Method and device for evaluating different gas production proportion of deep coal bed gas reservoir

Abstract

This application discloses a method and apparatus for evaluating the production ratio of different gases in deep coalbed methane reservoirs. The method includes: calculating the coal seam porosity and water saturation at the beginning of production after fracturing and flowback based on the physical properties of the target coal seam; calculating the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam based on the physical properties, porosity, and water saturation of the target coal seam; calculating the daily average coal seam pressure, cumulative free gas production, cumulative adsorbed gas production, and cumulative dissolved gas production of the target coal seam based on the daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity, water saturation, and physical properties of the target coal seam at the beginning of production after fracturing and flowback; and calculating the daily production of free gas, adsorbed gas, and dissolved gas in the target coalbed methane reservoir based on the cumulative production of each gas, thereby obtaining the daily production ratio of the three gases.

Description

Technical Field

[0001] This application relates to the field of coalbed methane reservoir development technology, specifically to a method and apparatus for evaluating the production ratio of different gases in deep coalbed methane reservoirs. Background Technology

[0002] As an important unconventional resource, target coalbed methane reservoirs can alleviate energy shortages, reduce coal mine safety accidents, and reduce environmental pressure, attracting widespread attention globally. In recent years, target coalbed methane reservoirs have developed rapidly, with several reservoir blocks achieving high-yield breakthroughs. This is because the gas types in target coalbed methane reservoirs include not only adsorbed gas but also abundant free gas and a certain amount of dissolved gas. Studying the proportion of different gas types in target coalbed methane reservoirs has significant theoretical and practical implications for reservoir reserve evaluation and geological sweet spot prediction.

[0003] Currently, there are many methods for assessing the proportion of different gas types in a target coalbed methane reservoir (i.e., its reserve proportion), but few methods for assessing the production proportion of different gas types in the same reservoir. Only a few studies have established evaluation methods for the adsorbed gas / free gas ratio in gas wells based on carbon isotope fractionation models. However, these methods require the installation of carbon isotope monitoring devices at the wellhead, limiting their application and failing to consider the proportion of dissolved gas production. Therefore, methods for evaluating the production proportion of different gas types in a target coalbed methane reservoir using only well production data are rarely reported. Summary of the Invention

[0004] The purpose of this application is to provide a method and apparatus for evaluating the production ratio of different gases in deep coalbed methane reservoirs, in order to solve the technical problem of large errors and high prediction costs in evaluating the production ratio of different gases in deep coalbed methane reservoirs.

[0005] To achieve the above objectives, the first aspect of this application provides a method for evaluating the proportion of different gas production in deep coalbed methane reservoirs. The method includes the following steps:

[0006] Obtain the physical properties of the target coal seam;

[0007] Before production begins after fracturing and flowback, the porosity and water saturation of the target coal seam are calculated based on the physical properties of the target coal seam at the beginning of production after fracturing and flowback.

[0008] The original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir are calculated based on the target coal seam's physical properties, porosity, and water saturation.

[0009] The average daily coal seam pressure value of the target coal seam is calculated based on the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir, the daily cumulative gas production, cumulative water production, cumulative water intrusion, the coal seam porosity, water saturation, and physical property parameters at the beginning of production after fracturing and flowback.

[0010] The cumulative production of free gas, adsorbed gas, and dissolved gas in the target coalbed methane reservoir are calculated based on the daily average coal seam pressure, the original reserves of adsorbed gas, the original reserves of free gas and dissolved gas, the daily cumulative gas production, the cumulative water production, the cumulative water intrusion, the coal seam porosity at the beginning of production after fracturing and flowback, the coal seam water saturation, and physical property parameters.

[0011] The daily production of free gas, adsorbed gas, and dissolved gas of the target coalbed methane reservoir is calculated based on the cumulative daily production of free gas, adsorbed gas, and dissolved gas.

[0012] The daily production ratio of the three gases in the target coalbed methane reservoir is calculated based on the daily production of free gas, adsorbed gas, and dissolved gas.

[0013] In this embodiment of the application, the steps of calculating the coal seam porosity and water saturation at the initial production stage of the target coal seam after fracturing and flowback, based on the physical property parameters of the target coal seam before production begins, include:

[0014] Obtain the total fracturing fluid volume and the cumulative flowback volume during the flowback process of the target coal seam;

[0015] Calculate the net injection volume of fracturing fluid based on the volume of fracturing fluid and the cumulative flowback volume;

[0016] The coal seam porosity at the beginning of production after fracturing and flowback is calculated based on the coal seam control volume, net fracturing injection volume, original porosity of the target coal seam, and water volume coefficient.

[0017] The water saturation of the coal seam is calculated based on the controlled volume of the coal seam, the original porosity of the target coal seam, the original water saturation, the net injection volume of fracturing, the volume coefficient of water, and the porosity of the target coal seam at the beginning of production after fracturing and flowback.

[0018] In this embodiment of the application, the step of calculating the daily average coal seam pressure value of the target coal seam based on the original reserves of adsorbed gas, original reserves of free gas, original reserves of dissolved gas, daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity at the beginning of production after fracturing and flowback, coal seam water saturation, and physical property parameters includes:

[0019] The material balance equation of adsorbed gas in adsorption pores is established based on the principle of material balance in adsorption gas desorption.

[0020] The material balance equation for free gas and dissolved gas in free pores is established based on the principle of material balance between free gas and dissolved gas.

[0021] The material balance equation for the target coalbed methane reservoir is established based on the material balance equations for adsorbed gas, free gas, and dissolved gas.

[0022] The original reserves of adsorbed gas, free gas, and dissolved gas in the target coalbed methane reservoir, the cumulative gas production, cumulative water production, cumulative water intrusion, the porosity of the coal seam at the beginning of production after fracturing and flowback, the water saturation of the coal seam, and the physical property parameters are substituted into the material balance equation. The average coal seam pressure value is calculated using one of the following methods: Newton's iteration method, secant method, or cubic function method.

[0023] In this embodiment of the application, the step of calculating the average coal seam pressure value using a cubic function method includes:

[0024] Based on the material balance equation of the target coalbed methane reservoir, a cubic function model in univariate was established.

[0025] The quadratic coefficient, linear coefficient, and constant term of the cubic function are calculated based on the original reserves of adsorbed gas, free gas, and dissolved gas in the target coalbed methane reservoir, the daily cumulative gas production, cumulative water production, cumulative water intrusion, the porosity of the coal seam at the beginning of production after fracturing and flowback, the water saturation of the coal seam, and the physical property parameters.

[0026] The average coal seam pressure is calculated based on the quadratic coefficient, linear coefficient, and constant term of a cubic function.

