RU2489568C1 - Production method of underwater deposits of gas hydrates, and underwater production complex of gas hydrates - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: pipeline is routed from a platform on sea surface to deposits of gas hydrates at sea bottom, which consists of an external pipe and an internal pipe. Sea water heated to 30...40 degrees Celsius is transported via the internal pipe immediately to a gas hydrate deposit. Bubbles of gaseous methane are transported together with water via the external pipe upward to the platform. Methane is separated from water. Methane is supplied to tanks or to the main pipeline. When sea water heated to 30...40 degrees Celsius is being supplied, granite chips are supplied in the ratio of 1:2 to fill in the inner volume of the formation, which has been released at extraction of gas hydrates. Underwater production complex includes a platform with a pipeline consisting of an internal sea water supply pipe immediately to gas hydrate deposit, which is heated to 30-40 degrees Celsius, and granite chips in the ratio of 1:2, and an external pipe for transportation of gaseous methane bubbles together with water upwards to the platform to separate methane from water. Besides, there are pumps, a gas-turbine plant rated at 6 MW and a thermal power plant to generate energy due to thermobaric difference of sea water. The platform is made in the form of a movable sea unit with a submersible tank by means of a telescopic device, inside which a pipeline made from propylene is arranged. Diameter of the external pipe increases in upward direction.EFFECT: reduction of environmental consequences at industrial development of underwater gas hydrate deposits and improvement of carrying capacity at transportation of gas hydrates.3 cl, 1 dwg

Description

The invention relates to the oil and gas industry, and more particularly, to facilities for offshore production of solid gas hydrates.

Gas hydrates are crystalline compounds in which voids inside the structures formed by water molecules fill gas molecules. Hydrocarbon hydrates are a potential key source of fuel and raw materials for the chemical industry; 160-180 m ^{3 of} methane are contained in one cubic meter of methane hydrate. Estimates of the volume of world hydrocarbon hydrate reserves vary by orders of magnitude, but most likely they exceed world reserves of natural gas. Some difficulties are the transportation of hydrates; then, at what pressure the gas begins to be released, depends not only on the chemical composition of the hydrate, but also on the conditions under which the latter was formed.

There are 3 main methods for extracting natural gas hydrates (thermal exposure, exposure to an inhibitor, pressure reduction).

All of them are based on the use of dissociation - a process during which a substance breaks down into simpler components. In the case of natural gas hydrates, dissociation occurs with increasing temperature and lowering pressure, when ice crystals melt or somehow change their shape, thereby releasing natural gas molecules enclosed within the crystal.

Thermal impact. This method is based on the supply of heat inside the crystalline structure of the hydrate in order to increase the temperature and accelerate the process of dissociation. A practical example of such a method is the pumping of warm sea water into a layer of gas hydrates lying at the bottom of the sea. Once the gas begins to be released from the marine sediment layer, it can be collected.

To obtain methane gas from solid gas hydrates, they must be melted, that is, heated.

A known method and device for the production of underwater gas hydrates, which consists in laying a special pipeline from the platform on the sea surface to the deposits of gas hydrates on the seabed. The peculiarity of the pipeline is that it consists of double-walled pipes. It is like two pipelines, of which one is passed through the other.

Seawater heated to 30 ... 40 degrees C is supplied through the inner pipe directly to the gas hydrate field, which begins to melt, and gas bubbles of methane are released from them, which together with water rise upward through the outer pipe to the platform where the methane is separated from water and is fed into tanks or main pipelines, and warm water is again pumped down to the gas hydrate deposits (Kh.Yu. Schults. Gas hydrate production technology. Source: Gas hydrates, http://nt.ru/tp/ie /gn.htm [1], Gorchilin V.A., Lebedev . .And Criteria for gas hydrate in the sediment of the Black Sea and the possible type of hydrocarbon traps // Geological Journal -. 1991. - №5 [2]).

Exposure to an inhibitor. Some types of alcohols, such as methanol, act as inhibitors when the gas hydrates are deposited inside the bed and cause a change in the composition of the hydrate. Inhibitors change the conditions of temperature and pressure, contributing to the dissociation of hydrates and the release of methane contained in them.

Pressure reduction. Some hydrate deposits have sites where natural gas is already in a free state. If a well is drilled in such a section to release natural gas, then after its production, the pressure in the layer containing hydrates will decrease. If such a pressure differential is sufficient to initiate dissociation, the process of natural gas release from the hydrate layer will begin.

Computer modeling of the process of thermal action on hydrates using hot water and steam showed that the volume of gas released by this method is large enough for production. However, the costs are too high.

