CN109902348A - Method for calculating medium-grade coal adsorption gas quantity based on vitrinite maximum reflectivity - Google Patents

Abstract

The present invention provides a method for calculating the amount of gas adsorbed by medium-rank coal based on the maximum reflectivity of the vitrinite group, comprising: calculating the adsorption flow coefficient B of the adsorption surface according to the maximum reflectivity of the vitrinite group of the coal sample; calculating the parameter of the influence of temperature on the adsorption amount according to the maximum reflectivity of the vitrinite group of the coal sample; calculating the parameter of the influence of pressure on the adsorption amount according to the maximum reflectivity of the vitrinite group of the coal sample: calculating the Celsius temperature of the adsorption temperature according to the burial depth of the coal sample and its corresponding geothermal gradient, and converting it into the adsorption thermodynamic temperature K; calculating the adsorption pressure P according to the burial depth of the coal sample and its corresponding geopressure gradient; substituting the above calculated data and the geometric shape constant A into the pressure-temperature adsorption equation to obtain the amount of gas adsorbed by the medium-rank coal. Compared with the related art, the method for calculating the amount of gas adsorbed by medium-rank coal based on the maximum reflectivity of the vitrinite group provided by the present invention is easy to learn, easy to use, efficient and highly accurate.

Description

A method for calculating the amount of gas adsorbed by medium-rank coal based on the maximum reflectance of vitrinite

technical field

The invention relates to the field of methods for calculating the amount of gas adsorbed by medium-rank coal, in particular to a method.

Background technique

The medium-rank coal measures refer to the vitrinite whose maximum reflectance (R ₀ ,max) is between 0.65% and 2.50%, including the main Mesozoic and Late Paleozoic coal fields or coal-bearing areas in Northeast China, North China, South China and Southwest China. All bituminous coals from gas coals to lean coals.

Coalbed methane is an unconventional natural gas generated and stored in the coalbed itself with methane as the main component and mainly adsorbed on the surface of the coal matrix particles. The main geological factors that control the content of coalbed methane are: coal metamorphism degree, burial depth, lithology of coal seam roof and floor, and fault structure. Among them, the degree of coal metamorphism plays a fundamental internal role, and the burial depth (different burial depths have different temperatures and different pressures) is an important external factor.

Vitrinite reflectance is not only an important indicator to characterize the degree of coalification, but also an important basis for studying the maturity of oil and gas source rocks and geothermal changes in petroleum geological exploration. Because the vitrinite reflectance is always sensitive to the influence of coalification, the reflectance of the matrix vitrinite is used as an index to mark the degree of coalification (coal rank) at home and abroad.

The Langmuir adsorption isotherm equation uses two parameters (Langmuir volume and Langmuir pressure) to express the relationship between adsorption capacity and adsorption pressure under isothermal conditions. Because temperature is not an independent variable of the Langmuir isotherm adsorption equation, the effect of temperature is obtained indirectly by comparing the magnitude and direction of the Langmuir parameter change at different temperatures. To clarify the quantitative relationship between the fundamental internal factors (the degree of coal metamorphism) and the important external factors (different temperatures, different pressures), it is necessary to simulate the saturated adsorption gas volume of different coal grades under different burial depths (temperature, pressure), and to explore the relationship between pressure and pressure. The comprehensive effect of temperature on the methane adsorption capacity of medium-rank coal has practical significance in predicting the amount of gas adsorbed by medium-rank coal.

The premise of using the difference method to compare the magnitude and direction of change of the Rankine volume _VL and the Rankine pressure _PL at two adjacent temperatures is that the effect of temperature on these two parameters is linear. However, a large number of experiments have confirmed that the effect of adsorption temperature on the Rankine volume _VL and the Rankine pressure _PL is not linear, so certain errors will occur. At the same time, the related calculations are indirect, which also makes it difficult to use. At the same time, there is no method to combine the pressure-temperature adsorption equation with the maximum reflectivity of vitrinite to calculate the amount of gas adsorbed by medium-rank coal.

