RU2788803C1 - Method for increasing the efficiency of gas production and an installation for its implementation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: group of inventions relates to the oil and gas industry. According to the proposed group of inventions, at the initial stage of operation of the reversible electric power generation and low-pressure gas compression unit (EPGLPGC) operates in the mode of an expansion machine. After reducing the wellhead pressure below the minimum required for gas treatment and its transfer to consumers, the EPGLPGC unit is switched to compression mode. The EPGLPGC unit contains a reversible screw expander compressor (RSEC) and a reversible electric generator motor. The RSEC is designed to perform the following technological functions: in the expander mode to produce mechanical energy at the initial stage of field operation, in the compressor mode to ensure an increase in the pressure of the gas flow after a decrease in the wellhead pressure. A reversible electric generator motor performs the functions of a consumer and a drive motor.

EFFECT: increase in the efficiency of technological processes of gas production as a result of the integrated use of reservoir gas pressure energy during the entire period of field development through the use of a reversible electric power generation and low-pressure gas compression unit (EPGLPGC).

2 cl, 2 dwg

Description

The group of inventions relates to the oil and gas industry and can be used in gas, oil and gas and oil and gas condensate fields, characterized at the initial stage of operation by excessively high wellhead pressures, two or more times higher than the values necessary for gas treatment and transmission to consumers in a non-compressor mode.

At present, excess pressure drop is compensated (“activated”) by means of a throttle, which significantly reduces the efficiency of using the available reservoir gas pressure drop, since part of the reservoir energy is irretrievably lost.

For the beneficial use of reservoir energy at the initial stage of field operation, it is known about the use of highly efficient expansion machines to compensate for excessive pressure drop on them and the subsequent conversion of the mechanical energy of the shaft rotation into electrical energy. However, the use of traditional expansion machines for converting excess pressure with ensuring the formation of a beneficial effect (generation of electrical energy) is characterized by a significant drawback: the period of their use is limited: after the wellhead pressure drops below the pressure necessary for preparing and supplying gas to consumers, the generation of electricity becomes impossible.

The closest technical solution (prototype) to the proposed group of inventions is a method of using the energy of the pressure drop of a natural gas source, an energy-refrigeration unit and a turbo-expander in the form of an energy drive with a bladed machine (RF patent No. 2098713, F17D 1/04, publ. 10.12.1997). High-pressure gas is supplied to the consumer through several series-connected turbo-expanders, and the work of expanding the gas is used to generate electricity and for cooling in refrigerators. To do this, depending on the value of the gas temperature difference at the outlet of the turboexpander, the gas flow is directed either to a heat exchanger, where the gas is heated by cooling the environment, or to the next turboexpander. To implement the method, an energy-refrigeration unit is used, in which a heat exchanger is installed behind each of the turboexpanders along the gas flow, containing a shut-off element in the inlet pipeline. At the same time, the inlet and outlet pipelines are connected by other locking elements with the possibility of directing the gas flow around the heat exchanger or turboexpander. In the energy-refrigeration unit, a turbo-expander (power drive with a blade machine) is used, the rotor of which is mounted on a shaft connected by a consumer shaft and equipped with a gas-dynamic sealing system. In addition to the gas supply nozzle with a gas flow rate meter, the power drive is equipped with a device for additional supply of gas jets, made in the form of a block of nozzles with a valve gas distributor and a logic block.

The disadvantage of the known solution is its ability to improve the efficiency of gas production only through the use of free gas pressure drop. In addition, the energy-refrigeration unit includes a turbo-expander - a dynamic blade machine, by means of which the principle of reversible operation cannot be implemented (both in the expander mode and in the co-priming mode), and which is inefficient to apply for multi-phase flows in well clusters and individual wells gas fields due to a decrease in the reliability and efficiency of this type of equipment during its operation.

The task to be solved by the present invention is the creation of a method for increasing the efficiency of gas production and a reversible installation for generating electricity and compressing low-pressure gas (GEiKNG) for its implementation.

The technical result, to which the proposed group of inventions is directed, is to increase the efficiency of technological processes of gas production as a result of the integrated use of the pressure energy of the reservoir gas throughout the entire period of field development through the use of a reversible GE&CNG unit, including a reversible screw expander-compressor (ROVC) of the volumetric principle action, the efficiency and reliability of which practically does not decrease in the conditions of work with multi-phase flows.

