A method for fitting carbon dioxide miscibility pressure in capillary tube experiments considering characteristic points

Abstract

The present application relates to a method for fitting carbon dioxide miscible pressure of capillary tube experiment considering feature points. The method comprises the following steps: drawing a carbon dioxide miscible pressure chart according to the displacement experiment result; determining a BIC binary interaction coefficient according to a high-pressure miscible point, determining a relative permeability curve according to a low-pressure immiscible point, and determining a critical interfacial tension according to a miscible inflection point based on the carbon dioxide miscible pressure chart, so as to determine a fitting sequence of the low-pressure immiscible point, the miscible inflection point and the high-pressure miscible point; calculating an initial parameter of the high-pressure miscible point based on the BIC binary interaction coefficient; and fitting the oil displacement efficiency of the high-pressure miscible point by adjusting the interaction coefficient of carbon dioxide and C7+, fitting the oil displacement efficiency of the low-pressure immiscible point by adjusting the oil displacement efficiency of the relative permeability curve, and fitting the oil displacement efficiency of the miscible inflection point by adjusting the value of the critical interfacial tension, so as to fit the oil displacement efficiency value of the carbon dioxide of the capillary tube experiment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of offshore oil and gas field development engineering, in particular to a method for fitting carbon dioxide miscibility pressure of a slim tube experiment considering feature points. BACKGROUND

[0002] Miscibility mechanism is the most important mechanism for improving oil recovery in carbon dioxide injection flooding technology. In the design of carbon dioxide miscible flooding scheme, accurate characterization of miscibility degree is the key to ensure the accuracy of development effect prediction. At present, the method for characterizing the miscibility degree of carbon dioxide is mainly to fit all experimental points of the slim tube experiment one by one. However, this method has large parameter adjustment range, and the selection of fitting points has great influence on the fitting effect, resulting in large fitting workload. SUMMARY

[0003] In view of the above problems, the purpose of the present application is to provide a method for quickly and efficiently fitting the minimum miscibility pressure curve in the development scheme design stage of offshore low-permeability sandstone oil reservoir carbon dioxide miscible flooding.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] A method for fitting carbon dioxide miscibility pressure of a slim tube experiment considering feature points, comprising:

[0006] drawing a carbon dioxide miscibility pressure chart according to the displacement experiment results;

[0007] determining the BIC binary interaction coefficient according to the high-pressure miscibility point, determining the relative permeability curve according to the low-pressure non-miscibility point, and determining the critical interfacial tension according to the miscibility inflection point, so as to determine the fitting order of the low-pressure non-miscibility point, the miscibility inflection point and the high-pressure miscibility point based on the carbon dioxide miscibility pressure chart;

[0008] calculating the initial parameters of the high-pressure miscibility point based on the BIC binary interaction coefficient; and

[0009] fitting the oil displacement efficiency of the high-pressure miscibility point by adjusting the action coefficient of carbon dioxide and C7+, fitting the oil displacement efficiency of the low-pressure non-miscibility point by adjusting the oil displacement efficiency of the relative permeability curve, and fitting the oil displacement efficiency of the miscibility inflection point by adjusting the value of the critical interfacial tension, so as to fit the carbon dioxide oil displacement efficiency value of the slim tube experiment.

[0010] The displacement experiment adopts the method of laboratory physical simulation, nitrogen or aviation kerosene is injected into the slim tube model, and then the experimental temperature and pressure are kept constant, the nitrogen or aviation kerosene in the slim tube is displaced by the formation crude oil sample, after displacement to 2 times the pore volume, the produced gas-oil ratio and the composition of the sample are measured at the outlet end of the slim tube, and during the displacement process, the produced oil and gas volume, pump reading, experimental pressure and back pressure are recorded once every 0.1-0.15 times the pore volume.

[0011] The initial parameters of the BIC binary interaction coefficient are calculated by fitting the constant volume expansion experiment, saturation pressure experiment, constant volume depletion experiment and viscosity experiment of the well stream.

[0012] The interaction coefficient of carbon dioxide and C7+ component is further optimized by linear interpolation of the interaction coefficient of carbon dioxide and C2-C3 component and C4-C6 component.

[0013] For the high-pressure miscible point, the point with the maximum pressure has the highest miscibility degree, and the oil displacement efficiency is mainly affected by the BIC binary interaction coefficient, and is less affected by the relative permeability curve and the critical surface tension.

