A CO2-depleted gas reservoir considering formation water 2 Calculation method of theoretical maximum storage capacity

Abstract

The present invention discloses a method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water, and belongs to the technical field of CO2 storage and application. The calculation method comprises the following steps: S1: establishing a calculation model for the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water; S2: obtaining the physical property parameters of the target gas reservoir with respect to the calculation model for the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water; S3: calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water according to the calculation model for the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water and in combination with the physical property parameters. The present invention takes into account the effects of formation water production and CO2 dissolution on the CO2 storage potential of a gas reservoir, and can more accurately calculate the theoretical maximum storage capacity of CO2 in a target depleted gas reservoir, and evaluate the CO2 geological storage capacity of the gas reservoir.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 storage and application, and in particular to a method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration. Background Art

[0002] In recent years, with the development of economy and the exploitation of oil and gas resources, environmental issues have received more and more attention. The combustion of fossil fuels and the emission of CO2 have caused global warming, and many emission reduction measures and projects have been launched for this purpose. One of the emission reduction measures is to combine the storage of CO2 with the improvement of oil recovery, so as to improve the benefits of oil and gas reservoirs while storing CO2 underground. Storing CO2 underground is a safe, environmentally friendly, efficient and technically feasible solution. Unexploitable coal seams, saline seams, depleted oil and gas reservoirs and deep sea are the main places for CO2 storage. Gas reservoir closures have good sealing properties, and CO2 is not easy to leak during storage. In addition, after the development of gas reservoirs, there is a complete well network and geological data, which can store CO2 at a lower cost. Therefore, it is more feasible to store CO2 in gas reservoirs.

[0003] At present, the prediction of CO2 storage potential in depleted gas reservoirs does not take into account the production of formation water and the impact of CO2 dissolution on the storage capacity. However, in actual mine applications, the influence of these factors cannot be ignored. Therefore, there is an urgent need for an effective method to calculate the theoretical maximum storage capacity of CO2 in depleted gas reservoirs taking formation water into account, to evaluate the CO2 storage capacity under formation conditions, which is conducive to efficient on-site construction and 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 theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking into account formation water.

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

[0006] A method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration comprises the following steps:

[0007] S1: Establish a calculation model for the theoretical maximum storage capacity of CO2 in depleted gas reservoirs taking into account formation water;

[0008] S2: obtaining physical property parameters of the target gas reservoir for the calculation model of the theoretical maximum storage capacity of CO2 in the depleted gas reservoir considering formation water;

[0009] S3: According to the calculation model of the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration, combined with the physical property parameters, the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration is calculated.

[0010] Preferably, in step S1, the theoretical maximum storage capacity calculation model of CO2 in a depleted gas reservoir considering formation water is:

[0011] (1)

[0012] Where: is the theoretical maximum storage capacity of CO2 in the gas reservoir volume under ground conditions, kg; is the volume of produced formation water, m 3 ; is the volume coefficient of formation water, dimensionless; is the volume of natural gas finally produced under the condition of gas reservoir abandonment, m 3 ; is the volume coefficient of natural gas under the original conditions of the gas reservoir, dimensionless; is the deviation factor of natural gas under original reservoir conditions, dimensionless; is the density of CO2 at ground level, kg / m 3 ; is the porosity factor, dimensionless; is the deviation factor of CO2 under the original gas reservoir conditions, dimensionless; is the area of ​​the gas reservoir, m 2 ; is the average thickness of the gas reservoir, m; is the average porosity of the gas reservoir, decimal; is the average water saturation of the gas reservoir, decimal; is the density of formation water, kg / m 3 ; is the average mass fraction of CO2 in the formation water when the formation water is saturated with CO2, %.

[0013] Preferably, the volume coefficient of the natural gas under the original conditions of the gas reservoir is Calculate using the following formula:

[0014] (2)

[0015] Where: is standard pressure, MPa; is the deviation factor of natural gas under standard conditions, dimensionless; is standard temperature, K; is the temperature of the gas under the original reservoir conditions, K; is the original formation pressure of the gas reservoir, MPa.

[0016] The beneficial effects of the present invention are:

[0017] The present invention takes into account the impact of formation water production and CO2 dissolution on the CO2 storage potential of gas reservoirs, and can more accurately calculate the theoretical maximum CO2 storage capacity of the target depleted gas reservoir and evaluate the CO2 geological storage capacity of the gas reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 A schematic diagram of the storage distribution of CO2 in a specific implementation of numerical simulation;

[0020] Figure 2 This is a schematic diagram of the CO2 storage results of a specific implementation of numerical simulation. DETAILED DESCRIPTION

[0021] 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 commonly 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.

