CN114016984A - Heat injection coal bed gas production increasing method based on hydraulic fracturing multi-branch horizontal well - Google Patents
Heat injection coal bed gas production increasing method based on hydraulic fracturing multi-branch horizontal well Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims abstract description 210
- 238000002347 injection Methods 0.000 title claims abstract description 58
- 239000007924 injection Substances 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 239000004094 surface-active agent Substances 0.000 claims abstract description 50
- 239000002923 metal particle Substances 0.000 claims abstract description 37
- 239000007788 liquid Substances 0.000 claims abstract description 26
- 239000011259 mixed solution Substances 0.000 claims abstract description 16
- 238000010438 heat treatment Methods 0.000 claims abstract description 9
- 230000003116 impacting effect Effects 0.000 claims abstract description 8
- 230000009471 action Effects 0.000 claims abstract description 6
- 230000008859 change Effects 0.000 claims abstract description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 92
- 238000002156 mixing Methods 0.000 claims description 33
- 238000003860 storage Methods 0.000 claims description 33
- 239000002105 nanoparticle Substances 0.000 claims description 22
- 238000010793 Steam injection (oil industry) Methods 0.000 claims description 21
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 18
- 238000009833 condensation Methods 0.000 claims description 8
- 230000005494 condensation Effects 0.000 claims description 8
- 238000003795 desorption Methods 0.000 claims description 8
- 238000000605 extraction Methods 0.000 claims description 6
- 239000002736 nonionic surfactant Substances 0.000 claims description 6
- 238000007789 sealing Methods 0.000 claims description 6
- 230000004048 modification Effects 0.000 claims description 5
- 238000012986 modification Methods 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 4
- 230000002209 hydrophobic effect Effects 0.000 claims description 4
- 230000006872 improvement Effects 0.000 claims description 4
- 239000003093 cationic surfactant Substances 0.000 claims description 3
- 230000009977 dual effect Effects 0.000 claims description 3
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 claims description 3
- 238000004868 gas analysis Methods 0.000 claims description 3
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 claims description 3
- 238000000746 purification Methods 0.000 claims description 3
- 238000013329 compounding Methods 0.000 claims description 2
- 238000012544 monitoring process Methods 0.000 claims description 2
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- 238000012546 transfer Methods 0.000 abstract description 6
- 239000007789 gas Substances 0.000 description 73
- 238000001179 sorption measurement Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
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- 230000006978 adaptation Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
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- 239000003345 natural gas Substances 0.000 description 1
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/2405—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection in association with fracturing or crevice forming processes
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- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/006—Production of coal-bed methane
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E21B43/25—Methods for stimulating production
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- E21B43/2605—Methods for stimulating production by forming crevices or fractures using gas or liquefied gas
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- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/2607—Surface equipment specially adapted for fracturing operations
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Abstract
The invention discloses a method for increasing the coal bed gas yield by heat injection based on a hydraulic fracturing multi-branch horizontal well, which comprises the following steps of injecting a mixed solution into a coal bed by adopting a pulse injection mode, enabling a surfactant and nano metal particles in the mixed solution to be fully contacted with the inside of a crack, enabling more nano metal particles to be adsorbed on the inner surface of the crack, and enabling the surfactant to be fully reacted with the surface of a coal body so as to change the surface property of the coal body; thereby greatly improving the heat conductivity of the coal bed; injecting high-temperature and high-pressure steam into the branch well, continuously impacting and pressurizing and heating the crack after the high-temperature and high-pressure steam enters the branch well, and further expanding and developing the coal seam crack under the action of high temperature and high pressure; after the coal bed is pretreated by using the surfactant, the liquid drops condensed in advance cannot cause great influence on the heat exchange efficiency of subsequent steam, the direct contact between the subsequent steam and nano metal particles is ensured, and finally, the heat transfer efficiency between the steam and the coal bed is continuously increased, so that the yield of the coal bed gas is greatly increased.
Description
Technical Field
The invention relates to a coal bed gas increasing method, in particular to a heat injection coal bed gas increasing method based on a hydraulic fracturing multi-branch horizontal well.
Background
The coal bed gas is unconventional natural gas and also is clean energy, the main component of the coal bed gas is methane, and the coal bed gas mainly exists in the coal bed in an adsorption state (more than 90 percent). However, currently, coal bed gas generally has the characteristics of deep burial, low permeability, high density, high pressure, strong adsorbability and the like, so that the coal bed gas exploitation efficiency is very low. In order to more effectively exploit coal bed gas, the reservoir needs to be reformed, thereby improving the permeability of the coal bed. The existing common reservoir stratum transformation methods comprise hydraulic fracturing, a gas flooding technology, a blasting technology and the like, however, the adsorption capacity of the coal bed gas is strong, a large amount of coal bed gas is still adsorbed in coal and cannot be exploited in the later exploitation stage of the coal bed gas, and the yield of a single well of the coal bed gas well is difficult to effectively increase after the yield is reduced. In this case, injecting heat into the coal bed is a feasible method, because the adsorption capacity of the coal bed gas is inversely related to the reservoir temperature, and the adsorption capacity of the coal bed gas is reduced by about 8% for every 1 ℃ rise of the coal bed temperature. In addition, after the temperature of the coal rises, the coal body can thermally expand, the coal matrixes are mutually extruded, and new cracks are generated, so that the permeability of the coal bed is increased.
