Device and method for determining flowing bottomhole pressure of each layer of coal bed gas multi-layer commingling production well

Abstract

The invention discloses a method for determining flowing bottomhole pressure of each layer of a coal bed gas multi-layer commingling production well. The method comprises the following steps that the flowing bottomhole pressure of the bottommost coal bed is obtained; calculating the vertical distance between each target coal seam and the bottommost coal seam; gas pressure in the casing pipe is obtained; the fluid state in the shaft is judged based on the bottom hole flowing pressure of the bottommost coal seam and the gas pressure in the casing pipe; and determining the flowing bottomhole pressure of each target coal seam according to the fluid state in the shaft, the vertical distance between each target coal seam and the bottommost coal seam, the flowing bottomhole pressure of the bottommost coal seam and the gas pressure in the sleeve. The invention further relates to a corresponding device. According to the method, the flowing bottomhole pressure of each target coal seam in the commingled production well can be rapidly and accurately calculated, a reasonable basis is provided for later productivity determination and formulation of a drainage and production system, and the method has a certain significance in reservoir productivity evaluation and yield improvement.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane development, and more specifically, relates to a device and method for determining the bottom hole flow pressure of each layer in a coalbed methane multi-layer combined production well. Background Art

[0002] Due to the influence of sedimentation, structure and other factors, coal seams have the characteristics of multiple vertical layers and small thickness, and multi-layer commingled production is often used for development. During commingled production, gas and liquid flow in the wellbore, and changes in the liquid level will cause a large difference in pressure between each layer in the wellbore. In the production process of coalbed methane wells, the bottom hole flow pressure is an independent parameter that affects the gas production. The size of the stable gas production will actually be controlled by the bottom hole flow pressure and drainage. The bottom hole flow pressure value of each coal seam in a multi-layer commingled well is the basis for the production capacity prediction of the coal seam and the formulation of a reasonable drainage system.

[0003] At present, there are many methods for predicting the bottom flow pressure of coalbed methane wells. For example, the bottom flow pressure of the target well is calculated by the relationship between various geological and production data in the study area and the bottom flow pressure; there are also methods such as Hasan-Kabir analytical method and Chen Jialang-Yue Xiangan method. The above methods are to obtain the relationship between other data and the bottom flow pressure through numerical simulation or experiments. First, due to the number of samples and the data itself in the study area, different relationship equations may be obtained, which will affect the calculation results of the bottom flow pressure; second, some data in the relationship equation obtained by the experiment are not easy to obtain in daily production, and the practicality is poor; third, the previous methods did not consider the impact of different fluid states on the coal seam during the drainage process of multi-layer combined production wells, and cannot be applied to multi-layer combined production wells.

[0004] Therefore, the prior art needs to be improved. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and develop a method for determining the bottom hole flow pressure of each layer in a multi-layer coalbed methane combined production well, thereby providing a reasonable basis for the subsequent production capacity determination and the formulation of a production system.

[0006] The technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well is provided, comprising the following steps:

[0008] Obtain the bottom hole flow pressure of the lowest coal seam;

[0009] Calculate the vertical distance between each target coal seam and the bottom coal seam;

[0010] Obtain the gas pressure in the casing;

[0011] Determine the fluid state in the wellbore based on the bottom hole flow pressure of the lowest coal seam and the gas pressure in the casing;

[0012] The bottom hole flow pressure of each target coal seam is determined according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

[0013] In one embodiment of the present invention, the step of obtaining the bottom hole flow pressure of the bottommost coal seam includes:

[0014] A pressure measuring device is lowered into the middle of the bottommost coal seam;

[0015] Read the pressure gauge;

[0016] The reading of the pressure measuring device is taken as the bottom hole flowing pressure of the lowest coal seam.

[0017] In one embodiment of the present invention, the pressure measuring device adopts a waterproof and explosion-proof digital pressure gauge.

[0018] In one embodiment of the present invention, the step of calculating the vertical distance between each target coal seam and the bottommost coal seam includes:

[0019] According to the logging data of a single well, the well depth in the middle of each target coal seam and the well depth in the middle of the bottom coal seam are obtained;

[0020] According to the well inclination data of a single well, the vertical depth of the middle of each target coal seam and the vertical depth of the middle of the bottom coal seam are calculated.