[0022] The present invention provides a method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration, comprising the following steps:

[0023] S1: Establish a calculation model for the theoretical maximum storage capacity of CO2 in depleted gas reservoirs taking into account formation water.

[0024] In a specific embodiment, the theoretical maximum storage capacity calculation model of CO2 in a depleted gas reservoir considering formation water is:

[0025] (1)

[0026] Where: is the theoretical maximum storage capacity of CO2 in the gas reservoir volume under ground conditions, kg; is the volume of produced formation water, m 3 ; is the volume coefficient of formation water, dimensionless; is the volume of natural gas finally produced under the condition of gas reservoir abandonment, m 3 ; is the volume coefficient of natural gas under the original conditions of the gas reservoir, dimensionless; is the deviation factor of natural gas under original reservoir conditions, dimensionless; is the density of CO2 at ground level, kg / m 3 ; is the porosity factor, dimensionless; is the deviation factor of CO2 under the original gas reservoir conditions, dimensionless; is the area of ​​the gas reservoir, m 2 ; is the average thickness of the gas reservoir, m; is the average porosity of the gas reservoir, decimal; is the average water saturation of the gas reservoir, decimal; is the density of formation water, kg / m 3 ; is the average mass fraction of CO2 in the formation water when the formation water is saturated with CO2, %.

[0027] In the above embodiment, the theoretical maximum storage capacity calculation model of CO2 in a depleted gas reservoir considering formation water is established by the following steps:

[0028] For depleted gas reservoirs with water, after CO2 is injected, CO2 has several states of existence: part of CO2 stays in the original natural gas pore volume, part of CO2 occupies the produced formation water pore volume, part of CO2 dissolves in the formation water of the reservoir, and part of CO2 undergoes mineralization reaction with the gas reservoir rock. However, the amount of CO2 gas that undergoes mineralization reaction is relatively small compared to other parts, so it can be ignored in the calculation. Therefore, the following CO2 storage calculation equation is established:

[0029] (3)

[0030] Where: is the amount of CO2 occupying the original natural gas pores under ground conditions, kg; is the amount of CO2 gas occupying the pores of the produced formation water under ground conditions, kg; is the amount of CO2 dissolved in formation water in the gas reservoir under ground conditions, kg.

[0031] In actual working conditions, the natural gas space produced in the gas reservoir cannot be fully used to store CO2, but only a certain percentage can be used to store CO2. Therefore, the effective storage capacity of CO2 in the gas reservoir can be calculated by the following formula:

[0032] (4)

[0033] Where: It is the molar ratio of CO2 to CH4 under the final storage conditions of the gas reservoir, dimensionless.

[0034] In the above embodiment, the volume of natural gas finally produced under the condition of gas reservoir abandonment is The porosity coefficient can be obtained through the actual development data of gas reservoirs. It refers to the percentage of pores where CO2 is stored in the original pores, which can usually be taken as 0.85.

[0035] The maximum formation pressure of CO2 in a gas reservoir cannot exceed the original formation pressure of the gas reservoir, so the upper limit pressure of CO2 storage is the original formation pressure of the gas reservoir P i . According to the gas laws:

[0036] (5)

[0037] Where: is the volume of gas under original reservoir conditions, m 3 ; is the deviation factor of gas under original gas reservoir conditions, dimensionless; is the number of moles of gas, mol; is the gas constant; is the temperature of the gas under the original reservoir conditions, K; is the original formation pressure of the gas reservoir, MPa.

[0038] The transformation of formula (5) can be obtained as follows:

[0039] (6)

[0040] Therefore, considering the same temperature, pressure and gas volume in the same gas reservoir, the molar numbers of CO2 and CH4 are:

[0041] (7)

[0042] (8)

[0043] Where: is the number of moles of CO2, mol; is the number of moles of CH4, mol.

[0044] According to equations (7) and (8), the molar ratio of CO2 to CH4 under the final storage conditions of the gas reservoir can be obtained: for:

[0045] (9)

[0046] Substituting formula (9) into formula (4), we get:

[0047] (10)

[0048] The amount of CO2 in the pores of the gas reservoir that occupies the produced formation water It is expressed as:

[0049] (11)

[0050] Where: is the underground volume of produced formation water converted to the original gas reservoir conditions, m 3 ; is the underground volume of produced natural gas converted to the original gas reservoir conditions, m 3 .

[0051] The underground volume of the produced formation water converted to the original gas reservoir conditions Calculate using the following formula:

[0052] (12)

[0053] The underground volume of the produced natural gas converted to the original gas reservoir conditions Calculate using the following formula:

[0054] (13)

[0055] Substituting equations (10), (12) and (13) into equation (11), we obtain:

[0056] (14)

[0057] Amount of CO2 dissolved in formation water in gas reservoirs It is expressed as:

[0058] (15)

[0059] Substituting equations (10), (14) and (15) into equation (3), we can obtain the theoretical maximum storage capacity calculation model for CO2 in depleted gas reservoirs considering formation water as shown in equation (1).