The specified technical result is achieved due to the fact that in the method of increasing the efficiency of gas production during the operation of the field, the natural gas stream coming from the wells is cleaned and separated into a gas stream and a liquid stream in a scrubber-separator, after which the gas stream is sent to a reversible screw expander-compressor . Moreover, at the stage of field operation, characterized by excessively high wellhead pressures, the gas flow in the reversible screw expander-compressor is expanded and cooled, followed by the transfer of the mechanical energy generated in this case to a reversible electric generator-motor to produce electrical energy. Then the cooled gas stream is sent to the gas-liquid mixing manifold.

The liquid stream from the scrubber-separator through the liquid line is also directed to the gas-liquid mixing manifold, from where the mixed gas-liquid stream is removed from the plant. At the stage of field operation, characterized by a decrease in wellhead pressure below the required value, the gas flow in the reversible screw expander-compressor is compressed to the pressure required for supply to consumers, due to the energy coming from the reversible electric generator-engine. Then said flow is cooled in the gas air cooler and sent to the gas-liquid mixing manifold. The liquid stream from the scrubber-separator is directed through a pump through a liquid line to a gas-liquid mixing manifold, from where the mixed gas-liquid stream is removed from the plant.

The plant includes connecting pipelines, shut-off and control valves, a reversible electric generator-engine, a reversible screw expander-compressor, a pump, a gas air-cooler, a gas-liquid mixing manifold, a liquid line and a scrubber-separator. The outlet of the scrubber-separator along the liquid flow through the pump is connected via the liquid line to the gas-liquid mixing manifold, and the gas-flow outlet is connected to a reversible screw expander-compressor, which is connected to the gas-to-liquid mixing manifold through the gas air cooler. In this case, the reversible screw expander-compressor comprises a housing with a screw pair placed in it, connected by an output shaft to a mechanical transmission, which is connected to a reversible electric generator-motor. The pump and the gas air cooler are installed with the possibility of switching them off and directing the gas flow and liquid flow through pipelines directly to the gas and liquid mixing manifold.

According to the proposed group of inventions, at the initial stage of field operation, the GE&KNG, designed to provide the necessary pressure at the inlet of the complex gas treatment unit (UKPG), operates in the expansion machine mode. After the wellhead pressure drops below the minimum required for gas treatment and its transfer to consumers, the GE&OOG unit is switched to the compression mode. It is possible to supply energy through the overhead power lines existing at the field from the power grid or from the auxiliary power plant (APS).

Figure 1 shows a schematic diagram of a reversible installation GEiKNG.

Figure 2 is a schematic diagram of the OVDC. Reversible GE&CNG setup includes:

- scrubber-separator 1;

- OVDC 2, containing a screw pair 3 placed in the housing 4, an output shaft 5, a mechanical transmission 6 and technological piping: pipelines 7, which ensure the operation of the screw pair 3 in the expander mode, pipelines 8, which ensure the operation of the screw pair 3 in the compressor mode;

- electric pump 9;

- reversible electric generator-motor 10;

- AVO gas 11;

- manifold 12 mixing gas and liquid;

- line 13 for liquid;

- shut-off and control valves (ZRA): shut-off valves, bypass valves, check valves;

- connecting pipelines (including bypass pipelines). The outlet of the scrubber-separator 1 in the liquid flow through the pump 9 through the liquid line 13 is connected to the manifold 12 for mixing gas and liquid, and the outlet of the scrubber-separator 1 in the gas stream is connected to the HVAC 2, which is connected through the AVO gas 11 to the manifold 12 for mixing gas and liquids. The screw pair 3 is connected by an output shaft 5 to a mechanical transmission 6, which is connected to a reversible electric generator-motor 10. The pump 9 and the air cooler of the gas 11 are installed with the possibility of turning them off and directing the gas flow and liquid directly into the manifold 12 for mixing gas and liquid with the help of ZRA and connecting pipelines (bypass pipelines).

The reversible GE&KNG unit is assembled from well-known industrial production devices, except for OVDK 2, the main differences of which from existing screw compressors and expanders are:

- the ability to operate the unit in both compressor and expander modes;

- the presence of technological piping (pipelines 7, 8) providing the ability to operate the unit both in compressor and expander modes;

- the presence of a mechanical transmission 6, which provides the connection of the output shaft of the HVDC 2, both with the payload - the consumer of the produced mechanical energy generated during the generation period, and with the drive motor, which provides electricity to the HVDC 2 in the compression mode. In the proposed GE&KNG installation, the functions of the consumer and the drive motor are performed by one element of the installation: a reversible electric generator-motor 10.