[0014] For the low-pressure miscible point, the point with the minimum pressure has the lowest miscibility degree, and the oil displacement efficiency is mainly affected by the relative permeability curve and the BIC binary interaction coefficient, and is less affected by the critical surface tension.

[0015] For the miscible inflection point, the pressure inflection point is at the junction of miscible and non-miscible, and the oil displacement efficiency is mainly affected by the relative permeability curve, the BIC binary interaction coefficient and the critical surface tension.

[0016] The BIC of CO2 and C7+ is 0.12, 0.110, 0.100 and 0.090 respectively.

[0017] The relative permeability curve is 20%, 40%, 60% and 80% respectively.

[0018] The critical surface tension is 0.050, 0.010, 0.200 and 0.300 respectively.

[0019] The present application has the following advantages due to the above technical scheme:

[0020] The method can be used for quickly and efficiently fitting the minimum miscible pressure curve in the development plan design stage of offshore low-permeability sandstone reservoir carbon dioxide miscible flooding. BRIEF DESCRIPTION OF DRAWINGS

[0021] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are intended to depict only preferred embodiments of the application, and therefore should not be considered to limit the scope of the application in any way. Wherever possible, like reference numbers have been used throughout the drawings to depict like components. In the drawings:

[0022] Figure 1 is a schematic diagram of the minimum miscible pressure experiment result of the capillary tube experiment CO2 flooding;

[0023] Figure 2is a high-pressure miscible point analysis schematic diagram of fitting sensitivity of CO2 flooding minimum miscibility pressure of a slim tube experiment;

[0024] Figure 3 is a low-pressure miscible point analysis schematic diagram of fitting sensitivity of CO2 flooding minimum miscibility pressure of a slim tube experiment; and

[0025] Figure 4 is a miscible corner analysis schematic diagram of fitting sensitivity of CO2 flooding minimum miscibility pressure of a slim tube experiment. DETAILED DESCRIPTION

[0026] Exemplary embodiments of the present application will be described in greater detail below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it is understood that the present application can be embodied in various forms without being limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0027] The present application relates to a method for quickly and efficiently fitting a minimum miscibility pressure curve in the development plan design stage of a low-permeability offshore sandstone oil reservoir using carbon dioxide miscible flooding.

[0028] Fitting of the minimum miscibility pressure of carbon dioxide flooding in a slim tube experiment is mainly affected by the bayesian information criterion (BIC) binary interaction coefficient, relative permeability curve, and critical surface tension. By sequentially adjusting and optimizing the fitting experimental point order of the fitting parameters, the fitting difficulty and uncertainty are reduced by being affected by only a single parameter at each fitting point.

[0029] The present application mainly uses laboratory experiments, reservoir engineering, and numerical simulation methods to fit the minimum miscibility pressure of carbon dioxide flooding in a slim tube experiment, including the following steps:

[0030] Step 1. Draw a carbon dioxide flooding minimum miscibility pressure chart

[0031] Using a method of indoor physical simulation, a 15m slim tube model is cleaned, nitrogen or aviation kerosene is injected, and the temperature and pressure are kept constant. The nitrogen or aviation kerosene in the slim tube is displaced by a formation crude oil sample at a displacement speed of 60cm 3 / h-90cm 3h. After displacing to 2 PV, the produced gas-oil ratio, composition of the sample was measured at the outlet end of the slim tube. When the composition was consistent with the formation crude sample, the displacement was stopped. The gas sample required for the experiment was filled in the middle container and allowed to equilibrate at the experimental temperature and pressure. The gas sample was displaced at a constant pressure of 0.05 MPa to 0.1 MPa above the experimental pressure using a syringe pump. After injecting 1.2 PV of the gas sample, the displacement experiment was terminated. During the displacement process, the produced oil, gas volume, pump reading, experimental pressure, and back pressure were recorded every time 0.1 PV to 0.15 PV was injected. The produced oil sample was measured using an automatic liquid collector, and the produced gas volume was measured using a fully automatic gas meter. The carbon dioxide flooding minimum miscibility pressure chart was plotted according to the experimental results, as shown in Figure 1

[0032] Step 2. Propose the fitting order of the carbon dioxide flooding minimum miscibility pressure experimental points of the slim tube experiment

[0033] Through the sensitivity analysis of different experimental points by the numerical simulation method, it is found that the point with the maximum pressure has the highest miscibility degree, and thus the oil displacement efficiency is mainly affected by the BIC binary interaction coefficient, and is less affected by the relative permeability curve and the critical interfacial tension; the point with the minimum pressure has the lowest miscibility degree, and thus the oil displacement efficiency is mainly affected by the relative permeability curve and the BIC binary interaction coefficient, and is less affected by the critical interfacial tension; the pressure inflection point is at the junction of miscible and immiscible phases, and thus the oil displacement efficiency is mainly affected by the relative permeability curve, the BIC binary interaction coefficient, and the critical interfacial tension.

