A novel method for predicting the minimum miscibility pressure of a CO2-paraffin multi-component oil system

Abstract

Accurate determination of the minimum miscibility pressure (MMP) of CO2 and paraffin multi-component oil is the key to the successful design of CO2 flooding process. Based on the different changes of the diffusion coefficients of CO2 and paraffin multi-component oil phase before and after reaching the miscible state, a new method for predicting the MMP of CO2 and paraffin multi-component oil system is proposed. The new method measures the diffusion coefficients of CO2 and paraffin multi-component oil phase under typical non-miscible pressure conditions and typical miscible pressure conditions by monitoring the change of the oil droplet suspension volume over time in CO2 environment. Under typical non-miscible pressure conditions, the diffusion coefficients between the two phases are low and change little with the increase of pressure, while under typical miscible pressure conditions, the diffusion coefficients between the two phases are large and change greatly with the increase of system pressure. The intersection of the fitting curves of the diffusion coefficients and pressure in the two pressure intervals is the predicted MMP of CO2 and paraffin multi-component oil system.

Description

Technical Field

[0001] This invention patent addresses the prediction of minimum miscibility pressure in a CO2 and paraffin multi-component oil system. Because the interphase diffusion coefficients of CO2 and the oil phase differ significantly before and after reaching a miscible state, this invention predicts the minimum miscibility pressure of the CO2 and paraffin multi-component oil system based on the relationship between the diffusion coefficients of CO2 and paraffin multi-component oil before and after reaching a miscible state and the changes in system pressure. This falls under the field of two-phase dynamic miscibility characteristic measurement. Background Technology

[0002] In industrial applications, enhanced oil recovery (EOR) often utilizes the miscibility of CO2 with crude oil. This is achieved by injecting CO2 and allowing it to dissolve into a single phase under formation conditions, thus improving oil extraction efficiency. Therefore, accurately predicting the minimum miscibility pressure (MPP) of CO2 and the oil phase is a crucial factor in EOR processes. Traditional methods for testing MPP include the capillary method, the foaming method, and the interfacial tension disappearance method. The capillary method is time-consuming, the foaming method relies on subjective human judgment, and the interfacial tension disappearance method has significant errors in predicting the MPP of multi-component oil phases with a large number of carbon atoms. Therefore, this invention, based on the different changes in the interphase diffusion coefficient of CO2 and the oil phase with pressure before and after achieving a miscible state, proposes a new method for predicting the MPP of a CO2-paraffin multi-component oil system. Summary of the Invention

[0003] Using dynamic suspended droplet volume analysis, the diffusion coefficients of CO2 and paraffin multi-component oil phases were experimentally measured under typical immiscible and typical miscible pressure conditions. The different trends in diffusion coefficient variation under these two typical conditions were used to predict the minimum miscibility pressure of the CO2-paraffin multi-component oil system. Under typical immiscible pressure conditions, the diffusion coefficient between the two phases was low and did not change significantly with increasing system pressure. However, under typical miscible pressure conditions, the diffusion coefficient was high and changed significantly with increasing system pressure. The intersection of the fitted curves representing the diffusion coefficient versus pressure under the two conditions was identified as the minimum miscibility pressure of the CO2-paraffin multi-component oil system.

[0004] To meet the above requirements, the technical solution adopted by this method to solve its technical problem is as follows: A novel method for predicting the minimum miscibility pressure of a CO2-paraffin multi-component oil system is presented. The experimental setup comprises: 1. an oil tank; 2. a hand-operated oil inlet pump; 3. an exhaust valve; 4. a computer; 5. a CCD camera; 6. a pressure gauge; 7. an observation chamber; 8. a temperature controller; 9. a drain valve; 10. a light source; 11. a hand-operated CO2 pump; 12. a water tank; 13. a CO2 gas cylinder; 14. a CO2 pressurization tank; and 15. a capillary tube. Measurements are performed using this setup. (See attached diagram) Figure 1 ).

[0005] The observation chamber 7 has transparent quartz glass at both ends, providing excellent light transmittance, sealing, and resistance to high temperature and pressure. A light source 10 is located on the right side of the chamber, and a CCD camera 5 is located on the left side, used to receive image signals from inside the chamber and transmit them to a computer 4 for processing. During the test, oil droplets are injected into the chamber through a capillary tube 15 and suspended within the CO2-filled chamber. The changes in oil droplet volume are measured in typical immiscible and typical miscible pressure ranges (see attached diagram). Figure 2 , attached Figure 3 The diffusion coefficient data between CO2 and paraffin multi-component oil were obtained, and the relationship between diffusion coefficient and pressure was fitted in typical immiscible and typical miscible pressure ranges, respectively. The intersection of the two pressure range diffusion coefficient fitting curves is the minimum miscibility pressure of CO2 and paraffin multi-component oil at the test temperature. (See attached diagram) Figure 4 ).

[0006] This test method is simple, flexible, and efficient, and can be widely used in the testing of minimum miscibility pressure of CO2 / multi-component oil phases, providing effective guidance for CO2 in-situ oil displacement processes. Attached Figure Description

[0007] Figure 1 This is a diagram of the experimental system of the present invention.

[0008] In the diagram: 1. Oil tank; 2. Hand pump for oil inlet; 3. Exhaust valve; 4. Computer; 5. CCD camera; 6. Pressure gauge; 7. Observation chamber; 8. Temperature controller; 9. Drain valve; 10. Light source; 11. CO2 hand pump; 12. Water tank; 13. CO2 gas tank; 14. CO2 pressurization tank; 15. Capillary tube.