OVDC 2 is designed to perform the following technological functions:

- in the expander mode, produce mechanical energy (by implementing the process of gas expansion from high gas pressure to the minimum required for the regular operation of field technological systems - gas gathering networks, GTP, etc.) to transfer it to an external payload to generate electrical energy.

- in the compressor mode, increase the pressure of the gas flow (from the pressure of the gas coming from the wells to the pressure necessary for the passage of gas through the gas gathering network to the GTP with the design pressure necessary for the process of gas preparation for transport).

The screw pair 3 consists of two shafts, the surface of each of which has a helical profile, one of the shafts is connected to the output shaft 5 and rotates, and the second is fixed in independent supports and is stationary. The shafts are located coaxially in the body 4 with the minimum allowable gap (determined by the strength characteristics of the shaft materials and the accuracy of their manufacture) between the screw profiles. Screw profiles are calculated and manufactured in such a way that the volume of free space between the shafts changes monotonously and continuously from the smallest value to the largest in such a way that there is a “narrow” and “wide” part of the screw pair 3 OVDK 2. The value of the smallest and largest volumes of free space between shafts is determined by the value of pressure, temperature and the amount of gas entering the OVDS 2 during its operation in the expander and compressor modes. Moreover, to implement the expansion process, it is necessary to ensure the movement of gas from the "narrow" part to the "wide" part of the screw pair, and to implement the compression process - from the "wide" part to the "narrow" part of the screw pair 3.

Screw pairs are widely used in industry to create screw expander and compressor units. A distinctive feature of the screw pair 3 used in OVDC 2 is that it is calculated to ensure the operation parameters of the installation both in compressor and expander modes.

The proposed method using the GEiKNG installation is carried out as follows.

At the initial stage of field operation, which is characterized by excessively high wellhead pressures (power generation mode), the natural gas flow from wells, which has a high pressure exceeding the value necessary to ensure gas treatment and transfer it to the consumer, is first sent to the scrubber-separator 1, to where it is separated into a gas stream and a liquid stream, after which the liquid stream is sent through the liquid line 13 to the gas-liquid mixing manifold 12. In the generation mode, the liquid has a high pressure, so the pump 9 is turned off by means of the ZRA and the liquid enters directly into the manifold 12 for mixing gas and liquid under its own pressure through the bypass pipelines. The gas flow from the scrubber-separator 1 is sent to the HVDC 2, which at this stage operates in the expander mode, where the gas flow through pipelines 7, which ensures the operation of the screw pair 3 in the expander mode, enters the screw pair 3 for expansion, i.e. to the "narrow" part. The gas flow expands in the screw pair 3, gradually passing through the free space formed by the screw profiles of the screw pair 3 from the “narrow” to the “wide” part, while the volume occupied by the gas increases, the gas pressure decreases (to the minimum required for the normal operation of field technological systems and mechanical work is produced, which is diverted to a reversible electric generator-engine 10 by means of an output shaft 5 and a mechanical transmission 6, where it is converted into electrical energy. gas is sent via bypass pipelines directly to the gas-liquid mixing manifold 12, where it is mixed with liquid and discharged to the gas collection network and further to consumers (to ensure transport, preparation and processing of gas, etc.). without fuel costs, used for their own technological needs at the field by transferring electrical energy to consumers via overhead power lines existing at the field and / or directing it to an external electrical network. The use of GE&OGG units makes it possible to replace a part of the energy generated by the ESS and reduce emissions of pollutants into the atmosphere generated during the operation of the ENG, or reduce the amount of electricity purchased from generating companies.

