 is hermetically sealed such that there is no shaft penetrating the pressure casing 25.

[0034] The motor 15 and compressor 20 are surrounded by the pressure casing 25 to keep the motor 15 and compressor 20 hermetically sealed. The pressure casing 25 is substantially cylindrical and may be supported by a plurality of support members 55 resting upon or coupled to a support, such as base plate 50. Fig. 2B is an end view of the system 200 that illustrates an embodiment of support members 55 and casing 25.

[0035] The conventional system 200 does not provide much flexibility to be able to match reservoir depletion pressure curves as it is typically designed for narrow input pressure ranges. Disclosed herein are compression systems that use modular components so that the systems can be quickly, efficiently, and cost-effectively reconfigured to adjust to decreasing inlet pressure.

[0036] Fig. 3 illustrates an example embodiment of a compression system 300 for compressing hydrocarbon gas. In some embodiments, the system 300 shares some similarities to system 200, and components that are similar to system 200 are labeled similarly and not explained further. The compression system 300 comprises pressure casing 325 that includes removable plates 65 and flanges 60. A cross-section of the system is shown in which an outline of the flanges 60 at the top and bottom of the pressure casing 325 are illustrated, but each flange 60 may wrap around a circumference of the pressure casing 325. All the flanges discussed herein may share this characteristic. The flange design and attachment method may be variable.

[0037] In some embodiments, the casing 325 includes a compressor compartment and a motor compartment. In an embodiment, the compartment within casing 325 corresponding to motor 15 and the compartment within casing 325 corresponding to compressor 20 are hermetically sealed, and the compartments may be isolated or sealed from each other by partition 35. The system 300 is a modular system that allows for removal of one or two of the plates 65 to add additional motors or compressors as needed, as explained more fully below. Although the removable plates 65 are illustrated as occupying an entire area of each end of the system 300, in an embodiment, a removable plate 65 may occupy only a portion of an end area to allow shaft penetration from another motor or compressor as explained more fully below.

[0038] As discussed previously, in some embodiments the motor 15 and compressor 20 each have separate pressure casings, in which case partition 35 represents adjacent end walls of two pressure casings that are coupled in known manners. Modular casings provide for replacing the current motor 15 or compressor 20 with one more suitable to a new compression duty by, for example, replacing the desired component along with its casing. In a configuration in which the compression system 300 comprises two pressure casings, one each for motor 15 and compressor 20, the two pressure casings may be referred to as a single pressure casing 325 of the compression system 300.

[0039] The casing 325 is strong and rigid enough that another motor or compressor can be added to either or both ends of system 300 without using support members to support the added motor and/or compressor. Also, the support members 55 and baseplate 50 in a modular system are designed to support additional weight to be added on either or both ends of system 300.

[0040] In an embodiment, the system 300 is a compressor-motor arrangement referred to as a hermetically sealed compact compressor (HSCC). HSCCs include motor-driven compressors in a single casing without machinery penetrations of the pressure envelope so that there are no rotary seals and the rotor system is supported via magnetic bearings that are cooled by the process gas. In contrast, in conventional compressors an oil system cools and lubricates one or more bearings which are in the atmosphere and separated from the process gas by the rotary seals.

[0041] Fig. 4 illustrates an example embodiment of a modular motor assembly 400. The motor assembly 400 comprises an electric motor 405, a shaft 470, a pressure casing 410, and a partition 465 configured as illustrated in Fig. 4. The electric motor 405 is an adjustable speed AC or DC motor. As one of ordinary skill in the art would understand, the assembly 400 also includes at least one bearing (not shown), which may include a radial bearing and/or thrust bearing. In an embodiment, the at least one bearing includes a magnetic bearing, and the motor assembly includes controls and a power supply for the magnetic bearing that is external to the pressure casing 410. In the exemplary embodiment shown, the motor 405 is a double-ended motor and can provide power off either end of the shaft 470. The motor assembly 400 is configured to be coupled to other modules to create a system for compressing hydrocarbon gas. In some embodiments, the motor assembly 400 is used to supplement the power provided in a preexisting modular compression system.

