Method for determining lower limit of CO2 content in CO2 flooding development reinjection gas

Abstract

The invention belongs to the technical field of oil and gas field development, and discloses a method for determining the lower limit of the CO2 content in CO2 flooding development reinjection gas, which comprises the following steps: S1, investigating the CO2 content range in the block output gas; s2, designing gas reinjection schemes with different CO2 contents; s3, through a crude oil component model / indoor test, MMP after the reinjection gas with different CO2 contents is in contact with the in-situ crude oil is obtained; s4, drawing an intersection by taking the CO2 content as an x axis and MMP as a y axis; and S5, analyzing to obtain the lower limit of the CO2 content when the reinjection gas is in contact with the in-situ crude oil to achieve a mixed phase. According to the method, the process of judging whether the produced gas containing CO2 can be used as the reinjection gas or not is systematically elaborated on the basis of actual data of the mine field in a numerical simulation or indoor experiment development mode, the judgment hysteresis in the mine field practice process is eliminated, the problem that CO2 is used as a newly-developing large thermal oil displacement medium but is insufficient in experience is solved to a certain extent, and the method is suitable for popularization and application. And a new thought is provided for treating CO2-containing output gas in a subsequent mine field.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development. Background Technology

[0002] CO2 is a typical displacement medium in gas drive in tertiary oil recovery technology. Utilizing it to drive oil recovery and improve storage technology is an important manifestation of utilization.

[0003] During CO2 injection for enhanced oil recovery, gas surge is highly likely to occur because the viscosity of CO2 fluid in underground reservoirs is much lower than that of crude oil and formation water. As development progresses, some CO2 will break through into the production wells along high-permeability layers, resulting in CO2 contamination in the produced gas. This produced gas contains a large amount of CO2 in addition to some light hydrocarbon components, making it unsuitable for use as fuel gas and unable to be directly released into the air. Therefore, finding a suitable pathway to process this gas is a major post-processing task in CO2 enhanced oil recovery.

[0004] Reinjecting CO2-containing produced gas into the formation is an economical and effective measure. However, the produced gas is only worthwhile when its CO2 content reaches a certain level. The most significant factor influencing whether the reinjected gas can effectively displace oil is the degree of miscibility between the injected gas and the crude oil. If they are relatively miscible, the impact on the final recovery rate is minimal; however, if the injected gas and formation crude oil are not effectively miscible, the final recovery rate of the reservoir will be reduced. Therefore, considering field capacity and costs, how to quickly and effectively determine whether CO2-containing produced gas can be used for reinjection is a crucial issue that urgently needs to be addressed. Summary of the Invention

[0005] This invention overcomes the lag and inefficiency of current mine methods for determining whether CO2-containing produced gas can be used as reinjection gas. It proposes a method for determining the lower limit of CO2 content in reinjection gas in CO2-driven development, which can realize dynamic storage while also processing CO2-containing produced gas.

[0006] The technical problem solved by this invention can be achieved by the following technical solutions:

[0007] A method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development includes the following steps:

[0008] S1. Range of CO2 content in the produced gas of the survey block;

[0009] S2. Design reinjection schemes with different CO2 contents;

[0010] S3. The MMP of reinjected gas with different CO2 contents after contact with formation crude oil was obtained through crude oil composition model / indoor test;

[0011] S4. Plot a cross plot with CO2 content as the x-axis and MMP as the y-axis;

[0012] S5. Analyze and obtain the lower limit of CO2 content when the reinjected gas and formation crude oil reach miscibility.

[0013] In S1, dynamic data on block production using CO2 as a displacement medium are acquired to investigate the range of CO2 content in the block's produced gas.

[0014] In S2, based on the range of CO2 content in the produced gas of the block obtained in S1, a reinjection gas scheme suitable for different CO2 contents in the block is designed.

[0015] In S3, based on the reinjection gas schemes with different CO2 contents designed in S2 for this block, the minimum miscible pressure (MMP) after the reinjection gas with different CO2 contents in this block comes into contact with the formation crude oil is obtained by calculation (or by conducting laboratory tests) using the crude oil composition model of this block.

[0016] In S4, based on the MMP of reinjected gas with different CO2 contents in S3 after contact with formation crude oil, a cross plot is drawn with CO2 content as the x-axis and MMP as the y-axis.

[0017] In S5, the cross-plot of the minimum miscibility pressure obtained after reinjection gas and formation crude oil come into contact with different CO2 contents obtained in S4 is analyzed, and the lower limit of CO2 content when reinjection gas and formation crude oil reach miscibility is obtained.

[0018] Furthermore, in S1, the survey found that the CO2 content in the produced gas of this block ranged from 80% to 90%.

[0019] Furthermore, in S2, there are 6-12 reinjection schemes.

[0020] Furthermore, in S2, the monitoring indicators for CO2 content include: X 1+ C 2+ C 3+ C 4+ C 5+ .

