A prediction method for the maximum explosion pressure of gas-liquid-solid multiphase fuel

Abstract

The present invention relates to the technical field of explosion-induced cracking, and in particular to a method for predicting the maximum explosion pressure of a gas-liquid-solid multiphase fuel; comprising the following steps: Step 1: According to the chemical reaction principle and the basis of combustion, the combustion heat after the free gas-combustion-aid system is completely reacted is analyzed to determine the maximum heat release of the free gas-combustion-aid system; Step 2: According to the heat energy conversion relationship, the maximum combustion temperature that the system can reach after the free gas-combustion-aid system releases the combustion heat; Step 3: According to the gas state equation, the maximum degree to which the system gas pressure can expand in the process of the free gas-combustion-aid system reaching the maximum combustion temperature is determined. The present invention can make a rapid prediction of the maximum explosion pressure of a multi-component, multi-phase, and multi-variable fuel system; based on the basic system of combustion thermodynamics, the present invention realizes the prediction of the maximum explosion pressure of a complex fuel system, and can supplement the maximum explosion pressure data of most multi-phase or single-phase fuel systems.

Description

Technical Field

[0001] The invention relates to the technical field of explosion-induced fracturing, and in particular to a method for predicting the maximum explosion pressure of gas-liquid-solid multiphase fuel. Background Art

[0002] The combustion and explosion fracturing technology aims to use the explosion pressure of free gas to fractur e shale reservoirs, providing a multi-scale migration network of pores and fissures for shale gas extraction. It is a cutting-edge permeability enhancement technology with faster fracturing efficiency and higher depth. One of its key issues is under what conditions and what proportions can the explosion overpressure of free gas mixed with the combustion aid break through the cracking toughness of the rock formation. Therefore, a method for predicting the maximum explosion pressure of gas-liquid-solid multiphase fuel is proposed, which provides a new direction for the development of combustion and explosion fracturing. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the maximum explosion pressure of gas-liquid-solid multiphase fuel, which provides a new direction for the development of explosion-induced cracking.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] A method for predicting the maximum explosion pressure of a gas-liquid-solid multiphase fuel is applied to the explosion-induced fracturing technology. When a multiphase combustion aid is injected into a shale reservoir, the multiphase combustion aid combines with free gas to form a gas-liquid-solid multiphase fuel system, which explodes after being induced by an ignition source. If the dissipation of heat conduction, heat radiation, etc. during the explosion process is ignored, the combustion heat of the fuel system is converted into gas internal energy, causing the system temperature and pressure to increase. The method for predicting the explosion pressure of the gas-liquid-solid multiphase fuel includes the following steps:

[0006] Step 1: According to the chemical reaction principle and combustion foundation, analyze the combustion heat of the free gas-combustion-supporting agent system after complete reaction, and determine the maximum heat release of the free gas-combustion-supporting agent system;

[0007] Step 2: According to the heat energy conversion relationship, determine the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat;

[0008] Step 3: Based on the gas state equation, determine the maximum extent to which the system gas pressure can expand when the free gas-oxidant system reaches the maximum combustion temperature.

[0009] Specifically, the steps for determining the maximum heat release after the free gas and the combustion aid are completely burned in step 1 are as follows:

[0010] The chemical formula of the free gas is set to be X(g); the chemical formula of the multiphase combustion aid is set to be Y(g; l; s); the air is regarded as a mixture of O2(g) and N2(g) with a volume ratio of 1:3.76, and its chemical formula is set to be Z(g); then the combustion reaction equation of X(g) in Z(g) with Y(g; l; s) is as follows:

[0011] eta1X(g)+eta2Y(g;l;s)+eta3Z(g)→eta'1CO2(g)+eta'2H2O(g)+ eta'3N2(g)+eta'4KCl(s)+eta'5K2O(s)+eta'6MnO2(s) (1)

[0012] Wherein, η1, η2, η3 are the stoichiometric coefficients of the first, second, and third reactants, respectively, 1; η'1, η'2, η'3, η'4, η'5, η'6 are the stoichiometric coefficients of the first, second, third, fourth, fifth, and sixth products, respectively, 1;

[0013] Furthermore, the free gas involved in the present invention is composed of elements such as C, H, O, N, P, S...; the multi-phase combustion aid is composed of substances such as O2(g), O3(g), H2O2(l), N2O4(l), KMnO4(s), KClO4(s)...