[0021] Calculate the vertical depth between the middle of each target coal seam and the middle of the bottom coal seam;

[0022] The calculated vertical depth distance is used as the vertical distance between each target coal seam and the bottom coal seam.

[0023] In one embodiment of the present invention, the step of obtaining the gas pressure in the casing comprises:

[0024] Read the casing pressure gauge installed at the wellhead;

[0025] The reading of the casing pressure gauge is taken as the gas pressure in the casing.

[0026] In one embodiment of the present invention, the step of determining the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing comprises:

[0027] If the gas pressure in the casing is zero, the fluid state in the wellbore is judged to be liquid;

[0028] If the gas pressure in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is greater than the gas pressure in the casing, it is judged that the fluid state in the wellbore is a mixed state of gas and liquid;

[0029] If the gas pressure in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is equal to the gas pressure in the casing, it is determined that the fluid state in the wellbore is a gas state.

[0030] In one embodiment of the present invention, the step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottommost coal seam, the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing comprises:

[0031] When the fluid state in the wellbore is judged to be liquid, the bottom hole flow pressure of each target coal seam = the bottom hole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01,

[0032] Among them, in the above formula, the bottom hole flow pressure of each target coal seam and the bottom hole flow pressure of the bottommost coal seam are both in MPa, and the vertical distance is in meters.

[0033] In one embodiment of the present invention, the step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottommost coal seam, the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing comprises:

[0034] When it is determined that the state of the fluid in the wellbore is a mixed state of gas and liquid, the height of the liquid level in the wellbore is first calculated by the following formula: liquid level = vertical depth of the middle of the bottommost coal seam - (bottomhole flow pressure of the bottommost coal seam - gas pressure in the casing) × 100; then the positional relationship between the liquid level and each target coal seam is determined, and when the liquid level is above the target coal seam, the bottomhole flow pressure of each target coal seam = the bottomhole flow pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam × 0.01, when the liquid level is below the target coal seam, the bottomhole flow pressure of each target coal seam = the gas pressure in the casing,

[0035] Among them, in the above formula, the liquid level height, the vertical depth and vertical distance of the middle of the bottom coal seam are all in meters, and the bottom hole flow pressure of the bottom coal seam, the bottom hole flow pressure of each target coal seam and the gas pressure in the casing are all in MPa.

[0036] In one embodiment of the present invention, the step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottommost coal seam, the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing comprises:

[0037] When the fluid state in the wellbore is judged to be gaseous, the bottom hole flow pressure of each target coal seam = the gas pressure in the casing.

[0038] Among them, in the above formula, the bottom hole flow pressure of each target coal seam and the gas pressure in the casing are both in MPa.

[0039] According to another aspect of the present invention, there is provided a device for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well, comprising:

[0040] A first module, the first module being configured to obtain a bottom hole flow pressure of a bottommost coal seam;

[0041] A second module, the second module is configured to calculate the vertical distance between each target coal seam and the bottommost coal seam;

[0042] a third module configured to obtain a gas pressure in the casing;

[0043] A fourth module configured to determine the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing; and

[0044] The fifth module is configured to determine the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

[0045] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0046] The present invention fully considers the influence of the fluid state of a multi-layer combined production well on each coal seam during different production processes. By obtaining the bottomhole flow pressure, casing pressure, well inclination data, liquid level data and vertical depth of the bottommost coal seam, the bottomhole flow pressure of each target coal seam can be calculated. The data of the present invention is easy to obtain and has strong practicality, which greatly shortens the calculation time and improves accuracy. The device and method for determining the bottomhole flow pressure of each layer of a multi-layer combined production well of coalbed methane provided by the present invention can quickly and accurately calculate the bottomhole flow pressure of each target coal seam in the combined production well, providing a reasonable basis for the later determination of production capacity and the formulation of a production system, and has a definite significance for reservoir production capacity evaluation and production improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 A schematic flow chart of a method for determining the bottom hole flow pressure of each layer of a coalbed methane multi-layer combined production well provided by the present invention is shown;