[0042] Figs. 5A and 5B illustrate example embodiments for coupling modular motor assembly 400 to a compression system, such as compression system 300. Fig. 5A illustrates a compression system 500 in which modular motor assembly 400 is coupled to a compressor 20 in a motor-compressor-motor configuration. The configuration in Fig. 5 A is an example of motors connected in a tandem configuration. Fig. 5B illustrates a compression system 510 in which modular motor assembly 400 is coupled to the compressor 20 in a motor-motor- compressor configuration. The configuration in Fig. 5B is an example of motors connected in a series or drive-through configuration.

[0043] In one embodiment, system 300 is originally configured or staged to receive gas at the inlet 40 at a specified range of pressures. For example, system 300 could be configured to receive gas at an initial point along a reservoir depletion curve for the reservoir that the system 300 is serving. Example reservoir depletion curves are discussed previously with respect to Figure 1. As the pressure of the inlet gas decreases over time, the system 300 may reach a point where an extra motor, such as motor assembly 400, is beneficial to drive the compressor 20. Referring to Fig. 5A, the shaft 470 is aligned with shaft 30 such that there is a common center of rotation.

[0044] The speed of the motor 405 is synchronized with the motor 15, and the power-split is controlled so that overload does not occur. A coupling 475 is used to transfer power from the motor 405 and shaft 470 to shaft 30. The coupling 475 is any known apparatus for mechanical power transmission. For example, the coupling 475 may be a stiff coupling, a flexible coupling, a fluid coupling, a gear, or any other suitable type of coupling. Thus, the shaft 470 is drivably connected to the shaft 30. [0045] When motor assembly 400 is first added, the demand for extra power from the motor 405 starts small and increase over time as inlet pressure decreases. At some point, the compressor 20 may also need to be resized or replaced to accommodate lower gas pressures. Flanges 60 and 460 are mated or coupled to attach motor assembly 400 to system 300. For example, flanges 60 and 460 may be configured such that bolts are inserted to couple the assembly 400 to system 300. In an embodiment, partition 465 keeps motor assembly 400 hermetically sealed from system 300. The partition 465 may include a plate having a hole for at least one radial bearing and the shaft 470. The In another embodiment, the system 500 is hermetically sealed, but partitions 35 and 465 either are not present or the partitions are not fully sealed so that motor 15, compressor 20, and/or motor 405 are not hermetically sealed from each other.

[0046] Fig. 5B illustrates a compression system 510 in which modular motor assembly 400 is coupled to a compressor 20 in a motor-motor-compressor configuration as illustrated. The configuration in Fig. 5B is an example of motors connected in a series or drive-through configuration. As described with respect to Fig. 5 A, in one embodiment, system 300 is originally configured or staged to receive gas at inlet at a specified range of pressures. As the pressure of the inlet gas decreases over time, the system 300 may reach a point where an extra motor, such as motor assembly 400, is beneficial to drive the compressor 20. The shaft 470 is aligned with shaft 30 such that there is a common center of rotation. Various shapes incorporated into the flanges 60 and 460 can be used to ensure alignment of rotating elements, such as shafts 30 and 470. For example, there may be one or more protrusions (not shown) extending from flange 60 and one or more corresponding indentions (not shown) in flange 460 that are configured to be mated to ensure alignment of rotating elements. An example of the mated protrusion(s) and indention(s) are male-female connections.

[0047] A coupling 475 is used to transfer power from the motor 405 and shaft 470 to shaft 30. The coupling 475 is any known apparatus for mechanical power transmission. Other details with respect to system 510 are similar to system 500. One exception is that when motors are connected in series, such as motors 15 and 405, the shaft on the motor delivering power to the compressor, in this case shaft 30, should be sized in accommodate a higher power delivery than just power delivered by motor 15 in isolation.

