CN104502236A - Method for measuring diffusion coefficient and equilibrium concentration of CO2 in process of diffusion from water phase to oil phase - Google Patents

Abstract

The invention relates to a method for measuring the diffusion coefficient and the equilibrium concentration of CO2 in the process of diffusion from a water phase to an oil phase. According to the method, the water-phase saturated CO2 at the bottom of a U-shaped pipe is formed into saturated carbonated water; CO2 is injected into the end a of the U-shaped pipe, and crude oil is injected into the end b of the U-shaped pipe; as CO2 in the water phase diffuses to the oil phase, CO2 in the saturated carbonated water is not saturated again, and therefore, the gaseous-phase CO2 is dissolved in the carbonated water. Pressure change due to the diffusion of the CO2 to the carbonated water is measured, and then the diffusion coefficient of the CO2 during diffusion from the water phase to the oil phase and the equilibrium concentration of the CO2 in the crude oil after equilibrium can be obtained in combination with a pressure drop formula. According to the method, the method for measuring the diffusion coefficient of the CO2 in the process of diffusion from the water phase to the oil phase by use of an improved PVT pressure drop method is provided for the first time, and the method is simple to operate and clear in principle; the diffusion coefficient can be obtained without directly measuring the concentration change of CO2 in the process of diffusion from the water phase to the oil phase; the method is significant for studying the migration and distribution of CO2 between the water phase and the oil phase and guiding oil-gas field development.

Description

A kind of measurement CO 2from aqueous phase to the method for coefficient of diffusion oil phase diffusion process and equilibrium concentration

Technical field

The present invention relates to a kind of measurement CO ₂from aqueous phase to the method for coefficient of diffusion oil phase diffusion process and equilibrium concentration, belong to the technical field of petrochemical complex.

Background technology

In recent years, require day by day to improve to reduction of greenhouse gas discharge all over the world, CO ₂the process of waste gas becomes society gradually urgently in the face of the difficult problem with solution.Oil field processes CO ₂most effectual way be injected into oil gas field exactly, not only sealed CO up for safekeeping ₂, also effectively improve the recovery ratio of oil gas field.Due to CO ₂there is unique phase behavior and oil recovery mechanism, make it more and more extensive in the application of LOW PERMEABILITY RESERVOIR, heavy crude reservoir exploitation.

At CO ₂drive, CO ₂handle up and CO ₂in water-air two-phase flow oil displacement process, crude oil, local water or injection water and CO ₂after contact, resident fluid will form oil gas water three phase system, CO ₂diffusion mass transfer between oil phase, aqueous phase and water-oil phase, is dissolved in the CO in crude oil ₂crude oil volumetric expansion can be made, increase resilient urging force, reduce former oil viscosity and oil water interfacial tension simultaneously, improve oil and water mobility ratio, make the crude oil in reservoir be easier to extraction.Research CO ₂at the quality transfer law of water-oil phase, inject CO in prediction ₂migration and redistribution feature in oil reservoir, improve oil recovery factor, instruct in effective exploitation of oil reservoir and play an important role.Therefore, CO is measured ₂in the alternate coefficient of diffusion of profit and equilibrium concentration for CO ₂the development of technology of reservoir sweep is significant.

The measuring method of coefficient of diffusion mainly contains the direct method of measurement and the indirect method of measurement, and due to direct method of measurement complicated operation, sampling requirement is high, therefore, the indirect method of measurement that adopts measures molecular diffusivity more both at home and abroad, and wherein, pressure breakdown method is indirect measurement method comparatively conventional at present.More representational pressure breakdown method has: (1) 1996 year, the constant volume PVT cylinder test solution-air coefficient of diffusion method that Riazi sets up; (2) 2000 years, Zhang etc. improved on the basis of Riazi test method, and test CO ₂coefficient of diffusion in dirty oil; (3) 2010 years, Guo's equality determined High Temperature High Pressure CO ₂-crude oil molecular diffusivity.

