WO2018170830A1 - 注高温空气增产煤层气的方法 - Google Patents

注高温空气增产煤层气的方法 Download PDF

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WO2018170830A1
WO2018170830A1 PCT/CN2017/077861 CN2017077861W WO2018170830A1 WO 2018170830 A1 WO2018170830 A1 WO 2018170830A1 CN 2017077861 W CN2017077861 W CN 2017077861W WO 2018170830 A1 WO2018170830 A1 WO 2018170830A1
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temperature
coal
gas
oxygen
coalbed methane
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PCT/CN2017/077861
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French (fr)
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陈信平
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陈信平
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP 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
    • E21B43/18—Repressuring or vacuum methods
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP 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
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP 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
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B47/00—Survey of boreholes or wells
    • E21B47/06—Measuring temperature or pressure
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
    • Y02P90/70—Combining sequestration of CO2 and exploitation of hydrocarbons by injecting CO2 or carbonated water in oil wells

Definitions

  • the invention relates to a method for injecting high temperature air into a coalbed methane reservoir to increase production of coalbed methane.
  • the present invention relates to a well that is connected to a coal seam from one or more ports (hereinafter referred to as a "injection well"), injecting high temperature air into the coal seam, wherein the nitrogen “peeling” and “discharging” coal micropores and crack surfaces
  • the adsorbed coalbed methane promotes the desorption of coalbed methane and migrates to the production well.
  • the low temperature oxidation causes the oxygen in the coal to be retained in the coal seam due to physical adsorption, chemical adsorption and oxidation reaction, and is consumed from multiple ports connected with the coal seam.
  • production well The method of collecting coalbed methane and coalbed methane and nitrogen mixed gas to improve the production of coalbed methane wells and coalbed methane recovery.
  • Coalbed methane is natural gas in coal seams, also known as gas, and its main component is methane. Coalbed methane is both a clean energy source for natural gas and a cause of coal mine gas outbursts and explosions.
  • Puri and Stein proposed a method for increasing the production of coalbed methane, which injects an inert gas (for example, nitrogen) or a gas that does not chemically react with coal (for example, CO 2 ) from a gas injection well to a coal seam, from a bite or Multi-port production wells obtain coalbed methane and can increase coalbed methane production (see Rajen Puri and Michael H. Stein. 1988. Method of coalbed methane production. US Patent No. 4883122). Puri and Stein's patented methods are only applicable to high-quality coalbed methane reservoirs with high permeability, which are not applicable to most coalbed methane reservoirs and cannot be implemented.
  • an inert gas for example, nitrogen
  • a gas that does not chemically react with coal for example, CO 2
  • Chen Xinping proposed a pressure control method for nitrogen injection to increase coalbed methane, which is suitable for nitrogen injection and enrichment of coal seam gas in any coal seam (see Chen Xinping. 2015. Pressure control method for nitrogen injection to increase coalbed methane. China Patent No. ZL201510467978.3).
  • Chen Xinping's patented method takes the parameters of wellhead pressure, gas production and nitrogen volume percentage of the production well as the reaction of the coalbed methane reservoir to the nitrogen injection pressure and nitrogen injection rate of the nitrogen injection well, and feeds back to the nitrogen injection well.
  • the nitrogen injection pressure and the nitrogen injection rate can inject nitrogen into the low permeability coal seam without fracturing the surrounding rock of the coal seam roof and floor.
  • the increase in the production of coalbed methane by N 2 is basically not harmful to future coal mining operations.
  • the cost of increasing production of coalbed methane by N 2 is high, which affects the promotion and application of the technology of increasing production of coalbed methane by injection of N 2 .
  • the cost of N 2 production of CBM technology itself is about 0.50 yuan / m 3 or so.
  • the current CBM wellhead price is between 1.20 and 1.50 yuan/m 3 .
  • the cost of N 2 accounts for 42% to 33% of the sales revenue of coalbed methane, which is too heavy, so that the production of coalbed methane by injection of N 2 has no economic benefit in most cases.
  • the cost of the N 2 production of CBM technology itself consists of two parts: (1) separation of nitrogen from air using a nitrogen generator or cryogenic process, mainly to separate oxygen from nitrogen; and (2) use of a high pressure supercharger Nitrogen is injected into the coal seam.
  • the cost of these two parts is basically equal. Therefore, if it is possible to inject nitrogen into the coal seam instead of nitrogen, and obtain the same or better stimulation effect as the injection of N 2 to produce coalbed methane, the cost will be only half of the cost of the production of coalbed methane by injection of N 2 , then such air injection increases.
  • the method of coalbed methane will be of great use value and will be a major contribution to the development of world coalbed methane.
  • the invention relates to a method for injecting high temperature air into a coalbed methane reservoir to increase production of coalbed methane.
  • the present invention relates to a well that is connected to a coal seam from one or more ports (hereinafter referred to as a "injection well"), injecting high temperature air into the coal seam, wherein the nitrogen “peeling” and “discharging” coal micropores and crack surfaces
  • the adsorbed coalbed methane promotes the desorption of coalbed methane and migrates to the production well.
  • the low temperature oxidation causes the oxygen in the coal to be retained in the coal seam due to physical adsorption, chemical adsorption and oxidation reaction, and is consumed from multiple ports and coal seams.
  • production well collects the produced coalbed methane and the mixed gas of coalbed methane and nitrogen, thereby improving the production of coalbed methane wells and the recovery of coalbed methane.
  • the invention relates to a method for injecting high temperature air into a coalbed methane reservoir to increase production of coalbed methane.
  • the present invention relates to a method for injecting high-temperature air into a coal seam from a well communicating with a coal seam with one or more ports, wherein the nitrogen "peeling", "discharging” coal micropores, adsorbing coalbed methane on the surface of the fracture, and promoting coalbed methane Desorbing and transporting to the production well, low-temperature oxidation causes the oxygen in it to remain in the coal seam due to physical adsorption, chemical adsorption, oxidation reaction, or is consumed, and the coalbed methane and coal seam collected from the wells connected with the coal seam A method of increasing the production of coalbed methane wells and coalbed methane recovery by mixing a gas with nitrogen.
  • step (h) When the temperature of the production well gas rises to near the maximum allowable temperature and the cooling effect of step (g) is poor or the step (g) cannot be carried out, the normal temperature air or the normal temperature nitrogen gas is re-injected until the temperature of the production well gas is sufficiently lowered.
  • the gas injection operation is started according to the initial temperature and the heating rate until the gas injection temperature reaches the normal working temperature, and the normal gas injection stimulation operation phase is re-entered;
  • Steps (d), (e), (g), and (h) may be repeated as many times as needed.
  • the method of the present invention injects air into the coal seam, and the nitrogen in the air "peeles” and “displaces” the adsorbed coalbed methane on the surface of the micropores of the coal, promotes the desorption of the coalbed methane and migrates to the production well, and plays the role of injection of N 2 to increase the coal seam.
  • the effect of increasing nitrogen production in the gas, the effect of increasing production is similar to the effect of increasing production of coalbed methane by injection of N 2 .
  • the method of the invention does not need to separate nitrogen and oxygen, and the low temperature oxidation of coal replaces the nitrogen generator, and the cost is only half of the cost of increasing the production of coalbed methane by injection of N 2 , which effectively reduces the cost of strengthening the development of coalbed methane.
  • the high temperature air injected into the coal layer by the method of the invention directly increases the temperature of the coal seam, and the physical adsorption, chemical adsorption and chemical reaction in the low temperature oxidation of the coal are all exothermic, and the temperature of the coal seam is also increased.
  • the adsorption of methane on coal is reduced by about 0.18 m 3 / ton on average (see Fu Xuehai, Qin Yong, Wei Chongzhen. 2007. Coalbed Methane Geology [M], Chapter 4, Section IV. Beijing: China University of Mining and Technology Press). Therefore, the method of the invention increases the temperature of the coal seam, promotes the desorption of the coalbed methane, can improve the coalbed methane recovery rate, and reduces the residual gas content of the coal seam to a lower level.
  • the world's CBM reserves are huge, and the output is very low, because the currently used CBM development technology can only develop the best quality CBM reservoirs, and is not suitable for most CBM reservoirs.
  • the technology provided by the present invention is capable of developing most coalbed methane reservoirs, so that huge amounts of coalbed methane resources benefit humanity.
  • Figure 1 is a graph showing the trend of oxygen uptake of different coal types under different adsorption ambient temperatures.
  • Figure 2 shows the oxygen consumption of coal under low temperature oxidation as a function of temperature.
  • Figure 3 is the oxygen consumption of coal oxidation for 1 hour at different temperatures of the same coal.
  • Figure 4 is a test result of oxygen consumption for different oxidation times at the same temperature of the same coal.
  • Figure 5 is a schematic diagram of coal seam temperature and low temperature oxidation of coal around the gas injection well after 4 years of high temperature injection.
  • coal ignition point increases with the increase of coal rank, from the ignition point of lignite (270-310 °C) to the ignition point of coking coal (350-370 °C).
  • the invention relates to low temperature oxidation of coal, which refers to the physical, physical-chemical and chemical interaction between coal and oxygen in an oxidizing environment far below the coal ignition point of the coal seam being injected, or, in other words,
  • the low temperature oxidation of coal referred to in the present invention is limited to a stable oxidation reaction process in which the generated heat is equal to the lost heat, and does not include the stage in which the oxidation reaction is automatically accelerated to an uncontrollable, spontaneous combustion.
  • the coal industry has made a comprehensive and comprehensive study on the low-temperature oxidation of coal, because the low-temperature oxidation stage is the initial stage of coal spontaneous combustion, which plays a decisive role in the development of coal spontaneous combustion.
  • the study of coal oxidation characteristics at this stage is to reveal the spontaneous combustion of coal.
  • the mechanism and the development of countermeasures from the source to prevent and control coal mine fires are of great significance.
  • the coal industry has accumulated a lot of literature on the low-temperature oxidation of coal, and has obtained research results in theoretical development, experimental equipment development, laboratory simulation test, numerical simulation, production application and so on. Practice has proved that the basic theory of low temperature oxidation of coal is correct and reliable.
  • An active structure capable of reacting with oxygen exists in coal almost at any temperature.
  • the functional composition has large changes in elemental composition and structure, so the activity changes greatly and has different oxidizing power.
  • the functional groups, the functional groups and the coal structure main body interact with each other and also make them active. Changes occur to alter the oxidizing power of the functional group; this allows the interaction between coal and oxygen in the coal body at almost any temperature.
  • the temperature at which the same functional group oxidizes in coal samples of different coal ranks is different.
  • the temperature at which the same functional group oxidizes in different coal samples of the same coal rank may also differ because the functional structure of the functional group is different.
  • the host structure affects the oxidative properties of the functional groups.
  • the main structure of the coal structure is basically unchanged. Since the main structure in the coal structure requires higher energy to be activated and the oxidation reaction occurs, the main structure in the coal structure generally does not change significantly under low temperature oxidation conditions below 200 °C.
