Method for dividing geological units of coal reservoir

Abstract

The invention relates to the field of coal reservoir geological unit division, in particular to a coal reservoir geological unit division method, which comprises the following steps of: calculating a saturated adsorption gas quantity conversion depth and a lateral pressure coefficient of a coal reservoir, and then calculating the coal reservoir geological unit according to the relationship between the saturated adsorption gas quantity conversion depth and the burial depth of the coal reservoir and the size of the lateral pressure coefficient. Coal reservoir geological units are divided into four types: a shallow low-stress geological unit, a stress transition type geological unit, a resource transition type geological unit and a deep high-stress geological unit. According to the embodiment of the invention, the geological units of the coal reservoir are divided by using the two parameters of the lateral pressure coefficient and the conversion depth of the saturated adsorption gas quantity of the coal reservoir, so that powerful reference is provided for evaluating the mining potential and the economic benefit of different types of geological units of the coal reservoir.

Description

Technical Field

[0001] The invention relates to the field of coal reservoir geological unit division, and in particular to a method for dividing coal reservoir geological units. Background Art

[0002] The occurrence and production of coalbed methane are affected by many factors such as formation temperature, pressure and ground stress state. With the increase of coal reservoir depth, changes in formation temperature and pressure cause the saturated adsorbed gas volume of the coal reservoir to reach a maximum value at a certain depth, namely, the "coal reservoir saturated adsorbed gas volume conversion depth". At the same time, the ground stress state also undergoes a conversion from horizontal stress-dominated to vertical stress-dominated at a specific depth, which is called the "ground stress conversion depth". Based on these key depth parameters, the lateral pressure coefficient and the coal reservoir saturated adsorbed gas volume conversion depth are used to divide the coal reservoir geological units, which is of great significance to improving the efficiency of coalbed methane exploration and development. Summary of the invention

[0003] The purpose of the present invention is to provide a method for dividing coal reservoir geological units, which aims to use two parameters, namely, lateral pressure coefficient and coal reservoir saturated adsorption gas conversion depth, to divide coal reservoir geological units and evaluate the mining potential and economic benefits of different types of coal reservoir geological units.

[0004] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0005] A method for dividing coal reservoir geological units is provided. The method calculates the saturated adsorption gas content conversion depth and the lateral pressure coefficient of the coal reservoir, and then divides the coal reservoir geological units into the following types according to the relationship between the saturated adsorption gas content conversion depth and the coal reservoir burial depth and the size of the lateral pressure coefficient: shallow low stress geological units, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient ≥ 1; stress transition geological units, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient < 1; resource transition geological units, saturated adsorption gas content conversion depth < coal reservoir burial depth, lateral pressure coefficient ≥ 1; deep high stress geological units, saturated adsorption gas content conversion depth < coal reservoir burial depth, lateral pressure coefficient < 1.

[0006] Further, the steps of calculating the saturated adsorption gas content conversion depth include: Step 1, predicting the formation temperature: T = 0.027H + 3.6 Step 2, establishing the coupling relationship between the Langmuir volume, Langmuir pressure, vitrinite reflectance, and formation temperature: Step 3: Establish the relationship between reservoir pressure and coal reservoir depth in the study area: P0 = 0.00885H-1.04 Step 4: Establish a prediction model for coal saturated adsorption gas volume: Combined with the above formula, a prediction model for coal saturated adsorption gas volume is established: Where, T is the formation temperature (℃), H is the depth of coal reservoir (m), R o,max is the vitrinite reflectance, P0 is the reservoir pressure (MPa); Step 5: Based on the coal saturated adsorption gas volume prediction model, obtain the saturated adsorption gas volume conversion depth: replace R in the coal saturated adsorption gas volume prediction model o,max is regarded as a constant, and then the first-order derivative of the coal saturated adsorbed gas volume prediction model is taken. When Q′=0, the coal reservoir burial depth (H) obtained is the coal reservoir saturated adsorbed gas volume conversion depth.

