RU2297520C2 - Method for low-pressure gas utilization - Google Patents

Abstract

FIELD: oil and gas production, particularly full low-pressure gas trapping (collecting) and gas losses prevention during hydrocarbon production and refinery.

SUBSTANCE: method for gas trapping with the use of ejector involves pumping working fluid under 2.3-9.5 MPa via ejector; mixing working fluid with low-pressure gas along with provision of hydrocarbon content in components to be mixed of at least 10% of component volumes; increasing pressure in flow-through ejector section and pipeline downstream the ejector; providing low-pressure gas compression up to 0.3-6.5MPa; moving water-and-gas mixture in separator to separate working fluid from gas; supplying gas with necessary transport pressure to main line; returning working fluid in ejector.

EFFECT: increased efficiency due to decreased time and costs of gas delivery to point of destination.

6 cl

Description

The invention relates to the oil and gas industry and, in particular, to the issues of complete capture (selection) of low-pressure gas, oil and / or gas wells and the prevention of its losses during various technological processes of production and / or processing of hydrocarbons.

Natural hydrocarbon low-pressure gas released, for example, from the annulus of wells and / or accompanying hydrocarbon processing processes, consists mainly of a mixture of saturated hydrocarbons and is, first of all, a valuable chemical raw material.

In addition, natural petroleum gas as a fuel for domestic and industrial needs has a number of advantages compared to liquid and solid fuels.

Despite this, low-pressure gas is not always trapped, since the low pressure of this gas does not ensure its transportation through the gas pipeline to the place of use.

Therefore, often low-pressure gas is flared with the loss of a high-value chemical and energy product with environmental pollution by combustion products.

A known method of compressing a low-pressure hydrocarbon gas by receiving it into the well and increasing its pressure by supplying liquid to the gas channel through the discharge line of the booster pump unit (see, for example, SU 1520920, class E21B 43/20, 1986).

The disadvantages of this method are the low productivity and low efficiency of the liquid pump as a result of cyclic fluid supply to the well and continuous pressure changes on the fluid supply line.

The technical result of the invention is to increase the efficiency of the method due to the possibility of reducing the time and cost of transporting gas to its destination.

The required technical result is achieved by the fact that the method of utilizing low-pressure gas involves trapping the low-pressure gas by an ejector, through which a working fluid is pumped under pressure in a range of 2.3–9.5 MPa, a working fluid is mixed with a low-pressure gas, while the hydrocarbon content in the mixed components provide at least 10% of the volume of these components, increase the pressure in the flow part of the ejector and the pipeline behind this ejector, provide compression of the low-pressure gas to a pressure in the range 0.37 ÷ 0.75 MPa, after ejecting the water-gas mixture is fed to a separator, where separation is carried out of the working fluid from the gas after the separator for transporting gas from the required pressure is directed into the main pipeline, and a working fluid, which compensate for losses is returned to the ejector.

Besides:

capture borehole low-pressure gas or low-pressure gas at any stage of hydrocarbon processing or chemical production;

water is used as a working fluid;

water after separation is made alkaline to a pH of more than 10;

distillate is used as a working fluid;

use a distillate of diesel or gas oil fraction.

The essence of the invention lies in the fact that it, being essentially a method of utilizing low-pressure gas, provides objects located at a considerable distance from the place of extraction (capture) of this gas, in contrast to traditional technology that provides objects located close to the place of gas production.

Using a vacuum compressor station, which belongs to a number of traditional technologies, the transportation distances are increased by compressing the selected low-pressure gas to the pressure necessary for transportation.

However, a vacuum compressor station, consisting of several compressors connected to an extended network through a trunk line, and having gas separators and condensing tanks, requires high operating costs, expenses for a highly branched gas pipeline network, and a special cooling system. Due to the large length of the vacuum network with a large number of connections, its complete sealing in the field is not possible. Therefore, air leaks into the network. As a result, condensate accumulates in certain sections of the gas pipeline. In addition, such a system does not provide complete gas extraction from objects far removed from the compressor station, due to large pressure losses in the lines of the vacuum network.