  • Coal rank (or degree of coalification, degree of coal metamorphism): It is generally believed that as the degree of coalification increases, the activity of low temperature oxidation of coal decreases. One of the reasons is that the low-order coal has a high oxygen content, and the chemical bonding ability to moisture is enhanced, so that the coal has more hydrophilicity and oxidation reaction ability.
  • ⁇ Sulfur content It is generally believed that the oxidation of pyrite can produce an exothermic effect, which is conducive to the continuous oxygen consumption between coal and oxygen, increasing the rate of oxygen consumption.
  • the inorganic sulfur and organic sulfur in coal behave differently in the oxidation reaction.
  • the oxidation of pyrite is remarkable at low temperatures (for example, 25 ° C), while the oxidation of organic sulfur is more pronounced at high temperatures (for example, 80 ° C).
  • the mechanism of sulfur oxidation is: H 2 SO 4 , a by-product of the oxidation of pyrite (FeS 2 ), not only improves the solubility and leaching ability of minerals in coal, but also reacts the oxidation of CH into oxygen-containing functional groups in the micro-components. catalytic, and therefore, the coal-rich FeS 2 is easier to be oxidized.
  • the particle size distribution of pyrite, the ability of the carbonate in the coal to neutralize the acid, etc. can also affect the oxidation rate.
  • Porosity and pore structure are beneficial to low temperature oxidation of coal, because these factors determine whether air can easily enter the coal, contact with effective surface area, and enter reactive vacancies. Based on laboratory measurements, the researchers found that the oxidation rate is proportional to the cube root of the internal surface area. Holes with a pore size >100 nm play an important role in coal oxidation.
  • the microscopic components affect the low temperature oxidation of coal.
  • the vitrinite, algae and spore powder are relatively easy to be oxidized, while the silky, horny and cork bodies are relatively difficult to be oxidized.
  • the calcareous component (CaCO 3 and its conversion product CaSO 4 ) catalyzes the low temperature oxidation of coal.
  • Time Under the restriction that the temperature is much lower than the coal burning point, although the coal oxygen adsorption process is very fast, the oxidation process is slow. The heat generated by the oxidation reaction under such a restriction is equal to the heat lost, and the oxidation reaction does not enter the automatic acceleration process. Therefore, this is a stable oxidation reaction process. Time is an important factor in this oxidation reaction process; only time is long enough, and the changes caused by this oxidation reaction process can be revealed; as long as the time is long enough, the change is often large.
  • Oxygen is the material basis for the coal-oxygen reaction.
  • the oxidation reaction of the surface active structure of coal is directly affected by the oxygen concentration of the environment in which it is located.
  • the oxygen concentration is different, the oxygen consumption rate of coal is different, the acceleration rate of oxidation reaction is different, and the acceleration limit is different.
  • Moisture can be considered as an intrinsic factor because moisture is one of the important components of coal; water can also be considered as an external factor because external intervention can greatly change the moisture content of coal. Moisture affects both the physical adsorption between coal and oxygen and the chemical reaction between coal and oxygen. The proper amount of water is beneficial to the low temperature oxidation of coal, and too much or too little water is not conducive to the low temperature oxidation of coal. If the coal body contains more water, excess water will form a water film on the surface of the coal body to isolate oxygen.
  • ⁇ Gas products a variety of gaseous products are produced during the low-temperature oxidation of coal. Commonly, CO, CO 2 , CH 4 , C 2 H 6 , C 3 H 6 , C 2 H 4 , H 2 O, etc. are also found in the literature. There are H 2 , C 3 H 8 , C 2 H 2 , C 4 H 10 , iC 4 H 10 and the like.
  • the type and sequence are CO, C 2 H 6 , C 2 H 4 , C 3 H 8 , H 2 , C 2 H 2 ; the type and sequence of gas produced by gas coal oxidation are CO, C 2 H 4 , H 2 (C 2 H 6 has already existed at the beginning of the experiment); the type and sequence of gas produced by gas-fertilizer coal oxidation are CO, C 2 H 4 , H 2 (C 2 H 6 , C 3 H 8 already existed at the beginning of the experiment)
  • the type and sequence of anthracite oxidation-generating gas are CO, H 2 , and although the temperature is raised from 20 ° C to 210 ° C, it is not oxidized to form C 2 H 6 , C 2 H 4 , C 3 H 8 .
  • ⁇ Indicator gas (or mark gas): A gas that is not originally found in the coal seam and is completely produced by the oxidation of coal. It is called “index gas”. CO is the most important indicator gas because CO is the gas that any coal can produce at lower temperatures. C 2 H 4 is also a commonly used indicator gas.
  • Non-gas products In fact, it has not been known so far which non-gas products and their quantities are produced during the low-temperature oxidation of coal, largely because it is difficult to distinguish between the original and non-gas products of coal. Furthermore, the present invention does not find a significant correlation between the non-gas products and the success or failure of high temperature air injection to increase coalbed methane. Thus, the present invention is abbreviated for non-gas products.
  • Low temperature oxidation mechanism of coal due to coal rank (coal type), coal grade (coal quality), microscopic composition and content, mineral composition and content, coal structure, porosity and pore structure, oxidation temperature, The difference in oxygen concentration, etc., due to the complexity of the low-temperature oxidation reaction itself, and the research methods (reaction devices, coal types, coal amount and analytical techniques) used by many researchers, the research on the mechanism of low-temperature oxidation of coal There are many consensuses and opposite opinions. The present invention sets forth the consensus of most investigators to clarify that the method of the present invention is the primary purpose and does not pursue all-encompassing.
  • the low temperature oxidation process of coal can be divided into the following three stages.
  • Adsorption is an interface phenomenon. When two phases are in contact, there is a region on the interface that has a composition and properties different from the inside of any phase. This interface phenomenon is called adsorption.
  • Coal-oxygen adsorption belongs to the category of solid-gas adsorption in physical adsorption. From the mechanism of general physical adsorption, adsorption is caused by excess surface free energy.
  • Surface free energy refers to the increase of the free energy of the system when the unit area of the adsorbent is increased under constant temperature and constant pressure, which is also called surface excess free energy or Gibbs free energy.
  • the interface has a tendency to spontaneously reduce the interface energy.
  • the solid interface is difficult to shrink due to the surface molecules or atoms not moving freely.
  • the bituminous coal with higher degree of metamorphism is affected by the ground pressure during the long metamorphosis process, the porosity of the coal is reduced, the coal quality tends to be dense, and the ability to adsorb oxygen is greatly reduced.
  • the further deterioration of coal under the high temperature and high pressure, many micropores are formed inside the coal body due to the dry distillation, the surface area is gradually enlarged, and the ability of anthracite to adsorb oxygen is increased.
  • the microscopic process of low temperature oxidation of coal is followed by physical adsorption, chemical adsorption and oxidation, and an oxygen molecule will also interact with the coal structure in this order.
  • one of the most important functions of the process of physical adsorption of oxygen by coal is to transport oxygen for the oxidation reaction and release the physical adsorption heat.
  • the physical adsorption of heat causes a slight increase in the temperature of the coal body, which is a prelude to the chemical activation and chemical reaction of the activated structure of the coal body and the absorption of oxygen, so that the low temperature oxidation process of the coal advances.
  • Coal-oxygen physical adsorption is before the oxidation reaction takes place It is mentioned that the oxidation reaction is the result of coal adsorption of oxygen.
  • Chemical adsorption and local chemical reaction stages Chemical adsorption is a transitional process between physical adsorption and chemical reaction of coal, or transition state. A surface chemical reaction occurs between the chemically adsorbed oxygen and the surface structure of the coal, and electron transfer occurs between the oxygen atoms and the atoms in the coal structure, and is combined with a surface bond force similar to a chemical bond. Chemical adsorption itself is a chemical reaction, and chemisorption heat is similar to chemical reaction heat.
  • Coal oxidation adsorption is the process in which the electrons of the coal-active structure enter the orbit of unpaired electrons of oxygen molecules, forming a relatively stable system and releasing heat. The force that produces chemisorption is the chemical bond force.
  • Accelerated oxidation stage deep oxidation, some bridge bonds on the coal molecular structure unit are oxidized, and the reaction speed is increased to generate H 2 and C 2 H 2 .
  • the chemical reactions at this stage are not limited to surface chemical reactions, but may penetrate deep into the coal structure. However, the chemical reaction at this stage is still limited to the side chains, bridge bonds, and functional groups of the coal structure, and does not involve the bulk structure of the coal.
  • the present invention states that the technical points and difficulties of the method for increasing the production of coalbed methane by high-temperature air are explained in detail, mainly how the oxygen in the air injected into the coal seam is consumed. How is the oxygen that is not consumed, staying in the coal seam without being discharged from the production well along with the coalbed methane and nitrogen?
  • Air composition The normal air content is calculated by volume fraction: nitrogen (N 2 ) is about 78.07%, oxygen (O 2 ) is about 20.94%, and rare gas is about 0.93% ( ⁇ He, ⁇ Ne, argon Ar) , ⁇ Kr, ⁇ Xe, ⁇ Rn), carbon dioxide (CO 2 ) accounts for about 0.031%, and other gases and impurities account for about 0.03% (such as ozone (O 3 ), nitrogen monoxide (NO), nitrogen dioxide ( NO 2 ), water vapor (H 2 O), etc.).
  • ⁇ Nitrogen including helium, neon, argon, neon, xenon, krypton: rare gases such as helium, neon, argon, neon, xenon, krypton and nitrogen are all inert gases, and their functions and fate are the same. Nitrogen is representative. Nitrogen “peeling” and “discharging” coal micropores and adsorbed coalbed methane on the surface of the fracture promote the desorption of coalbed methane and migration to production wells. Note that the increase in production of coalbed methane by high-temperature air is mainly borne by nitrogen. For the principle of nitrogen production to increase coalbed methane, please refer to U.S. Patent No. 4,883,122 and Chinese Patent No.
  • H 2 O is originally one of the components of coalbed methane. It enters the gathering system as one of the gas components of the production well and is dehydrated by the post-treatment equipment.
  • the gaseous products produced during the low temperature oxidation of coal are all combustible gases, and their calorific value is much higher than the calorific value of the main component of coalbed methane, which is a high calorific value natural gas component.
  • coalbed methane components they are discharged from the production wells into the coalbed methane gathering and transportation system, which is beneficial to the production of coalbed methane.
  • Oxygen The role and destination of oxygen is the most complex, and the success of high-temperature air to increase production of coalbed methane is also the most critical. Need to be discussed in detail as follows:
  • Oxygen retained in the coal seam Free oxygen is retained in the coal seam in the following three forms.
  • Oxygen is not easily soluble in water, and only about 30 mL of oxygen can be dissolved in 1 L of water.
  • high temperature air is used to increase the production of coalbed methane
  • most of the water in the coal seam fissures, large, medium and small pores is driven out of the coalbed methane well by the high pressure gas, and only the water in the micropores is retained temporarily, and in the micropores
  • the water will eventually be expelled into the fissure and then driven out of the CBM well.
