Method for determining physical property parameters of acidic natural gas

Abstract

The invention relates to a method for determining physical property parameters of acidic natural gas. The method comprises the following steps: step 1, inputting temperature, pressure and fluid basic property parameters; 2, calculating the apparent relative molecular mass of the acidic natural gas; 3, calculating the values of the attraction coefficient ai and the molar volume bi of each component parameter of the acidic natural gas; step 4, calculating a binary interaction coefficient delta ij between the components; 5, calculating the attraction coefficient a and the molar volume b of the acidic natural gas; 6, the natural gas molar volume is calculated through a Newton iteration method; according to the method, the interaction of all components in the acid natural gas is described through the binary interaction coefficient, the Peng-Robinson state equation is solved through the Newton iteration method, the model precision is improved in combination with the corrected alpha function, and therefore the density, the deviation coefficient, the viscosity and the gas-liquid interfacial tension of the acid natural gas are calculated. Therefore, support is provided for efficient development of deep natural gas.

Description

Technical Field

[0001] The present invention relates to a method for determining physical property parameters of sour natural gas, belonging to the technical field of natural gas development. Background Art

[0003] Under the strategic situation of deeply promoting energy transformation, in recent years, deep natural gas reservoirs have been successively discovered in Sichuan, Tarim, Junggar and other basins in China. Their efficient exploration and development is the top priority for ensuring China's energy security at present. For example, the deep marine natural gas in the northwest of Sichuan is an important block for increasing reserves and production in the Sichuan Basin of China at present. However, the structures in this area often have the characteristics of ultra-deep, high temperature and high pressure, and the produced natural gas contains H 2 S and CO 2 and other acidic components.

[0004] During the development of deep gas reservoirs, physical property parameters such as the density, deviation factor, viscosity and gas-liquid interfacial tension of sour natural gas will change significantly with the large changes in temperature and pressure. The physical property parameters of high-temperature and high-pressure sour natural gas are of great significance for calculating the wellbore pressure distribution, determining the gas well operating regime, calculating the gas reservoir reserves, analyzing the production performance and designing the gathering and transportation process flow. Therefore, accurately calculating the physical property parameters of sour natural gas under high temperature and high pressure is the key to the efficient development of gas reservoirs.

[0005] At present, with the progress of laboratory experiments and the development of corresponding theoretical research, domestic and foreign experts and scholars have achieved many results in the research of physical property parameters such as the deviation coefficient, density and viscosity of high-temperature and high-pressure sour natural gas. However, there are still some problems, which are summarized as follows:

[0006] (1) At present, the physical property parameters of natural gas are mainly calculated through laboratory experiments, referring to relevant charts or using empirical formulas obtained from fitting charts. The laboratory experiments have high accuracy, but the high-temperature and high-pressure characteristics of the gas reservoirs in the northwest of Sichuan require extremely high temperature and pressure resistance of the equipment, resulting in high experimental costs; the existing charts are generally outdated, with large errors under high-temperature and high-pressure conditions, time-consuming and laborious for manual reference, and there are also problems with the calculation accuracy of the formulas obtained from the fitting charts;

[0007] (2) The natural gas produced in the northwest of Sichuan often contains a certain amount of H 2 S and CO 2 and other acidic components, which will make the equipment more prone to corrosion during experiments, and there are also great risks in experiments such as natural gas compounding.

[0008] (3) At present, when calculating the wellbore pressure distribution and liquid holdup on site, the viscosity of natural gas and the gas-liquid interfacial tension are generally taken as constants, which will bring relatively large calculation errors. The existing calculation methods do not consider the influence of non-hydrocarbon components on the viscosity of natural gas, and the research on the influence of non-hydrocarbon components on the viscosity of sour natural gas is still in the development stage. It is still unclear which correction method can calculate the viscosity of sour natural gas most accurately.

