Method for determining free gas saturation and gas content proportion of deep coal bed methane

Abstract

The present application relates to the field of gas reservoir development, and discloses a method for determining free gas saturation and gas content proportion of deep coalbed methane, which comprises the following steps: obtaining basic parameters of deep coal reservoir, determining theoretical ton coal adsorption capacity, ton coal non-adsorbed gas content, cubic coal non-adsorbed gas content, coalbed methane dissolution coefficient, gas volume coefficient and cubic coal maximum dissolved gas content according to the basic parameters, and then determining free gas saturation, and finally determining the percentage of adsorbed gas, dissolved gas and free gas by using the free gas saturation. The method can effectively determine and evaluate the free gas saturation of deep coalbed methane and the gas content proportion in different occurrence states, and the required parameters are less and easy to obtain and operate. In addition, the method is suitable for coal reservoirs with all structural characteristics and has good practicability.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir development technology, specifically, it relates to a method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane. Background Technology

[0002] The free gas saturation and the proportion of gases in different occurrence states of deep coalbed methane are important parameters in deep coalbed methane development, and are frequently used for coalbed methane reserve evaluation, production capacity evaluation, and optimization design of drainage and production systems. Deep coalbed methane exists in three different occurrence states: adsorbed gas, dissolved gas, and free gas.

[0003] Currently, due to the significant differences in temperature, pressure, and geostress between deep and shallow coalbed methane layers, it is difficult to determine and evaluate the free gas saturation and the proportion of gas content in different occurrence states of deep coalbed methane. Summary of the Invention

[0004] In view of the above-mentioned deficiencies or defects in the prior art, the present invention provides a method for determining the free gas saturation and gas content ratio of deep coalbed methane, aiming to solve the technical problem that it is difficult to determine and evaluate the free gas saturation and gas content ratio of different occurrence states in deep coalbed methane.

[0005] To achieve the above objectives, the present invention provides a method for determining the free gas saturation and gas content ratio of deep coalbed methane, comprising:

[0006] Obtain basic parameters of deep coal reservoirs, including the Langmuir volume V. L , Langevin pressure p L Original formation pressure p i Measured gas content V per ton of coal R Coal and rock density ρ c Coal reservoir temperature T, coal porosity φ, and coalbed methane relative density γ g ;

[0007] According to the Langfel volume V L The original formation pressure p i and the aforementioned Randolph pressure p L Determine the theoretical adsorption capacity V per ton of coal. i ;

[0008] According to the theoretical adsorption capacity V per ton of coal i and the measured gas content V per ton of coal R Determine the non-adsorbed gas content V per ton of coal b ;

[0009] According to the non-adsorbed gas content V per ton of coal b and the coal and rock density ρ cDetermine the non-adsorbed gas content V in the coal. bsc ;

[0010] The coalbed methane solubility coefficient C is determined based on the coal reservoir temperature T. s ;

[0011] According to the relative density γ of coalbed methane g The coal reservoir temperature T and the original formation pressure p i Determine the gas volume coefficient B gi ;

[0012] Based on the coal porosity φ and the coalbed methane solubility coefficient C s Original formation pressure p i Determine the maximum dissolved gas content V of the coal. smax ;

[0013] Based on the coal porosity φ and the coalbed methane solubility coefficient C s The original formation pressure p i The maximum dissolved gas content V of the coal. smax The non-adsorbed gas content V of the coal bsc and the gas volume coefficient B gi Determine the free gas saturation S g ;

[0014] Using the free gas saturation S g Determine the dissolved gas content V of the coal. sg V content of free gas in coal fg ;

[0015] According to the theoretical adsorption capacity V per ton of coal i The measured gas content V per ton of coal R The original formation pressure p i The aforementioned Randolph pressure p L The Langfel volume V L and the coal and rock density ρ c Determine the adsorbed gas content V in the coal. ag ;

[0016] According to the measured gas content V per ton of coal R and coal and rock density ρ c Determine the measured gas content V of the coal. Rsc ;

[0017] According to the dissolved gas content V of the coal sg The free gas content V of the coal fg The adsorbed gas content V of the coal ag and the measured gas content V of the coal. RscDetermine the percentage of adsorbed gas, dissolved gas, and free gas.

[0018] Optionally, the step based on the Langmuir volume V L The original formation pressure p i and the aforementioned Randolph pressure p L Determine the theoretical adsorption capacity V per ton of coal. i ,include:

[0019] The theoretical adsorption capacity per ton of coal, V i It is calculated using the following formula:

[0020]

[0021] Among them, V i V represents the theoretical adsorption capacity per ton of coal. L For the Langführer volume, p L For the Langevin pressure, p i This represents the original formation pressure.

[0022] Optionally, the adsorption capacity V per ton of coal is based on the theoretical adsorption capacity. i and the measured gas content V per ton of coal R Determine the non-adsorbed gas content V per ton of coal b ,include:

[0023] If the measured gas content per ton of coal V R Less than or equal to the theoretical adsorption capacity V per ton of coal i The non-adsorbed gas content V per ton of coal b The measured gas content per ton of coal, V, is 0; R Greater than the theoretical adsorption capacity V per ton of coal i The non-adsorbed gas content per ton of coal is calculated using the following formula:

[0024] V b =V R -V i V R >V i

[0025] Among them, V b V represents the non-adsorbed gas content per ton of coal. R To measure the gas content per ton of coal, V i This represents the theoretical adsorption capacity per ton of coal.