[0048] There are no feet on motor assembly 400, which is part of the benefit of using a modular approach. A new baseplate 50 does not need to be used when modular components are added as the baseplate 50 is pre-selected to accommodate any additional weight that could be added later by adding modular components. That is, the motor assembly 400 is cantilevered from the system 300 with its weight only supported by the attachment to the system 300. In some embodiments, the base plate is sized to accommodate support members attached only to the system 300, and since the motor assembly 400 is suspended or cantilevered by the assembly 300, there is no need for a larger or a second base plate.

[0049] Furthermore, the flanges 60 and 460 may be designed to support this cantilevered configuration. For example, a thickness of at least one of the flanges 60 and 460 may be engineered to support the weight of motor assembly 400. Fasteners, such as bolts, that couple the flanges 60 and 460 together may be similarly engineered. One or more parts of the flanges 60 and 460 may be characterized as an interface structure.

[0050] Fig. 6 illustrates an example embodiment of a modular compressor assembly 600. The compressor assembly 600 comprises compressor 620, shaft 670, pressure casing 610 with flange 660, inlet 640, outlet 645, and partition 665 configured as illustrated in Fig. 6. The compressor assembly 600 is configured to be coupled to other modules to create a system for compressing hydrocarbon gas. In some embodiments, the compressor assembly 600 is used to supplement the compression capability of a preexisting compression system.

[0051] Fig. 7 illustrates an example embodiment of a modular compression system 700. The modular compression system 700 includes a compressor assembly 600 coupled to the compression system 500. In this embodiment, compressor assembly 600 is coupled to the system 500 described earlier, in which motor assembly 400 is added to system 300. The system 700 is configured such that compressor 20 receives gas from a reservoir via inlet 40 and discharges gas via outlet 45. Additional piping may be needed to connect outlet 45 to inlet 640 of compressor assembly 600 to further compress the gas flow. Gas is discharged via outlet 645. In some embodiments, a cooler is included in the external piping connecting compressor 20 to compressor 620. The cooler may be used to cool the temperature of the gas processed by compressor 20 before gas is channeled to the compressor 620.

[0052] In one embodiment, once power needed from motor 405 exceeds a threshold, compressor assembly 600 is added to the compression system. A coupling 675 is used to transfer power from the motor 405 and shaft 470 to compressor shaft 670. The coupling 675 is any known apparatus for transmitting mechanical power from one shaft to another.

[0053] Fig. 8 illustrates another example embodiment of a modular compression system 800. The modular compression system includes system 700 described previously and further includes a heat exchanger 750 and a separator 805. A stream of a hydrocarbon mixture including gas is illustrated as 760a. The stream enters heat exchanger 750 and is cooled before leaving heat exchanger and entering separator 805.

[0054] The stream exiting the heat exchanger 750 may enter separator 805 and may include a mixture of free liquid or liquid aerosols and gas. The separator 805 separates these liquids from the gas. In one embodiment, the stream exiting the heat exchanger 750 includes oil, water, and gas, and the separator 805 separates these components. As illustrated, oil exits in stream 810, water exits the separator 805 in stream 820, and gas exits the separator 805 in stream 760b. Alternatively, the separator 805 may function as three-phase separator, for example separating sand, liquid (e.g., more than one type of liquid), and gas. Regardless of the type of separation, the stream 760b includes primarily gas. The stream 760b enters a casing housing compressor 20 followed by compression by another compressor 620, and the stream exits the casing housing compressor 620 as stream 760c.

[0055] Thus, a modular compression system may include not only compressors and motors, but rather all the components typically needed for a full compression system, including heat exchangers and separators. A heat exchanger and separator may be modular as well. For example, as illustrated in Fig. 8, the heat exchanger 750 includes a flange 860. The flange 860 is mated or coupled to flange 60 to attach the separator 805 to the system 300. The heat exchanger 750 may be integral with the separator 805, or the heat exchanger 750 may be modular with a flange (not shown) for mating the heat exchanger 750 to the separator 805.