Based on the above principles, injection of steam into a coal seam is considered to be an economical and effective method: the steam molecules have high energy and can enter the internal pore cracks of the coal; the steam is condensed after contacting with the coal, and the condensation heat exchange coefficient is far larger than that of other heat exchange modes such as heat conduction and the like, so that the temperature of the coal bed can be increased and the adsorption capacity of the coal bed gas can be reduced after the steam is injected into the coal bed; in addition, because the adsorption of coal to water molecules is much greater than that of methane molecules, water vapor also has a methane displacement effect. However, because the thermal conductivity of coal itself is poor, for some coal seams with few cracks and compactness, if steam is directly injected, the steam is difficult to enter the deep part of the coal body, and finally, effective heat exchange cannot be carried out inside the coal body. Therefore, how to provide a method can firstly pretreat the coal bed, increase the crack and the heat conduction capability of the coal, and can further improve the heat exchange efficiency between the coal bed and the water vapor when the water vapor is injected subsequently, thereby realizing the rapid and large-range improvement of the temperature of the coal bed, effectively promoting the desorption of the coal bed gas, and finally improving the yield of the coal bed gas is a research direction of the industry.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for increasing the coal bed methane by heat injection based on a hydraulic fracturing multi-branch horizontal well, which can be used for pretreating a coal bed to increase the crack and the heat conduction capability of coal and further improving the heat exchange efficiency between the coal bed and steam when steam is injected subsequently, thereby realizing the purposes of quickly increasing the temperature of the coal bed in a large range, effectively promoting the desorption of the coal bed methane and finally improving the yield of the coal bed methane.
In order to achieve the purpose, the invention adopts the technical scheme that: a method for increasing coal bed gas production by heat injection based on hydraulic fracturing multi-branch horizontal well comprises the following specific steps:
A. assembling a heat injection production increasing system: the heat injection yield increasing system comprises a steam generation station, a superheater, a first booster pump, a second booster pump, a negative pressure pump, a gas separator, a pulsating pressure controller, a mixing chamber, a nanoparticle storage tank, a surfactant storage tank, a packer, a water injection pipe and a steam injection pipe, wherein an outlet of the steam generation station is connected with an inlet of the superheater through a pipeline, an outlet of the superheater is connected with an inlet of the first booster pump through a pipeline, and an outlet of the first booster pump is connected with one end of the water injection pipe through a pipeline; the nanoparticle storage tank and the surfactant storage tank are respectively connected with an inlet of the mixing chamber through pipelines, an outlet of the mixing chamber is connected with an inlet of a second booster pump through a pipeline, an outlet of the second booster pump is connected with one end of the steam injection pipe through a pipeline, and the pulsating pressure controller is used for controlling the pulsating pressure frequency and the pressure variation range of the second booster pump; the other end of the water injection pipe and the other end of the steam injection pipe extend into the main well to reach the inlet of the branch well, the packers are arranged at the other ends of the water injection pipe and the steam injection pipe and used for sealing the inlet of the branch well, and the packers are provided with controllable pressure relief valves; then sealing the well mouth of the main well, connecting the inlet of the gas separator with the outlet of the negative pressure pump through a pipeline, connecting the inlet of the negative pressure pump with the interior of the main well through a pipeline, and installing a first one-way valve on the pipeline between the steam generation station and the superheater, wherein the inlet of the first one-way valve faces the steam generation station; a second one-way valve is arranged on a pipeline between the first booster pump and the superheater, and an inlet of the second one-way valve faces the superheater; a third one-way valve is arranged on a pipeline between the first booster pump and the water injection pipe, and the inlet of the third one-way valve faces the first booster pump; a pipeline between the negative pressure pump and the main well is provided with a fourth one-way valve, and the inlet of the fourth one-way valve faces the main well; a pipeline between the second booster pump and the steam injection pipe is provided with a fifth one-way valve, and the inlet of the fifth one-way valve faces the second booster pump; a pipeline between the second booster pump and the mixing chamber is provided with a sixth one-way valve, and the inlet of the sixth one-way valve faces the mixing chamber; a seventh one-way valve is arranged on a pipeline between the nanoparticle storage tank and the mixing chamber, and an inlet of the seventh one-way valve faces the nanoparticle storage tank; an eighth one-way valve is arranged on a pipeline between the surfactant storage tank and the mixing chamber, and an inlet of the eighth one-way valve faces the surfactant storage tank; completing the assembly of the heat injection production increasing system, wherein each one-way valve is in a closed state initially;
