CN110318675B - A method of thermal co-mining of deep coalbed methane - Google Patents

Abstract

The invention discloses a method for thermal co-mining of deep coalbed methane. The first step is to construct a first vertical drilling, and the wellbore is gas-sealed and thermally protected by using a thermal insulation casing; In the construction of horizontal wells, the number of layers K is determined according to the true thickness M of the coal seam and the gas drainage radius R; let K=M/2R; the third step is to construct the second vertical drilling; the fourth step is to construct the circumferential dispersion of the horizontal well In the fifth step, hydraulic fracturing is performed on each borehole to form a three-dimensional fracture network for secondary gas drainage; in the sixth step, the first vertical drilling is used as a water injection well, and the second vertical The drilling is used as a steam well, and water is injected into the deep coal seam, and the geothermal energy is transferred to the steam by the principle of heat transfer, and the steam is extracted and utilized. It can carry out gas extraction and geothermal energy extraction for deep coal seams of 1500-3000 meters, improve the efficiency of geothermal extraction, save energy and reduce emissions, and prevent geological environmental problems such as water and soil pollution and thermal pollution.

Description

A method of thermal co-mining of deep coalbed methane

technical field

The invention belongs to the field of geothermal and coalbed methane exploitation, and specifically provides a method for co-exploitation of deep coalbed methane heat.

Background technique

The total amount of coalbed methane resources shallower than 3000 meters in my country is about 55 trillion cubic meters, and the national coalbed methane resources shallower than 3000 meters are about 55 trillion cubic meters, of which the coalbed methane resources with a buried depth of 1500-3000 meters account for 54.5%. At present, most of the coal seams and coalbed methane that are shallower than 1500 meters are exploited in underground coal mines and coalbed methane development. In addition, the in-situ stress of deep coal seams is relatively high, and the permeability of coal seams is low, which seriously restricts the efficiency of coalbed methane exploitation.

Geothermal resources are a kind of green and clean energy, and there are huge reserves in the earth's crust. The global geothermal resources below 5000m underground are about 4948 trillion tons of standard coal, which has become a new energy source that countries around the world are scrambling to exploit. The geothermal energy that can be developed in my country at a depth of 2 to 3 km is about 140 billion tons of standard coal.

Geothermal resources development and utilization technology has undergone two generations of evolution. The basic characteristics of the first generation of geothermal energy mining technology are direct mining, direct supply, and direct discharge, which is the most traditional technical method. The initial utilization of mine geothermal starts from the mine return air, and the hot air with higher temperature generated by the geothermal is introduced into the wellhead to solve the problem of freezing the well in winter, saving the energy consumption of artificial preheating air source; when there is hot water gushing out The mines often use the mine's geothermal water to heat bathing and domestic water, or use the mine drainage as a source of cold and heat, transport the underground thermal energy to the ground through the mine drainage system, and establish a heat exchange station in the industrial square to use the obtained thermal energy for wellhead antifreeze And building heating on the well. The first generation of technical methods has a very low level of environmental protection and is not very sustainable. The second generation is the combination of harvesting and irrigation, using heat without water, that is, mining geothermal energy in the form of groundwater heat, extracting heat energy and then recharging. The disadvantage of the second-generation technology is that the connectivity between the extraction and irrigation wells is not easy to determine, and the reinjection efficiency is low, which will pollute the groundwater to varying degrees. part of the advantage.

Existing geothermal resource mining technology is limited to geothermal mining, and there is no relevant technical information on co-mining of coalbed methane and geothermal in deep coal seams, and high drilling cost is a major factor restricting geothermal mining.

SUMMARY OF THE INVENTION

The invention aims to provide a method for mining coalbed methane and geothermal energy in deep coal seams in the range of 1500-3000 meters.

To this end, the technical solution adopted in the present invention is: a deep coalbed methane thermal co-mining method, the steps of which are:

The first step is to construct the first vertical drilling down the surface of the coal mining field. The first vertical drilling passes through the overlying strata of the deep coal seam and the shallow mined coal seam. The wellbore is sealed and protected by thermal insulation casing. ;

In the second step, after the first vertical drilling reaches the deepest layer of the deep coal seam, the construction of each layered horizontal well is carried out in sequence from top to bottom according to the thickness of the coal seam. A circular arc is used between the first vertical drilling and each layered horizontal well. In transition, the length and number of horizontal wells in each layer are determined by the scope of mining coal fields, and the number of layers K is determined according to the following methods:

(1) Determine the true thickness M of the coal seam according to the geological data and actual drilling data;

(2) Construct the evolution model of coal permeability under the action of mechanical and thermal coupling, and calculate the gas drainage radius R under the condition of natural desorption of deep coal seam in combination with the coal seam permeability coefficient λ;

(3) Determine the number of layers K according to the true thickness M of the coal seam and the gas drainage radius R;

Let K=M/2R, when K<1, N takes 1, when K>1, N takes the integer part of K;

The third step is to construct the second vertical drilling, and the second vertical drilling is vertically connected with each layered horizontal well;

The fourth step is to construct circumferential dispersion holes on each layered horizontal well, and then use the first and second vertical drilling to conduct the first gas extraction;

The fifth step is to place gas concentration and flow monitoring sensors in the gas extraction pipeline to monitor the gas concentration and flow in real time. When the concentration and flow reach the set minimum value, hydraulic fracturing is performed on each borehole to form a three-dimensional Fracture network for secondary gas extraction;

The sixth step, after the gas drainage is completed, the first vertical drilling is used as a water injection well, and the second vertical drilling is used as a steam outlet, water is injected into the deep coal seam, and the geothermal energy is transferred to the water vapor by the principle of heat transfer, and the Extraction and utilization of water vapor.

