A device for determining the bottom hole flowing pressure of each layer of a coalbed gas multilayer commingled production well and a method thereof

Abstract

The application discloses a method for determining the bottom hole flowing pressure of each layer of a coalbed gas multilayer commingled production well, and the steps are as follows: obtaining the bottom hole flowing pressure of the bottommost coalbed; calculating the vertical distance between each target coalbed and the bottommost coalbed; obtaining the gas pressure in the casing; judging the fluid state in the wellbore based on the bottom hole flowing pressure of the bottommost coalbed and the gas pressure in the casing; and determining the bottom hole flowing pressure of each target coalbed according to the fluid state in the wellbore, the vertical distance between each target coalbed and the bottommost coalbed, the bottom hole flowing pressure of the bottommost coalbed and the gas pressure in the casing. In addition, the application also relates to a corresponding device. The application can quickly and accurately calculate the bottom hole flowing pressure of each target coalbed in the commingled production well, provides a reasonable basis for the determination of the later production capacity and the establishment of the drainage and production system, and has a certain significance for the reservoir production capacity evaluation and the production capacity improvement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coalbed methane development, and more particularly, relates to a device for determining the bottom-hole flowing pressure of each layer of a coalbed methane multilayer commingled production well and a method thereof. BACKGROUND

[0002] Due to the influence of factors such as deposition and structure, coal seams have the characteristics of multiple vertical positions and small thickness, and a development method of multilayer commingled production is often used. During commingled production, gas and liquid two-phase flow in the wellbore, and the change in liquid level height will cause a large difference in pressure of each layer at the wellbore. In the production process of a coalbed methane well, the bottom-hole flowing pressure is an independent parameter affecting the gas production rate, and the size of the stable gas production rate will be actually controlled by the bottom-hole flowing pressure and the drainage rate. The bottom-hole flowing pressure value of each coal seam in a multilayer commingled production well is the basis for the development of coal seam productivity prediction and reasonable drainage system.

[0003] At present, there are many methods for predicting the bottom-hole flowing pressure of a coalbed methane well, such as calculating the bottom-hole flowing pressure of a target well by studying the relationship between various geological and production data in the study area and the bottom-hole flowing pressure; and Hasan-Kabir analytical method and Chen Jialang-Yue Xiang'an method. The above methods obtain the relationship between other data and the bottom-hole flowing pressure through numerical simulation or experiments, which is affected by the number of samples in the study area and the data itself, and different relationship formulas may be obtained, which affects the calculation result of the bottom-hole flowing pressure. Some data obtained by experiments are not easy to obtain in daily production, and the practicability is poor. The previous methods do not consider the influence of different fluid states on coal seams during the drainage process of a multilayer commingled production well, and cannot be applied to a multilayer commingled production well.

[0004] Therefore, the prior art needs to be improved. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and to develop a method for determining the bottom-hole flowing pressure of each layer of a coalbed methane multilayer commingled production well, which provides a reasonable basis for the development of later productivity and drainage system.

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

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

[0008] Obtaining the bottom-hole flowing pressure of the bottommost coal seam;

[0009] Calculating the vertical distance between each target coal seam and the bottommost coal seam;

[0010] Obtaining the gas pressure in the casing;

[0011] Judging the fluid state in the wellbore based on the bottom-hole flowing pressure of the bottommost coal seam and the gas pressure in the casing;

[0012] The bottom-hole flowing 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 bottommost coal seam, the bottom-hole flowing pressure of the bottommost coal seam and the gas pressure in the casing.

[0013] In one embodiment of the present application, the step of obtaining the bottom-hole flowing pressure of the bottommost coal seam comprises:

[0014] lowering a pressure measuring device in the middle of the bottommost coal seam;

[0015] reading the reading of the pressure measuring device;

[0016] taking the reading of the pressure measuring device as the bottom-hole flowing pressure of the bottommost coal seam.

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

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

[0019] obtaining the depth of the middle of each target coal seam and the depth of the middle of the bottommost coal seam according to the logging data of the single well;

[0020] calculating the vertical depth of the middle of each target coal seam and the vertical depth of the middle of the bottommost coal seam according to the deviation data of the single well,

[0021] calculating the vertical depth distance between the middle of each target coal seam and the middle of the bottommost coal seam;

[0022] taking the calculated vertical depth distance as the vertical distance between each target coal seam and the bottommost coal seam.

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

[0024] reading the reading of the casing pressure gauge installed at the wellhead;

[0025] taking the reading of the casing pressure gauge as the gas pressure in the casing.

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

[0027] if the gas pressure in the casing is zero, judging that the fluid state in the wellbore is a liquid state;

[0028] if the gas pressure in the casing is greater than zero and the bottom-hole flowing pressure of the bottommost coal seam is greater than the gas pressure in the casing, judging 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 bottom hole pressure of the bottommost coal seam is equal to the gas pressure in the casing, the fluid state in the wellbore is determined to be a gas state.