[0014] According to Gass's law, the enthalpy of a chemical reaction is equal to the sum of the standard molar enthalpies of the products minus the sum of the standard molar enthalpies of the reactants, and the heat of combustion is the inverse of the chemical reaction enthalpy. The heat of combustion is as follows:

[0015]

[0016] Where Q is the heat of combustion, kJ / mol; ΔH is the chemical reaction enthalpy, kJ / mol; Δ f H m θ i is the standard molar formation enthalpy of the i-th reactant, kJ / mol; Δ f H m θ ' i is the standard molar formation enthalpy of the ith product, kJ / mol;

[0017] In a system with a volume of V, in order to maximize the heat release of the combustion of free gas and oxidant, the following two conditions must be met: the ratio of the amount of free gas to the oxidant is equal to the ratio of the stoichiometric numbers; the sum of the volume of the free gas and the oxidant is equal to the volume of the system. When the above two conditions are met at the same time, the system is filled with free gas and oxidant and no longer contains air. At this time, the free gas and oxidant burn most completely and consume the largest amount, and the heat release also reaches the maximum;

[0018]

[0019] Q m =n1Q (3)

[0020] Where n1 and n2 are the amount of free gas and combustion aid, mol; M1 and M2 are the molar mass of free gas and combustion aid, g / mol; ρ1 and ρ2 are the density of free gas and combustion aid, g / L; V m1 With V m2 is the molar volume of free gas and combustion aid, L / mol; Q m It is the maximum heat released after the free gas and the combustion aid are completely burned, kJ / mol.

[0021] Specifically, the steps of determining the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat in step 2 are as follows:

[0022] From the heat calculation formula, we can know that the free gas-combustion aid system releases heat Q m After that, the highest temperature that the system can reach is:

[0023]

[0024] Where T0 is the initial temperature of the system, K; V' i is the volume of the i-th product, m 3 ;c p,a ' i is the average isobaric heat capacity of the ith product, kJ / (m 3 K);

[0025] The average isobaric heat capacity refers to the amount of heat required for a system to reach its maximum combustion temperature when its temperature rises by 1K.

[0026]

[0027] In the formula, c p is the isobaric heat capacity, kJ / (m 3 K);

[0028] The average isobaric heat capacity of CO2(g), H2O(g), and N2(g) in the temperature range of 773-2773K was obtained by consulting the literature. When the consumption of free gas is large enough, the combustion temperature will exceed 2773K. In order to determine the average isobaric heat capacity of each gaseous product after 2773K, c p,a -T curve, set two maximum combustion temperatures T m1 and T m2 , and based on c p,a -T curve, determine the corresponding c p,a1 and c p,a2, determine Q through formula (4) m1 , Q m2 Until Q m1 m m2 And T m2 -T m1 <10K, determine T m1 +T m2 / 2 is the maximum combustion temperature T that can be reached after the free gas-combustion-supporting agent system burns m .

[0029] Specifically, the steps for determining the maximum extent to which the gas pressure of the system can expand during the process of the free gas-combustion-supporting agent system reaching the maximum combustion temperature in step 3 are as follows:

[0030] According to the gas state equations of the initial and final combustion states, the predicted value p of the maximum explosion pressure of the free gas-combustion aid system is obtained by the ratio of the two. m as follows:

[0031]

[0032] Where p0 is the initial pressure of the free gas-combustion-supporting agent system, MPa; R is the gas state constant, 8.314 J / (mol·K); n i is the amount of substance of the i-th reactant, mol; n' i is the amount of substance of the ith product, mol.

