A method for preventing downhole explosion in an oxygen-containing gas injection well

Abstract

The present invention particularly relates to a method for preventing downhole explosion in an oxygen-injected gas well, belonging to the technical field of oil exploitation. The method includes: obtaining associated oilfield gas; measuring the gas components of the associated oilfield gas to obtain the associated oilfield gas components; obtaining the explosion limit of the associated oilfield gas at normal temperature and pressure according to the associated oilfield gas components; obtaining the critical oxygen content of the associated oilfield gas according to the associated oilfield gas components and the explosion limit; obtaining the lower explosion limit and the upper explosion limit at constant temperature and pressure according to the explosion limit; obtaining the critical oxygen content at constant temperature and pressure according to the critical oxygen content; predicting downhole explosion according to the lower explosion limit at constant temperature and pressure, the upper explosion limit at constant temperature and pressure, and the critical oxygen content at constant temperature and pressure; giving the critical conditions for the explosion of oxygen and combustible gas in the wellbore, thereby ensuring the downhole safety of oil and gas wells and reducing the occurrence risk of potential hazards.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil extraction, and particularly relates to a method for preventing downhole explosion in an oxygen-containing gas injection well. Background Art

[0002] In deep medium-low permeability oil reservoirs, it is difficult to inject water, and gas injection development is an effective means to solve the decline of formation energy. Common injected gases include air, oxygen-depleted air, nitrogen, and natural gas. When injecting air and oxygen-depleted air, due to the oxygen contained in the injected medium, it will react with the original natural gas in the formation under certain conditions to cause downhole explosion reactions, seriously threatening the production safety of oil and gas wells. And this kind of explosion is random, hidden, and cannot be monitored. Summary of the Invention

[0003] In view of the above problems, the present invention is proposed to provide a method for preventing downhole explosion in an oxygen-containing gas injection well that overcomes or at least partially solves the above problems.

[0004] An embodiment of the present invention provides a method for preventing downhole explosion in an oxygen-containing gas injection well, the method comprising:

[0005] Obtain associated oilfield gas;

[0006] Measure the gas components of the associated oilfield gas to obtain the gas components of the associated oilfield gas;

[0007] According to the gas components of the associated oilfield gas, obtain the explosion limit of the associated oilfield gas at normal temperature and pressure;

[0008] According to the explosion limit at normal temperature and pressure, obtain the lower explosion limit and the upper explosion limit at constant temperature and pressure;

[0009] According to the gas components of the associated oilfield gas and the explosion limit at normal temperature and pressure, obtain the first critical oxygen content of the associated oilfield gas at normal temperature and pressure;

[0010] According to the first critical oxygen content at normal temperature and pressure, obtain the second critical oxygen content at constant temperature and pressure;

[0011] According to the lower explosion limit, the upper explosion limit and the second critical oxygen content at constant temperature and pressure, obtain the safe injection amount of the oxygen-containing gas to prevent downhole explosion.

[0012] Optionally, in the step of measuring the gas components of the associated oilfield gas to obtain the gas components of the associated oilfield gas, the method for component measurement includes: chromatographic analysis, infrared analysis, zirconia oxygen analysis, magnetic oxygen analysis, nitrogen oxide analysis, and physical method.

[0013] Optionally, in obtaining the explosion limit of the associated oilfield gas at normal temperature and pressure according to the gas components of the associated oilfield gas,

[0014] if all components of the associated oilfield gas are combustible gases, the calculation formula for the explosion limit is as follows:

[0015]

[0016] where C m is the explosion limit of the associated oilfield gas at normal temperature and pressure, %; V1, V2,..., V n are the volume percentages of each component in the mixed gas, %, and their sum is 100%; C1, C2,..., C n are the explosion limits of each component in oxygen or air, %.