[0027] In this embodiment, the cumulative free gas production in the target coalbed methane reservoir is calculated using the following formula:

[0028]

[0029] Among them, G pf The cumulative daily free gas production of the target coalbed methane reservoir, 10 6 m 3 G fi W represents the initial free gas reserves controlled by the target coalbed methane reservoir. p For the cumulative water production of the target coalbed methane reservoir, 10 6 m 3 W e The cumulative water intrusion during the production process, 10 6 m 3 ;φ ipV represents the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; V is the control volume of the coal seam, 10 6 m 3 S wip p represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. sc The pressure under standard conditions is expressed in MPa, with a value of 0.101325; T sc The temperature under standard conditions is K, with a value of 293.15; Z sc Z is the deviation coefficient for natural gas under standard conditions, dimensionless, and has a value of 1; T is the target coal seam temperature, in K; Z is the deviation coefficient for natural gas under standard conditions, dimensionless, and has a value of 1. i p is the deviation coefficient of the gas under the original coal seam pressure, dimensionless; L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the coal seam, in MPa; p i ρ is the original coal seam pressure, MPa; p is the average coal storage pressure, MPa; Z is the deviation coefficient of gas under the average coal seam pressure, dimensionless; C p The pore volume compressibility coefficient is given in MPa. -1 C w The isothermal compressibility coefficient of water is given in MPa. -1 C s The solubility coefficient of the target coalbed methane reservoir in water, in MPa -1 B w Let m be the volume index of water. 3 / m 3 C a is the coal matrix shrinkage coefficient, which is dimensionless.

[0030] In this embodiment, the cumulative dissolved gas production in the target coalbed methane reservoir is calculated using the following formula:

[0031]

[0032] Among them, G ps The cumulative daily dissolved gas production of the target coalbed methane reservoir, 10 6 m 3 G si The original dissolved gas reserves controlled by the target coalbed methane reservoir; W p For the cumulative water production of the target coalbed methane reservoir, 10 6 m 3 W e The cumulative water intrusion during the production process, 10 6 m 3 ;φ ip V represents the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; V is the control volume of the coal seam, 10 6 m3 S wip p represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. i p is the original coal seam pressure, MPa; p is the average coal storage pressure, MPa; C s The solubility coefficient of the target coalbed methane reservoir in water, in MPa -1 B w Let m be the volume index of water. 3 / m 3 C w The isothermal compressibility coefficient of water is given in MPa. -1 .

[0033] In this embodiment, the cumulative production of adsorbed gas in the target coalbed methane reservoir is calculated using the following formula:

[0034]

[0035] Among them, G pa The cumulative amount of adsorbed gas desorbed into free pores in the target coalbed methane reservoir, i.e., the cumulative production of adsorbed gas, 10 6 m 3 ;ρ c The density of coal and rock is t / m³. 3 V L For the Langmuir volume, m 3 / t;p L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the target coal seam, in MPa; p i ρ is the original coal seam pressure, MPa; p is the average coal seam pressure, MPa.

[0036] In this embodiment, the daily production of free gas in the target coalbed methane reservoir is calculated using the following formula:

[0037]

[0038] Where, q pf,j Let m be the daily free gas production of the target coalbed methane reservoir on day j. 3 / d;G pf,j The cumulative free gas production of the target coalbed methane reservoir on that day (day j), 10 6 m 3 G pf,j-1 The cumulative free gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 .

[0039] In this embodiment, the daily adsorption gas production is calculated using the following formula:

[0040]

[0041] Where, q pa,j Let m be the daily adsorbed gas production of the target coalbed methane reservoir on day j. 3 / d;G pa,j The cumulative adsorbed gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G pa,j-1 The cumulative adsorbed gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 ;

[0042] The daily production of dissolved gas is calculated using the following formula:

[0043]

[0044] Where, q ps,j Let m be the daily dissolved gas production of the target coalbed methane reservoir on day j. 3 / d;G ps,j The cumulative dissolved gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G ps,j-1 The cumulative dissolved gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 .

[0045] The second aspect of this application provides a device for evaluating the proportion of different gas contents in a target coalbed methane reservoir, comprising:

[0046] The memory is configured to store instructions; and

[0047] The processor is configured to retrieve instructions from memory and, when executing instructions, to implement the evaluation method for the production ratio of different gases in deep coalbed methane reservoirs as described above.

[0048] Using the above technical solution, when calculating the gas production ratio, the physical properties of the target coal seam are first obtained; before production begins after fracturing and flowback, the porosity and water saturation of the coal seam at the start of production are calculated based on the physical properties of the target coal seam; the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir are calculated based on the physical properties, porosity, and water saturation of the target coal seam; and the average daily coal seam pressure is calculated based on the original reserves of adsorbed gas, free gas, and dissolved gas, the cumulative daily gas production, cumulative water production, cumulative water intrusion, the porosity and water saturation of the target coal seam at the start of production after fracturing and flowback, and the physical properties. Based on the daily average coal seam pressure, the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir, the daily cumulative gas production, cumulative water production, cumulative water intrusion, the coal seam porosity at the beginning of production after fracturing and flowback, the coal seam water saturation, and physical property parameters, calculate the cumulative free gas production, cumulative adsorbed gas production, and cumulative dissolved gas production of the target coal seam gas reservoir; based on the daily cumulative free gas production, cumulative adsorbed gas production, and cumulative dissolved gas production of the target coal seam gas reservoir, calculate the daily free gas production, daily adsorbed gas production, and daily dissolved gas production of the target coal seam gas reservoir; based on the daily free gas production, daily adsorbed gas production, and daily dissolved gas production, calculate the daily gas production ratio of the three gases in the target coal seam gas reservoir. The method for evaluating the production ratio of adsorbed gas, free gas, and dissolved gas in deep coalbed methane reservoirs proposed in this patent requires fewer parameters, does not require the installation of carbon isotope monitoring devices at the wellhead, is applicable to all deep coalbed methane reservoirs, and is easy to promote and apply on a large scale.

[0049] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings:

[0051] Figure 1 The schematic diagram illustrates a flowchart of a method for evaluating the proportion of different gas production in deep coalbed methane reservoirs according to an embodiment of this application;

[0052] Figure 2 The diagram illustrates the daily cumulative gas production (Gp) and cumulative water production (Wp) curves of a deep coalbed methane reservoir.

[0053] Figure 3 This diagram illustrates the daily average coal seam pressure p-curve of a deep coalbed methane reservoir.

[0054] Figure 4 The diagram illustrates the daily cumulative gas production, adsorbed gas production, free gas production, and dissolved gas production curves of deep coalbed methane reservoirs.