[0033] Furthermore, the maximum explosion pressure involved in the present invention is positively correlated with the ratio of the stoichiometric coefficients of products to reactants, the ratio of the theoretical combustion temperature to the initial temperature, and the initial pressure.

[0034] The beneficial effects of the present invention are:

[0035] (1) The present invention is applicable to work sites related to multiphase fuel systems, such as explosive blasting, coal mining, and chemical production. The present method can quickly predict the maximum explosion pressure of multi-component, multi-phase, and multi-variable fuel systems;

[0036] (2) The present invention is based on the basic system of combustion thermodynamics. The method can predict the maximum explosion pressure of complex fuel systems and can supplement the maximum explosion pressure data of most multi-phase or single-phase fuel systems.

[0037] (3) The present invention can be compiled into a program using a computer language. By calculating the maximum explosion pressure of the fuel system, it can guide the optimization of fuel formulas such as explosives, combustion aids, and propellants, thus providing a new direction for the development of combustion, explosion, and cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] ​​Figure 1 It is a flow chart of a method for predicting the maximum explosion pressure of gas-liquid-solid multiphase fuel according to an embodiment of the present invention;

[0039] Figure 2 Embodiment c of the present invention p,a - Attached diagram of T curve;

[0040] Figure 3 T is the explosion of CH4-O2-N2 in different proportions in the system with a volume of V in Example 1 of the present invention. m / p m The accompanying figure shows the comparison curve between theoretical value and experimental value, where 3(a) shows the T of different ratios of CH4-O2-N2 when they explode in a system with a volume of V. m Figure 3(b) shows the explosion of CH4-O2-N2 with different ratios in a system with a volume of V. m Attached pictures. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Reference Figure 1 A method for predicting the maximum explosion pressure of a gas-liquid-solid multiphase fuel is used in the explosion-induced fracturing technology. When a multiphase combustion aid is injected into a shale reservoir, the multiphase combustion aid combines with free gas to form a gas-liquid-solid multiphase fuel system, which explodes after being induced by an ignition source. If the dissipation of heat conduction, heat radiation, etc. during the explosion process is ignored, the combustion heat of the fuel system is converted into gas internal energy, causing the system temperature and pressure to increase. The method for predicting the explosion pressure of a gas-liquid-solid multiphase fuel includes the following steps:

[0043] Step 1: According to the chemical reaction principle and combustion foundation, analyze the combustion heat of the free gas-combustion-supporting agent system after complete reaction, and determine the maximum heat release of the free gas-combustion-supporting agent system;

[0044] Step 2: According to the heat energy conversion relationship, determine the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat;

[0045] Step 3: Based on the gas state equation, determine the maximum extent to which the system gas pressure can expand when the free gas-oxidant system reaches the maximum combustion temperature.

[0046] Specifically, the steps for determining the maximum heat release after the free gas and the combustion aid are completely burned in step 1 are as follows:

[0047] The chemical formula of the free gas is set to be X(g); the chemical formula of the multiphase combustion aid is set to be Y(g; l; s); the air is regarded as a mixture of O2(g) and N2(g) with a volume ratio of 1:3.76, and its chemical formula is set to be Z(g); then the combustion reaction equation of X(g) in Z(g) with Y(g; l; s) is as follows:

[0048] eta1X(g)+eta2Y(g;l;s)+eta3Z(g)→eta'1CO2(g)+eta'2H2O(g)+ eta'3N2(g)+eta'4KCl(s)+eta'5K2O(s)+eta'6MnO2(s) (1)

[0049] Wherein, η1, η2, η3 are the stoichiometric coefficients of the first, second, and third reactants, respectively, 1; η'1, η'2, η'3, η'4, η'5, η'6 are the stoichiometric coefficients of the first, second, third, fourth, fifth, and sixth products, respectively, 1;

[0050] Furthermore, the free gas involved in the present invention is composed of elements such as C, H, O, N, P, S...; the multi-phase combustion aid is composed of substances such as O2(g), O3(g), H2O2(l), N2O4(l), KMnO4(s), KClO4(s)...