[0017] Optionally, in obtaining the explosion limit of the associated oilfield gas at normal temperature and pressure according to the gas components of the associated oilfield gas,

[0018] if the components of the associated oilfield gas contain inert gases, the calculation formula for the explosion limit is as follows:

[0019]

[0020] where B is the volume fraction of the inert gas, %; C m is the explosion limit of the combustible part of the associated oilfield gas at normal temperature and pressure, %, and the calculation formula is as follows:

[0021]

[0022] where V1, V2,..., V n are the volume percentages of each component in the mixed gas, %, and their sum is 100%; C1, C2,..., C n are the explosion limits of each component in oxygen or air, %; C m ' is the explosion limit of the associated oilfield gas at normal temperature and pressure, %.

[0023] Optionally, in obtaining the first critical oxygen content of the associated oilfield gas at normal temperature and pressure according to the gas components of the associated oilfield gas and the explosion limit at normal temperature and pressure, the calculation method of the first critical oxygen content is the stoichiometric method and / or the explosion range triangle diagram method.

[0024] Optionally, the first critical oxygen content is the average value of the critical oxygen content calculated by the stoichiometric method and the critical oxygen content calculated by the explosion range triangle diagram.

[0025] Optionally, in obtaining the lower and upper explosion limits at constant temperature and pressure based on the explosion limit under normal temperature and pressure, the calculation of the lower explosion limit at constant temperature and pressure is as follows:

[0026] Calculate the lower explosion coefficients b1, b2, b3, b4 at a given temperature:

[0027] b1 = -0.1305(T / 40) 2 + 0.3205(T / 40) + 1.241

[0028] b2 = -0.2125(T / 40) 2 + 0.8475(T / 40) - 0.196

[0029] b3 = 2.6125(T / 40) 2 - 9.4755(T / 40) + 9.988

[0030] b4 = 0.601(T / 40) 2 - 2.426(T / 40) + 3.64

[0031] where T is the given temperature;

[0032] Through the lower explosion coefficients b1, b2, b3, b4, obtain the lower explosion limit value L at any temperature. The calculation formula for the lower explosion limit value L is as follows:

[0033]

[0034] where C m is the explosion limit of the associated gas in the oilfield under normal temperature and pressure, and P is the given pressure.

[0035] Optionally, in obtaining the lower and upper explosion limits at constant temperature and pressure based on the explosion limit under normal temperature and pressure, the calculation of the upper explosion limit at constant temperature and pressure is as follows:

[0036] Calculate the upper explosion coefficients d1, d2, d3 at a given temperature:

[0037] d1 = 0.24(T / 40) 2 + 4.084(T / 40) + 53.246

[0038] d2 = 0.1875(T / 40) 2 + 3.2795(T / 40) + 33.281

[0039] d3 = 0.0045(T / 40) 2 + 0.7645(T / 40) + 5.682

[0040] Among them, T is the given temperature;

[0041] Through the upper limit explosion coefficients d1, d2, and d3, the upper explosion limit U at any temperature is obtained. The calculation formula for the upper explosion limit U is as follows:

[0042]

[0043] Among them, C m is the explosion limit of associated gas in the oilfield under normal temperature and pressure, and P is the given pressure.

[0044] Optionally, according to the first critical oxygen content under normal temperature and pressure, the second critical oxygen content under constant temperature and pressure is obtained. The calculation of the second critical oxygen content under constant temperature and pressure is as follows:

[0045] Calculate the critical explosion coefficient e under normal pressure:

[0046] C m = eδ 3 -7.8494eδ 2 +20.0066eδ - 15.0100

[0047] Among them, C m is the critical oxygen content, and the calculation formula for δ is as follows:

[0048] δ = ((T - 0.95) 0.5 -2.0125) / 2.236

[0049] Among them, T is the temperature;

[0050] Calculate the critical explosion coefficients f1, f2, and f3 at the given temperature:

[0051] f1 = -0.5305(T / 40) 2 +2.1775(T / 40) - 0.133

[0052] f2 = -0.2205(T / 40) 2 +0.9005(T / 40) + 2.515

[0053] f3 = 0.185(T / 40) 2 -1.058(T / 40) + 9.604

[0054] Among them, T is the given temperature;

[0055] Through the critical explosion coefficients f1, f2, and f3, the critical oxygen content LOC at any temperature is obtained. The calculation formula for the critical oxygen content LOC is as follows:

[0056]

[0057] Among them, C m is the explosion limit of associated gas in oil fields under normal temperature and pressure, and P is the given pressure.