[0007] Furthermore, step 1 includes: conducting an isothermal adsorption experiment on the well core to obtain the average geothermal gradient G (°C). Under the action of the geothermal field, the buried depth of the coal reservoir (H, m) is positively correlated with the formation temperature: T = T0 + G (HH M ) Where T0 is the annual average temperature in the constant temperature zone (℃), H m is the depth of the isothermal zone (m); combining the above formula and parameters, the formula for predicting the formation temperature is calculated.

[0008] Furthermore, step 2 includes: performing a vitrinite reflectance test on the coal sample to obtain the maximum vitrinite reflectance (R o,max ).

[0009] Further, the step of calculating the lateral pressure coefficient of the coal reservoir includes: calculating the maximum horizontal principal stress, the minimum horizontal principal stress and the vertical stress of the formation through the fracture pressure, the closure pressure and the reservoir pressure obtained during the injection / pressure reduction process: Among them, P f is the bursting pressure (MPa), P c is the closure pressure (MPa), P0 is the reservoir pressure (MPa), ρ d is the formation density (g / cm 3 ), h is the burial depth (m), σ H is the maximum horizontal principal stress, σ h is the minimum horizontal principal stress, σ v is the vertical stress, T is the tensile strength of rock (MPa), and g is the gravitational acceleration; the lateral pressure coefficient is calculated by the maximum horizontal principal stress, minimum horizontal principal stress and vertical stress of the formation: Where m is the lateral pressure coefficient.

[0010] Furthermore, based on the maximum horizontal principal stress, minimum horizontal principal stress and vertical stress of the formation, as well as the lateral pressure coefficient, the relationship between the coal reservoir and the ground stress conversion depth is obtained: m>1, the coal reservoir is shallower than the ground stress conversion depth, σ H and σ h The stress difference between H >σ V ; m<1, the stress conversion depth of coal reservoir is deeper, σH and σ h The stress difference between H <σ V .

[0011] Furthermore, the combined spring model is used to invert the well logging ground stress: According to the shear wave time difference and longitudinal wave time difference of the stratum, the dynamic elastic modulus and dynamic Poisson's ratio of the rock are calculated: Based on the static elastic modulus and static Poisson's ratio of rocks, combined with the longitudinal wave time difference data of the corresponding depth of the core, the correlation between the dynamic and static elastic moduli and the dynamic and static Poisson's ratio of the coal reservoir in the study area is established: E s =0.62E d -3.14μ s =1.50μ d Substitute -0.017 into the relevant parameters of coal reservoir ground stress to obtain the horizontal strain coefficient: Combining the maximum and minimum horizontal strain coefficients, the horizontal strain coefficient at any position of the coal reservoir is obtained according to the Kriging interpolation method; where μ s is the static Poisson's ratio; α is the Biot coefficient; E s is the static Young's modulus (GPa); ξ h is the strain coefficient in the direction of minimum stress; ξ H is the strain coefficient in the direction of maximum stress, C is the compression coefficient of rock skeleton particles, C m is the rock volume compressibility coefficient, ρ m is the density of coal (g / cm 3 ), DTS is the shear wave time difference, DTC is the longitudinal wave time difference, E s is the static elastic modulus, μ s is the static Poisson's ratio, ξ H is the maximum horizontal strain coefficient, ξ h is the minimum horizontal strain coefficient.

[0012] Furthermore, full array acoustic logging or conventional acoustic logging is used to obtain the longitudinal wave time difference, and the longitudinal wave time difference is used to obtain the shear wave time difference of the well coal reservoir: DTS=1.53DTC+78.5.

[0013] Furthermore, the static elastic modulus and static Poisson's ratio of the rock were obtained using uniaxial compression tests on well cores.

[0014] Furthermore, water injection / pressure drop test was used to measure the parameters related to the in-situ stress of the coal reservoir.