B. the coal seam carries out the promotion of initial crack extension and heat conductivity: opening an eighth one-way valve, injecting a surfactant and water into a mixing chamber, wherein the water temperature is 25-30 ℃, opening a seventh one-way valve after the surfactant and the water are uniformly mixed, injecting nano metal particles, and then uniformly mixing the nano metal particles, the surfactant and the water to form a mixed solution; then opening a fifth one-way valve and a sixth one-way valve, and controlling a second booster pump to generate periodically-changed pulsating pressure through a pulsating pressure controller, wherein the frequency of the pulsating pressure is 20Hz, and the pressure change range is 0.5-3 MPa; injecting the mixed solution into a branch well through a water injection pipe, impacting a main crack and a secondary crack which originally exist in a coal bed after the mixed solution enters the branch well, further expanding the cracks to generate new fine cracks, wherein nano metal particles in the mixed solution are adsorbed in the cracks of the coal bed after impacting the cracks, and meanwhile, a surfactant is attached to the surface of the coal bed to perform hydrophobic modification on the surface of the coal bed; after the continuous operation is carried out for 15-20 minutes, closing the fifth one-way valve to the eighth one-way valve, stopping the operation of the second booster pump, disconnecting the second booster pump from the water injection pipe, and discharging the residual mixed liquid in the branch well through the water suction pump and the water injection pipe, thereby completing the expansion of the initial crack of the coal seam and the improvement of the heat conductivity;
C. performing secondary crack propagation and coal bed gas analysis on the coal bed: opening the first one-way valve to the third one-way valve, enabling the steam generation station, the superheater and the first booster pump to start working, enabling water to enter the steam generation station through a water injection port, enabling the steam generation station to generate steam with the temperature of 100-130 ℃, enabling the steam to enter the superheater, and heating the steam to be superheated steam with the temperature of 200-300 ℃; the method comprises the following steps that superheated steam enters a first booster pump, the pressure of the superheated steam is increased to 5-8 Mpa to form high-temperature high-pressure steam, the high-temperature high-pressure steam is injected into a branch well through a steam injection pipe, the high-temperature high-pressure steam impacts and heats a main crack and a secondary crack originally existing in a coal seam after entering the branch well, and the coal seam crack is further expanded and developed after being acted by high temperature and high pressure; the nano metal particles in the cracks have better heat conduction capacity, so that the heat exchange efficiency between the coal bed and high-temperature high-pressure steam can be greatly improved when the high-temperature high-pressure steam enters the cracks, the high-temperature high-pressure steam can heat the coal bed in a wider range, the high-temperature high-pressure steam can be condensed into water after heat exchange with the coal bed, the water wettability of the coal is changed due to the action of the surfactant, the contact angle between the coal and the water is increased, at the moment, the condensed water forms liquid drops on the surface of the coal in a bead-shaped manner, and the heat exchange efficiency of the subsequent high-temperature high-pressure steam and the coal bed is further ensured;
D. extracting coal bed gas: after high-temperature high-pressure steam is continuously injected for 10-15 hours, stopping injecting, closing all one-way valves and stopping the steam generation station, the superheater and the first booster pump from working, fully heating the coal bed while further pressurizing and expanding the cracks by using the high-temperature high-pressure steam through a well, and reducing the adsorbability of the coal bed to coal bed gas after the temperature of the coal bed rises, so that the desorption of the coal bed gas is realized under the dual effects of further expanding and expanding the cracks of the coal bed and heating the coal bed; meanwhile, continuously monitoring the pressure in the branch well through a controllable pressure relief valve, discharging condensed water out of the branch well through a water injection pipe through a water suction pump after the pressure is reduced to be below 0.5MPa, finally opening a controllable pressure relief valve and a fourth one-way valve, starting a negative pressure pump to extract mixed gas of redundant steam and coal bed gas, enabling the mixed gas to enter a gas separator through the negative pressure pump, separating in the gas separator, recycling the redundant steam after condensation and purification, and storing the separated coal bed gas in a gas storage tank;
E. circularly treating and continuously extracting coal bed gas: and C, continuously extracting the coal bed gas until the pressure in the branch well monitored by the controllable pressure relief valve is reduced to be below 0.08MPa and continues for 10 hours, stopping extraction, repeating the steps B to D again, continuously extracting the coal bed gas, detecting the content of the coal bed gas in the mixed gas, repeating the steps for a plurality of times, and stopping the extraction of the coal bed gas in the well until the content of the coal bed gas in the mixed gas is not increased after one-time coal bed gas desorption treatment is completed.
Further, the mass ratio of the nano metal particles to the water in the mixing chamber is 1: 10. The surfactant is nonionic surfactant OP-10 or is formed by compounding cationic surfactant YS-1, fluorocarbon surfactant FS-2 and nonionic surfactant FS-1.
Furthermore, the controllable pressure relief valve is an electric pressure relief valve with a gas pressure sensor.
Further, the nano metal particles are Fe3O4Nanoparticles or CuO nanoparticles. The nano metal particles not only have better heat-conducting property, but also have stronger adsorbability, and the impact property of the nano metal particles is higher than that of water molecules, so that the nano metal particles can improve the impact effect of the mixed liquid on cracks when the mixed liquid impacts the cracks of the coal seam, and can be adsorbed in the cracks after impact, thereby greatly improving the heat-conducting property of the coal seam.