As a preference of the above solution, the high-temperature water vapor formed by mining reaches the ground through the second vertical drilling well to generate electricity. Due to the high temperature of deep geothermal and higher utilization value, it is used for power generation, and its social and economic benefits are more significant.

It is further preferred that three horizontal wells are arranged in each of the layers, and the three horizontal wells are arranged at equal intervals. The horizontal wells in the center are vertically bent and connected, and the whole is arranged in the shape of a "Sun". On the premise of ensuring complete gas and heat extraction, the layout of horizontal wells in each layer is optimized as much as possible to reduce drilling complexity and improve extraction efficiency.

In the same way, each of the layered horizontal wells is arranged in the front and rear center and the left and right centers in the deep coal seam.

Beneficial effects of the present invention:

(1) In this deep coalbed methane thermal co-mining method, the first and second vertical drilling of the construction can penetrate deep into the 1500-3000 meters deep coal seam, and the circumferential dispersion holes are constructed on each layered horizontal well. The construction of holes increases the permeability of coal body, forms a three-dimensional high-permeability coal body fissure network, and greatly improves the extraction effect of coalbed methane;

(2) First, the drilling gas is used for the first extraction. When the gas concentration reaches the set minimum value, hydraulic fracturing is performed to increase the permeability of the coal seam and form a three-dimensional fracture network with higher permeability and stronger connectivity. Hydraulic fracturing also has the effect of water injection to drive gas; then secondary extraction of coalbed methane is carried out to improve resource extraction rate and avoid energy waste;

(3) When the gas extraction is completed, the surface water is sent to the deep high-temperature coal seam by drilling, and the geothermal energy is transferred to the water by the principle of heat transfer, and the water is vaporized and turned into a mixture of water and water vapor (the specific The shape is determined by the geothermal temperature of the deep coal seam), and then the second directional well is directly used to extract it to the surface for comprehensive utilization; the deep coalbed methane thermal co-mining method utilizes the drilling and drilling of the coalbed methane to directly exploit the geothermal resources, improving the It has obvious technological advancement and high efficiency characteristics, and has practical application value.

Description of drawings

Figure 1 is a schematic structural diagram of the invention.

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1 .

Figure 3 is a schematic diagram of arranging a horizontal well in a deep coal seam with a coal seam thickness of 5 meters and a drainage radius of 3 meters.

Figure 4 is a schematic diagram of arranging one horizontal well when the thickness of the deep coal seam is 10 meters and the drainage radius is 3 meters.

Figure 5 is a schematic diagram of arranging two horizontal wells when the thickness of the deep coal seam is 15 meters and the drainage radius is 3 meters.

Fig. 6 is a horizontal well constructed with circumferentially dispersed holes.

Detailed ways

Below by embodiment and in conjunction with accompanying drawing, the present invention is further described:

Referring to Figures 1 and 2, a deep coalbed methane thermal co-mining method is suitable for gas extraction and geothermal energy mining in deep coalbeds below 3,000 meters, and mainly includes the following steps:

The first step is to construct the first vertical well 1 downward on the surface of the mining coal field. The first vertical well 1 passes through the overlying strata of the deep coal seam and the shallow coal seam, and the wellbore is sealed with thermal insulation casing 2. Thermal insulation protection; thermal insulation casing 2 maintains low heat exchange with the outside world while ensuring good air tightness of the wellbore to reduce heat loss.

In the second step, after the first vertical drilling 1 reaches the deepest layer of the deep coal seam 3, the construction of each layered horizontal well 4 is carried out sequentially from top to bottom according to the thickness of the coal seam. The first vertical drilling 1 and each layered horizontal well Arc transition is used between 4. The length and number of horizontal wells in each layer are determined by the scope of coal mining.

Preferably, as shown in FIG. 2, three horizontal wells 4 are arranged in each layer, and the three horizontal wells 4 are arranged at equal intervals, and the central horizontal well 4 is facing the first vertical drilling 1 and the second vertical well 4. Drilling 5, the left and right ends of the horizontal wells 4 on both sides are respectively bent vertically toward the central horizontal well 4 and connected to each other, and the whole is arranged in the shape of a "Sun". On the premise of ensuring complete gas and heat extraction, the layout of horizontal wells in each layer is optimized as much as possible to reduce drilling complexity and improve extraction efficiency. In addition, the horizontal wells 4 of each layer are preferably arranged in the center of the front and rear and the center of the left and right in the deep coal seam. The number of layers K is determined according to the following method:

(1) Determine the true thickness M of the coal seam according to the geological data and actual drilling data;

(2) Construct the evolution model of coal permeability under the action of mechanical and thermal coupling, and calculate the gas drainage radius R under the condition of natural desorption of deep coal seam in combination with the coal seam permeability coefficient λ;

(3) Determine the number of layers K according to the true thickness M of the coal seam and the gas drainage radius R;

Let K=M/2R, when K<1, N takes 1, and when K>1, N takes the integer part of K.

