CN112983358A

CN112983358A - Method for exploiting coal bed gas by injecting carbon dioxide between same well seams of horizontal well

Info

Publication number: CN112983358A
Application number: CN202110185434.3A
Authority: CN
Inventors: 于海洋; 韩晓冰; 杨海烽; 汪洋; 程时清
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2021-02-10
Filing date: 2021-02-10
Publication date: 2021-06-18

Abstract

The invention provides a method for exploiting coal bed gas by injecting carbon dioxide between same well seams of a horizontal well, belonging to the technical field of oil exploitation. The method comprises the following steps: fracturing the horizontal well shaft in a staged manner by using fracturing fluid to form a plurality of fracturing fractures vertical to the horizontal well shaft, wherein the fracturing fractures are divided into a first group of fracturing fractures and a second group of fracturing fractures; perforating the tubing at locations corresponding to the first set of fractures; injecting carbon dioxide into the second set of fractured fractures via the annulus formed by the tubing and casing; and opening an oil extraction valve arranged at the wellhead of the horizontal well, and allowing the coal bed gas produced by carbon dioxide displacement to enter the oil pipe through the perforation corresponding to the first group of fracturing fractures and be extracted. Through the technical scheme, the carbon dioxide is injected into the gaps of the same well, so that the injected carbon dioxide can go deep into the coal bed, the injection amount can be increased, the recovery ratio of coal bed gas is improved, and the occurrence probability of gas accidents can be reduced.

Description

Method for exploiting coal bed gas by injecting carbon dioxide between same well seams of horizontal well

Technical Field

The invention relates to the technical field of oil exploitation, in particular to a method for exploiting coal bed methane by injecting carbon dioxide between same well seams of a horizontal well.

Background

The coal bed gas is hydrocarbon gas (10-20%) stored in a coal bed, takes methane as a main component, is adsorbed on the surface of coal matrix particles as a main component, is partially dissociated in coal pores or dissolved in coal bed water, belongs to unconventional natural gas, and is clean and high-quality energy and chemical raw material which is grown internationally in nearly twenty years. Meanwhile, the coal bed gas is also the main reason for gas explosion, so that reasonable exploitation of the coal bed gas is also very important for safe production of coal mines.

Because the permeability of the coal bed is generally low, the desorption and migration of the coal bed gas are difficult, and the coal bed gas exploitation effect is generally poor, so that a coal bed gas yield increasing technology which is higher in efficiency and effective is urgently needed to be found, the recovery ratio of the coal bed gas is improved, the resource waste is reduced, and the safe production of a coal mine is realized.

The existing scheme usually adopts methods such as hydraulic fracturing technology and high-pressure water injection to solve the problem of poor permeability of the coal bed, so that coal bed gas is desorbed, and the purpose of increasing the yield of the coal bed gas is achieved. However, the effects achieved by the methods are not ideal, and the problem of low-permeability coal seam development cannot be fundamentally solved.

Disclosure of Invention

The embodiment of the invention aims to provide a method for exploiting coal bed gas by injecting carbon dioxide between same well seams of a horizontal well, which is used for solving one or more of the technical problems.

In order to achieve the above object, an embodiment of the present invention provides a method for mining coal bed methane, including: fracturing the horizontal well shaft in a staged manner by using fracturing fluid to form a plurality of fracturing fractures vertical to the horizontal well shaft, wherein the fracturing fractures are divided into a first group of fracturing fractures and a second group of fracturing fractures; perforating the tubing at locations corresponding to the first set of fractures; injecting carbon dioxide into the second set of fractured fractures via the annulus formed by the tubing and casing; and opening an oil extraction valve arranged at the wellhead of the horizontal well, and allowing the coal bed gas produced by carbon dioxide displacement to enter the oil pipe through the perforation corresponding to the first group of fracturing fractures and be extracted.

Optionally, the fracturing fluid includes carbon dioxide.

Optionally, before fracturing the horizontal well bore section, the method further comprises: detecting the temperature and the pressure of a coal bed gas reservoir where the horizontal well is located; and when the temperature is not in a preset temperature range and/or the pressure is not in a preset pressure range, determining that the carbon dioxide injected into the second group of fracturing fractures is carbon dioxide in a supercritical state.