[0051] According to Gass's law, the enthalpy of a chemical reaction is equal to the sum of the standard molar enthalpies of the products minus the sum of the standard molar enthalpies of the reactants, and the heat of combustion is the inverse of the chemical reaction enthalpy. The heat of combustion is as follows:

[0052]

[0053] Where Q is the heat of combustion, kJ / mol; ΔH is the chemical reaction enthalpy, kJ / mol; Δ f H m θ i is the standard molar formation enthalpy of the i-th reactant, kJ / mol; Δ f H m θ ' i is the standard molar formation enthalpy of the ith product, kJ / mol;

[0054] In a system with a volume of V, in order to maximize the heat release of the combustion of free gas and oxidant, the following two conditions must be met: the ratio of the amount of free gas to the oxidant is equal to the ratio of the stoichiometric numbers; the sum of the volume of the free gas and the oxidant is equal to the volume of the system. When the above two conditions are met at the same time, the system is filled with free gas and oxidant and no longer contains air. At this time, the free gas and oxidant burn most completely and consume the largest amount, and the heat release also reaches the maximum;

[0055]

[0056] Q m =n1Q (3)

[0057] Where n1 and n2 are the amount of free gas and combustion aid, mol; M1 and M2 are the molar mass of free gas and combustion aid, g / mol; ρ1 and ρ2 are the density of free gas and combustion aid, g / L; V m1 With V m2 is the molar volume of free gas and combustion aid, L / mol; Q m It is the maximum heat released after the free gas and the combustion aid are completely burned, kJ / mol.

[0058] Specifically, the steps of determining the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat in step 2 are as follows:

[0059] From the heat calculation formula, we can know that the free gas-combustion aid system releases heat Q m After that, the highest temperature that the system can reach is:

[0060]

[0061] Where T0 is the initial temperature of the system, K; V' i is the volume of the i-th product, m 3 ;c' p,ai is the average isobaric heat capacity of the ith product, kJ / (m 3 K);

[0062] The average isobaric heat capacity refers to the amount of heat required for a system to reach its maximum combustion temperature when its temperature rises by 1K.

[0063]

[0064] In the formula, c p is the isobaric heat capacity, kJ / (m 3 K);

[0065] Reference Figure 2, consult the literature to obtain the average isobaric heat capacity of CO2(g), H2O(g), and N2(g) in the temperature range of 773-2773K. When the consumption of free gas is large enough, the combustion temperature will exceed 2773K. In order to determine the average isobaric heat capacity of each gaseous product after 2773K, plot c p,a -T curve, set two maximum combustion temperatures T m1 and T m2 , and based on c p,a -T curve, determine the corresponding c p,a1 and c p,a2 , determine Q through formula (4) m1 , Q m2 Until Q m1 m m2 And T m2 -T m1 <10K, determine T m1 +T m2 / 2 is the maximum combustion temperature T that can be reached after the free gas-combustion-supporting agent system burns m , and the error is generally within 1K.

[0066] By the attached Figure 2 It can be seen that the average isobaric heat capacity of CO2(g) and N2(g) has a cubic function relationship with temperature, and the average isobaric heat capacity of H2O(g) has a linear relationship with temperature, and the correlation coefficients are all over 0.99.

[0067] Specifically, the steps for determining the maximum extent to which the gas pressure of the system can expand during the process of the free gas-combustion-supporting agent system reaching the maximum combustion temperature in step 3 are as follows:

[0068] According to the gas state equations of the initial and final combustion states, the predicted value p of the maximum explosion pressure of the free gas-combustion aid system is obtained by the ratio of the two. m as follows:

[0069]

[0070] Where p0 is the initial pressure of the free gas-combustion-supporting agent system, MPa; R is the gas state constant, 8.314 J / (mol·K); n i is the amount of substance of the i-th reactant, mol; n' i is the amount of substance of the ith product, mol.