[0058] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0059] The method for preventing downhole explosion in an oxygen-containing gas injection well provided by the embodiment of the present invention includes: obtaining associated gas in an oil field; measuring the gas components of the associated gas in the oil field to obtain the associated gas components; obtaining the explosion limit of the associated gas in the oil field under normal temperature and pressure according to the associated gas components; obtaining the critical oxygen content of the associated gas in the oil field according to the associated gas components and the explosion limit; obtaining the lower explosion limit and the upper explosion limit under constant temperature and pressure according to the explosion limit; obtaining the critical oxygen content under constant temperature and pressure according to the critical oxygen content; predicting downhole explosion according to the lower explosion limit under constant temperature and pressure, the upper explosion limit under constant temperature and pressure, and the critical oxygen content under constant temperature and pressure; giving the critical conditions for the explosion of oxygen and combustible gas in the downhole, thereby ensuring the downhole safety of oil and gas wells and reducing the risk of potential hazards.

[0060] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically describes the specific embodiments of the present invention. Brief Description of the Drawings

[0061] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to these drawings.

[0062] Figure 1 is the flowchart of the method provided by the embodiment of the present invention;

[0063] Figure 2 is the schematic diagram of the graphical method provided by the embodiment of the present invention;

[0064] Figure 3 is the calculation schematic diagram of the graphical method provided by Embodiment 1 of the present invention. Detailed Description of the Embodiments

[0065] The present invention will be specifically described below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention, rather than limiting the present invention.

[0066] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention pertains. In case of any contradiction, this specification shall prevail.

[0067] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0068] The technical solution of the embodiment of the present application is to solve the above technical problems, and the general idea is as follows: By a specific method, obtain the upper and lower limits of the critical explosion of combustible gas under a certain temperature and pressure condition, and the critical content of oxygen that can cause explosion under a certain temperature and pressure condition, and then guide the wellbore and surface process design.

[0069] According to a typical embodiment of the present invention, a method for preventing downhole explosion in an oxygen-containing gas injection well is provided, and the method includes:

[0070] S1. Obtain associated oilfield gas;

[0071] S2. Measure the gas components of the associated oilfield gas to obtain the gas components of the associated oilfield gas;

[0072] S3. Obtain the explosion limit of the associated oilfield gas at normal temperature and pressure according to the gas components of the associated oilfield gas;

[0073] S4. Obtain the lower and upper limits of explosion at constant temperature and pressure according to the explosion limit at normal temperature and pressure;

[0074] S5. Obtain the first critical oxygen content of the associated oilfield gas at normal temperature and pressure according to the gas components of the associated oilfield gas and the explosion limit at normal temperature and pressure;

[0075] S6. Obtain the second critical oxygen content at constant temperature and pressure according to the first critical oxygen content at normal temperature and pressure;

[0076] S7. Obtain the safe injection amount of oxygen-containing gas according to the lower and upper limits of explosion and the second critical oxygen content at constant temperature and pressure to prevent downhole explosion.

[0077] Specifically, in S2, a gas component measuring instrument is used to measure the components of associated gas in the oilfield. The methods for gas component measurement include gas chromatography, infrared analysis, zirconia oxygen analysis, magnetic oxygen analysis, nitrogen oxide analysis, physical method, etc. The embodiments of the present invention do not have specific requirements and can be selected according to actual situations. The above-listed methods are only used to illustrate that the present invention can be implemented and are not used to limit the present invention. In other embodiments, other implementation manners can also be used to detect gas components.