Compared with the prior art, the method adopts a pulse injection mode to inject the mixed solution into the coal bed, so that the surfactant and the nano metal particles in the mixed solution are fully contacted with the inside of the crack, more nano metal particles are adsorbed on the inner surface of the crack, and the surfactant fully reacts with the surface of the coal body to change the surface performance of the coal body; the nano metal particles not only have better heat conducting property, but also have stronger adsorbability, and the impact property of the nano metal particles is higher than that of water molecules, so that the nano metal particles can implement better pulse impact on existing cracks in a coal seam when the mixed liquid performs pulse impact on the cracks of the coal seam, the cracks are caused to be damaged by fatigue, the cracks are easier to expand and extend, a large-range crack network is formed, steam can heat the coal seam in a larger range through the cracks when the steam is injected subsequently, and meanwhile, the steam can be adsorbed in the cracks after the impact, so that the heat conducting capacity of the coal seam is greatly improved; injecting high-temperature and high-pressure steam into the branch well, continuously impacting, pressurizing and heating the primary cracks and the secondary cracks originally existing in the coal seam after the high-temperature and high-pressure steam enters the branch well, and further expanding and developing the coal seam cracks under the action of high temperature and high pressure; because the nano metal particles in the cracks have better heat conduction capacity, the heat exchange efficiency between the coal bed and the high-temperature high-pressure steam can be greatly improved when the high-temperature high-pressure steam enters the cracks, the high-temperature high-pressure steam can heat the coal bed in a wider range, the high-temperature high-pressure steam can be condensed into water after heat exchange with the coal bed, the water wettability of the coal is changed due to the action of the surfactant, the contact angle between the coal and the water is increased, at the moment, the condensed water forms liquid drops on the surface of the coal in a bead-shaped mode, and the heat transfer coefficient of the bead-shaped condensation is 5-10 times larger than that of the film-shaped condensation, so that after the coal bed is pretreated by the surfactant, the liquid drops condensed in the early stage cannot cause great influence on the heat exchange efficiency of subsequent steam, and the nano metal particles on the surface cannot be covered by the condensed water due to the liquid drop form, thereby ensuring the direct contact between the subsequent steam and the nano metal particles, finally, the heat transfer efficiency between the steam and the coal bed is continuously increased, and finally, the coal bed gas with stronger adsorptivity can be desorbed, so that the yield of the coal bed gas is greatly increased.
Drawings
FIG. 1 is a schematic view of the overall layout of the heat injection stimulation system of the present invention;
FIG. 2 is a schematic diagram of the positional relationship of the controllable pressure relief valve, the packer, the water injection line and the steam injection line in the present invention;
FIG. 3 is a schematic diagram of a part A in FIG. 1 showing the adsorption of nanoparticles in the coal body cracks in an enlarged manner;
FIG. 4 is a schematic diagram comparing different condensing modes of steam in a coal seam crack according to the invention;
fig. 5 is a schematic view of the pulsating pressure generated in the pulsating pressure controller of the present invention.
In the figure: 1-water injection port, 2-steam generation station, 3-1-first one-way valve, 3-2-second one-way valve, 3-3-third one-way valve, 3-4-fourth one-way valve, 3-5-fifth one-way valve, 3-6-sixth one-way valve, 3-7-seventh one-way valve, 3-8-eighth one-way valve, 4-superheater, 5-1-first booster pump, 5-2-second booster pump, 6-negative pressure pump, 7-gas separator, 8-pulsating pressure controller, 9-mixing chamber, 10-nanoparticle storage tank, 11-surfactant storage tank, 12-casing pipe, 13-main well, 14-water injection pipe, 15-steam injection pipe, 16-branch well, 17-main crack, 18-secondary crack, 19-controllable pressure relief valve, 20-packer, 21-coal bed, 22-nano metal particle, 23-crack surface, 24-liquid film, 25-liquid drop.
Detailed Description
The present invention will be further explained below.
The method is applied in the later period of exploitation of the conventional coal bed gas horizontal branch well under the condition that hydraulic fracturing and drainage depressurization cannot meet production requirements and the yield of the coal bed gas cannot be improved.
