Method for measuring vapor pressure of unconventional crude oil

Abstract

The present invention belongs to the field of unconventional oil and gas technologies, and particularly relates to a method for measuring the vapor pressure of unconventional crude oil. The method includes the following steps: (1) taking an unconventional crude oil sample, adding a treating agent and mixing to obtain a mixed solution; (2) measuring the vapor pressure of the mixed solution according to the expansion method, and then calculating the vapor pressure of the unconventional crude oil sample according to Raoult's law and Henry's law. When the vapor pressure of the crude oil is lower than the lower limit range of 25 kPa for the determination in GB / T 11059-2011, the measurement and conversion of the vapor pressure of the crude oil are solved, and the method has the characteristics of simple experimental operation and reliable method principle.

Description

Technical Field

[0001] The present invention belongs to the technical field of unconventional oil and gas, and particularly relates to a method for measuring the vapor pressure of unconventional crude oil. Background Art

[0002] Unconventional crude oil generally refers to extra-heavy crude oil, tight oil, shale oil, etc. Such crude oil has the characteristics of high viscosity, high density, large viscosity, low content of light hydrocarbon components, and high content of non-hydrocarbon (sulfur, nitrogen, oxygen and metal) compounds. With the reduction of conventional petroleum resources and the progress of production technology, unconventional crude oil has been gradually developed and utilized. Doing a good job in the emission control of pollutants is a new challenge faced in the process of unconventional crude oil exploitation.

[0003] The release and implementation of the "Emission Standard of Air Pollutants for Onshore Oil and Gas" (GB39728-2020) have put forward clear requirements for the emission control of air pollutants in the onshore oil and gas exploitation industry. Among them, for the storage of crude oil, different control requirements are stipulated according to the true vapor pressure of the material and the single-tank design volume. For example, in key areas for air pollution control, when the single-tank design volume is greater than or equal to 150 m3 and the true vapor pressure of the material is greater than or equal to 5.2 kPa and less than 27.6 kPa, the control requirements for crude oil storage shall meet one of the following: a) using a floating roof tank; b) using a fixed roof tank and collecting and treating the discharged waste gas, with the removal efficiency of non-methane total hydrocarbons not less than 90%; c) using a vapor balance system; d) taking other equivalent measures. Therefore, the size of the true vapor pressure of crude oil is directly related to the design, operation and maintenance of crude oil storage tanks.

[0004] The "Determination of Vapor Pressure of Crude Oil - Expansion Method" (GB / T11059-2011) is the method for measuring the true vapor pressure of crude oil cited in GB39728-2020. However, GB / T11059-2011 is applicable to measuring the vapor pressure of crude oil with a vapor pressure of 25 kPa - 180 kPa. Moreover, in the detection of crude oil samples, it is found that the true vapor pressure of a considerable part of heavy oil and viscous oil is lower than 25 kPa. This indicates that directly applying GB / T11059-2011 makes it impossible to determine the true vapor pressure of some unconventional crude oils, and further leads to the inability to implement the air pollutant emission control measures in GB39728-2020. Therefore, a method for calculating the vapor pressure of crude oil based on GB / T11059-2011 is needed to detect oils such as unconventional crude oil with a vapor pressure lower than 25 kPa, so as to provide a basis for implementing the air pollutant emission control measures in GB39728-2020.

[0005] The present invention aims to propose a method for measuring the true vapor pressure of unconventional crude oil, so as to be applicable to the measurement of the vapor pressure of crude oil samples with a vapor pressure lower than 25 kPa. Summary of the Invention

[0006] To overcome the above technical problems, the present invention provides a method for determining the vapor pressure of unconventional crude oil, which is applicable to the determination of the vapor pressure of crude oil samples with a vapor pressure lower than 25 kPa.

[0007] To achieve the above object, the technical solution provided by the present invention is as follows:

[0008] A method for determining the vapor pressure of unconventional crude oil, comprising the following steps:

[0009] (1) Take an unconventional crude oil sample A, add a treating agent B and mix to obtain a mixed solution C;

[0010] (2) After measuring the vapor pressure of the mixed solution C according to the expansion method, then calculate the vapor pressure of the unconventional crude oil sample A according to Raoult's law and Henry's law.

[0011] Preferably, the treating agent B is a volatile solvent;

[0012] Preferably, the treating agent B is any one or more of pentane, hexane, heptane, octane, benzene, toluene, dichloromethane, chloroform, tetrachloroethylene, carbon tetrachloride, ethanol, propanol, acetone, butanone, propyl ether, and anisole.

[0013] Preferably, the treating agent B is any one or more mixtures of n-hexane, benzene, and chloroform.

[0014] Preferably, the treating agent B is a mixture of hexane, benzene, and chloroform.

[0015] Preferably, the volume ratio of hexane, benzene, and chloroform in the mixture of n-hexane, benzene, and chloroform is 1:1 - 3:1 - 3, preferably 1:1:1.

[0016] Preferably, the vapor pressure of the mixed solution C is 25 - 180 kPa.