In the case of exposure to inhibitors, the situation is similar - from an environmental and economic point of view, this method of extraction is impractical. To date, the most promising method of production seems to be the production method with lowering the pressure. However, this method also has its drawbacks: it can only be used in fields where there are already accumulations of natural gas in a free state in the hydrate layer; when producing free natural gas accumulated in the hydrate layer, a change in the structure and shape of the layer is possible under the influence of the process of dissociation and the formation of voids.

The stability of the state of oceanic methane hydrates depends not only on the pressure (depth) and ambient temperature, but also on the level of methane concentration or solubility in marine sediments.

Salt is known to help ice melt, as it lowers the freezing point of water. At the same time, concentrated brine will act in the same way on gas hydrates, helping them to melt and give off the methane contained in them. To do this, in the known method for producing underwater gas hydrates, it is proposed to install a semi-submersible floating platform above the explored gas hydrate reservoir, from which it is necessary to drill two wells in gas hydrated soil. Concentrated saline solution (with a salt concentration of 31.7%) will be supplied to one of them, injection, and methane will be extracted from the other, exhaust. In the warm season, it is proposed to pump not a salt concentrate, but warm sea water into the gas hydrate deposit.

However, in order for the salt concentrate to start acting, the gas hydrate deposit must first be “exploded”, for example, by supplying gas under high pressure (it can be done using a special gas gun). Methane, which is released from its ice houses and rushes to the surface of the sea, will either end up in a gas gathering cap installed under water or directly from the well into a reservoir on a floating platform, where it will be liquefied and poured into low-temperature containers.

To ensure the operation of a floating platform (a device for the extraction of methane, a liquefier of combustible gas, pumps, a gas gun, etc.), it is proposed to use a gas turbine unit with a capacity of 6 MW and a heat power unit that generates energy due to the thermobaric difference in sea water (temperature and pressure differences deep in the sea and on its surface). In the summer, the thermobaric difference in seawater will be enough to supply the platform’s thermal power installation with electricity, and in the cold months of the year, about one and a half percent of the produced gas will have to be burned to ensure the operation of the gas turbine installation.

Onshore gas production infrastructure includes barges that will deliver methane ashore already in liquefied form. There he will get to special coastal bases or ports, from where he can be transported by rail or road, or pumped through the pipeline.

It is proposed to obtain salt concentrate on the shore - for this it is enough to pass water through a freezing desalination plant.

However, the depression of a gas hydrate formation, that is, heating it to decompose gas hydrates, does little, and introducing various solutions into this formation that replace methane in such a complex is a complicated and unworked technology.

In addition, this technology is burdened by the fact that it has these two weaknesses: the so-called gas hydrate bomb - uncontrolled supply of large thermal power to the gas hydrate formation, which can cause a sudden increase in pressure in it and a local explosion that threatens to sink the floating platform; and a “black hole” - if a significant part of the gas hydrate formation comes off the bottom and floats up, then quickly melted it will release a large amount of gas, which again is fraught with the shipwreck of a floating platform.

In addition, the hydrate formed in the pores is “cement” and serves as an impermeable tire under which hydrate accumulates. As a result of hydrate decomposition, the host rocks can turn into a semi-liquid mass (with all the ensuing consequences for engineering objects located in the zone of formation of gas hydrates). Moreover, large-scale field development can cause underwater landslides and, as a result, destructive waves - tsunamis (Gas hydrates. / Higrate ipg - en.wikipedia.org/ [3]).

The objective of the proposed technical solution is to reduce the environmental consequences during the industrial development of subsea gas hydrate deposits and increase throughput in the transportation of gas hydrates.

The problem is solved due to the fact that in the method of producing underwater gas hydrates, which consists in laying a pipeline from a platform on the sea surface to gas hydrate deposits on the seabed, consisting of an outer and inner pipe, heated seawater is supplied through the inner pipe up to 30 ... 40 degrees C, directly to the gas hydrate field, in transporting methane gas bubbles along with water through an outer pipe up to the platform, separating methane from water, supplying methane to tanks or mages trawling line, unlike known solutions - simultaneously with the supply of sea water, heated to 30 ... 40 ° C, is fed granite chippings in a ratio of 1: 2, with methane feed pipings - methane is compressed to 38-41 MPa.

And in the underwater gas hydrate production complex, which includes a platform with a pipeline consisting of an external and internal pipe, pumps, a gas turbine unit with a capacity of 6 MW and a heat power unit that generates energy due to the thermobaric difference of sea water - the platform is made in the form of a moving marine apparatus with a submersible by tender, by means of a telescopic device inside which a pipe made of propylene is placed, while the diameter of the outer pipe increases from bottom to top.

The essence of the proposed technical solution is illustrated by the drawing (figure).

Figure. Underwater mining complex of gas hydrates.