[0055] Figure 5 The diagram illustrates the daily gas production curves for deep coalbed methane reservoirs, including the daily production of adsorbed gas, free gas, and dissolved gas.

[0056] Figure 6 The diagram illustrates the daily production percentages of adsorbed gas, free gas, and dissolved gas in deep coalbed methane reservoirs. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0058] It should be noted that the acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with the relevant provisions of national laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0059] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0060] like Figure 1 As shown in the embodiment of this application, a method for evaluating the proportion of different gas production in deep coalbed methane reservoirs is provided. The method for evaluating the proportion of different gas production in deep coalbed methane reservoirs includes the following steps:

[0061] S10: Obtain the physical properties of the target coal seam;

[0062] The physical properties of the target coal seam include: coal and rock density ρ c Original coal seam pressure p i Coal seam temperature T, coal seam control volume V, and original coal seam porosity φ i Original water saturation of coal seam S wi Pore ​​compressibility coefficient C p The average pore size D of the coal matrix micropores a The average pore size D of the coal matrix mesopores f Coal matrix surface wetting angle θ, coal matrix shrinkage coefficient C a Adsorbed gas Langmuir volume V L Adsorption gas Langmuir pressure p L gas relative density γ g The volume coefficient of water, B w The isothermal compressibility coefficient of water, C w The solubility coefficient C of coalbed methane in water s σ of the gas-water interfacial tension gw。

[0063] Furthermore, the coal seam control volume V can be calculated using equation (1):

[0064] V = Ah = L H Lh (1)

[0065] In the formula, V is the controlled volume of the coal seam, 10 6 m 3 A represents the controlled area of ​​the target coalbed methane reservoir, in km². 2 h represents the thickness of the target coal seam, in meters; L H L represents the length of the horizontal section of the target coal seam, in km; L represents the distance between horizontal wells in the target coal seam, in km.

[0066] S20: Before production begins after fracturing and flowback, calculate the coal seam porosity and water saturation at the start of production based on the physical property parameters of the target coal seam after fracturing and flowback.

[0067] S30: Calculate the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir based on the target coal seam's physical properties, porosity, and water saturation.

[0068] S40: Calculate the average daily coal seam pressure value of the target coal seam based on the original reserves of adsorbed gas, free gas, dissolved gas, daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity, coal seam water saturation, and physical property parameters at the beginning of production after fracturing and flowback.

[0069] S50: Calculate the cumulative production of free gas, adsorbed gas, and dissolved gas of the target coalbed methane reservoir based on the daily average coal seam pressure, original reserves of adsorbed gas, original reserves of free gas, original reserves of dissolved gas, daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity at the beginning of production after fracturing and flowback, coal seam water saturation, and physical property parameters.

[0070] S60: Calculate the daily production of free gas, adsorbed gas, and dissolved gas of the target coalbed methane reservoir based on the daily cumulative production of free gas, adsorbed gas, and dissolved gas.

[0071] S70: Calculate the daily production ratio of the three gases in the target coalbed methane reservoir based on the daily production of free gas, adsorbed gas, and dissolved gas.

[0072] This patent, based on the material balance principle of deep coalbed methane reservoirs, considers the pressure difference between adsorbed and free gas pores, the impact of fracturing on coal reservoir properties, and the influence of dissolved gas. It calculates the cumulative production of free gas, adsorbed gas, and dissolved gas in the target coalbed methane reservoir, and then calculates the daily production of free gas, adsorbed gas, and dissolved gas based on these figures, thereby obtaining the production ratio of the three gases. This application proposes a method for evaluating the production ratio of adsorbed gas, free gas, and dissolved gas in deep coalbed methane reservoirs. It only requires known coal reservoir properties, fluid properties, and dynamic production data of the coalbed methane wells to calculate the daily production ratio of different types of gases in deep coalbed methane reservoirs in real time, providing a reference for the dynamic analysis of gas well production.

[0073] In this embodiment of the application, the step of calculating the coal seam porosity and water saturation at the initial production stage of the target coal seam after fracturing and flowback, based on the physical property parameters of the target coal seam, includes:

[0074] Obtain the total fracturing fluid volume and the cumulative flowback volume during the flowback process of the target coal seam;

[0075] Calculate the net injection volume of fracturing fluid based on the volume of fracturing fluid and the cumulative flowback volume;

[0076] The coal seam porosity at the beginning of production after fracturing and flowback is calculated based on the coal seam control volume, net fracturing injection volume, original porosity of the target coal seam, and water volume coefficient.

[0077] The water saturation of the coal seam is calculated based on the controlled volume of the coal seam, the original porosity of the target coal seam, the original water saturation, the net injection volume of fracturing, the volume coefficient of water, and the porosity of the target coal seam at the beginning of production after fracturing and flowback.

[0078] In this embodiment, the adsorbed gas from the target coalbed methane is mainly stored in the micropores (pore size less than 2 nm) of the coal matrix, while free gas, dissolved gas, and water are stored in cleavage fractures (pore size greater than 1000 nm), macropores (pore size between 50 nm and 1000 nm), and mesopores (pore size between 2 nm and 50 nm). The original coal seam pressure p i In reality, this represents the original pressure of the fluid within the coal seam's cleavage fractures, macropores, and mesopores; it is the original pressure of the free pores. While the matrix micropores do not contain an aqueous phase, the micropores themselves do. Therefore, capillary pressure exists between the matrix micropores and mesopores, calculated using the following formula:

[0079]

[0080] In the formula, p c D is the capillary pressure between the micropores and mesopores of the coal seam, in MPa. a D represents the average pore size of the coal matrix micropores, in nm. f σ represents the average pore size of the coal matrix mesopores, in nm; gw θ represents the interfacial tension between air and water, in mN / m; θ represents the wetting angle of the coal matrix surface, in °.

[0081] Given the original coal seam pressure p i The initial pressure p of the adsorbed gas in the adsorption pores of the coal seam can be calculated using the following formula. mi :

[0082] p mi =p i +p c (3)

[0083] In formula (3), p mi The initial pressure of the adsorbed gas in the adsorption pores of the coal seam is given in MPa; p i The original coal seam pressure is given in MPa; p c This represents the capillary pressure between the micropores and mesopores of the coal seam, in MPa.

[0084] The total fracturing fluid volume W during the target coal seam fracturing process is statistically analyzed. fi And the cumulative amount of wastewater discharged during the discharge process, W fp The net injection volume W for fracturing is calculated using the following formula. fin :

[0085] W fin =W fi -W fp (4)

[0086] In formula (4), W fin This is the net injection volume for fracturing, 10 6 m 3 W fiThe total fracturing fluid volume during the target coal seam fracturing process is 10. 6 m 3 W fp This represents the cumulative amount of wastewater discharged during the discharge process, 10 6 m 3 .

