CN105863589A - Method for vertical shaft electric-heating-assisted depressurizing production of natural gas hydrate reservoir - Google Patents

Abstract

The invention discloses a method for exploiting natural gas hydrate reservoirs by using electric heating in vertical wells to assist depressurization. The electrode is mainly installed at the lower end of the tubing, combined with the depressurization of natural gas hydrate, forcing the current to pass through the natural gas hydrate reservoir, forming a current loop, realizing the thermal exploitation of natural gas hydrate, and improving the recovery rate of natural gas hydrate reservoir. The specific method is as follows: the electrode is installed at the lower end of the oil pipe, the ground power adjustment equipment transmits the current to the downhole electrode through the cable, and the natural gas hydrate is partially decomposed through decompression mining, and the water produced by the decomposition of the natural gas hydrate is used as the conductor. The natural gas hydrate reservoir is used as resistance for heating to realize the thermal exploitation of natural gas hydrate. The method has the advantages of simple structure, energy saving, environmental protection and easy control, and provides effective measures for the development of natural gas hydrate reservoirs.

Description

A method of using vertical well electric heating to assist decompression to exploit natural gas hydrate reservoirs

technical field

The invention relates to a method for exploiting a natural gas hydrate reservoir, in particular to a method for exploiting a natural gas hydrate reservoir by using electric heating in a vertical well to assist depressurization.

Background technique

Gas hydrate is a crystalline substance produced by natural gas and water under high pressure and low temperature conditions, and is mainly distributed in seabed sediments and some terrestrial permafrost zones. Natural gas hydrate is widely distributed and has high energy density. Its organic carbon content is twice the total carbon content of coal, oil, and natural gas.

The exploitation of natural gas hydrate is to destroy the phase balance of natural gas hydrate, make it decompose into natural gas and water and carry out exploitation. At present, the mining methods of natural gas hydrate are mainly divided into the following four categories: depressurization mining method, heat injection method, inhibitor injection method and carbon dioxide replacement method. Among the above mining methods, the depressurization mining method has a very slow mining speed and is a relatively passive mining method; the heat injection method needs to directly inject hot water or steam into the natural gas hydrate reservoir, which is costly and easy to cause reservoir damage; The inhibitor injection method pollutes the environment seriously and the inhibitor is expensive; the key to the carbon dioxide replacement method is to find a suitable carbon dioxide gas source, and its application is relatively limited. The use of electric heating to exploit natural gas hydrate reservoirs can convert electrical energy into thermal energy for exploiting natural gas hydrate reservoirs. The equipment is simple and the energy utilization rate is high, and it has attracted more and more attention. However, there is no one that uses vertical well electric heating to assist The method of depressurization to exploit gas hydrate reservoirs seriously restricts the research progress of gas hydrate reservoir development.

Contents of the invention

The main purpose of the present invention is to provide a method for exploiting natural gas hydrate reservoirs by using electric heating in vertical wells to assist depressurization, which can greatly increase the recovery rate of natural gas hydrate reservoirs.

The purpose of the present invention is mainly achieved by the following methods: the electrode is installed at the lower end of the oil pipe, the water produced by the decomposition of natural gas hydrate is used as a conductor, the current passes through the natural gas hydrate reservoir, and returns to the ground through an ordinary steel casing to form a circuit, and the natural gas hydrate The reservoir is heated as a resistance to realize the thermal exploitation of natural gas hydrate, which specifically includes the following steps:

(1) According to the geological data of natural gas hydrate reservoirs, the natural gas hydrate reservoirs with an average effective thickness greater than 20m are preferred, a vertical well is drilled, and the well is completed with a casing. The casing is made of stainless steel in the gas hydrate reservoir section. A section at the upper boundary of the natural gas hydrate reservoir is made of glass fiber reinforced plastics, forcing the current on the stainless steel casing of the natural gas hydrate reservoir to pass through the natural gas hydrate reservoir, thereby achieving the purpose of heating the natural gas hydrate reservoir;

(2) The control cabinet is installed on the ground. The control cabinet is composed of power supply, power conditioning equipment and switch. Switches are installed between the equipment for connection control. The power conditioning equipment uses 480V AC, the current frequency range is 50-60Hz, and the output power range is 100-120kW;