[0071] Furthermore, the maximum explosion pressure involved in the present invention is positively correlated with the ratio of the stoichiometric coefficients of products to reactants, the ratio of the theoretical combustion temperature to the initial temperature, and the initial pressure.

[0072] ​​Furthermore, the standard molar enthalpy of formation (Δ f H m θ ) Refer to Table 1 below and the average isobaric heat capacity of the main substances (c p,a ) Refer to Table 2 below.

[0073] Table 1 Standard molar formation enthalpy of main substances (Δ f H m θ )

[0074]

[0075] Table 2 Average isobaric heat capacity of main substances (c p,a )

[0076]

[0077] Furthermore, this embodiment illustrates a method for predicting explosion pressure of gas-liquid-solid multiphase fuel.

[0078] Example 1: Calculation of the maximum explosion pressure of CH4-O2-N2 mixed gas

[0079] By using the method of steps 1 to 3 above, the maximum explosion pressure of CH4-O2-N2 mixed gases with different ratios is calculated and compared with the experimental results, the error of the prediction method is discussed, and the stoichiometric coefficients of reactants and products when CH4-O2-N2 explodes with different ratios are obtained, refer to Table 3 below.

[0080] Table 3 Stoichiometric numbers of reactants and products in different ratios of CH4-O2-N2 explosion

[0081]

[0082] From Table 3, we can know the standard molar formation enthalpy of each substance. Combining with formula (2), we can calculate the combustion heat of CH4-O2-N2 mixed gas with different proportions. It is not difficult to find that the N2 content does not affect the combustion heat of CH4 and O2. The calculation results are:

[0083] Q=-ΔH

[0084] (-74.847×1+0×2+0×7.52)-(-393.511×1+(-241.825)×2+0×7.52)=802.25(kJ / mol)

[0085] (-74.847×1+0×2+0×4.70)-(-393.511×1+(-241.825)×2+0×4.70)=802.25(kJ / mol)

[0086] (-74.847×1+0×2+0×3.00)-(-393.511×1+(-241.825)×2+0×3.00)=802.25(kJ / mol)

[0087] (-74.847×1+0×2+0×1.34)-(-393.511×1+(-241.825)×2+0×1.34)=802.25(kJ / mol)

[0088] (-74.847×1+0×2+0×0.50)-(-393.511×1+(-241.825)×2+0×0.50)=802.25(kJ / mol)

[0089] (-74.847×1+0×2+0×0.00)-(-393.511×1+(-241.825)×2+0×0.00)=802.25(kJ / mol) (7)

[0090] Furthermore, according to formula (3), the maximum heat release when different proportions of CH4-O2-N2 explode in a system with a volume of V is:

[0091]

[0092] (1×V×802.25) / (1×22.4+9.52×22.4)=3.4044V(kJ / L)

[0093] (1×V×802.25) / (1×22.4+6.70×22.4)=4.6513V(kJ / L)

[0094] (1×V×802.25) / (1×22.4+5.00×22.4)=5.9691V(kJ / L)

[0095] (1×V×802.25) / (1×22.4+3.34×22.4)=8.2522V(kJ / L)

[0096] (1×V×802.25) / (1×22.4+2.50×22.4)=10.233V(kJ / L)

[0097] (1×V×802.25) / (1×22.4+2.00×22.4)=11.938V(kJ / L) (8)

[0098] At this point, the method in step 2 is used to determine the maximum combustion temperature T that can be reached when different ratios of CH4-O2-N2 explode in a system with a volume of V. m, the results are shown in Table 4 below.

[0099] Table 4 Maximum combustion temperature T of different ratios of CH4-O2-N2 when they explode in a system with a volume of V m

[0100]

[0101] Finally, through step three, T m Determine the maximum extent p to which the gas pressure can expand when different ratios of CH4-O2-N2 explode in a system of volume V. m , and compared the theoretical value with the experimental value. The results are shown in Table 5 and Figure 3 shown.