[0015] Compared with the prior art, this application has the following beneficial effects:

[0016] A method for dividing coal reservoir geological units is provided. An embodiment of the present invention uses two parameters, namely, lateral pressure coefficient and coal reservoir saturated adsorbed gas conversion depth, to divide coal reservoir geological units, providing a powerful reference for evaluating the mining potential and economic benefits of different types of coal reservoir geological units. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0018] Figure 1 Four types of coal reservoir geological units classified according to an embodiment of the present invention;

[0019] Figure 2 The relevant parameters and results of the well core isothermal adsorption experiment of the embodiment of the present invention;

[0020] Figure 3 : is the coupling relationship between the Langmuir volume (A), Langmuir pressure (B), vitrinite reflectance and formation temperature in an embodiment of the present invention;

[0021] Figure 4 A statistical diagram of the correlation between the coal reservoir depth and the reservoir pressure according to an embodiment of the present invention;

[0022] Figure 5 The injection / pressure drop test data and the calculation results of the ground stress of the embodiment of the present invention;

[0023] Figure 6 The correlation between the shear wave time difference (DTS) and the longitudinal wave time difference (DTC) of the coal reservoir in the embodiment of the present invention;

[0024] Figure 7 The figure is the correlation between the dynamic-static elastic modulus (A) and the dynamic-static Poisson's ratio (B) of the coal in the embodiment of the present invention;

[0025] Figure 8 The well logging geostress calculation process parameters of the embodiment of the present invention;

[0026] Fig. 9 This is the application result of the embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The occurrence and production of coalbed methane are affected by many factors such as formation temperature, pressure and ground stress state. With the increase of coal reservoir depth, changes in formation temperature and pressure cause the saturated adsorbed gas volume of the coal reservoir to reach a maximum value at a certain depth, namely, the "coal reservoir saturated adsorbed gas volume conversion depth". At the same time, the ground stress state also undergoes a conversion from horizontal stress-dominated to vertical stress-dominated at a specific depth, which is called the "ground stress conversion depth". Based on these key depth parameters, the lateral pressure coefficient and the coal reservoir saturated adsorbed gas volume conversion depth are used to divide the coal reservoir geological units, which is of great significance to improving the efficiency of coalbed methane exploration and development.

[0029] Therefore, a method for dividing coal reservoir geological units is provided below, which aims to use two parameters, namely, the lateral pressure coefficient and the conversion depth of saturated adsorbed gas in coal reservoirs, to divide coal reservoir geological units, evaluate the mining potential and economic benefits of different types of coal reservoir geological units, optimize mining strategies, reduce risks, and thus develop and utilize coal reservoir methane resources more scientifically and effectively.

[0030] Among them, the reason for using the lateral pressure coefficient to divide the coal reservoir geological units is that as the burial depth of the formation increases, the ratio of the maximum horizontal stress to the vertical stress decreases in a power function. At a certain coal reservoir burial depth, the maximum horizontal ground stress value and the vertical ground stress value will be equivalent. This depth is the "ground stress conversion depth". The lateral pressure coefficient can be used to characterize the ground stress state and conversion depth. A lateral pressure coefficient greater than 1 indicates that the area is dominated by horizontal stress, while a lateral pressure coefficient less than 1 indicates that the area is dominated by vertical stress. This difference in the state of the stress field will inevitably lead to differences in the geological characteristics and transformability of the coalbed methane reservoir. Therefore, the lateral pressure coefficient can be used to divide the coal reservoir geological units.