(3) The electrode is installed at a distance of 0.5-1m above the end of the oil pipe. In order to prevent the current from directly passing through the oil pipe to form a loop, there is a section of glass fiber reinforced plastic oil pipe between the oil pipe and the downhole electrode. A contactor is installed on the electrode. The contactor is Made of stainless steel, it is used to connect the electrode with the casing of the natural gas hydrate reservoir, so that the current on the electrode is transmitted to the casing, and the electrode is connected to the electric power in the ground control cabinet through the cable in the oil jacket annulus. The regulating equipment is connected, the oil pipe is connected with the surface separator, and the water and gas produced by the decomposition of natural gas hydrate are separated and processed through the surface separator;

(4) According to the geological conditions of natural gas hydrate reservoirs, design the pressure parameters of natural gas hydrate reservoirs for depressurized exploitation of vertical wells and the critical parameters of thermally exploited natural gas hydrate reservoirs, including the wellbore pressure range of 1.5-4.5MPa during depressurized exploitation , the closing critical gas production rate is 500-1000m3/d, and the critical closing gas production rate is 1500-2000m3/d;

(5) According to the pressure parameters of the natural gas hydrate reservoir for depressurization exploitation of the vertical well, the depressurization exploitation of the natural gas hydrate reservoir is carried out until the daily gas production rate is lower than the closing critical daily gas production rate, and the depressurization exploitation ends;

(6) Close the electric switch in the ground control cabinet, use the water produced by decompression mining as a conductor, and use the natural gas hydrate reservoir as a resistance to heat, so as to realize the thermal exploitation of natural gas hydrate. When the critical daily gas production rate of the sluice is reached, the electric sluice is disconnected to stop mining.

Beneficial effects of the present invention: firstly, depressurize the natural gas hydrate reservoir, then use the water produced by the decomposition of natural gas hydrate as a conductor, force the current to pass through the natural gas hydrate reservoir through electrodes, and use the natural gas hydrate reservoir as a resistance for heating , realize the thermal recovery of natural gas hydrate, thereby greatly increasing the recovery rate of natural gas hydrate. The method is suitable for the exploitation of various types of natural gas hydrate reservoirs. It is energy-saving and environmentally friendly, has a simple structure and is easy to control, and provides effective measures for the exploitation of natural gas hydrate reservoirs.

Description of drawings

Fig. 1 is a schematic diagram of a gas hydrate reservoir exploited by using electric heating in a vertical well to assist depressurization.

Figure 2 is an enlarged view of the wellbore.

Among them, 1. Ground control cabinet; 2. Electric gate; 3. Power conditioning equipment; 4. Power supply; 5. Cable; 6. Oil pipe; 7. Fiberglass oil pipe; 8. Fiberglass casing; 9. Perforation; 10. ; 11. Electrodes; 12. Contactors; 13. Natural gas hydrate pools; 14. Ground separators.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings, but the implementation scope of the present invention is not limited.

(1) According to the geological data of natural gas hydrate reservoirs, a natural gas hydrate reservoir with an average effective thickness of 30 m is selected, a vertical well is drilled, and the well is completed with casing 10, which is made of stainless steel. There is a glass fiber reinforced plastic casing 8 at the boundary, forcing the current on the stainless steel casing of the natural gas hydrate reservoir section to pass through the natural gas hydrate reservoir 13, so as to achieve the purpose of heating the natural gas hydrate reservoir. Object possession 13;

(2) Install the ground control cabinet 1. The control cabinet is composed of a power supply 4, power conditioning equipment 3 and switch 2, wherein the power supply 4 is used to provide the AC power required for heating the natural gas hydrate reservoir 13, and the power conditioning equipment 3 is used to control the power output Power, install switch 2 between power supply 4 and power conditioning equipment 3 for connection control, power conditioning equipment 3 uses 480V AC, current frequency is 55Hz, output power is 110kW;

(3) An electrode 11 is installed 0.5m above the end of the oil pipe 6. In order to prevent the current from directly passing through the oil pipe 6 to form a loop, there is a section of glass fiber reinforced plastic oil pipe 7 between the oil pipe 6 and the downhole electrode 11, and a contactor is installed on the electrode 11. 12. The contactor 12 is made of stainless steel, and is used to connect the electrode 11 with the casing at the natural gas hydrate reservoir 13, so that the current on the electrode 11 is transmitted to the casing, and the electrode 11 passes through the oil jacket The cable 5 in the annular space is connected to the power conditioning equipment 3 in the ground control cabinet 1, the oil pipe 6 is connected to the ground separator 14, and the water and gas produced by the decomposition of natural gas hydrate are separated and processed through the ground separator 14;

