CN104849256A - Method for obtaining trapping pressure of pure methane inclusion - Google Patents

Abstract

The invention discloses a method for obtaining a trapping pressure of a pure methane inclusion, and belongs to the technical field of geological exploration. The method for obtaining the trapping pressure of the pure methane inclusion comprises the following steps: obtaining a methane laser Raman scattering peak v1 of the pure methane inclusion; according to the methane laser Raman scattering peak v1 of the pure methane inclusion, obtaining the density of the methane inclusion; obtaining a trapping temperature of a gas-liquid two-phase salt water inclusion formed at a same period as the pure methane inclusion; and according to the density of the pure methane inclusion and the trapping temperature of the gas-liquid two-phase salt water having the same period as the pure methane inclusion, obtaining the trapping pressure of the pure methane inclusion. The method for obtaining the trapping pressure of the pure methane inclusion has lower requirements on experimental samples, and is fast in experimental data reading and processing speed, and high in measuring accuracy.

Description

A kind of method obtaining pure methane inclusion trapping pressure

Technical field

The present invention relates to technical field of geological exploration, particularly a kind of method obtaining pure methane inclusion trapping pressure.

Background technology

In focusing masonry dam shale gas exploratory development research, prove that burnt masonry dam five peaks-Longma small stream group shale reservoir is overpressure system, superpressure and shale gas are preserved and the relation of enrichment has become the hot issue that Present Domestic studies.Before the structure uplift erosion of the Yanshan Mountain in evening, burnt masonry dam shale gas field, the recovery of formation pore fluid pressure is the key parameter of research shale gas-bearing formation overpressure evolution and overpressure evolution and shale gas enrichment relation.Fluid inclusion deposits body as effective tax of ancient geologic fluids raw information, becomes the important evidence understanding shale gas reservoir fluid palaeotemperature, paleopressure condition.But the analog computation of fluid inclusion trapping pressure, the impact by inclusion component is comparatively large, and multi-component fluid inclusion is difficult to the component concentration in Accurate Measurement separate fluid inclution, therefore about the pressure simulation calculating of polycomponent inclusion may be not too accurate.And pure methane inclusion component is single, it is the ideal object of renwing stratum pore-fluid pressure.The method of traditional calculations methane inclusion trapping pressure calculates out according to the homogenization temperature of methane inclusion, and the reliable acquisition of methane inclusion homogenization temperature data needs to select form rule, the methane inclusion that long axis length is greater than 6 μm carries out homogenization temperature test, methane inclusion in most of oil gas reservoir does not meet laboratory sample requirement, and methane inclusion homogenization temperature test process is loaded down with trivial details, consuming time longer.

Summary of the invention

The invention provides a kind of method obtaining pure methane inclusion trapping pressure, to solve or part solves that prior art obtains that methane inclusion trapping pressure experimental procedure is many, experimental data and the larger technical matters of error calculated.

For solving the problems of the technologies described above, the invention provides a kind of method obtaining pure methane inclusion trapping pressure, comprising the following steps: obtain pure methane inclusion methane laser raman scattering peak v ₁; According to pure methane inclusion methane laser raman scattering peak v ₁obtain the density of pure methane inclusion; What obtain the solution-air two-phase saline inclusion formed the same period with pure methane inclusion catches temperature; According to pure methane inclusion density with catch temperature with methane inclusion solution-air same period two-phase salt solution and obtain pure methane inclusion trapping pressure.

Further, described acquisition pure methane inclusion methane laser raman scattering peak v ₁comprise the inclusion thin slice obtaining rock sample, Raman microprobe test is carried out to the host minerals of catching pure methane inclusion, judges host minerals composition in conjunction with Arthroscopic characteristic; The mineral fluid inclusions of catching in sample is carried out to the Raman microprobe test of 300 gratings; 1800 gratings are carried out to pure methane inclusion, Ne lamp correct Raman microprobe test, for obtaining pure methane inclusion methane laser raman scattering peak v _measwith two measurement peak position v of Ne lamp _meas; According to the nonlinear relationship of optical splitter, utilize the laser Raman spectroscopy base peak Ne of neon lamp ₁, i.e. v _realfor 2836.9888cm ^-1with base peak Ne ₂, i.e. v _realfor 3008.12744cm ^-1) methane Raman scattering peak v to methane inclusion _meascorrect, and then determine methane inclusion real laser raman scattering peak v accurately _corr, methane inclusion real Raman scattering peak v _corr, methane inclusion measure Raman scattering peak v _meas, neon lamp peak, i.e. Ne ₁and Ne ₂base peak position v _realwith measurement peak position v _measthere is following relation:

$v_{\mathrm{corr}}^{{\mathrm{CH}}_4}=\frac{1}{2}\left\{\right[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_1,2836.98}-v_{\mathrm{meas}}^{{\mathrm{Ne}}_1,2836.98})]+[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_2,3008.13}-v_{\mathrm{neas}}^{{\mathrm{Ne}}_2,3008.13})\left]\right\}$ (1), methane inclusion methane laser raman scattering peak v can be calculated accurately according to formula (1) ₁, unit is cm ^-1.

Further, the density obtaining methane inclusion described in comprises by measuring methane Raman scattering peak v under different pressures condition in glass capillary system ₁displacement, obtains methane Raman scattering peak v ₁the relation of displacement, methane density and pressure, methane inclusion methane Raman scattering peak v ₁there is linear relationship in displacement and methane inclusion density p:

ρ (g/cm ³)=-5.17331 × 10 ^-5d ³+ 5.53081 × 10 ^-4d ²-3.51387 × 10 ^-2d (2), related coefficient is 0.9987, wherein: D=v ₁-v ₀, v ₁the methane Raman scattering peak of the actual measurement methane inclusion after neon lamp corrects, v ₀for when pressure close to 0 time the methane Raman scattering peak of methane inclusion; By methane Raman scattering peak v ₁relation formula (2) with methane inclusion density p, calculates methane inclusion density, and unit is g/cm ³.

Further, the temperature of catching of the solution-air two-phase saline inclusion that described acquisition and pure methane inclusion are formed the same period comprises methane inclusion and catches with the solution-air two-phase saline inclusion of methane inclusion symbiosis simultaneously, inclusion is trapped in the not mixing binary system of saturated methane, and what the homogenization temperature of solution-air two-phase saline inclusion can represent methane inclusion catches temperature.

Further, what obtain described in that pure methane inclusion trapping pressure comprises foundation is applicable to CH ₄the state equation of system calculates the trapping pressure of methane inclusion:

$Z=\frac{\mathrm{PV}}{\mathrm{RT}}=\frac{P_r{V}_r}{T_r}=1+\frac{B}{V_r}+\frac{C}{V_r^2}+\frac{D}{V_r^4}+\frac{E}{V_r^5}+\frac{F}{V_r^2}(\mathrm{\β}+\frac{\mathrm{\γ}}{V_r^2})\exp (-\frac{\mathrm{\γ}}{V_r^2})---\left(3\right),$ Wherein: $B=a_1+\frac{a_2}{T_r^2}+\frac{a_3}{T_r^3};C=a_4+\frac{a_5}{T_r^2}+\frac{a_6}{T_r^3};D=a_7+\frac{a_8}{T_r^2}+\frac{a_9}{T_r^3};E=a_{10}+\frac{a_{11}}{T_r^2}+\frac{a_{12}}{T_r^3};$ $F=\frac{\mathrm{\α}}{T_r^3};P_r=\frac{P}{P_c};T_r=\frac{T}{T_c};V_r=\frac{V}{V_c};V_c=\frac{{\mathrm{RT}}_c}{P_c};$ In formula, P is pressure (bar); T is temperature (K); R is gas law constant (R=0.08314467bardm ³k ^-1mol ^-1); V is molar volume (dm ³/ mol), can be calculated by the density p of methane inclusion and molal weight; Z is compressibility factor; Pr, Tr are respectively reduced pressure, reduced temperature, and its dimension is 1; Pc, Tc are respectively emergent pressure and critical temperature, unit and P, T-phase with; a ₁=0.0872553928; a ₂=-0.752599476; a ₃=0.375419887; a ₄=0.0107291342; a ₅=0.0054962636; a ₆=-0.0184772802; a ₇=0.000318993183; a ₈=0.000211079375; a ₉=0.0000201682801; a ₁₀=-0.0000165606189; a ₁₁=0.000119614546; a ₁₂=-0.000108087289; α=0.0448262295; β=0.75397; γ=0.077167.