Therefore, it is necessary to provide a new method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectance of vitrinite to solve the above problems.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide an easy-to-learn, easy-to-use, high-efficiency and high-accuracy method for calculating the amount of gas adsorbed by medium-rank coal based on the maximum reflectance of vitrinite.

In order to solve the above problems, the present invention provides a method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectivity of vitrinite, taking the medium-rank coal as a coal sample, and the method includes the following steps:

Step S1, calculate the adsorption flow coefficient B of the adsorption surface according to the maximum vitrinite reflectance of the coal sample:

Step S2, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of temperature on the adsorption capacity:

Step S3, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of pressure on the adsorption capacity:

Step S4, according to the burial depth of the coal sample and its corresponding ground temperature gradient, calculate the adsorption temperature in degrees Celsius, and convert it into the adsorption thermodynamic temperature K:

K=273+°C.

Step S5: Calculate the adsorption pressure P according to the buried depth of the coal sample and its corresponding ground pressure gradient.

Step S6, the adsorption flow coefficient B, the parameter that the temperature affects the adsorption capacity, the parameter that the pressure affects the adsorption capacity, the adsorption thermodynamic temperature K, the adsorption pressure P and the geometric constant A obtained from the above calculation Substitute into the following pressure-temperature adsorption equation to obtain the amount of dry ash-free base coalbed methane adsorbed by this kind of medium-rank coal under the condition of equilibrium water at a specific burial depth:

where V is the amount of adsorbed gas, in cm ³ /g; M is the molecular weight, and the molecular weight of methane is 16; T is the thermodynamic temperature K; P is the adsorption pressure, in MPa; A is the geometric constant; B is the adsorption on the adsorption surface Flow coefficient; Δ is a parameter that measures the effect of temperature on the adsorption capacity; β is a parameter that measures the effect of pressure on the adsorption capacity.

Preferably, the geometric shape constant A=0.168.

Preferably, before step S1, it further includes the following steps: step S0, establishing an experimental database of original medium-rank coal, including the maximum reflectivity of vitrinite, test temperature, test pressure and adsorbed gas amount.

Preferably, the coal sample of the medium coal rank coal is shallower than 1200 meters deep in the reservoir.

Preferably, the maximum reflectance R _0,max of the vitrinite is between 0.65% and 2.50%.

Compared with the related art, the method for calculating the amount of adsorbed gas of medium coal rank coal based on the maximum reflectivity of vitrinite of the present invention calculates the humidity and pressure of the reservoir according to the reservoir depth, ground pressure gradient and ground temperature gradient of the target medium coal rank coal. Dry ash-free base coalbed methane adsorbed gas volume under balanced water conditions, output the calculation results, and directly calculate the adsorbed gas volume of medium-rank coal in the reservoir shallower than 1200 meters by using the maximum reflectivity of vitrinite, and the method is easy to learn and use , efficient and accurate.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, under the premise of no creative work, other drawings can also be obtained from these drawings, wherein:

FIG. 1 is a flow chart of the method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectance of vitrinite according to the present invention.

2 is a graph showing the natural logarithm of the adsorption flow coefficient B representing the adsorption surface of the medium-rank coal in the method for calculating the amount of adsorbed gas of the medium-rank coal based on the maximum reflectivity of the vitrinite of the present invention.

Fig. 3 is a graph of calculating a parameter for measuring the influence of temperature on the adsorption capacity of medium-rank coal in the method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectivity of vitrinite according to the present invention;

FIG. 4 is a graph showing parameters that measure the influence of pressure on the adsorption capacity of medium-rank coal calculated in the method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectivity of vitrinite of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in the figure, the present invention provides a method for calculating the amount of adsorbed gas of medium-rank coal based on the maximum reflectivity of vitrinite, taking the medium-rank coal as a coal sample, and the method includes the following steps:

Step S0, establish the original medium-rank coal experimental database, including the maximum reflectivity of vitrinite, test temperature, test pressure and adsorbed gas amount. This step is a conventional step. It is mainly used to provide the maximum reflectivity of the vitrinite in the experimental database, and use the existing pressure-temperature adsorption equation to calculate the above parameters. If the maximum reflectivity of the vitrinite is determined, this step can be omitted. In the method of the present invention, the coal sample of the medium-rank coal is a reservoir with a buried depth of less than 1200 meters (20°C to 50°C, 1 to 12 MPa), and the maximum reflectance of the vitrinite R _0,max is medium Between 0.65% and 2.50%.

