A method for calculating the replacement efficiency of CO2 for methane in the storage process

Abstract

The present invention discloses a method for calculating the displacement efficiency of methane during the CO2 sequestration process, which includes the following steps: S1: Obtain formation water and core samples and measure their basic physical properties; S2: Saturate with formation water under formation conditions to obtain a core sample saturated with formation water and its mass m1; S3: Perform methane displacement under formation conditions to obtain a core sample in the state of irreducible water saturation and its mass m2; Measure the solubility of methane under different pressure conditions at the formation temperature to obtain the correlation coefficients A and B; S4: Use CO2 to displace under formation conditions, measure the volume V3 of the displaced gas sample and the proportion C of methane content therein; S5: Establish a calculation model for the displacement efficiency of methane during the CO2 sequestration process and calculate the displacement efficiency of methane during the CO2 sequestration process. The present invention can calculate the displacement efficiency of CO2 for methane under formation temperature and pressure conditions of the reservoir, and the result is more reasonable and reliable, which can provide technical support for maximizing the benefits of CO2 sequestration.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 storage and utilization (CCUS) development, and in particular to a method for calculating the replacement efficiency of methane in a CO2 storage process. Background Art

[0002] The main geological sites for storage include: depleted oil and gas reservoirs, deep saline water layers, and coal seams that are difficult to mine. Among them, the storage of depleted oil and gas reservoirs is widely used, and pilot tests have been carried out in mines. A large number of domestic and foreign literature also shows that injecting CO2 into the formation can not only improve the greenhouse effect through storage, but also improve the later recovery rate of oil and gas reservoirs and increase the economic benefits of oil fields. It has certain economic value and huge ecological and environmental benefits. At the same time, when depleted gas reservoirs are used as CO2 storage sites, due to the different solubility of methane and CO2 in formation water, the remaining methane in the depleted gas reservoir will be replaced during the CO2 storage process, which will further increase the economic value of CO2 geological storage.

[0003] At present, there are few methods for studying the methane replacement capacity of CO2 geological storage, and there is a lack of quantitative experimental data. Therefore, there is an urgent need for a method to calculate the methane replacement efficiency of CO2 storage process and evaluate the methane replacement capacity of CO2 under formation pressure conditions, so as to facilitate the timely adjustment of parameters in the subsequent CO2 storage scheme design, which is conducive to efficient construction on site and the improvement of the economic benefits of CO2 geological storage. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a method for calculating the replacement efficiency of methane in the CO2 storage process.

[0005] The technical solution of the present invention is as follows:

[0006] A method for calculating the replacement efficiency of methane in a CO2 storage process comprises the following steps:

[0007] S1: Obtain formation water samples and core samples of the target CO2 storage layer, and measure the basic physical properties of the formation water samples and the core samples;

[0008] S2: saturating the core sample with formation water using the formation water sample under formation conditions to obtain a core sample saturated with formation water, and measuring the mass m1 of the core sample saturated with formation water;

[0009] S3: displacing the core sample saturated with formation water with methane under formation conditions to obtain a core sample in a state of irreducible water saturation, and measuring the mass m2 of the core sample in the state of irreducible water saturation;

[0010] Under formation temperature conditions, measuring the solubility of methane in the formation water sample under different pressure conditions to obtain correlation coefficient A and correlation coefficient B;

[0011] S4: using CO2 to displace the core sample at the irreducible water saturation state under formation conditions to obtain a gas sample displaced by CO2, and measuring the volume V3 of the gas sample displaced by CO2 and the proportion C of methane therein;

[0012] S5: Establish a calculation model for the replacement efficiency of methane in the CO2 storage process, and calculate the replacement efficiency of methane in the CO2 storage process of the target CO2 storage layer based on the calculation model for the replacement efficiency of methane in the CO2 storage process and the parameters obtained in steps S1-S4.

[0013] Preferably, in step S1, the basic physical properties of the formation water sample include the density of the formation water, and the basic physical properties of the core sample include the length of the core, the diameter of the core and the porosity of the core.

[0014] Preferably, in step S3, the correlation coefficient A and the correlation coefficient B are obtained by fitting the following formula:

[0015] ω=Ap B (1)

[0016] Where: ω is the solubility of methane in the formation water sample, cm 3 / cm 3 ; p is pressure, MPa.

[0017] Preferably, in step S5, the calculation model of the replacement efficiency of methane in the CO2 storage process is:

[0018]

[0019] Where: is the replacement efficiency of methane in the CO2 storage process, %; p1 is the ground standard pressure, MPa; Z2 is the deviation factor of methane under formation conditions, dimensionless; T2 is the formation temperature, K; ρ w is the density of the formation water sample, g / cm 3 ; p2 is the formation pressure, MPa; Z1 is the deviation factor under the ground standard state, dimensionless; T1 is the ground standard temperature, K; R is the radius of the core sample, cm; h is the length of the core sample, cm; θ is the porosity of the core sample, dimensionless.