(4) According to the geological conditions of natural gas hydrate reservoirs, design the pressure parameters of natural gas hydrate reservoirs for depressurization exploitation of vertical wells and the critical parameters of thermal exploitation of natural gas hydrate reservoirs, including that the wellbore pressure is 3MPa during depressurization exploitation, and the combination The critical daily gas production of the gate is 800m3/d, and the critical daily gas production of the gate is 1500m3/d;

(5) According to the pressure parameters of the natural gas hydrate reservoir for depressurization exploitation of the vertical well, the depressurization exploitation of the natural gas hydrate reservoir is carried out until the daily gas production rate is lower than the closing critical daily gas production rate, and the depressurization exploitation ends;

(6) Close the switch 2 in the ground control cabinet 1, use the water produced by decompression mining as a conductor, and use the natural gas hydrate reservoir 13 as a resistance to heat, so as to realize the thermal exploitation of natural gas hydrate. When the critical daily gas production rate is lower than the critical daily gas production rate, the electric switch 2 is disconnected to stop mining.

Claims (9)

1. utilizing the method that straight well electrical heating secondary buck exploitation of gas hydrate is hidden, electrode is arranged on oil pipe lower end by it, with gas water The water that compound decomposition produces, as electric conductor, heats using gas hydrates as resistance, it is achieved the heat exploitation of gas hydrates, thus The recovery ratio of gas hydrates is greatly improved, it is characterised in that comprise the steps:

(1) it is more than the gas hydrates of 20m according to the geologic information of gas hydrates, preferably average effective caliper, drills through a bite straight well, Use cased hole completion；

(2) switch board is installed on ground, and switch board is made up of power supply, electric adjustment equipment and electric brake, and wherein power supply is used for providing heated natural gas to be hydrated Alternating current needed for thing Tibetan, electric adjustment equipment is used for controlling electrical output power, installs electric brake and connect between power supply with electric adjustment equipment Control；

(3) installing electrode at above oil pipe end 0.5～1m, electrode is installed catalyst, electrode is by cable and described ground control cabinet Electric adjustment equipment connects；

(4) according to the geological conditions of gas hydrates, pressure parameter and the heat of hiding straight well blood pressure lowering exploitation of gas hydrate tap natural gas water The critical parameters that compound is hidden are designed, wellbore pressure when exploiting including blood pressure lowering, the combined floodgate critical day gas production of described electric brake and disconnected lock when heat is exploited Critical day gas production；

(5) pressure parameter hidden according to described straight well blood pressure lowering exploitation of gas hydrate, carries out blood pressure lowering exploitation to gas hydrates, adopted the same day When tolerance is less than described combined floodgate critical day gas production, blood pressure lowering exploitation terminates；

(6) electric brake in described ground control cabinet is closed, decomposes the water of output as electric conductor using blood pressure lowering exploitation, using gas hydrates as Resistance heats, it is achieved the heat exploitation of gas hydrates, when the same day, gas production was less than described disconnected lock critical day gas production, is disconnected by described electric brake, Stop exploitation.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute Stating sleeve pipe in gas hydrates section is stainless steel, and having one section at the coboundary of gas hydrates is glass steel material, forces described Electric current on gas hydrates section rustless steel sleeve pipe passes gas hydrates, thus plays the purpose that heated natural gas hydrate is hidden.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute State straight well and connect gas hydrates by well-case perforating.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute The electric adjustment equipment in switch board of stating uses 480V alternating current, and current frequency range is 50～60Hz, and output power range is 100～120kW.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute Stating oil pipe to be connected with surface separator, the water of gas hydrate dissociation generation is gentle carries out separating treatment by described surface separator.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that for Prevent electric current from directly forming loop by oil pipe, between described oil pipe and Electrodes In Shallow Wells, have one section of glass fiber reinforced plastic oil pipe.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute Stating catalyst is stainless steel, telescopic joint at by electrode and gas hydrates, makes the electric current on electrode be sent to described set Guan Shang.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute State cable to be placed in oil jacket annular space, be connected with described electrode.

A kind of method utilizing straight well electrical heating secondary buck exploitation of gas hydrate to hide the most according to claim 1, it is characterised in that institute When stating blood pressure lowering exploitation, wellbore pressure scope is 1.5～4.5MPa, and described combined floodgate critical day gas production is 500～1000m³/ d, described disconnected lock critical day gas production Amount is 1500～2000m³/d。