CN110685655A - Natural gas hydrate exploitation method for heating stratum by electric pulse - Google Patents

Abstract

The invention discloses a natural gas hydrate mining method using electric pulse heating formation. Its main steps include: 1. arranging electrodes in the mining wells and connecting them to the surface; 2. inserting the hydrate reservoirs at equal intervals between the mining wells 3. Connect the two adjacent electrodes to the positive and negative electrodes of the high-voltage pulse discharge equipment respectively, to discharge and heat the hydrate reservoir; 4. Through the pulse discharge operation, the hydrate reservoir is suitable for exploitation. The invention can improve the energy efficiency of natural gas hydrate exploitation.

Description

A kind of natural gas hydrate exploitation method of electric pulse heating formation

technical field

The invention belongs to the field of natural gas hydrate research, and in particular relates to a natural gas hydrate exploitation method for electric pulse heating formation, which is suitable for the exploitation of natural gas hydrate in permafrost and marine areas.

Background technique

Natural gas hydrate has attracted extensive attention as a future replacement energy due to its huge reserves, high efficiency and cleanliness. How to realize the economical, efficient and safe exploitation of natural gas hydrate in the reservoir has become the main content of natural gas hydrate research. Since natural gas hydrate needs a certain temperature and pressure to exist stably, increasing the temperature of the reservoir or reducing the pressure of the reservoir can realize the exploitation of hydrate in the reservoir. Based on the above principles, the current gas hydrate extraction methods are mainly divided into pressure reduction method and heat shock method.

The depressurization method depressurizes the reservoir by extracting the fluid from the reservoir to break the natural gas hydrate phase balance and realize the exploitation. Since it consumes part of the external energy to extract the formation fluid, it does not require the injection of other energy and substances, so it is a relatively economical exploitation. method. However, since hydrate decomposition is an endothermic process, a large amount of reservoir heat will be consumed in the process of hydrate decomposition and production due to depressurization, resulting in a decrease in reservoir temperature, and hydrate decomposition cannot be maintained continuously. At the same time, it will lead to the formation of secondary hydrate in the formation. When the temperature of the reservoir drops below 0 °C, the reservoir water will freeze and block the fluid channel. Therefore, the pressure reduction method cannot realize the continuous exploitation of natural gas hydrate.

The heat shock method is considered to be an effective technical means to solve the problem that the formation energy in the depressurization method cannot maintain the continuous decomposition of hydrates. At present, heat shock methods mainly include high-temperature steam input into the reservoir, high-temperature hot water input into the reservoir, high-temperature brine input into the reservoir, in-situ methane oxidation heating, in-situ electric heating and other methods. The distance of the heat pipeline is long, and the formation permeability and thermal conductivity are low, resulting in more heat loss and less effective heat utilization in the existing heat shock mining. ratio to injected heat) is lower. Therefore, it is necessary to propose an efficient formation heating method to solve many problems of the current heat shock method.

In this application, natural gas hydrate is referred to as hydrate for short.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a natural gas hydrate extraction method for electric pulse heating formation, which can improve the energy efficiency of natural gas hydrate extraction.

The technical problem to be solved by this invention is realized through such technical scheme, and it comprises the following steps:

1. According to the conventional method, lay the production well on the hydrate reservoir;

2. Arrange electrodes in the production well and wire them to the surface, and fill the well below the top surface of the hydrate reservoir with seawater to realize the coupling between the electrode and the hydrate reservoir;

3. Insert electrodes and temperature probes into the hydrate reservoir by tamping the pipe at equal intervals between two adjacent production wells. The electrodes are arranged in a straight line and wired to the surface;

4. Connect the two adjacent electrodes to the positive and negative poles of the high-voltage pulse discharge device respectively; after the high-voltage pulse discharge device is charged by the ground power supply, the discharge switch is turned on, and the high-voltage pulse energy passes through the two adjacent electrodes to realize the discharge of the hydrate reservoir. discharge heating;

5. According to the temperature change of the formation tested by the probe, determine the formation temperature rise for a single discharge, and calculate the heat required for hydrate decomposition according to the formation hydrate saturation, and determine the number of pulse discharge operations until the hydrate reservoir is suitable for exploitation;

The number of reservoir discharges = the heat required for the complete decomposition of hydrate under the corresponding hydrate saturation condition / the heat generated by the formation in a single discharge, the formation temperature is just enough to maintain the complete decomposition of hydrate, that is, to meet the requirements of hydrate reservoir production.