[0031] Among them, the reason for using the saturated adsorbed gas volume of coal reservoirs to divide coal reservoir geological units is that the increase of formation temperature and formation pressure has negative and positive effects on coal adsorption capacity respectively, and the formation temperature and formation pressure are positively correlated with the burial depth of coal reservoirs. As the burial depth of coal reservoirs increases, there will inevitably be a "critical depth" that makes the saturated adsorbed gas volume of coal reservoirs reach a maximum value. This critical depth is the "coal reservoir saturated adsorbed gas volume conversion depth". Below the conversion depth, the saturated adsorbed gas volume of coal reservoirs increases with the increase of burial depth; above the conversion depth, the saturated adsorbed gas volume of coal reservoirs decreases with the increase of burial depth. This law has been verified in practice in many coalbed methane exploration and development areas, such as the Linxing block in the Ordos Basin. Since the saturated adsorbed gas volume of coal reservoirs is closely related to the gas content of coal reservoirs, the saturated adsorbed gas volume conversion depth of coal reservoirs is used to divide coal reservoir geological units.

[0032] Combination Figure 1 , coal reservoir geological units can be divided into four types, including:

[0033] Shallow low-stress geological units, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient ≥ 1;

[0034] Stress transition geological unit, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient <1;

[0035] Resource transition geological unit, saturated adsorption gas content conversion depth < coal reservoir burial depth, lateral pressure coefficient ≥ 1;

[0036] In deep high-stress geological units, the saturated adsorption gas content conversion depth is less than the coal reservoir burial depth, and the lateral pressure coefficient is less than 1.

[0037] Resource transitional geological units and stress transitional geological units belong to transitional zone coal reservoir gas. Both of them and deep high stress geological units belong to the category of broad deep high stress geological units.

[0038] The calculation method of the parameter of saturated adsorption gas content conversion depth is: based on the isothermal adsorption experiments of field outcrops or coal mine working face samples, the Langmuir volume and Langmuir pressure values ​​are measured, and the Langmuir prediction model under reservoir temperature and pressure conditions is established to obtain the adsorption characteristics of coal in a certain area, among which the Langmuir volume is the maximum adsorption amount of coal under a certain temperature and pressure, and the larger the value, the stronger the adsorption capacity of the coal; the Langmuir pressure is the pressure corresponding to the time when the coal adsorption amount reaches 1 / 2 of the Langmuir volume, reflecting the difficulty of coal adsorbing gas.

[0039] Specifically, the method for calculating the saturated adsorption gas content conversion depth is divided into four steps:

[0040] Step 1: Predict the formation temperature using the formula T = 0.027H + 3.6, where T is the formation temperature and H is the depth of the coal reservoir.

[0041] The derivation process of the formation temperature prediction formula is as follows:

[0042] The crust is divided into variable temperature zone, constant temperature zone and warming zone from top to bottom. Under the influence of geothermal field, the burial depth of coal reservoir (H, m) is positively correlated with the formation temperature.

[0043] Formula 1: T = T0 + G (HH M )

[0044] Where, T0 is the annual average temperature of the isothermal zone (℃), G is the average geothermal gradient (℃), H is the burial depth of the coal reservoir (m); H m is the depth of the isothermal zone (m).

[0045] Among the above parameters, the annual average temperature of the isothermal zone in the study area (T0) is about 9°C, the depth of the isothermal zone (H m ) is about 20m, and the average geothermal gradient G is obtained based on the well core isothermal adsorption experiment.

[0046] Figure 2 In order to evaluate the relevant parameters and results of the well core isothermal adsorption experiment, Figure 2 Among the relevant parameters: Ro,max is the maximum vitrinite reflectance (%); T is the formation temperature = adsorption experiment temperature (℃); P0 is the formation pressure (MPa), which is the burial depth budget value; VL is the air-dry basis Rankine volume (m3); PL is the air-dry basis Rankine pressure (MPa); the coal samples selected for the well core isothermal adsorption experiment have Ro,max between 1.8% and 4.3%, formation temperature (T, ℃) between 19 and 45℃, and formation pressure between 4.4 and 13.6MPa.

[0047] Combination Figure 2 The correlation between Ro,max, formation temperature and formation pressure and Lang's parameter was deeply analyzed, and a prediction model for saturated adsorbed gas volume of coal reservoirs was established for the coal reservoirs in the study area. The average geothermal gradient (G) in the study area was calculated to be about 2.7℃ / 100m.