[0087] The value of the coal seam control volume V and the original porosity φ of the coal seam are used. i Net injection volume W for fracturing fin The volume coefficient of water, B w Substituting into formula (5), calculate the coal seam porosity φ of the target coalbed methane reservoir at the beginning of production after fracturing and flowback. ip :

[0088]

[0089] In formula (5), φ ip This refers to the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; φ i W represents the original porosity of the coal seam. fin This is the net injection volume for fracturing, 10 6 m 3 B w Let m be the volume index of water. 3 / m 3 V represents the control volume of the coal seam, 10 6 m 3 .

[0090] The value of the coal seam control volume V and the original porosity φ of the coal seam are used. i Original water saturation of coal seam S wi Net injection volume W for fracturing fin The volume coefficient of water, B w The calculated coal seam porosity φ at the initial production stage of the target coalbed methane reservoir after fracturing and flowback. ip Substituting into formula (6), calculate the water saturation S of the coal seam at the initial stage of production of the target coalbed methane reservoir after fracturing and flowback. wip :

[0091]

[0092] In formula (6), S wip φ represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; i S represents the original porosity of the coal seam. wi W represents the original water saturation of the coal seam. fin This is the net injection volume for fracturing, 10 6 m 3 B w Let m be the volume index of water. 3 / m3 V represents the control volume of the coal seam, 10 6 m 3 ;φ ip This represents the porosity of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir.

[0093] In this embodiment of the application, the step of calculating the daily average coal seam pressure value of the target coal seam based on the original reserves of adsorbed gas, original reserves of free gas, original reserves of dissolved gas, daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity at the beginning of production after fracturing and flowback, coal seam water saturation, and physical property parameters includes:

[0094] The material balance equation of adsorbed gas in adsorption pores is established based on the principle of material balance in adsorption gas desorption.

[0095] The material balance equation for free gas and dissolved gas in free pores is established based on the principle of material balance between free gas and dissolved gas.

[0096] The material balance equation for the target coalbed methane reservoir is established based on the material balance equations for adsorbed gas, free gas, and dissolved gas.

[0097] The original reserves of adsorbed gas, free gas, and dissolved gas in the target coalbed methane reservoir, the cumulative gas production, cumulative water production, cumulative water intrusion, the porosity of the coal seam at the beginning of production after fracturing and flowback, the water saturation of the coal seam, and the physical property parameters are substituted into the material balance equation. The average coal seam pressure value is calculated using one of the following methods: Newton's iteration method, secant method, or cubic function method.

[0098] In this embodiment, based on the principle of adsorbed gas desorption mass balance, the cumulative amount of adsorbed gas desorbed from the adsorbed pores to the free pores in the target coalbed gas reservoir is equal to the original state adsorbed gas reserves minus the current state remaining adsorbed gas reserves. Therefore, the mass balance equation for adsorbed gas in the adsorbed pores is established as follows:

[0099]

[0100] In the formula, G pa The cumulative amount of adsorbed gas desorbed from the adsorbed pores to the free pores in the target coalbed methane reservoir is called the cumulative production of adsorbed gas. 6 m 3 ;ρ c The density of coal and rock is t / m³. 3 V L For the Langmuir volume, m 3 / t;p L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the coal seam, in MPa; pi ρ is the original coal seam pressure, MPa; p is the average coal seam pressure, MPa.

[0101] During the production process of the target coal seam, gas wells extract coalbed methane from free pores, while adsorbed pores supply desorbed gas to the free pores. Therefore, for the free pores of the target coal seam, the cumulative gas production from gas wells is an outflow, while the cumulative desorption from adsorbed pores is a supply. The net cumulative gas production of the free pores of the target coal seam (cumulative gas production from gas wells minus cumulative desorption from adsorbed pores) equals the sum of the original reserves of free gas and dissolved gas in the free pores minus the current reserves of free gas and dissolved gas in the free pores. Therefore, the material balance equation for free gas and dissolved gas in the free pores of the target coal seam gas reservoir is established as follows:

[0102]

[0103] In the formula, G p The cumulative gas production of the target coalbed methane reservoir, 10 6 m 3 W p The cumulative water production of the target coalbed methane reservoir, 10 6 m 3 W e The cumulative water intrusion during the production process, 10 6 m 3 ;φ ip S represents the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; wip p represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. sc The pressure under standard conditions is expressed in MPa, with a value of 0.101325; T sc The temperature under standard conditions is K, with a value of 293.15; Z sc p is the deviation coefficient for natural gas under standard conditions, dimensionless, and has a value of 1. i The original coal seam pressure is given by: T (MPa); T (K) is given by: Z (K). i Z is the deviation coefficient of gas under the original coal seam pressure, dimensionless; p is the average coal storage pressure, MPa; Z is the deviation coefficient of gas under the average coal seam pressure, dimensionless; C p The pore volume compressibility coefficient is given in MPa. -1 C w The isothermal compressibility coefficient of water is given in MPa. -1 C s The solubility coefficient of coalbed methane in water, in MPa -1 B w Let m be the volume index of water. 3 / m 3 C a is the coal matrix shrinkage coefficient, which is dimensionless.

[0104] Adding equations (7) and (8), we obtain the target coalbed methane reservoir material balance equation considering the pressure difference between adsorbed pores and free pores and the influence of fracturing fluid, as shown in equation (9):

[0105]

[0106] In this embodiment, the cumulative daily gas production G of the target coal seam is... p Cumulative water production W p Cumulative water intrusion W e (Usually taken as 0, unless the aquifer is accidentally breached during fracturing, and water from the aquifer gradually intrudes into the coal seam as fluid is extracted during the mining process.) Coal seam porosity φ at the beginning of production of the target coalbed gas reservoir after fracturing and flowback. ip The water saturation S of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. wip Substituting the physical properties of the target coal seam into formula (9), the average daily coal seam pressure can be calculated using the Newton-Raphson iteration method or the secant method. In the solution process, the Dranchuk-Abou-Kassem method is applied, based on the relative density γ of natural gas. g Given the reservoir temperature T, calculate the average gas deviation coefficient Z under any formation pressure.

[0107] Since both Newton's iterative method and the secant method are implicit solution methods, they require complex iterative loops and thus necessitate the assistance of computer programs. To simplify the calculation, a convenient explicit method for calculating the average reservoir pressure is proposed.