[0034] According to the above analysis, the fitting order of the three characteristic points is determined according to the principle of controlling a single variable, that is, the BIC binary interaction coefficient is determined at the high-pressure miscible point, the relative permeability curve is determined at the low-pressure immiscible point, and the critical interfacial tension is determined at the miscible inflection point.

[0035] Step 3. Determine the initial parameters of the BIC binary interaction coefficient of the high-pressure miscible point

[0036] The constant mass expansion experiment, saturation pressure experiment, constant volume depletion experiment, and viscosity experiment of the well stream were fitted using the FluidModeler software, and the initial value of the BIC binary interaction coefficient was finally calculated, as shown in Table 1.

[0037] The main component in the injected gas is carbon dioxide, and the main component in the crude oil is C7+, and thus the action coefficient of carbon dioxide and C7+ is a key parameter affecting the oil displacement efficiency under the miscible condition. The value at * in Table 1 is linearly interpolated by the action coefficients of carbon dioxide and C2-C3 components and C4-C6 components, and the action coefficient of carbon dioxide and C7+ components is further optimized.

[0038] Table 1 BIC binary interaction coefficient table​

[0039]

[0040]

[0041] Step 4. Fitting the carbon dioxide oil displacement efficiency values for the slim tube experiment

[0042] On the basis of steps 1, 2, 3, the oil displacement efficiency of the high pressure miscibility point is fitted by adjusting the interaction coefficient of carbon dioxide and C7+. The oil displacement efficiency of the low pressure immiscibility point is fitted by adjusting the oil displacement efficiency of the relative permeability curve. The oil displacement efficiency of the miscibility inflection point is fitted by adjusting the value of the critical interfacial tension. The other experimental points are automatically fitted by adjusting the injection pressure after fitting the three characteristic points, as shown in Figure 1 .

[0043] As shown in Figure 2 , for the high pressure miscibility point, the point with the highest pressure has the highest miscibility degree, so the oil displacement efficiency is mainly affected by the BIC binary interaction coefficient, and is less affected by the relative permeability curve and the critical surface tension.

[0044] As shown in Figure 2 (a), the abscissa is the BIC of CO2 and C7+, which is 0.12, 0.110, 0.100 and 0.090 respectively, and the corresponding oil displacement efficiency on the ordinate is 95%, 93%, 82% and 75% respectively, which shows a gradually decreasing trend as a whole;

[0045] As shown in Figure 2 (b), the abscissa is the relative permeability curve, which is 20%, 40%, 60% and 80% respectively, and the corresponding oil displacement efficiency on the ordinate is basically unchanged, remaining at 95%;

[0046] As shown in Figure 2 (c), the abscissa is the critical surface tension, which is 0.050, 0.010, 0.200 and 0.300 respectively, and the corresponding oil displacement efficiency on the ordinate is unchanged, remaining at 95%.

[0047] As shown in Figure 3 , for the low pressure miscibility point, the point with the lowest pressure has the lowest miscibility degree, so the oil displacement efficiency is mainly affected by the relative permeability curve and the BIC binary interaction coefficient, and is less affected by the critical surface tension.

[0048] As shown in Figure 3 (a), the abscissa is the BIC of CO2 and C7+, which is 0.12, 0.110, 0.100 and 0.090 respectively, and the corresponding oil displacement efficiency on the ordinate is 35%, 25%, 20% and 15% respectively, which shows a gradually decreasing trend as a whole;

[0049] As Figure 3 As shown in (b) of the figure, the abscissa is the relative permeability curve, and the corresponding oil displacement efficiency on the ordinate is 20%, 22%, 60% and 80%, respectively, and the overall trend is gradually increasing;

[0050] As Figure 3 As shown in (c) of the figure, the abscissa is the critical surface tension, and the corresponding oil displacement efficiency on the ordinate is 0.050, 0.010, 0.200 and 0.300, respectively, and the oil displacement efficiency is kept at 24%.

[0051] As Figure 4 As shown in the figure, for the miscible phase inflection point, the pressure inflection point is at the junction of miscible phase and non-miscible phase, so the oil displacement efficiency is mainly affected by the relative permeability curve, the BIC binary interaction coefficient and the critical surface tension.