[0078] S3. According to the measured gas components, if the mixed gas is all combustible gas, the explosion limit of the mixed gas at normal temperature and pressure (20 °C, 0.1 MPa) can be calculated by the following formula.

[0079]

[0080] In the formula, C m is the explosion limit of the multi-component combustible gas mixture, %; V1, V2,..., V n are the volume percentages of each component in the mixed gas, %, and their sum is 100%; C1, C2,..., C n are the explosion limits of each component in oxygen or air, which can be obtained from academic literature and books, %.

[0081] If the mixed gas contains inert gas, it can be corrected by the following formula.

[0082]

[0083] In the formula, C m is the explosion limit of the combustible part in the mixed gas, %; C m ′ is the explosion limit of the combustible mixed gas containing inert gas, %; B is the volume fraction of the inert gas, %.

[0084] S4. Calculate the critical oxygen content of the mixed gas at normal temperature and pressure. In this embodiment, two methods are used for comprehensive determination, that is, the critical oxygen content is the average value of the results measured by the two methods.

[0085] The first is the stoichiometric method. The safe oxygen content limit refers to the safe oxygen content in the mixed gas that forms an explosive atmosphere in a closed device. There are mainly two situations. One is the maximum oxygen concentration required to form a non-explosive mixed gas by replacing the flammable gas in a storage tank or pipeline with inert gases such as nitrogen and carbon dioxide, or the critical value of the oxygen concentration required for the mixed gas that just explodes at the edge of the explosion range. The other is the minimum oxygen concentration required for a certain fixed concentration of flammable gas to just burn or explode when sufficient ignition energy is given and some inert gas is added. For the sake of distinction, the former is called the critical oxygen concentration or the maximum allowable oxygen concentration, that is, the safe oxygen content limit, and the latter is called the minimum oxygen concentration.

[0086] Therefore, when a flammable gas undergoes complete combustion with oxygen, the concentration of the flammable gas component at complete reaction can be obtained from the chemical reaction formula.

[0087]

[0088] In the formula, n, m, λ, and f represent the number of atoms of carbon, hydrogen, oxygen, and halogen elements respectively.

[0089] Theoretically, the concentration of the flammable gas that completely burns with 1 mol of oxygen is:

[0090]

[0091] When the concentration of the flammable gas is between C st and the lower explosion limit L, the reaction at this time is a complete combustion chemical reaction. If the concentration is L at this time, the theoretical minimum oxygen concentration is:

[0092]

[0093] The second is the graphical method, see Figure 2 .

[0094] (1) Draw an equilateral triangle, and the vertices F, O, and N represent the flammable gas, oxygen, and nitrogen respectively;

[0095] (2) Draw the air line F—A, and take the lower explosion limit X1’ and upper explosion limit X2’ of the flammable gas in oxygen on the F—O side;

[0096] (3) Take the lower explosion limit X1 and upper explosion limit X2 of the flammable gas in air on the F—A line;

[0097] (4) Connect X1, X1’, and extend; connect X2, X2’, and extend to intersect X1X1’ at point C;

[0098] (5) Draw a tangent parallel to FN through point C and intersect ON at point P, then point P is the critical oxygen concentration.

[0099] Take the median of the two methods as the critical oxygen content at normal temperature and pressure (20 °C, 0.1 MPa) for the final calculation.

[0100] In the actual application process, it is found that the stoichiometric method and the graphical method each have their own advantages, and their accuracies are different for different working conditions. The applicant finds that taking the median of the two methods can make the prediction result more accurate and more universal.

[0101] S5. Calculate the lower explosion limit of the mixed gas under the given temperature and pressure conditions.

[0102] Through the following formula, the lower explosion coefficients b1, b2, b3, and b4 at the given temperature are obtained.