Optionally, the number of the horizontal wells is multiple, and before staged fracturing of the wellbore of the horizontal well, the method further includes: detecting the temperature and the pressure of a coal bed gas reservoir where the horizontal well is located; comparing the temperature to a preset temperature and the pressure to a preset pressure range; and when the temperature is within a preset temperature range and the pressure is within a preset pressure range, performing staged fracturing on the horizontal well shaft.

Optionally, the carbon dioxide injected into the second set of fracturing fractures is gaseous carbon dioxide, and the gaseous carbon dioxide is converted into a supercritical state in the second set of fracturing fractures.

Optionally, an injection valve is arranged at a casing position corresponding to the second group of fractures, and the injection valve is used for controlling the injection speed of the carbon dioxide.

Optionally, the method further includes: and arranging an injection-production separation device at a position corresponding to the first group of fracturing fractures in the annular space, wherein the outer wall of the oil pipe and the inner wall of the sleeve are used as supporting end surfaces of the injection-production separation device.

The injection-production separation device comprises: two packers; and the flow guide pipe is arranged between the two packers and communicated with the annular space.

Optionally, the fractures in the first set of fractured fractures are spaced apart from the fractures in the second set of fractured fractures.

Optionally, the first set of fractured fractures are odd-numbered fractures, and the second set of fractured fractures are even-numbered fractures.

Through the technical scheme, the carbon dioxide is injected into the gaps of the same well, so that the injected carbon dioxide can go deep into the coal bed, the injection amount can be increased, the recovery ratio of coal bed gas is improved, and the occurrence probability of gas accidents can be reduced.

Additional features and advantages of embodiments of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the embodiments of the invention without limiting the embodiments of the invention. In the drawings:

fig. 1 is a schematic structural diagram of an injection-production separation device provided in an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of an injection-production separation apparatus provided in an embodiment of the present invention;

fig. 3 is a process schematic diagram of a method for exploiting coal bed gas between horizontal well same-well seams provided by the embodiment of the invention.

Description of the reference numerals

1A packer and 1B flow guide pipe of 1 injection-production separation device

2 casing 3 oil pipe 4 even-numbered stage crack

5 odd-level crack 6 annular space 7 fracturing horizontal well

8 dispensing valve and 9 filling hole

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration and explanation only, not limitation.

It should be noted at the outset that the terms "first," "second," and the like in the embodiments of the present invention are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature and, where desired, the effect achieved by the feature may be substantially the same.

For the method for mining the coal bed gas provided by any embodiment of the invention, one or more valves can be arranged at the position of the pipeline corresponding to the hole and the position of the pipeline connection position according to the actual situation so as to adjust the progress in the process of mining the coal bed gas.

For example, during the process of mining coal bed gas, carbon dioxide needs to be injected into the fractured fractures, so it can be considered to provide a dispensing valve on the casing at a position corresponding to the fractured fractures for controlling whether the carbon dioxide can be injected into the coal bed, the injection speed of the carbon dioxide into the coal bed, and the like.

For example, a valve may also be provided between the casing and tubing for controlling fluid flow in the annulus between the casing and tubing or for controlling fluid flow within the tubing. In the solution provided by the embodiment of the present invention, perforations need to be made on the oil pipe so that the coal bed gas can be produced through the oil pipe, and thus the position of the valve can correspond to the position of the perforations.

The embodiment of the invention also provides an injection-production separation device which can be arranged between the casing and the oil pipe, and the coal bed gas entering the separation device through the oil pipe can enter the oil pipe through the perforation on the oil pipe and then is reserved at a wellhead to realize the exploitation of the coal bed gas.

Fig. 1 is a schematic structural diagram of an injection-production separation device according to an embodiment of the present invention. As shown in fig. 1, the injection-production separation device 1 is mainly divided into two parts, i.e., a packer 1A and a draft tube 1B. Wherein, each injection-production separation device 1 is provided with two packers 1A, and a flow guide pipe 1B is arranged between the two packers 1A, and the packers 1A can control the fluid movement in the flow guide pipe 1B.

The injection-production spacer 1 shown in fig. 1 is arranged between the casing and the tubing, and a schematic cross-sectional view of the corresponding injection-production spacer is shown in fig. 2.

Specifically, when the injection-production separation device 1 is arranged between the casing 2 and the oil pipe 3, the outer wall of the oil pipe 3 and the inner wall of the casing 2 can serve as the supporting end faces of the injection-production separation device 1. Wherein, if the packer 1A in the injection-production separation device 1 is in a closed state, the fluid between the two packers 1A can not enter the oil pipe.