[0009] Due to the existence of the above deficiencies, it is difficult to calculate the physical property parameters such as the deviation factor, density, viscosity and interfacial tension of high-temperature and high-pressure sour natural gas efficiently and accurately, which cannot meet the needs of efficient development of deep natural gas in the northwest Sichuan region and will reduce the efficiency and accuracy of gas reservoir dynamic analysis. Therefore, through in-depth research on the phase change characteristics of sour natural gas at different temperatures and pressures, the present invention has formed a method for determining the physical property parameters of high-temperature and high-pressure sour natural gas, which can efficiently and accurately predict a large number of physical property parameters of sour natural gas, thereby providing support for the efficient development of deep natural gas. Summary of the Invention

[0010] During the development of deep gas reservoirs, physical property parameters such as the density, deviation factor, viscosity and gas-liquid interfacial tension of sour natural gas will change significantly with the large changes in temperature and pressure. The physical property parameters of high-temperature and high-pressure sour natural gas are of great significance for wellbore pressure distribution calculation, gas well operating regime determination, gas reservoir reserve calculation, production dynamic analysis and gathering and transportation process design. However, due to the high cost and safety risks of current laboratory experiments, the calculation accuracy of the chart method and the formula obtained by fitting the chart at high temperature and high pressure is poor, resulting in inaccurate calculation of natural gas physical property parameters and affecting the development of deep sour natural gas.

[0011] Aiming at the above deficiencies in the prior art, the present invention describes the interaction of each component in sour natural gas through binary interaction coefficients, proposes to solve the Peng-Robinson equation of state by the Newton-Raphson method, and improves the model accuracy by combining the modified α function, thereby calculating the density and deviation factor of sour natural gas. By using the calculated value of natural gas density and combining the optimized calculation models of sour natural gas viscosity and gas-liquid interfacial tension, a method for determining the physical property parameters of high-temperature and high-pressure sour natural gas is established. This method can accurately calculate the density, deviation factor, viscosity and gas-liquid interfacial tension of sour natural gas at any temperature and pressure, thereby providing support for the efficient development of deep natural gas. The specific technical solution of the present invention is as follows:

[0012] A method for determining the physical property parameters of sour natural gas, comprising the following steps:

[0013] Step 1. Determine the number of components n in sour natural gas; the relative molecular mass M of each component i (i = 1, 2, 3, ···, n); the mole fraction x of each component i(i = 1, 2, 3, ···, n), temperature T, pressure P, formation water salinity, and by referring to the physical and chemical parameter table of natural gas components, determine the critical parameters of each component in the sour natural gas, including the critical pressure P ci , critical temperature T ci , critical molar volume V ci (i = 1, 2, 3, ···, n), determine the acentric factor of each component in the sour natural gas by referring to the main thermodynamic parameter table of pure substances;

[0014] Step 2. Determine the apparent relative molecular mass of natural gas according to Kay's mixing rule:

[0015]

[0016] In the formula, M g is the apparent relative molecular mass of natural gas, g / mol; n is the number of components in the natural gas system; x i is the mole fraction of component i in natural gas, mol%; M i is the relative molecular mass of component i, g / mol.

[0017] Step 3. Calculate the parameters a i (attraction coefficient) and b i (van der Waals molar volume) values of each component in the sour natural gas, where the dimensionless parameter a i in formula (2) is calculated according to the modified α i function preferred by the present invention, that is, formulas (4)-(5):

[0018]

[0019]

[0020]

[0021] T ri = T / T ci (i = 1, 2, 3, …, n) (5)

[0022] In the formula, a i is the attraction coefficient of component i in the sour natural gas, dimensionless; α i is the formula parameter of component i in the sour natural gas, dimensionless; R is the universal gas constant, kPa·m 3 ·(K·kmol) -1 ; b i is the van der Waals molar volume of component i in the sour natural gas, m 3 ·kmol-1 ; T ci is the critical temperature of component i in sour natural gas, K; P ci is the critical pressure of component i in sour natural gas, kPa; T ri is the reduced temperature of component i in sour natural gas, dimensionless; T is the temperature, K; ω i is the acentric factor of component i in sour natural gas, dimensionless.

[0023] Step 4. Determine the binary interaction coefficient δ between each component in natural gas according to formula (6) ij :

[0024]

[0025] In the formula, δ ij is the binary interaction coefficient between component i and component j, dimensionless; V ci is the critical molar volume of component i in sour natural gas, m 3 ·kmol -1 .

[0026] Step 5. Since sour natural gas is a mixed system, the interactions between each gas component are corrected through the van der Waals mixing rules, namely formulas (7) and (8), and the attractive coefficient a and the van der Waals molar volume b of sour natural gas are calculated:

[0027]

[0028]

[0029] In the formula, a is the attractive coefficient of sour natural gas, dimensionless; b is the van der Waals molar volume of sour natural gas, m 3 ·kmol -1 .

