CN105464634A - Method for exploiting methane hydrate by using stored carbon dioxide - Google Patents

Abstract

The invention provides a method for exploiting methane hydrate by storing carbon dioxide, which includes the following steps: selecting a methane hydrate soil layer with a suitable depth under the seabed, and then erecting a carbon dioxide mine connected to the methane hydrate soil layer from an ocean platform according to geological information. Injection well; inject liquid carbon dioxide into the carbon dioxide injection well. After the liquid carbon dioxide diffuses and percolates in the methane hydrate soil layer, it will be replaced with methane hydrate to generate methane gas; the production time will be determined according to the replacement efficiency of carbon dioxide and methane hydrate. Then erect a methane production well leading to the methane hydrate soil layer within the replacement range of the carbon dioxide injection well to realize the production of methane gas. After the carbon dioxide is injected and stored in the present invention, the carbon dioxide will replace the methane hydrate in these areas during the seepage process. During this process, the mechanical properties of the formation change little, which can avoid geological disasters caused by methane hydrate pumping and mining, and reduce greenhouse gases at the same time. .

Description

A method for exploiting methane hydrate by storing carbon dioxide

technical field

The invention relates to the field of deep-sea resource exploitation, in particular to a method for replacing recoverable methane gas by storing carbon dioxide in seabed methane hydrate soil layers.

Background technique

At present, the oil and gas well depressurization mining method and heating mining method for exploiting methane gas in the subsea methane hydrate soil layer have been proved by the international methane hydrate experimental mining in the United States, Japan and Canada, and their efficiency can neither meet the needs of commercial exploitation nor meet the needs of commercial exploitation. It will cause geological and environmental effects that are unfavorable to humans. Therefore, it is necessary to propose a new economical and safe mining technology for methane hydrate, so as to provide technical reserves for the commercial utilization of methane hydrate.

Contents of the invention

The purpose of the present invention is to provide a method for exploiting the methane gas in the hydrate layer under the seabed, so as to avoid the geological damage caused by direct exploitation.

In particular, the present invention provides a method for exploiting methane hydrate by storing carbon dioxide, comprising the following steps:

Step 101, selecting a methane hydrate soil layer at a suitable depth under the seabed, and erecting a carbon dioxide injection well connected from the offshore platform to the methane hydrate soil layer according to geological information;

Step 102, inject liquid carbon dioxide into the carbon dioxide injection well, and after the liquid carbon dioxide diffuses and percolates in the methane hydrate soil layer, it replaces with the methane hydrate to generate methane gas;

Step 103, according to the replacement efficiency of carbon dioxide and methane hydrate, determine the production time, and then set up a methane production well leading to the methane hydrate soil layer within the replacement range of the carbon dioxide injection well, so as to realize the production of methane gas.

Further, a horizontal well extending horizontally is arranged at the bottom of the carbon dioxide injection well.

Further, the horizontal well is located at the bottom of the methane hydrate soil layer, and a plurality of through holes are provided on the wellbore to facilitate the diffusion and seepage of carbon dioxide to the outside.

Further, the seawater depth at the methane hydrate soil layer is at least greater than 800 meters.

Further, the geological information includes methane hydrate content, permeability, water content, porosity, mechanical stiffness and strength, pore liquid pressure and temperature parameters of the methane hydrate soil layer.

Further, when erecting the carbon dioxide injection well, the carbon dioxide injection rate, injection time, injection pressure and injection temperature are determined according to the geological information.

Further, the injection quantity Q of carbon dioxide is determined by the following formula:

Q＝π·x ² ·L/2

Among them, L is the length of the horizontal well, and x is the length of the carbon dioxide injection well.

Further, the length x of the carbon dioxide injection well is determined by the following formula:

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;c</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}\mathrm{<span\; class="notranslate">\; t</span>}}$

Among them, k _e is the permeability of methane hydrate soil layer, φ _e is the porosity of methane hydrate soil layer, μ is the viscosity coefficient of carbon dioxide, c _t is the compressibility coefficient of formation, and t is the injection time of carbon dioxide.

Further, in step 103, in the process of exploiting methane gas, it is necessary to determine the permeability of carbon dioxide in the methane hydrate soil layer according to the replacement of carbon dioxide and methane hydrate, and then adjust the injection amount of carbon dioxide to balance the methane gas The production rate and production rate of the carbon dioxide gas in the methane _hydrate soil layer are calculated using the following formula:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; N</span>}}$

Among them, k _e is the permeability of methane hydrate soil layer, ΔS _h is the change value of hydrate saturation, _Sh is the hydrate saturation, and N is the decrease index of hydrate soil permeability with the increase of hydrate saturation.

Further, the effective porosity of the methane hydrate soil layer after being replaced by carbon dioxide Calculated using the following formula:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>$

Among them, _φe is the porosity of methane hydrate soil layer.