Step S1: Calculate the adsorption flow coefficient B of the adsorption surface according to the maximum vitrinite reflectance of the coal sample, as shown in Figure 2:

Step S2, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters that affect the adsorption capacity of the temperature, as shown in Fig. 3:

Step S3 , according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of pressure on the adsorption amount, as shown in FIG. 4 :

Step S4, according to the burial depth of the coal sample and its corresponding ground temperature gradient, calculate the adsorption temperature in degrees Celsius, and convert it into the adsorption thermodynamic temperature K:

K=273+°C.

Step S5: Calculate the adsorption pressure P according to the buried depth of the coal sample and its corresponding ground pressure gradient.

Step S6, the adsorption flow coefficient B, the parameter that the temperature affects the adsorption capacity, the parameter that the pressure affects the adsorption capacity, the adsorption thermodynamic temperature K, the adsorption pressure P and the geometric constant A obtained from the above calculation Substitute into the following pressure-temperature adsorption equation to obtain the amount of dry ash-free base coalbed methane adsorbed by this kind of medium-rank coal under the condition of equilibrium water at a specific burial depth:

Wherein, V is the amount of adsorbed gas, unit cm ³ /g; M is the molecular weight, the molecular weight of methane is 16; T is the thermodynamic temperature K; P is the adsorption pressure, the unit is MPa; 0.168; B is the adsorption flow coefficient of the adsorption surface; Δ is a parameter that measures the effect of temperature on the adsorption capacity; β is a parameter that measures the effect of pressure on the adsorption capacity.

In the specific embodiment of the present invention, the temperature of the surface constant temperature zone is set to be 15°C, according to the normal ground temperature gradient of 3°C/100 meters, the hydrostatic pressure gradient of the formation water, that is, the ground pressure gradient, is 1 MPa/100 meters:

Example 1

The maximum vitrinite reflectance R ₀ ,max=0.8 of a certain medium-rank coal, and the reservoir burial depth is 900 meters. The method for calculating the amount of gas adsorbed by the medium-rank coal is as follows:

Step S1: Calculate the adsorption flow coefficient B of the adsorption surface according to the maximum vitrinite reflectance of the coal sample, as shown in Figure 2:

Then the adsorption flow coefficient of the adsorption surface is B=0.0000002574.

Step S2, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters that affect the adsorption capacity of the temperature, as shown in Fig. 3:

The parameters that affect the adsorption capacity of temperature.

Step S3 , according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of pressure on the adsorption amount, as shown in FIG. 4 :

Then the parameter of the effect of pressure on the adsorption amount=0.5166.

Step S4, according to the burial depth of the coal sample and its corresponding ground temperature gradient, calculate the temperature in degrees Celsius of the adsorption temperature T, and convert it into the adsorption thermodynamic temperature K:

K=273+℃;

Then T=42°C, which is converted into adsorption thermodynamic temperature K=315.

In step S5, the adsorption pressure P=9 MPa is calculated according to the buried depth of the coal sample and its corresponding ground pressure gradient.

Step S6, the adsorption flow coefficient B, the parameter that the temperature affects the adsorption capacity, the parameter that the pressure affects the adsorption capacity, the adsorption thermodynamic temperature K, the adsorption pressure P and the geometric constant A obtained from the above calculation Substitute into the following pressure-temperature adsorption equation to obtain the amount of dry ash-free base coalbed methane adsorbed by this kind of medium-rank coal under the condition of equilibrium water at a specific burial depth:

Wherein, V is the amount of adsorbed gas, unit cm ³ /g; M is the molecular weight, the molecular weight of methane is 16; T is the thermodynamic temperature K; P is the adsorption pressure, the unit is MPa; A is the geometric constant, in the present invention, A = 0.168; B is the adsorption flow coefficient of the adsorption surface; Δ is a parameter that measures the effect of temperature on the adsorption capacity; β is a parameter that measures the effect of pressure on the adsorption capacity;

Then the amount of adsorbed gas of dry ash-free base coalbed methane under the equilibrium water condition of this kind of medium coal rank coal is V=6.45cm ³ /g.