[0056] The heat exchanger 750 and separator 805 do not include separate support members, as the support members 55 below the system 300 are designed to support additional weight to be added on either or both ends of system 300 to allow for a flexible, modular configuration.

[0057] As shown in Fig. 8, the streams 760a-760c flow between sections or modules external to the sections. For example, piping external to the sections shown in Fig. 8 is used to route gas streams. However, the gas routing may also be performed using internal passages between sections. Register fits may be incorporated into flanges that couple one section to another to ensure alignment of internal piping. Internal piping may be coupled and sealed in a manner similar to coupling and sealing of shafts 30 and 470 described previously. In embodiments with internal piping, an in-line cooler (in the piping) or a cooling jacket around the casing circumference may be used, thus helping to cool the gas as it is being compressed, as opposed to waiting for the final discharge. Such embodiments can save external piping connections, space, and weight.

[0058] In some circumstances, gas flow is too high to be processed by a single compressor. In such circumstances, a gas stream need not be processed all in series, e.g., from one compressor into another such as shown in Fig. 8 (i.e., gas is processed first by compressor 20 followed by compressor 620). For example, a gas stream may be divided into two or more streams and processed in parallel. In an embodiment, a gas stream is divided into two streams, with a first stream including a first fraction of the total gas stream and a second stream including a second fraction of the total gas stream. The two streams may be processed in different parts of a compressor or other part of a modular system.

[0059] In an embodiment, a gas stream is divided into two streams, with a first stream processed by a first compressor, such as compressor 20 in modular system 700, and a second stream processed by a second compressor, such as compressor 620. In an embodiment, the first stream flows into inlet 40 and is discharged out of outlet 45, and the second stream flows into inlet 640 and is discharged out of outlet 645. In this manner, the first and second streams can be processed in parallel.

[0060] Fig. 9 is a flowchart setting forth an exemplary embodiment of a method 900 for processing a gas stream. The method 900 may be implemented using a modular compression system, such as any of the modular compression systems described herein. The method begins in block 910. In block 910, a gas stream is compressed using a modular compressor system, such as system 300. For example, a gas stream derived from a reservoir is received at an inlet, compressed by a compressor, and discharged at an outlet of the compressor. The compressor is powered by a motor, such as motor 15.

[0061] Next in decision block 920, a determination is made whether the pressure of the input gas stream has fallen below a threshold pressure. The pressure may decrease over time due to the characteristics of the gas reservoir being depleted. For example, as discussed previously with respect to Fig. 1, gas reservoir pressure typically declines in a gradual manner. The compression system may include a pressure sensor located at or near an inlet for measuring the pressure. The sensor may send electrical signals to a controller or other measurement system.

[0062] If it is determined that pressure exceeds a threshold, the method returns to block 910 and gas continues to be processed using the original modular compressor system. However, if it is determined that pressure is less than the threshold, the method 900 proceeds to block 930. In block 930, one or more additional sections or components are added to the modular compressor system. For example, as shown in Figs. 5A and 5B, an additional motor assembly, such as motor assembly 400 may be added. As another example, an additional compressor assembly, such as compressor assembly 600, may be added instead of or in addition to another motor assembly. Additional motors and/or compressors may be added in any order. For example, motors may be connected in a series (e.g., see Fig. 5B) or in a tandem configuration (e.g., see Fig. 5A). The same may be done with compressors.

[0063] During block 930, gas processing may be temporarily halted or suspended while the modular compressor system is being reconfigured. Further, during block 930, a portion of a pressure casing may be removed to allow a modular motor assembly, such as motor assembly 400, to couple to the compressor, such as compressor 20. For example, pressure casing 325 is one example of a pressure casing, and removable plate 65 may be removed during block 930 in order to connect the motor assembly 400 to the compressor 20.