The injection-production separation device provided by the embodiment of the invention not only can seal the annular space formed by the oil pipe and the casing pipe, but also can play a role in heat insulation.

Example one

Aiming at the problems of poor safety and low recovery ratio of coal bed gas exploitation in the prior art, the invention provides a method for exploiting coal bed gas between same well seams of horizontal wells. Specifically, the specific steps of the method for mining coal bed gas provided by the embodiment of the invention are as follows.

Step 1: fracturing fluid is firstly adopted to fracture the shaft of the horizontal well in a staged way so as to form a plurality of cracks. And selecting a part of fractured fractures vertical to the horizontal well shaft from the plurality of fractures as a first group of fractured fractures, and selecting a part of fractured fractures vertical to the horizontal well shaft from the plurality of fractures as a second group of fractured fractures.

Step 2: perforating the tubing at locations corresponding to the first set of fractures.

And step 3: injecting carbon dioxide into an annulus formed by the tubing and casing to enable the carbon dioxide to be injected into the second set of fractured fractures.

And 4, step 4: and opening an oil extraction valve at the wellhead of the horizontal well, and allowing the coal bed gas produced by carbon dioxide displacement to enter an oil pipe through the perforations corresponding to the first group of fracturing cracks to be extracted.

According to the scheme provided by the embodiment of the invention, carbon dioxide is injected into part of the fractured fractures corresponding to the horizontal well, and the coal bed gas extracted by carbon dioxide displacement can be produced through the rest of the fractured fractures corresponding to the horizontal well. That is to say, this scheme can accomplish the displacement and the exploitation to coal bed gas through a well, therefore can effectively reduce coal bed gas exploitation cost, promote economic benefits to can also improve well average output. And in the process of exploiting the coal bed gas by injecting the carbon dioxide, the injected carbon dioxide can be sealed in the coal bed, so that the aim of reducing the greenhouse gas can be achieved while the recovery efficiency of the coal bed gas can be improved.

Compared with the existing method for exploiting the coal bed gas, the method provided by the embodiment of the invention has the advantages that the injected carbon dioxide can penetrate into the coal bed by injecting the carbon dioxide into the gaps of the same well. The scheme provided by the embodiment of the invention changes the problem of the low-permeability coal bed gas between wells into the problem of the gaps, so that the injection pressure can be effectively reduced, the injection amount is increased, the recovery ratio of the coal bed gas is improved, and the occurrence probability of gas accidents can be reduced.

In some optional embodiments, the fractures in the first set of fractured fractures may be arranged at intervals from the fractures in the second set of fractured fractures. For example, the first set of fractures and the second set of fractures may be arranged in a crossing manner (i.e., the first set of fractures is odd-numbered fractures and the second set of fractures is even-numbered fractures), or the first set of fractures may be interspersed between every two second sets of fractures, or the first set of fractures and the second set of fractures may be arranged in a plurality of regular combinations, and so on. The method has the advantages that the well yield can be effectively improved and the production cost can be effectively reduced by selecting a proper sequencing mode, so that the specific sequencing between the first group of fracturing fractures and the second group of fracturing fractures can be comprehensively determined according to the distribution condition of the fracturing fractures, the self state (such as the length and the width of the fracturing fractures) of the fracturing fractures, the state of a coal bed and the like.

In some optional embodiments, the fracturing fluid containing carbon dioxide can be used for staged fracturing on the horizontal well shaft, so as to improve the structure of gaps and cracks and improve the recovery efficiency of coal bed gas.

Example two

The method for exploiting the coal bed gas between the same well seams of the horizontal well provided by the invention is explained by combining a specific embodiment.

Firstly, injecting fracturing fluid into a horizontal well to enable a reservoir to generate fracturing fractures, selecting fractures in a certain interval range, dividing the selected fractures into two groups according to odd-level fractures and even-level fractures, and selecting at least three-level fractures. The odd-numbered stages of cracks can be used as channels for coal bed gas circulation, and the even-numbered stages of cracks can be used as channels for injecting carbon dioxide.

The tubing is then inserted into the casing such that an annular space is formed between the tubing and the casing. The annular space formed between the oil pipe and the casing pipe is used as a passage for feeding electric heating materials and heating wires and a passage for crude oil to flow to a wellhead. The oil pipe is used as a channel for crude oil to flow to a wellhead.

Taking out the oil pipe, arranging a valve at a corresponding position on the oil pipe according to requirements, perforating at a position on the oil pipe corresponding to the odd-level cracks, and then putting the oil pipe and the casing pipe into the corresponding position (namely the position before taking out).