[0102] Table 5 Maximum explosion pressure p of different ratios of CH4-O2-N2 when they explode in a system with a volume of V m

[0103]

[0104] Comprehensive Table 5 and Appendix Figure 3 (a) It can be seen that when different ratios of CH4-O2-N2 explode in a system with a volume of V, T m In the calculation results, the maximum and minimum absolute deviations between the theoretical and experimental values ​​are 407K and 57K respectively, the maximum and minimum relative deviations are 14.1% and 1.7% respectively, and the average absolute and relative deviations are 304K and 8.8% respectively.

[0105] Comprehensive Table 5 and Appendix Figure 3 (b) It can be seen that when different ratios of CH4-O2-N2 explode in a system with a volume of V, p m In the calculation results, the maximum and minimum absolute deviations between the theoretical value and the experimental value are 0.136MPa and 0.019MPa, respectively, the maximum and minimum relative deviations are 14.0% and 1.7%, respectively, and the average absolute and relative deviations are 0.110MPa and 9.2%, respectively. It can be seen that the results of predicting the maximum explosion pressure of the mixed gas using the method from step 1 to step 3 are generally about 10% higher, because the heat loss during the explosion process is ignored during the prediction. In other words, this method can predict the maximum explosion pressure of the mixed gas within 10% accuracy.

[0106] Example 2: Calculation of the maximum explosion pressure of a methane-combustion-supporting agent multiphase system

[0107] The reliability of the prediction method has been verified in Example 1. In this example, a multiphase fuel system consisting of methane and an oxidant is used as the object to calculate the maximum explosion pressure after complete combustion, and the universality of the prediction method is discussed. Here, six oxidants, O2(g), O3(g), H2O2(l), N2O4(l), KMnO4(s), and KClO4(s), are used as the objects and calculated respectively.

[0108] First, consider the chemical reaction mechanism of each of the six combustion aids when methane is mixed with them and explodes. Obviously, when methane is mixed with gaseous combustion aids such as O2(g) and O3(g) and explodes, gaseous products such as CO2(g) and H2O(g) will be generated in one step. When methane is mixed with liquid or solid combustion aids such as H2O2(l), N2O4(l), KMnO4(s), and KClO4(s) and explodes, it can only combine with methane to generate gaseous products such as CO2(g) and H2O(g) after vaporization or thermal decomposition. Based on this, the chemical reaction mechanism of the explosion when methane is mixed with the six combustion aids is shown in Table 6 below.

[0109] Table 6 Chemical reaction mechanism of explosion after methane mixed with six combustion aids

[0110]

[0111] Similarly, according to the method in step 1, the heat of combustion when methane is mixed with six combustion aids and explodes is calculated. The result is:

[0112] Q=-ΔH

[0113] (-74.847×1+0×2)-(-393.511×1+(-241.825)×2)=802.25(kJ / mol)

[0114] (-74.847×1+0×1.33)-(-393.511×1+(-241.825)×2)=992.52(kJ / mol)

[0115] (-74.847×1+(-187.61)×4)-(-393.511×1+(-241.825)×6)=1018.25(kJ / mol)

[0116] (-74.847×1+(-19.5)×1)-(-393.511×1+(-241.825)×2+0×1)=782.75(kJ / mol)

[0117]

[0118] (-74.847×1+(-432.8)×1)-(-393.511×1+(-241.825)×2+(-436.5)×1)=805.95(kJ / mol) (9)

[0119] Similarly, the maximum heat release when methane and six combustion aids are mixed and exploded in a system with a volume of V is calculated according to formula (3):

[0120]

[0121] (1×V×802.25) / (1×22.4+2×22.4)=11.938V(kJ / L)

[0122] (1×V×992.52) / (1×22.4+1.33×22.4)=18.989V(kJ / L)