The method of acquisition pure methane inclusion trapping pressure provided by the invention, comprises the following steps and obtains pure methane inclusion methane laser raman scattering peak v ₁, according to pure methane inclusion methane laser raman scattering peak v ₁obtain the density of methane inclusion, what obtain the solution-air two-phase saline inclusion formed the same period with pure methane inclusion catches temperature (homogenization temperature), according to pure methane inclusion density with catch temperature (homogenization temperature) with methane inclusion solution-air same period two-phase salt solution and obtain pure methane inclusion trapping pressure, require low to laboratory sample, experimental data reads and processing speed is fast, estimating precision is high.

Accompanying drawing explanation

The schematic flow sheet of the method for the acquisition pure methane inclusion trapping pressure that Fig. 1 provides for the embodiment of the present invention;

300 rastering laser Raman spectrograms of pure methane inclusion in the quartz vein that Fig. 2 provides for the embodiment of the present invention;

1800 rastering laser Raman spectrograms of pure methane inclusion in the quartz vein that Fig. 3 provides for the embodiment of the present invention.

Embodiment

See Fig. 1, a kind of method obtaining pure methane inclusion trapping pressure that the embodiment of the present invention provides comprises the following steps:

Step 1, obtains pure methane inclusion methane laser raman scattering peak v ₁.

Step 2, according to pure methane inclusion methane laser raman scattering peak v ₁obtain the density of methane inclusion; The confocal effect of Laser-Raman microspectroscopy can reach laterally 0.1 μm, and the spatial resolution that the degree of depth is about 0.3 μm is measured, and the methane inclusion that long axis length reaches 1 μm in theory just meets experimental apparatus to laboratory sample requirement; Laser-Raman microspectroscopy data acquisition time is generally 10-100s, compared with methane inclusion homogenization temperature test process, substantially reduces experimental period.

Step 3, what obtain the solution-air two-phase saline inclusion formed the same period with pure methane inclusion catches temperature (homogenization temperature).

Step 4, according to pure methane inclusion density with catch temperature (homogenization temperature) with methane inclusion solution-air same period two-phase salt solution and obtain pure methane inclusion trapping pressure.

Introduce step 1 in detail.

Described acquisition pure methane inclusion methane laser raman scattering peak v ₁comprise the inclusion thin slice obtaining rock sample, Raman microprobe test is carried out to the host minerals of catching pure methane inclusion, judges host minerals composition in conjunction with Arthroscopic characteristic.The mineral fluid inclusions of catching in sample is carried out to the Raman microprobe test of 300 gratings; 300 gratings have 2.97cm ^-1spectral resolution, Raman spectrum peak-to-peak signal is comparatively strong, and can quick obtaining, for qualitative analysis Fluid inclusions Body components, selects pure methane inclusion.1800 gratings are carried out to pure methane inclusion, Ne lamp correct Raman microprobe test, for obtaining methane inclusion laser raman scattering peak v ₁(v _meas) and two of Ne lamp measure peak position v _meas; 1800 gratings have 0.35cm ^-1spectral resolution, accurate compared with 300 rastering laser Raman spectrum data.Due to when carrying out Raman microprobe test, can there is skew to a certain degree in the laser raman scattering peak position of material, according to the nonlinear relationship of optical splitter, utilize the laser Raman spectroscopy base peak Ne of neon lamp ₁(v _realfor 2836.9888cm ^-1) and base peak Ne ₂(v _realfor 3008.12744cm ^-1) methane Raman scattering peak v to methane inclusion ₁(v _meas) correct, and then determine methane inclusion real laser raman scattering peak v accurately ₁(v _corr), methane inclusion real Raman scattering peak v ₁(v _corr), methane inclusion measure Raman scattering peak v ₁(v _meas), neon lamp peak (Ne ₁, Ne ₂) base peak position v _realwith measurement peak position v _measthere is following relation:

$v_{\mathrm{corr}}^{{\mathrm{CH}}_4}=\frac{1}{2}\left\{\right[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_1,2836.98}-v_{\mathrm{meas}}^{{\mathrm{Ne}}_1,2836.98})]+[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_2,3008.13}-v_{\mathrm{neas}}^{{\mathrm{Ne}}_2,3008.13})\left]\right\}$ (1), methane inclusion laser raman scattering peak v can be calculated accurately according to formula (1) ₁, unit is cm ^-1.

Introduce step 2 in detail.