  • There will be only a small amount of water in the coal seam which will meet the water demand of low temperature oxidation of coal. Therefore, it is possible to ignore the dissolved oxygen in the coal seam.
  • Free Oxygen Free oxygen is present in coal seam fissures, large, medium, and small pores and enters the micropores as a single molecule. Therefore, coal seam porosity is the main factor affecting the free oxygen content.
  • the high-pressure free oxygen and nitrogen are filled together in the coal seam cracks, large, medium and small pores, and enter the micropores as a single molecule. Due to the dynamics of coal adsorption oxygen in coal low-temperature oxidation, the free oxygen content in the coal seam is dynamically changed; when the oxygen supply is sufficient, the free oxygen content is large; when the oxygen supply is insufficient or the oxygen supply is stopped, the free oxygen content is converted by free oxygen.
  • the method of increasing the production of coalbed methane by high temperature air does not care about the dynamic change of free oxygen content in the coal seam, but cares about the percentage of oxygen content in the production well gas, and in the implementation step, the parameter of “accelerating oxygen consumption temperature” is designed when the production well When the percentage of oxygen in the gas increases abnormally or the oxygen content in the production well gas exceeds the standard specified in the CBM production specification, the method of the present invention raises the injection temperature to accelerate the oxygen consumption temperature until the oxygen content in the production well gas returns to normal. .
  • FIG. 1 is a graph showing the change trend of the amount of adsorbed oxygen in different coal types under different adsorption ambient temperatures (see ⁇ , Wang Deming, Zhong Xiaoxing, Gu Junjie, Hu Zhenguo. (Year unknown). Low temperature stage coal-oxygen compounding process Experimental research. China Science and Technology Paper Online, http://www.paper.edu.cn). It can be seen from Fig. 1 that as the temperature of the coal sample increases, the oxygen absorption of coal as a whole shows a decreasing trend.
  • the adsorption of O 2 by coal mainly has two forms of physical adsorption and chemical adsorption, and the main oxygen absorption method in the low temperature stage is physical oxygen absorption.
  • the oxygen absorption in the low temperature stage of coal is related to the degree of metamorphism of coal, but the oxygen uptake is not simply reduced with the deepening of coal metamorphism, but generally shows the law of oxygen consumption of lignite > anthracite > bituminous coal.
  • the oxygen uptake of each coal type is basically around 0.5ml / g, indicating that the oxygen uptake at this temperature is not affected by the degree of coal metamorphism.
  • Figure 1 is only indicative and its data cannot be used to estimate the oxygen uptake of underground coal seams because (1) Figure 1 is plotted using data measured at atmospheric pressure (one atmosphere, or 0.1 MPa), while the coal seam The buried depth of the gas reservoir is usually between 500 and 1000 m, and the normal reservoir pressure is usually between 5 and 10 MPa. And the adsorption amount of coal to any kind of gas increases sensitively with the increase of pressure, so It is possible to estimate the oxygen uptake of coal when it is underground in situ based on the amount of oxygen absorbed by coal at atmospheric pressure. (2) In the laboratory measurement, it is difficult to distinguish the oxygen uptake of coal from the oxygen demand of coal oxidation reaction.
  • the present invention estimates the amount of oxygen absorbed by the coal based on the amount of nitrogen absorbed by the coal.
  • the basis for this estimation is as follows: (1) Under the condition of similar molecular affinity, the adsorption amount of coal to a gas is closely and positively correlated with the molecular weight of the gas. The molecular weight of oxygen (32) is greater than but close to the molecular weight of nitrogen (28). Under the assumption that coal molecules have similar affinity to nitrogen and oxygen, and the environmental conditions are the same, the oxygen absorption of coal should be greater than the nitrogen absorption of coal.
  • Nitrogen is an inert gas, and oxygen is a chemically active gas. Therefore, under the same conditions, the oxygen absorption of coal should be greater than the nitrogen absorption of coal.
  • the nitrogen absorption of coal is between 5 ⁇ 7.5m 3 /ton (see Yao Yanbin. 2009. Selectivity of coal to methane, carbon dioxide and nitrogen) Adsorption and Desorption Characteristics Research. 2009 Asia Pacific International Coalbed Methane Conference and 2009 China Coalbed Methane Symposium). According to the present invention, the amount of oxygen absorbed by the coal is estimated to be between 4.0 and 7.0 m 3 /ton under the same conditions; this is a fairly conservative estimate.
  • the coal seam is a huge oxygen reservoir.
  • CBM development practice has proved that in most cases, there is only a trace amount of oxygen in the coalbed methane or no oxygen at all. It is speculated that the underground in-situ coal seam contains only trace oxygen or no oxygen at all. Even in the history of coal formation, the coal layer once contained oxygen, which has been in the long geological history, because the low-temperature oxidation is exhausted. Today's CBM reservoirs are a huge empty reservoir of oxygen. Continued injection of high-temperature air to increase production of coalbed methane for several years and more than ten years is impossible to fill this oxygen storage.
  • FIG. 2 shows the relationship between oxygen consumption and temperature change of a lean coal and an anthracite coal (see Yin Xiaodan, Wang Deming, Zhong Xiaoxing. 2010. Low-temperature oxidation of coal based on oxygen consumption) Reactive activation energy research. Coal Mine Safety, 2010 (07): 12-15).
  • the vertical axis is the difference between the oxygen concentration of the inlet gas of the experimental apparatus and the oxygen concentration of the outlet gas. The larger the difference is, the more oxygen consumption is consumed by the low temperature oxidation. It can be seen from Fig. 2 that the oxygen consumption generally shows a trend of decreasing first and then increasing.
  • the physical adsorption occurs first when the coal oxygen contacts, and the adsorption process is very fast.
  • the physical adsorption can reach about 80% of the saturated oxygen absorption in a few seconds, and then the adsorption rate drops sharply, and finally reaches the adsorption equilibrium.
  • the physical adsorption gradually transitions to chemisorption, and a chemical reaction begins between the coal and oxygen, and the oxygen consumption increases.
  • the specific temperature range is about 65 ° C
  • the Qianling anthracite The specific temperature range is between 80 ° C and 90 ° C.
  • Table 1 shows the oxygen consumption of coal oxidation in five different coal types at 70 °C for 1 hour (see Lu Wei. Study on the spontaneous self-activation process of coal spontaneous combustion [D]. Xuzhou: China University of Mining and Technology, 2006).
  • the test conditions and data recording and finishing methods are as follows: the coal sample size is 80-120 mesh (0.20-0.125 mm), the coal sample volume is 40 g, the coal sample is placed in a distillation flask, and the volume inside the flask is 1000 ml, that is, the air volume is 1000 ml. After constant temperature oxidation for 1 hour at an ambient temperature of 70 ° C, the oxygen concentration in the flask was tested, and the oxygen consumption per gram of coal was determined from the amount of change in oxygen concentration.
  • Table 1 shows that at this ambient temperature, the oxygen consumption decreases as the coal rank increases.
  • Table 1 only shows that the oxygen consumption of different coal types is different at the same ambient temperature. Coal with a higher coal rank consumes less oxygen, probably because the ambient temperature has not yet reached a specific temperature range where the rate of oxygen consumption has increased significantly.
  • Table 2 and Figure 3 show the oxygen consumption of coal oxidation for the same coal type (Chaili gas-fertilized coal) at different temperatures for 1 hour (see Lu Wei. Ibid.). The test conditions and data recording and finishing methods are the same as in Table 1, except that the ambient temperature of each test is different, and fresh coal samples are used for each test.
  • the percentage next to each data point in Figure 3 is the oxygen concentration of the gas in the distillation flask at the end of the test. It can be seen from Table 2 and Figure 3 that under the same oxidation time, the oxygen consumption of the same coal type coal oxidation increases significantly with the increase of the ambient temperature, and the oxygen concentration of the gas in the distillation flask is more than 13% before the end of the test. The amount of oxygen increases more sharply with increasing temperature. Oxygen consumption increases with temperature after the oxygen concentration is less than 13% due to the decrease in oxygen concentration at higher temperatures The increase has become slower. This is essentially the same as the conclusion obtained by Figure 1.
  • Table 3 and Figure 4 show the oxygen consumption test results for the same temperature (70 ° C) of the same coal type (Chai Li gas and fat coal) at different temperatures (see Lu Wei. Ibid.).
  • the test conditions and data recording and finishing methods were the same as in Table 1, Table 2, and Figure 3, and the experimental temperature was 70 °C. It can be seen from Table 3 and Figure 4 that as the oxidation time increases, the oxygen consumption of coal gradually increases, that is, the degree of oxidation of coal gradually increases, but when the oxidation time reaches 40 minutes (in terms of the coal type), consumption The increase in oxygen is not significant, which means that coal has been more fully oxidized in this environment.
  • FIG. 5 is a plan view of a planar view of the coal seam temperature around the nitrogen injection well as a result of the injection of high temperature gas under this assumed condition.
  • the black circle at the center is a gas injection well, and the gas injection temperature is 150 ° C;
  • a central set of thick black concentric rings indicates a range of coal seam temperatures greater than 70 ° C; a thin set of thin black concentric rings indicates a range of coal seam temperatures between 70 ° C and 43 ° C, the last fine black
  • the radius of the concentric circle is approximately equal to 245 m; the four gray-filled black circles on the thin black concentric circle represent the four production wells closest to the gas injection well, which is equivalent to the first production well of the 250 m*250 m CBM well pattern surrounding the gas injection well.
  • the peripheral black dotted concentric ring indicates a range of coal seam temperatures less than 43 ° C, which range is not limited to the black dotted concentric rings in the figure, but expands outward until it abuts the range of influence of adjacent gas injection wells.
  • the influence range of a gas injection well depends on factors such as coalbed methane reservoir characteristics, gas injection operation parameters, length of gas injection time, and the like, ranging from several hundred meters to several kilometers.
  • the low temperature oxidation of coal is dominated by chemical reactions within the temperature range indicated by the thick black concentric rings, so it is called the “chemical reaction zone”; within the temperature range indicated by the thin black concentric rings,
  • the low-temperature oxidation of coal is mainly chemical adsorption, and has a local chemical reaction. Therefore, it is called “chemical adsorption and local chemical reaction zone”; the temperature range indicated by the black dotted concentric ring, and the low temperature oxidation of coal by physical adsorption
  • the Lord therefore, calls it the "physical adsorption zone.”
  • Each zone has a specific function of consuming or retaining oxygen, as detailed below:
  • the closure of the underground coal seam closure system is basically not changed, and therefore, with the high temperature gas injection time shift
  • the lost heat can effectively expand the range of the chemical reaction zone.
  • the oxygen consumption is limited due to the limited range of the chemical reaction zone.
  • the range of the chemical reaction zone is expanded, the oxygen consumption is gradually increased, and becomes an important oxygen-consuming space after 1 to 2 years.