[0026] Optionally, the step of determining the non-adsorbed gas content V per ton of coal... b and the coal and rock density ρ c Determine the non-adsorbed gas content V in the coal. bsc ,include:

[0027] The non-adsorbent gas content V of the coalbsc It is calculated using the following formula:

[0028] V bsc =V b ×ρ c

[0029] Among them, V bsc V represents the non-adsorbed gas content of coal. b ρ represents the non-adsorbed gas content per ton of coal. c This represents the density of coal and rock.

[0030] Optionally, the coalbed methane solubility coefficient C is determined based on the coal reservoir temperature T. s ,include:

[0031] The Henry's constant H is calculated using the following formula:

[0032] H = 68.629 × T + 2475.7

[0033] Where H is Henry's constant and T is the coal reservoir temperature;

[0034] The coalbed methane solubility coefficient C s It is calculated using the following formula:

[0035]

[0036] Where H is the Henry's constant, C s This is the coalbed methane solubility coefficient.

[0037] Optionally, the step of basin-gas relative density γ g The coal reservoir temperature T and the original formation pressure p i Determine the gas volume coefficient B gi ,include:

[0038] Using the Dranchuk-Abou-Kassem method, based on the relative density γ of the coalbed methane... g Based on the coal reservoir temperature T, the original formation pressure p is determined. i The compressibility factor Z of lower coalbed methane;

[0039] The gas volume coefficient B gi It is calculated using the following formula:

[0040]

[0041] Among them, B gi It is the gas volume coefficient, p i Where is the original formation pressure, T is the coal reservoir temperature, and Z is the compressibility factor.

[0042] Optionally, the step of determining the coal porosity φ and the coalbed methane solubility coefficient C... s Original formation pressure p i Determine the maximum dissolved gas content V of the coal. smax ,include:

[0043] The maximum dissolved gas content V of the coal smax It is calculated using the following formula:

[0044] V smax =φ×C s ×p i

[0045] Among them, V smax The maximum dissolved gas content of the coal is given by φ, where φ is the coal porosity and C is the stoichiometric coefficient. s p is the solubility coefficient of coalbed methane. i This represents the original formation pressure.

[0046] Optionally, the step of determining the coal porosity φ and the coalbed methane solubility coefficient C... s The original formation pressure p i The maximum dissolved gas content V of the coal. smax The non-adsorbed gas content V of the coal bsc and the gas volume coefficient B gi Determine the free gas saturation S g ,include:

[0047] If the non-adsorbent gas content of the coal is V bsc Less than or equal to the maximum dissolved gas content V of the coal. smax The free gas saturation S g The content of non-adsorbed gas in the coal is 0; bsc Greater than the maximum dissolved gas content V of the coal smax The free gas saturation S g It is calculated using the following formula:

[0048]

[0049] Among them, S g V represents free gas saturation, φ represents coal porosity, and V represents free gas saturation. bsc B represents the non-adsorbed gas content of the coal. gi p is the gas volume coefficient. i For the original formation pressure, C s V is the solubility coefficient of coalbed methane. smax This represents the maximum dissolved gas content of the coal.

[0050] Optionally, the utilization of the free gas saturation S g Determine the dissolved gas content V of the coal.sg V content of free gas in coal fg ,include:

[0051] If the non-adsorbent gas content of the coal is V bsc If the dissolved gas content V of the coal is equal to 0, then... sg The content of non-adsorbed gas in the coal is 0; bsc The maximum dissolved gas content V of the coal is greater than 0 and less than or equal to that of the coal. smax The dissolved gas content V of the coal is... sg Equal to the non-adsorbed gas content V of the coal bsc If the non-adsorbed gas content of the coal is V bsc Greater than the maximum dissolved gas content V of the coal smax The dissolved gas content V of the coal is... sg It is calculated using the following formula:

[0052] V sg =φ(1-S g C s p i

[0053] Among them, V sg φ represents the dissolved gas content of the coal, φ represents the coal porosity, and C represents the dissolved gas content of the coal. s p is the solubility coefficient of coalbed methane. i S represents the original formation pressure. g Free gas saturation;

[0054] The free gas content V of the coal fg It is calculated using the following formula:

[0055]

[0056] Among them, V fg φ represents the free gas content of the coal, φ represents the coal porosity, and B represents the free gas content of the coal. gi S is the gas volume coefficient. g This represents the free gas saturation.

[0057] Optionally, the adsorption capacity V per ton of coal is based on the theoretical adsorption capacity. i The measured gas content V per ton of coal R The original formation pressure p i The aforementioned Randolph pressure p L The Langfel volume V L and the coal and rock density ρ c Determine the adsorbed gas content V in the coal. ag ,include:

[0058] Determine the critical desorption pressure p d If the measured gas content V per ton of coalR Greater than or equal to the theoretical adsorption capacity V per ton of coal i Then the critical desorption pressure p d Equal to the original formation pressure p i If the measured gas content per ton of coal V R Less than the theoretical adsorption capacity V per ton of coal i Then the critical desorption pressure p d It is calculated using the following formula:

[0059]

[0060] Where, p d V is the critical desorption pressure. R To measure the gas content per ton of coal, V L For the Langführer volume, p L It is the Langevin pressure;

[0061] The adsorbed gas content V per ton of coal is calculated using the following formula. a :

[0062]

[0063] Among them, V a V represents the adsorbed gas content per ton of coal. L For the Langführer volume, p d p is the critical desorption pressure. L It is the Langevin pressure;

[0064] The adsorbed gas content V of the square coal ag It is calculated using the following formula:

[0065] V ag =V a ×ρ c

[0066] Among them, V ag V represents the adsorbed gas content of kerosene. a ρ is the adsorbed gas content per ton of coal. c The density of coal and rock;

[0067] The measured gas content V per ton of coal R and coal and rock density ρ c Determine the measured gas content V of the coal. Rsc ,include:

[0068] The measured gas content V of the coal Rsc It is calculated using the following formula:

[0069] V Rsc =V R ×ρ c

[0070] Among them, V Rsc To measure the gas content of coal, V R To measure the gas content per ton of coal, ρ c The density of coal and rock;

[0071] The dissolved gas content V of the coal sg The free gas content V of the coal fg The adsorbed gas content V of the coal ag and the measured gas content V of the coal. Rsc Determine the percentage of adsorbed gas, dissolved gas, and free gas, including:

[0072] The percentage of the adsorbed gas is calculated using the following formula:

[0073]

[0074] Among them, f ag It is the percentage of adsorbed gas, V ag It is the adsorbed gas content of coal, V Rsc This is the measured gas content of the coal.

[0075] The percentage of dissolved gas is calculated using the following formula:

[0076]

[0077] Among them, f sg It is the percentage of dissolved gas, V sg It is the dissolved gas content of coal, V Rsc This is the measured gas content of the coal.

[0078] The percentage of free gas is calculated using the following formula:

[0079]

[0080] Among them, f fg It is the percentage of free gas, V fg It is the free gas content of kerosene, V Rsc This is the measured gas content of the coal.

[0081] The above technical solution only requires obtaining the Langevin volume V. L , Langevin pressure p L Original formation pressure p i Measured gas content V per ton of coal R Coal and rock density ρ c Coal reservoir temperature T, coal porosity φ, and coalbed methane relative density γ g These basic parameters are sufficient to determine the free gas saturation S of deep coalbed methane. gV content of adsorbed gas in coal ag and measured gas content V of coal Rsc Then, using the free gas saturation S g The dissolved gas content V of the coal can be determined. sg V content of free gas in coal fg Finally, by measuring the dissolved gas content V in the coal... sg V content of free gas in coal fg V content of adsorbed gas in coal ag and measured gas content V of coal Rsc The percentage of adsorbed gas, dissolved gas, and free gas can be determined. Thus, the determination method of the present invention can effectively determine and evaluate the free gas saturation and the proportion of gas content in different occurrence states of deep coalbed methane. It requires fewer parameters, and the parameters are easy to obtain and operate. In addition, the determination method of the present invention is applicable to coal reservoirs with all structural characteristics and has good practicality.

[0082] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0083] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0084] Figure 1 This is a flowchart illustrating the method for determining the saturation of free gas and the percentage of gas content in deep coalbed methane according to the present invention. Detailed Implementation

[0085] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0086] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0087] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used to describe the relative positions of components in relation to the directions shown in the accompanying drawings or in relation to the vertical, perpendicular, or gravitational directions.

[0088] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0089] This invention first provides a method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane.

[0090] In one implementation, refer to the appendix. Figure 1 As shown, the methods for determining the free gas saturation and gas content ratio of deep coalbed methane include:

[0091] To obtain the basic parameters of deep coal reservoirs, including the Langmuir volume V L , Langevin pressure p L Original formation pressure p i Measured gas content V per ton of coal R Coal and rock density ρ c Coal reservoir temperature T, coal porosity φ, and coalbed methane relative density γ g ;

[0092] According to the Langevin volume V L Original formation pressure p i and the Langevin pressure p L Determine the theoretical adsorption capacity V per ton of coal. i ;

[0093] Based on the theoretical adsorption capacity V per ton of coal i And measured gas content V per ton of coal R Determine the non-adsorbed gas content V per ton of coal b ;

[0094] Based on the non-adsorbed gas content V per ton of coal b and coal and rock density ρ c Determine the non-adsorbed gas content V in the coal. bsc ;

[0095] Determine the coalbed methane solubility coefficient C based on the coal reservoir temperature T. s ;

[0096] Based on the relative density γ of coalbed methane g Coal reservoir temperature T and original formation pressure p i Determine the gas volume coefficient B gi ;

[0097] Based on coal porosity φ and coalbed methane solubility coefficient C s Original formation pressure p i Determine the maximum dissolved gas content V of the coal. smax ;

[0098] Based on coal porosity φ and coalbed methane solubility coefficient C s Original formation pressure p i Maximum dissolved gas content V in coal smax Non-adsorbed gas content V in coal bsc and gas volume coefficient B gi Determine the free gas saturation S g ;

[0099] Using free gas saturation S g Determine the dissolved gas content V of the coal. sg V content of free gas in coal fg According to the theoretical adsorption capacity V per ton of coal i Measured gas content V per ton of coal R Original formation pressure p i , Langevin pressure p L , Langevin volume V L and coal and rock density ρ c Determine the adsorbed gas content V in the coal. ag ;

[0100] Based on the measured gas content V per ton of coal R and coal and rock density ρ c Determine the measured gas content V of the coal. Rsc ;

[0101] According to the dissolved gas content V of the coal sg V content of free gas in coal fg V content of adsorbed gas in coal ag and measured gas content V of coal Rsc Determine the percentage of adsorbed gas, dissolved gas, and free gas.