Chinese patent literature CN102706779A discloses a kind of measurement CO ₂in the method for diffusion coefficient of rock.This invention is by measuring CO ₂the change of gaseous tension obtains CO ₂at diffusion coefficient of rock.In addition, CO ₂equilibrium concentration in the liquid phase mainly directly measures by acid-base neutralization method or gas-liquid separation the CO be dissolved in a certain amount of liquid phase ₂content, thus obtain the CO dissolved in the liquid phase ₂concentration.

Above-mentioned more representational pressure breakdown method and Chinese patent literature CN102706779A disclosed measurement CO ₂the method of diffusion coefficient of rock be all for gas-liquid two-phase between molecular diffusivity, at present, for CO ₂mass transfer diffusion research, particularly CO between immiscible water-oil phase ₂from aqueous phase to the mensuration of coefficient of diffusion oil phase diffusion process, yet there are no relevant report both at home and abroad.

Summary of the invention

Summary of the invention

For the deficiencies in the prior art, the invention discloses a kind of measurement CO ₂from aqueous phase to the method for coefficient of diffusion oil phase diffusion process and equilibrium concentration.

The present invention divides oil removal, gas, water three-phase by U-tube, by saturated for distilled water bottom U-tube CO ₂, form saturated carbon sour water, CO is injected in U-tube one end ₂, the other end injects crude oil, due to the CO in carbonated water ₂to oil phase diffusion, carbonated water is no longer saturated, thus impels gas phase CO ₂be dissolved in carbonated water.Utilize gaseous state CO ₂the pressure caused after being dissolved in saturated carbon sour water variation relation in time, according to the coefficient of diffusion mathematical model that Riazi and Zhang sets up, extrapolates the CO in saturated carbon sour water indirectly ₂to coefficient of diffusion and the CO of oil phase migration ₂equilibrium concentration in oil phase.

Technical scheme of the present invention is as follows:

A kind of CO ₂from aqueous phase to the measuring method of coefficient of diffusion oil phase diffusion process and equilibrium concentration, wherein, the method practice measurement mechanism, described measurement mechanism comprises the U-tube be vertically fixedly installed, described U-tube comprises a end and b end, and described a end and described b hold all opening up; Concrete steps comprise:

(1) described U-tube volume V is measured ₁and described U-tube internal diameter cross-sectional area A ₁, check the impermeability of whole described measurement mechanism;

(2) be that the distilled water of T injects described U-tube by temperature, make to be full of distilled water in described U-tube, the span of described T is 25 DEG C-90 DEG C;

(3) check valve connecting backpressure pump is connected to described U-tube b to hold, be communicated with back pressure, described backpressure pump is set to predetermined pressure P ₀, described P ₀span be 0.1MPa-25MPa;

(4) by CO ₂inject described U-tube from described a end, injected slurry volume is V ₂, described V ₂span is 1/4V ₁-1/3V ₁, injection process keeps pressure P ₀constant;

(5) airtight described U-tube, by the initial balance pressure P in U-tube described in pressure transducer record ₁, described initial balance pressure P ₁pressure when the pressure drop amplitude referring in described U-tube is no more than 1KPa in described U-tube;

In step (5), CO ₂after injection, described U-tube b end is without CO ₂assemble, distilled water is saturated CO gradually ₂;

(6) check valve connecting backpressure pump is connected to described U-tube a to hold, be communicated with back pressure, described backpressure pump is set to described pressure P ₁;

(7) crude oil is injected described U-tube from described b end, injected slurry volume is V ₃, V ₃span is 1/3V ₂-2/3V ₂, injection process keeps pressure P ₁constant;

In step (7), after crude oil injects, described U-tube a end is assembled without crude oil, and the injection of crude oil causes pressure increase in described U-tube, because described U-tube a end exists back pressure P ₁, cause having and inject the isopyknic CO of crude oil ₂discharge from described a end, thus the pressure maintained in described U-tube is constant;