[0048] Set the parameters T0, G, H m Substituting into the above formula, we can finally obtain the formation temperature prediction formula for coal reservoirs at any depth in the study area:

[0049] Formula 2: T = 0.027H + 3.6.

[0050] Step 2: Based on the results of the core isothermal adsorption experiment under layer temperature and pressure conditions ( Figure 2 ), and the vitrinite reflectance of the coal rock in the study area ( Figure 3 ), using the nonlinear curved edge fitting method, the Langmuir volume (V_L, m 3), the coupling relationship between Langmuir pressure (P_L, MPa) and vitrinite reflectance and formation temperature:

[0051] Formula 3 V L =(11.45R o,max +12.71)e -0.011T

[0052] Formula 4

[0053] Figure 3 The coupling relationship between Langmuir volume (A), Langmuir pressure (B), vitrinite reflectance and formation temperature.

[0054] Step 3: Based on the core isothermal adsorption test results under layer temperature and pressure conditions ( Figure 2 ), and establish the correlation between reservoir pressure and coal reservoir depth in the study area:

[0055] Formula 5: P0 = 0.00885H-1.04

[0056] Among them, P0 is the reservoir pressure in the study area (MPa), and H is the burial depth of the coal reservoir (m).

[0057] Figure 4 It is a statistical chart of the correlation between coal reservoir depth and reservoir pressure, combined with Figure 4 It can be seen that the reservoir pressure (P_0, MPa) and the coal reservoir burial depth (H, m) in the study area show a good linear positive correlation, and the correlation coefficient is 0.77.

[0058] Step 4: Establish a prediction model for coal saturated adsorption gas volume.

[0059] Substitute the coupling relationship between Langmuir volume, Langmuir pressure, coal rock vitrinite reflectance and formation temperature (Equation 3 and Equation 4) into the Langmuir adsorption model The correlation between saturated adsorbed gas volume and maximum vitrinite reflectance - formation temperature - reservoir pressure is obtained:

[0060] Formula 6

[0061] Where P0 is the reservoir pressure (MPa); Q is the saturated adsorbed gas content (m 3 / t).

[0062] The formation temperature prediction formula of deep coal reservoir (Formula 2) and the correlation between reservoir pressure and coal reservoir burial depth (Formula 5) are introduced into the correlation between saturated adsorbed gas volume and maximum vitrinite reflectance-formation temperature-reservoir pressure (Formula 6), and finally a coal saturated adsorbed gas volume prediction model based on maximum vitrinite reflectance-coal reservoir burial depth is established:

[0063] Formula 7

[0064] Step 5: Based on the coal saturated adsorption gas volume prediction model, obtain the saturated adsorption gas volume conversion depth:

[0065] Consider Ro,max in Formula 7 as a constant, and then take the first-order derivative of Formula 7. When Q′=0, the coal reservoir burial depth (H) obtained is the conversion depth of the saturated adsorbed gas volume of the coal reservoir.

[0066] The calculation method of the lateral pressure coefficient of the coal reservoir is: the fracture pressure (P f , MPa), closing pressure (P c , MPa) and reservoir pressure (P0, MPa) and other parameters to calculate the maximum horizontal principal stress (σ H ), minimum horizontal principal stress (σ h ) and vertical stress (σ v ), and then, the lateral pressure coefficient (m) of the coal reservoir is calculated based on the above parameters.

[0067] The lateral pressure coefficient (m) is the minimum horizontal principal stress (σ H ) and the maximum horizontal principal stress (σ h ) and the vertical stress (σ v ) ratio:

[0068] Formula 8

[0069] When m>1, the coal reservoir is shallow in the in-situ stress conversion depth, σ H and σ h The stress difference between them is large, and σ H >σ V ; When m<1, the stress conversion depth of coal reservoir is deeper, σ H and σ h The stress difference between them is relatively small, and σ H <σ V .