Embodiment 2

The maximum vitrinite reflectance R ₀ ,max=1.2 of a certain medium-rank coal, and the reservoir burial depth is 1000 meters. The method for calculating the amount of gas adsorbed by the medium-rank coal is as follows:

Step S1: Calculate the adsorption flow coefficient B of the adsorption surface according to the maximum vitrinite reflectance of the coal sample, as shown in Figure 2:

Then the adsorption flow coefficient of the adsorption surface is B=0.0000228.

Step S2, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters that affect the adsorption capacity of the temperature, as shown in Fig. 3:

The parameters that affect the adsorption capacity of temperature.

Step S3 , according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of pressure on the adsorption amount, as shown in FIG. 4 :

Then the parameter of the effect of pressure on the adsorption amount = 0.4142.

Step S4, according to the burial depth of the coal sample and its corresponding ground temperature gradient, calculate the temperature in degrees Celsius of the adsorption temperature T, and convert it into the adsorption thermodynamic temperature K:

K=273+℃;

Then T=45℃, which is converted into adsorption thermodynamic temperature K=318.

Step S5, calculating the adsorption pressure P=10 MPa according to the buried depth of the coal sample and its corresponding ground pressure gradient.

Step S6, the adsorption flow coefficient B, the parameter that the temperature affects the adsorption capacity, the parameter that the pressure affects the adsorption capacity, the adsorption thermodynamic temperature K, the adsorption pressure P and the geometric constant A obtained from the above calculation Substitute into the following pressure-temperature adsorption equation to obtain the amount of dry ash-free base coalbed methane adsorbed by this kind of medium-rank coal under the condition of equilibrium water at a specific burial depth:

Wherein, V is the amount of adsorbed gas, unit cm ³ /g; M is the molecular weight, the molecular weight of methane is 16; T is the thermodynamic temperature K; P is the adsorption pressure, the unit is MPa; A is the geometric constant, in the present invention, A = 0.168; B is the adsorption flow coefficient of the adsorption surface; Δ is a parameter that measures the effect of temperature on the adsorption capacity; β is a parameter that measures the effect of pressure on the adsorption capacity;

Then the amount of adsorbed gas of dry ash-free base coalbed methane under the equilibrium water condition of this kind of medium coal rank coal is V=11.80 cm ³ /g.

Embodiment 3

The maximum vitrinite reflectance R ₀ ,max=1.6 of a certain medium-rank coal, and the burial depth of the reservoir is 1200 meters. The method for calculating the amount of gas adsorbed by the medium-rank coal is as follows:

Step S1: Calculate the adsorption flow coefficient B of the adsorption surface according to the maximum vitrinite reflectance of the coal sample, as shown in Figure 2:

Then the adsorption flow coefficient of the adsorption surface is B=0.0003056.

Step S2, according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters that affect the adsorption capacity of the temperature, as shown in Fig. 3:

The parameters that affect the adsorption capacity of temperature.

Step S3 , according to the maximum reflectivity of the vitrinite of the coal sample, calculate the parameters of the influence of pressure on the adsorption amount, as shown in FIG. 4 :

Then the parameter of the influence of pressure on the adsorption amount = 0.3505.

Step S4, according to the burial depth of the coal sample and its corresponding ground temperature gradient, calculate the adsorption temperature in degrees Celsius, and convert it into the adsorption thermodynamic temperature K:

K=273+℃;

Then T=51℃, which is converted into adsorption thermodynamic temperature K=324.

In step S5, the adsorption pressure P=12 MPa is calculated according to the buried depth of the coal sample and its corresponding ground pressure gradient.