The described density obtaining methane inclusion comprises: by measuring methane Raman scattering peak v under different pressures condition in glass capillary system ₁displacement, obtains methane Raman scattering peak v ₁the relation of displacement, methane density and pressure, methane inclusion methane Raman scattering peak v ₁there is linear relationship in displacement and methane inclusion density p:

ρ (g/cm ³)=-5.17331 × 10 ^-5d ³+ 5.53081 × 10 ^-4d ²-3.51387 × 10 ^-2d (2), related coefficient is 0.9987, wherein: D=v ₁-v ₀, v ₁the methane Raman scattering peak of the actual measurement methane inclusion after neon lamp corrects, v ₀for when pressure close to 0 time the methane Raman scattering peak of methane inclusion, v ₀the main impact by laboratory bearing calibration, different experiments room v ₀value different.By methane Raman scattering peak v ₁relation formula (2) with methane inclusion density p, calculates methane inclusion density, and unit is g/cm ³.

Introduce step 3 in detail.

The temperature of catching of the solution-air two-phase saline inclusion that described acquisition and pure methane inclusion are formed the same period comprises methane inclusion and catches with the solution-air two-phase saline inclusion of methane inclusion symbiosis simultaneously, inclusion is trapped in the not mixing binary system of saturated methane, and what the homogenization temperature of solution-air two-phase saline inclusion can represent methane inclusion catches temperature.

Introduce step 4 in detail.

Described obtain that pure methane inclusion trapping pressure comprises foundation be applicable to CH ₄the state equation of system calculates the trapping pressure of methane inclusion:

$Z=\frac{\mathrm{PV}}{\mathrm{RT}}=\frac{P_r{V}_r}{T_r}=1+\frac{B}{V_r}+\frac{C}{V_r^2}+\frac{D}{V_r^4}+\frac{E}{V_r^5}+\frac{F}{V_r^2}(\mathrm{\β}+\frac{\mathrm{\γ}}{V_r^2})\exp (-\frac{\mathrm{\γ}}{V_r^2})---\left(3\right),$ Wherein:

$B=a_1+\frac{a_2}{T_r^2}+\frac{a_3}{T_r^3};C=a_4+\frac{a_5}{T_r^2}+\frac{a_6}{T_r^3};D=a_7+\frac{a_8}{T_r^2}+\frac{a_9}{T_r^3};E=a_{10}+\frac{a_{11}}{T_r^2}+\frac{a_{12}}{T_r^3};$

$F=\frac{\mathrm{\α}}{T_r^3};P_r=\frac{P}{P_c};T_r=\frac{T}{T_c};V_r=\frac{V}{V_c};V_c=\frac{{\mathrm{RT}}_c}{P_c};$

In formula, P is pressure (bar); T is temperature (K); R is gas law constant (R=0.08314467bardm ³k ^-1mol ^-1); V is molar volume (dm ³/ mol), can be calculated by the density p of methane inclusion and molal weight; Z is compressibility factor; Pr, Tr are respectively reduced pressure, reduced temperature, and its dimension is 1; Pc, Tc are respectively emergent pressure and critical temperature, unit and P, T-phase with; a ₁=0.0872553928; a ₂=-0.752599476; a ₃=0.375419887; a ₄=0.0107291342; a ₅=0.0054962636; a ₆=-0.0184772802; a ₇=0.000318993183; a ₈=0.000211079375; a ₉=0.0000201682801; a ₁₀=-0.0000165606189; a ₁₁=0.000119614546; a ₁₂=-0.000108087289; α=0.0448262295; β=0.75397; γ=0.077167.

Introduce the embodiment of the present invention in order to clearer, introduced from the using method of the embodiment of the present invention below.

In the shale gas well quartz vein of burnt masonry dam shale gas field, pure methane inclusion trapping pressure calculates.

In conjunction with Arthroscopic characteristic, step 1: obtain the inclusion thin slice containing quartz vein shale samples, carry out Raman microprobe test to the host minerals of catching pure methane inclusion, judges that host minerals composition is as quartz.

See Fig. 2, then the mineral fluid inclusions of catching in sample is carried out to the Raman microprobe test of 300 gratings: the fluid inclusion of mensuration has pentagon.At the 0-4000cm of 300 gratings ^-1in scan light spectrogram, 2917.21cm ^-1for the methane Raman scattering peak that intensity is very high, except the methane scattering peak of high strength, other obvious Raman peaks is the Raman scattering peak of reflection host minerals quartz, and inclusion fluid components is single, illustrates that fluid inclusion is pure methane inclusion.