[0070] Specifically, the calculation method of the lateral pressure coefficient of the coal reservoir includes the following steps:

[0071] Step 6: Calculate the maximum horizontal principal stress (σ H ), minimum horizontal principal stress (σ h ) and vertical stress (σ v ).

[0072] Minimum horizontal principal stress (σ H ) is approximately equal to the closing pressure (P c ).

[0073] Formula 9σ h =Pc .

[0074] Maximum horizontal principal stress (σ H ) can be calculated by the following formula:

[0075] Formula + σ H =3σ h -P f -P0+T

[0076] Where T is the tensile strength of rock (MPa).

[0077] Vertical stress (σ v , MPa) depends on the pressure of the overlying strata, which can be obtained from the burial depth of the overlying strata (h, m), the stratum density (ρ d , g / cm 3 ) and gravitational acceleration (g, 9.8N / kg); obtain:

[0078] Formula 11

[0079] Figure 5 The injection / pressure drop test data and the results of geostress calculations are combined with Figure 5 , the water injection / pressure drop test data are substituted into equations 9, 10, and 11 to calculate the maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress. The results show that the maximum horizontal principal stress has the largest range of variation, mainly between 14.2 and 45.9 MPa, with an average of about 29.3 MPa; the minimum horizontal principal stress is between 10.5 and 29.1 MPa, with an average of about 18.5 MPa; the vertical stress is between 12.8 and 33.1 MPa, with an average of about 21.4 MPa.

[0080] Then, the combined spring model is used to invert the well logging ground stress:

[0081] Formula 12

[0082] Form Thirteen

[0083] μ s is the static Poisson's ratio; α is the Biot coefficient; E s is the static Young's modulus (GPa); ξ h is the strain coefficient in the direction of minimum stress; ξ H is the strain coefficient in the direction of maximum stress.

[0084] The parameters required for calculating the geostress using the combined spring model include: Biot coefficient, static Young's modulus, static Poisson's ratio, strain coefficients in the minimum and maximum stress directions, vertical stress, and reservoir pressure.

[0085] Among them, the vertical stress can be obtained by formula 11, and the reservoir pressure can be obtained by formula 5.

[0086] The Biot coefficient (α) reflects the influence of rock pore space on rock elastic characteristics. Generally speaking, the α value of dense rock is small, while the α value of loose rock is large. The Biot coefficient can be obtained by the rock skeleton particle compression coefficient (C) and the rock volume compression coefficient (C m ) is calculated to obtain:

[0087] Formula 14

[0088] C can be calculated based on the static elastic modulus and static Poisson's ratio of the rock:

[0089] Formula 15

[0090] C m It can be calculated based on the logging shear wave time difference (DTS, us / m) and compressional wave time difference (DTC, us / m):

[0091] Formula 16

[0092] Among them, ρ m is the density of coal (g / cm 3 ).

[0093] The shear wave time difference and compression wave time difference of the formation can be obtained by full array acoustic logging. The shear wave time difference and compression wave time difference data of multiple wells are collected and fitted to obtain the following: Figure 6 The correlation between the shear wave time difference (DTS) and the longitudinal wave time difference (DTC) of the coal reservoir in the study area is shown, and then the following is obtained:

[0094] Formula 17: DTS = 1.53DTC + 78.5

[0095] Therefore, the P-wave time difference can be used to calculate the S-wave time difference of the coal reservoir. In addition, the P-wave time difference can be obtained by conventional acoustic logging in addition to full array acoustic logging.

[0096] Step 7: Calculate the static elastic modulus (E s ) and static Poisson's ratio (μ s ).