In the present invention, after the carbon dioxide is injected and stored, it will seep in a certain range in the hydrate formation for decades, and the carbon dioxide will replace the methane hydrate in these areas during the seepage process, thereby obtaining methane gas in a free state. After decades of accumulation Methane gas mining can be carried out directly. During this process, the mechanical properties of the formation change little, which can avoid geological disasters caused by methane hydrate pumping and mining, and reduce greenhouse gases at the same time.

Description of drawings

Fig. 1 is a schematic flow chart of a method according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of carbon dioxide injection and extraction according to an embodiment of the present invention;

In the figure: 10-seawater layer, 20-overlying soil layer, 30-hydrate layer, 40-carbon dioxide injection well, 50-methane production well, 60-horizontal well, 61-through hole.

detailed description

As shown in FIG. 1 , an embodiment of the present invention discloses an implementation process of a method for exploiting methane hydrate by storing carbon dioxide. The soil below the seawater layer 10 is generally divided into an upper overlying soil layer 20 and a lower hydrate layer 20, and the hydrate layer will form a corresponding hydrate layer, such as a methane hydrate layer, because it contains different minerals. In this embodiment, the methane in the methane hydrate is converted into gas by means of replacement, and then exploited, thereby reducing the damage to the geology. The method generally includes the following steps:

Step 101, selecting a methane hydrate soil layer at a suitable depth under the seabed, and erecting a carbon dioxide injection well connected from the offshore platform to the methane hydrate soil layer according to geological information;

In this embodiment, the depth of the seawater layer 10 at the methane hydrate soil layer is generally greater than 800 meters. Before setting up the carbon dioxide injection well 40, first obtain the methane hydrate content, permeability, water content, porosity, mechanical stiffness and strength, pore liquid pressure and temperature of the current methane hydrate soil layer according to geophysical exploration and geological drilling data parameters and other geological information.

In order to improve the replacement effect of carbon dioxide, a horizontal well 60 extending horizontally along the methane hydrate layer can be arranged at the bottom of the carbon dioxide injection well 40, and the horizontal well 60 is used to vertically connect the carbon dioxide injection well 40 to transfer the injected carbon dioxide to a further far away. The horizontal well 60 may be located at the bottom of the methane hydrate layer to facilitate the upward diffusion of carbon dioxide. Further, in order to speed up the discharge rate of carbon dioxide, a plurality of through holes 61 facing different directions may be arranged on the wellbore of the horizontal well 60 .

Among them, the injection quantity Q of carbon dioxide is determined by the following formula:

Q＝π·x ² ·L/2

In the formula, L is the length of the horizontal well 60, and x is the length of the carbon dioxide injection well 40.

The length x of the carbon dioxide injection well 40 is determined by the following formula:

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;c</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}\mathrm{<span\; class="notranslate">\; t</span>}}$

In the formula, k _e is the permeability of methane hydrate soil layer, φ _e is the porosity of methane hydrate soil layer, μ is the viscosity coefficient of carbon dioxide, c _t is the formation compressibility coefficient, and t is the injection time of carbon dioxide.

On the basis of the above geological information, the carbon dioxide injection rate, injection time, injection pressure, injection temperature and other parameters of the erected carbon dioxide injection well 40 are determined.

Step 102, inject liquid carbon dioxide into the carbon dioxide injection well, and after the liquid carbon dioxide diffuses and percolates in the methane hydrate soil layer, it replaces with the methane hydrate to generate methane gas.

After carbon dioxide enters the methane hydrate soil layer, it will replace with methane in the methane hydrate to form carbon dioxide hydrate. At the same time, the replaced methane is stored in the pores of the formation in a free gas state.

Step 103, according to the replacement efficiency of carbon dioxide and methane hydrate, determine the production time, and then set up a methane production well leading to the methane hydrate soil layer within the replacement range of the carbon dioxide injection well, so as to realize the production of methane gas.

The replacement efficiency in this step needs to be determined based on information such as carbon dioxide permeability and replacement efficiency, and then determine whether the amount of methane generated in the methane hydrate soil layer meets the standard for exploitation according to the replacement efficiency. The methane recovery well 50 can be erected on the side of the permeable area formed by the carbon dioxide injection well 40 or the horizontal well 60 to collect the squeezed methane gas from the periphery. A plurality of methane production wells 50 at different locations can be erected according to the methane distribution information displayed by the formation monitoring information.

In addition, in this step, it is also necessary to consider that with the gradual infiltration and replacement of carbon dioxide, the permeability and porosity of the methane hydrate soil layer will also change, so the injection rate of carbon dioxide and the production rate of methane also need to be adjusted accordingly. Adjustment.

Among them, the permeability k _ec of carbon dioxide in the methane hydrate soil layer is calculated by the following formula:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; N</span>}}$

In the formula, ΔS _h is the change value of hydrate saturation, _Sh is the hydrate saturation, and N is the decrease index of hydrate soil permeability with the increase of hydrate saturation.