[0030] Step 6. Calculate the molar volume and density of sour natural gas through the Peng-Robinson equation of state. Since the original formula of the Peng-Robinson equation of state is complex and difficult to differentiate, the present invention proposes to organize it into the following format for convenient calculation using the Newton iteration method:

[0031] PV M 3 +(bP - RT)V M 2 +(a - 3b 2 P - 2bRT)V M +b 3 P + RTb 2 - ab = 0 (9)

[0032]

[0033] Wherein, P is the pressure, kPa; V M is the molar volume of the sour natural gas, m 3 / kmol; ρ g is the density of the sour natural gas, kg / m 3 .

[0034] Step 7. Calculate the deviation factor of the sour natural gas according to formula (11):

[0035]

[0036] Wherein, Z is the deviation factor of the sour natural gas, dimensionless.

[0037] Step 8. Calculate the viscosity of the natural gas according to the preferred sour gas viscosity correction method of the present invention, i.e., formulas (12)-(17):

[0038]

[0039]

[0040]

[0041]

[0042] Y = 2.447 - 0.2224X (16)

[0043] T L = 1.8(T - 273.15) + 492 (17)

[0044] Wherein, μ g is the viscosity of the natural gas, mPa·s; K, X, Y are formula parameters, dimensionless; is the formula correction parameter, dimensionless; T L is the Rankine temperature, °R; are respectively H 2 S, CO 2 and N 2 's relative densities, dimensionless, and their values are 1.189, 1.529 and 0.97 respectively; ρ pr is the relative density of the natural gas, dimensionless, and its calculation formula is as follows:

[0045]

[0046] Step 9. Calculate the interfacial tension according to the preferred sour natural gas gas-liquid interfacial tension calculation model of the present invention, i.e., formula (19):

[0047]

[0048] In the formula, σ is the gas-liquid interfacial tension, N / m; C s is the formation water salinity, mg / L, a 1 -a 10 is a formula parameter, dimensionless, and its specific value will be given in the embodiments.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. At present, the determination of the natural gas deviation factor is mainly calculated through indoor experiments, referring to relevant charts or using empirical formulas obtained from fitting charts. High-temperature and high-pressure natural gas requires high equipment requirements and high experimental costs; while the existing charts are generally relatively old, and there are large errors in the charts under high-temperature and high-pressure conditions. Manual reference is time-consuming and laborious, and there are also problems with the calculation accuracy of the formulas obtained from fitting charts; the calculation method described in the present invention can accurately calculate the deviation factor of high-temperature and high-pressure sour natural gas, and clarify the variation characteristics of the deviation factor with temperature and pressure, which is of great significance for the development of deep sour natural gas.

[0051] 2. The natural gas produced in the northwest Sichuan region often contains certain H 2 S and CO 2 and other acidic components. During experiments, it will make the equipment more vulnerable to corrosion, and there are also great risks in the experiments such as natural gas compounding. However, the calculation method proposed in the present invention no longer relies on experimental determination, reducing the safety risk.

[0052] 3. At present, when calculating the wellbore pressure distribution, critical liquid-carrying flow rate, etc. on site, the natural gas viscosity and interfacial tension are generally taken as constants, which will bring calculation errors. The present invention preferably selects a method that can accurately correct the viscosity for non-hydrocarbon components. The calculation method described can accurately calculate parameters such as the viscosity and interfacial tension of high-temperature and high-pressure sour natural gas.

[0053] 4. The calculation method described in the present invention is simple and clear, requires fewer basic physical and chemical property parameters and is easy to obtain, is convenient for programming, and can meet the needs of on-site technicians to quickly and accurately calculate the physical property parameters of high-temperature and high-pressure sour natural gas in the initial stage of deep natural gas development.

[0054] 5. The physical property parameters of high-temperature and high-pressure sour natural gas obtained by the calculation method described in the present invention are of great significance for wellbore pressure distribution calculation, gas well operating regime determination, gas reservoir reserve calculation, production performance analysis and gathering and transportation process design, etc. Therefore, it can better support the development of deep sour natural gas. Brief Description of the Drawings

[0055] Figure 1Flow chart for calculating physical property parameters of high-temperature and high-pressure sour natural gas according to the present invention;

[0056] Figure 2 Curve showing the variation of the deviation factor of sour natural gas with pressure at different temperatures in Example 2.