Step S6, the adsorption flow coefficient B, the parameter that the temperature affects the adsorption capacity, the parameter that the pressure affects the adsorption capacity, the adsorption thermodynamic temperature K, the adsorption pressure P and the geometric constant A obtained from the above calculation Substitute into the following pressure-temperature adsorption equation to obtain the amount of dry ash-free base coalbed methane adsorbed by this kind of medium-rank coal under the condition of equilibrium water at a specific burial depth:

Wherein, V is the amount of adsorbed gas, unit cm ³ /g; M is the molecular weight, the molecular weight of methane is 16; T is the thermodynamic temperature K; P is the adsorption pressure, the unit is MPa; A is the geometric constant, in the present invention, A = 0.168; B is the adsorption flow coefficient of the adsorption surface; Δ is a parameter that measures the effect of temperature on the adsorption capacity; β is a parameter that measures the effect of pressure on the adsorption capacity;

Then the amount of adsorbed gas of dry ash-free base coalbed methane under the equilibrium water condition of this kind of medium coal rank coal is V=17.27 cm ³ /g.

Compared with the related art, the method for calculating the amount of adsorbed gas of medium coal rank coal based on the maximum reflectivity of vitrinite of the present invention calculates the humidity and pressure of the reservoir according to the reservoir depth, ground pressure gradient and ground temperature gradient of the target medium coal rank coal. Dry ash-free base coalbed methane adsorbed gas volume under balanced water conditions, output the calculation results, and directly calculate the adsorbed gas volume of medium-rank coal in the reservoir shallower than 1200 meters by using the maximum reflectivity of vitrinite, and the method is easy to learn and use , efficient and accurate.

The above descriptions are only the embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related technologies Fields are similarly included in the scope of patent protection of the present invention.

Claims (5)

1. it is a kind of based on maximum reflectance of vitrinite calculate in rank coal absorption tolerance method, take middle rank coal as coal sample, This method comprises the following steps:

Step S1, the absorption flow coefficient B of absorption surface is calculated according to the maximum reflectance of vitrinite of coal sample:

Step S2, the parameter that temperature influences adsorbance is calculated according to the maximum reflectance of vitrinite of coal sample:

Step S3, the parameter that pressure influences adsorbance is calculated according to the maximum reflectance of vitrinite of coal sample:

Step S4, the Celsius temperature DEG C of adsorption temp is calculated according to the buried depth of coal sample and its corresponding geothermal gradient, and be converted into Adsorption thermodynamics temperature K:

K=273+ DEG C；

Step S5, adsorptive pressure P is calculated according to the buried depth of coal sample and its corresponding pressure gradient；

Step S6, the resulting absorption flow coefficient B, parameter that the temperature influences adsorbance, described will be calculated above Parameter, the Adsorption thermodynamics temperature K, adsorptive pressure P and the geometrical body constant A that pressure influences adsorbance are substituted into as pushed Power temperature adsorption equation obtains rank coal dry ash free basis coal bed gas under the conditions of the equilibrium water of specific buried depth in this kind and adsorbs Tolerance:

Wherein, V is absorption tolerance, unit cm³/g；M is molecular weight, and the molecular weight of methane is 16；T is thermodynamic temperature K；P is to inhale Enclosure pressure, unit megapascal；A is geometrical body constant；B is the absorption flow coefficient of absorption surface；Δ is to measure temperature to absorption Measure the parameter influenced；β is the parameter measuring pressure and influencing on adsorbance.

2. the method according to claim 1 based on rank coal absorption tolerance in maximum reflectance of vitrinite calculating, special Sign is, the geometrical body constant A=0.168.

3. the method according to claim 1 based on rank coal absorption tolerance in maximum reflectance of vitrinite calculating, special Sign is, further includes following steps before step S1:

Step S0, original middle rank coal experimental data base, including maximum reflectance of vitrinite, test temperature, test pressure are established And absorption tolerance.

4. the method according to claim 1 based on rank coal absorption tolerance in maximum reflectance of vitrinite calculating, special Sign is that the coal sample of the middle rank coal is 1200 meters of reservoir buried depth with shallow.

5. the method according to claim 4 based on rank coal absorption tolerance in maximum reflectance of vitrinite calculating, special Sign is, the maximum reflectance of vitrinite R_0,maxBetween 0.65%~2.50%.