CN101864937A - Exploitation of marine natural gas hydrate by geothermal energy - Google Patents

Abstract

The invention relates to a technique for exploiting marine natural gas hydrate by using geothermal energy, which comprises the following steps: 1) drilling a branch well to a target hot rock layer; 2) drilling a directional well to the target hot rock layer by using a casing to pass through a natural gas hydrate reservoir , perforate the casing passing through the natural gas hydrate reservoir, and then seal the wellhead; 3) Use a pump to press seawater into the target hot rock formation, and the seawater is pressed into the directional well after being heated by heat exchange. Into the area where the natural gas hydrate reservoir flows into, decomposed natural gas hydrate and cooled seawater are obtained; 4) The natural gas hydrate and cooled seawater are transported to the sea surface through the gas-liquid recovery pipe, and the natural gas is collected by separation at the outlet. The invention has the beneficial effects of greatly reducing the cost of heat injection in the mining process, enabling the sustainable development of the mining process, and causing little environmental damage and pollution. Various technical requirements in the mining process can be referred to in the existing oil mining process, reducing The difficulty of mining technology realization.

Description

Exploitation of marine natural gas hydrate by geothermal energy

technical field

The invention relates to a technique for exploiting marine natural gas hydrate by utilizing geothermal energy.

Background technique

For nearly a century, traditional energy sources such as oil and coal have been exhausted, but people's demand for energy has continued unabated. Due to its huge reserves, high energy density, wide distribution, and large scale, natural gas hydrate is considered to be the most ideal alternative energy source in the 21st century. But gas hydrate can only become a real energy source if the problem of its exploitation is solved. After long-term research, the industry has proposed three typical traditional mining methods: thermal activation method, decompression method and chemical inhibitor injection method. However, these mining methods have some defects that cannot meet commercial mining. The thermal excitation method has low efficiency, and the heating area is small, and the energy consumption is large; for the decompression method, it is economically feasible only when the gas hydrate reservoir is located near the temperature-pressure equilibrium boundary. After a period of time, the decomposing method slows down or even stops decomposing; the chemical inhibitor injection method has a slow effect on the natural gas hydrate layer, and the cost of chemical reagents required is very high, and it will also bring some adverse environmental problems. Studies have shown that my country's South China Sea seabed Both natural gas hydrate and geothermal resources are very rich, how to develop such resources reasonably and effectively has become the focus of researchers.

Contents of the invention

The problem to be solved by the present invention is to propose a process for exploiting marine natural gas hydrate by using geothermal heat, which saves energy, has little damage to the environment, and has strong feasibility.

The solution that the present invention adopts for solving the above-mentioned problem is: utilize the technique of geothermal exploitation marine natural gas hydrate, it is characterized in that comprising the following steps:

1) Drill branch wells in the target hot rock layer first: use hydraulic fracturing to form interconnected rock fractures in the target hot rock layer area;

2) Use the casing to pass through the gas hydrate reservoir, drill a directional well into the target hot rock formation, perforate the casing passing through the gas hydrate reservoir, and then seal the wellhead;

3) Use a pump to press seawater into the target hot rock formation. After being heated by heat exchange, the seawater is pressed into the directional well, and flows into the area of the gas hydrate reservoir at the perforation of the casing, providing hot seawater for the decomposition of gas hydrate. Decomposed gas hydrates and cooled seawater;

4) The decomposed natural gas hydrate obtained in step 3) and the cooled seawater are transported to the sea surface through the gas-liquid recovery pipe, separated by a gas-liquid separator at the outlet, and the natural gas is collected.

According to the above scheme, the number of directional wells is 3-5.

According to the above scheme, the bottom end of the directional well is connected with a slotted casing to protect the well wall.

The beneficial effects of the present invention are:

There are abundant natural gas hydrate resources in the seabed, and there are also a large number of geothermal resources in the deep seabed. Utilizing the geothermal resources of the seabed itself to mine natural gas hydrate can greatly reduce the cost of heat injection in the mining process, enable the sustainable development of the mining process, and cause little environmental damage and pollution. Various technical requirements in the mining process can be referred to in the existing There is an oil extraction process, which reduces the difficulty of realizing the extraction process.