[0123] (1×V×1018.25) / (1×22.4+4×0.0232)=45.215V(kJ / L)

[0124] (1×V×782.75) / (1×22.4+1×0.0634)=34.845V(kJ / L)

[0125] (1×V×1315.16) / (1×22.4+2.67×0.0585)=58.306V(kJ / L)

[0126] (1×V×805.95) / (1×22.4+1×0.0549)=35.892V(kJ / L) (10)

[0127] It can be seen from formula (10) that when the combustion aid is liquid or solid, its molar volume Vm2≈0, so it can be directly ignored in the calculation. In other words, the maximum heat release Qm after the free gas and the liquid or solid combustion aid are completely burned is:

[0128]

[0129] Similarly, using the method in step 2, determine the maximum combustion temperature T that can be reached when methane and six combustion aids are mixed in a system with a volume of V and explode. m ; At the same time, through step three, by T m Determine the maximum expansion p of the gas pressure when methane and six combustion aids are mixed in a system with a volume of V and explode. m , the results are shown in Table 7 below.

[0130] Table 7 Maximum combustion temperature and maximum explosion pressure of methane and six combustion aids when they explode in a system with a volume of V

[0131]

[0132] The results show that the sequence of the combustion-supporting efficiency of each phase of combustion-supporting agent for methane is liquid phase>solid phase>gas phase. Generally, the efficiency of liquid or solid combustion-supporting agent is more than 3 times that of gaseous combustion-supporting agent (8.067 / 2.687). The reason is that in a system with a volume of V, compared with a gaseous combustion-supporting agent, the volume fraction of liquid or solid combustion-supporting agent is smaller, and the methane content that can be detonated in a limited space is higher, resulting in a higher maximum combustion temperature that the fuel system can reach and a greater maximum degree to which the system gas pressure can expand. In short, Example 2 illustrates that this prediction method is applicable to the calculation of the maximum explosion pressure of a gas-liquid-solid multiphase fuel system. In other words, this prediction method not only has a prediction accuracy within 10%, but also has the universality applicable to gas-liquid-solid multiphase fuel systems.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for predicting the maximum explosion pressure of gas-liquid-solid multiphase fuel, characterized in that: Applied in the explosion-induced fracturing technology, when a multiphase combustion aid is injected into a shale reservoir, the multiphase combustion aid combines with free gas to form a gas-liquid-solid multiphase fuel system, which explodes after being induced by an ignition source. If the heat conduction and heat radiation dissipation during the explosion are ignored, the combustion heat of the fuel system is converted into gas internal energy, causing the system temperature and pressure to increase. The prediction method of the explosion pressure of the gas-liquid-solid multiphase fuel includes the following steps: Step 1: According to the chemical reaction principle and combustion foundation, analyze the combustion heat of the free gas-combustion-supporting agent system after complete reaction, and determine the maximum heat release of the free gas-combustion-supporting agent system; Step 2: According to the heat energy conversion relationship, determine the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat; Step 3: According to the gas state equation, determine the maximum extent to which the system gas pressure can expand when the free gas-combustion-supporting agent system reaches the maximum combustion temperature; The steps for determining the maximum heat release after the free gas and the combustion aid are completely burned in step 1 are as follows: The chemical formula of the free gas is set to be X(g); the chemical formula of the multiphase combustion aid is set to be Y(g; l; s); the air is regarded as a mixture of O2(g) and N2(g) with a volume ratio of 1:3.76, and its chemical formula is set to be Z(g); then the combustion reaction equation of X(g) in Z(g) with Y(g; l; s) is as follows: eta1X(g)+eta2Y(g;l;s)+eta3Z(g)→eta'1CO2(g)+eta'2H2O(g)+ eta'3N2(g)+eta'4KCl(s)+eta'5K2O(s)+eta'6MnO2(s)(1) Where η1, η2, and η3 are the stoichiometric coefficients of the first, second, and third reactants, respectively, 1; η'1, η'2, η'3, η'4, η'5, and η'6 are the stoichiometric numbers of the 1st, 2nd, 3rd, 4th, 5th, and 6th products, respectively, 1; According to Gass's law, the enthalpy of a chemical reaction is equal to the sum of the standard molar enthalpies of the products minus the sum of the standard molar enthalpies of the reactants, and the heat of combustion is the inverse of the chemical reaction enthalpy. The heat of combustion is as follows: Where, Q is the heat of combustion, kJ / mol; ΔH is the chemical reaction enthalpy, kJ / mol; η i is the stoichiometric number of the i-th reactant, 1; η' i is the stoichiometric number of the i-th product, 1; Δ f H m θ i is the standard molar formation enthalpy of the i-th reactant, kJ / mol; Δ f H m θ' i is the standard molar formation enthalpy of the ith product, kJ / mol; In a system with a volume of V, in order to maximize the heat release of the combustion of free gas and oxidant, the following two conditions must be met: the ratio of the amount of free gas to the oxidant is equal to the ratio of the stoichiometric numbers; the sum of the volume of the free gas and the oxidant is equal to the volume of the system. When the above two conditions are met at the same time, the system is filled with free gas and oxidant and no longer contains air. At this time, the free gas and oxidant burn most completely and consume the largest amount, and the heat release also reaches the maximum; In the formula, n1 and n2 are the amount of free gas and combustion aid, mol; M1 and M2 are the molar masses of free gas and combustion aid, g / mol; ρ1 and ρ2 are the densities of free gas and combustion aid, g / L; V m1 With V m2 is the molar volume of free gas and combustion aid, L / mol; Q m It is the maximum heat released after the free gas and the combustion aid are completely burned, kJ / mol.