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] Based on actual field data, this invention systematically elucidates the process of determining whether CO2-containing produced gas can be used as reinjection gas through numerical simulation or indoor experiments. This eliminates the lag in judgment during field practice and to some extent solves the problem of insufficient experience with CO2 as an emerging high-temperature oil displacement medium. It provides a new approach for subsequent application of CO2-containing produced gas in the field. Attached Figure Description

[0023] To more clearly explain the technical solution of this invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the drawings described below are only some examples of this invention. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0024] Figure 1 This is a schematic flowchart of the method of the present invention;

[0025] Figure 2 This is a cross-plot of CO2 content and MMP. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The following will provide a detailed description of the technical solution for controlling gas channeling during carbon dioxide flooding provided by this invention, through a specific embodiment of a certain area in Jilin Oilfield using CO2 as the displacement medium. This area in Jilin Oilfield began CO2 development in October 2014. It is a block developed based on the original water-drive well network. Due to the continuous extension of development time, the gas produced by most production wells contains CO2.

[0028] like Figure 1 As shown, a method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding includes the following steps:

[0029] S1. Range of CO2 content in the produced gas of the survey block;

[0030] By obtaining production dynamic data of the block using CO2 as a displacement medium from the oilfield, the survey found that the CO2 content in the produced gas of the block ranges from 80% to 90%.

[0031] S2. Design reinjection schemes with different CO2 contents;

[0032] Given that the CO2 content in the produced gas from this block obtained in S1 ranges from 80% to 90%, a reinjection gas scheme suitable for different CO2 contents in this block was designed (see Table 1).

[0033] Table 1. Statistical table of reinjection schemes with different CO2 contents.

[0034]

[0035] S3. The MMP of reinjected gas with different CO2 contents after contact with formation crude oil was obtained through crude oil composition model / indoor test;

[0036] Due to its long development history, this block has established relatively complete geological and numerical models. Based on the crude oil composition experimental model, MMP calculations were performed on reinjection schemes with different CO2 contents designed in S2, and the MMP under reinjection gas with different CO2 contents was obtained.

[0037] S4. Plot a cross plot with CO2 content as the x-axis and MMP as the y-axis;

[0038] Based on the MMP under reinjected gas with different CO2 contents obtained in S3, a cross plot was drawn with CO2 content as the x-axis and MMP as the y-axis (see...). Figure 2 ).

[0039] S5. Analyze and obtain the lower limit of CO2 content when the reinjected gas and formation crude oil reach miscibility.

[0040] Analysis of the cross-plot of CO2 content and MMP in S4 reveals that as the CO2 content in the injected gas decreases, the MMP increases more rapidly, making it increasingly difficult for the produced gas to miscible with the formation crude oil. When the CO2 content in the produced gas falls below 85%, the miscibility pressure curve rises rapidly, with an accelerated trend. At a CO2 content of 70%, the MMP reaches as high as 35 MPa. For typical mining areas, it is difficult to achieve such a high formation pressure under conventional injection conditions, and this pressure is essentially on the edge of the fracture pressure, causing significant damage to the reservoir. Therefore, the lower limit of CO2 content for achieving miscibility between the reinjected gas and the formation crude oil is determined to be 85%. The produced gas in this block can then be directly reinjected into the formation as reinjection gas.

[0041] The method for determining the lower limit of CO2 content in CO2-driven reinjection gas is not limited to the above embodiments. The technical solutions of each embodiment can be combined with each other, but it must be based on the ability of a person skilled in the art to implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

Claims

1. A method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development, characterized in that, Includes the following steps: S1. Range of CO2 content in the produced gas of the survey block; S2. Design reinjection schemes with different CO2 contents; S3. Obtain the minimum miscibility pressure (MMP) after reinjected gas with different CO2 contents in this block comes into contact with formation crude oil. S4. Plot a cross plot with CO2 content as the x-axis and MMP as the y-axis; S5. Analyze and obtain the lower limit of CO2 content when the reinjected gas and formation crude oil reach miscibility.

2. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S1, dynamic data on block production using CO2 as a displacement medium are obtained to investigate the range of CO2 content in the block's produced gas.

3. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S2, based on the range of CO2 content in the produced gas of the block obtained in S1, a reinjection gas scheme suitable for different CO2 contents in the block is designed.

4. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S3, the MMP is calculated based on the reinjection gas scheme with different CO2 contents designed in S2 for this block, using the crude oil composition model of this block.

5. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, In S3, MMP is obtained through indoor testing.

6. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S4, based on the MMP of reinjected gas with different CO2 contents in S3 after contact with formation crude oil, a cross plot is drawn with CO2 content as the x-axis and MMP as the y-axis.

7. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S5, the cross-plot of the minimum miscibility pressure obtained after reinjection gas comes into contact with formation crude oil under different CO2 contents obtained in S4 is analyzed, and the lower limit of CO2 content when reinjection gas and formation crude oil reach miscibility is obtained.

8. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S1, the survey found that the CO2 content in the produced gas of this block ranged from 80% to 90%.

9. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, In S2, there are 6-12 reinjection schemes.

10. The method for determining the lower limit of CO2 content in reinjected gas during CO2 flooding development according to claim 1, characterized in that, in In S2, the monitoring indicators for CO2 content include: X 1+ C 2+ C 3+ C 4+ C 5+ .

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