[0017] Preferably, the calculation method is:

[0018] P A =P A * ×x A

[0019] P B =k x,B ×x B

[0020] P C =P A +P B

[0021]

[0022] Wherein: P A * is the saturated vapor pressure of A, which is the object to be calculated; P B is the vapor pressure of B;

[0023] P C is the vapor pressure of solution C, which can be experimentally determined by GB / T11059-2011;

[0024] K X，B is the Henry's law constant of B, which can be obtained through experiments or by referring to the physical property handbook;

[0025] X A , X B are the mole fractions of A and B respectively, which are calculated according to the ratio when preparing solution C.

[0026] Preferably, the X A = 0.5 - 0.99, X B = 0.01 - 0.5.

[0027] Preferably, the expansion method is the expansion method for measuring the vapor pressure of crude oil recorded in the national standard GB / T11059-2011.

[0028] Preferably, the specific steps of the expansion method are as follows: Transfer the crude oil sample to a temperature-controlled measuring chamber with a movable piston inside, seal it, expand the volume of the measuring chamber by moving the piston to reach the gas-liquid ratio, then adjust the temperature of the measuring chamber to the measuring temperature, oscillate, and when the temperature and pressure reach equilibrium, the measured pressure is the vapor pressure of the crude oil sample of the sample.

[0029] Preferably, the gas-liquid ratio is 3 - 6:1, preferably 4:1.

[0030] Compared with the prior art, the technical advantages of the present invention are as follows:

[0031] The present invention solves the problem of the determination and conversion of the vapor pressure of crude oil when the vapor pressure of crude oil is lower than the lower limit range of 25 kPa of the "Expansion Method for Measuring the Vapor Pressure of Crude Oil" GB / T11059-2011, and has the characteristics of simple experimental operation and reliable method principle. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 : Schematic diagram of the principle of the method for measuring the vapor pressure of unconventional crude oil of the present invention;

[0033] The specific meanings of the marks in the drawings are as follows:

[0034] P A * is the saturated vapor pressure of A;

[0035] P B * is the saturated vapor pressure of B;

[0036] 1 is the vapor pressure curve of the mixed solution C;

[0037] 2 is the component - partial pressure curve of the treating agent B;

[0038] 3 is the component - partial pressure curve of the sample A.

[0039] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Specific embodiments

[0040] The present invention will be described below through specific embodiments to make the technical solutions of the present invention easier to understand and master, but the present invention is not limited thereto. The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0041] Example 1

[0042] Weigh 21.1 g of the crude oil sample (A) from the No. 2 Heavy Oil Combined Station in the Fengcheng Operation Area of Xinjiang Oilfield, with a density (at 20 °C) of 0.963 g / cm 3 and a viscosity (at 50 °C) of 14325 mPa·s, add 3.2 g of n - hexane (B), and mix the two evenly to obtain the mixed solution C (X A = 0.868, X B = 0.132). Use an HVP972 type vapor pressure measuring instrument to measure the vapor pressure of the mixed solution at 60 °C as 28.5 kPa (Pc). Also, knowing that the Henry's coefficient of n - hexane at this temperature is 78.2 kPa, the true vapor pressure P A * of this heavy oil sample is calculated to be 20.9 kPa. (When directly measured using the national standard, the vapor pressure of this heavy oil sample is 18.8 kPa, and the relative deviation from the measurement method of the present invention is 10.0%).

[0043] Example 2

[0044] Weigh 16.3 g of the crude oil sample (A) from the 91# station of Xinjiang Oilfield Xingang Company, with a density (at 20 °C) of 0.932 g / cm 3 and a viscosity (at 20 °C) of 7263 mPa·s, add 5.3 g of dichloromethane (B), and mix the two evenly to obtain the mixed solution C (X A = 0.755, X B = 0.245). Use an HVP972 type vapor pressure measuring instrument to measure the vapor pressure of the mixed solution at 30 °C as 27.2 kPa (Pc). Also, knowing that the Henry's coefficient of dichloromethane at this temperature is 70.6 kPa, the true vapor pressure P A* is 13.1 kPa. (When directly measured using the national standard, the vapor pressure of this heavy oil sample is 11.2 kPa, with a relative deviation of 14.5% from the measurement method of the present invention.)

[0045] Example 3

[0046] Weigh 15.4 g of the crude oil sample (A) from the Wuerhe light oil treatment station of Xinjiang Oilfield with a density (at 20 °C) of 0.877 g / cm 3 and a viscosity (at 50 °C) of 96.3 mPa·s, add 6.2 g of n-pentane (B), and mix the two evenly to obtain a mixed solution C (X A = 0.713, X B = 0.287). Use an HVP972 type vapor pressure measuring instrument to measure the vapor pressure of the mixed solution at 20 °C as 29.6 kPa (Pc). Also, know that the Henry's law constant of n-pentane at this temperature is 56.8 kPa, and thus calculate the true vapor pressure P A * of this light oil sample is 18.7 kPa. (When directly measured using the national standard, the vapor pressure of this light oil sample is 16.1 kPa, with a relative deviation of 13.9% from the measurement method of the present invention.)