[0108] The expressions for the original reserves of adsorbed gas, free gas, and dissolved gas in formula (9) are respectively represented by G. ai G fi and G si This means, that is:

[0109]

[0110] Substituting formula (11) into formula (9) yields:

[0111]

[0112] Multiply both sides of formula (12) by (p) L +p c +p), and rearranged into a cubic equation for the average coal seam pressure p, we get:

[0113] p 3 +bp 2 +cp+d=0 (13)

[0114] In the formula, the expression for the coefficient b is:

[0115]

[0116] In the formula, the expression for the coefficient c is:

[0117]

[0118] In the formula, the expression for the coefficient d is:

[0119]

[0120] Rearrange formula (13) to y 3 If the form is +C1y+C2=0, then y, C1, and C2 are respectively:

[0121]

[0122] Equation y 3 One of the real solutions to +C1y+C2=0 is:

[0123]

[0124] The average daily coal seam pressure p of the target coal seam can then be obtained through the conversion formula (17), i.e., formula (21):

[0125]

[0126] When calculating coefficients b, c, and d, the value of V can be given directly, or formula (1) can be used for calculation; G ai G fi and G si The value of Z can be given directly based on prior knowledge, or it can be calculated using formula (11); the value of Z can be determined by first taking Z. i The value is used as the initial value. When the new average coal seam pressure p is calculated, the new Z is calculated using formula (10). Then, the new Z is used to replace the Z in the previous step. The calculation of p is repeated until the relative error between the two calculations of p satisfies 1×10. -6 When the time is up, exit the loop and use the last calculated value of p as the final value of the average coal seam pressure p.

[0127] In this embodiment, the cumulative free gas production in the target coalbed methane reservoir is calculated using the following formula:

[0128]

[0129] Among them, G pf The cumulative daily free gas production of the target coalbed methane reservoir, 10 6 m3 .

[0130] In this embodiment, the cumulative dissolved gas production in the target coalbed methane reservoir is calculated using the following formula:

[0131]

[0132] Among them, G ps The cumulative daily dissolved gas production of the target coalbed methane reservoir, 10 6 m 3 ; .

[0133] In this embodiment, the cumulative production of adsorbed gas in the target coalbed methane reservoir is calculated using the following formula:

[0134]

[0135] Among them, G pa The cumulative amount of adsorbed gas desorbed into free pores in the target coalbed methane reservoir, i.e., the cumulative production of adsorbed gas, 10 6 m 3 ;ρ c The density of coal and rock is t / m³. 3 V L For the Langmuir volume, m 3 / t;p L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the target coal seam, in MPa; p i ρ is the original coal seam pressure, MPa; p is the average coal seam pressure, MPa.

[0136] In some implementations, if the cumulative free gas production on a given day is greater than the cumulative free gas production on the previous day, the daily free gas production on that day is equal to the cumulative free gas production on that day minus the cumulative free gas production on the previous day; if the cumulative free gas production on a given day is less than or equal to the cumulative free gas production on the previous day, then the daily free gas production on that day is zero. Therefore, the daily free gas production in the target coalbed methane reservoir is calculated using the following formula (24):

[0137]

[0138] Where, q pf,j Let m be the daily free gas production of the target coalbed methane reservoir on day j. 3 / d;G pf,j The cumulative free gas production of the target coalbed methane reservoir on that day (day j), 10 6 m 3 G pf,j-1 The cumulative free gas production of the target coalbed methane reservoir on the previous day (day j-1), 106 m 3 .

[0139] In some implementations, if the cumulative free gas production on a given day is greater than the cumulative free gas production on the previous day, the daily adsorbed gas production on that day is equal to the cumulative adsorbed gas production on that day minus the cumulative adsorbed gas production on the previous day; if the cumulative free gas production on a given day is less than or equal to the cumulative free gas production on the previous day, then the daily adsorbed gas production on that day is equal to the cumulative adsorbed gas production on that day minus the cumulative adsorbed gas production on the previous day plus the cumulative free gas production on that day minus the cumulative free gas production on the previous day. Therefore, the daily adsorbed gas production can be calculated using the following formula (25):

[0140]

[0141] Where, q pa,j Let m be the daily adsorbed gas production of the target coalbed methane reservoir on day j. 3 / d;G pa,j The cumulative adsorbed gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G pa,j-1 The cumulative adsorbed gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 ;

[0142] Furthermore, by subtracting the cumulative dissolved gas production of the previous day from the cumulative dissolved gas production of the current day, the daily dissolved gas production can be calculated. Therefore, the daily dissolved gas production is calculated using the following formula (26):

[0143]

[0144] Where, q ps,j Let m be the daily dissolved gas production of the target coalbed methane reservoir on day j. 3 / d;G ps,j The cumulative dissolved gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G ps,j-1 The cumulative dissolved gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 .

[0145] Furthermore, using formula (27), the proportion of daily free gas production f of the target coal seam on the day (day j) is calculated. qpf :

[0146]

[0147] In formula (27), f qpf,j This represents the percentage of free gas produced by a coalbed methane well on the current day (day j).

[0148] Formula (28) is used to calculate the percentage of daily adsorbed gas production f of the target coal seam on the day (day j). qpa :

[0149]

[0150] In the formula, f qpa,j This represents the percentage of daily adsorbed gas production from the coalbed methane well on the current day (day j).

[0151] Using formula (29), the percentage of daily dissolved gas production fqps of the target coal seam on the day (day j) is calculated:

[0152]

[0153] In the formula, f qps,j This represents the percentage of dissolved gas produced by the coalbed methane well on that day (day j).

[0154] Finally, to further illustrate the evaluation process of the method for evaluating the proportion of different gas production in coalbed methane reservoirs in this application, the following example of the gas production proportion evaluation process in a deep coal reservoir is used for illustration:

[0155] First, the overall physical and fluid properties of this deep coal reservoir are shown in Table 1 below:

[0156] Table 1. Statistical table of physical property parameters of a deep coal reservoir after fracturing.

[0157]

[0158] In the table above, the control volume V of the deep coalbed methane reservoir can be calculated using equation (1), where the thickness of the deep coal reservoir h = 10m and the length of the horizontal well section L of the deep coalbed methane reservoir are given. H =1.002km, and the horizontal well spacing L = 0.35km in the deep coalbed methane reservoir is substituted into formula (1) to obtain the control volume V = 3.507(10 6 m 3 ).