For example, as shown in Figure 3, when the thickness of the deep coal seam 3 is 5 meters and the drainage radius is 3 meters, K=0.83, and N is 1, that is, a layer of horizontal well 4 is arranged in the coal seam.

As shown in Figure 4, when the coal seam thickness of the deep coal seam 3 is 10 meters and the drainage radius is 3 meters, K=1.67, and N still takes 1, that is, a layer of horizontal well 4 is arranged in the coal seam, which cannot be drained under natural conditions. The gas will be extracted after hydraulic fracturing measures are taken;

As shown in Figure 5, when the thickness of the deep coal seam 3 is 15 meters and the drainage radius is 3 meters, K=2.5, and N is 2, that is, two layers of horizontal wells 4 are arranged in the coal seam.

The number of horizontal wells 4 in each layer is determined according to the scope of the mining area. When the scope of the mining area is large, multiple horizontal wells 4 can be set in each layer, and each horizontal well 4 in the same layer is connected to the first vertical drilling 1 respectively, such as As shown in FIG. 2 , three horizontal wells 4 are arranged on the first floor, and three horizontal wells are arranged according to the thickness of the coal seam in the deep coal seam.

The third step is to construct the second vertical well 5, which is in vertical communication with each layered horizontal well 4, and the second vertical well 5 is completed in one drilling.

The fourth step is to construct circumferential dispersion holes 6 (as shown in Figure 6) on each layered horizontal well 4 to increase the coal permeability, and then use the first vertical drilling 4 and the second vertical drilling 5 to carry out the first gas drilling. Drain.

The fifth step is to place gas concentration and flow monitoring sensors in the gas extraction pipeline to monitor the gas concentration and flow in real time. When the concentration and flow reach the set minimum value, the gas extraction efficiency drops significantly. The pores are hydraulically fractured to form a three-dimensional fracture network for secondary gas extraction.

Step 6: After the gas extraction, the first vertical drilling 1 is used as a water injection well, and the second vertical drilling 5 is used as a steam outlet. , and the extraction and utilization of water vapor.

The high-temperature water vapor formed by mining reaches the ground through the second vertical drilling and can be used directly or generate electricity.

Claims (4)

1. a deep coalbed methane thermal co-mining method, is characterized in that, comprises the following steps: The first step is to construct the first vertical drilling down the surface of the coal mining field. The first vertical drilling passes through the overlying strata of the deep coal seam and the shallow mined coal seam. The wellbore is sealed and protected by thermal insulation casing. ; In the second step, after the first vertical drilling reaches the deepest layer of the deep coal seam, the construction of each layered horizontal well is carried out in sequence from top to bottom according to the thickness of the deep coal seam. For arc transition, the length and number of horizontal wells in each layer are determined by the scope of the mining coal field, and the number of layers K is determined according to the following methods: (1) Determine the true thickness M of the deep coal seam according to the geological data and actual drilling data; (2) Construct the evolution model of coal permeability under the action of mechanical and thermal coupling, and calculate the gas drainage radius R under the condition of natural desorption of deep coal seam in combination with the permeability coefficient λ of the deep coal seam; (3) Determine the number of layers K according to the true thickness M of the deep coal seam and the gas drainage radius R; Let K=M/2R, when K<1, N takes 1, when K>1, N takes the integer part of K; The third step is to construct the second vertical drilling, and the second vertical drilling is vertically connected with each layered horizontal well; The fourth step is to construct circumferential dispersion holes on each layered horizontal well, and then use the first and second vertical drilling to conduct the first gas extraction; The fifth step is to place gas concentration and flow monitoring sensors in the gas extraction pipeline to monitor the gas concentration and flow in real time. Three-dimensional fracture network for secondary gas extraction; The sixth step, after the gas drainage is completed, the first vertical drilling is used as a water injection well, and the second vertical drilling is used as a steam outlet, water is injected into the deep coal seam, and the geothermal energy is transferred to the water vapor by the principle of heat transfer, and the Extraction and utilization of water vapor. 2 . The thermal co-mining method of deep coalbed methane according to claim 1 , wherein the high-temperature water vapor formed by mining reaches the ground through the second vertical drilling to generate electricity. 3 . 3. The thermal co-mining method for deep coalbed methane according to claim 1 or 2, characterized in that: three horizontal wells are arranged in each of the layers, the three horizontal wells are arranged at equal intervals, and the central horizontal well is For the first and second vertical drilling, the left and right ends of the horizontal wells on both sides are respectively bent vertically toward the central horizontal well and then connected, and the whole is arranged in the shape of a "Sun". 4 . The thermal co-mining method for deep coalbed methane according to claim 1 or 2 , wherein each of the layered horizontal wells is arranged in the center of the deep coal seam in the front and rear and in the left and right centers. 5 .

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