As shown in fig. 1, the specific steps of this embodiment are:
A. assembling a heat injection production increasing system: the heat injection production increasing system comprises a steam generation station 2, a superheater 4, a first booster pump 5-1, a second booster pump 5-2, a negative pressure pump 6, a gas separator 7, a pulsating pressure controller 8, a mixing chamber 9, a nanoparticle storage tank 10, a surfactant storage tank 11, a packer 20, a water injection pipe 14 and a steam injection pipe 15, wherein an outlet of the steam generation station 2 is connected with an inlet of the superheater 4 through a pipeline, an outlet of the superheater 4 is connected with an inlet of the first booster pump 5-1 through a pipeline, and an outlet of the first booster pump 5-1 is connected with one end of the water injection pipe 14 through a pipeline; the nanoparticle storage tank 10 and the surfactant storage tank 11 are respectively connected with an inlet of the mixing chamber 9 through a pipeline, an outlet of the mixing chamber 9 is connected with an inlet of the second booster pump 5-2 through a pipeline, an outlet of the second booster pump 5-2 is connected with one end of the steam injection pipe 15 through a pipeline, and the pulsating pressure controller 8 is used for controlling the pulsating pressure frequency and the pressure variation range of the second booster pump 5-2; the other end of the water injection pipe 14 and the other end of the steam injection pipe 15 extend into the main well 13 to reach the inlet of the branch well 16, as shown in fig. 2, a packer 20 is installed at the other end of the water injection pipe 14 and the other end of the steam injection pipe 15 and is used for sealing the inlet of the branch well 16, a controllable pressure relief valve 19 is installed on the packer 20, and the controllable pressure relief valve 19 is an electric pressure relief valve with a gas pressure sensor; then sealing the well mouth of the main well 13, connecting the inlet of the gas separator 7 with the outlet of the negative pressure pump 6 through a pipeline, connecting the inlet of the negative pressure pump 6 with the inside of the main well 13 through a pipeline, installing a first one-way valve 3-1 on the pipeline between the steam generation station 2 and the superheater 4, and enabling the inlet of the first one-way valve 3-1 to face the steam generation station 2; a second one-way valve 3-2 is arranged on a pipeline between the first booster pump 5-1 and the superheater 4, and an inlet of the second one-way valve 3-2 faces the superheater 4; a third one-way valve 3-3 is arranged on a pipeline between the first booster pump 5-1 and the water injection pipe 14, and the inlet of the third one-way valve 3-3 faces the first booster pump 5-1; a pipeline between the negative pressure pump 6 and the main well 13 is provided with a fourth one-way valve 3-4, and the inlet of the fourth one-way valve 3-4 faces the main well 13; a fifth one-way valve 3-5 is arranged on a pipeline between the second booster pump 5-2 and the steam injection pipe 15, and the inlet of the fifth one-way valve 3-5 faces the second booster pump 5-2; a pipeline between the second booster pump 5-2 and the mixing chamber 9 is provided with a sixth one-way valve 3-6, and the inlet of the sixth one-way valve 3-6 faces the mixing chamber 9; a seventh one-way valve 3-7 is arranged on a pipeline between the nanoparticle storage tank 10 and the mixing chamber 9, and an inlet of the seventh one-way valve 3-7 faces the nanoparticle storage tank 10; an eighth check valve 3-8 is arranged on a pipeline between the surfactant storage tank 11 and the mixing chamber 9, and an inlet of the eighth check valve 3-8 faces the surfactant storage tank 11; completing the assembly of the heat injection production increasing system, wherein each one-way valve is in a closed state initially;
the steam generation station 2, the superheater 4, the first booster pump 5-1, the second booster pump 5-2, the negative pressure pump 6, the gas separator 7, the pulsating pressure controller 8, the mixing chamber 9, the nanoparticle storage tank 10, the surfactant storage tank 11, the packer 20, the controllable pressure relief valve 19 and the check valves are all existing devices or components; and each check valve is a check valve with a valve. Each one-way valve has the function of ensuring that gas or liquid flowing through the one-way valve can only flow in a single direction after the valve is opened, and stopping the flow of the gas or the liquid after the valve is closed.
B. The coal seam carries out the promotion of initial crack extension and heat conductivity: opening the eighth one-way valve 3-8, injecting a surfactant and water into the mixing chamber 9, wherein the water temperature is 25-30 ℃, opening the seventh one-way valve 3-7 after the surfactant and the water are uniformly mixed, injecting nano metal particles, and then uniformly mixing the nano metal particles, the surfactant and the water to form a mixed solution; wherein, the mass ratio of the nano metal particles to the water is 1:10, the surfactant can adopt a surfactant with emulsification such as a nonionic surfactant OP-10, or a mixture of several surfactants such as a cationic surfactant YS-1, a fluorocarbon surfactant FS-2 and a nonionic surfactant FS-1, so as to achieve the effect of hydrophobic modification on the coal; because the surface properties of different types of coal are greatly different, in order to determine the proportion (concentration value) of various surfactants and water, the method is used for determining the proportion of various surfactants and waterBefore the surfactant is used, an on-site coal sample is taken in a laboratory to measure the contact angle between coal and water, and a group of mixture ratios which enable the contact angle between the coal and the water to be relatively greatly increased are selected as the mixture ratio of the surfactant to the water in the mixed liquid. The nano metal particles 22 are Fe3O4Nanoparticles or CuO nanoparticles; as shown in fig. 3, the nano metal particles 22 not only have good thermal conductivity, but also have strong adsorbability, and the impact property thereof is higher than that of water molecules, so that the nano metal particles 22 can improve the impact effect of the mixed liquid on the cracks when the mixed liquid impacts the cracks of the coal seam, and can be adsorbed in the cracks after impact, thereby greatly improving the thermal conductivity of the coal seam.