[0047] Comparative Example 1

[0048] Weigh 15.6 g of the sample (A) from the No. 2 heavy oil combined station in the Fengcheng operation area of Xinjiang Oilfield with a density (at 20 °C) of 0.963 g / cm 3 and a viscosity (at 50 °C) of 14325 mPa·s, add 3.2 g of methanol (B). Since the solubility of heavy oil and methanol is poor, the two cannot be mixed to obtain a uniform mixed solution C, so the vapor pressure of the mixed solution cannot be measured by the "Expansion Method for the Determination of Crude Oil Vapor Pressure", indicating that the solvent selection has failed.

[0049] Comparative Example 2

[0050] Weigh 18.3 g of the crude oil sample (A) from the 91# station of Xinjiang Oilfield Xingang Company with a density (at 20 °C) of 0.932 g / cm 3 , a viscosity (at 20 °C) of 7263 mPa·s, add 3.6 g of dichloromethane (B), and mix the two evenly to obtain a mixed solution C (X A = 0.836, X B = 0.164). Use an HVP972 type vapor pressure measuring instrument to measure the vapor pressure of the mixed solution at 30 °C as 22.5 kPa (Pc). The measured vapor pressure is less than 25 kPa, not meeting the measurement requirements of the "Expansion Method for the Determination of Crude Oil Vapor Pressure". This indicates that the addition amount of dichloromethane is insufficient.

[0051] Effect Evaluation

[0052] Weigh 17.8 g of n-heptane and add 8.6 g of n-pentane (B). Mix the two evenly to obtain a mixed solution C (X A = 0.674, X B = 0.326). Use an HVP972 type vapor pressure measuring instrument to measure the vapor pressure of the mixed solution at 30 °C, which is 32.2 kPa (Pc). Also, know that the Henry's law constant of n-pentane at this temperature is 82.0 kPa. Thus, calculate the true vapor pressure P A * of n-heptane to be 8.1 kPa. (If calculated using the Antoine empirical formula, the vapor pressure of n-heptane at 30 °C is 7.8 kPa, and the relative deviation is 3.7%.)

[0053] After verification with n-heptane, the relative deviation between its true vapor pressure and the detected value is only 3.7%. This shows that the measurement method provided by the present invention can accurately measure the vapor pressure of unconventional crude oil.

[0054] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or change without departing from the present invention shall be included within the scope of the technical solution of the present invention.

Claims

1. A method for determining the vapor pressure of unconventional crude oil, characterized in that, it includes the following steps: (1) Take unconventional crude oil sample A, add treatment agent B and mix to obtain mixed solution C; (2) After measuring the vapor pressure of mixed solution C according to the expansion method, then calculate the vapor pressure of unconventional crude oil sample A according to Raoult's law and Henry's law; The formula for the calculation is: P B = k x,B × x B P C = P A + P B Where: P A * is the saturated vapor pressure of A, which is the object to be calculated; P C is the vapor pressure of solution C, which can be experimentally determined by GB / T 11059-2011; P B is the vapor pressure of B; k X，B is the Henry's law constant of B, which can be determined experimentally or obtained from a physical property handbook; x A ,x B are the mole fractions of A and B, respectively, and are calculated from the ratios when preparing solution C.

2. The method for determining the vapor pressure of unconventional crude oil according to claim 1, characterized in that, the treatment agent B is any one or more of pentane, hexane, heptane, octane, benzene, toluene, dichloromethane, chloroform, tetrachloroethylene, carbon tetrachloride, ethanol, propanol, acetone, butanone, propyl ether, anisole.

3. The method for determining the vapor pressure of unconventional crude oil according to claim 2, characterized in that, the treatment agent B is any one or more mixtures of n - hexane, benzene and chloroform.

4. The method for determining the vapor pressure of unconventional crude oil according to claim 3, characterized in that, the treatment agent B is a mixture of n - hexane, benzene and chloroform, and the volume ratio of n - hexane, benzene and chloroform in the mixture is 1:1 - 3:1 - 3.

5. The method for determining the vapor pressure of unconventional crude oil according to claim 3, characterized in that, the treatment agent B is a mixture of n - hexane, benzene and chloroform, and the volume ratio of n - hexane, benzene and chloroform in the mixture is 1:1:

1.

6. The method for determining the vapor pressure of unconventional crude oil according to claim 1, characterized in that, by selecting the vapor pressure of the mixed solution C to be 25 - 180 kPa when formulating the treatment agent B.

7. The method for determining the vapor pressure of unconventional crude oil according to claim 1, characterized in that, x A = 0.5 to 0.99, x B = 0.01 to 0.

5.

8. The method for determining the vapor pressure of unconventional crude oil according to claim 1, characterized in that, The specific operation process of the expansion method is: transfer the crude oil sample to a temperature - controllable measuring chamber with a movable piston inside, seal it, expand the volume of the measuring chamber by moving the piston until the gas - liquid ratio reaches 3 - 6:1, then adjust the temperature of the measuring chamber to the measuring temperature, oscillate, and when the temperature and pressure reach equilibrium, the measured pressure is the vapor pressure of the crude oil sample.

9. The method for determining the vapor pressure of unconventional crude oil according to claim 8, characterized in that, the gas - liquid ratio is 4:1.

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