Procedure for extraction of gas and fresh water from underwater gas-hydrate by dropping hydro-static pressure

FIELD: oil and gas production.

SUBSTANCE: convex catcher of products of gas-hydrates decomposition (CPGHD) is lowered to sea bottom on suspended device from water-craft board. Internal volume of CPGHD is isolated from external sea medium. Sea water with bottom sediments is pumped off from the catcher by means of an electric pump; thus reduced hydro-static pressure in the catcher facilitates decomposition of gas-hydrate under the catcher into fresh water and gas. Gas is withdrawn into reservoirs of the water-craft or into gasholders, or to the shore for successive utilisation via a flexible pipe. If necessary, produced fresh water is pumped via another flexible pipe with its own electric pump to the water-craft or to the shore. Under effect of proper weight CPGHD sinks into a basin till process of decomposition of gas-hydrate reaches sole of its reservoir. CPGHD is lifted to bottom surface and is transferred to a neighbour section of a gas-hydrate deposit.

EFFECT: raised efficiency of extraction of methane and fresh water on shelf and continental slope of World ocean in arid regions.

1 dwg

The invention relates to the extraction of minerals.

The gas hydrates are solid ice-like compounds natural gas (methane, ethane, propane, isobutane, carbon dioxide, hydrogen sulfide and others) and water formed under certain thermodynamic conditions, the combinations of high pressure and relatively low temperatures [1].

The area of possible hydrate formation covers 90% of the bottom area of the World ocean, including 10% of the shelf and 100% of the continental slope, regardless of latitude. For example, the resources of methane in hydrocarbon gas hydrates of the World ocean is estimated orders of magnitude higher than the recoverable hydrocarbon reserves of all known traditional fields of the world.

Theoretically, it is known that the decomposition of gas hydrate in the gas and water may be carried out by thermal effects, the injection of methanol, calcium bromide, or other inhibitors, as well as reduced pressure.

Gas hydrate deposits in nature is represented by two types, they differ substantially in their industrial development. The first type is the deposits with a powerful lithological tires that do not have exits to the surface of the seabed. The second type is the most widespread in the World ocean is deposits of gas hydrates 1 (see drawing)that do not have a lithologic tires, roofing which often coincides with the surface Mor is one bottom or closed in varying degrees permeable bottom sediments 2 (Sands, silts) are usually small (fractions of a meter) power. It is recognized that the methodology and technology of gas production from these deposits at the present time have not yet been developed [2]. In respect of this second type deposits of gas hydrates is the claimed method of extraction of gas and fresh water reduction of hydrostatic pressure.

Described below is the method involves the use of a special device that allows to decompose the hydrates the reduction of hydrostatic pressure, to adjust the intensity (speed) of the decomposition of gas hydrates, to accumulate (to catch) the decomposition products (gas and fresh water) and transport them for later use.

This device is an artificial convex upward dome outdoor bottom trap 3 products of the decomposition of gas hydrates (gas and water), put on a suspension device (possibly - wire) 4 aboard mobile watercraft (boat, barge, pontoon, platform etc) on the seabed with gas hydrate deposits.

The edge of the trap on the bottom perimeter of the 5 - acute, deepening the seabed under its own weight of the trap, which ensures the sealing of the internal volume of the trap from the outside of the marine environment. Sealing may be further provided with gas - and waterproof elastic apron 6 attached on the this perimeter to the lower part of the body of the trap. Deepening the sharp edges of the trap can be adjusted (increase) electrovibration 7, fastened to the body of the trap. On the body of the trap are mounted the pump 8 is connected by a cable 9 with the craft. When enabled, the pump pumps out from under the trap of sea water, bottom sediments and mineral part of the gas hydrate 10 outside through the flexible tube 11, lowering the internal pressure under the trap, resulting in gas hydrates decompose from the surface (roof) with intensity proportional to the difference between the internal pressure and pressure on their roof, created when pumping water from the trap. Allocating the free gas volume of 80-120 amounts of decomposed gas hydrate rushes into the flexible pipe 12 extending from the upper part of the body of the trap, and goes through that pipe on Board the boats, or floating in the gas tank, or to shore for further use.

When pumping of sediments and mineral decomposed formation of gas hydrates under the trap in the gas hydrate layer is formed of an artificial basin, in which as the deepening of the trap is lowered under its own weight.