[0103] b1 = -0.1305(T / 40) 2 + 0.3205(T / 40) + 1.241

[0104] b2 = -0.2125(T / 40) 2 + 0.8475(T / 40) - 0.196

[0105] b3 = 2.6125(T / 40) 2 - 9.4755(T / 40) + 9.988

[0106] b4 = 0.601(T / 40) 2 - 2.426(T / 40) + 3.64

[0107] Using the explosion limit value C of the mixed gas at normal temperature and pressure obtained previously m1 , through the following formula, the lower explosion limit value L at a certain temperature is obtained under the given pressure.

[0108]

[0109] S6. Calculate the upper explosion limit of the mixed gas under the given temperature and pressure conditions.

[0110] Through the following formula, the upper explosion coefficients d1, d2, and d3 at the given temperature are obtained.

[0111] d1 = 0.24(T / 40) 2 + 4.084(T / 40) + 53.246

[0112] d2 = 0.1875(T / 40) 2 + 3.2795(T / 40) + 33.281

[0113] d3 = 0.0045(T / 40) 2+0.7645(T / 40)+5.682

[0114] Using the explosion limit value C of the mixed gas at normal temperature and pressure obtained previously m2 , through the following formula, the upper explosion limit value U at a certain temperature is obtained under a given pressure.

[0115]

[0116] S7. Calculate the critical content of oxygen under given temperature and pressure conditions.

[0117] Through the following formula, the critical oxygen content coefficients f1, f2, and f3 at a given temperature are obtained.

[0118] f1 = -0.5305(T / 40) 2 +2.1775(T / 40)-0.133

[0119] f2 = -0.2205(T / 40) 2 +0.9005(T / 40)+2.515

[0120] f3 = 0.185(T / 40) 2 -1.058(T / 40)+9.604

[0121] Using the explosion limit value C of the mixed gas at normal temperature and pressure obtained previously m3 , through the following formula, the critical oxygen content LOC at a certain temperature is obtained under a given pressure.

[0122]

[0123] Finally, based on the above calculation indexes, the control requirements for combustible gas and critical oxygen content in the oilfield are given.

[0124] Finally, based on the above calculation indexes, the control requirements for combustible gas and critical oxygen content in the oilfield are given.

[0125] Next, the method for preventing downhole explosion in an oxygen-containing gas injection well of the present application will be described in detail in combination with examples, comparative examples, and experimental data.

[0126] Example 1

[0127] (1) The produced associated gas components of a certain oilfield are shown in the following table.

[0128] Produced associated gas components

[0129] Methane Ethane Propane Butane 82.90 9.42 5.03 2.65

[0130] (2) Calculate that the upper explosion limit of the mixed gas at normal temperature and pressure is 14.33%, and the lower explosion limit is 4.26%.

[0131]

[0132]

[0133] (3) Calculate the critical oxygen content at normal temperature and pressure to be 11.25%.

[0134] n = (82.90 + 2×9.42 + 3×5.03 + 4×2.65) / 100 = 1.27

[0135] m = (4×82.90 + 6×9.42 + 8×5.03 + 10×2.65) / 100 = 4.55

[0136]

[0137] The combustible components in associated gas are a mixed gas. When calculating its critical oxygen content using the explosion triangle diagram, it can only be simplified into a single gas, which is allowed for ideal gases.

[0138] First, obtain the upper and lower explosion limits of the combustible components in the mixed gas in air and oxygen.

[0139] The explosion limits of the mixed combustible components in oxygen are obtained as:

[0140]

[0141]

[0142] Let X1 = 4.26, X2 = 14.33, X 11 = 4.34, X 22 = 60.71. Draw the explosion limits X1 and X2 of the mixed combustible components in air in the form of points on the air line, and then draw the explosion limits X 11 , X 22 of the mixed combustible components in oxygen in the form of points on the oxygen axis. Connect X1 and X 11 , and extend it. Then connect X2 and X 22 , and extend it. The intersection with X1X 11 is at point C. Draw a line parallel to the fuel axis through point C, and the safe oxygen content can be obtained as 12.22%, as Figure 3 shown.