  • Chemical adsorption is essentially a chemical reaction because there is electron transfer between the adsorbate and the adsorbent. It is called chemisorption and is not called a chemical reaction, mainly because chemical adsorption is reversible, and chemical reactions, including local chemistry. The reaction is generally irreversible. Chemical reactions occurring in chemical adsorption and local chemical reaction zones are called "local chemical reactions". On the one hand, the subsequent chemical reactions caused by the selectivity of chemical adsorption only occur locally or preferentially locally.
  • the chemical reaction in this area only occurs on the surface of coal micropores and fissures, which is a surface chemical reaction. Since the temperature rise can increase the activation energy of the active structure, which is favorable for chemisorption, increasing the temperature can increase the chemisorption rate and the adsorption amount, and increase the range, rate and strength of the local chemical reaction.
  • the amount of oxygen consumed and retained in the physical adsorption zone is much larger than the sum of the chemical reaction zone and the oxygen consumption of the chemical adsorption zone and the local chemical reaction zone. This is mainly due to the following three reasons: (1) Physical adsorption zone Large space capacity. The coal seam needs to reach a certain temperature before it can become a chemical reaction zone, a chemical adsorption zone and a local chemical reaction zone. Prior to this, it was a physical adsorption zone. Although the chemical reaction zone, chemisorption and local chemical reaction zones will expand rapidly with the prolonged gas injection time, the amount of air injected into the coal seam is small, and the gas heat capacity is small.
  • both physical adsorption and chemisorption are the preparation and prelude of the oxidation reaction, and the oxygen adsorbed on the micropores and crack surfaces of the coal will eventually be consumed by the oxidation reaction.
  • the correct use of the high-temperature air-enhanced coalbed methane method provided by the present invention will never achieve saturation of the oxygen absorption of the coalbed methane reservoir. Therefore, the physical adsorption zone is the last and most reliable guarantee for the injection of high temperature air to increase the production of coalbed methane, ensuring that no excess oxygen reaches the production well.
  • the invention discusses in detail the theoretical basis, technical points and difficulties of high temperature air stimulation of coalbed methane production, and summarizes the method for increasing the production of coalbed methane by the high temperature air provided by the invention as follows:
  • the invention relates to a method for injecting high temperature air into a coalbed methane reservoir to increase production of coalbed methane.
  • the present invention relates to a method for injecting high-temperature air into a coal seam from a well communicating with a coal seam with one or more ports, wherein the nitrogen "peeling", "discharging” coal micropores, adsorbing coalbed methane on the surface of the fracture, and promoting coalbed methane Desorbing and transporting to the production well, low-temperature oxidation causes the oxygen in it to remain in the coal seam due to physical adsorption, chemical adsorption, oxidation reaction or is consumed, and is connected to the coal seam from multiple ports.
  • the well collects the produced coalbed methane and the mixed gas of coalbed methane and nitrogen, thereby increasing the production of the coalbed methane well and the recovery method of the coalbed methane.
  • step (h) When the temperature of the production well gas rises to near the maximum allowable temperature and the cooling effect of step (g) is poor or the step (g) cannot be carried out, the normal temperature air or the normal temperature nitrogen gas is re-injected until the temperature of the production well gas is sufficiently lowered.
  • the gas injection operation is started according to the initial temperature and the heating rate until the gas injection temperature reaches the normal working temperature, and the normal gas injection stimulation operation phase is re-entered;
  • Steps (d), (e), (g), and (h) may be repeated as many times as needed.

Abstract

一种向煤层注入高温空气增产煤层气的方法。该方法从一口或多口注气井向煤层注入高温空气，其中的氮气"剥离"、"驱排"煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗掉，从多口生产井采集煤层气或煤层气与氮气的混合气体，提高煤层气井产量和煤层气采收率的方法。注高温空气能够获得与注氮相同或更好的增产效果。

Description

注高温空气增产煤层气的方法 技术领域
本发明涉及一种向煤层气储层注入高温空气增产煤层气的方法。具体地，本发明涉及一种从一口或多口与煤层连通的井(以下简称为“注气井”)向煤层注入高温空气，其中的氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗，从多口与煤层连通的井(以下简称为“生产井”)采集产出的煤层气以及煤层气与氮气的混合气体，从而提高煤层气井产量和煤层气采收率的方法。
背景技术
煤层气是煤层中的天然气，又称为瓦斯，其主要成分是甲烷。煤层气既是天然气清洁能源，又是导致煤矿瓦斯突出和爆炸的原因。