The deepening depression and lowering of the trap lasts as long as the vertical decomposition of the formation of gas hydrates will not reach it under what you 13, what will indicate the termination of receipt of dissolved gas, although the process can be stopped at any time terminate the operation of the pump 8).

Then the trap is raised to the surface of the bottom and move it to a neighboring area of gas hydrate deposits. Decomposition of gas hydrates is repeated in a similar way in a new place, and pumped sediment and mineral part of hydrates discharged through the pipe 11 formed during the previous cycle decomposition of gas hydrates basin, which reduces environmental damage to benthic biota and reduces the degree of contamination of the entire thickness of sea water and seabed, including over yet undeveloped area of gas hydrate deposits.

If necessary, especially in tropical and subtropical arid (dry) climate conditions, eye-catching fresh water (in volume 0,99 of the volume of gas hydrate) it is advisable not to drop, and roll out the middle part of the volume of the trap 14 to separate the flexible tube 15 by a pump 16 is located on the upper end of the pipe 15, into the drive on the boat or on the Bank for future use.

The design of the trap must meet the following requirements:

the trap must be able to withstand high external hydrostatic pressure;

the trap must have sufficient weight to Modestovich pop-up moment equal to the weight of sea water displaced them and gas beneath it.

New in the proposed method is in contrast to known methods of decomposition of marine gas hydrates is the following:

practically implementing the principle of pressure reduction for the decomposition of gas hydrates;

- does not require expensive bulky underwater drilling;

- does not require energy-consuming artificial water heating for thermal decomposition of gas hydrate;

- not require extensive use of inhibitors (methanol and others);

- the possibility of simultaneous use of many traps in the complex on the same craft that allows you to bring the performance of a single complex to hundreds of millions of m³gas per year or more, which is comparable with the classical technologies of gas production from wells on the largest inland gas fields (for example, in the North of Western Siberia).

Literature

1. Geology and Geochemistry of oil and gas: the Textbook/Ackbarow, Uchbersen, Basicola, Wehen. - M.: Publishing house of Moscow state University; Izdat. Center "Academy", 2004, - 415 S.

2. Ocean mineral resources: Textbook/WAN, USB, Inthamara, Evito. - M.: Moscow state University press, 2000, - 160 C.

Method of production of gases, in particular methane, and fresh water from the submarine gas hydrates by the reduction of hydrostatic pressure, the realization of what has been created on the bottom shelf and the continental slope of any waters of the oceans and inland seas, namely, that the coincidence of the roof of the formation of gas hydrate with the surface of the seabed or are usually of small capacity overlying deposits of gas hydrate sediments from the craft - vessels, barges, pontoons, platforms on the seabed lower on the suspension device cable artificial convex upward dome outdoor bottom trap products of decomposition of gas hydrate (UPRG), in its upper part connected with the lower end of the first flexible tube for gas sampling, the upper end of which is connected to a collection device or further transportation of gas, for which this upper end may be displayed on the Board above the craft, his UPRG the lower sharp edge, advanced framed outside gas - and waterproof elastic apron, under the action of its weight, and, if necessary, under the action attached to its walls electric vibrators, deepen the seabed isolated from outside its walls the marine benthic environment, its internal volume of which is mounted on the wall UPRG electric pump connected to the craft by the cable, the second flexible tube pump outside UPRG along the sea bottom sea water together with bottom sediments and mineral part of the formation of gas hydrate and thus reduce the pressure internally in the volume UPRG, causing the hydrate to decompose methane, carbon dioxide or hydrogen sulfide selected by the first flexible tube in the side of vessel craft or floating tanks or ashore and for fresh water, which if necessary can also be used after pumping through a third flexible pipe from the inner volume UPRG in a device for collecting water or further pumping, when the selection of the products of decomposition of gas hydrate and sediments under UPRG form a deepening depression, which UPRG under its own weight down up until the decomposition of gas hydrate will not reach the soles of his formation, which will be to specify the termination of receipt of dissolved gas, then UPRG raise again to the surface of the bottom and move to a neighboring area of gas hydrate deposits, in which the decomposition of gas hydrate again, and sediment and mineral part of the gas hydrate with the water pumped in formed during the previous cycle decomposition of gas hydrate depression, which reduces environmental damage to benthic biota, reduces the degree of contamination of the entire thickness of sea water and seabed, including over yet undeveloped part of the deposits of gas hydrate.