[0020] The beneficial effects of the present invention are:

[0021] The calculation model of the replacement efficiency of methane in the CO2 storage process established by the present invention uses the parameters obtained under formation conditions as basic data, and can accurately calculate the replacement efficiency of methane in the CO2 geological storage process. It can solve the problem of the replacement efficiency of methane in the CO2 storage process at home and abroad, and its results are more reasonable and reliable, which can well meet the needs of rationally planning CO2 storage sites and increasing the economic benefits of CO2 storage. In addition, the present invention can also be extended to calculate the replacement capacity of methane dissolved in formation water in the CO2 flooding process, and has a wide range of application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 A schematic flow chart of a method for calculating the replacement efficiency of methane in a CO2 storage process according to the present invention;

[0024] Figure 2 It is a schematic diagram of the test results of the solubility of methane in formation water under different pressure conditions in a specific embodiment;

[0025] Figure 3 It is a schematic diagram of the calculation results of the replacement efficiency of methane in the CO2 storage process in a specific embodiment. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0027] like Figure 1 As shown, the present invention provides a method for calculating the replacement efficiency of methane in a CO2 storage process, comprising the following steps:

[0028] S1: Obtain formation water samples and core samples of the target CO2 storage layer, and measure the basic physical properties of the formation water samples and the core samples.

[0029] In a specific embodiment, the core sample is a standard core (2.5 cm in diameter and 3-5 cm in length) of a target layer of a target CO2 storage layer.

[0030] In a specific embodiment, the basic physical properties of the formation water sample include the density of the formation water, and the basic physical properties of the core sample include the length of the core, the diameter of the core, and the porosity of the core.

[0031] S2: using the formation water sample to saturate the core sample with formation water under formation conditions to obtain a core sample saturated with formation water, and measuring the mass m1 of the core sample saturated with formation water.

[0032] S3: displacing the core sample saturated with formation water with methane under formation conditions to obtain a core sample in a state of irreducible water saturation, and measuring the mass m2 of the core sample in the state of irreducible water saturation;

[0033] Under formation temperature conditions, the solubility of methane in the formation water sample under different pressure conditions is measured to obtain correlation coefficient A and correlation coefficient B.

[0034] In a specific embodiment, the correlation coefficient A and the correlation coefficient B are obtained by fitting the following formula:

[0035] ω=Ap B (1)

[0036] Where: ω is the solubility of methane in the formation water sample, cm 3 / cm 3 ; p is pressure, MPa.

[0037] It should be noted that the correlation coefficient A and the correlation coefficient B are mainly obtained by fitting the test results of the solubility of methane in the formation water sample under different pressure conditions. In addition to the fitting formula adopted in the above embodiment, other fitting formulas with better fitting relationships can also be applied to the present invention.

[0038] S4: Using CO2 to displace the core sample in the irreducible water saturation state under formation conditions to obtain a gas sample displaced by CO2, and measuring the volume V3 of the gas sample displaced by CO2 and the methane content proportion C therein.

[0039] It should be noted that m1 in step S2, m2 in step S3, V3 and C in step S4 are all parameters measured under ground conditions. Among them, methane will escape after the measurement of m2, affecting the irreducible water saturation state of the core sample. Therefore, the core sample under the irreducible water saturation state used in the CO2 displacement in step S4 is the core sample under the irreducible water saturation state obtained by re-performing methane displacement after measuring m2.

[0040] S5: Establish a calculation model for the replacement efficiency of methane in the CO2 storage process, and calculate the replacement efficiency of methane in the CO2 storage process of the target CO2 storage layer based on the calculation model for the replacement efficiency of methane in the CO2 storage process and the parameters obtained in steps S1-S4.

[0041] In a specific embodiment, the calculation model of the replacement efficiency of methane in the CO2 storage process is:

[0042]

[0043] Where: is the replacement efficiency of methane in the CO2 storage process, %; p1 is the ground standard pressure, MPa; Z2 is the deviation factor of methane under formation conditions, dimensionless; T2 is the formation temperature, K; ρ w is the density of the formation water sample, g / cm 3 ; p2 is the formation pressure, MPa; Z1 is the deviation factor under the ground standard state, dimensionless; T1 is the ground standard temperature, K; R is the radius of the core sample, cm; h is the length of the core sample, cm; θ is the porosity of the core sample, dimensionless.