[0064] After additional sections are added in block 930 to create a rerated modular compressor system, the process proceeds to block 940. In block 940, the gas stream is compressed using the rerated modular compressor system.

[0065] Blocks 920-940 may be repeated as needed during the life of a reservoir. For example, additional sections or components may be added as needed each time inlet pressure falls below a threshold. Thus, there may be a series of progressively decreasing pressure thresholds below which an additional section is added. In this manner, a modular compression system can efficiently track a reservoir depletion pressure or flow rate curve to provide satisfactory compression performance at different points on the pressure curve.

[0066] Although exemplary embodiments discussed herein in with respect to Figs. 2-9 are directed to compression systems, a person of ordinary skill in the art would understand that the principles apply to many systems that include a driver and a driven element, such as a pump. Furthermore, turbines are sometimes used in compression systems, in addition to or in lieu of electric motors, to recover energy from fluid streams. Thus, turbines can be one of the modular components in a modular compression system as disclosed herein. For example, the compressor 20 in Fig. 3 may be driven by either a motor, a turbine, or both. As another example, the compressor 20 or compressor 620 in the system 700 in Fig. 7 may also be driven by either a motor, a turbine, or both. The terms "driver" and "driving element" may be used synonymously. Examples of a "driving element" include an electric motor and a turbine. [0067] Embodiments of the invention may include any combinations of the methods and systems shown in the following numbered paragraphs. This is not to be considered a complete listing of all possible embodiments, as any number of variations can be envisioned from the description above.

1. A modular compression system for matching an operation range to a reservoir depletion condition, the modular compression system comprising:

a compressor arranged to compress a hydrocarbon gas from a well in the reservoir; a driving element coupled to the compressor and configured to provide power to the compressor;

a pressure casing surrounding the compressor and the driving element; and a modular electric motor assembly configured to be selectively attachable and coupled to the compressor and the pressure casing, the modular electric motor being arranged to provide supplemental power to the compressor to change the capacity of the modular compression system to compress the hydrocarbon gas.

2. The modular compression system of paragraph 1, further comprising:

a base plate; and

at least one support member connected between the pressure casing and the base plate configured to support the compressor, the driving element, and the modular electric motor.

3. The modular compression system of paragraph 2, further comprising:

a first flange on the pressure casing;

a second flange on the modular electric motor, wherein the first flange is connected to the second flange, and wherein the modular electric motor assembly is not in contact with any support members connected to the base plate.

4. The modular compression system of any of paragraphs 1-3, wherein the modular electric motor assembly is coupled to the driving element in a series driving configuration or in a tandem configuration.

5. The modular compression system of any of paragraphs 1-3, further comprising a cooling water jacket on the periphery of the pressure casing.

6. The modular compression system of any of paragraphs 1-5, further comprising: a modular separator having a first inlet configured to receive a fluid mixture and an outlet configured to produce a gas, and wherein the outlet is coupled to the compressor at a second inlet of the compressor.

7. The modular compression system of paragraph 6, further comprising:

a modular heat exchanger coupled to an end of the modular separator, the modular separator coupled to an end of the compressor.

8. The modular compression system of any of paragraphs 1 -7, further comprising a modular compression assembly drivably connected to both the driving element and the modular electric motor assembly.

9. The modular compression system of paragraph 8, wherein the modular compression system is configured to divide the input gas stream into a first gas stream and a second gas stream, and wherein the modular compression system is configured to compress the first gas stream and the second gas stream in parallel.

10. The modular compression system of any of paragraphs 1 -9, wherein the driving element is an electric motor.

11. The modular compression system of any of paragraphs 1 -9, wherein the driving element is a turbine.

12. A method for processing a gas stream using a modular compression system, wherein the modular compression system comprises a driving element mechanically coupled to a compressor by at least one shaft, and wherein the modular compression system further comprises a pressure casing surrounding the driving element and the compressor, the method comprising: removing a portion of the pressure casing to allow a modular electric motor assembly to couple to the compression system; and

connecting the modular electric motor to the compression system to boost drive power supplied to the compressor.