Then, the fifth check valve 3-5 and the sixth check valve 3-6 are opened, and the second booster pump 5-2 is controlled by the pulsating pressure controller 8 to generate pulsating pressure which changes periodically, wherein a pulsating pressure change schematic diagram and other pulsating pressure parameters are shown in fig. 5, and the meanings of the parameters in the diagram are as follows: t-time, P-instantaneous pressure (pressure at each moment), T-period (here 0.05s), PminMinimum pressure (minimum of instantaneous pressure in one cycle, here 0.5MPa), PmaxMaximum pressure (maximum of instantaneous pressure in one cycle, here 3MPa), PaveMean pressure (mean value of pressure over time), PAPressure amplitude (difference between maximum and minimum values of pulsating pressure within a period, here 2.5 MPa);
injecting a mixed solution into the branch well 16 through the water injection pipe 14, impacting a main crack 17 and a secondary crack 18 originally existing in the coal seam 21 after the mixed solution enters the branch well 16, further expanding the cracks to generate new fine cracks, wherein nano metal particles 22 in the mixed solution are adsorbed in the cracks of the coal seam after impacting the cracks, and meanwhile, a surfactant is attached to the surface of the coal seam to perform hydrophobic modification on the surface of the coal seam; after the continuous operation is carried out for 15-20 minutes, the fifth one-way valve 3-5 to the eighth one-way valve 3-8 are closed, the second booster pump 5-2 is stopped to work, the connection between the second booster pump 5-2 and the water injection pipe 14 is disconnected, and the residual mixed liquid in the branch well 16 is discharged through the water suction pump and the water injection pipe 14, so that the expansion of the initial crack of the coal seam and the improvement of the heat conduction capability are completed;
C. performing secondary crack propagation and coal bed gas analysis on the coal bed: opening a first one-way valve 3-1 to a third one-way valve 3-3, enabling a steam generation station 2, a superheater 4 and a first booster pump 5-1 to start working, enabling water to enter the steam generation station 2 through a water injection port 1, enabling the steam generation station 2 to generate steam with the temperature of 100-130 ℃, enabling the steam to enter the superheater 4, and heating the steam into superheated steam with the temperature of 200-300 ℃; the superheated steam enters the first booster pump 5-1, the pressure of the superheated steam is increased to 5-8 Mpa to form high-temperature high-pressure steam, the high-temperature high-pressure steam is injected into the branch well 16 through the steam injection pipe 15, the high-temperature high-pressure steam impacts and heats a main crack 17 and a secondary crack 18 originally existing in the coal seam after entering the branch well 15, and the coal seam cracks further expand and develop after being acted by high-temperature and high-pressure forces; because the nano metal particles 22 in the cracks have good heat conduction capability, the heat exchange efficiency between the coal bed 21 and high-temperature high-pressure steam can be greatly improved when the high-temperature high-pressure steam enters the cracks, the high-temperature high-pressure steam can heat the coal bed 21 in a wider range, the high-temperature high-pressure steam can be condensed into water after heat exchange with the coal bed 21, the water wettability of coal is changed due to the action of a surfactant, the contact angle between the coal and the water is increased, liquid drops 25 are formed on the surface of the coal by the condensed water in a bead-shaped manner, and the heat exchange efficiency of the subsequent high-temperature high-pressure steam and the coal bed is further ensured;
if the coal body is not pretreated, the steam condenses in the coal to form a liquid film 24 on the fracture surface 23 due to the small contact angle between the coal and water, which hinders the heat transfer efficiency of the subsequent steam to the coal, as shown in fig. 4. After the coal body is treated with the surfactant, the water wettability of the coal is changed, the contact angle between the coal and water is increased, and at this time, the steam is condensed in a bead-like manner on the coal surface, that is, liquid droplets 25 are formed on the coal surface. Because the heat transfer coefficient of the bead-shaped condensation is 5-10 times larger than that of the film-shaped condensation, after the coal seam 21 is pretreated by using the surfactant, the liquid drops condensed in advance do not have great influence on the heat exchange efficiency of subsequent steam, and the condensed water does not cover the nano metal particles 22 on the surface due to the liquid drop form, so that the direct contact between the subsequent steam and the nano metal particles 22 is ensured, and the heat transfer efficiency between the steam and the coal seam 21 is continuously increased finally. In addition, the steam condensate is in the form of liquid drops 25 and is not easy to be adsorbed on the surface of the crack, so that the crack is not blocked, and the liquid is easier to flow back.