[0057] Figure 3 Curve showing the variation of the density of sour natural gas with pressure at different temperatures in Example 2.

[0058] Figure 4 Curve showing the variation of the viscosity of sour natural gas with pressure at different temperatures in Example 2.

[0059] Figure 5 Curve showing the variation of the gas-liquid interfacial tension of sour natural gas with pressure at different temperatures in Example 2.

[0060] Figure 6 Comparison chart of the calculated value and experimental value of the deviation factor of sour natural gas in the effectiveness example of the present invention.

[0061] Figure 7 Comparison chart of the calculated value and experimental value of the density of sour natural gas in the effectiveness example of the present invention.

[0062] Figure 8 Comparison chart of the calculated value and experimental value of the viscosity of sour natural gas in the effectiveness example of the present invention.

[0063] Figure 9 Comparison chart of the calculated value and experimental value of the gas-liquid interfacial tension of sour natural gas in the effectiveness example of the present invention. Detailed implementation manner

[0064] In order to enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0065] The present invention will be described in detail below with reference to the embodiments and the accompanying drawings of the specification, but the protection scope is not limited thereto.

[0066] In the embodiment, a high-pressure physical property experiment of natural gas was carried out using the produced gas in a certain block. By comparing the results of the high-pressure physical property experiment of natural gas with the calculation results of the method described in the present invention, the reliability of the calculation method described in the present invention was verified.

[0067] Example 1

[0068] A method for determining the physical property parameters of sour natural gas, the calculation flow chart is as Figure 1 shown, and the calculation is carried out according to the following steps:

[0069] Step 1. Input temperature, pressure and fluid basic property parameters, and the specific steps are as follows:

[0070] Input the number of components \(n\) in the sour natural gas; the relative molecular mass \(M\) of each component i (\(i = 1, 2, 3, ···, n\)); the molar fraction \(x\) of each component i (\(i = 1, 2, 3, ···, n\)), temperature \(T\), pressure \(P\), formation water salinity, and by referring to the physical and chemical parameter table of natural gas components, determine the critical parameters of each component in the sour natural gas, including the critical pressure \(P\) ci 、critical temperature \(T\) ci 、critical molar volume \(V\) ci (\(i = 1, 2, 3, ···, n\)), determine the acentric factor of each component in the sour natural gas by referring to the main thermodynamic parameter table of pure substances;

[0071] In this embodiment, the produced gas components in this block are \(CH\) 4 、\(C\) 2 \(H\) 6 、\(CO\) 2 and \(N\) 2 , so the number of components \(n\) is 4; the relative molecular mass \(M\) of \(CH\) 4 in the natural gas is 16.04 g / mol; the relative molecular mass \(M\) of \(C\) 1 is 30.74 g / mol; the relative molecular mass \(M\) of \(CO\) 2 \(H\) 6 is 44.01 g / mol; the relative molecular mass \(M\) of \(N\) 2 is 28.02 g / mol; the gas molar fraction \(x\) of \(CH\) 2 in the natural gas is 89.37 mol%; the gas molar fraction \(x\) of \(C\) 3 \(H\) 2 is 0.22 mol%; the gas molar fraction \(x\) of \(CO\) 4 is 8.39 mol%; the gas molar fraction \(x\) of \(N\) 4 is 1.901 mol%; the temperature \(T\) is 363.15 K; the pressure is 90.00 MPa; the formation water salinity \(C\) 1 is 25463.80 mg / L. And by referring to the physical and chemical parameter table of natural gas components ("Reservoir Physics", written by Zhao Chunsen, etc.), determine the critical parameters of each component in the sour natural gas as shown in Table 1, and by referring to the main thermodynamic parameter table of pure substances ("Practical Data Handbook for Chemical Engineers - Perry's Standard Charts and Formulas", written by J.G Speight), determine the acentric factor of each component in the sour natural gas: the gas acentric factor \(\omega\) of \(CH\) 2 \(H\) 6 of 2 is 2 ; the gas molar fraction \(x\) of 3 is 2 ; the gas molar fraction \(x\) of 4 is s ; 4 is1 is 0.008; C 2 H 6 gas acentric factor ω 2 is 0.009949; CO 2 gas acentric factor ω 3 is 0.0940; N 2 gas acentric factor ω 4 is 0.03772.