[0159] V = Ah = L H Lh=1.002×0.35×10=3.507(10 6 m 3 )

[0160] Furthermore, the capillary pressure between the matrix micropores and mesopores is calculated using formula (2), where the average pore diameter D of the coal matrix micropores is used. a=2nm, average pore size D of coal matrix mesopores f =10nm, gas-water interfacial tension σ gw Substituting 60 mN / m and the wetting angle θ = 90° on the coal matrix surface into formula (2), the capillary pressure p between the micropores and mesopores of the coal reservoir is obtained. c = 0.8377 (MPa).

[0161]

[0162] The original coal reservoir pressure p i =21MPa and capillary pressure p between micropores and mesopores in the coal reservoir c Substituting 0.8377 MPa into formula (3), the original pressure p of the adsorbed gas in the adsorption pores of the coal reservoir is calculated. mi =21.8377 (MPa).

[0163] p mi =p i +p c =21 + 0.8377 = 21.8377 (MPa)

[0164] Statistical analysis of the total fracturing fluid volume W during the fracturing process in deep coalbed methane reservoirs. fi =0.03(10 6 m 3 ) and the cumulative amount of wastewater discharged during the discharge process W fp =0.0075(10 6 m 3 The net injection volume W for fracturing is calculated using formula (4). fin =0.0225(10 6 m 3 ).

[0165] W fin =W fi -W fp =0.03-0.0075=0.0225(10 6 m 3 )

[0166] The results are recorded in Table 2 below:

[0167] Table 2. Statistical Table of Fracturing and Flowback Data for Deep Coalbed Methane Reservoirs

[0168] parameter Value unit <![CDATA[Total fracturing fluid volume W fi > 0.03 <![CDATA[10 6 m 3 ]]> <![CDATA[Cumulative backflow volume W fp > 0.0075 <![CDATA[10 6 m 3 ]]> <![CDATA[Net fracturing injection volume W fin > 0.0225 <![CDATA[10 6 m 3 ]]>

[0169] The control volume of the coalbed methane well is V = 3.507(10). 6 m 3 ), original porosity φ of coal reservoir i =0.07, Net injection volume W for fracturing fin=0.0225(10 6 m 3 ) and the volume factor B of water w Substituting 1 into formula (5), calculate the coal reservoir porosity φ at the beginning of production after fracturing and flowback of the gas well. ip =0.07642.

[0170]

[0171] The control volume of the coalbed methane well is V = 3.507(10). 6 m 3 ), original porosity φ of coal reservoir i =0.07, original water saturation of coal reservoir S wi =0.60433, Net injection volume W for fracturing fin =0.0225(10 6 m 3 ), water volume factor B w =1 and the calculated coal reservoir porosity φ at the beginning of production after fracturing and flowback of the gas well. ip Substituting 0.07642 into formula (6), we can calculate the water saturation S of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. wip =0.63755.

[0172]

[0173] Furthermore, applying the Dranchuk-Abou-Kassem method, based on the relative density γ of natural gas... g Given the reservoir temperature T, calculate the average gas deviation coefficient Z under any formation pressure, and fit it using a univariate quartic polynomial of pressure to determine the expression for Z:

[0174] Z = A4p 4 +A3p 3 +A2p 2 +A1p+A0

[0175] = -4.2357 × 10 -7 p 4 +2.3073×10 -5 p 3 +3.5607×10 -5 p 2 -1.2258×10 -2 p+1

[0176] Therefore, the fourth power coefficient of pressure is determined to be A4 = -4.2357 × 10⁴. -7 MPa -4 The cubic coefficient of pressure, A3, is 2.3073 × 10⁻⁶.-5 MPa -3 The pressure square coefficient A2 = 3.5607 × 10 -5 MPa -2 The first-order coefficient of pressure, A1, is -1.2258 × 10⁻⁶. -2 MPa -1 The constant term coefficient A0 = 1.

[0177] The control volume of the coalbed methane well is V = 3.507(10). 6 m 3 ), the porosity φ of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. ip =0.07642, the water saturation of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. wip Substituting 0.63755 and the parameters in Table 1 into formula (11), the original storage capacity G of the adsorbed gas is calculated. ai =114.658463(10 6 m 3 ), Free gas original reserves G fi =19.334369(10 6 m 3 ) and the original reserves of dissolved gas G si =0.609958(10 6 m 3 ).

[0178]

[0179] The above results show that the daily cumulative gas production G of deep coalbed methane reservoirs is... p and cumulative water production W p Curves Figure 2 As shown.

[0180] Taking the production data of a deep coalbed methane reservoir on day 100 as an example, the cumulative gas production G on day 100 is... p =6.942087(10 6 m 3 Cumulative water production W p =0.00582697(10 6 m 3 ), cumulative water intrusion W e =0, the porosity φ of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. ip =0.07642, the water saturation of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. wip Substituting 0.63755 and the physical properties of the deep coal reservoir in Table 1 into formulas (14), (15), and (16), the initial value of Z is set as Z. iThe value is 0.8895, from which we calculate:

[0181] The coefficient b is:

[0182]

[0183] The coefficient c is:

[0184]

[0185] The coefficient d is:

[0186]

[0187] The values ​​of C1 and C2 are calculated using formulas (18) and (19) respectively:

[0188]

[0189] Using formula (20), the value of y is calculated:

[0190]

[0191] The average coal seam pressure p of a deep coalbed methane reservoir over 100 days is calculated using formula (21):

[0192]

[0193] Substituting the calculated average coal reservoir pressure p = 16.97308 (MPa) on the 100th day into formula (10), the new Z is calculated:

[0194] Z = A4p 4 +A3p 3 +A2p 2 +A1p+A0

[0195] = -4.2357 × 10 -7 p 4 +2.3073×10 -5 p 3 +3.5607×10 -5 p 2 -1.2258×10 -2 p+1

[0196] = -4.2357 × 10 -7 ×16.97308 4 +2.3073×10 -5 ×16.97308 3 +3.5607×10 -5 ×16.97308 2 -1.2258×10-2 ×16.97308+1

[0197] =0.87986839

[0198] Then, the calculated new Z replaces the Z from the previous step, and the calculation of p is repeated iteratively. It is found that after three iterations, the relative error between the two calculations of p satisfies 1 × 10⁻⁶. -6 At this point, exit the loop, and take the last calculated p = 16.89144 (MPa) as the final value of the average coal reservoir pressure p for the 100th day. Plot the daily average coal reservoir pressure p together with the measured casing pressure and bottom hole flowing pressure on the same graph, ultimately forming a graph as shown below. Figure 3 The curve shown.