[0102] In the determination method of this embodiment, only the Langmuir volume V needs to be obtained. L , Langevin pressure p L Original formation pressure p i Measured gas content V per ton of coal R Coal and rock density ρ c Coal reservoir temperature T, coal porosity φ, and coalbed methane relative density γ g These basic parameters are sufficient to determine the free gas saturation S of deep coalbed methane. g V content of adsorbed gas in coal ag and measured gas content V of coal Rsc Then, using the free gas saturation S g The dissolved gas content V of the coal can be determined. sg V content of free gas in coal fg Finally, by measuring the dissolved gas content V in the coal... sg V content of free gas in coal fg V content of adsorbed gas in coal ag and measured gas content V of coal RscThe percentage of adsorbed gas, dissolved gas, and free gas can be determined. Thus, the determination method of this embodiment can effectively determine and evaluate the free gas saturation and the proportion of gas content in different occurrence states of deep coalbed methane. It requires few parameters, and the parameters are easy to obtain and operate. In addition, the determination method of this invention is applicable to coal reservoirs with all structural characteristics and has good practicality.

[0103] In one implementation, based on the Langevin volume V L Original formation pressure p i and the Langevin pressure p L Determine the theoretical adsorption capacity V per ton of coal. i ,include:

[0104] Theoretical adsorption capacity per ton of coal V i It is calculated using the following formula:

[0105]

[0106] Among them, V i V represents the theoretical adsorption capacity per ton of coal. L For the Langführer volume, p L For the Langevin pressure, p i This represents the original formation pressure.

[0107] Understandably, the theoretical adsorption capacity V per ton of coal i Defined as the volume of gas adsorbed in each ton of coal and rock under the original formation pressure.

[0108] In one implementation, based on the theoretical adsorption capacity V per ton of coal i And measured gas content V per ton of coal R Determine the non-adsorbed gas content V per ton of coal b ,include:

[0109] If the measured gas content per ton of coal is V R Less than or equal to the theoretical adsorption capacity V per ton of coal i Then the non-adsorbed gas content V per ton of coal b The value is 0; if the measured gas content V per ton of coal is... R Greater than the theoretical adsorption capacity per ton of coal V i The non-adsorbed gas content per ton of coal is calculated using the following formula:

[0110] V b =V R -V i V R >V i Equation (2)

[0111] Among them, V b V represents the non-adsorbed gas content per ton of coal. RTo measure the gas content per ton of coal, V i This represents the theoretical adsorption capacity per ton of coal.

[0112] Understandably, the non-adsorbed gas content V per ton of coal b Defined as the amount of gas content per ton of coal that exceeds the theoretical adsorption capacity per ton of coal by the measured gas content per ton of coal.

[0113] In one embodiment, based on the non-adsorbed gas content V per ton of coal b and coal and rock density ρ c Determine the non-adsorbed gas content V in the coal. bsc ,include:

[0114] Non-adsorbed gas content V in coal bsc It is calculated using the following formula:

[0115] V bsc =V b ×ρ c Equation (3)

[0116] Among them, V bsc V represents the non-adsorbed gas content of coal. b ρ represents the non-adsorbed gas content per ton of coal. c This represents the density of coal and rock.

[0117] Understandably, the non-adsorbed gas content V in square coal... bsc Defined as the volume of non-adsorbed gas in each cubic meter of coal.

[0118] In one embodiment, the coalbed methane solubility coefficient C is determined based on the coal reservoir temperature T. s ,include:

[0119] The Henry's constant H is calculated using the following formula:

[0120] H = 68.629 × T + 2475.7 Equation (4)

[0121] Where H is Henry's constant and T is the coal reservoir temperature;

[0122] Coalbed methane solubility coefficient C s It is calculated using the following formula:

[0123]

[0124] Where H is the Henry's constant, C s This is the coalbed methane solubility coefficient.

[0125] Understandably, the solubility coefficient C of coalbed methane s Defined as the solubility coefficient of coalbed methane in water.

[0126] In one embodiment, based on the relative density γ of coalbed methaneg Coal reservoir temperature T and original formation pressure p i Determine the gas volume coefficient B gi ,include:

[0127] Using the Dranchuk-Abou-Kassem method, based on the relative density γ of coalbed methane... g Determine the original formation pressure p based on the coal reservoir temperature T. i The compressibility factor Z of lower coalbed methane;

[0128] Gas volume coefficient B gi It is calculated using the following formula:

[0129]

[0130] Among them, B gi It is the gas volume coefficient, p i Where is the original formation pressure, T is the coal reservoir temperature, and Z is the compressibility factor.

[0131] It should be noted that the Dranchuk-Abou-Kassem method is well known to those skilled in the art, therefore, its specific principles will not be elaborated here.

[0132] In one embodiment, based on the coal porosity φ and the coalbed methane solubility coefficient C... s Original formation pressure p i Determine the maximum dissolved gas content V of the coal. smax ,include:

[0133] Maximum dissolved gas content V in square coal smax It is calculated using the following formula:

[0134] V smax =φ×C s ×p i Equation (7)

[0135] Among them, V smax The maximum dissolved gas content of the coal is given by φ, where φ is the coal porosity and C is the stoichiometric coefficient. s p is the solubility coefficient of coalbed methane. i This represents the original formation pressure.

[0136] Understandably, the maximum dissolved gas content V in square coal... smax Defined as the volume of dissolved gas in water when the pores of a cubic meter of coal are filled with water.