13. The method of paragraph 12, further comprising:

measuring an inlet gas pressure; and

determining that the inlet gas pressure is less than a threshold,

wherein the removing and the connecting are performed in response to the determining that the inlet gas pressure is less than a threshold.

14. The method of paragraph 13, wherein the method further comprises:

determining that the inlet gas pressure is less than a second threshold;

in response to the determining that the inlet gas pressure is less than the second threshold, connecting a modular compressor assembly to the modular electric motor to provide additional compression to the gas stream.

15. The method of any of paragraphs 12-14, wherein the modular electric motor connects to the compressor to drive the compressor in a tandem motor configuration or a drive-through configuration.

16. The method of any of paragraphs 12-14, wherein the method further comprises:

determining that the inlet gas pressure is less than a second threshold;

in response to the determining that the inlet gas pressure is less than the second threshold:

opening the pressure casing; removing a component, wherein the component comprises either the compressor or the driving element; replacing the component with a second component of increased capacity to provide greater compression to the gas stream; and

closing the pressure casing.

17. The method of any of paragraphs 12-16, wherein the driving element is one of an electric motor and a turbine.

18. A modular apparatus comprising:

a modular electric motor assembly configured to selectively attach to and provide supplemental power to a compression system, wherein the compression system comprises a first motor, the modular electric motor assembly comprising:

a shaft configured to couple to the compression system;

a second motor coupled the shaft and configured to provide the supplemental power; and an interface structure configured to be selectively affixed to the compression system to attach the modular electric motor assembly to the compression system.

19. The modular apparatus of paragraph 18, wherein the modular electric motor assembly further comprises a partition, and wherein the shaft extends beyond the partition and is mechanically coupled to the compression system.

20. The modular apparatus of paragraphs 18 or 19, further comprising a compression system, wherein the compression system further comprises a first compressor and a second shaft, and wherein the shaft is mechanically coupled to the second shaft to assist with driving the first compressor.

21. The modular apparatus of paragraph 20, further comprising a modular compressor assembly selectively and mechanically coupled to the compression system, wherein the modular compressor assembly comprises a second compressor.

22. The modular apparatus of paragraph 21, wherein the first motor and the second motor are configured to transfer mechanical power to the first compressor and the second compressor.

23. The modular apparatus of paragraph 19, wherein the modular electric motor assembly further comprises:

a pressure casing; and

a flange surrounding a circumference of the pressure casing,

wherein the flange is configured to couple to the interface structure of the modular electric motor assembly, the flange being configured to support the weight of the modular electric motor assembly.

[0068] While the present techniques may be susceptible to various modifications and alternative forms, the embodiments discussed above have been shown only by way of example. However, it should again be understood that the techniques is not intended to be limited to the particular embodiments disclosed herein. Indeed, the present techniques include all alternatives, modifications, and equivalents falling within the true spirit and scope of the appended claims.

Claims

1. A modular compression system comprising:

a compressor arranged to compress a gas;

a driving element coupled to the compressor and configured to provide power to the compressor;

a pressure casing surrounding the compressor and the driving element; and a modular motor assembly configured to be selectively attachable and coupled to the compressor and the pressure casing, the modular motor being arranged to provide supplemental power to the compressor to change the capacity of the modular compression system to compress the gas.

2. The modular compression system of claim 1, further comprising:

a base plate; and

at least one support member connected between the pressure casing and the base plate configured to support the compressor, the driving element, and the modular motor.

3. The modular compression system of claim 2, further comprising:

a first flange on the pressure casing;

a second flange on the modular motor, wherein the first flange is connected to the second flange, and wherein the modular motor assembly is not in contact with any support members connected to the base plate.