[0052] As Figure 4 As shown in (a) of the figure, the abscissa is the BIC of CO2 and C7+, and the corresponding oil displacement efficiency on the ordinate is 90%, 85%, 80% and 70%, respectively, and the overall trend is gradually decreasing;

[0053] As Figure 4 As shown in (b) of the figure, the abscissa is the relative permeability curve, and the corresponding oil displacement efficiency on the ordinate is 82%, 86%, 88% and 90%, respectively, and the overall trend is gradually increasing;

[0054] As Figure 4 As shown in (c) of the figure, the abscissa is the critical surface tension, and the corresponding oil displacement efficiency on the ordinate is 77%, 86%, 88% and 90%, respectively, and the overall trend is gradually increasing.

[0055] The present application provides a set of technical methods, and the method can be used for quickly and efficiently fitting the minimum miscible pressure curve in the development plan design stage of offshore low-permeability sandstone oil reservoir carbon dioxide miscible phase flooding.

[0056] The present application provides a quantitative and operable technical method and implementation steps.

[0057] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points, characterized in that, include: A carbon dioxide miscibility pressure chart was drawn based on the displacement experiment results; Based on the aforementioned carbon dioxide miscibility pressure chart, the BIC binary interaction coefficient is determined according to the high-pressure miscibility point, the relative permeability curve is determined according to the low-pressure immiscibility point, and the critical surface tension is determined according to the miscibility inflection point, so as to determine the fitting order of the low-pressure immiscibility point, the miscibility inflection point, and the high-pressure miscibility point. Calculate the initial parameters of the high-pressure miscibility point based on the BIC binary interaction coefficient; and The oil displacement efficiency of carbon dioxide in capillary tube experiments was fitted by adjusting the interaction coefficient between carbon dioxide and C7+ to fit the high-pressure miscible point, by adjusting the oil displacement efficiency of the relative permeability curve to fit the low-pressure immiscible point, and by adjusting the critical interfacial tension value to fit the oil displacement efficiency of the miscible inflection point.

2. The carbon dioxide miscibility pressure fitting method for capillary experiments considering characteristic points according to claim 1, characterized in that, The displacement experiment employs an indoor physical simulation method. Nitrogen or aviation kerosene is injected into a capillary model and kept constant at the experimental temperature and pressure. Formation crude oil samples are used to displace the nitrogen or aviation kerosene in the capillary. After displacement to twice the pore volume, the gas-oil ratio and sample composition are measured at the capillary outlet. During the displacement process, the oil and gas volume, pump reading, experimental pressure, and back pressure are recorded every time 0.1 to 0.15 times the pore volume is injected.

3. The carbon dioxide miscibility pressure fitting method for capillary experiments considering characteristic points according to claim 1, characterized in that, The initial parameters of the BIC binary interaction coefficients were calculated by fitting the constant mass expansion experiment, saturated pressure experiment, constant volume exhaustion experiment, and viscosity experiment of the well fluid.

4. The carbon dioxide miscibility pressure fitting method for capillary experiments considering characteristic points according to claim 1, characterized in that, The interaction coefficients between carbon dioxide and C2-C3 and C4-C6 components were linearly interpolated to further optimize the interaction coefficients between carbon dioxide and C7+ components.

5. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, For high-pressure miscibility points, the point with the highest pressure has the highest degree of miscibility, and the oil displacement efficiency is mainly affected by the binary interaction coefficient of BIC, with little influence from the relative permeability curve and critical surface tension.

6. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, For low-pressure miscibility points, the point with the lowest pressure has the lowest degree of miscibility. Therefore, the oil displacement efficiency is mainly affected by the relative permeability curve and the BIC binary interaction coefficient, and is less affected by the critical surface tension.

7. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, For the miscibility inflection point, the pressure inflection point is located at the boundary between miscible and immiscible phases. Therefore, the oil displacement efficiency is mainly affected by the relative permeability curve, the BIC binary interaction coefficient, and the critical surface tension.

8. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, The BIC values ​​for CO2 and C7+ were 0.12, 0.110, 0.100, and 0.090, respectively.

9. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, The relative permeability curves are for 20%, 40%, 60%, and 80%, respectively.

10. The method for fitting the carbon dioxide miscibility pressure in a capillary tube experiment considering characteristic points according to claim 1, characterized in that, The critical surface tensions are 0.050, 0.010, 0.200 and 0.300, respectively.

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