[0137] In one embodiment, based on the coal porosity φ and the coalbed methane solubility coefficient C... s Original formation pressure p i Maximum dissolved gas content V in coal smaxNon-adsorbed gas content V in coal bsc and gas volume coefficient B gi Determine the free gas saturation S g ,include:

[0138] If the non-adsorbed gas content of the coal is V bsc Less than or equal to the maximum dissolved gas content V of cubic coal smax Then the free gas saturation S g The content of non-adsorbed gas in the coal is 0; bsc Greater than the maximum dissolved gas content V of coal smax Then the free gas saturation S g It is calculated using the following formula:

[0139]

[0140] Among them, S g V represents free gas saturation, φ represents coal porosity, and V represents free gas saturation. bsc B represents the non-adsorbed gas content of the coal. gi p is the gas volume coefficient. i For the original formation pressure, C s V is the solubility coefficient of coalbed methane. smax This represents the maximum dissolved gas content of the coal.

[0141] Understandably, the free gas saturation S g Defined as the proportion of free gas volume to the pore volume of coal and rock.

[0142] In one implementation, the free gas saturation S is utilized. g Determine the dissolved gas content V of the coal. sg V content of free gas in coal fg ,include:

[0143] If the non-adsorbed gas content of the coal is V bsc If the dissolved gas content V of the coal is equal to 0, then the dissolved gas content V of the coal is equal to 0. sg The content of non-adsorbed gas in the coal is 0; bsc The maximum dissolved gas content V of the coal is greater than 0 and less than or equal to 0. smax The dissolved gas content V of the coal sg Equal to the non-adsorbed gas content V of coal bsc If the non-adsorbed gas content of the coal is V bsc Greater than the maximum dissolved gas content V of coal smax The dissolved gas content V of the coal sg It is calculated using the following formula:

[0144] V sg =φ(1-S g C s p iEquation (9)

[0145] Among them, V sg φ represents the dissolved gas content of the coal, φ represents the coal porosity, and C represents the dissolved gas content of the coal. s p is the solubility coefficient of coalbed methane. i S represents the original formation pressure. g Free gas saturation;

[0146] V content of free gas in coal fg It is calculated using the following formula:

[0147]

[0148] Among them, V fg φ represents the free gas content of the coal, φ represents the coal porosity, and B represents the free gas content of the coal. gi S is the gas volume coefficient. g This represents the free gas saturation.

[0149] Understandably, the dissolved gas content V in square coal sg Defined as the volume of coalbed methane dissolved in the pore water per cubic meter of coal; V is the free gas content of the coal. fg Defined as the volume of coalbed methane in free state per cubic meter of coal.

[0150] In one implementation, based on the theoretical adsorption capacity V per ton of coal i Measured gas content V per ton of coal R Original formation pressure p i , Langevin pressure p L , Langevin volume V L and coal rock density ρ c Determine the adsorbed gas content V in the coal. ag ,include:

[0151] Determine the critical desorption pressure p d If the measured gas content V per ton of coal R Greater than or equal to the theoretical adsorption capacity V per ton of coal i Then the critical desorption pressure p d Equal to the original formation pressure p i If the measured gas content V per ton of coal R Less than the theoretical adsorption capacity per ton of coal V i Then the critical desorption pressure p d It is calculated using the following formula:

[0152]

[0153] Where, p d V is the critical desorption pressure. R To measure the gas content per ton of coal, V L For the Langführer volume, p LIt is the Langevin pressure;

[0154] Understandably, the critical desorption pressure p d Defined as the pressure at which the adsorbed gas begins to desorb.

[0155] The adsorbed gas content V per ton of coal is calculated using the following formula. a :

[0156]

[0157] Among them, V a V represents the adsorbed gas content per ton of coal. L For the Langführer volume, p d p is the critical desorption pressure. L It is the Langevin pressure;

[0158] Understandably, the adsorbed gas content V per ton of coal a Defined as the volume of adsorbed gas per ton of coal at the critical desorption pressure.

[0159] V content of adsorbed gas in coal ag It is calculated using the following formula:

[0160] V ag =V a ×ρ c Equation (13)

[0161] Among them, V ag V represents the adsorbed gas content of kerosene. a ρ is the adsorbed gas content per ton of coal. c This represents the density of coal and rock.

[0162] Understandably, the adsorbed gas content V in square coal ag Defined as the volume of coalbed methane adsorbed per cubic meter of coal.

[0163] In one implementation, based on the measured gas content V per ton of coal R and coal and rock density ρ c Determine the measured gas content V of the coal. Rsc ,include:

[0164] Measured gas content V of coal Rsc It is calculated using the following formula:

[0165] V Rsc =V R ×ρ c Equation (14)

[0166] Among them, V Rsc To measure the gas content of coal, V R To measure the gas content per ton of coal, ρ c This represents the density of coal and rock.

[0167] Understandably, the measured gas content V of the coal is... Rsc Defined as the measured gas volume per cubic meter of coal.

[0168] In one embodiment, based on the dissolved gas content V of the coal... sg V content of free gas in coal fg V content of adsorbed gas in coal ag and measured gas content V of coal Rsc Determine the percentage of adsorbed gas, dissolved gas, and free gas, including:

[0169] The percentage of adsorbed gas is calculated using the following formula:

[0170]

[0171] Among them, f ag It is the percentage of adsorbed gas, V ag It is the adsorbed gas content of coal, V Rsc This is the measured gas content of the coal.

[0172] The percentage of dissolved gas is calculated using the following formula:

[0173]

[0174] Among them, f sg It is the percentage of dissolved gas, V sg It is the dissolved gas content of coal, V Rsc This is the measured gas content of the coal.

[0175] The percentage of free gas is calculated using the following formula:

[0176]

[0177] Among them, f fg It is the percentage of free gas, V fg It is the free gas content of kerosene, V Rsc This is the measured gas content of the coal.