[0049] Figure 2 The schematic diagram of the structure of the device for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane combined production well provided by the present invention is shown. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0051] like Figure 1 As shown, the present invention provides a method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well, comprising the following steps:

[0052] Step S101: obtaining the bottom hole flow pressure of the bottom coal seam;

[0053] Step S102: Calculate the vertical distance between each target coal seam and the bottom coal seam;

[0054] Step S103: obtaining the gas pressure in the casing;

[0055] Step S104: judging the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing;

[0056] Step S105: Determine the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

[0057] The present invention fully considers the influence of the fluid state of multi-layer combined production wells on each coal seam during different production processes. By obtaining the bottom hole flow pressure, casing pressure, well inclination data, liquid level data and vertical depth of the bottom coal seam, the bottom hole flow pressure of each target coal seam can be calculated.

[0058] In the above method, step S101 includes:

[0059] A pressure measuring device is lowered into the middle of the bottommost coal seam;

[0060] Read the pressure gauge;

[0061] The reading of the pressure measuring device is taken as the bottom hole flowing pressure of the lowest coal seam.

[0062] In the above method, the pressure measuring device preferably adopts a waterproof and explosion-proof digital pressure gauge.

[0063] The present invention can directly measure the bottom hole flow pressure of the bottom coal seam through the waterproof and explosion-proof digital pressure gauge, and the data is easy to obtain and has strong practicality.

[0064] In the above method, step S102 includes:

[0065] According to the logging data of a single well, the well depth in the middle of each target coal seam and the well depth in the middle of the bottom coal seam are obtained;

[0066] According to the well inclination data of a single well, the vertical depth of the middle of each target coal seam and the vertical depth of the middle of the bottom coal seam are calculated.

[0067] Calculate the vertical depth between the middle of each target coal seam and the middle of the bottom coal seam;

[0068] The calculated vertical depth distance is used as the vertical distance between the target coal seam and the bottom coal seam.

[0069] In the present invention, the vertical depth of the middle of each target coal seam and the vertical depth of the middle of the bottom coal seam can be calculated based on the logging data and well deviation data of a single well, which greatly shortens the calculation time and improves the accuracy.

[0070] In the above method, step S103 includes:

[0071] Read the casing pressure gauge installed at the wellhead;

[0072] The reading of the casing pressure gauge is taken as the gas pressure in the casing.

[0073] The present invention can directly obtain the gas pressure in the casing through the casing pressure gauge installed at the wellhead, and the data is easy to obtain, intuitive and clear, and highly practical.

[0074] In the above method, step S104 includes:

[0075] Based on the gas pressure in the casing and the relationship between the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing, the fluid state in the wellbore is judged, specifically:

[0076] If the gas pressure in the casing is zero, the fluid state in the wellbore is judged to be liquid;

[0077] If the gas pressure in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is greater than the gas pressure in the casing, it is judged that the fluid state in the wellbore is a mixed state of gas and liquid;

[0078] If the gas pressure in the casing is greater than zero and the bottom hole flow pressure of the bottommost coal seam is equal to the gas pressure in the casing, it is judged that the fluid state in the wellbore is a gas state.

[0079] The present invention fully considers the fluid state of the multi-layer combined production well in different production processes, and determines the bottom hole flow pressure of the corresponding target coal seam by determining the corresponding fluid.

[0080] In the above method, step S105 includes:

[0081] When the fluid state in the wellbore is judged to be liquid, the bottom hole flow pressure of each target coal seam = the bottom hole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01;

[0082] When it is determined that the state of the fluid in the wellbore is a mixed state of gas and liquid, the height of the liquid level in the wellbore is first calculated by the following formula: liquid level = vertical depth of the middle of the bottom coal seam - (bottom hole flow pressure of the bottom coal seam - gas pressure in the casing) × 100; then the positional relationship between the liquid level and each target coal seam is determined, and when the liquid level is above the target coal seam, the bottom hole flow pressure of each target coal seam = the bottom hole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01, and when the liquid level is below the target coal seam, the bottom hole flow pressure of each target coal seam = the gas pressure in the casing;

[0083] When the fluid state in the wellbore is judged to be gaseous, the bottom hole flow pressure of each target coal seam = the gas pressure in the casing.