(8) airtight described U-tube, utilizes pressure P (t) t delta data in time in U-tube described in pressure transducer record, measures final equalized pressure P _eq, the pressure when pressure drop amplitude that described final equalized pressure refers in described U-tube is no more than 1KPa in described U-tube; Calculate different time t downforce P (t) and final equalized pressure P _eqbetween pressure reduction △ P and the logarithm Ln (△ P) of △ P, obtain pressure P (t) in described U-tube, final equalized pressure P _eq, the logarithm Ln (△ P) of △ P and the relation table of time t; Be depicted as pressure vs time diagram and pressure reduction logarithm-time chart; Be in final equilibrium state in described U-tube, calculating crude oil height in described U-tube is: cO in described U-tube ₂be highly:

(9) in conjunction with the coefficient of diffusion mathematical model that Riazi and Zhang sets up:

$\mathrm{In}[P\left(t\right)-P_{\mathrm{eq}}]=\mathrm{In}\frac{{8z}_g{\mathrm{RTAC}}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}-D{\left(\frac{\mathrm{\π}}{2L}\right)}^{2}t---\left(I\right)$

In formula (I), the force value that P (t) is t, unit is Pa; P _eqfor the final equalized pressure obtained in step (8), unit is Pa; z _gfor CO ₂compressibility factor; R is gas law constant, R=8.314m ³paK ^-1mol ^-1; T is step (2) described temperature T, and unit is DEG C; A is described U-shaped internal diameter cross-sectional area A ₁, unit is m ²; C _eqfor CO ₂the equilibrium concentration spread from aqueous phase to oil phase, unit is mol/L; L is the crude oil height injecting described U-tube in step (8), and unit is m; V _gfor injecting the CO in described U-tube ₂volume, unit is m ³; D is coefficient of diffusion, and unit is m ²/ s; T is diffusion time, and unit is s;

By formula (I) known pressure reduction logarithm Ln [P (t)-P _eq] and time t linear correlation, therefore, linear fit is carried out to pressure reduction logarithm-time chart, obtains the slope k in matching formula and intercept a, can obtain according to formula (I):

Slope $k=D{\left(\frac{\mathrm{\π}}{2L}\right)}^2---\left(\mathrm{II}\right)$

That is: $D=\frac{{4L}^{2}k}{{\mathrm{\π}}^2}---\left(\mathrm{III}\right)$

According to formula (III), CO can be tried to achieve ₂from aqueous phase to the diffusion coefficient D of oil phase diffusion process;

Intercept $a=\mathrm{In}\frac{{8z}_g{\mathrm{RTAC}}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}---\left(\mathrm{IV}\right)$

That is: $C_{\mathrm{eq}}=\frac{e^a{\mathrm{\π}}^2{V}_g}{{8z}_g\mathrm{RTAL}}=\frac{e^a{\mathrm{\π}}^2{h}_g}{{8z}_g\mathrm{RTL}}=\frac{e^a{\mathrm{\π}}^2{h}_g{\mathrm{\ρ}}_g}{8\mathrm{PML}}---\left(V\right)$

In formula (V), h _gfor injecting the CO of described U-tube in step (8) ₂highly, unit is m; P is the mean pressure in test process, unit is Pa; ρ _gfor CO under mean pressure and corresponding temperature ₂density, unit is kg/m ³, CO under the different Temperature-pressure Conditions that its value reference National Institute of Standards and Technology NIST provides ₂density value; M is CO ₂molal weight, M=44 × 10 ^-3kg/mol;

According to formula (V), try to achieve CO ₂the equilibrium concentration C spread from aqueous phase to oil phase _eq.

Preferred according to the present invention, described measurement mechanism also comprises the CO be flexibly connected with described U-tube respectively ₂gas tank, distillation water pot and petroleum tank, described CO ₂gas tank, described distillation water pot and described petroleum tank connect constant-flux pump respectively.

Utilize described constant-flux pump by CO ₂cO in gas tank ₂, distilled water in distillation water pot and crude oil in petroleum tank pumps into described U-tube respectively.

Preferred according to the present invention, inject CO to described U-tube ₂, before distilled water and crude oil, to described CO ₂gas tank, described distillation water pot, described petroleum tank and described U-tube carry out vacuumizing process.