[0044] In a specific embodiment, taking the X well of the Sha 4 group of Wen 23 underground gas storage as an example, the method for calculating the replacement efficiency of methane in the CO2 storage process of the present invention is used to calculate the efficiency of replacing methane in the CO2 geological storage process. In this embodiment, the gas layer temperature of the X well is 120°C, the original formation pressure is 60MPa, the deviation factor Z1 under the ground standard state is 1.0059, and the deviation factor Z2 of methane under the formation condition is 0.7936. The method specifically includes the following steps:

[0045] (1) Formation water, natural gas and cores were obtained from the Sha 4 Group X Well of Wen 23 underground gas storage, the formation water was filtered and put into use, the pressure of the natural gas was increased to 5 MPa and put into use, and the basic physical properties of the cores and the formation water were measured. The results are shown in Table 1:

[0046] Table 1 Basic physical properties of target reservoir

[0047] Core length (cm) Core diameter (cm) Core porosity (%) <![CDATA[Density of formation water (g / cm 3 ) <!-- 3 -->]]> 3.491 2.501 16.414 1.151

[0048] (2) performing formation water saturation and natural gas displacement on the core in sequence under formation conditions, and measuring the mass of the core saturated with formation water and the mass of the core under irreducible water saturation respectively;

[0049] In this example, when natural gas displacement was performed, the core saturated with formation water was displaced at a low rate of 10 mL / min for 20 min, and the mass of the core before and after displacement was 44.377 g and 42.434 g, respectively;

[0050] (3) Under formation temperature conditions, the solubility of the natural gas in the formation water under different pressure conditions is measured. The results are as follows: Figure 2 shown; according to Figure 2 The test results are fitted by formula (1) to obtain the correlation coefficient A of 0.3577 and the correlation coefficient B of 0.7325;

[0051] (4) Under formation conditions, CO2 was used to displace the core at the bound water saturation state. The gas samples displaced were collected and recorded every 3-5 PV displacement, and the total volume of the collected gas and the proportion of methane content were measured. The results are shown in Table 2:

[0052] Table 2 Total volume of collected gas and proportion of methane content

[0053] PV <![CDATA[Total volume of gas (cm 3 )]]> Methane content ratio (%) PV <![CDATA[Total volume of gas (cm 3 )]]> Methane content ratio (%) 1 4625.2 16.76 20 30426.01 2.71 8 12044.20 6.64 23 35084.21 2.38 12 18192.80 4.45 28 53970.22 1.55 17 25737.80 3.2 - - -

[0054] (5) According to the calculation model of the replacement efficiency of CO2 storage process for methane shown in formula (2), combined with the parameters obtained in steps (1)-(4), the replacement efficiency of CO2 storage process for methane in the target CO2 storage layer is calculated. The result is as follows: Figure 3 shown.

[0055] In summary, the present invention can accurately calculate the replacement efficiency of methane in the CO2 storage process based on the parameters of the actual formation conditions. Compared with the prior art, the present invention has significant progress.

[0056] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the replacement efficiency of methane in a CO2 storage process, characterized in that: The following steps are involved: S1: Obtain formation water samples and core samples of the target CO2 storage layer, and measure the basic physical properties of the formation water samples and the core samples; S2: saturating the core sample with formation water using the formation water sample under formation conditions to obtain a core sample saturated with formation water, and measuring the mass m1 of the core sample saturated with formation water; S3: displacing the core sample saturated with formation water with methane under formation conditions to obtain a core sample in a state of irreducible water saturation, and measuring the mass m2 of the core sample in the state of irreducible water saturation; Under formation temperature conditions, the solubility of methane in the formation water sample under different pressure conditions is measured to obtain correlation coefficient A and correlation coefficient B; the correlation coefficient A and correlation coefficient B are obtained by fitting the following formula: （1） Where: ω is the solubility of methane in the formation water sample, cm 3 / cm 3 ; p is pressure, MPa; S4: using CO2 to displace the core sample at the irreducible water saturation state under formation conditions to obtain a gas sample displaced by CO2, and measuring the volume V3 of the gas sample displaced by CO2 and the proportion C of methane therein; S5: Establish a calculation model for the replacement efficiency of methane in the CO2 storage process, and calculate the replacement efficiency of methane in the CO2 storage process of the target CO2 storage layer according to the calculation model for the replacement efficiency of methane in the CO2 storage process and the parameters obtained in steps S1-S4; the calculation model for the replacement efficiency of methane in the CO2 storage process is: （2） Where: CH4 is the replacement efficiency of CO2 storage process for methane, %; p1 is the ground standard pressure, MPa; Z2 is the deviation factor of methane under formation conditions, dimensionless; T2 is the formation temperature, K; ρ w is the density of the formation water sample, g / cm 3 ; p2 is the formation pressure, MPa; Z1 is the deviation factor under the ground standard state, dimensionless; T1 is the ground standard temperature, K; R is the radius of the core sample, cm; h is the length of the core sample, cm; θ is the porosity of the core sample, dimensionless.

2. The method for calculating the replacement efficiency of CO2 storage process for methane according to claim 1, characterized in that: In step S1, the basic physical properties of the formation water sample include the density of the formation water, and the basic physical properties of the core sample include the length of the core, the diameter of the core, and the porosity of the core.

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