[0178] Understandably, the percentage of adsorbed gas, dissolved gas, and free gas is defined as the proportion of adsorbed gas content, dissolved gas content, and free gas content in the pulverized coal to the measured gas content of the pulverized coal.

[0179] For ease of understanding, a specific application of the method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane of the present invention is provided below.

[0180] The specific values ​​of the basic parameters of the deep coal reservoir obtained are shown in the table below:

[0181] parameter numerical values unit <![CDATA[Langmuir volume V L > 20 <![CDATA[m 3 / t]]> <![CDATA[Lange pressure p L > 3.7 MPa <![CDATA[Original formation pressure p i > 20 MPa <![CDATA[Measured gas content per ton of coal V R > 18 <![CDATA[m 3 / t]]> <![CDATA[Coal-rock density ρ c > 1.4 <![CDATA[t / m 3 ]]> Coal reservoir temperature T 54.7 ℃ Coal and rock porosity φ 0.033 Decimals <![CDATA[Relative density of natural gas γ g > 0.56 Dimensionless

[0182] Step 1. Calculate the theoretical adsorption capacity per ton of coal

[0183] The Langführer volume V L , Langevin pressure p L Original formation pressure p i Substituting the numerical value into equation (1), we get That is, the theoretical adsorption capacity V per ton of coal i =16.878m 3 / t.

[0184] Step 2. Calculate the non-adsorbed gas content per ton of coal.

[0185] Due to the measured gas content V per ton of coal R Greater than the theoretical adsorption capacity per ton of coal V i Therefore, the measured gas content V per ton of coal will be... R Theoretical adsorption capacity per ton of coal V i Substituting the numerical value into equation (2), we obtain V. b =V R -V i =18-16.878=1.122(m) 3 / t),V R >V i That is, the non-adsorbed gas content V per ton of coal b =1.122m 3 / t.

[0186] Step 3. Calculate the non-adsorbed gas content of the coal.

[0187] The non-adsorbent gas content per ton of coal V b Coal and rock density ρ c Substituting the numerical value into equation (3), we obtain V. bsc =V b ×ρ c =1.122 × 1.4 = 1.5708 (m) 3 / m 3 ), that is, the non-adsorbed gas content V of the coal. bsc =1.5708m 3 / m 3 .

[0188] Step 4. Calculate the Henry's constant.

[0189] Substituting the value of the coal reservoir temperature T into equation (4), we get H = 68.629 × T + 2475.7 = 68.629 × 54.7 + 2475.7 = 6229.7 (MPa), which is the Henry's constant H = 6229.7 MPa.

[0190] Step 5. Calculate the coalbed methane solubility coefficient

[0191] Substituting the value of the Henry's constant H into equation (5), we get That is, the solubility coefficient C of coalbed methane s =0.19976MPa -1 .

[0192] Step 6. Calculate the compression factor

[0193] Using the Dranchuk-Abou-Kassem method, based on the relative density γ of coalbed methane... g Given the coal reservoir temperature T, calculate the original formation pressure p. i The compressibility factor of lower coalbed methane is Z = 0.8768.

[0194] Step 7. Calculate the gas volume coefficient

[0195] The coal reservoir temperature T, compressibility factor Z, and original formation pressure p are used. i Substituting the numerical value into equation (6), we get That is, the gas volume coefficient B gi =0.004968.

[0196] Step 8. Calculate the maximum dissolved gas content of the coal.

[0197] The solubility coefficient of coalbed methane C s Coal porosity φ, original formation pressure p i Substituting the numerical value into equation (7), we obtain V. smax =φ×C s ×p i =0.033×0.19976×20=0.132(m 3 / m 3 ), that is, the maximum dissolved gas content V of square coal. smax =0.132m 3 / m 3 .

[0198] Step 9. Calculate the free gas saturation.

[0199] Due to the non-adsorbed gas content V in the coal bsc Greater than the maximum dissolved gas content V of coal smax Therefore, the solubility coefficient C of coalbed methane is... s Non-adsorbed gas content V in coal bsc Original formation pressure p i Substituting the numerical value of coal and rock porosity φ into equation (8), we obtain... That is, free gas saturation S g =22.1%.

[0200] Step 10. Calculate the dissolved gas content of the coal.

[0201] Due to the non-adsorbed gas content V in the coal bsc Greater than the maximum dissolved gas content V of coal smax The porosity φ of coal and rock, and the free gas saturation S g Coalbed methane solubility coefficient C s Original formation pressure p i Substituting the value into equation (9), we get V. sg =φ(1-S g C s p i =0.033×(1-22.1%)×0.19976×20=0.103(m 3 / m 3 ), that is, the dissolved gas content V of coal. sg =0.103m 3 / m 3 .

[0202] Step 11. Calculate the free gas content of the coal.

[0203] Coal porosity φ and free gas saturation S g Gas volume coefficient B gi Substituting the numerical value into equation (10), we get That is, the free gas content V of coal fg =1.468m 3 / m 3 .

[0204] Step 12. Calculate the critical desorption pressure

[0205] Due to the measured gas content V per ton of coal R Greater than the theoretical adsorption capacity per ton of coal V i Therefore, the critical desorption pressure p d Equal to the original formation pressure p i That is, the critical desorption pressure p d =20MPa.

[0206] Step 13: Calculate the adsorbed gas content per ton of coal.

[0207] The critical desorption pressure p d Langevin volume V L , Langevin pressure p L Substituting the numerical value into equation (12), we get That is, the adsorbed gas content V per ton of coal a =16.878m 3 / t.