[0084] Among them, in the above formulas, the bottomhole flow pressure of each target coal seam, the bottomhole flow pressure of the bottommost coal seam and the gas pressure in the casing are all in MPa, and the liquid level, the vertical depth and vertical distance of the middle of the bottommost coal seam are all in meters.

[0085] The present invention fully considers the influence of the flow state of a multi-layer combined production well on each coal seam during different production processes, and adopts different methods to determine the bottom hole flow pressure of each target coal seam according to different fluid states.

[0086] like Figure 2 As shown, the present invention also provides a device 20 for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane combined production well, comprising:

[0087] A first module 21, the first module 21 is configured to obtain the bottom hole flow pressure of the bottommost coal seam;

[0088] A second module 22, the second module 22 is configured to calculate the vertical distance between each target coal seam and the bottommost coal seam;

[0089] A third module 23, the third module 23 is configured to obtain the gas pressure in the casing;

[0090] A fourth module 24 configured to determine the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal layer and the gas pressure in the casing; and

[0091] The fifth module 25 is configured to determine the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

[0092] The above technical solution of the present invention is described below through specific implementation methods.

[0093] Example 1

[0094] There is a well Z1-1 in the X well area, which is a multi-coal seam commingled mining well. The coal seams are 3 from top to bottom. # Coal seam, 9 # Coal seam and 15 # Coal seam joint production wells now need to determine 3 # The bottom hole flow pressure of the coal seam. The steps are as follows:

[0095] (1) Get 15 # The bottom flow pressure of the coal seam. # A bottom-hole pressure gauge is inserted into the middle of the coal seam, and the reading of the bottom-hole pressure gauge is 2Mpa, i.e. 15 # The bottom hole flow pressure of the coal seam is 2Mpa.

[0096] (2) Calculate 3 # Coal seam and 15 # The vertical distance between coal seams. The well logging data of this well shows that 3 # The depth of the well in the middle of the coal seam is 654 meters. # The depth of the well in the middle of the coal seam is 776 meters; the vertical depth is calculated based on the well inclination data: 3 # The vertical depth of the middle part of the coal seam is 642 meters. # The vertical depth of the middle of the coal seam is 756 meters; the vertical depth distance between the two coal seams is calculated as: 756 meters - 642 meters = 114 meters, that is, 3 # Coal seam and 15 # The vertical distance between coal seams.

[0097] (3) Obtain the gas pressure in the casing of Well Z1-1. The casing pressure gauge installed at the wellhead reads 0.5 MPa, which means the gas pressure in the casing is 0.5 MPa.

[0098] (4) Determine the fluid state in the wellbore. # The bottom hole flow pressure of the coal seam is greater than the gas pressure in the casing, indicating that the fluid in the wellbore is a mixture of gas and liquid.

[0099] (5) Determine 3 according to the fluid state # Bottom hole flow pressure of coal seam. At present, the fluid in the wellbore is a mixture of gas and liquid. First calculate the liquid level in the wellbore, liquid level = 756m-(2MPa-0.5MPa)×100=606m. The liquid level is above the 3# coal seam. The bottom hole flow pressure of the 3# coal seam = 2MPa-114×0.01=0.86MPa.

[0100] Example 2

[0101] There is a well Z1-1 in the X well area, which is a multi-coal seam commingled mining well. The coal seams are 3 from top to bottom. # Coal seam, 9 # Coal seam and 15 # Coal seam joint production wells, now need to determine 9 # Bottom hole flow pressure of coal seam.

[0102] (1) Get 15 # The bottom flow pressure of the coal seam. # A bottom-hole pressure gauge is inserted into the middle of the coal seam, and the reading of the bottom-hole pressure gauge is 2Mpa, i.e. 15 # The bottom hole flow pressure of the coal seam is 2Mpa.