4. The modular compression system of any of claims 1-3, wherein the modular motor assembly is coupled to the driving element in a series driving configuration or a tandem configuration.

5. The modular compression system of any of claims 1 -3, further comprising a cooling water jacket on the periphery of the pressure casing.

6. The modular compression system of any of claims 1 -5, further comprising:

a modular separator having a first inlet configured to receive a fluid mixture and an outlet configured to produce a gas, and wherein the outlet is coupled to the compressor at a second inlet of the compressor.

7. The modular compression system of claim 6, further comprising:

8. The modular compression system of any of claims 1-7, further comprising a modular compression assembly drivably connected to both the driving element and the modular motor assembly.

9. The modular compression system of claim 8, wherein the modular compression system is configured to divide the input gas stream into a first gas stream and a second gas stream, and wherein the modular compression system is configured to compress the first gas stream and the second gas stream in parallel.

10. The modular compression system of any of claims 1 -9, wherein the driving element is an electric motor.

11. The modular compression system of any of claims 1 -9, wherein the driving element is a turbine.

12. A method for processing a gas stream using a modular compression system, wherein the modular compression system comprises a driving element mechanically coupled to a compressor by at least one shaft, and wherein the modular compression system further comprises a pressure casing surrounding the driving element and the compressor, the method comprising:

removing a portion of the pressure casing to allow a modular motor assembly to couple to the compression system; and

connecting the modular motor to the compression system to boost drive power supplied to the compressor.

13. The method of claim 12, further comprising:

measuring an inlet gas pressure; and

determining that the inlet gas pressure is less than a threshold, wherein the removing and the connecting are performed in response to the determining that the inlet gas pressure is less than a threshold.

14. The method of claim 13, wherein the method further comprises:

determining that the inlet gas pressure is less than a second threshold;

in response to the determining that the inlet gas pressure is less than the second threshold, connecting a modular compressor assembly to the modular motor to provide additional compression to the gas stream.

15. The method of any of claims 12-14, wherein the modular motor connects to the compressor to drive the compressor in a tandem motor configuration or a drive-through configuration.

16. The method of any of claims 12-14, wherein the method further comprises:

determining that the inlet gas pressure is less than a second threshold;

opening the pressure casing;

removing a component, wherein the component comprises either the compressor or the driving element;

replacing the component with a second component of increased capacity to provide greater compression to the gas stream; and

closing the pressure casing.

17. The method of any of claims 12-16, wherein the driving element is one of an electric motor and a turbine.

18. A modular apparatus comprising:

a modular motor assembly configured to selectively attach to and provide supplemental power to a compression system, wherein the compression system comprises a first motor, the modular motor assembly comprising:

a shaft configured to couple to the compression system;

a second motor coupled the shaft and configured to provide the supplemental power; and

an interface structure configured to be selectively affixed to the compression system to attach the modular motor assembly to the compression system.

19. The modular apparatus of claim 18, wherein the modular motor assembly further comprises a partition, and wherein the shaft extends beyond the partition and is mechanically coupled to the compression system.

20. The modular apparatus of any of claims 18-19, further comprising a compression system, wherein the compression system further comprises a first compressor and a second shaft, and wherein the shaft is mechanically coupled to the second shaft to assist with driving the first compressor.

21. The modular apparatus of claim 20, further comprising a modular compressor assembly selectively and mechanically coupled to the compression system, wherein the modular compressor assembly comprises a second compressor.

22. The modular apparatus of claim 21 , wherein the first motor and the second motor are configured to transfer mechanical power to the first compressor and the second compressor.

23. The modular apparatus of claim 19, wherein the modular motor assembly further comprises:

a pressure casing; and

a flange surrounding a circumference of the pressure casing,

wherein the flange is configured to couple to the interface structure of the modular motor assembly, the flange being configured to support the weight of the modular motor assembly.