[0199] Taking the data from the 100th day of this deep coalbed methane reservoir as an example, the calculated average coal reservoir pressure on the 100th day is p = 16.89144 (MPa), and the original free gas reserves controlled by the coalbed methane well are G. fi =19.334369(10 6 m 3 ), Cumulative gas production G on day 100 p =6.942087(10 6 m 3 Cumulative water production W p =0.00582697(10 6 m 3 ), cumulative water intrusion W e =0, the porosity φ of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. ip =0.07642, the water saturation of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. wip Substituting 0.63755 and some of the required parameters from Table 1 into formula (22), calculate the cumulative free gas production G of the deep coalbed methane reservoir on day 100. pf =3.499893(10 6 m 3 ).

[0200]

[0201] Substituting the calculated average coal reservoir pressure p = 16.89144 (MPa) on day 100 of the deep coalbed methane reservoir and some of the required parameters in Table 1 into formula (7), the cumulative adsorbed gas production G on day 100 of the deep coalbed methane reservoir is calculated. pa =3.307003(10 6 m 3 ).

[0202]

[0203] The calculated average coal reservoir pressure on day 100 of the deep coalbed methane reservoir is p = 16.89144 (MPa), and the original dissolved gas reserves controlled by the coalbed methane well are G. si =0.609958(10 6 m 3 Cumulative gas production G on day 100 p =6.942087(10 6 m 3 Cumulative water production W p =0.00582697(10 6 m 3 ), cumulative water intrusion W e =0, the porosity φ of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. ip =0.07642, the water saturation of the coal reservoir at the beginning of production after fracturing and flowback of the gas well. wip Substituting 0.63755 and some of the required parameters from Table 1 into formula (23), calculate the cumulative dissolved gas production G on day 100 of the deep coalbed methane reservoir. ps =0.119336(10 6 m 3 ).

[0204]

[0205] Using the same method, the daily cumulative adsorbed gas production G of this deep coalbed methane reservoir was calculated. pa Cumulative production of free gas G pf Cumulative production of dissolved gas G ps It is plotted on the same graph as the total cumulative gas production, such as... Figure 4 As shown.

[0206] Taking the data from the 100th and 99th days of this deep coalbed methane reservoir as an example, we calculate the daily production of free gas, adsorbed gas, and dissolved gas on the 100th day of the deep coalbed methane reservoir.

[0207] The cumulative free gas production on day 100 was 3.499893 (10 6 m 3 The cumulative free gas production on day 99 was 3.463176 (10) 6 m 3 The daily free gas production q on the 100th day is calculated using formula (24). pf,100 =36717(m) 3 / d).

[0208]

[0209] The cumulative free gas production on day 100 was 3.499893 (10 6 m 3 The cumulative free gas production on day 99 was 3.463176 (10) 6 m 3 Substituting the cumulative adsorbed gas production on day 100 and day 99 into formula (25), the daily adsorbed gas production q on day 100 is calculated. pa,100 =33855(m) 3 / d).

[0210]

[0211] Substituting the cumulative dissolved gas production on day 100 and day 99 into formula (26), the daily dissolved gas production q on day 100 is calculated. ps,100 =1023(m) 3 / d).

[0212]

[0213] Using the same method, the daily adsorbed gas production q of this deep coalbed methane reservoir was calculated. pa,j Daily free gas production q pf,j Dissolved gas daily production q ps,j The daily gas production of the gas well is plotted on the same graph as the daily gas production of the gas well, such as... Figure 5 As shown.

[0214] Taking the data from the 100th day of this deep coalbed methane reservoir as an example, formula (27) is used to calculate the proportion of free gas daily production f of the deep coalbed methane reservoir on the 100th day. qpf =51.28%.

[0215]

[0216] Formula (28) is used to calculate the percentage of daily adsorbed gas production f on the 100th day in deep coalbed methane reservoirs. qpa =47.29%.

[0217]

[0218] Formula (29) is used to calculate the proportion of dissolved gas daily production f on the 100th day in deep coalbed methane reservoirs. qps =1.43%.

[0219]

[0220] Using the same method, the daily free gas production ratio f of this deep coalbed methane reservoir was calculated. qpf,j The proportion of daily adsorbed gas production fqpa,j and the proportion of daily dissolved gas production f qps,j And drawn in the same diagram, such as Figure 6 As shown.

[0221] The second aspect of this application provides a device for evaluating the proportion of different gas contents in a target coalbed methane reservoir, comprising:

[0222] The memory is configured to store instructions; and

[0223] The processor is configured to retrieve instructions from memory and, when executing instructions, to implement the evaluation method for the production ratio of different gases in deep coalbed methane reservoirs as described above.

[0224] The memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0225] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0226] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0227] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for evaluating the production ratio of different gases in deep coalbed methane reservoirs, characterized in that, The method for evaluating the production ratio of different gases in deep coalbed methane reservoirs includes the following steps: Obtain the physical properties of the target coal seam; Before production begins after fracturing and flowback, the porosity and water saturation of the target coal seam are calculated based on its physical properties. The original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir are calculated based on the physical properties of the target coal seam, the porosity of the coal seam, and the water saturation of the coal seam. The average daily coal seam pressure value of the target coal seam is calculated based on the original reserves of adsorbed gas, free gas, and dissolved gas in the target coal seam gas reservoir, the daily cumulative gas production, cumulative water production, cumulative water intrusion, the coal seam porosity and water saturation at the beginning of production after fracturing and flowback, and the physical property parameters. The cumulative production of free gas, cumulative production of adsorbed gas, and cumulative production of dissolved gas in the target coalbed methane reservoir are calculated based on the daily average coal seam pressure, the original reserves of adsorbed gas, the original reserves of free gas, the original reserves of dissolved gas, the daily cumulative gas production, the cumulative water production, the cumulative water intrusion, the coal seam porosity at the beginning of production after fracturing and flowback, the coal seam water saturation, and the physical property parameters. The daily production of free gas, adsorbed gas, and dissolved gas of the target coalbed methane reservoir are calculated based on the daily cumulative production of free gas, adsorbed gas, and dissolved gas. The daily production ratio of the three gases in the target coalbed methane reservoir is calculated based on the daily production of free gas, adsorbed gas, and dissolved gas.

2. The method according to claim 1, characterized in that, The step of calculating the coal seam porosity and water saturation at the initial production stage after fracturing and flowback, based on the physical properties of the target coal seam before production begins, includes: Obtain the total fracturing fluid volume and the cumulative flowback volume during the flowback process of the target coal seam; Calculate the net fracturing injection volume based on the fracturing fluid volume and the cumulative flowback volume; The coal seam porosity at the beginning of production after fracturing and flowback is calculated based on the coal seam control volume, the net injection volume of fracturing, the original porosity of the target coal seam, and the volume coefficient of water. The water saturation of the coal seam is calculated based on the controlled volume of the coal seam, the original porosity of the target coal seam, the original water saturation, the net injection volume of fracturing, the volume coefficient of water, and the porosity of the target coal seam at the beginning of production after fracturing and flowback.

