CN110318675A - A kind of Deep Coalbed Methane heat is total to mining method - Google Patents

Abstract

The invention discloses a method for thermal co-mining of deep coal seam gas. The first step is to construct the first vertical drilling, and the wellbore adopts an insulating casing for gas sealing and heat insulation protection; the second step is to carry out layered water according to the coal seam thickness For the construction of flat wells, the number of layers K is determined according to the true thickness of the coal seam M 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 wells Then the first gas extraction is carried out; the fifth step is to perform hydraulic fracturing on each borehole to form a three-dimensional fracture network for secondary gas extraction; the sixth step is to use the first vertical drilling as a water injection well, and the second vertical drilling Drilling wells are used as steam wells to inject water into deep coal seams, use the principle of heat transfer to transfer geothermal energy into water vapor, and use water vapor extraction. It can carry out gas drainage and geothermal energy mining for deep coal seams of 1500-3000 meters, improve the efficiency of geothermal drainage, save energy and reduce emissions, and prevent geological environmental problems such as water and soil pollution and thermal pollution.

Description

A method for thermal co-mining of deep coalbed methane

technical field

The invention belongs to the field of geothermal and coal-bed methane exploitation, and specifically proposes a method for deep coal-bed methane thermal co-exploitation.

Background technique

The total amount of coalbed methane resources shallower than 3,000 meters in my country is about 55 trillion cubic meters, and the national coalbed methane resources of shallower than 3,000 meters are about 55 trillion cubic meters, of which coalbed methane resources with a coal seam buried depth of 1,500-3,000 meters account for 54.5%. At present, most of underground coal mining and coal bed methane development and mining are coal seams and coal bed methane shallower than 1500 meters, and there are great technical difficulties in the mining of deep coal bed methane. In addition, deep coal seams are subjected to high in-situ stress and low coal seam permeability, which seriously restricts the efficiency of coalbed methane extraction.

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

Geothermal resource 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 earliest utilization of mine geothermal energy starts from the return air of the mine, and the hot air generated by geothermal heat 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 hot water gushes out In mines, geothermal water is often used to heat bathing and domestic water, or mine drainage is used as a cold and heat source to transport underground heat to the ground through the mine drainage system, and a heat exchange station is established in the industrial square to use the obtained heat for wellhead antifreeze and Inoue building heating. The first-generation technical method has a very low level of environmental protection and is not sustainable. The second generation is the combination of mining and irrigation, using heat without using water, that is, exploiting geothermal energy in the form of groundwater heat, and recharging after extracting heat energy. The disadvantage of the second-generation technology is that the connectivity between production and irrigation wells is not easy to determine, and the recharge efficiency is low, and it will also pollute the groundwater to varying degrees. partial advantage.

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

Contents of the invention

The invention aims to provide a method for mining coal bed methane and geothermal energy in deep coal seams with a depth of 1500-3000 meters.

For this reason, the technical scheme that the present invention adopts is: a kind of deep coal bed gas thermal co-extraction method, its steps are:

The first step is to construct the first vertical drilling down the surface of the mining coal field. The first vertical drilling passes through the overburden of the deep coal seam and the shallow coal seam that has been mined. The wellbore is sealed and protected by heat insulation ;

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 sequentially from top to bottom according to the thickness of the coal seam. In transition, the length and number of horizontal wells in each layer are determined by the scope of the coal field to be exploited, and the number of layers K is determined according to the following method:

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

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

(3) Determine the number of layers K according to the real 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, construction of the second vertical drilling well, the second vertical drilling well is vertically connected with each layered horizontal well;

The fourth step is to construct circumferential scattered 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 drainage pipeline to monitor the gas concentration and flow in real time. When the concentration and flow reach the set minimum value, perform hydraulic fracturing on each borehole to form a three-dimensional Fracture network for secondary gas extraction;

Step 6: After the gas extraction is completed, the first vertical well is used as a water injection well, and the second vertical well is used as a steam well to inject water into the deep coal seam, using the principle of heat transfer to transfer geothermal energy into water vapor, and Use for water vapor extraction.

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

It is further preferred that three horizontal wells are arranged in each layer, and the three horizontal wells are equidistantly spaced, the horizontal well in the middle is facing the first and second vertical wells, and the left and right ends of the horizontal wells on both sides They are respectively bent vertically toward the horizontal well in the center and then connected, and the overall arrangement is in the shape of a "day". On the premise of ensuring thorough gas-heat drainage, optimize the layout of horizontal wells in each layer as much as possible to reduce drilling complexity and improve drainage efficiency.

Similarly, the horizontal wells of each layer are arranged front to back and left to right in the deep coal seam.

Beneficial effects of the present invention:

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

(2) First use the drilling gas for the first drainage. When the gas concentration reaches the set minimum value, hydraulic fracturing is performed to increase the air permeability of the coal seam and form a three-dimensional fracture network with higher permeability and stronger connectivity. At the same time, Hydraulic fracturing also has the effect of water injection to drive gas; followed by secondary extraction of coalbed methane to improve resource recovery 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 using the principle of heat transfer to vaporize the water and turn the water into a mixture of water and water vapor (the specific content of water) The shape is determined by the ground temperature of the deep coal seam), and then directly use the second directional well to drain to the ground for comprehensive utilization; the deep coalbed methane thermal co-extraction method uses the drilling and drilling of the coalbed methane to directly exploit geothermal resources, improving It improves the utilization rate of drilling wells, and has the characteristics of obvious technological advancement and high efficiency, and has practical application value.

Description of drawings

Fig. 1 is the structural representation of invention.