Description of drawings

Fig. 1 is a schematic diagram of the process of exploiting marine natural gas hydrate by using geothermal energy according to the present invention.

Detailed ways

The present invention will be further described in detail through the embodiments below in conjunction with the accompanying drawings, but the embodiments will not constitute a limitation to the present invention.

As shown in Figure 1, branch wells 8 are first drilled in the target hot rock formation 6, and the hydraulic fracturing method commonly used in oil exploitation is used to form a large number of interconnected rock fractures in the target rock formation area, creating channels for the free circulation of fluid, and increasing the size of the well. heat exchange surface to obtain a good heat exchange effect, provide sufficient hot seawater for the thermal activation method, and then use the casing 4 to pass through the natural gas hydrate reservoir 3, and drill three directional wells 5 into the target hot rock formation (the bottom of the well can be slotted Casing is connected to protect the well wall), and then the casing passing through the gas hydrate reservoir is perforated, and then the wellhead is sealed9. Use the pump 1 to press the seawater into the target hot rock formation through the seawater injection pipe 7. After the seawater is heated by heat exchange, it is pressed into the directional well 5, and flows into the gas hydrate reservoir area at the perforation 10, providing a steady stream for the decomposition of the gas hydrate. The hot seawater, decomposed natural gas and cooled seawater are transported to the sea surface through the gas-liquid recovery pipe, and the gas and liquid are separated by the gas-liquid separator 2 at the outlet to collect the natural gas, and the cold seawater is directly discharged into the sea.

The equipment used in this process mainly includes (1) water injection pump, (2) seawater injection pipe, (3) hot seawater input pipe, (4) gas-liquid recovery pipe, (5) gas-liquid separator, etc.

(1) Water injection pump

The water injection pump directly pumps seawater into the seawater injection pipe, and provides a certain pressure to meet the circulation of seawater in the system.

(2) Seawater injection pipe

The main function of the seawater injection pipe is to inject seawater into the target hot rock formation, so that the seawater can be circulated and heated in the rock fractures.

(3) Hot sea water input pipe

The heated seawater in the rock fractures of the target hot rock layer flows into the hot seawater input pipe (ie, directional well) under the action of pressure, and then the hot seawater flows into the gas hydrate reservoir area at the perforation of the casing;

(4) Gas-liquid recovery pipe

The natural gas and water generated by heating and decomposing hot seawater and the cooled seawater are pumped to the working platform on the sea surface through the gas-liquid recovery pipe;

(5) Gas-liquid separator

The gas-liquid mixture pumped to the offshore working platform is separated into natural gas and seawater through the gas-liquid separator.

Claims (3)

1. The technique of exploiting marine natural gas hydrate by geothermal energy is characterized in that it comprises the following steps: 1) Drill branch wells in the target hot rock layer first: use hydraulic fracturing to form interconnected rock fractures in the target hot rock layer area; 2) Use the casing to pass through the gas hydrate reservoir, drill a directional well into the target hot rock formation, perforate the casing passing through the gas hydrate reservoir, and then seal the wellhead; 3) Use a pump to press seawater into the target hot rock formation. After being heated by heat exchange, the seawater is pressed into the directional well, and flows into the area of the gas hydrate reservoir at the perforation of the casing, providing hot seawater for the decomposition of gas hydrate. Decomposed gas hydrates and cooled seawater; 4) The decomposed natural gas hydrate obtained in step 3) and the cooled seawater are transported to the sea surface through the gas-liquid recovery pipe, separated by a gas-liquid separator at the outlet, and the natural gas is collected. 2. The technique for exploiting marine natural gas hydrate by utilizing geothermal energy according to claim 1, characterized in that the number of directional wells is 3-5. 3. The technique for exploiting marine natural gas hydrate by utilizing geothermal heat according to claim 1 or 2, characterized in that the bottom end of the directional well is connected with a slotted casing to protect the well wall.