[0143]

[0144] (4) Calculate the lower explosion coefficient at normal pressure (0.1 MPa)

[0145] First, obtain the lower explosion coefficients b1, b2, b3, and b4 at the given temperature.

[0146] b1 = -0.1305(80 / 40) 2 +0.3205(80 / 40)+1.241 = 1.36

[0147] b2 = -0.2125(80 / 40) 2 +0.8475(80 / 40)-0.196 = 0.649

[0148] b3 = 2.6125(80 / 40) 2 -9.4755(80 / 40)+9.988 = 1.487

[0149] b4 = 0.601(80 / 40) 2 -2.426(80 / 40)+3.64 = 1.192

[0150] Then, at a given pressure, the lower explosion limit value L at a certain temperature is obtained.

[0151] L = (0.0791×4.26 + 0.7){1.36 + 0.649 / [1+(20 / 1.487) 1.192} = 1.44

[0152] (5) Calculate the upper explosion limit of the mixed gas under given temperature and pressure conditions.

[0153] First, the upper explosion coefficients d1, d2, and d3 at a given temperature are obtained.

[0154] d1 = 0.24(80 / 40) 2 +4.084(80 / 40)+53.246 = 62.374

[0155] d2 = 0.1875(80 / 40) 2 +3.2795(80 / 40)+33.281 = 40.59

[0156] d3 = 0.0045(80 / 40) 2 +0.7645(80 / 40)+5.682 = 7.229

[0157] Then, at a given pressure, the upper and lower explosion limit values U at a certain temperature are obtained.

[0158] U = (-0.0584×14.33 + 1.92)(62,374 - 40.59e -20 / 7.229 ) = 64.79

[0159] (6) Calculate the critical content of oxygen under given temperature and pressure conditions.

[0160] Obtain the critical oxygen content coefficients f1, f2, and f3 at a given temperature.

[0161] f1 = -0.5305(T / 40) 2 +2.1775(T / 40) - 0.133 = 2.1

[0162] f2 = -0.2205(T / 40) 2 +0.9005(T / 40) + 2.515 = 3.434

[0163] f3 = 0.185(T / 40) 2 -1.058(T / 40) + 9.604 = 8.228

[0164] Then, at a given pressure, obtain the critical oxygen content LOC at a certain temperature.

[0165] LOC = (-0.0866×11.25 + 2.0)(2.1e -20 / 3.434 +8.228) = 8.44

[0166] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0167] (1) The method for preventing downhole explosion in an oxygen-injected gas well provided by the embodiments of the present invention gives the critical conditions for the explosion of oxygen and combustible gas in the downhole through the composition of the downhole associated gas, thereby ensuring the downhole safety of the oil and gas well and reducing the risk of potential hazards.

[0168] (2) The method for preventing downhole explosion in an oxygen-injected gas well provided by the embodiments of the present invention can guide the wellbore and surface process design.

[0169] Finally, it should also be noted that the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device.