[0072] Table 1 Critical Parameter Table of Each Component in Acidic Natural Gas in a Certain Block

[0073]

[0074] Step 2. Calculate the apparent relative molecular mass of natural gas according to Kay's mixing rule:

[0075]

[0076] In the formula, M g is the apparent relative molecular mass of natural gas, g / mol; n is the number of components in the natural gas system; x i is the mole fraction of component i in natural gas, mol%; M i is the relative molecular mass of component i, g / mol.

[0077] In this embodiment, the apparent relative molecular mass of natural gas is calculated according to formula (1), and the obtained apparent relative molecular mass is 18.5908 g / mol.

[0078] Step 3. Calculate the parameters a i (attraction coefficient) and b i (vander Waals molar volume) values of each component in acidic natural gas, where the dimensionless parameter a i in formula (2) is calculated according to the modified α i function preferred by the present invention, that is, formulas (4)-(5):

[0079]

[0080]

[0081]

[0082] T ri = T / T ci (i = 1, 2, 3,..., n) (5)

[0083] In the formula, a i is the attraction coefficient of component i in acidic natural gas, dimensionless; αi is the formula parameter of component i in sour natural gas, dimensionless; R is the universal gas constant, kPa·m 3 ·(K·kmol) -1 ; b i is the van der Waals molar volume of component i in sour natural gas, m 3 ·kmol -1 ; T ci is the critical temperature of component i in sour natural gas, K; P ci is the critical pressure of component i in sour natural gas, kPa; T ri is the corresponding temperature of component i in sour natural gas, dimensionless; T is the temperature, K; ω i is the acentric factor of component i in sour natural gas, dimensionless.

[0084] Table 2 Calculated values of a, α and b for each component in the sour natural gas of a certain block

[0085]

[0086] Step 4. Determine the binary interaction coefficient δ between each component in natural gas according to formula (6) ij :

[0087]

[0088] In the formula, δ ij is the binary interaction coefficient between component i and component j, dimensionless; V ci is the critical molar volume of component i in sour natural gas, m 3 ·kmol -1 .

[0089] In this embodiment, the binary interaction coefficient δ between each component is determined according to formula (6) ij , and the calculation results are shown in Table 3:

[0090] Step 5. Since sour natural gas is a mixed system, the interaction between each gas component is corrected by the van der Waals mixing rules, namely formulas (7) and (8), and the attractive coefficient a and van der Waals molar volume b of sour natural gas are calculated:

[0091]

[0092]

[0093] In the formula, a is the attractive coefficient of sour natural gas, dimensionless; b is the van der Waals molar volume of sour natural gas, m 3 ·kmol-1 。

[0094] In this embodiment, the attractive coefficient a of the sour natural gas is determined according to formula (7), and its value is 234.39. The van der Waals molar volume of the sour natural gas is determined according to formula (7), and its value is 0.0267 m 3 ·kmol -1 。

[0095] Table 3 Binary interaction coefficients between components in the sour natural gas of a certain block

[0096]

[0097] Step 6 Calculate the molar volume of the sour natural gas by the Peng-Robinson equation of state through the Newton iteration method;

[0098] Step 7 Calculate the density of the sour natural gas,

[0099] Since the original formula of the Peng-Robinson equation of state is complex and difficult to differentiate, in steps 6 and 7 of the present invention, it is rearranged into the following format for easy calculation using the Newton iteration method:

[0100] PV M 3 +(bP - RT)V M 2 +(a - 3b 2 P - 2bRT)V M +b 3 P + RTb 2 - ab = 0 (9)

[0101]

[0102] In the formula, P is the pressure, kPa; V M is the molar volume of the sour natural gas, m 3 / kmol; ρ g is the density of the sour natural gas, kg / m 3 。

[0103] In this embodiment, according to formula (9), the Newton iteration method is used to calculate the molar volume V M of the sour natural gas, and its value is 0.0472 m 3 / kmol. The density ρ g of the sour natural gas is determined according to formula (10), and its value is 394.11 kg / m 3 。

[0104] Step 8. Calculate the deviation factor of the sour natural gas according to formula (11):

[0105]

[0106] In the formula, Z is the deviation factor of sour natural gas, dimensionless.