Wherein, the reasoning process of formula I is:

With reference to the pressure decline method that Zhang (2000) improves, meet following assumed conditions:

1. CO ₂diffusion process liquid does not expand, and gas-water interface and oil-water interface position remain unchanged;

2. there is not resistance to mass tranfer in gas-water interface;

3. in same group of system of determination process, CO ₂compressibility factor Z is constant;

4. CO ₂obviously do not change because of the change of concentration from aqueous phase to diffusion coefficient D oil phase diffusion process;

5. crude oil is non-volatile;

6. CO in water ₂all the time state of saturation is maintained.

According to Fick's second law, be can be calculated by semiinfinite Mass Transfer Model:

$\frac{\∂C(x,t)}{\∂t}=D\frac{{\∂}^{2}C(x,t)}{{\∂x}^2}---\left(\mathrm{VI}\right)$

Boundary condition and starting condition are:

C(x,t)Ι _t＝0＝0(0≤x≤L) (Ⅶ)

C(x,t)Ι _t＝0＝C _eq＝C*(P _eq)(t≥0) (Ⅷ)

$\frac{\∂C(x,t)}{\∂x}{I}_{x=L}=0(t\≥0)---\left(\mathrm{IX}\right)$

$C(x,t)I_{t=0}=C_{\mathrm{eq}}-\frac{{4C}_{\mathrm{eq}}}{\mathrm{\π}}\underset{n=0}{\overset{\∞}{\mathrm{\Σ}}}\frac{1}{2n+1}\×\sin \left(\frac{(2n+1)\mathrm{\πx}}{2L}\right)\×\exp (-\frac{{(2n+1)}^2{\mathrm{\π}}^{2}D}{{4L}^2})---\left(X\right)$

Wherein, C (x, t) for the gas concentration of x position, t in aqueous phase, unit be mol/L.

According to conservation of matter equation:

$\frac{V}{z_g\mathrm{RT}}\frac{\mathrm{dP}}{\mathrm{dt}}=-\mathrm{DA}\left(\frac{\mathrm{dx}}{\mathrm{dz}}\right)---\left(\mathrm{XI}\right)$

Carry out necessary simplify processes, obtain the relation of pressure and time:

$P\left(t\right)=P_{\mathrm{eq}}+\frac{{8z}_g{\mathrm{RTAC}}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}\exp [-D{\left(\frac{\mathrm{\π}}{2L}\right)}^{2}t]---\left(\mathrm{XII}\right)$

Above formula transplants and final formula (I) of taking the logarithm.

Beneficial effect of the present invention is:

The present invention proposes first and utilizes the PVT pressure decline method improved to measure CO ₂from aqueous phase to the coefficient of diffusion oil phase diffusion process, the method is simple to operate, clear principle, need not by directly measuring CO ₂can coefficient of diffusion be obtained from aqueous phase to the concentration change oil phase diffusion process, in addition, can also CO be obtained while asking for coefficient of diffusion ₂equilibrium concentration in oil phase, therefore, the present invention is for research CO ₂at the alternate moving distribution of profit with instruct oil-gas field development significant.

Accompanying drawing explanation

Fig. 1 is described U-tube structural representation;

In Fig. 1,1, a end; 2, b end; 3, CO ₂; 4, oil phase; 5, aqueous phase;

Fig. 2 is pressure vs time diagram;

Fig. 3 is pressure reduction logarithm-time chart.

Embodiment

According to embodiment and Figure of description, the present invention is described in detail below, but is not limited thereto.

Embodiment 1

A kind of CO ₂from aqueous phase to the measuring method of coefficient of diffusion oil phase diffusion process and equilibrium concentration, wherein, the method practice measurement mechanism, described measurement mechanism comprises the U-tube be vertically fixedly installed, described U-tube comprises a end 1 and b end 2, described a end 1 and described b and holds 2 all opening up; Concrete steps comprise:

(1) described U-tube volume V is measured ₁for 250mL and described U-tube internal diameter cross-sectional area A ₁for 8cm ², check the impermeability of whole described measurement mechanism;

(2) be that the distilled water of T injects described U-tube by temperature, make to be full of distilled water in described U-tube, the value of described T is 50 DEG C;