The gas hydrate subsea production complex consists of a platform 1 on which pumps 2, a pipeline 3, a gas turbine installation 4, a heat installation 5, a tender 6, a telescopic device 7, a loading hopper 8, a compressor station 9, in which expansion joints are installed with the possibility of gas compression, are installed to a pressure of 38-41 MPa, at which the properties of natural gas comply with the laws of an ideal gas, immersed tender 9.

Platform 1 is a movable underwater marine apparatus with an immersion tender 6, by means of a telescopic device 7, inside which a pipe 3 is made of elastic material, while the diameter of the outer pipe increases from bottom to top. As a mobile submarine vehicle, a submarine with standard means and automation systems can be used. An analogue of platform 1 with tender 6 is a submarine for marine research, a description of which is given in the sources: New items in the world of military equipment in 2008, nvo.ng.ru, 2008-12-26, and Taras A.E. Nuclear submarine fleet 1955-2005. M .: ACT, Harvest, 2006, pp. 41-216. ISBN 985-13-8436-4.

The pipeline 3 consists of an inner 10 and an outer 11 pipe. The diameter of the outer pipe 11 increases from bottom to top. The telescopic device 7 is equipped with a drilling device 12, which is driven by the corresponding mechanisms 13, located in the internal compartments of the tender 6, which also contains instrumentation 14 for monitoring the operation of the pipeline and measuring equipment 15 for searching gas hydrates. In the figure, the positions also indicate the sea surface 16, the seabed 17, the soil 18, the well 19, the roof 20 of the gas hydrate formation 21, the main pipeline 22, the articulation device 23 of the main pipeline 22 with the platform 1.

The pipeline 3 is made of polypropylene of the HDPE type, having a weight of 5-7 times less than that of steel pipes, a roughness coefficient of which is 7 times less than that of steel pipes.

The technical essence of the proposed method is as follows. When underwater gas hydrates are detected in the amount that ensures their industrial production, a well 19 is equipped with a drilling device 19 through a telescopic device 7, a pipe 3 is inserted into the well 19 through the inner pipe 10 of which, through a drilling device 13, in the soil 18 of the seabed to the roof 20 of the formation 21 with gas hydrates seawater heated to 30 ... 40 degrees C and granite crumb in a ratio of 1: 2 are supplied from the loading hopper 8. directly to the gas hydrate field, which begin to melt, while methane gas bubbles are released from them, which together with water rise upward through the outer pipe 11, to the platform where methane is separated from the water and fed into tanks or main pipelines, and warm water again pumped down to the gas hydrate deposits. By means of a compressor station 9, in which the compensators are installed with the possibility of compressing gas to a pressure of 38-41 MPa, at which the properties of natural gas comply with the laws of ideal gas, the extracted methane is fed into the main pipe 22 through the articulation device 23 of the main pipe 22 with platform 1.

When extracting gas hydrates from the reservoir 21, the freed up internal volume of the reservoir 21 is filled with granite chips, which will reduce the likelihood of landslides.

The implementation of the platform 1 in the form of a moving underwater marine apparatus with an immersion tender 6, allows for mining operations with the platform at various depths, which allows the use of less powerful communications.

Information sources

1. Gas hydrates, http://n-t.ru/tp/ie/gn.htm.

2. Gorchilin V.A., Lebedev L.I. On the signs of gas hydrates in the sedimentary stratum of the Black Sea and the possible type of hydrocarbon traps // Geological journal. - 1991. - No. 5.

3. Gas hydrates. / Higrate ipg - en.wikipedia.org/.

Claims (3)

1. The method of extraction of underwater gas hydrates, which consists in laying a pipeline from a platform on the sea surface to gas hydrate deposits on the seabed, consisting of an external and an internal pipe, supplying sea water heated to 30-40 ° C through an internal pipe, directly to the gas hydrate field, methane gas bubbles are transported together with water through an external pipe upward, methane is separated from the water to the platform, methane is supplied to tanks or main pipelines, while supplying sea water heated to 30-40 ° C, granite chips fed in a ratio of 1: 2 to fill the internal volume of the reservoir, to release the extraction of gas hydrates. 2. The method of production of underwater gas hydrates according to claim 1, characterized in that the methane is compressed to 38-41 MPa. 3. An underwater mining complex of gas hydrates, including a platform with a pipeline consisting of an internal pipe for supplying sea water directly to the gas hydrate field heated to 30-40 ° C, and granite chips in a 1: 2 ratio, and an external pipe for transporting bubbles methane gas together with water up to the platform for separating methane from water, pumps, a 6 MW gas turbine unit and a thermal power plant for generating energy due to the thermobaric difference of sea water, while the platform polyene as a mobile unit with sea submersible tender by a telescopic device, which is placed inside the pipe made of propylene, wherein the diameter of the outer tube rises upwards.

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