[0170] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0171] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preventing downhole explosion in an oxygen-containing gas injection well, characterized in that, The method includes: Obtaining associated gas from the oilfield; Measuring the gas components of the associated gas from the oilfield to obtain the gas components of the associated gas from the oilfield; Obtaining the explosion limit of the associated gas from the oilfield at normal temperature and pressure according to the gas components of the associated gas from the oilfield; Obtaining the lower explosion limit and the upper explosion limit at constant temperature and pressure according to the explosion limit at normal temperature and pressure; Obtaining the first critical oxygen content of the associated gas from the oilfield at normal temperature and pressure according to the gas components of the associated gas from the oilfield and the explosion limit at normal temperature and pressure; Obtaining the second critical oxygen content at constant temperature and pressure according to the first critical oxygen content at normal temperature and pressure; Obtaining the safe injection amount of oxygen-containing gas according to the lower explosion limit, the upper explosion limit and the second critical oxygen content at constant temperature and pressure to prevent downhole explosion; The calculation of the lower explosion limit at constant temperature and pressure is as follows: Calculating the lower explosion coefficients b1, b2, b3, b4 at a given temperature: Where T is the given temperature; Obtaining the lower explosion limit value L at any temperature through the lower explosion coefficients b1, b2, b3, b4, and the calculation formula of the lower explosion limit value L is as follows: is the explosion limit of associated gas in oilfield under normal temperature and pressure, and P is the given pressure; The calculation of the upper explosion limit at constant temperature and pressure is as follows: Calculating the upper explosion coefficients d1, d2, d3 at a given temperature: Obtaining the upper explosion limit U at any temperature through the upper explosion coefficients d1, d2, d3, and the calculation formula of the upper explosion limit U is as follows: ； The calculation of the second critical oxygen content at constant temperature and pressure is as follows: Calculating the critical explosion coefficient e at normal pressure: Among them, is the critical oxygen content, and its calculation formula is as follows: Where T is the temperature; Calculating the critical explosion coefficients f1, f2, f3 at a given temperature: Where T is the given temperature; Obtaining the critical oxygen content LOC at any temperature through the critical explosion coefficients f1, f2, f3, and the calculation formula of the critical oxygen content LOC is as follows: 。 2. The method for preventing downhole explosion in an oxygen-containing gas injection well according to claim 1, wherein When measuring the gas components of the associated gas from the oilfield to obtain the gas components of the associated gas from the oilfield, the methods for the component measurement include: chromatographic analysis, infrared analysis, zirconia oxygen analysis, magnetic oxygen analysis, nitrogen oxide analysis and physical method.

3. The method for preventing downhole explosion in an oxygen-containing gas injection well according to claim 1, wherein In the process of obtaining the explosion limit of the associated gas from the oilfield at normal temperature and pressure according to the gas components of the associated gas from the oilfield, If all components of the associated gas from the oilfield are combustible gases, the calculation formula of the explosion limit is as follows: Among them, is the explosion limit of associated gas in oilfield under normal temperature and pressure, %; , ,…, are the volume percentages of each component in the mixed gas, %, and their sum is 100%; , ,…, are the explosion limits of each component in oxygen or air, %.

4. The method for preventing downhole explosion in an oxygen-containing gas injection well according to claim 1, wherein In the process of obtaining the explosion limit of the associated gas from the oilfield at normal temperature and pressure according to the gas components of the associated gas from the oilfield, If the components of the associated gas from the oilfield contain inert gases, the calculation formula of the explosion limit is as follows: wherein, B is the volume fraction of inert gas, %; is the explosion limit of the combustible part of associated gas in oilfield under normal temperature and pressure, %; the calculation formula is as follows: wherein, , , …, are the volume percentages of the respective components in the mixed gas, %, and their sum is 100%; , , …, are the explosion limits of the respective components in oxygen or air, %; is the explosion limit of associated gas in oilfields at normal temperature and pressure, %.

5. The method for preventing downhole explosion in an oxygen-containing gas injection well according to claim 1, wherein In the process of obtaining the first critical oxygen content of the associated gas from the oilfield at normal temperature and pressure according to the gas components of the associated gas from the oilfield and the explosion limit at normal temperature and pressure, the calculation method of the first critical oxygen content is the stoichiometric method and / or the explosion range triangle diagram method.

6. The method for preventing downhole explosion in an oxygen-containing gas injection well according to claim 5, characterized in that, The first critical oxygen content is the average value of the critical oxygen content calculated by the stoichiometric method and the critical oxygen content calculated by the explosion range triangle diagram.

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