[0097] According to the transverse wave time difference and longitudinal wave time difference of the stratum, the dynamic elastic modulus and dynamic Poisson's ratio of the rock can be calculated by the following formula:

[0098] Form 18

[0099] Formula 19

[0100] Based on the results of the uniaxial compression test of the well core, the static elastic modulus and static Poisson's ratio of the rock are obtained. Combined with the longitudinal wave time difference data at the corresponding depth of the core, the correlation between the dynamic and static elastic moduli and the dynamic and static Poisson's ratios of the coal reservoir in the study area is established:

[0101] Formula 19E s =0.62E d -3.14

[0102] Formula 20μ s =1.50μ d -0.017

[0103] Figure 7 This is the correlation between the dynamic-static elastic modulus (A) and the dynamic-static Poisson's ratio (B) of coal.

[0104] Step 8. Calculate the maximum and minimum horizontal strain coefficients (ξ H ,ξ h ).

[0105] Substituting the relevant parameters of coal reservoir in-situ stress measured by water injection / pressure drop test into equation 12 and equation 13, the horizontal strain coefficient (ξ H ,ξ h ),get:

[0106] Formula 21

[0107] Formula 22

[0108] According to Formula 21 and Formula 22, combined Figure 8 The parameters of the well logging geostress calculation process in the study area are shown in the figure, and the horizontal strain coefficient (ξ H ,ξ h ), the horizontal strain coefficient at any location in the study area can be obtained based on the Kriging interpolation method.

[0109] The actual application results of dividing coal reservoir geological units based on this embodiment are as follows: Fig. 9 As shown, there are two deep high-stress geological units D, two shallow low-stress geological units Q and one stress transitional geological unit Y in the study area. Since there are no resource transitional geological units in the area, the resource transitional geological units are not shown in the figure.

[0110] The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

Claims

1. A method for dividing coal reservoir geological units, characterized in that: The saturated adsorbed gas conversion depth and lateral pressure coefficient of the coal reservoir are calculated, and then the coal reservoir geological units are divided into: Shallow low-stress geological units, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient ≥ 1; Stress transition geological unit, saturated adsorption gas content conversion depth ≥ coal reservoir burial depth, lateral pressure coefficient <1; Resource transition geological unit, saturated adsorption gas content conversion depth < coal reservoir burial depth, lateral pressure coefficient ≥ 1; In deep high-stress geological units, the saturated adsorption gas content conversion depth is less than the coal reservoir burial depth, and the lateral pressure coefficient is less than 1.

2. A method for dividing coal reservoir geological units according to claim 1, characterized in that: The steps for calculating the conversion depth of saturated adsorption gas content include: Step 1: Predict formation temperature: T=0.027H+3.6 Step 2: Establish the coupling relationship between Langmuir volume, Langmuir pressure, vitrinite reflectance and formation temperature: V L =(11.45R o,max +12.71)e -0.011T Step 3: Establish the relationship between reservoir pressure and coal reservoir depth in the study area: P0=0.00885H-1.04 Step 4: Establish a prediction model for coal saturated adsorption gas volume: Combined with the above formula, a prediction model for coal saturated adsorption gas volume is established: Where, T is the formation temperature (℃), H is the depth of coal reservoir (m), R o,max is the vitrinite reflectance, P0 is the reservoir pressure (MPa); Step 5: Based on the coal saturated adsorption gas volume prediction model, obtain the saturated adsorption gas volume conversion depth: The R in the prediction model of coal saturated adsorption gas volume o,max is regarded as a constant, and then the first-order derivative of the coal saturated adsorbed gas volume prediction model is taken. When Q′=0, the coal reservoir burial depth (H) obtained is the coal reservoir saturated adsorbed gas volume conversion depth.

3. A method for dividing coal reservoir geological units according to claim 2, characterized in that: Step one includes: The well core isothermal adsorption experiment was carried out to obtain the average geothermal gradient G (℃). Under the action of the geothermal field, the coal reservoir depth (H, m) is positively correlated with the formation temperature: T=T0+G(H-H M ) Among them, T0 is the annual average temperature in the constant temperature zone (℃), H m is the depth of the isothermal zone (m); Combining the above formula and parameters, the formula for predicting formation temperature is calculated.