(3) check valve connecting backpressure pump is connected to described U-tube b and holds 2, be communicated with back pressure, described backpressure pump is set to predetermined pressure P ₀, described P ₀value be 6MPa;

(4) by CO ₂inject described U-tube from described a end 1, injected slurry volume is V ₂, described V ₂value is 80mL, and injection process keeps pressure P ₀constant;

(5) airtight described U-tube, by the initial balance pressure P in U-tube described in pressure transducer record ₁for 4.758MPa, described initial balance pressure P ₁pressure when the pressure drop amplitude referring in described U-tube is no more than 1KPa in described U-tube;

In step (5), CO ₂after injection, described U-tube b end 2 is without CO ₂assemble, distilled water is saturated CO gradually ₂;

(6) check valve connecting backpressure pump is connected to described U-tube a and holds 1, be communicated with back pressure, described backpressure pump is set to described pressure P ₁;

(7) crude oil is injected described U-tube from described b end 2, injected slurry volume is V ₃, V ₃value is 32mL, and injection process keeps pressure P ₁constant;

In step (7), after crude oil injects, described U-tube a end 1 is assembled without crude oil, and the injection of crude oil causes pressure increase in described U-tube, because described U-tube a end 1 exists back pressure P ₁, cause having and inject the isopyknic CO of crude oil ₂discharge from described a end 1, thus the pressure maintained in described U-tube is constant;

(8) airtight described U-tube, utilizes pressure P (t) t delta data in time in U-tube described in pressure transducer record, measures final equalized pressure P _eq, the pressure when pressure drop amplitude that described final equalized pressure refers in described U-tube is no more than 1KPa in described U-tube; Calculate different time t downforce P (t) and final equalized pressure P _eqbetween pressure reduction △ P and the logarithm Ln (△ P) of △ P, obtain pressure P (t) in described U-tube, final equalized pressure P _eq, the logarithm Ln (△ P) of △ P and the relation table of time t, as shown in table 1; Be depicted as pressure vs time diagram (Fig. 2) and pressure reduction logarithm-time chart (Fig. 3); Be in final equilibrium state in described U-tube, calculating crude oil height in described U-tube is: $L=\frac{V_3}{A_1}=\frac{32}{8}\mathrm{cm}=0.04m;$ CO in described U-tube ₂be highly: $h_g=\frac{V_2-V_3}{A_1}=\frac{80-32}{8}\mathrm{cm}=0.06m;$

(9) in conjunction with the coefficient of diffusion mathematical model that Riazi and Zhang sets up:

$\mathrm{In}[P\left(t\right)-P_{\mathrm{eq}}]=\mathrm{In}\frac{{8z}_g{\mathrm{RTAC}}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}-D{\left(\frac{\mathrm{\π}}{2L}\right)}^{2}t---\left(I\right)$

In formula (I), the force value that P (t) is t, unit is Pa; P _eqfor the final equalized pressure obtained in step (8), unit is Pa; z _gfor CO ₂compressibility factor; R is gas law constant, R=8.314m ³paK ^-1mol ^-1; T is step (2) described temperature T, and unit is DEG C; A is described U-shaped internal diameter cross-sectional area A ₁, unit is m ²; C _eqfor CO ₂the equilibrium concentration spread from aqueous phase to oil phase, unit is mol/L; L is the crude oil height injecting described U-tube in step (8), and unit is m; V _gfor injecting the CO in described U-tube ₂volume, unit is m ³; D is coefficient of diffusion, and unit is m ²/ s; T is diffusion time, and unit is s;

By formula (I) known pressure reduction logarithm Ln [P (t)-P _eq] and time t linear correlation, therefore, linear fit is carried out to the steady section in described Fig. 3, obtains slope k=0.0000462 of fitting a straight line, intercept a=12.555, can obtain according to formula (I):

Slope $k=D{\left(\frac{\mathrm{\π}}{2L}\right)}^2=0.0000462---\left(\mathrm{II}\right)$