[0208] Step 14. Calculate the adsorbed gas content of the coal.

[0209] V of adsorbed gas content per ton of coal a Coal and rock density ρc Substituting the numerical value into equation (13), we obtain V. ag =V a ×ρ c =16.878 × 1.4 = 23.629 (m) 3 / m 3 ), that is, the adsorbed gas content V of the coal. ag =23 . 629m 3 / m 3 .

[0210] Step 15. Calculate the gas content of the measured coal.

[0211] The measured gas content V per ton of coal R Coal and rock density ρ c Substituting the numerical value into equation (14), we obtain V. Rsc =V R ×ρ c =18 × 1.4 = 25.2 (m) 3 / m 3 ), that is, the measured gas content V of the coal. Rsc =25.2m 3 / m 3 .

[0212] Step 16. Calculate the percentage of adsorbed gas, dissolved gas, and free gas.

[0213] The measured gas content V of the coal Rsc Hefang coal adsorbed gas content V ag Substituting the numerical value into equation (15), we get That is, the percentage of adsorbed gas f ag =93.77%;

[0214] The measured gas content V of the coal Rsc Dissolved gas content V in coal sg Substituting the numerical value into equation (16), we get That is, the percentage of dissolved gas f sg =0.41%;

[0215] The measured gas content V of the coal Rsc V content of free gas in coal fg Substituting the numerical value into equation (17), we get That is, the percentage of free gas f fg =5.82%.

[0216] Based on the obtained basic parameters, the above steps can be used to determine that the free gas saturation is 22.1%, the percentage of adsorbed gas is 93.77%, the percentage of dissolved gas is 0.41%, and the percentage of free gas is 5.82%.

[0217] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0218] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0219] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for determining the saturation of free gas and the percentage of gas content in deep coalbed methane, characterized in that, include: Obtain basic parameters of deep coal reservoirs, including the Langmuir volume. V L Langevin pressure p L Original formation pressure p i Actual gas content per ton of coal V R Coal and rock density ρ c Coal reservoir temperature T Coal and rock porosity φ and the relative density of coalbed methane γ g ; According to the Langführer volume V L The original formation pressure p i and the aforementioned Randolph pressure p L Determine the theoretical adsorption capacity per ton of coal V i ; Based on the theoretical adsorption capacity per ton of coal V i and the measured gas content per ton of coal V R Determine the non-adsorbed gas content per ton of coal V b ; Based on the non-adsorbed gas content per ton of coal V b and the coal and rock density ρ c Determine the non-adsorbed gas content of coal. V bsc ; Based on the coal reservoir temperature T Determine the solubility coefficient of coalbed methane C s ; Based on the relative density of coalbed methane γ g The coal reservoir temperature T and original formation pressure p i Determine the gas volume coefficient B gi ; According to the coal and rock porosity φ The solubility coefficient of coalbed methane C s Original formation pressure p i Determine the maximum dissolved gas content of coal. V smax ; According to the coal and rock porosity φ The solubility coefficient of coalbed methane C s The original formation pressure p i The maximum dissolved gas content of the coal. V smax The non-adsorbed gas content of the coal. V bsc and the gas volume coefficient B gi Determine the free gas saturation S g ; Using the free gas saturation S g Determine the dissolved gas content of coal. V sg Free gas content of coal V fg ; Based on the theoretical adsorption capacity per ton of coal V i The measured gas content per ton of coal V R The original formation pressure p i The aforementioned Randolph pressure p L The Langfel volume V L and the coal and rock density ρ c Determine the adsorbed gas content of the coal. V ag ; Based on the measured gas content per ton of coal V R and coal and rock density ρ c Determine the gas content of the measured coal. V Rsc ; Based on the dissolved gas content of the coal V sg The free gas content of the coal V fg The adsorbed gas content of the coal V ag and the measured gas content of the coal. V Rsc Determine the percentage of adsorbed gas, dissolved gas, and free gas; According to the theoretical adsorption capacity per ton of coal V i and the measured gas content per ton of coal V R Determine the non-adsorbed gas content per ton of coal V b ,include: If the measured gas content per ton of coal V R Less than or equal to the theoretical adsorption capacity per ton of coal V i The non-adsorbed gas content per ton of coal V b The value is 0; if the measured gas content per ton of coal is 0. V R Greater than the theoretical adsorption capacity per ton of coal V i The non-adsorbed gas content per ton of coal is calculated using the following formula: in, V b The content of non-adsorbed gas per ton of coal. V R To measure the gas content per ton of coal, V i This represents the theoretical adsorption capacity per ton of coal. The non-adsorbent gas content per ton of coal V b and the coal and rock density ρ c Determine the non-adsorbed gas content of coal. V bsc ,include: The non-adsorbent gas content of the coal V bsc It is calculated using the following formula: in, V bsc This refers to the non-adsorbed gas content in square coal. V b The content of non-adsorbed gas per ton of coal. ρ c The density of coal and rock; The basis of the coal and rock porosity φ The solubility coefficient of coalbed methane C s Original formation pressure p i Determine the maximum dissolved gas content of coal. V smax ,include: The maximum dissolved gas content of the coal V smax It is calculated using the following formula: in, V smax This represents the maximum dissolved gas content of the coal. φ For coal and rock porosity, C s The solubility coefficient of coalbed methane. p i This represents the original formation pressure; The basis of the coal and rock porosity φ The solubility coefficient of coalbed methane C s The original formation pressure p i The maximum dissolved gas content of the coal. V smax The non-adsorbed gas content of the coal. V bsc and the gas volume coefficient B gi Determine the free gas saturation S g ,include: If the non-adsorbent gas content of the coal V bsc Less than or equal to the maximum dissolved gas content of the coal. V smax The free gas saturation S g The content of non-adsorbed gas in the coal is 0; V bsc Greater than the maximum dissolved gas content of the coal. V smax The free gas saturation S g It is calculated using the following formula: in, S g Free gas saturation φ For coal and rock porosity, V bsc This refers to the non-adsorbed gas content in square coal. B gi The gas volume coefficient, p i The original formation pressure, C s The solubility coefficient of coalbed methane. V smax This represents the maximum dissolved gas content of square coal. The utilization of the free gas saturation S g Determine the dissolved gas content of coal. V sg Free gas content of coal V fg ,include: If the non-adsorbent gas content of the coal V bsc If the dissolved gas content of the coal is equal to 0, then the dissolved gas content of the coal is... V sg The content of non-adsorbed gas in the coal is 0; V bsc Greater than 0 and less than or equal to the maximum dissolved gas content of the coal. V smax The dissolved gas content of the coal is... V sg Equal to the non-adsorbed gas content of the coal. V bsc If the non-adsorbed gas content of the coal is... V bsc Greater than the maximum dissolved gas content of the coal. V smax The dissolved gas content of the coal is... V sg It is calculated using the following formula: in, V sg The dissolved gas content of coal. φ For coal and rock porosity, C s The solubility coefficient of coalbed methane. p i The original formation pressure, S g Free gas saturation; The free gas content of the coal V fg It is calculated using the following formula: in, V fg The free gas content of kerosene. φ For coal and rock porosity, B gi The gas volume coefficient, S g Free gas saturation; According to the theoretical adsorption capacity per ton of coal V i The measured gas content per ton of coal V R The original formation pressure p i The aforementioned Randolph pressure p L The Langfel volume V L and the coal and rock density ρ c Determine the adsorbed gas content of the coal. V ag ,include: Determine the critical desorption pressure p d If the measured gas content per ton of coal V R Greater than or equal to the theoretical adsorption capacity per ton of coal V i The critical desorption pressure p d Equal to the original formation pressure p i If the measured gas content per ton of coal V R Less than the theoretical adsorption capacity per ton of coal V i The critical desorption pressure p d It is calculated using the following formula: in, p d This is the critical desorption pressure. V R To measure the gas content per ton of coal, V L For the Langevin volume, p L It is the Langevin pressure; The adsorbed gas content per ton of coal is calculated using the following formula. V a : in, V a The adsorbed gas content per ton of coal. V L For the Langevin volume, p d This is the critical desorption pressure. p L It is the Langevin pressure; The adsorbed gas content of the square coal V ag It is calculated using the following formula: in, V ag The adsorbed gas content of the coal. V a The adsorbed gas content per ton of coal. ρ c The density of coal and rock; The measured gas content per ton of coal V R and coal and rock density ρ c Determine the gas content of the measured coal. V Rsc ,include: The measured gas content of the coal V Rsc It is calculated using the following formula: in, V Rsc To measure the gas content of coal, V R To measure the gas content per ton of coal, ρ c This represents the density of coal and rock.