[0103] (2) Calculate 9 # Coal seam and 15 # The vertical distance between coal seams. The well logging data of this well shows that # The depth of the coal seam is 410 meters. # The depth of the coal seam is 510 meters; the vertical depth is calculated based on the well inclination data: 9 # The vertical depth of the coal seam is 402 meters, 15 # The vertical depth of the coal seam is 480 meters; the vertical depth between the two coal seams is calculated to be 78 meters, or 9 # Coal seam and 15 # The vertical distance between coal seams.

[0104] (3) Obtain the gas pressure in the casing of Well Z1-1. The casing pressure gauge installed at the wellhead reads 2 MPa, which means the gas pressure in the casing is 2 MPa.

[0105] (4) Determine the fluid state in the wellbore. # The bottom hole flow pressure of the coal seam is equal to the gas pressure in the casing, indicating that all the fluid in the wellbore is gas.

[0106] (5) Determine according to the fluid state 9 # The bottom flow pressure of the coal seam. At present, all the fluid in the wellbore is gas. # The bottom hole flow pressure of the coal seam = 2Mpa.

[0107] Example 3

[0108] There is a well Z2-1 in the X well area, which is a multi-coal seam commingled mining well. The coal seams are 4 from top to bottom. # Coal seam, 8 # Coal seam and 16 # Coal seam joint production wells now need to determine 4 # Bottom hole flow pressure of coal seam.

[0109] (1) Get 16 # The bottom flow pressure of the coal seam. # A bottom-hole pressure gauge is inserted into the middle of the coal seam, and the reading of the bottom-hole pressure gauge is 1.5Mpa, i.e. 16 # The bottom hole flow pressure of the coal seam is 1.5Mpa.

[0110] (2) Calculation 4 # Coal seam and 16 # The vertical distance between coal seams. The well logging data of this well shows that 4 # The depth of the coal seam is 520 meters. # The depth of the coal seam is 634 meters; the vertical depth is calculated based on the well inclination data: 4 # The vertical depth of the coal seam is 508 meters, 16 # The vertical depth of the coal seam is 614 meters; the vertical depth distance between the two coal seams is calculated as: 614 meters - 508 meters = 106 meters, that is, 4 # Coal seam and 16 # The vertical distance between coal seams.

[0111] (3) Obtain the gas pressure in the casing of Well Z2-1. The casing pressure gauge installed at the wellhead reads 0 MPa, which means the gas pressure in the casing is 0 MPa.

[0112] (4) Determine the state of the fluid in the wellbore. If the gas pressure in the casing is currently 0 MPa, it is determined that the fluid in the wellbore is all liquid.

[0113] (5) Determine 4 according to the fluid state # The bottom flow pressure of the coal seam. At present, all the fluids in the wellbore are liquid. # The bottom hole flow pressure of the coal seam = 1.5Mpa-106×0.01=0.44Mpa.

[0114] Through the above-mentioned Examples 1-3, it can be seen that the present invention can calculate the bottomhole flow pressure of each target coal seam by obtaining the bottomhole flow pressure, casing pressure, well inclination data, liquid level data and vertical depth of the bottommost coal seam. The data of the present invention is easy to obtain and has strong practicality, which greatly shortens the calculation time and improves the accuracy. The method for determining the bottomhole flow pressure of a coalbed methane multi-layer combined production well provided by the present invention can quickly and accurately calculate the bottomhole flow pressure of the target coal seam in the combined production well, which provides a reasonable basis for the later determination of production capacity and the formulation of the drainage system, and has a definite significance for reservoir production capacity evaluation and production improvement.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. If the present invention is modified or replaced by equivalents without departing from the spirit and scope of the present invention, it should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well, characterized in that: The following steps are involved: Obtain the bottom hole flow pressure of the lowest coal seam; Calculate the vertical distance between each target coal seam and the bottom coal seam; Obtain the gas pressure in the casing; Determine the fluid state in the wellbore based on the bottom hole flow pressure of the lowest coal seam and the gas pressure in the casing; The bottom hole flow pressure of each target coal seam is determined according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

2. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 1, characterized in that: The step of obtaining the bottom hole flow pressure of the bottom coal seam comprises: A pressure measuring device is lowered into the middle of the bottommost coal seam; Read the pressure gauge; The reading of the pressure measuring device is taken as the bottom hole flowing pressure of the lowest coal seam.

3. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 2, characterized in that: The pressure measuring device adopts a waterproof and explosion-proof digital pressure gauge.

4. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 1, characterized in that: The step of calculating the vertical distance between each target coal seam and the bottom coal seam comprises: According to the logging data of a single well, the well depth in the middle of each target coal seam and the well depth in the middle of the bottom coal seam are obtained; According to the well inclination data of a single well, the vertical depth of the middle of each target coal seam and the vertical depth of the middle of the bottom coal seam are calculated. Calculate the vertical depth between the middle of each target coal seam and the middle of the bottom coal seam; The calculated vertical depth distance is used as the vertical distance between each target coal seam and the bottom coal seam.

5. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 1, characterized in that: The step of obtaining the gas pressure in the casing comprises: Read the casing pressure gauge installed at the wellhead; The reading of the casing pressure gauge is taken as the gas pressure in the casing.

6. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 1, characterized in that: The step of judging the fluid state in the wellbore based on the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing comprises: If the gas pressure in the casing is zero, the fluid state in the wellbore is judged to be liquid; If the gas pressure in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is greater than the gas pressure in the casing, it is judged that the fluid state in the wellbore is a mixed state of gas and liquid; If the gas pressure in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is equal to the gas pressure in the casing, it is determined that the fluid state in the wellbore is a gas state.

7. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 6, characterized in that: The step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing comprises: When the fluid state in the wellbore is judged to be liquid, the bottom hole flow pressure of each target coal seam = the bottom hole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01, Among them, in the above formula, the bottom hole flow pressure of each target coal seam and the bottom hole flow pressure of the bottommost coal seam are both in MPa, and the vertical distance is in meters.

8. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 6, characterized in that: The step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing comprises: When it is determined that the state of the fluid in the wellbore is a mixed state of gas and liquid, the height of the liquid level in the wellbore is first calculated by the following formula: liquid level = vertical depth of the middle of the bottommost coal seam - (bottomhole flow pressure of the bottommost coal seam - gas pressure in the casing) × 100; then the positional relationship between the liquid level and each target coal seam is determined, and when the liquid level is above the target coal seam, the bottomhole flow pressure of each target coal seam = the bottomhole flow pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam × 0.01, when the liquid level is below the target coal seam, the bottomhole flow pressure of each target coal seam = the gas pressure in the casing, Among them, in the above formula, the liquid level height, the vertical depth and vertical distance of the middle of the bottom coal seam are all in meters, and the bottom hole flow pressure of the bottom coal seam, the bottom hole flow pressure of each target coal seam and the gas pressure in the casing are all in MPa.

9. The method for determining the bottom hole flow pressure of each layer of a multi-layer coalbed methane commingled production well according to claim 6, characterized in that: The step of determining the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing comprises: When the fluid state in the wellbore is judged to be gaseous, the bottom hole flow pressure of each target coal seam = the gas pressure in the casing. Among them, in the above formula, the bottom hole flow pressure of each target coal seam and the gas pressure in the casing are both in MPa.

10. A device for determining the bottom hole flow pressure of each layer in a multi-layer coalbed methane commingled production well, characterized in that: include: a first module, the first module being configured to obtain a bottom hole flow pressure of a bottommost coal seam; A second module, the second module is configured to calculate the vertical distance between each target coal seam and the bottommost coal seam; a third module, the third module being configured to obtain the gas pressure in the casing; A fourth module, the fourth module being configured to determine the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal seam and the gas pressure in the casing; as well as The fifth module is configured to determine the bottom hole flow pressure of each target coal seam according to the fluid state in the wellbore, the vertical distance between each target coal seam and the bottom coal seam, the bottom hole flow pressure of the bottom coal seam and the gas pressure in the casing.

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