[0009] Figure 2 This describes the change in oil droplet volume with system pressure in a CO2 environment under typical immiscible pressure conditions.

[0010] Figure 3 This describes how the volume of oil droplets changes with system pressure in a CO2 environment under typical miscible pressure conditions.

[0011] Figure 4 The minimum miscibility pressure of CO2 and paraffin multi-component oil is determined by the intersection of the fitting line of the interphase diffusion coefficient under the typical immiscible pressure range and the fitting line of the interphase diffusion coefficient under the typical miscible pressure range. Detailed Implementation

[0012] The following section uses a CO2 and paraffin multi-component oil system at a certain temperature as an example, and describes in detail a new method for predicting the minimum miscibility pressure of a CO2 and paraffin multi-component oil system according to the present invention, with reference to the accompanying drawings.

[0013] The specific implementation steps are as follows: (1) As attached Figure 1 Use temperature controller 8 to adjust the temperature inside the observation chamber to the required experimental temperature. Open CO2 pressurization tank 14 and slowly inject CO2 gas into the observation chamber 7 to 1 MPa, stabilizing for 3 minutes. Open the observation chamber exhaust valve 3 to release the gas, repeating three times. This step is to purge the air from the chamber. (2) Slowly inject CO2 into the observation chamber 7 to 1 MPa, maintain the system pressure stable for 15 minutes, and ensure that the observation chamber 7 reaches pressure and heat equilibrium; (3) Use the valve to slowly squeeze oil droplets into the observation chamber 7 and hang them at the end of the capillary tube 15, then close the valve to form a closed system in the observation chamber; (4) The changes in the oil droplets inside the observation cavity were recorded using a CCD camera 5, and the changes in the oil droplets were quantitatively analyzed using the built-in software of the computer 4 to obtain the dynamic volume change data of the oil droplets within 30 seconds, as shown in the attached figure. Figure 2 ; (5) Using the formula (1) for calculating the diffusion coefficient of immiscible phases, the diffusion coefficient between CO2 and paraffin multi-component oil phases under typical immiscible conditions is calculated: (1) In the formula, It is the interphase diffusion coefficient under typical immiscible pressure conditions. It is the density of CO2. It is the density of paraffin wax. It is the mass of CO2. It's about the quality of the paraffin oil. This represents the slope of the change in oil droplet diameter over time at time t; (6) Continue to inject CO2 into the chamber and increase the pressure at 1 MPa intervals within the typical immiscible pressure range. After maintaining the system pressure stable for 15 minutes, repeat steps (3)-(5). (7) Complete the diffusion coefficient under different pressure conditions within the typical immiscible pressure range according to step (6); (8) Increase the system pressure to the typical miscible pressure condition, maintain the system pressure stable for 15 minutes, and repeat steps (3)-(4). Observe the changes in oil droplets in the cavity under the typical miscible condition as shown in the attached figure. Figure 3 ; (9) Using formula (2) for calculating the diffusion coefficient of miscibility, calculate the diffusion coefficient between CO2 and paraffin multi-component oil phases under typical miscibility conditions: (2) In the formula, It is the interphase diffusion coefficient under typical miscible pressure; (10) Continue to inject CO2 into the chamber and increase the pressure at 1 MPa intervals within the typical miscible pressure range. After maintaining the system pressure and temperature stable for 15 min, repeat steps (3)-(4) and (9). (11) Follow step (10) to complete the diffusion coefficient test under different pressure conditions within the typical miscibility pressure range; (12) The relationship between the diffusion coefficient and the system pressure under typical immiscible pressure conditions and typical miscible pressure conditions was fitted respectively. The pressure value at the intersection of the fitted lines under the two conditions is the minimum miscibility pressure of the CO2 and paraffin multi-component oil system at that temperature, as shown in the attached figure. Figure 4 .

[0014] The above embodiments are for illustrative purposes only and are not intended to limit the technical solutions of this invention. Any modifications or partial substitutions that do not depart from the spirit of this invention should be covered within the scope of the claims of this invention.

Claims

1. A novel method for predicting the minimum miscibility pressure of a CO2-paraffin multi-component oil system, characterized by: The minimum miscibility pressure of a CO2-paraffin multi-component oil system is predicted by measuring and calculating the changes in the diffusion coefficients of CO2 and paraffin multi-component oil phases under typical immiscible and typical miscible pressure conditions. This method includes the following steps: (1) Under typical immiscible pressure conditions, the dynamic suspended droplet volume analysis method was used to monitor the change in oil droplet volume in the CO2 environment and to calculate the diffusion coefficient between CO2 and paraffin multi-component oil under immiscible conditions using the formula for calculating the diffusion coefficient of immiscible conditions. (2) Under typical miscible pressure conditions, the dynamic suspended droplet volume analysis method was used to monitor the change in oil droplet volume in the CO2 environment and to calculate the diffusion coefficient between CO2 and paraffin multi-component oil under miscible conditions using the formula for calculating the miscible diffusion coefficient. (3) The diffusion coefficient variation characteristics with pressure under typical immiscible pressure conditions and typical miscible pressure conditions were fitted respectively. Under typical immiscible pressure conditions, the diffusion coefficient between the two phases was low and did not change much with the increase of system pressure. Under typical miscible pressure conditions, the diffusion coefficient between the two phases was large and changed much with the increase of system pressure. The intersection of the diffusion coefficient and pressure fitting curves under the two conditions is the minimum miscibility pressure of CO2 and paraffin multi-component oil phase.

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