Carbon dioxide is injected from the wellhead into the annulus formed about the casing, which flows into the even-numbered stages of fractures and diffuses.

And (3) opening the well for production, wherein the coal bed gas is produced from the odd-level cracks, firstly enters the annular space, and then enters the oil pipe through the perforations corresponding to the odd-level cracks, so that the recovery of the coal bed gas is realized.

EXAMPLE III

The process of exploiting the coal bed gas by using the method for exploiting the coal bed gas between the same well seams of the multi-stage fractured horizontal well provided by the embodiment of the invention is explained in detail by combining with the figure 3.

As shown in fig. 3, an oil pipe 3 and a casing 2 sleeved outside the oil pipe 3 are placed in a shaft of the fractured horizontal well 7, and an annular space 6 is formed between the oil pipe 3 and the casing 2.

And the pipeline corresponding to the even-level cracks 4 is provided with an injection allocation valve 8 (arranged at the sleeve 3) and an injection hole 9, and the pipeline corresponding to the odd-level cracks 5 is provided with an injection-production separation device 1 (corresponding to the perforation of the oil pipe 2 and arranged in the annular space 6).

And opening the injection allocation valve 8, injecting carbon dioxide into the annular space 6, and allowing the carbon dioxide to flow through the injection-production separation device 1 and enter the coal bed from the even-level cracks 4. Due to the arrangement of the injection allocation valve 8 and the injection-production separation device 1, the injected carbon dioxide can only enter even-level cracks of two-level, four-level, six-level and eight-level shown in fig. 3, and can not enter odd-level cracks of one-level, three-level, five-level, seven-level and nine-level.

And (3) opening a production oil valve (not shown in the figure), and expressing the displaced coal bed gas from the odd-level cracks 5 into an annular space formed by the guide pipe of the injection-production separation device 1, the casing 2 and the oil pipe 3, and then entering the oil pipe 3 through the perforation holes on the oil pipe 3 corresponding to the positions of the odd-level cracks to be produced.

Example four

The embodiment of the invention also provides a method for mining the coal bed gas between the same well seams of the horizontal well. This embodiment differs from the previous embodiments in that the state of the coal bed methane interior needs to be determined prior to staged fracturing of the horizontal well bore.

Specifically, the temperature and the pressure of the coal bed methane reservoir where the horizontal well is located are detected, and then the detected temperature and the detected pressure of the coal bed methane reservoir where the horizontal well is located are compared with a preset temperature range and a preset pressure range respectively.

And when the temperature of the coal bed gas reservoir where the horizontal well is located is not in a preset temperature range and/or the pressure of the coal bed gas reservoir where the horizontal well is located is not in a preset pressure range, injecting carbon dioxide in a supercritical state into the second group of fractured fractures.

When the temperature of the coal bed gas reservoir where the horizontal well is located is within a preset temperature range and the pressure of the coal bed gas reservoir where the horizontal well is located is within a preset pressure range, it is shown that carbon dioxide is easy to change into a supercritical state in the coal bed gas reservoir. Therefore, for the horizontal well, the gaseous carbon dioxide can be directly injected to exploit coal bed gas, and the gaseous carbon dioxide is not required to be converted into supercritical carbon dioxide and then injected into the horizontal well.

In some optional implementations, ordinary carbon dioxide can be directly injected into a horizontal well with a coal seam depth of more than 800m without detecting the temperature and pressure of a coal bed gas reservoir where the horizontal well is located and without injecting carbon dioxide in a supercritical state.

When at least one of the temperature and/or the pressure of the coal bed where the horizontal well is located does not reach the critical temperature and the critical pressure, in order to improve the recovery efficiency and the recovery efficiency of the coal bed gas, heating equipment and pressurizing equipment can be arranged, so that the carbon dioxide output by the gas storage tank is heated by the heating equipment and pressurized by the pressurizing equipment and then injected into the reservoir.

The heating temperature of the heating device is required to be more than 31.2 ℃, and the pressure of the pressurizing device is required to be more than 9.38 MPa. Wherein, in order to shorten the state transition time of the carbon dioxide, the heating temperature and the pressurizing pressure can be increased correspondingly. For example, the heating temperature is more than 35 ℃, the pressurizing pressure is more than 9.5MPa, and the like.