4. A method for dividing coal reservoir geological units according to claim 2, characterized in that: Step 2 includes: The vitrinite reflectance test of coal samples was carried out to obtain the maximum vitrinite reflectance (R o,max ).

5. A method for dividing coal reservoir geological units according to claim 1, characterized in that: The steps for calculating the lateral pressure coefficient of coal reservoirs include: The maximum horizontal principal stress, minimum horizontal principal stress and vertical stress of the formation are calculated by using the fracture pressure, closure pressure and reservoir pressure obtained during the injection / pressure reduction process: s h =P c s H =3σ h -P f -P0+T Among them, P f is the bursting pressure (MPa), P c is the closure pressure (MPa), P0 is the reservoir pressure (MPa), ρ d is the formation density (g / cm 3 ), h is the burial depth (m), σ H is the maximum horizontal principal stress, σ h is the minimum horizontal principal stress, σ v is the vertical stress, T is the tensile strength of rock (MPa), and g is the gravitational acceleration; The lateral pressure coefficient is calculated by the maximum horizontal principal stress, minimum horizontal principal stress and vertical stress of the formation: Where m is the lateral pressure coefficient.

6. A method for dividing coal reservoir geological units according to claim 5, characterized in that: Based on the maximum horizontal principal stress, minimum horizontal principal stress and vertical stress of the formation, as well as the lateral pressure coefficient, the relationship between the coal reservoir and the ground stress conversion depth is obtained: m>1, the coal reservoir is shallow in the in-situ stress conversion depth, σ H and σ h The stress difference between H >σ V ; m<1, the stress conversion depth of coal reservoir is deeper, σ H and σ h The stress difference between H <σ V .

7. A method for dividing coal reservoir geological units according to claim 5, characterized in that: Inverse well logging geostress using the combined spring model: According to the shear wave time difference and longitudinal wave time difference of the stratum, the dynamic elastic modulus and dynamic Poisson's ratio of the rock are calculated: Based on the static elastic modulus and static Poisson's ratio of rocks, combined with the longitudinal wave time difference data of the corresponding depth of the core, the correlation between the dynamic and static elastic moduli and the dynamic and static Poisson's ratios of the coal reservoir in the study area is established: E s =0.62E d -3.14 m s =1.50m d -0.017 Substituting the relevant parameters of coal reservoir ground stress, the horizontal strain coefficient is obtained: Combining the maximum and minimum horizontal strain coefficients, the horizontal strain coefficient at any position of the coal reservoir is obtained according to the Kriging interpolation method; Among them, μ s is the static Poisson's ratio; α is the Biot coefficient; E s is the static Young's modulus (GPa); ξ h is the strain coefficient in the direction of minimum stress; ξ H is the strain coefficient in the direction of maximum stress, C is the compression coefficient of rock skeleton particles, C m is the rock volume compressibility coefficient, ρ m is the density of coal (g / cm 3 ), DTS is the shear wave time difference, DTC is the longitudinal wave time difference, E s is the static elastic modulus, μ s is the static Poisson's ratio, ξ H is the maximum horizontal strain coefficient, ξ h is the minimum horizontal strain coefficient.

8. A method for dividing coal reservoir geological units according to claim 7, characterized in that: Use full array acoustic logging or conventional acoustic logging to obtain the P-wave time difference, and use the P-wave time difference to obtain the S-wave time difference of the coal reservoir: DTS=1.53DTC+78.

5.

9. A method for dividing coal reservoir geological units according to claim 7, characterized in that: The static elastic modulus and static Poisson's ratio of the rock were obtained using uniaxial compression tests on well cores.

10. A method for dividing coal reservoir geological units according to claim 7, characterized in that: Coal reservoir in-situ stress related parameters measured using water injection / pressure drawdown testing.

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