3. The method according to claim 1, characterized in that, The step of calculating the daily average coal seam pressure value of the target coal seam based on the original reserves of adsorbed gas, original reserves of free gas, original reserves of dissolved gas, daily cumulative gas production, cumulative water production, cumulative water intrusion, coal seam porosity at the beginning of production after fracturing and flowback, coal seam water saturation, and the physical property parameters includes: The material balance equation of adsorbed gas in adsorption pores is established based on the principle of material balance in adsorption gas desorption. The material balance equation for free gas and dissolved gas in free pores is established based on the principle of material balance between free gas and dissolved gas. The material balance equation for the target coalbed methane reservoir is established based on the material balance equations for adsorbed gas, free gas, and dissolved gas. The original reserves of adsorbed gas, free gas, and dissolved gas in the target coalbed methane reservoir, the cumulative gas production, cumulative water production, cumulative water intrusion, the porosity of the coal seam at the beginning of production after fracturing and flowback, the water saturation of the coal seam, and the physical property parameters are substituted into the material balance equation, and the average coal seam pressure value is calculated using one of the following methods: Newton's iteration method, secant method, or cubic function calculation method.

4. The method according to claim 3, characterized in that, The step of calculating the average coal seam pressure value using the cubic function method includes: A cubic model of univariate function is established based on the material balance equation of the target coalbed methane reservoir. The quadratic coefficient, linear coefficient, and constant term of the cubic function are calculated based on the original reserves of adsorbed gas, free gas, and dissolved gas in the target coalbed methane reservoir, the daily cumulative gas production, cumulative water production, cumulative water intrusion, the porosity of the target coal seam at the beginning of production after fracturing and flowback, the water saturation of the coal seam, and the physical property parameters. The average coal seam pressure value is calculated based on the quadratic coefficient, linear coefficient, and constant term of the cubic function.

5. The method according to claim 1, characterized in that, The cumulative free gas production in the target coalbed methane reservoir is calculated using the following formula: Among them, G pf The cumulative daily free gas production of the target coalbed methane reservoir, 10 6 m 3 G fi W represents the initial free gas reserves controlled by the target coalbed methane reservoir. p For the cumulative water production of the target coalbed methane reservoir, 10 6 m 3 W e The cumulative water intrusion during the production process, 10 6 m 3 ;φ ip V represents the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; V is the control volume of the coal seam, 10 6 m 3 S wip p represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. sc The pressure under standard conditions is expressed in MPa, with a value of 0.101325; T sc The temperature under standard conditions is K, with a value of 293.15; Z sc Z is the deviation coefficient for natural gas under standard conditions, dimensionless, and has a value of 1; T is the target coal seam temperature, in K; Z is the deviation coefficient for natural gas under standard conditions, dimensionless, and has a value of 1. i p is the deviation coefficient of the gas under the original coal seam pressure, dimensionless; L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the coal seam, in MPa; p i ρ is the original coal seam pressure, MPa; p is the average coal storage pressure, MPa; Z is the deviation coefficient of gas under the average coal seam pressure, dimensionless; C p The pore volume compressibility coefficient is given in MPa. -1 C w The isothermal compressibility coefficient of water is given in MPa. -1 C s The solubility coefficient of the target coalbed methane reservoir in water, in MPa -1 B w Let m be the volume index of water. 3 / m 3 C a is the coal matrix shrinkage coefficient, which is dimensionless.

6. The method according to claim 1, characterized in that, The cumulative dissolved gas production in the target coalbed methane reservoir is calculated using the following formula: Among them, G ps The cumulative daily dissolved gas production of the target coalbed methane reservoir, 10 6 m 3 G si The original dissolved gas reserves controlled by the target coalbed methane reservoir; W p For the cumulative water production of the target coalbed methane reservoir, 10 6 m 3 W e The cumulative water intrusion during the production process, 10 6 m 3 ;φ ip V represents the coal seam porosity at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir; V is the control volume of the coal seam, 10 6 m 3 S wip p represents the water saturation of the coal seam at the initial stage of production after fracturing and flowback of the target coalbed methane reservoir. i p is the original coal seam pressure, MPa; p is the average coal storage pressure, MPa; C s The solubility coefficient of the target coalbed methane reservoir in water, in MPa -1 B w Let m be the volume index of water. 3 / m 3 C w The isothermal compressibility coefficient of water is given in MPa. -1 .

7. The method according to claim 1, characterized in that, The cumulative production of adsorbed gas in the target coalbed methane reservoir is calculated using the following formula: Among them, G pa The cumulative amount of adsorbed gas desorbed into free pores in the target coalbed methane reservoir, i.e., the cumulative production of adsorbed gas, 10 6 m 3 ;ρ c The density of coal and rock is t / m³. 3 V L For the Langmuir volume, m 3 / t;p L Langmuir pressure, MPa; p c The capillary pressure between the micropores and mesopores of the target coal seam, in MPa; p i ρ is the original coal seam pressure, MPa; p is the average coal seam pressure, MPa.

8. The method according to claim 1, characterized in that, The daily production of free gas in the target coalbed methane reservoir was calculated using the following formula: Where, q pf,j Let m be the daily free gas production of the target coalbed methane reservoir on day j. 3 / d;G pf,j The cumulative free gas production of the target coalbed methane reservoir on that day (day j), 10 6 m 3 G pf,j-1 The cumulative free gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 .

9. The method according to claim 1, characterized in that, The daily production of the adsorbed gas is calculated using the following formula: Where, q pa,j Let m be the daily adsorbed gas production of the target coalbed methane reservoir on day j. 3 / d;G pa,j The cumulative adsorbed gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G pa,j-1 The cumulative adsorbed gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 ; The daily production of dissolved gas is calculated using the following formula: Where, q ps,j Let m be the daily dissolved gas production of the target coalbed methane reservoir on day j. 3 / d;G ps,j The cumulative dissolved gas production of the target coalbed methane reservoir on the current day (day j), 10 6 m 3 G ps,j-1 The cumulative dissolved gas production of the target coalbed methane reservoir on the previous day (day j-1), 10 6 m 3 .

10. A device for evaluating the proportion of different gases in a target coalbed methane reservoir, characterized in that, include: The memory is configured to store instructions; and The processor is configured to retrieve the instructions from the memory and, when executing the instructions, to implement the method for evaluating the proportion of different gas production in deep coalbed methane reservoirs according to any one of claims 1 to 9.

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