6. Connect the electrodes arranged between two adjacent production wells to high-voltage pulse discharge equipment in turn, and repeat steps 4 and 5 to achieve uniform heating of the hydrate reservoir between the two adjacent production wells.

Preferably, the spacing of the production wells is 500m, and the electrode spacing between the production wells is 50m.

The working principle of the present invention is:

According to the document "Research and Application of High Voltage Electric Pulse Treatment Technology for Reservoir", Yang Fumin et al.. Oil Drilling and Production Technology, 1998, 20(5), 64-67 and the document "Pulse Discharge Technology for Dredging Oil and Water Wells" Han Bo et al. .. Logging Technology, 1998, 22 (2), 123-126 records: High-voltage pulse discharge has been widely used in oil and gas well stimulation and reconstruction construction, and achieved remarkable results. However, in the application of high-voltage electrical pulses, the effect of high-intensity pulsed shock waves generated by high-voltage pulsed discharge is mainly used, and the thermal effect generated by high-voltage pulsed discharge is not used. Since hydrate reservoirs, especially marine hydrate reservoirs are generally filled with formation water with relatively high salt concentration, when high-voltage pulses are passed into the formation through electrodes, the formation water with high salt concentration has good electrical conductivity, which can achieve relatively high salt concentration. Long-distance high-voltage pulse discharge, the instantaneous high current of high-voltage pulse discharge can produce shock wave effect and thermal effect in hydrate reservoir. Among them, the shock wave effect can generate micro-fractures in the hydrate reservoir, improve the permeability of the hydrate reservoir, and facilitate the discharge of methane and water from the decomposition of the hydrate; while the thermal effect can directly heat the hydrate reservoir at a high speed, which is Formation hydrate decomposition provides heat.

The technical effect of the present invention is:

The exploitation of natural gas hydrate through the electric pulse heating formation of the invention can realize the efficient and rapid heating of the hydrate reservoir, and overcome the process of slow heat transfer from the wellbore to the formation in the heating method in the prior art; The method does not need to inject additional substances into the formation, thus overcoming the disadvantage that the existing steam injection and hot water injection heating methods are difficult to penetrate into the hydrate reservoir due to the low formation permeability. At the same time, the invention adopts the method of directly energizing the hydrate reservoir electrode to realize the heating and permeation enhancement of the hydrate reservoir, which avoids problems such as heat loss caused by excessively long pipelines from the ground to the reservoir due to steam injection or hot water injection. . In addition, in the present invention, there is no need to drill wells for electrode layout between productions, and a rammed pipe is directly used for insertion, which reduces the cost of electrode layout and ensures that the electrodes can be well coupled with the hydrate reservoir. The invention can effectively realize the high-efficiency heating and permeability enhancement of the hydrate reservoir, and improve the energy efficiency and economy of natural gas hydrate exploitation.

Claims (2)

1. a natural gas hydrate exploitation method of electric pulse heating formation, is characterized in that: comprise the following steps: 1) According to the conventional method, lay the production well on the hydrate reservoir; 2) Arrange electrodes in the production well and wire them to the surface, and fill the well below the top surface of the hydrate reservoir with seawater to realize the coupling between the electrode and the hydrate reservoir; 3) Insert electrodes into the hydrate reservoir by tamping the pipe at equal intervals between two adjacent production wells, and the electrodes are arranged in a straight line and wired to the surface; 4) Connect the two adjacent electrodes to the positive and negative poles of the high-voltage pulse discharge device respectively; after the high-voltage pulse discharge device is charged with a ground power supply, the discharge switch is turned on, and the high-voltage pulse energy can store the hydrate through the two adjacent electrodes. Layer discharge heating; 5) Determine the number of pulse discharge operations according to the change of formation temperature until the hydrate reservoir is suitable for exploitation; 6) Connect the electrodes arranged between two adjacent production wells with high-voltage pulse discharge equipment in turn, and repeat steps 4) and 5) to achieve uniform heating of the hydrate reservoir between the adjacent two production wells. 2 . The natural gas hydrate mining method of electric pulse heating formation according to claim 1 , wherein the spacing between the mining wells is 500 m, and the spacing between the mining wells is 50 m. 3 .