D. Extracting coal bed gas: after high-temperature high-pressure steam is continuously injected for 10-15 hours, the injection is stopped, all one-way valves are closed, the steam generation station 2, the superheater 4 and the first booster pump 5-1 are stopped from working, the well is closed, the high-temperature high-pressure steam further applies pressure to cracks to expand and develop, and simultaneously fully heats the coal bed 21, the adsorption of the coal bed to coal bed gas is reduced after the temperature of the coal bed 21 is increased, and therefore the desorption of the coal bed gas is realized under the dual effects of further expansion and development of the coal bed cracks and temperature rise of the coal bed; meanwhile, the pressure in the branch well 16 is continuously monitored through the controllable pressure relief valve 19, after the pressure is reduced to be below 0.5MPa, condensed water is discharged out of the branch well 16 through the water injection pipe 14 through the water suction pump, finally, the controllable pressure relief valve 19 and the fourth one-way valve 3-4 are opened, the negative pressure pump 6 is started to extract mixed gas of redundant steam and coal bed gas, the mixed gas enters the gas separator 7 through the negative pressure pump 6 and is separated in the gas separator 7, the redundant steam can be recycled after condensation and purification, and the separated coal bed gas is stored in the gas storage tank;
E. circularly treating and continuously extracting coal bed gas: and C, continuously extracting the coal bed gas until the pressure in the branch well 16 monitored by the controllable pressure relief valve 19 is reduced to be below 0.08MPa and continues for 10 hours, stopping extraction, repeating the steps B to D again, continuously extracting the coal bed gas, detecting the content of the coal bed gas in the mixed gas, repeating the steps for a plurality of times, and stopping the extraction of the coal bed gas in the well until the content of the coal bed gas in the mixed gas is not increased after one-time coal bed gas desorption treatment is completed.
The scheme of the embodiment only describes a treatment method of a single branch well 16, and for other branch wells 16, the same method is adopted for treatment, a plurality of steam injection pipes 15 and water injection pipes 14 can be selected to be respectively placed into each branch well 16, then the analysis and yield increase of the coal bed gas can be carried out by the same heat injection yield increase system, several branch wells can be simultaneously treated, and after one branch well is treated, the other branch wells can be treated.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (4)
1. A method for increasing coal bed gas through heat injection based on hydraulic fracturing of a multi-branch horizontal well is characterized by comprising the following specific steps:
A. assembling a heat injection production increasing system: the heat injection yield increasing system comprises a steam generation station, a superheater, a first booster pump, a second booster pump, a negative pressure pump, a gas separator, a pulsating pressure controller, a mixing chamber, a nanoparticle storage tank, a surfactant storage tank, a packer, a water injection pipe and a steam injection pipe, wherein an outlet of the steam generation station is connected with an inlet of the superheater through a pipeline, an outlet of the superheater is connected with an inlet of the first booster pump through a pipeline, and an outlet of the first booster pump is connected with one end of the water injection pipe through a pipeline; the nanoparticle storage tank and the surfactant storage tank are respectively connected with an inlet of the mixing chamber through pipelines, an outlet of the mixing chamber is connected with an inlet of a second booster pump through a pipeline, an outlet of the second booster pump is connected with one end of the steam injection pipe through a pipeline, and the pulsating pressure controller is used for controlling the pulsating pressure frequency and the pressure variation range of the second booster pump; the other end of the water injection pipe and the other end of the steam injection pipe extend into the main well to reach the inlet of the branch well, the packers are arranged at the other ends of the water injection pipe and the steam injection pipe and used for sealing the inlet of the branch well, and the packers are provided with controllable pressure relief valves; then sealing the well mouth of the main well, connecting the inlet of the gas separator with the outlet of the negative pressure pump through a pipeline, connecting the inlet of the negative pressure pump with the interior of the main well through a pipeline, and installing a first one-way valve on the pipeline between the steam generation station and the superheater, wherein the inlet of the first one-way valve faces the steam generation station; a second one-way valve is arranged on a pipeline between the first booster pump and the superheater, and an inlet of the second one-way valve faces the superheater; a third one-way valve is arranged on a pipeline between the first booster pump and the water injection pipe, and the inlet of the third one-way valve faces the first booster pump; a pipeline between the negative pressure pump and the main well is provided with a fourth one-way valve, and the inlet of the fourth one-way valve faces the main well; a pipeline between the second booster pump and the steam injection pipe is provided with a fifth one-way valve, and the inlet of the fifth one-way valve faces the second booster pump; a pipeline between the second booster pump and the mixing chamber is provided with a sixth one-way valve, and the inlet of the sixth one-way valve faces the mixing chamber; a seventh one-way valve is arranged on a pipeline between the nanoparticle storage tank and the mixing chamber, and an inlet of the seventh one-way valve faces the nanoparticle storage tank; an eighth one-way valve is arranged on a pipeline between the surfactant storage tank and the mixing chamber, and an inlet of the eighth one-way valve faces the surfactant storage tank; completing the assembly of the heat injection production increasing system, wherein each one-way valve is in a closed state initially;