That is: $D=\frac{{4L}^{2}k}{{\mathrm{\π}}^2}=\frac{4\×{0.04}^2\×0.0000462}{{\mathrm{\π}}^2}=3.0\×{10}^{-8}{m}^2/s;---\left(\mathrm{III}\right)$

According to formula (III), CO can be tried to achieve ₂from aqueous phase to diffusion coefficient D=3.0 × 10 of oil phase diffusion process ^-8m ²/ s;

Intercept $a=\mathrm{In}\frac{{8z}_g{\mathrm{RTAC}}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}---\left(\mathrm{IV}\right)$

That is: $C_{\mathrm{eq}}=\frac{e^a{\mathrm{\π}}^2{h}_g{\mathrm{\ρ}}_g}{8\mathrm{PML}}=\frac{e^{12.555}\×{\mathrm{\π}}^2\×0.06\×94.27}{8\×4609000\×0.044\×0.04\×1000}=0.244\mathrm{mol}/L;---\left(V\right)$

In formula (V), h _gfor injecting the CO of described U-tube in step (8) ₂highly, unit is m; P is the mean pressure in test process, ρ _g=94.27kg/m ³, be CO at mean pressure and 50 DEG C ₂density; M is CO ₂molal weight, M=44 × 10 ^-3kg/mol;

According to formula (V), try to achieve CO ₂the equilibrium concentration C spread from aqueous phase to oil phase _eq=0.244mol/L;

As can be seen from Figure 3 spread initial period pressure drop very fast, not linear, this is mainly because this stage is diffusion unstable state state; When reaching diffusion lower state, logarithm and the time of pressure reduction are linear.

Table 2 is each parameter value in embodiment 1.

Table 1

Table 2

Embodiment 2

Measuring method according to embodiment 1, its difference is, described measurement mechanism also comprises the CO be flexibly connected with described U-tube respectively ₂gas tank, distillation water pot and petroleum tank, described CO ₂gas tank, described distillation water pot and described petroleum tank connect constant-flux pump respectively.

Utilize described constant-flux pump by CO ₂cO in gas tank ₂, distilled water in distillation water pot and crude oil in petroleum tank pumps into described U-tube respectively.

Embodiment 3

Measuring method according to embodiment 1 or 2, its difference is, injects CO to described U-tube ₂, before distilled water and crude oil, to described CO ₂gas tank, described distillation water pot, described petroleum tank and described U-tube carry out vacuumizing process.

Claims (3)

1. a CO ₂from aqueous phase to the measuring method of coefficient of diffusion oil phase diffusion process and equilibrium concentration, it is characterized in that, wherein, the method practice measurement mechanism, described measurement mechanism comprises the U-tube be vertically fixedly installed, described U-tube comprises a end and b end, and described a end and described b hold all opening up; Concrete steps comprise:

(1) described U-tube volume V is measured ₁and described U-tube internal diameter cross-sectional area A ₁, check the impermeability of whole described measurement mechanism;

(2) be that the distilled water of T injects described U-tube by temperature, make to be full of distilled water in described U-tube, the span of described T is 25 DEG C-90 DEG C;

(3) check valve connecting backpressure pump is connected to described U-tube b to hold, be communicated with back pressure, described backpressure pump is set to predetermined pressure P ₀, described P ₀span be 0.1MPa-25MPa;

(4) by CO ₂inject described U-tube from described a end, injected slurry volume is V ₂, described V ₂span is 1/4V ₁-1/3V ₁, injection process keeps pressure P ₀constant;

(5) airtight described U-tube, by the initial balance pressure P in U-tube described in pressure transducer record ₁, described initial balance pressure P ₁pressure when the pressure drop amplitude referring in described U-tube is no more than 1KPa in described U-tube;

(6) check valve connecting backpressure pump is connected to described U-tube a to hold, be communicated with back pressure, described backpressure pump is set to described pressure P ₁;

(7) crude oil is injected described U-tube from described b end, injected slurry volume is V ₃, V ₃span is 1/3V ₂-2/3V ₂, injection process keeps pressure P ₁constant;