As a low-pressure gas, one can use not only borehole gas, but also gas at any stage of hydrocarbon processing or chemical production. For transportation and / or purification of low-pressure gas, various types of liquids can be used as a working fluid, for example, water or distillate (diesel or gas oil fraction). In this case, the low-pressure gas can be sampled (captured) by an ejector through which the working fluid is pumped with the required pressure to transport the low-pressure gas. After ejection, the water-gas mixture with the required pressure is fed to a separator, where the liquid is separated from the gas. The process of compressing a low-pressure gas and transporting it to a separator is often carried out exclusively by using the mechanical energy of the ejector jet. This is carried out in the case when the working fluid does not have the properties of an additional, except mechanical, interaction with the gas.

It is possible in some cases to use additional processes of interaction of the working fluid and gas, especially if we consider that hydrocarbon gases are capable of dissolving with certain types of working fluid, for example, a hydrocarbon-containing liquid (distillate). This allows you to reduce the energy consumption for compression of a low-pressure gas. This process is intensified by increasing the pressure in the flow part of the ejector and the pipeline behind this ejector.

Compressed gas with a composition different from the initial low-pressure gas is separated from the obtained gas-liquid hydrocarbon mixture in a separator. Compressed gas already contains a smaller amount of heavy hydrocarbons, such as propane, butane, propylene, etc., and harmful impurities, such as hydrogen sulfide. In this case, it is possible to hydrotreat the spent working fluid. Heavy hydrocarbons can be used as valuable chemical raw materials.

The specific compression scheme of the low-pressure gas depends on the specific conditions at the facility, the properties of the low-pressure gas and the working fluid used.

When using the simplest scheme of mechanical compression of a low-pressure gas using water as a working fluid, measures are taken to reduce the amount of residual gas in the water after separation of the gas-water mixture. To do this, alkalize the water. The alkali concentration is taken in an amount of 0.04-4.9% at a pH of more than 10. NaOH or KOH is used as alkali for water treatment. After the separator, the gas with the pressure required for transportation is sent to the main gas pipeline, and the working fluid, in particular water, is returned to the ejector. If necessary, the loss of the working fluid (water) is made up.

At the same time, it is taken into account that the working fluid purified in the hydrotreatment unit, in particular the distillate, from sulfur-containing impurities has a higher sorption capacity than the hydrocarbon-containing medium circulating as the working fluid. The more distillate purified from impurities that enters to feed the circulating working fluid, the more hydrogen sulfide and other harmful impurities are absorbed from the compressible low-pressure hydrocarbon-containing gas, and the more pure the consumer receives.

The most optimal next mode of the low-pressure gas utilization cycle has been experimentally established:

the supply of working fluid by a pump under pressure in the range of 2.3-9.5 MPa into the ejector;

maintaining the pressure at the inlet to the pressure ejector in the range of 0.1-0.27 MPa;

mixing the working fluid with a low-pressure gas and compressing the latter to a pressure in the range of 0.3-6.5 MPa.

In this case, the hydrocarbon content in the mixed components should be at least 10% of the volume of these components.

In this case, they provide minimum energy consumption for compression, a sufficient degree of gas purification and ensuring stable operation of the ejector without interruptions in its operation.

The ejector can be made with a multi-jet active nozzle, thereby increasing the productivity of mixing low-pressure gas with a working fluid.

Claims (6)

1. A method of utilizing a low-pressure gas, including trapping a low-pressure gas by an ejector, through which a working fluid is pumped by a pump under a pressure of 2.3–9.5 MPa, the working fluid is mixed with a low-pressure gas, while the hydrocarbon content in the mixed components provides at least 10% of the volume of these components, increase the pressure in the flow part of the ejector and the pipeline behind this ejector, provide compression of the low-pressure gas to a pressure of 0.3 ÷ 6.5 MPa, after ejection, the gas-water mixture is fed to the separator, where fected separation of working fluid from the gas after the separator for transporting gas from the required pressure is directed into the main pipeline, and a working fluid, which compensate for losses is returned to the ejector. 2. The method according to claim 1, characterized in that the downhole low pressure gas or low pressure gas is captured at any stage of hydrocarbon processing or chemical production. 3. The method according to claim 1, characterized in that water is used as the working fluid. 4. The method according to claim 3, characterized in that the water after separation is alkalinized to a pH of more than 10. 5. The method according to claim 1, characterized in that the distillate is used as the working fluid. 6. The method according to claim 4, characterized in that the distillate of the diesel or gas oil fraction is used.