B. the coal seam carries out the promotion of initial crack extension and heat conductivity: opening a seventh one-way valve and an eighth one-way valve, putting the nano metal particles in the nano particle storage tank and the surfactant in the surfactant storage tank into a mixing chamber, injecting a certain amount of water into the mixing chamber, wherein the water temperature is 25-30 ℃, and then uniformly mixing the nano metal particles, the surfactant and the water in the mixing chamber to form a mixed solution; then opening a fifth one-way valve and a sixth one-way valve, and controlling a second booster pump to generate periodically-changed pulsating pressure through a pulsating pressure controller, wherein the frequency of the pulsating pressure is 20Hz, and the pressure change range is 0.5-3 MPa; injecting the mixed solution into a branch well through a water injection pipe, impacting a main crack and a secondary crack which originally exist in a coal bed after the mixed solution enters the branch well, further expanding the cracks to generate new fine cracks, wherein nano metal particles in the mixed solution are adsorbed in the cracks of the coal bed after impacting the cracks, and meanwhile, a surfactant is attached to the surface of the coal bed to perform hydrophobic modification on the surface of the coal bed; after the continuous operation is carried out for 15-20 minutes, closing the fifth one-way valve to the eighth one-way valve, stopping the operation of the second booster pump, disconnecting the second booster pump from the water injection pipe, and discharging the residual mixed liquid in the branch well through the water suction pump and the water injection pipe, thereby completing the expansion of the initial crack of the coal seam and the improvement of the heat conductivity;
C. performing secondary crack propagation and coal bed gas analysis on the coal bed: opening the first one-way valve to the third one-way valve, enabling the steam generation station, the superheater and the first booster pump to start working, enabling water to enter the steam generation station through a water injection port, enabling the steam generation station to generate steam with the temperature of 100-130 ℃, enabling the steam to enter the superheater, and heating the steam to be superheated steam with the temperature of 200-300 ℃; the method comprises the following steps that superheated steam enters a first booster pump, the pressure of the superheated steam is increased to 5-8 Mpa to form high-temperature high-pressure steam, the high-temperature high-pressure steam is injected into a branch well through a steam injection pipe, the high-temperature high-pressure steam impacts and heats a main crack and a secondary crack originally existing in a coal seam after entering the branch well, and the coal seam crack is further expanded and developed after being acted by high temperature and high pressure; the nano metal particles in the cracks have better heat conduction capacity, so that the heat exchange efficiency between the coal bed and high-temperature high-pressure steam can be greatly improved when the high-temperature high-pressure steam enters the cracks, the high-temperature high-pressure steam can heat the coal bed in a wider range, the high-temperature high-pressure steam can be condensed into water after heat exchange with the coal bed, the water wettability of the coal is changed due to the action of the surfactant, the contact angle between the coal and the water is increased, at the moment, the condensed water forms liquid drops on the surface of the coal in a bead-shaped manner, and the heat exchange efficiency of the subsequent high-temperature high-pressure steam and the coal bed is further ensured;
D. extracting coal bed gas: after high-temperature high-pressure steam is continuously injected for 10-15 hours, stopping injecting, closing all one-way valves and stopping the steam generation station, the superheater and the first booster pump from working, fully heating the coal bed while further pressurizing and expanding the cracks by using the high-temperature high-pressure steam through a well, and reducing the adsorbability of the coal bed to coal bed gas after the temperature of the coal bed rises, so that the desorption of the coal bed gas is realized under the dual effects of further expanding and expanding the cracks of the coal bed and heating the coal bed; meanwhile, continuously monitoring the pressure in the branch well through a controllable pressure relief valve, discharging condensed water out of the branch well through a water injection pipe through a water suction pump after the pressure is reduced to be below 0.5MPa, finally opening a controllable pressure relief valve and a fourth one-way valve, starting a negative pressure pump to extract mixed gas of redundant steam and coal bed gas, enabling the mixed gas to enter a gas separator through the negative pressure pump, separating in the gas separator, recycling the redundant steam after condensation and purification, and storing the separated coal bed gas in a gas storage tank;
E. circularly treating and continuously extracting coal bed gas: and C, continuously extracting the coal bed gas until the pressure in the branched well 16 monitored by the controllable pressure relief valve is reduced to be below 0.08MPa and continues for 10 hours, stopping extraction, repeating the steps B to D again, continuously extracting the coal bed gas, detecting the content of the coal bed gas in the mixed gas, repeating the steps for a plurality of times, and stopping the extraction of the coal bed gas in the well until the content of the coal bed gas in the mixed gas is not increased after one-time coal bed gas desorption treatment is completed.
2. The method for increasing the coal bed methane by heat injection based on the hydraulic fracturing multi-branch horizontal well is characterized in that the mass ratio of the nano metal particles to the water in the mixing chamber is 1: 10; the surfactant is nonionic surfactant OP-10 or is formed by compounding cationic surfactant YS-1, fluorocarbon surfactant FS-2 and nonionic surfactant FS-1.
3. The method for injecting heat and increasing the coal bed gas based on the hydraulic fracturing multi-branch horizontal well is characterized in that the controllable pressure relief valve is an electric pressure relief valve with a gas pressure sensor.
4. The method for increasing coal bed methane by heat injection based on hydraulic fracturing multi-branch horizontal well according to claim 1, wherein the nano metal particles are Fe3O4Nanoparticles or CuO nanoparticles.
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