(8) airtight described U-tube, utilizes pressure P (t) t delta data in time in U-tube described in pressure transducer record, measures final equalized pressure P _eq, the pressure when pressure drop amplitude that described final equalized pressure refers in described U-tube is no more than 1KPa in described U-tube; Calculate different time t downforce P (t) and final equalized pressure P _eqbetween pressure reduction △ P and the logarithm Ln (△ P) of △ P, obtain pressure P (t) in described U-tube, final equalized pressure P _eq, the logarithm Ln (△ P) of △ P and the relation table of time t; Be depicted as pressure vs time diagram and pressure reduction logarithm-time chart; Be in final equilibrium state in described U-tube, calculating crude oil height in described U-tube is: cO in described U-tube ₂be highly:

(9) in conjunction with the coefficient of diffusion mathematical model that Riazi and Zhang sets up:

$\mathrm{In}[P\left(t\right)-P_{\mathrm{eq}}]=\mathrm{In}\frac{8z_g\mathrm{RTA}{C}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}-D{\left(\frac{\mathrm{\π}}{2L}\right)}^{2}t---\left(I\right)$

In formula (I), the force value that P (t) is t, unit is Pa; P _eqfor the final equalized pressure obtained in step (8), unit is Pa; z _gfor CO ₂compressibility factor; R is gas law constant, R=8.314m ³paK ^-1mol ^-1; T is step (2) described temperature T, and unit is DEG C; A is described U-shaped internal diameter cross-sectional area A ₁, unit is m ²; C _eqfor CO ₂the equilibrium concentration spread from aqueous phase to oil phase, unit is mol/L; L is the crude oil height injecting described U-tube in step (8), and unit is m; V _gfor injecting the CO in described U-tube ₂volume, unit is m ³; D is coefficient of diffusion, and unit is m ²/ s; T is diffusion time, and unit is s;

By formula (I) known pressure reduction logarithm Ln [P (t)-P _eq] and time t linear correlation, therefore, linear fit is carried out to pressure reduction logarithm-time chart, obtains the slope k in matching formula and intercept a, can obtain according to formula (I):

Slope $k=D{\left(\frac{\mathrm{\π}}{2L}\right)}^2---\left(\mathrm{II}\right)$

That is: $D=\frac{4L^{2}k}{{\mathrm{\π}}^2}---\left(\mathrm{III}\right)$

According to formula (III), CO can be tried to achieve ₂from aqueous phase to the diffusion coefficient D of oil phase diffusion process;

Intercept $a=\mathrm{In}\frac{8z_g\mathrm{RTA}{C}_{\mathrm{eq}}L}{V_g{\mathrm{\π}}^2}---\left(\mathrm{IV}\right)$

That is: $C_{\mathrm{eq}}=\frac{e^a{\mathrm{\π}}^2{V}_g}{8z_g\mathrm{RTAL}}=\frac{e^a{\mathrm{\π}}^2{h}_g}{8z_g\mathrm{RTL}}=\frac{e^a{\mathrm{\π}}^2{h}_g{\mathrm{\ρ}}_g}{8\mathrm{PML}}---\left(V\right)$

In formula (V), h _gfor injecting the CO of described U-tube in step (8) ₂highly, unit is m; P is the mean pressure in test process, unit is Pa; ρ _gfor CO under mean pressure and corresponding temperature ₂density, unit is kg/m ³, CO under the different Temperature-pressure Conditions that its value reference National Institute of Standards and Technology NIST provides ₂density value; M is CO ₂molal weight, M=44 × 10 ^-3kg/mol;

According to formula (V), try to achieve CO ₂the equilibrium concentration C spread from aqueous phase to oil phase _eq.

2. measuring method according to claim 1, it is characterized in that, described measurement mechanism also comprises the CO be flexibly connected with described U-tube respectively ₂gas tank, distillation water pot and petroleum tank, described CO ₂gas tank, described distillation water pot and described petroleum tank connect constant-flux pump respectively.

3. measuring method according to claim 2, is characterized in that, injects CO to described U-tube ₂, before distilled water and crude oil, to described CO ₂gas tank, described distillation water pot, described petroleum tank and described U-tube carry out vacuumizing process.