At a later stage of the field operation, as the formation pressure decreases to a value at which it is impossible to provide gas treatment and its transfer to consumers, the pump 9 and gas air cooler 11 are connected by switching shut-off valves and the GE&CNG unit is switched to the low-pressure gas compression mode. The flow of natural gas from wells, which has a low pressure, is sent to the scrubber-separator 1, in which it is separated into a gas stream and a liquid stream. Since the liquid has a low pressure in the low-pressure gas compression mode, it is sent after the scrubber-separator 1 through the pump 9, in which the liquid pressure is increased to the pressure necessary for supply to the gas collection network, through the liquid line 13 to the gas-liquid mixing manifold 12. The gas flow after the scrubber-separator 1 is sent to the HVDC 2, which at this stage operates in the compressor mode. In this case, the gas flow entering the inlet of the HVDC 2 with low pressure enters through pipelines 8, which ensure the operation of the screw pair 3 in the compressor mode, for compression, i.e. to the "wide" part. The gas flow is compressed in the screw pair OVDK 2, gradually passing it through the free space formed by the profiles of the screw pair, from the "wide" to the "narrow" part. In this case, the volume occupied by gas decreases and its pressure rises to the value necessary for the passage of gas through the gas gathering network with the design pressure necessary for the process of preparing gas for transport. The operation of the HVDC 2 in compressor mode is provided by the energy of a reversible electric generator-motor 10, which operates in the mode of an electric motor during the compression of low-pressure gas, the electrical energy necessary for its operation is supplied through the overhead electric lines of the field or from the ESN. The energy of the reversible electric generator-motor 10 is transmitted to the screw pair 3 of the HVDC 2 by means of a mechanical transmission 6 and the output shaft 5. After compression, the gas flow has high temperatures, so the gas flow after compression in the HVDC 2 is sent to the AVO of gas 11, in which it is cooled to a temperature sufficient to prevent hydrate formation, and sent to the manifold 12 mixing gas and liquid. In the gas-liquid mixing manifold 12, the liquid stream is mixed with the gas stream, after which the mixed gas-liquid stream is discharged into the gas collection network. As a result, the gas pressure is increased to a pressure determined taking into account the pressure loss in the gas transmission system (GTS) and the required pressure at the inlet to the GTP, while reducing the gas flow rates in the GTS, which eliminates the need to ensure acceptable gas velocities in the GTS by increasing the area , through which the gas passes, i.e. exclude the use of loopings (additional pipes installed in parallel with the existing ones), as well as delay the commissioning of the booster compressor station (BCS) and reduce its required capacity compared to the option of field development without the use of HPCNG units.

Thus, the implementation of the proposed group of inventions provides an increase in the efficiency of gas production, which is due to:

- reducing the need to purchase or generate electricity for the needs of the field;

- optimization of technical solutions for booster compressor stations (postponement of commissioning dates, power reduction, etc.) or complete elimination of the need for booster compressor stations due to the transition to work at the field according to the distributed compression scheme with a decrease in reservoir pressure. At the same time, there is no need for additional capital investments, because GE&CNG installations are reversible;

- an increase in the useful life of the equipment throughout the entire period of operation of the field in comparison with the use of traditional expansion machines;

- optimization of technical solutions for gas gathering networks (elimination of the need for loopings due to the transition to the operation of the field according to the distributed compression scheme, in which it is possible to increase the pressure in the pipelines, which leads to a decrease in gas velocities to acceptable values without looping).

Claims (2)

1. A method for increasing the efficiency of gas production, which consists in the fact that during the operation of the field, the natural gas stream coming from the wells is cleaned and separated into a gas stream and a liquid stream in a scrubber-separator, after which the gas stream is sent to a reversible screw expander-compressor, and at the stage of field operation, characterized by excessively high wellhead pressures, the gas flow in the reversible screw expander-compressor is expanded and cooled, followed by the transfer of the mechanical energy generated in this case to a reversible electric generator-engine to generate electrical energy, then the cooled gas flow is sent to the gas mixing manifold and liquid, the liquid flow from the scrubber-separator along the liquid line is also sent to the gas-liquid mixing header, from where the mixed gas-liquid in a reversible screw expander-compressor, it is compressed to the pressure required for supply to consumers, due to the energy coming from a reversible electric generator-motor, then the said flow is cooled in an air-cooling gas apparatus and sent to a gas-liquid mixing manifold, the liquid flow from the scrubber- The separator is sent through the pump through the liquid line to the gas-liquid mixing manifold, from where the mixed gas-liquid stream is removed from the plant. 2. Installation for implementing the method according to claim 1, including connecting pipelines, shut-off and control valves, a reversible electric generator-engine, a reversible screw expander-compressor, a pump, an air-cooling apparatus for gas, a gas-liquid mixing manifold, a liquid line and a scrubber- a separator, the outlet of which in the liquid flow through the pump is connected through the liquid line to the gas and liquid mixing manifold, and the outlet in the gas flow is connected to a reversible screw expander-compressor, which is connected to the gas and liquid mixing manifold through the gas air cooler, while the reversible screw expander-compressor contains a housing with a screw pair placed in it, connected by an output shaft to a mechanical transmission, which is connected to a reversible electric generator-engine, and the pump and the gas air-cooling apparatus are installed with the possibility of their shutdown and directing the gas flow and liquid flow directly into gas-liquid mixing manifold .

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