世界煤层气储量巨大，而产量很低，是因为当前煤层气开发使用的源自美国的“钻井-压裂-排水-降压-采气”技术模式只能开发最优质的煤层气储层，不适用于绝大多数煤层气储层。当前煤层气主流开发技术的这一致命缺陷导致收回投资和赢利的煤层气区块或有此前景的煤层气开发区块是低概率幸运事件，世界和中国皆然。世界煤层气产业未盛已衰，成功的仅仅是少数例外。世界各国唯有根据各自的国情，发展适合本国的新的煤层气开发技术，才能够有经济效益地开发本国的煤层气资源。
1998年，Puri和Stein提出一种增产煤层气的方法，该方法从一口注气井向煤层注入惰性气体(例如，氮气)或不与煤发生化学反应的气体(例如，CO2)，从一口或多口生产井获得煤层气，能够提高煤层气产量(参见Rajen Puri and Michael H.Stein.1988年.Method of coalbed methane production.美国专利号4883122)。Puri和Stein的专利方法仅适用于渗透率高的优质煤层气储层，对绝大多数煤层气储层是不适用的，无法实施的。2015年，陈信平提出了一种注氮增产煤层气的压力控制方法，适用于任意煤层的注氮增解增产煤层气(参见陈信平.2015年.注氮增产煤层气的压力控制方法.中国专利号ZL201510467978.3)。陈信平的专利方法将生产井的井口压力、产气量、氮气体积百分含量的变化等参数作为煤层气储层对注氮井注氮压力、注氮速率的反应，反馈到注氮井，调整注氮压力、注氮速率，从而能够将氮气注入低渗透煤层，又不压裂煤层顶板和底板围岩。
注CO2增产煤层气不仅成本高昂，而且使瓦斯煤层转变为二氧化碳煤层。对于煤炭开采，CO2与甲烷同样有害，甚至CO2害处更大，因为CO2更难以被抽排。澳大利亚有大量高CO2煤层，因为CO2难以被治理，无法开采。因此，注CO2增产煤层气不是能够被广泛使用的煤层气开发技术。
注N2增产煤层气基本上不妨害将来的采煤作业，但是，注N2增产煤层气成本高昂，影响了注N2增产煤层气技术的推广应用。注N2增产煤层气技术本身的成本大约在0.50元/m3左右。当前煤层气井口价格在1.20～1.50元/m3之间。注N2成本占煤层气销售收益的42％～33％，占比太重，致使注N2增产煤层气在多数情况下没有经济效益。注N2增产煤层气技术本身的成本由两部分构成：(1)使用制氮机或深冷法从空气中分离氮气，主要是将氧气与氮气分离；和(2)使用高压增压机将氮气注入煤层。这两部分成本基本上相等。因此，如果能够用空气代替氮气注入煤层，获得与注N2增产煤层气相同或更好的增产效果，其成本将仅相当于注N2增产煤层气成本的一半，那么，这样的注空气增产煤层气的方法将是有重大使用价值的，将是对世界煤层气开发的重大贡献。
发明内容
本发明涉及一种向煤层气储层注入高温空气增产煤层气的方法。具体地，本发明涉及一种从一口或多口与煤层连通的井(以下简称为“注气井”)向煤层注入高温空气，其中的氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗掉，从多口与煤层连通的井(以下简称为“生产井”)采集产出的煤层气以及煤层气与氮气的混合气体，从而提高煤层气井产量和煤层气采收率的方法。
本发明是采用以下技术手段实现的：
本发明涉及一种向煤层气储层注入高温空气增产煤层气的方法。具体地，本发明涉及一种从一口或多口与煤层连通的井向煤层注入高温空气，其中的氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗掉，从多口与煤层连通的井采集产出的煤层气以及煤层气与氮气的混合气体，从而提高煤层气井产量和煤层气采收率的方法。
具体的向煤层注入高温空气增产煤层气方法的实施步骤和特征如下：
(a)根据煤层气储层特性确定向煤层注入空气的初始温度、升温速率、正常作业温度、加速耗氧温度；
(b)在注气开始阶段，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，进入正常注气增产作业阶段；
(c)监测注气井井底压力和温度，监测生产井气体成分、井底压力和井底温度、井口压力和井口温度；
(d)当生产井气体中的水分含量显著减少时，开启注气井井口或注气管道中的注水高压开关，直到生产井气体中的水分含量恢复正常时，关闭注气井井口的注水高压开关；
(e)当生产井气体中的氧气含量异常增加或者生产井气体中的氧气含量超过煤层气生产规范规定的标准时，升高注气温度至加速耗氧温度，直到生产井气体中的氧含量恢复正常时，降低注气温度至正常作业温度；
(f)根据煤层气储层特性和煤层气后处理设备性能，确定生产井气体最高允许温度；
(g)当生产井气体温度升高到接近最高允许温度时，停止注气作业，直到生产井井底压力降低到接近煤层气储层静水压力时，或者直到生产井气体产量降低到接近经济门限值时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
(h)当生产井气体温度升高到接近最高允许温度并且步骤(g)降温效果差或因故不能够实施步骤(g)时，改注常温空气或常温氮气，直到生产井气体温度充分降低时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
(i)根据需要，步骤(d)、(e)、(g)和(h)可以重复多次。
本发明方法与现有技术相比，具有以下明显的有益效果和优势：
首先，本发明方法将空气注入煤层，空气中的氮气“剥离”、“驱排”煤微孔隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，起到了注N2增产煤层气中氮气所起的增产作用，增产的效果与注N2增产煤层气的增产效果相似。
其次，本发明方法不需要分离氮气和氧气，煤低温氧化作用代替了制氮机，成本仅相当于注N2增产煤层气成本的一半，有效地降低了强化开发煤层气的成本。
第三，本发明方法注入煤层的高温空气直接提高了煤层的温度，煤低温氧化作用中的物理吸附、化学吸附、化学反应都是放热的，也将提高煤层的温度。据研究，从30℃到40℃，温度每升高1℃，煤对甲烷的吸附量平均约减少0.18m3/吨(参见傅雪海，秦勇，韦重韬.2007. 煤层气地质学[M]，第四章第四节.北京：中国矿业大学出版社)。因此，本发明方法提高了煤层的温度，促进煤层气解吸，能够提高煤层气采收率，将煤层残余瓦斯含量降低到更低的水平。
世界煤层气储量巨大，而产量很低，是因为当前使用的煤层气开发技术只能够开发最优质的煤层气储层，不适用于绝大多数煤层气储层。本发明提供的技术能够开发大多数煤层气储层，使巨量煤层气资源造福人类。
附图说明
图1是不同吸附环境温度下不同煤种的吸氧量变化趋势图。
图2是煤低温氧化作用耗氧量随温度的变化。
图3是同一煤种不同温度恒温1小时煤氧化作用耗氧量。
图4是同一煤种相同温度不同氧化时间耗氧量测试结果。
图5是注高温空气4年后注气井周围煤层温度及煤低温氧化作用示意图。
具体实施方式
以下结合具体实施方式，对本发明做进一步说明。
煤低温氧化理论要点
在科技文献中，所谓“煤低温氧化”指的是在低于煤燃点的氧化环境中，煤与氧元素之间发生的物理、物理-化学、化学作用。煤燃点随煤阶升高而升高，从褐煤的燃点(270～310℃)直到焦煤的燃点(350～370℃)。本发明所说是煤低温氧化指的是，在远低于被注气煤层煤炭燃点的氧化环境中，煤与氧元素之间发生的物理、物理-化学、化学作用，或者，换句话说，本发明所说的煤低温氧化仅限于产生的热量等于散失的热量的稳定氧化反应过程，而不包括氧化反应自动加速，达到不可控，发生自燃的那一阶段。
煤炭行业已经对煤低温氧化问题做了长期地全面地充分地研究，因为低温氧化阶段是煤自燃的起始阶段，对煤自燃的发展起决定性作用，研究该阶段煤氧化特性对于揭示煤自燃的机理和从源头上制定对策防治煤矿火灾有重要意义。煤炭行业在煤低温氧化方面积累的文献汗牛充栋，在理论发展、试验设备研制、实验室模拟试验、数值模拟、生产应用等方面都获得了研究成果。实践已经证明，煤低温氧化的基本理论是正确和可靠的，尽管由于煤结构极其复杂多变，仍然存在不同观点之间的争议，存在诸多不完全清晰之处。下面总结陈述的是与本发明密切相关的并且得到煤炭行业普遍承认的煤低温氧化理论要点(参见①李文，李保 庆.1995.煤的低温氧化与自燃.煤炭转化，18(1):10-17；②戴广龙.2008.煤低温氧化与吸氧试验研究.辽宁工程技术大学学报(自然科学版)，27(2):172-175；③徐精彩，薛韩玲，文虎，李莉.2001.煤氧复合热效应的影响因素分析[J].中国安全科学学报，11(2):31-36；④郭小云，王德明，李金帅.2011.煤低温氧化阶段气体吸附与解析过程特性研究.煤炭工程,2011(5):102-104；⑤王彩萍，王伟峰，邓军.2013.不同煤种低温氧化过程指标气体变化规律研究[J].煤炭工程，2013(2):109-114；⑥吴阳阳，穆朝民，胡嘉伟，陈磊.2014.煤低温氧化标志性气体变化规律.矿业工程研究，29(3):52-57；⑦戴广龙.2007.煤低温氧化过程气体产物变化规律研究.煤矿安全，(2007)01:1-4；⑧陆伟,胡千庭.2007.煤低温氧化结构变化规律与煤自燃过程之间的关系.煤炭学报，32(9):939-944；⑨谢克昌.煤的结构与反应性〔M〕.北京:科学出版社，2002)：
●包括无烟煤在内的所有煤，包括惰性组分在内的所有煤岩成分，对氧化都是敏感的，尽管不同的煤，不同的煤岩成分，对氧化的敏感程度差异大。
●几乎在任何温度条件下煤中都存在能够与氧反应的活性结构。在煤结构中有多种官能团，官能团的元素组成、结构变化大，因而其活性变化大，具有不同的氧化能力；并且官能团之间、官能团与煤结构主体之间都会相互影响，也使其活性发生变化，改变官能团的氧化能力；这使得几乎在任何温度条件下煤体中都存在煤氧之间的作用。
●随氧化温度升高，芳香酮、醛类羰基、酚、醇、醚、酯氧键等官能团数量增加，或者从无到有并逐渐增加。这类官能团主要是含氧官能团，因为煤氧化过程中，氧原子与还原性较强的官能团结合。因此，这类官能团在低温氧化过程中随温度升高数量增加。
●随氧化温度升高，大部分官能团数量不同程度的减少，甚至在某一温度之后某一官能团不复存在。这类官能团一般属于脂肪类结构，大部分位于煤分子结构中的支链部分，表现出比较强的还原性。
●同一种官能团在不同煤阶的煤样中发生氧化的温度不同，同一种官能团在相同煤阶的不同煤样中发生氧化的温度也可能有差异，原因是官能团所在的主体结构不同。主体结构影响官能团的氧化性。
●煤在低温氧化过程中，煤结构中的主体结构基本没有变化。由于煤结构中的主体结构需要较高的能量才能被活化而发生氧化反应，因此，在200℃以下低温氧化条件下，煤结构中的主体结构一般没有明显变化。
●煤与氧气一接触就会发生物理吸附和化学吸附，放出热量，使煤中最容易活化的，也就是需要活化能较低的结构，由于物理吸附、化学吸附放出的热量而被活化，进而与氧气发生化学反应，在放出热量的同时释放出包括指标气体在内的反应产物；随着最开始氧化反应放出热量使煤体温度上升，体系能量进一步增加，从而使另外一些需要更大活化能(更高温度)的官能团被活化而发生化学反应，释放出更多的热量，使煤体温度进一步上升，体系能量进一步增加，又使需要更大活化能的结构和官能团活化而发生氧化反应，使煤体温度不断升高。但是，这一氧化反应自动加速将因为氧气供应不足而减速和停止。
●影响煤低温氧化的内在因素：
■煤阶(或煤化程度、煤变质程度)：一般认为随着煤化程度的提高，煤低温氧化的活性降低。其原因之一是，低阶煤中氧含量较高，对水分的化学结合能力增强，使煤更具有亲水性和氧化反应能力。