Effective porosity of methane hydrate soil layers replaced by carbon dioxide Calculated using the following formula:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>$

In the formula, ΔS _h is the change value of hydrate saturation, and _Sh is the hydrate saturation.

According to the method of the present invention: the length of the horizontal well 60 is 1000m, the injection time of carbon dioxide is 20 years, the hydrate saturation of the methane hydrate soil layer is 50%, the effective permeability is ^{10-17 m2} , the effective porosity is 20%, and the carbon dioxide The length of the seepage front from the wellbore is about 160m, and the injection volume of liquid carbon dioxide is about 8×10 ⁷ m ⁶ . Taking 20 years as an example, carbon dioxide seeps into the methane hydrate soil layer, and carbon dioxide replaces the methane in the hydrate to form carbon dioxide hydrate. Then there are two types of hydrate in the formation, one is the hydration of the remaining methane after replacement The second is the hydrate formed by carbon dioxide. By monitoring the distribution of methane concentration in the formation along the depth of the formation, the concentration of free methane is determined. After the concentration reaches the index of mining economy, the mining layer is selected, and the method of carbon dioxide flooding is used to mine free methane gas.

In the present invention, multiple carbon dioxide injection wells 40 can be drilled simultaneously in the same methane hydrate soil zone according to geological information. In addition, one carbon dioxide injection well 40 can also be connected to multiple horizontal wells 60 facing different directions at the same time.

So far, those skilled in the art should appreciate that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, without departing from the spirit and scope of the present invention, the disclosed embodiments of the present invention can still be used. Many other variations or modifications consistent with the principles of the invention are directly identified or derived from the content. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims (10)

1. A method for exploiting methane hydrate by storing carbon dioxide, characterized in that, comprising the steps: Step 101, selecting a methane hydrate soil layer at a suitable depth under the seabed, and erecting a carbon dioxide injection well connected from the offshore platform to the methane hydrate soil layer according to geological information; Step 102, injecting liquid carbon dioxide into the carbon dioxide injection well, after the liquid carbon dioxide diffuses and percolates in the methane hydrate soil layer, it replaces with the methane hydrate to generate methane gas; Step 103, according to the replacement efficiency of carbon dioxide and methane hydrate, determine the production time, and then set up a methane production well leading to the methane hydrate soil layer within the replacement range of the carbon dioxide injection well, so as to realize the production of methane gas. 2. The method of claim 1, wherein, A horizontal well extending horizontally is arranged at the bottom of the carbon dioxide injection well. 3. The method of claim 2, wherein, The horizontal well is located at the bottom of the methane hydrate soil layer, and a plurality of through holes are arranged on the well body to facilitate the diffusion and seepage of carbon dioxide to the outside. 4. The method of claim 1, wherein, The seawater depth at the methane hydrate soil layer is at least greater than 800 meters. 5. The method of claim 1, wherein, The geological information includes methane hydrate content, permeability, water content, porosity, mechanical stiffness and strength, pore liquid pressure and temperature parameters of the methane hydrate soil layer. 6. The method of claim 5, wherein, When erecting the carbon dioxide injection well, the carbon dioxide injection rate, injection time, injection pressure and injection temperature are determined according to the geological information. 7. The method of claim 5, wherein, The injection quantity Q of carbon dioxide is determined by the following formula: Q＝π·x ² ·L/2 Among them, L is the length of the horizontal well, and x is the length of the carbon dioxide injection well. 8. The method of claim 7, wherein, The length x of the carbon dioxide injection well is determined by the following formula: $\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;c</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}\mathrm{<span\; class="notranslate">\; t</span>}}$ Among them, k _e is the permeability of methane hydrate soil layer, φ _e is the porosity of methane hydrate soil layer, μ is the viscosity coefficient of carbon dioxide, c _t is the compressibility coefficient of formation, and t is the injection time of carbon dioxide. 9. The method of claim 1, wherein, In the step 103, in the process of exploiting methane gas, it is necessary to determine the permeability of carbon dioxide in the methane hydrate soil layer according to the replacement situation of carbon dioxide and methane hydrate, and then adjust the injection amount of carbon dioxide to balance the extraction rate of methane gas and generation rate, the permeability k _ec of carbon dioxide in the methane hydrate soil layer is calculated by the following formula: ${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; N</span>}}$ Among them, k _e is the permeability of methane hydrate soil layer, ΔS _h is the change value of hydrate saturation, _Sh is the hydrate saturation, and N is the decrease index of hydrate soil permeability with the increase of hydrate saturation. 10. The method of claim 9, wherein, The effective porosity of the methane hydrate soil layer after being replaced by carbon dioxide Calculated using the following formula: ${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; )</span>$ Among them, _φe is the porosity of methane hydrate soil layer.