[0107] In this embodiment, the deviation factor Z of sour natural gas is calculated according to formula (11), and its value is 1.64.

[0108] Step 9. Calculate the natural gas viscosity according to the preferred sour gas viscosity correction method of the present invention, i.e., formulas (12)-(17):

[0109]

[0110]

[0111]

[0112]

[0113] Y = 2.447 - 0.2224X (16)

[0114] T L = 1.8(T - 273.15) + 492 (17)

[0115] In the formula, μ g is the natural gas viscosity, mPa·s; K, X, and Y are formula parameters, dimensionless; is the formula correction parameter, dimensionless; T L is the Rankine temperature, °R; are respectively the relative densities of H 2 S, CO 2 and N 2 respectively, dimensionless, and their values are 1.189, 1.529, and 0.97; ρ pr is the natural gas relative density, dimensionless, and its calculation formula is as follows:

[0116]

[0117] In this embodiment, the viscosity μ of sour natural gas is calculated according to the preferred sour gas viscosity correction method of the present invention, i.e., formulas (12)-(17) g , and its value is 0.0611 mPa·s.

[0118] Step 10. Calculate the interfacial tension according to the preferred sour natural gas gas-liquid interfacial tension calculation model of the present invention, i.e., formula (19):

[0119]

[0120] where σ is the gas-liquid interfacial tension, N / m; C s is the formation water salinity, mg / L, a 1 -a 10 is a formula parameter, dimensionless, and its specific values are shown in Table 4.

[0121] In this embodiment, according to the preferred acidic gas-liquid interfacial tension formula of the present invention, i.e., formula (19), the interfacial tension σ of the acidic natural gas is calculated, and its value is 0.0145 N / m.

[0122] Table 4 a in formula (19) 1 -a 10 Parameter values

[0123]

[0124] Example 2

[0125] A method for determining physical property parameters of high-temperature and high-pressure acidic natural gas

[0126] Similar to the method for determining physical property parameters of high-temperature and high-pressure acidic natural gas described in Example 1, the difference in Example 2 is that the values of temperature and pressure are changed, and then the physical property parameters of high-temperature and high-pressure acidic natural gas at different temperatures and pressures are calculated according to the calculation steps of Example 1. The results are as Figures 2 - 5 shown.

[0127] Effect example

[0128] To verify the accuracy of the calculation results obtained by the present invention, based on the produced gas in a certain block in northwestern Sichuan, through equipment such as PVT meters, densimeters, viscometers, and gas-liquid interfacial tension meters, the gas deviation factor, density, viscosity, and gas-liquid interfacial tension of natural gas at different pressures at 90 °C were experimentally measured. The comparison results between the calculated values and experimental values of the gas deviation factor, density, viscosity, and gas-liquid interfacial tension of natural gas are respectively as Figures 6 - 9 shown.

[0129] It can be seen from Figures 6 - 9 that the differences between the calculated values and experimental values of the gas deviation factor, density, viscosity, and gas-liquid interfacial tension of natural gas are very small, thus verifying the accuracy of the model. The correlation coefficient R between the calculated values and experimental values of each physical property parameter 2 is shown in Table 5, and the R of all physical property parameters 2 is greater than 0.996, further proving the accuracy of the prediction effect of the present invention.

[0130] Table 5 Correlation coefficient table of calculated values and experimental values of physical property parameters

[0131]

[0132] The above are only embodiments of the present invention. Common knowledge such as specific structures and characteristics known in the art is not described in detail herein. Those of ordinary skill in the art know all the common general technical knowledge in the technical field to which the invention pertains before the filing date or the priority date, are able to know all the prior art in this field, and have the ability to apply conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, combine their own abilities to complete and implement this solution. Some typical well-known structures or well-known methods should not become obstacles for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can still be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. A method for determining the physical property parameters of acidic natural gas, characterized in that: The steps include: Step 1: Input temperature, pressure and basic fluid property parameters; Step 2: Calculate the apparent relative molecular mass of the sour natural gas; Step 3 Calculate the attraction coefficient a of each component parameter of sour natural gas i With molar volume b i The value of Step 4 Calculate the binary interaction coefficient δ between each component ij : Step 5: Calculate the attraction coefficient a and molar volume b of the sour natural gas; Step 6: Calculate the molar volume of natural gas by Newton's iteration method; Step 7 calculates the density of sour natural gas.