2. A method for predicting the maximum explosion pressure of a gas-liquid-solid multiphase fuel according to claim 1, characterized in that: The steps of determining the maximum combustion temperature that the free gas-combustion-supporting agent system can reach after releasing the combustion heat in step 2 are as follows: From the heat calculation formula, we can know that the free gas-combustion aid system releases heat Q m After that, the highest temperature that the system can reach is: Where T0 is the initial temperature of the system, K; V' i is the volume of the i-th product, m 3 ;c p,a ' i is the average isobaric heat capacity of the ith product, kJ / (m 3 K); The average isobaric heat capacity refers to the amount of heat required for a system to reach its maximum combustion temperature when its temperature rises by 1K. In the formula, c p is the isobaric heat capacity, kJ / (m 3 K); Obtain the average isobaric heat capacity of CO2(g), H2O(g), and N2(g) in the temperature range of 773-2773K. When the combustion temperature exceeds 2773K, in order to determine the average isobaric heat capacity of each gaseous product after 2773K, plot c p,a -T curve, set two maximum combustion temperatures T m1 and T m2 , and based on c p,a -T curve, determine the corresponding c p,a1 and c p,a2 , determine Q through formula (4) m1 , Q m2 Until Q m1 m m2 And T m2 -T m1 <10K, determine T m1 +T m2 / 2 is the maximum combustion temperature T that can be reached after the free gas-combustion-supporting agent system burns m .​​ 3. The method for predicting the maximum explosion pressure of a gas-liquid-solid multiphase fuel according to claim 1, characterized in that: The steps for determining the maximum extent to which the gas pressure of the system can expand in the process of the free gas-combustion-supporting agent system reaching the maximum combustion temperature in step 3 are as follows: According to the gas state equations of the initial and final combustion states, the predicted value p of the maximum explosion pressure of the free gas-combustion aid system is obtained by the ratio of the two. m as follows: Where p0 is the initial pressure of the free gas-combustion-supporting agent system, MPa; R is the gas state constant, 8.314 J / (mol·K); n i is the amount of substance of the i-th reactant, mol; n' i is the amount of substance of the ith product, mol.

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