■硫含量：一般认为黄铁矿的氧化可产生放热效应，有利于煤-氧之间的耗氧作用持续进行，增大耗氧速率。煤中的无机硫和有机硫在氧化反应中的行为不同。低温时(例如，25℃)时黄铁矿的氧化显著，而高温(例如，80℃)时有机硫的氧化较明显。硫氧化机理是：黄铁矿(FeS2)氧化的副产物H2SO4不仅提高了煤中矿物质的可溶性和浸取能力，而且对显微组分中C-H被氧化为含氧官能团的反应起催化作用，因此，富含FeS2的煤较易被氧化。此外黄铁矿的粒径分布、煤中碳酸盐中和酸的能力等亦可影响氧化速率。
■孔隙度和孔隙结构：孔隙度大，孔隙连通性好，内表面积大，都有利于煤低温氧化，因为这些因素决定空气能否容易地进入煤中，接触有效的表面积，进入反应性空位。研究者根据实验室测定数据，分别发现氧化速率与内表面积的立方根成正比，孔径>100nm的孔在煤氧化中起重要作用。
■其它影响因素：显微组分影响煤低温氧化，镜质体、藻类体、孢粉体比较容易被氧化，而丝质体、角质体、木栓质体相对地难于被氧化。钙质组分(CaCO3及其转化产物CaSO4)对煤的低温氧化起催化作用。
●影响煤低温氧化的外部因素：
■温度：当其它条件不变时，温度不同，化学反应速度不同，导致煤的耗氧速率不同，化学反应常数及表面反应热都是温度的函数。随着煤温升高，煤样耗氧速率及氧化放热强度均升高，且温度越高，耗氧速率及放热强度随温度升高的 幅度越大。氧化气体的生成量随氧化温度增加而增加，多数气体生成量随温度升高按指数规律增加。
■时间：在温度远低于煤燃点的限制条件下，尽管煤氧吸附过程是很快的，但是氧化过程是缓慢的。这种限制条件下的氧化反应过程产生的热量等于散失的热量，氧化反应不会进入自动加速过程，因此，这是一个稳定的氧化反应过程。对于这种氧化反应过程，时间是一个重要因素；只有时间足够长，这个氧化反应过程导致的变化才能够显现出来；只要时间足够长，变化常常是很大的。例如，有观察者发现，露天堆放的无烟煤，随着氧化时间的增加，煤粒表面孔洞增加，且沿着孔洞出现裂隙；这些都是长时间低温氧化的效应。
■氧浓度：氧是煤氧反应的物质基础。煤体表面活性结构发生氧化反应直接受其所在环境氧浓度的影响。氧浓度不同，煤的耗氧速率不同，氧化反应的加速率不同，加速的限度不同。
■水分：水分既可以视为内在因素，因为水分是煤的重要成分之一；水分也可以视为外部因素，因为外部干预能够极大地改变煤中的水分含量。水分既影响煤-氧之间的物理吸附，也影响煤-氧之间的化学反应。适量的水分有利于煤低温氧化作用，而过多或过少的水分极不利于煤低温氧化作用。如果煤体含有较多的水分，过量的水分就会在煤体的表面形成一层水膜，隔绝氧气，即便有少量的氧气被煤体吸附，因吸附而放出的热量的大部分也会因水分蒸发而吸收和消耗掉，使煤体周围的热量难以积聚，从而延缓煤的自热升温。但是，当煤中的水分减少到一定程度时，煤物理吸附氧的能力减少，干燥煤基本上不吸附氧。煤-氧之间的物理吸附是煤-氧之间的化学反应的前奏，没有这个前奏很难有后继的氧化反应。此外，水分可促进煤-氧反应的中间产物过氧化物的分解，对煤氧反应有催化作用。因此，保持煤层中有适量的水分，是低温氧化持续进行的条件之一。
●煤低温氧化过程中的产物
■气体产物：煤低温氧化过程中产生多种气态产物，常见的有CO、CO2、CH4、C2H6、C3H6、C2H4、H2O等，见于文献的还有H2、C3H8、C2H2、C4H10、iC4H10等。
◆除CO2和H2O外，煤低温氧化过程中产生的气态产物都是可燃气体。
◆不同煤种生成同一种气体的温度不同，产气速率也不同：例如，褐煤在常 温下氧化即可产生CO，而无烟煤在温度超过80℃时，才能够生产CO。一般说来，产生同一种气体的温度随着煤阶升高而升高，产气速率随着煤阶升高而降低。
◆同一煤种产生不同气体的初始温度不同，结束温度也不同，每种气体的生成都有特定的温度范围，尽管产生不同气体的温度范围可能重叠或部分重叠：例如，有研究者发现，褐煤氧化产生的气体变化规律是：刚接触空气就氧化产生CO气体，4O℃氧化生成C2H6气体，90℃氧化生成C2H4气体，120℃氧化生成C3H8气体，140℃氧化生成H2气体，随氧化加深，160℃氧化生成C2H2气体。
◆不同煤种生成的气体种类及其顺序不同，甚至同一煤种不同地区煤样生成的气体种类及其顺序也有差异：例如，有研究者发现，在相同的升温实验条件下，褐煤氧化产生气体的种类和先后顺序是CO、C2H6、C2H4、C3H8、H2、C2H2；气煤氧化产生气体的种类和先后顺序是CO、C2H4、H2(C2H6实验开始时已存在)；气肥煤氧化产生气体的种类和先后顺序是CO、C2H4、H2(C2H6、C3H8实验开始时已存在)；无烟煤氧化产生气体的种类和先后顺序是CO、H2，尽管温度从20℃升高到210℃，但是，没有氧化生成C2H6、C2H4、C3H8。
◆指标气体(或标志气体)：煤层中原来没有的，完全由煤氧化作用产生的气体，被称为“指标气体”。CO是最主要的指标气体，因为CO是任何煤在较低温度下就能够生成的气体。C2H4也是常用的指标气体。
■非气体产物：实际上，人们至今并不确切地知道煤低温氧化过程中产生了哪些非气体产物及其数量，很大程度上是因为很难区分煤的原有成分与非气体产物。再者，本发明没有发现非气体产物与注高温空气增产煤层气的成败重大相关。因此，本发明对非气体产物它们略而不论。
●煤低温氧化机理：由于煤阶(煤种)、煤的品级(煤质)、显微组分及其含量、矿物质成分及其含量、煤的结构、孔隙度和孔隙结构、氧化温度、氧浓度等的不同，由于低温氧化反应本身的复杂性，再加上众多研究者所采用的研究手段(反应装置、煤种、煤量和分析技术)不同，关于煤低温氧化机理的研究，虽有诸多共识，也有相反的意见。本发明陈述的是多数研究者的共识，以阐明本发明方法为主要目的，而不追求包罗万象。煤低温氧化过程可以划分为如下三个阶段
■物理吸附阶段：吸附是一种界面现象，当两相接触时，界面上存在一个组成及性质不同于任一相内部的区域，这一界面现象被称为吸附。煤-氧吸附属于物理吸附中的固-气吸附范畴。从一般性物理吸附的机理得知，吸附作用是由过剩的表面自由能引起的。表面自由能是指在恒温恒压下，增加吸附剂单位面积时体系自由能的增量，又称为表面过剩自由能或Gibbs自由能。界面都有自发降低界面能的倾向，固体界面因表面分子或原子不能自由移动而难以收缩，只有通过吸附其它分子以降低表面自由能；这是固体表面产生吸附的根本动力。固体的表面自由能越大，通过吸附气体降低能量的动力就越大，单位面积上吸附气体的量也相应增大。煤的物理吸附机理有其特殊性。煤具有类似于高聚物分子的结构，在高分子链中存在一定数量的化学键，作为交链使高聚物形成三维网状结构。煤的变质程度越低，其三维网状结构越发育。气体分子进入到大分子结构的网格中，进入到这些高分子包围的空隙中，从而形成被吸附的假象，其实这是一种“溶解现象”，气体分子被“吸收”到固体内部，有时称为“固溶现象”。因此，煤吸附气体的能力远高于其他物质。煤吸附氧气又有不同于煤吸附其他气体的特殊性，即动态性。氧气分子附着在煤表面上后的去向有两种，一种是转化为化学吸附，为化学反应做准备；另外一种是脱离煤表面而重新变为气相。当某一氧气分子离开其物理吸附位置时，那么就会由另外的氧分子来补充该位置。因此，在煤低温氧化过程中的物理吸附由于氧化反应的存在而变成动态吸附过程。这种动态过程总的来说是进入煤体的氧气分子大于从煤中出来的氧气分子，两者之差就是煤氧化反应而消耗的氧气量。煤的物理吸氧量与煤的变质程度有关，随变质程度的增加呈先增加后减少的变化趋势。变质程度低的煤，结构疏松，孔隙率大，从而具有很强的物理吸附能力。变质程度较高的烟煤，因在漫长的变质过程中受地压的作用，煤的孔隙率减小，煤质趋于致密，吸附氧的能力大大降低。随着煤的进一步变质，在高温高压下，煤体内部因干馏作用而生成许多微孔隙，表面积逐渐变大，无烟煤吸附氧的能力又增大。煤低温氧化微观过程依次为物理吸附、化学吸附和氧化反应，一个氧气分子也将按照这个顺序与煤结构发生作用。因此，煤物理吸附氧气的过程最主要的作用之一是为氧化反应输送氧，并放出物理吸附热。该物理吸附热量使得煤体温度有一微小上升，是煤体内极易被活化的结构活化而吸收氧气发生化学吸附和化学反应的前奏，使煤的低温氧化进程向前发展。煤-氧物理吸附是发生氧化反应的前 提，氧化反应是煤吸附氧气的结果。
■化学吸附及局部化学反应阶段：化学吸附是煤的物理吸附到化学反应之间的过渡过程，或者叫过渡态。化学吸附的氧气和煤表面结构之间本质上发生了表面化学反应，氧原子与煤结构中的原子间发生了电子转移，且以相似于化学键的表面键力相结合。化学吸附本身是一个化学反应，化学吸附热与化学反应热相似。煤氧化学吸附就是煤活性结构的电子进入氧分子未成对电子的轨道中，形成较稳定的体系，同时放出热量的过程。产生化学吸附的作用力是化学键力。在化学吸附的过程中可以发生电子的转移、原子的重排、化学键的破坏与形成等过程。在此阶段，煤表面及孔隙内对氧的化学吸附形成不稳定的固态中间煤氧络合物，该络合物又进一步分解为气态产物和稳定的固态化合物。在此阶段一部分煤、氧快速反应生成氧化产物放出热量，一部分发生化学吸附生成不稳定络合物，不稳定络合物再分解成气态产物和固态化合物，同时放热。这两部分热量的积累导致了温度的升高，促使煤氧化作用进入下一阶段。在此阶段，生产的气体产物主要是CO、CO2、H2O。
■化学反应阶段：该阶段又可以分为两个前后衔接的子阶段：
◆自热氧化阶段：随煤温升高，氧化速度加快，脂肪侧链氧化，生成气态烃，C2H4，C2H6和C3H8。
◆加速氧化阶段：深度氧化，煤分子结构单元上部分桥键被氧化，反应速度加快，生成H2和C2H2。
◆该阶段的化学反应不限于表面化学反应，而可能深入煤结构内部。但是，该阶段的化学反应仍然限于煤结构的侧链、桥键、官能团，而不涉及煤的主体结构。
注高温空气增产煤层气方法的技术要点和难点详解
在煤低温氧化理论的基础上，本发明陈述注高温空气增产煤层气方法的技术要点和难点详解，主要是注入煤层的空气中的氧气怎样被消耗掉？没有被消耗掉的氧气，如何滞留在煤层中而不随同煤层气、氮气一起从生产井排出？
●空气的成分：正常的空气成分按体积分数计算是：氮(N2)约占78.07％，氧(O2)约占20.94％，稀有气体约占0.93％(氦He、氖Ne、氩Ar、氪Kr、氙Xe、氡Rn)，二氧化碳(CO2)约占0.031％，还有其他气体和杂质约占0.03％(例如臭氧(O3)、一氧化氮(NO)、二氧化氮(NO2)、水蒸气(H2O)等)。
●注入煤层的空气各成分以及煤低温氧化作用过程中生成的气体各成分的作用和归宿
■氮气(包括氦、氖、氩、氪、氙、氡)：稀有气体氦、氖、氩、氪、氙、氡与氮气性质相同，都是惰性气体，它们的作用和归宿也相同，故以氮气为代表论述之。氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移。注高温空气增产煤层气的增产作用主要是由氮气承担的。氮气增产煤层气的原理请参见美国专利号4883122和中国专利号201510467978.3，此不赘述。少部分氮气被煤层吸附，滞留在煤层中，大部分氮气随同被“驱排”的煤层气一起，运移到生产井，进入煤层气集输系统，并最终返回大气中。注高温空气初期，生产井所产气体中氮气的百分含量为零或接近于零；随着注气时间延长，氮气百分含量增大。
