Equivalent adsorption thermal desorption calculation method in shale gas adsorption process

Abstract

The invention relates to the technical field of oil and gas field development, in particular to an equivalent adsorption thermal analysis calculation method in the shale gas adsorption process. The invention discloses an equivalent adsorption thermal desorption calculation method in a shale gas adsorption process. The method comprises the following steps: acquiring isothermal adsorption curves at different temperatures; fitting the isothermal adsorption equation with isothermal adsorption curves at different temperatures so as to obtain a fitting result of adsorption characteristic energy and saturated adsorption quantity with the temperature, and substituting the fitting result into a formula 8, so as to obtain an equivalent adsorption thermal desorption solution; and combining the equivalent adsorption thermal desorption solution with the isothermal adsorption curves at different temperatures to obtain an equivalent adsorption thermal result. According to the method, an isothermal adsorption equation is introduced into an equivalent adsorption heat definition formula, the equivalent adsorption heat analytical calculation method suitable for the shale gas adsorption process is provided, and quantitative characterization of an equivalent adsorption heat curve at different temperatures can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a method for calculating isosteric adsorption heat analysis in a shale gas adsorption process. Background Art

[0002] The isosteric heat of adsorption of solid-gas adsorption systems is a key thermodynamic parameter for the design of gas separation, gas storage, and adsorption refrigeration systems. It reflects the strength of the interaction between the adsorbent and the adsorbate, and between the adsorbates themselves. In recent years, this has been extensively studied in the field of unconventional natural gas.

[0003] The isosteric heat of adsorption (ICH) of shale gas adsorption is widely calculated using the isosteric line plotting method. This method simplifies the theoretical framework of ICH by assuming an ideal bulk gas and neglecting the volume of the adsorbed phase. The isosteric heat of adsorption is then derived by performing coordinate transformation and function fitting on the isothermal adsorption data. However, since shale gas is in a supercritical state under in situ conditions, the assumptions underlying the ICH method are not applicable to shale gas adsorption. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes to introduce the isothermal adsorption equation into the definition of isosteric adsorption heat, and proposes an isosteric adsorption heat analytical calculation method suitable for shale gas adsorption process.

[0005] The technical solution of the present invention is: A method for calculating the isosteric adsorption heat analysis of shale gas adsorption process is calculated using the following formula: Where: q st is the isosteric heat of adsorption, J / mol; T is the temperature, K; n0 is the saturated adsorption capacity, mmol / g; n is the adsorption amount, mmol / g; E is the adsorption characteristic energy, J / mol; R is the universal gas constant, which is 8.314, J / (mol·K).

[0006] The specific derivation process is as follows.

[0007] The isosteric heat of adsorption is defined as: q st =-RT 2 (dlnP / dT) n (Formula 1) Where: P is the gas phase pressure, Pa; The isothermal adsorption equation is expressed as: n=n0exp[﹣(ε / E) 2 ] (Formula 2) Where: ε is the adsorption potential, J / mol; The adsorption potential ε is expressed as: ε=RTln(P s / P) (Formula 3) Where: P s is the virtual saturated vapor pressure, MPa; Virtual saturated vapor pressure P s Expressed as: P s =P c (T / T c ) 2 (Formula 4) Where: P c is the critical pressure of the adsorbate, MPa; T c is the critical temperature of the adsorbate, K; Transform both ends of Equation 2 and differentiate with respect to T to obtain: Solving the second term on the right side of Equation 5 and differentiating it with respect to T yields: By transforming both ends of Equation 4 and differentiating it with respect to T, we obtain: d(lnP s ) / dT=2 / T (Equation 7) Combining Equations 1, 5, 6, and 7, the isosteric heat of adsorption is expressed as:

[0008] The technical effects of the present invention are: The present invention introduces the isothermal adsorption equation into the definition of isosteric adsorption heat, and proposes an isosteric adsorption heat analytical calculation method suitable for the shale gas adsorption process, which can achieve quantitative characterization of isosteric adsorption heat curves at different temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is the fitting curve of adsorption characteristic energy E, saturated adsorption amount n0 and temperature T.

[0010] Figure 2 The isosteric adsorption heat curves at different temperatures. DETAILED DESCRIPTION

[0011] Example 1 A method for calculating the isosteric adsorption heat analysis of shale gas adsorption process is calculated using the following formula:

[0012] Example 2 A method for calculating the isosteric adsorption heat analysis of shale gas adsorption process is as follows: Obtain isothermal adsorption curves at different temperatures T; The isothermal adsorption equation is fitted with the isothermal adsorption curves at different temperatures T, and then the fitting results of the adsorption characteristic energy E and the saturated adsorption amount n0 and temperature T are obtained. The above fitting results are substituted into Equation 8 to obtain the isosteric adsorption heat analytical solution q st ; Solve the isosteric adsorption heat by analyzing q st Combined with the isothermal adsorption curves at different temperatures T, the isosteric adsorption heat results are obtained.

[0013] Specific implementation cases This case study takes the Chang 7 shale of the Yanchang Formation as an example to calculate the isosteric heat of adsorption of CH4 in the Chang 7 shale.

[0014] The isothermal adsorption data of Chang 7 shale at different temperatures T are shown in Table 1: Table 1 Isothermal adsorption data of Chang 7 shale at different temperatures T The isothermal adsorption equation is fitted with the isothermal adsorption curves at different temperatures to obtain the fitting relationship between the adsorption characteristic energy E and the saturated adsorption amount n0 and the temperature T. The fitting results are as follows: Figure 1 , detailed data are shown in Table 2:

[0015] Table 2 Fitting results of adsorption characteristic energy E and saturated adsorption amount n0 and temperature T

[0016] Substituting the fitting function of the adsorption characteristic energy E and the saturated adsorption amount n0 into Equation 8, the isosteric adsorption heat analytical solution is obtained: Using the isosteric adsorption heat to solve Equation 9, combined with the isothermal adsorption curves at different temperatures, the isosteric adsorption heat of the shale in the 7th section of the extended formation is obtained, as follows: Figure 2 shown.

Claims

1. A method for calculating isosteric adsorption heat analysis in shale gas adsorption process, characterized in that: Calculated by the following formula: Where: q st is the isosteric heat of adsorption, J / mol; T is the temperature, K; n0 is the saturated adsorption capacity, mmol / g; n is the adsorption amount, mmol / g; E is the adsorption characteristic energy, J / mol; R is the universal gas constant, which is 8.314, J / (mol·K).

2. The isosteric adsorption heat analysis calculation method for shale gas adsorption process according to claim 1 is characterized in that: The adsorption characteristic energy E, saturated adsorption amount n0 and temperature T are obtained by fitting the isothermal adsorption equation with the isothermal adsorption curves at different temperatures.

3. The isosteric adsorption heat analysis calculation method for shale gas adsorption process according to claim 2 is characterized in that: Here’s how: Obtain isothermal adsorption curves at different temperatures T; The isothermal adsorption equation is fitted with the isothermal adsorption curves at different temperatures T, and then the fitting results of the adsorption characteristic energy E and the saturated adsorption amount n0 and temperature T are obtained. The above fitting results are substituted into Equation 8 to obtain the isosteric adsorption heat analytical solution q st ; Solve the isosteric adsorption heat by analyzing q st Combined with the isothermal adsorption curves at different temperatures T, the isosteric adsorption heat results are obtained.

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