See Fig. 3, the 1800 grating pair pure methane inclusions being furnished with the correction of Ne lamp are then utilized to carry out 2750-3080cm ^-1laser Raman spectroscopy scans among a small circle, for obtaining methane inclusion methane laser raman scattering peak v (v _meas) and two of Ne lamp measure peak position v _meas; The methane Raman scattering peak v of the pure methane inclusion measured ₁(v _meas) be 2908.470cm ^-1, Ne ₁raman scattering peak v _measfor 2834.46cm ^-1, Ne ₂raman scattering peak v _measfor 3005.76cm ^-1, bring formula into

$v_{\mathrm{corr}}^{{\mathrm{CH}}_4}=\frac{1}{2}\left\{\right[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_1,2836.98}-v_{\mathrm{meas}}^{{\mathrm{Ne}}_1,2836.98})]+[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_2,3008.13}-v_{\mathrm{neas}}^{{\mathrm{Ne}}_2,3008.13})\left]\right\}$ (1) the real methane Raman scattering peak v of pure methane inclusion is calculated ₁(v _corr) be 2910.919cm ^-1.

Step 2: according to methane Raman scattering peak v ₁with the relation formula ρ (g/cm of methane inclusion density p ³)=-5.17331 × 10 ^-5d ³+ 5.53081 × 10 ^-4d ²-3.51387 × 10 ^-2d (2), calculating pure methane inclusion density is 0.271g/cm ³.Wherein: v in formula (2) ₀value adopts key lab of structure and hydrocarbon resources education portion of China Geological Univ. Wuhan laser raman Laboratory Calibration value.

Step 3: the solution-air two-phase saline inclusion of fluid inclusion microexamination searching and the symbiosis of methane inclusion, then fluid inclusion microthermometry is carried out, obtain the solution-air two-phase saline inclusion homogenization temperature with the symbiosis of methane inclusion, namely for methane inclusion catch temperature, for 216.3-227.2 DEG C, what represent methane inclusion for solution-air two-phase saline inclusion homogenization temperature minimum 216.3 DEG C catches temperature.

Step 4: by pure methane inclusion density 0.271g/cm ³with catch temperature 216.3 DEG C and bring formula into $Z=\frac{\mathrm{PV}}{\mathrm{RT}}=\frac{P_r{V}_r}{T_r}=1+\frac{B}{V_r}+\frac{C}{V_r^2}+\frac{D}{V_r^4}+\frac{E}{V_r^5}+\frac{F}{V_r^2}(\mathrm{\β}+\frac{\mathrm{\γ}}{V_r^2})\exp (-\frac{\mathrm{\γ}}{V_r^2})---\left(3\right),$ Can obtain the trapping pressure of pure methane inclusion, be 117.70MPa.

It should be noted last that, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to example to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not departing from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of right of the present invention.

Claims (5)

1. obtain a method for pure methane inclusion trapping pressure, it is characterized in that, comprise the following steps:

Obtain pure methane inclusion methane laser raman scattering peak v ₁;

According to described methane laser raman scattering peak v ₁obtain the density of described pure methane inclusion;

What obtain the solution-air two-phase saline inclusion formed the same period with described pure methane inclusion catches temperature;

Pure methane inclusion trapping pressure is obtained according to described density and described temperature of catching.

2. method according to claim 1, is characterized in that, described acquisition pure methane inclusion methane laser raman scattering peak v ₁comprise:

Obtain the inclusion thin slice of rock sample, Raman microprobe test is carried out to the host minerals of catching pure methane inclusion, judges host minerals composition in conjunction with Arthroscopic characteristic;

The mineral fluid inclusions of catching in sample is carried out to the Raman microprobe test of 300 gratings;

1800 gratings are carried out to pure methane inclusion, Ne lamp correct Raman microprobe test, for obtaining methane inclusion methane laser raman scattering peak v _measwith two measurement peak position v of Ne lamp _meas;

According to the nonlinear relationship of optical splitter, utilize the laser Raman spectroscopy base peak Ne of neon lamp ₁, i.e. v _realfor 2836.9888cm ^-1, and base peak Ne ₂, i.e. v _realfor 3008.12744cm ^-1to the methane Raman scattering peak v of methane inclusion _meascorrect, and then determine methane inclusion real laser raman scattering peak v accurately _corr, methane inclusion real Raman scattering peak v _corr, methane inclusion measure Raman scattering peak v _meas, neon lamp peak, i.e. Ne ₁and Ne ₂base peak position v _realwith measurement peak position v _measthere is following relation:

$v_{\mathrm{corr}}^{{\mathrm{CH}}_4}=\frac{1}{2}\left\{\right[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_1,2836.98}-v_{\mathrm{meas}}^{{\mathrm{Ne}}_1,2836.98})]+[v_{\mathrm{meas}}^{{\mathrm{CH}}_4}+(v_{\mathrm{real}}^{{\mathrm{Ne}}_2,3008.13}-v_{\mathrm{meas}}^{{\mathrm{Ne}}_2,3008.13})\left]\right\}$ (1), methane inclusion methane laser raman scattering peak v can be calculated accurately according to formula (1) ₁, unit is cm ^-1.

3. method according to claim 1, is characterized in that, described in obtain methane inclusion density comprise:

By measuring methane Raman scattering peak v under different pressures condition in glass capillary system ₁displacement, obtains methane Raman scattering peak v ₁the relation of displacement, methane density and pressure, methane inclusion methane Raman scattering peak v ₁there is linear relationship in displacement and methane inclusion density p:

ρ (g/cm ³)=-5.17331 × 10 ^-5d ³+ 5.53081 × 10 ^-4d ²-3.51387 × 10 ^-2d (2), related coefficient is 0.9987, wherein: D=v ₁-v ₀, v ₁the methane Raman scattering peak of the actual measurement methane inclusion after neon lamp corrects, v ₀for when pressure close to 0 time the methane Raman scattering peak of methane inclusion;

By methane Raman scattering peak v ₁relation formula (2) with methane inclusion density p, calculates methane inclusion density, and unit is g/cm ³.

4. method according to claim 1, is characterized in that, the temperature of catching of the solution-air two-phase saline inclusion that described acquisition and pure methane inclusion are formed the same period comprises:

Methane inclusion and simultaneously catching with the solution-air two-phase saline inclusion of methane inclusion symbiosis, inclusion is trapped in the not mixing binary system of saturated methane, and what the homogenization temperature of solution-air two-phase saline inclusion can represent methane inclusion catches temperature.

5. method according to claim 1, is characterized in that, described in obtain pure methane inclusion trapping pressure and comprise:

That sets up is applicable to CH ₄the state equation of system calculates the trapping pressure of methane inclusion:

$Z=\frac{\mathrm{PV}}{\mathrm{RT}}=\frac{P_r{V}_r}{T_r}=1+\frac{B}{V_r}+\frac{C}{V_r^2}+\frac{D}{V_r^4}+\frac{E}{V_r^5}+\frac{E}{V_r^2}(\mathrm{\β}+\frac{\mathrm{\γ}}{V_r^2})\exp (-\frac{\mathrm{\γ}}{V_r^2})---\left(3\right),$ Wherein:

$B=a_1+\frac{a_2}{T_r^2}+\frac{a_3}{T_r^3};C=a_4+\frac{a_5}{T_r^2}+\frac{a_6}{T_r^3};D=a_7+\frac{a_8}{T_r^2}+\frac{a_9}{T_r^3};E=a_{10}+\frac{a_{11}}{T_r^2}+\frac{a_{12}}{T_r^3};$

$F=\frac{\mathrm{\α}}{T_r^3};P_r=\frac{P}{P_c};T_r=\frac{T}{T_c};V_r=\frac{V}{V_c};V_c=\frac{{\mathrm{RT}}_c}{P_c};$ In formula, P is pressure (bar); T is temperature (K); R is gas law constant (R=0.08314467bardm ³k ^-1mol ^-1); V is molar volume (dm ³/ mol), can be calculated by the density p of methane inclusion and molal weight; Z is compressibility factor; Pr, Tr are respectively reduced pressure, reduced temperature, and its dimension is 1; Pc, Tc are respectively emergent pressure and critical temperature, unit and P, T-phase with; a ₁=0.0872553928; a ₂=-0.752599476; a ₃=0.375419887; a ₄=0.0107291342; a ₅=0.0054962636; a ₆=-0.0184772802; a ₇=0.000318993183; a ₈=0.000211079375; a ₉=0.0000201682801; a ₁₀=-0.0000165606189; a ₁₁=0.000119614546; a ₁₂=-0.000108087289; α=0.0448262295; β=0.75397; γ=0.077167.