■二氧化碳(包括煤低温氧化产生的二氧化碳)：煤层有极强大的吸附CO2的能力，因为CO2的较大的克分子量和煤对CO2的亲和力导致CO2具有很大的兰氏体积和很低的兰氏压力。因此，注入煤层中的高温空气中的微量CO2以及煤低温氧化产生的二氧化碳，绝大部分将被煤层吸附，滞留在煤层中，只可能有极其微量的CO2到达生产井。这是吸附解吸孔隙介质中多成分多相流体流动理论已经证明的(参见Zhu,J.2003.Multicomponent multiphase flow in porous media with temperature variation or adsorption,Ph.D.Dissertation.Stanford University,Online at http://pangea.stanford.edu/ERE/pdf/pereports/PhD/Zhu03.pdf)，也是经多个实验室实验证实的(参见Parakh,S.,2007,Experimental Investigation of Enhanced Coal Bed Methane Recovery,Ph.D.Dissertation.Stanford University)。CO2被煤层吸附的同时置换吸附态的煤层气，也有增产煤层气的作用(参见叶建平，冯三利，范志强，王国强.2007.沁水盆地南部注二氧化碳提高煤层气采收率微型先导性试验研究.石油学报，28(4):77-80)。
■煤低温氧化作用过程中生成的气体(除CO2外)：H2O原本是煤层气的成分之一，作为生产井气体成分之一进入集输系统，并被后处理设备脱水去除。除CO2和H2O外，煤低温氧化过程中产生的气态产物都是可燃气体，并且它们的热值都比煤层气主要成分甲烷热值高得多，是高热值天然气成分。它们作为煤层气成分，从生产井被排入煤层气集输系统，对煤层气生产有益无害。
■氧气：氧气的作用和归宿最复杂，对注高温空气增产煤层气的成功也最关键， 需要详细论述如下：
◆滞留在煤层中的氧气：自由态氧气以如下三种形态滞留在煤层中。
Figure PCTCN2017077861-appb-000001
溶解态氧气：氧气不易溶于水，1L水中仅能溶解约30mL氧气。注高温空气增产煤层气时，煤层裂隙、大、中、小孔隙中的水大部分被高压气体驱排到煤层气井区之外，暂时得到保留的只有微孔隙中的水，并且微孔隙中的水也最终将被驱排到裂隙中，继而被驱排到了煤层气井区之外。煤层中将只有微量的水分，满足煤低温氧化作用对水分的需求。因此，可以忽略不计煤层中的溶解态氧气。
Figure PCTCN2017077861-appb-000002
游离态氧气：游离态氧气存在于煤层裂隙、大、中、小孔隙中，并以单分子进入微孔隙中。因此，煤层孔隙度是影响游离态氧气含量的主要因素。注高温空气增产煤层气时，高压游离态氧气和氮气一起充满煤层裂隙、大、中、小孔隙中，并以单分子进入微孔隙中。由于煤低温氧化作用中煤吸附氧的动态性，煤层中游离态氧气含量是动态变化的；氧气供应充足时，游离态氧气含量大；氧气供应不充足或停止氧气供应时，游离态氧气含量因为游离态氧气转换为物理吸附态，再转换为化学吸附态，再接着发生化学反应而被消耗掉。因此，注高温空气增产煤层气方法不关心煤层中动态变化的游离态氧气含量，而关心生产井气体的氧气含量百分比，并在实施步骤中设计了“加速耗氧温度”这一参数，当生产井气体中的氧气含量百分比异常增加或者生产井气体中的氧气含量超过煤层气生产规范规定的标准时，本发明方法将升高注气温度至加速耗氧温度，直到生产井气体中的氧含量恢复正常。
Figure PCTCN2017077861-appb-000003
吸附态氧气：图1是不同吸附环境温度下不同煤种的吸附氧气量的变化趋势图(参见戚绪尧，王德明，仲晓星，顾俊杰，胡争国.(年份不详).低温阶段煤氧复合过程的实验研究.中国科技论文在线，http://www.paper.edu.cn)。由图1可见，随着煤样温度的升高，煤吸氧量整体呈现减小的趋势。煤对O2的吸附主要有物理吸附和化学吸附两种形式，低温阶段的主要吸氧方式为物理吸氧。随煤样所处环境温度的升高，O2分子具有的动能变大，而煤表面对O2的吸附力受温度变化的影响较小，因此O2更容易从煤表面脱附，造成煤物理吸氧量减少。煤的化学吸附则随吸附环境温度的升高而增大，但是，由于化学吸附在煤温 达到一定温度之前增长速度缓慢，其绝对增长量不足以抵消煤物理吸附的减少量，故表现为煤吸氧总量的减少。另外，煤低温阶段吸氧量与煤的变质程度有关，但吸氧量并非简单地随煤变质程度的加深而减小，而是大致呈现出褐煤吸氧量＞无烟煤＞烟煤的规律。随着温度升高，变质程度对吸氧量的影响减小。在100℃吸附环境温度下，各个煤种吸氧量基本上位于0.5ml/g左右，说明该温度下吸氧量受煤变质程度的影响不大。应当注意，图1只有指示性意义，其数据不能用于推测地下煤层的吸氧量，因为(1)图1是使用常压(一个大气压，即0.1MPa)下测定的数据绘制的，而煤层气储层埋深通常在500～1000m之间，正常储层压力通常在5～10MPa之间；并且煤对任何一种气体的吸附量都随压力增大而敏感地快速增大，因此，不可能根据常压下的煤吸氧量估算煤在地下原位时的吸氧量。(2)在实验室测定中，很难区分煤吸氧量与煤氧化反应耗氧量，文献中有关煤吸氧量的测定成果很少，也没有煤层气储层压力条件下煤吸氧量的测定成果。因此，本发明根据煤吸氮量估算煤吸氧量。做此一估算的依据如下：(1)在分子亲和性相近的条件下，煤对一种气体的吸附量与该气体的分子量大小密切地正相关。氧气分子量(32)大于但接近于氮气分子量(28)。在假定煤分子对氮气、氧气亲和性相近，并且环境条件相同的情况下，煤吸氧量应当大于煤吸氮量。(2)氮气是惰性气体，而氧气是化学活性极大的气体，由此肯定，相同条件下，煤吸氧量应当大于煤吸氮量。(3)在5～10MPa压力和煤层地下原位温度30℃条件下，煤吸氮量在5～7.5m3/吨之间(参见姚艳斌.2009年.煤对甲烷、二氧化碳和氮气的选择性吸附解吸特征研究.2009亚洲太平洋国际煤层气会议暨2009年中国煤层气学术研讨会)。本发明据此将相同条件下，煤吸氧量推定为4.0～7.0m3/吨之间；这是一个相当保守的估计。因此，煤层是一个巨大的氧气储藏库。煤层气开发实践证明，绝大多数情况下，煤层气中只有微量氧气或者完全没有氧气，由此推测，地下原位煤层也只含有微量氧气或者完全不含氧气。即使煤生成历史上，煤层中曾经含有氧气，这些氧气已经在漫长的地质历史中，因为低温氧化作用消耗殆尽了。今天的煤层气储层是一个巨大的空空如也的氧气储藏库。持续注高温空气增产煤层气数年、十多年，也不可能填 满这个氧气储藏库。因为它是一个漏底的库——物理吸附＝》化学吸附＝》氧化反应这个过程最终将消耗吸附态氧气。因此，正确的注高温空气增产煤层气作业，能够保证永远不填满这个氧气储藏库。
◆被消耗掉的氧气：图2是一种贫煤和一种无烟煤的低温氧化作用耗氧量随温度变化的关系(参见尹晓丹，王德明，仲晓星.2010.基于耗氧量的煤低温氧化反应活化能研究.煤矿安全，2010(07):12-15)。在该图中，纵轴是实验装置入口气体的氧气浓度与出口气体的氧气浓度之差，此差值越大表示低温氧化作用耗氧量越多。由图2可见，耗氧量总体呈现先减小后增大的趋势。煤氧接触时首先发生物理吸附，并且吸附过程非常快，在数秒时间内物理吸附就能够达饱和吸氧量的80％左右，而后吸附速率急剧下降，最后达到吸附平衡。随着温度的增加，物理吸附逐渐过渡为化学吸附，煤氧之间开始发生化学反应，耗氧量增加。并且，在温度升高到某一个特定温度范围时，耗氧量急剧增大，即耗氧量速率明显地增大；对北场贫煤，该特定温度范围在65℃左右，对前岭无烟煤，该特定温度范围在80℃～90℃之间。表1是五个不同煤种70℃恒温氧化1小时煤氧化作用耗氧量(参见陆伟.煤自燃逐步自活化反应过程研究〔D〕.徐州：中国矿业大学，2006)。试验条件和数据记录、整理方法是：煤样粒度为80～120目(0.20～0.125mm)，煤样量为40g，煤样置于蒸馏烧瓶内，烧瓶内体积1000ml，即空气量为1000ml，在环境温度70℃的情况下恒温氧化1小时后，测试烧瓶内氧气浓度，根据氧气浓度变化量求得每克煤耗氧量。由表1可见，在该环境温度下，耗氧量随煤阶升高而减少。表1仅仅表明在相同环境温度下，不同煤种的耗氧量不同。煤阶较高的煤的耗氧量较少，可能是因为环境温度尚未达到耗氧量速率明显地增大的特定温度范围。表2和图3是同一煤种(柴里气肥煤)不同温度恒温1小时煤氧化作用耗氧量(参见陆伟.同上)。试验条件以及数据记录、整理方法与表1相同，但是，每次试验的环境温度不同，每次试验都使用新鲜的煤样。图3中每个数据点旁边的百分数是试验结束时蒸馏烧瓶内气体的氧气浓度。由表2和图3可见，在相同氧化作用时间下，同一煤种煤氧化作用耗氧量随环境温度升高明显增大，并且在试验结束时蒸馏烧瓶内气体的氧气浓度大于13％之前耗氧量随温度升高增加比较剧烈。由于温度较高时氧气浓度的下降，在氧气浓度小于13％之后，耗氧量随温度升高 增加变得比较缓慢。这与由图1获得的结论实质上是相同的。表3和图4是同一煤种(柴里气肥煤)相同温度(70℃)不同氧化时间耗氧量测试结果(参见陆伟.同上)。试验条件以及数据记录、整理方法与表1、表2以及图3相同，实验温度为70℃。由表3和图4可见，随着氧化时间增加，煤的耗氧量逐渐增大，即煤的氧化程度逐渐增大，但是当氧化时间达到40分钟以后(就本煤种而言)，耗氧量增加不明显，这就说明煤在这种环境下已经比较充分地被氧化了。
表1 不同煤种70℃恒温氧化1小时煤氧化作用耗氧量
Figure PCTCN2017077861-appb-000004
表2 同一煤种不同温度恒温1小时煤氧化作用耗氧量
Figure PCTCN2017077861-appb-000005
表3 同一煤种相同温度不同氧化时间耗氧量测试结果
Figure PCTCN2017077861-appb-000006
●绝大部分氧气将滞留在煤层中或消耗在煤层中：前述煤低温氧化理论要点以及对注入煤层的空气各成分和煤低温氧化作用过程中生成的气体各成分的作用和归宿的讨论，已经保证了能够将绝大部分氧气滞留在煤层中或消耗在煤层中。为了更清楚地说明空气中的氧气怎样滞留在煤层中或被消耗在煤层中，图5示意性地展示了注高温空气4年后注气井周围煤层的温度状况，煤层被假定为褐煤。在绘制图5时假定了煤层气储层特性是各向同性的，高温气体对煤层的热传导在各个方向都相同，煤层自身不同部分之间的热传导在各个方向都相同，因此，煤层因高温气体注入而升温的状况，在各个方向都是相同的。图5是在这个假定条件下，注氮井周围煤层温度因为注入高温气体而升高的平面图像即鸟瞰图。在图5中，中心的黑色圆圈是注气井，注气温度为150℃；十字线的右侧水平线上，由外向内，依次标出了第1、4、6、9个同心圆的半径：300m、254m、200m、100m；十字线的下部垂直线上，由下而上，依次标出了第1、4、6、9个同心圆位置附近煤层的温度：40℃、43℃、50℃、70℃。在该图中，中心一组粗黑色同心圆环指示了煤层温度大于70℃的范围；中间一组细黑色同心圆环指示了煤层温度在70℃～43℃之间的范围，最后一个细黑色同心圆半径约等于245m；该细黑色同心圆上的四个灰色填充的黑色圆圈代表离注气井最近的四口生产井，相当于250m*250m煤层气井井网环绕注气井的第一圈生产井；外围的黑色虚线同心圆环指示煤层温度小于43℃的范围，该范围不限于图中的黑色虚线同心圆环，而是向外扩张，直至邻接到相邻注气井的影响范围。一口注气井的影响范围决定于煤层气储层特性、注气作业参数、注气时间长度等等因素，从几百米到数千米。由于假定煤层为褐煤，粗黑色同心圆环指示的温度范围内，煤低温氧化作用以化学反应为主，因此将其称之为“化学反应区”；细黑色同心圆环指示的温度范围内，煤低温氧化作用以化学吸附为主，兼有局部化学反应，因此将其称之为“化学吸附及局部化学反应区”；黑色虚线同心圆环指示的温度范围，煤低温氧化作用以物理吸附为主，因此将其称之为“物理吸附区”。每个区域各有特定的消耗或滞留氧气的功能，详细说明如下：