2. The method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane according to claim 1, characterized in that, The according to the Langfel volume V L The original formation pressure p i and the aforementioned Randolph pressure p L Determine the theoretical adsorption capacity per ton of coal V i ,include: The theoretical adsorption capacity per ton of coal V i It is calculated using the following formula: in, V i This represents the theoretical adsorption capacity per ton of coal. V L For the Langevin volume, p L For the Lange pressure, p i This represents the original formation pressure.

3. The method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane according to claim 1, characterized in that, According to the coal reservoir temperature T Determine the solubility coefficient of coalbed methane C s , include: The Henry constant is calculated using the following formula. H : in, H Henry's constant, T Temperature of the coal reservoir; The coalbed methane solubility coefficient C s It is calculated using the following formula: in, H Henry's constant, C s This is the coalbed methane solubility coefficient.

4. The method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane according to claim 1, characterized in that, The relative density of the coalbed methane γ g The coal reservoir temperature T and original formation pressure p i Determine the gas volume coefficient B gi ,include: The Dranchuk-Abou-Kassem method was used, based on the relative density of the coalbed methane. γ g and the temperature of the coal reservoir T Determine the original formation pressure p i Compressibility factor of lower coalbed methane Z ; The gas volume coefficient B gi It is calculated using the following formula: in, B gi It is the gas volume coefficient. p i The original formation pressure, T It is the temperature of the coal reservoir. Z It is the compression factor.

5. The method for determining the saturation of free gas and the proportion of gas content in deep coalbed methane according to claim 1, characterized in that, The dissolved gas content of the coal V sg The free gas content of the coal V fg The adsorbed gas content of the coal V ag and the measured gas content of the coal. V Rsc Determine the percentage of adsorbed gas, dissolved gas, and free gas, including: The percentage of the adsorbed gas is calculated using the following formula: in, f ag It represents the percentage of adsorbed gas. V ag It refers to the adsorbed gas content of the coal. V Rsc This is the measured gas content of the coal. The percentage of dissolved gas is calculated using the following formula: in, f sg It is the percentage of dissolved gas. V sg It refers to the dissolved gas content of coal. V Rsc This is the measured gas content of the coal. The percentage of free gas is calculated using the following formula: in, f fg It is the percentage of free gas. V fg It refers to the free gas content of kerosene. V Rsc This is the measured gas content of the coal.

Images