In addition, in order to better control the process of converting carbon dioxide into supercritical carbon dioxide, a device capable of detecting temperature, such as a thermometer, may be provided in the heating device, and a device capable of detecting pressure, such as an air pressure sensor, may be provided in the pressurizing device, so that the pressurizing temperature, the pressurizing pressure, and the like may be adjusted in real time according to the detection result.

In some optional embodiments, if there are multiple horizontal wells, the temperature and pressure of the coal bed gas reservoir where each horizontal well is located may be detected first, and the horizontal well where the temperature of the reservoir is within a preset temperature range and the pressure is within a preset pressure range is selected to inject carbon dioxide, so that the injected carbon dioxide may be converted from a gaseous state to a supercritical state in the fracture. Therefore, the gaseous carbon dioxide does not need to be heated and pressurized in advance, and the coal bed gas exploitation cost can be effectively reduced.

The solution provided by this embodiment of the invention takes into account that the carbon dioxide may be in a gaseous state or in a supercritical state. The diffusion coefficient of the carbon dioxide in the supercritical state is 100 times that of the liquid, the dissolving capacity is good, organic matters such as ester, ether, lactone and epoxy compounds in the coal matrix can be dissolved, the desorption of the gas in the adsorption state can be promoted, the pore and crack of the coal body can be effectively expanded, the permeability of the coal bed is improved, the structure of the pore and crack is improved, and the separation of the gas is facilitated. That is, the recovery rate of the coal bed gas produced by displacement with carbon dioxide in a supercritical state is much higher than the recovery rate of carbon dioxide in a gaseous state, and therefore it is proposed in this embodiment that the state of carbon dioxide injected into a horizontal well can be determined based on the state of the coal bed gas reservoir in which the horizontal well is located.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.

The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for mining coalbed methane, characterized in that the method comprises:

The horizontal wellbore is staged by fracturing fluid to form a plurality of fracturing fractures perpendicular to the horizontal wellbore, and the fracturing fractures are divided into a first group of fracturing fractures and a second group of fracturing fractures;

perforating the tubing at locations corresponding to the first group of fracturing fractures;

injecting carbon dioxide into the second set of fracturing fractures via the annular space formed by the tubing and casing; and

The oil production valve disposed at the wellhead of the horizontal well is opened, and the coalbed methane produced by the displacement of the carbon dioxide enters the oil pipe through the perforations corresponding to the first group of fracturing fractures to be produced.

2. The method of claim 1, wherein the fracturing fluid includes carbon dioxide.

3. The method according to claim 1, characterized in that before staged fracturing of the horizontal wellbore, the method further comprises:

detecting the temperature and pressure of the coalbed methane reservoir in which the horizontal well is located; and

When the temperature is not within the preset temperature range, and/or the pressure is not within the preset pressure range, it is determined that the carbon dioxide injected into the second group of fracturing fractures is carbon dioxide in a supercritical state.

4 . The method according to claim 1 , wherein the number of the horizontal wells is multiple, and before the staged fracturing of the wellbore of the horizontal wells, the method further comprises: 5 .

detecting the temperature and pressure of the coalbed methane reservoir where the horizontal well is located;

comparing the temperature to a preset temperature and comparing the pressure to a preset pressure range; and

When the temperature is within a preset temperature range and the pressure is within a preset pressure range, staged fracturing is performed on the horizontal wellbore.

5. The method according to claim 4, wherein the carbon dioxide injected into the second group of fracturing fractures is gaseous carbon dioxide, and the gaseous carbon dioxide is transformed in the second group of fracturing fractures to a supercritical state.

6 . The method according to claim 1 , wherein an injection valve is provided at the position of the casing corresponding to the second group of fracturing fractures, and the injection valve is used to control the injection rate of the carbon dioxide. 7 . .

7. The method of claim 1, wherein the method further comprises:

An injection-production separation device is arranged in the annular space at a position corresponding to the first group of fracturing fractures, and the outer wall of the oil pipe and the inner wall of the casing serve as supporting end faces of the injection-production separation device.

8. The method according to claim 7, wherein the injection-production separation device comprises:

two packers; and

A guide pipe is arranged between the two packers and communicates with the annular space.

9. The method of claim 1, wherein the fractures in the first group of fracturing fractures are spaced apart from the fractures in the second group of fracturing fractures.

10. The method according to any one of claims 1 to 9, wherein the first group of fracturing fractures are odd-numbered fractures, and the second group of fracturing fractures are even-numbered fractures.