■在化学反应区，煤-氧之间的物理吸附很快转换为化学吸附，化学吸附又很快转换为化学反应，化学反应热和高温空气带来的热量共同维持该区内化学反应有限的自动加速。之所以说“有限的自动加速”，是因为注入煤层的高温空气数量 有限，携带的氧气有限，煤氧化反应不可能自动加速到不可控、燃烧的阶段，而是从注气井向周边，随着距离增大，氧气浓度下降，煤氧化反应自动加速率很快降低到零，进入稳定的氧化反应过程，即氧化反应过程产生的热量等于散失的热量。由于地下煤层是一个封闭的系统，尽管注气井和生产井在这个封闭的系统上造就了几个奇点，但是基本上没有改变地下煤层封闭系统的封闭性，因此，随着高温注气时间推移，该散失的热量能够有效地扩大化学反应区的范围。注高温空气初期，由于该化学反应区范围有限，耗氧量也有限。随着注气时间延长，该化学反应区范围扩展，耗氧量逐渐增加，并在1～2年后成为重要的耗氧空间。
■在化学吸附及局部化学反应区，不仅煤-氧之间的物理吸附转换为化学吸附的过程延长了，而且化学吸附转换为化学反应的过程既缓慢又限于煤层中那些只需要较低的温度就能够发生化学反应的活性结构。这种局部化学反应源自化学吸附自身很强的选择性。因为化学吸附需要一定的活化能，因此，化学吸附总是首先选择活化能较高的活性结构。这一化学吸附本身的选择特性，因为煤有机质的化学结构的复杂和差异，显得更为突出。煤低温氧化中，化学吸附的另一个重要特点是，先形成不稳定的固态中间煤氧络合物，该络合物又进一步分解为气态产物和稳定的固态化合物。化学吸附实质上是化学反应，因为吸附质与吸附剂之间有电子转移，之所以称其为化学吸附而不称其为化学反应，主要因为化学吸附是可逆的，而化学反应，包括局部化学反应，一般是不可逆的。在化学吸附及局部化学反应区发生的化学反应，之所以被称为“局部化学反应”，一方面是因为化学吸附的选择性导致的后继化学反应只发生在局部或优先地发生在局部，另一方面是因为该区域的化学反应只发生在煤微孔隙、裂隙的表面，是表面化学反应。由于温度升高能够增大活性结构的活化能，有利于化学吸附，因此，升高温度可以提高化学吸附速率和吸附量，提高局部化学反应的范围、速率和强度。化学吸附放热、局部化学反应热，和来自高温空气流的热量、来自化学反应区的传导热量一起，提高化学吸附及局部化学反应区的温度，一方面使与化学反应区邻接的化学吸附及局部化学反应区转变为化学反应区，另一方面扩大化学吸附及局部化学反应区。由于化学吸附及局部化学反应区的范围远大于注气井周围的化学反应区，该区消耗和滞留氧气的数量可以大于化学反应区的耗氧量。
■在物理吸附区：物理吸附区消耗和滞留氧气的数量远大于化学反应区和化学吸附及局部化学反应区的耗氧量之和，这主要是因为如下三个原因：(1)物理吸附区空间容量大。煤层需要达到一定的温度，才能够成为化学反应区、化学吸附及局部化学反应区。在此之前，都是物理吸附区。尽管随着注气时间延长化学反应区、化学吸附及局部化学反应区都将迅速扩大，但是，注入煤层的空气量小，气体热容量小，依靠高温空气直接加热煤层是一个缓慢渐进的过程；而在注高温空气增产煤层气条件下，受到氧气供应量的限制，化学反应热对提高煤层温度的贡献，也是一个缓慢渐进的过程。出于经济效益考虑，注气井井距通常应当大于1000m。因此，即使在注气若干年后，物理吸附区空间容量都将远大于化学反应区和化学吸附及局部化学反应区的空间容量之和。(2)煤的吸氧量巨大。假定注气井井距为1000m，煤层厚度6m，煤的密度1.4吨/m3，那么，一口注气井影响的圆柱体形空间内煤的质量等于π5002*6*1.4＝6594000吨；再假定注气增压机容量为1000m3/小时，那么，一天注入煤层的氧气约等于5040m3；继续假定煤饱和吸氧量为5.0m3/吨，那么，在完全不考虑化学吸附和化学反应耗氧的条件下，也需要17.9年才能够使注气井为中心、半径500m的圆柱体形空间内的煤吸氧量达到饱和。(3)如前述讨论，物理吸附区是一个漏底的氧气储藏库，因为物理吸附＝》化学吸附＝》氧化反应这个过程最终将消耗物理吸附态氧气。只要时间足够长，物理吸附和化学吸附都是氧化反应的预备和前奏，吸附在煤微孔隙、裂隙表面的氧气最终将被氧化反应消耗掉。换句话说，正确使用本发明提供的注高温空气增产煤层气方法，煤层气储层吸氧量将永远不可能达到饱和。因此，物理吸附区是注高温空气增产煤层气的最后和最可靠的保障，保证没有过多的氧气到达生产井。
本发明在详细论述了注高温空气增产煤层气的理论基础、技术要点和难点之后，总结本发明提供的注高温空气增产煤层气方法如下：
本发明是采用以下技术手段实现的：
本发明涉及一种向煤层气储层注入高温空气增产煤层气的方法。具体地，本发明涉及一种从一口或多口与煤层连通的井向煤层注入高温空气，其中的氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗掉，从多口与煤层连通 的井采集产出的煤层气以及煤层气与氮气的混合气体，从而提高煤层气井产量和煤层气采收率的方法。
具体的注入高温空气增产煤层气的方法的实施步骤和特征如下：
(a)根据煤层气储层特性，确定向煤层注入空气的初始温度、升温速率、正常作业温度、加速耗氧温度；
(b)在注气开始阶段，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，进入正常注气增产作业阶段；
(c)监测注气井井底压力和温度，监测生产井气体成分、井底压力和井底温度、井口压力和井口温度；
(d)当生产井气体中的水分含量显著减少时，开启注气井井口或注气管道中的注水高压开关，直到生产井气体中的水分含量恢复正常时，关闭注气井井口的注水高压开关；
(e)当生产井气体中的氧气含量异常增加或者生产井气体中的氧气含量超过煤层气生产规范规定的标准时，升高注气温度至加速耗氧温度，直到生产井气体中的氧含量恢复正常时，降低注气温度至正常作业温度；
(f)根据煤层气储层特性和煤层气后处理设备性能，确定生产井气体最高允许温度；
(g)当生产井气体温度升高到接近最高允许温度时，停止注气作业，直到生产井井底压力降低到接近煤层气储层静水压力时，或者直到生产井气体产量降低到接近经济门限值时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
(h)当生产井气体温度升高到接近最高允许温度并且步骤(g)降温效果差或因故不能够实施步骤(g)时，改注常温空气或常温氮气，直到生产井气体温度充分降低时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
(i)根据需要，步骤(d)、(e)、(g)和(h)可以重复多次。
最后应说明的是，尽管本说明书对本发明已进行了详细的说明，但是，本领域的普通技术人员应当理解，仍然可以对本发明进行修改或等同替换；而一切不脱离本发明的精神和范围的技术方案及其改进，均应涵盖在本发明的权利要求范围中。

Claims (12)

  1. 一种从一口或多口与煤层气储层连通的注气井向煤层注入高温空气，其中的氮气“剥离”、“驱排”煤微孔隙、裂隙表面的吸附态煤层气，促进煤层气解吸并向生产井运移，低温氧化作用使其中的氧气因为物理吸附、化学吸附、氧化反应而滞留在煤层中或被消耗掉，从多口与煤层连通的生产井采集产出的煤层气以及煤层气与氮气的混合气体，从而提高煤层气井产量和煤层气采收率的方法，其特征是：
    (a)根据煤层气储层特性，确定向煤层注入空气的初始温度、升温速率、正常作业温度、加速耗氧温度；
    (b)在注气开始阶段，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，进入正常注气增产作业阶段；
    (c)监测注气井井底压力和温度，监测生产井气体成分、井底压力和井底温度、井口压力和井口温度；
    (d)当生产井气体中的水分含量显著减少时，开启注气井井口或注气管道中的注水高压开关，直到生产井气体中的水分含量恢复正常时，关闭注气井井口的注水高压开关；
    (e)当生产井气体中的氧气含量异常增加或者生产井气体中的氧气含量超过煤层气生产规范规定的标准时，升高注气温度至加速耗氧温度，直到生产井气体中的氧含量恢复正常时，降低注气温度至正常作业温度；
    (f)根据煤层气储层特性和煤层气后处理设备性能，确定生产井气体最高允许温度；
    (g)当生产井气体温度升高到接近最高允许温度时，停止注气作业，直到生产井井底压力降低到接近煤层气储层静水压力时，或者直到生产井气体产量降低到接近经济门限值时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
    (h)当生产井气体温度升高到接近最高允许温度并且步骤(g)降温效果差或因故不能够实施步骤(g)时，改注常温空气或常温氮气，直到生产井气体温度充分降低时，再按照注气开始阶段的作业程序，根据初始温度、升温速率开始注气作业，直到注气温度达到正常作业温度，重新进入正常注气增产作业阶段；
    (i)根据需要，步骤(d)、(e)、(g)和(h)可以重复多次。
  2. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，注入煤层的是空气。
  3. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，注入煤层的空气的温度高于常温。
  4. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，设立初始温度、升温速率、正常作业温度、加速耗氧温度，保证注气安全，保证氧气滞留在煤层中或被消耗在煤层气中。
  5. 根据权利要求1，其中所述的初始温度，其特征是在常温到70℃之间选择，其中所述的升温速率，其特征是在20℃/天到10℃/月之间选择，其中所述的正常作业温度，其特征是在被注气煤层煤炭燃点温度的伍分之叁左右选择，其中所述的加速耗氧温度，其特征是在被注气煤层煤炭燃点温度的肆分之叁左右选择。
  6. 根据权利要求1，其中所述的初始温度、升温速率、正常作业温度、加速耗氧温度，其特征是，根据实验室测定的煤层样品的低温氧化作用耗氧量随温度变化的规律，选择确定之。
  7. 根据权利要求1，其中所述的初始温度、升温速率、正常作业温度、加速耗氧温度，其特征是，综合考虑煤层气储层的多种特性，选择确定之，并随着注高温空气时间延长，导致煤层气储层特性变化，必要时调整之。
  8. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，向注气管道中加入水分，催化煤氧之间的反应。
  9. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，当生产井气体中的氧气含量高于预期时，提高注气温度，增强煤氧之间的化学反应，增加耗氧量。
  10. 根据权利要求1，其中所述的增产煤层气的方法，其特征是，当生产井气体温度升高超过预期时，停止注气，或者改注常温空气，或者改注常温氮气，直接降低煤层温度，并且减弱煤氧之间的化学反应，减少化学反应热对煤层的升温作用。
  11. 根据权利要求1，其中所述的高温空气，其特征是，使用末级冷却器可调的增压机，调节增压机的末级冷却器，获得所需要的空气温度，或者使用温度可调节的管道气体加热器，加热增压机输出的高压空气，获得所需要的空气温度，或者同时使用末级冷却器可调的增压机和温度可调节的管道气体加热器，获得所需要的空气温度，或者使用任何其他方式加热增压机输出的高压空气，获得所需要的空气温度。
  12. 根据权利要求1，其中所述的生产井气体最高允许温度，其特征是，在注高温空气之前煤层气储层在地下原位的温度与煤层气后处理设备允许的温度之间，选择确定之。
PCT/CN2017/077861 2017-03-23 2017-03-23 注高温空气增产煤层气的方法 WO2018170830A1 (zh)

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