2. The method according to claim 1, characterized in that: The specific steps of step 1 are as follows: Step 1. Determine the number of components n in sour natural gas; the relative molecular mass Mi (i=1,2,3,···,n) of each component; the mole fraction xi (i=1,2,3,···,n), temperature T, pressure P, and formation water salinity of each component; determine the critical parameters of each component in sour natural gas, including critical pressure Pci, critical temperature Tci, and critical molar volume Vci (i=1,2,3,···,n); determine the eccentricity factor of each component in sour natural gas.

3. The method according to claim 1, characterized in that: The specific steps of step 2 are as follows: Step 2. Determine the apparent molecular mass of natural gas according to Kay's mixing rule: Where M g is the apparent relative molecular mass of natural gas, g / mol; n is the number of components in the natural gas system; x i is the molar fraction of component i in natural gas, mol%; M i is the relative molecular mass of component i, g / mol.

4. The method according to claim 1, characterized in that: The specific steps of step 3 are as follows: Step 3. Calculate the parameter attraction coefficient a of each component in the sour natural gas by formula (2)-(3): i With molar volume b i The value of , where the dimensionless parameter a in formula (2) i According to the modified α i The function is calculated, that is, formula (4)-(5) T ri =T / T ci (i=1,2,3,…,n) (5) In the formula, a i is the attraction coefficient of component i in sour natural gas, dimensionless; α i is the formula parameter of component i in sour natural gas, dimensionless; R is the universal gas constant, kPa·m 3 ·(K·kmol) -1 ; b i is the vander Waals molar volume of component i in sour natural gas, m 3 kmol -1 ; T ci is the critical temperature of component i in acidic natural gas, K; P ci is the critical pressure of component i in sour natural gas, kPa; T ri is the corresponding temperature of component i in sour natural gas, dimensionless; T is temperature, K; ω i is the eccentricity factor of component i in sour natural gas, dimensionless.

5. The method according to claim 1, characterized in that: The specific steps of step 4 are as follows: Step 4. Determine the binary interaction coefficient δ between the components in natural gas according to formula (6): ij : In the formula, δ ij is the binary interaction coefficient between component i and component j, dimensionless; V ci is the critical molar volume of component i in sour natural gas, m 3 kmol -1 .

6. The method according to claim 1, characterized in that: The specific steps of step 5 are as follows: Step 5. Since the sour natural gas is a mixed system, the interaction between the gas components is corrected according to formulas (7) and (8), and the corrected attraction coefficient a and molar volume b of the sour natural gas are calculated: Where a is the corrected attraction coefficient of sour natural gas, dimensionless; b is the corrected molar volume of sour natural gas, m 3 kmol -1 .

7. The method according to claim 1, characterized in that: The specific steps of steps 6 and 7 are as follows: According to formulas (9)-(10), the molar volume and density of natural gas are calculated: PV M 3 +(bP-RT)V M 2 +(a-3b 2 P-2bRT)V M +b 3 P+RTb 2 -ab=0 (9) Where, P is pressure, kPa; V M is the molar volume of sour natural gas, m 3 / kmol; g is the density of sour natural gas, kg / m 3 .

8. The method according to claims 1-7, characterized in that: Also includes step 8, Step 8. Calculate the sour natural gas deviation factor according to formula (11): Where Z is the sour natural gas deviation factor, dimensionless.

9. The method according to claim 8, characterized in that: Also includes step 9 Step 9. Calculate the natural gas viscosity according to formulas (12)-(17): Y=2.447-0.2224X (16) T L =1.8(T-273.15)+492 (17) In the formula, μ g is the viscosity of natural gas, mPa·s; K, X, and Y are formula parameters, dimensionless; is the formula correction parameter, dimensionless; T L is the Rankine temperature, °R; are the relative densities of H2S, CO2 and N2, dimensionless, with values ​​of 1.189, 1.529 and 0.97 respectively; ρ pr is the relative density of natural gas, dimensionless, and its calculation formula is as follows:

10. The method according to claim 9, characterized in that: Also includes step 10 Step 10: Calculate the interfacial tension according to formula (19): Where, σ is the gas-liquid interfacial tension, N / m; C s is the mineralization of formation water, mg / L, a1-a 10 is a formula parameter, dimensionless.

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