[0060] In a specific embodiment, the volume coefficient of the natural gas under the original conditions of the gas reservoir is Calculate using the following formula:

[0061] (2)

[0062] Where: is standard pressure, MPa; is the deviation factor of natural gas under standard conditions, dimensionless; is the standard temperature, K.

[0063] S2: Obtain the physical property parameters of the target gas reservoir with respect to the calculation model of the theoretical maximum storage capacity of CO2 in the depleted gas reservoir taking formation water into consideration.

[0064] S3: According to the calculation model of the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration, combined with the physical property parameters, the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration is calculated.

[0065] In a specific embodiment, taking a gas reservoir as an example, the method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water according to the present invention is used to calculate the theoretical maximum storage capacity of CO2, which specifically includes the following steps:

[0066] (1) A theoretical maximum storage capacity calculation model for CO2 in depleted gas reservoirs considering formation water is established as shown in equation (1).

[0067] (2) Obtaining the physical property parameters of the target gas reservoir with respect to the calculation model of the theoretical maximum storage capacity of CO2 in the depleted gas reservoir taking formation water into consideration.

[0068] In this embodiment, the physical property parameters obtained are shown in Table 1:

[0069] Table 1 Physical parameters of target gas reservoirs related to calculation model

[0070]

[0071] According to formula (2), combined with the physical parameters in Table 1, the volume coefficient of natural gas under the original conditions of the gas reservoir is calculated. =0.0048.

[0072] (3) According to the calculation model of the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water shown in formula (1) established in step (1), combined with the physical property parameters obtained in step (2), the theoretical maximum storage capacity of CO2 in a depleted gas reservoir considering formation water of the target gas reservoir is calculated. =2295881503kg≈229.59×10 4 t.

[0073] The numerical simulation was used to verify the CO2 geological storage of the target gas reservoir. CO2 was injected from the original formation pressure to the abandoned pressure. The injection rate was set at 20×10 4 m 3 / d, and finally restored to the original formation pressure of 25MPa. In this numerical simulation, the CO2 storage distribution is as follows Figure 1 The CO2 storage results are shown in Figure 2As shown in the numerical simulation, the maximum storage capacity is 219.7×10 4 By comparing the numerical simulation results with the calculation results of the present invention, it can be seen that the relative error between the calculated value of the present invention and the numerical simulation value is 4.5%, indicating that the present invention can accurately calculate the theoretical maximum storage capacity of CO2 in depleted gas reservoirs.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments 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 according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into account, characterized in that: The following steps are involved: S1: Establish a calculation model for the theoretical maximum storage capacity of CO2 in depleted gas reservoirs taking into account formation water; the calculation model for the theoretical maximum storage capacity of CO2 in depleted gas reservoirs taking into account formation water is: （1） Where: is the theoretical maximum storage capacity of CO2 in the gas reservoir volume under ground conditions, kg; is the volume of produced formation water, m 3 ; is the volume coefficient of formation water, dimensionless; is the volume of natural gas finally produced under the condition of gas reservoir abandonment, m 3 ; is the volume coefficient of natural gas under the original conditions of the gas reservoir, dimensionless; is the deviation factor of natural gas under original reservoir conditions, dimensionless; is the density of CO2 at ground level, kg / m 3 ; is the porosity factor, dimensionless; is the deviation factor of CO2 under the original gas reservoir conditions, dimensionless; is the area of ​​the gas reservoir, m 2 ; is the average thickness of the gas reservoir, m; is the average porosity of the gas reservoir, decimal; is the average water saturation of the gas reservoir, decimal; is the density of formation water, kg / m 3 ; is the average mass fraction of CO2 in formation water when the formation water is saturated with CO2, %; S2: obtaining physical property parameters of the target gas reservoir for the calculation model of the theoretical maximum storage capacity of CO2 in the depleted gas reservoir considering formation water; S3: According to the calculation model of the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration, combined with the physical property parameters, the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration is calculated.

2. The method for calculating the theoretical maximum storage capacity of CO2 in a depleted gas reservoir taking formation water into consideration according to claim 1 is characterized in that: The volume coefficient of the natural gas under the original conditions of the gas reservoir is Calculate using the following formula: （2） Where: is standard pressure, MPa; is the deviation factor of natural gas under standard conditions, dimensionless; is standard temperature, K; is the temperature of the gas under the original reservoir conditions, K; is the original formation pressure of the gas reservoir, MPa.

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