Fig. 2 is a sectional view along line A-A of Fig. 1 .

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

Fig. 4 is a schematic diagram of a horizontal well arranged in a deep coal seam when the thickness of the coal seam is 10 meters and the drainage radius is 3 meters.

Figure 5 is a schematic diagram of the arrangement of two layers of 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 with circumferentially dispersed holes.

Detailed ways

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

As shown in Figure 1 and Figure 2, a deep coalbed gas thermal co-extraction method is suitable for gas drainage and geothermal energy extraction in deep coal seams below 3000 meters, mainly including the following steps:

The first step is to construct the first vertical drilling 1 downwards on the surface of the mining coal field. The first vertical drilling 1 passes through the overburden of the deep coal seam and the shallow coal seam that has been mined. Heat insulation protection: while the insulation casing 2 ensures good airtightness of the wellbore, it also maintains low heat exchange with the outside world 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 according to the thickness of the coal seam from top to bottom. The first vertical drilling 1 and each layered horizontal well 4 between the arc transition. The length and number of horizontal wells in each layer are determined by the scope of the mining coal field.

Preferably, as shown in Figure 2, three horizontal wells 4 are arranged in each layer, and the three horizontal wells 4 are equidistantly spaced, and the centered horizontal well 4 is facing the first vertical well 1, the second vertical well Drilling well 5, the left and right ends of the horizontal wells 4 on both sides are respectively bent vertically towards the horizontal well 4 in the middle and connected to each other, and the whole is arranged in a "day" shape. On the premise of ensuring thorough gas-heat drainage, optimize the layout of horizontal wells in each layer as much as possible to reduce drilling complexity and improve drainage efficiency. In addition, the horizontal well 4 of each layer is preferably arranged in the center of the front and back, 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 geological data and actual drilling data;

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

(3) Determine the number of layers K according to the real 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 coal seam thickness of the deep coal seam 3 is 5 meters and the drainage radius is 3 meters, K=0.83, and N is taken as 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 is still taken as 1, that is, a layer of horizontal well 4 is arranged in the coal seam, and drainage cannot be performed under natural conditions The gas will be extracted after hydraulic fracturing measures are taken;

As shown in Figure 5, when the coal seam 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 production area. When the scope of the production area is large, a plurality of horizontal wells 4 can be arranged in each layer, and each horizontal well 4 of the same layer communicates with the first vertical well 1 respectively, such as As shown in Fig. 2, three horizontal wells 4 are arranged on one layer, and three layers of horizontal wells are arranged according to the coal seam thickness of the deep coal seam.

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

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

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

Step 6: After the gas extraction is completed, the first vertical drilling 1 is used as a water injection well, and the second vertical drilling 5 is used as a steam outlet well to inject water into the deep coal seam, and use the principle of heat transfer to transfer geothermal energy into water vapor , and use of water vapor extraction.

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

Claims (4)

1. a kind of Deep Coalbed Methane heat is total to mining method, which comprises the following steps:

The first step is constructed downwards the first vertical drilling well in mine coal field table, and the first vertical drilling well passes through overlying strata on deep fractures Mining coal seam, wellbore carry out hermetic seal and thermal insulation protection using thermal insulation casing for layer, superficial part；

After second step, the first vertical drilling well reach the most deep layering of deep fractures, successively carried out from top to bottom according to coal seam thickness each It is layered the construction of horizontal well, arc transition, the length of every layering horizontal well are used between the first vertical drilling well and each layering horizontal well Degree, quantity determine that layering quantity K is determined by the following method by exploiting coalfield range:

(1) the true thickness M in coal seam is determined according to geologic information and practical drilling data；

(2) building power thermal coupling acts on lower coal body permeability evolution model and calculates deep fractures in conjunction with Permeability Coefficent in Coal Seam λ Gas drainage under suction radius R under natural desorption condition；

(3) layering quantity K is determined according to digital well logging degree M and gas drainage under suction radius R；

K=M/2R is enabled, as K<1, N takes 1, and as K>1, N takes the integer part of K；

Third step, the second vertical drilling well of construction, the second vertical drilling well and the equal vertical connection of each layering horizontal well；

It is first to carry out gas followed by the first, second vertical drilling well for 4th step, circumferential dispersion hole of constructing on each layering horizontal well Secondary extraction；

5th step places gas density, flow monitoring inductor, real-time monitoring gas density and stream in methane gas extraction pipeline Amount carries out hydraulic fracturing to each drilling, forms three-dimensional fracture network, carry out after concentration reaches the minimum of setting with flow The secondary extraction of gas；

After 6th step, gas drainage, the first vertical drilling well, will as steam well is gone out as water injection well, the second vertical drilling well Water injects deep fractures, geothermal energy is transferred in vapor using the principle of heat transmitting, and to vapor methane drainage and utilization project.

2. Deep Coalbed Methane heat described in accordance with the claim 1 is total to mining method, it is characterised in that: exploit the high-temperature vapor of formation Ground is reached through the second vertical drilling well to generate electricity.

3. Deep Coalbed Methane heat according to claim 1 or 2 is total to mining method, it is characterised in that: set in each layering It sets there are three horizontal well, three horizontal well equidistant intervals are arranged, the vertical drilling well of horizontal well face first, second placed in the middle, two sides The left and right ends of horizontal well be connected respectively towards after the vertical bending of horizontal well placed in the middle, it is whole to be arranged in " day " font.

4. Deep Coalbed Methane heat according to claim 1 or 2 is total to mining method, it is characterised in that: the water of each layering Horizontal well front and back in deep fractures is placed in the middle, center ofthe is arranged.