[0030] In one embodiment of the present application, the step of determining the bottom hole 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 pressure of the bottommost coal seam, and the gas pressure in the casing includes:

[0031] In the case where the fluid state in the wellbore is determined to be a liquid state, the bottom hole pressure of each target coal seam = the bottom hole pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam x 0.01,

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

[0033] In one embodiment of the present application, the step of determining the bottom hole 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 pressure of the bottommost coal seam, and the gas pressure in the casing includes:

[0034] In the case where the fluid state in the wellbore is determined to be a mixed state of gas and liquid, the liquid level in the wellbore is first calculated by the following formula: liquid level = the vertical depth of the middle of the bottommost coal seam - (the bottom hole pressure of the bottommost coal seam - the gas pressure in the casing) x 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 pressure of each target coal seam = the bottom hole pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam x 0.01, and when the liquid level is below the target coal seam, the bottom hole pressure of each target coal seam = the gas pressure in the casing,

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

[0036] In one embodiment of the present application, the step of determining the bottom hole 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 pressure of the bottommost coal seam, and the gas pressure in the casing includes:

[0037] In the case where the fluid state in the wellbore is determined to be a gas state, the bottom hole pressure of each target coal seam = the gas pressure in the casing,

[0038] wherein, in the above formula, the wellbore bottom flow pressure of each target coal seam and the gas pressure in the casing are both in units of MPa.

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

[0040] a first module configured to acquire the wellbore bottom flow pressure of the bottommost coal seam;

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

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

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

[0044] a fifth module configured to determine the wellbore bottom 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 wellbore bottom flow pressure of the bottommost coal seam and the gas pressure in the casing.

[0045] With the above technical solution, the present application has at least the following beneficial effects:

[0046] The present application takes full account of the influence of the fluid state of a multilayer commingled production well on each coal seam during different drainage processes, and by acquiring the wellbore bottom flow pressure of the bottommost coal seam, the casing pressure, the well deviation data, the liquid level data and the coal seam vertical depth, the wellbore bottom flow pressure of each target coal seam can be calculated. The data of the present application is easy to obtain and has strong practicability, greatly shortening the calculation time and improving the precision. The device and method for determining the wellbore bottom flow pressure of each layer of a coalbed methane multilayer commingled production well provided by the present application can quickly and accurately calculate the wellbore bottom flow pressure of each target coal seam in the commingled production well, providing a reasonable basis for the determination of the later-stage productivity and the formulation of the drainage system, and having a definite significance for the evaluation of the reservoir productivity and the improvement of the production. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed by the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0048] Figure 1 A flowchart of the method for determining the wellbore bottom flow pressure of each layer of a coalbed methane multilayer commingled production well provided by the present application is shown;

[0049] Figure 2 The structure diagram of the device for determining the bottom hole flowing pressure of each layer of a coalbed gas multi-layer commingled well is shown. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions and advantages of the present application clearer, the embodiments of the present application are further described in detail below with reference to the drawings.

[0051] As shown in the drawings, the present application provides a method for determining the bottom hole flowing pressure of each layer of a coalbed gas multi-layer commingled well, comprising the following steps: Figure 1

[0052] Step S101: obtaining the bottom hole flowing pressure of the bottommost coalbed;

[0053] Step S102: calculating the vertical distance between each target coalbed and the bottommost coalbed;

[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 flowing pressure of the bottommost coalbed and the gas pressure in the casing;

[0056] Step S105: determining the bottom hole flowing pressure of each target coalbed according to the fluid state in the wellbore, the vertical distance between each target coalbed and the bottommost coalbed, the bottom hole flowing pressure of the bottommost coalbed and the gas pressure in the casing.

[0057] The present application fully considers the influence of the fluid state of a multi-layer commingled well in different drainage processes on each coalbed, and through obtaining the bottom hole flowing pressure of the bottommost coalbed, the casing pressure, the well deviation data, the liquid level data and the coalbed vertical depth, the bottom hole flowing pressure of each target coalbed can be calculated.

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

[0059] lowering the pressure measuring device in the middle of the bottommost coalbed;

[0060] reading the reading of the pressure measuring device;

[0061] taking the reading of the pressure measuring device as the bottom hole flowing pressure of the bottommost coalbed.

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

[0063] The present application can directly measure the bottom hole flowing pressure of the bottommost coalbed through the waterproof and explosion-proof digital pressure gauge, the data is easy to obtain, and the practicability is strong.

[0064] In the above method, step S102 comprises: ​

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

[0066] According to the inclination data of single well, the vertical depth of the middle part of each target coal seam and the vertical depth of the middle part of the bottommost coal seam are converted,

[0067] The vertical depth distance between the middle part of each target coal seam and the middle part of the bottommost coal seam is calculated;

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

[0069] In the present application, the vertical depth of the middle part of each target coal seam and the vertical depth of the middle part of the bottommost coal seam can be converted according to the logging data and the inclination data of single well, which greatly shortens the calculation time and improves the accuracy.

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

[0071] Reading the reading of the casing pressure gauge installed at the wellhead;

[0072] Taking the reading of the casing pressure gauge as the gas pressure in the casing.

[0073] In the present application, the gas pressure in the casing can be obtained directly through the casing pressure gauge installed at the wellhead, and the data is easy to obtain, intuitive and practical.

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

[0075] Based on the gas pressure in the casing and the relationship between the bottomhole flowing pressure of the bottommost coal seam and the gas pressure in the casing, the fluid state in the wellbore is determined, specifically:

[0076] If the gas pressure in the casing is zero, the fluid state in the wellbore is determined as liquid state;

[0077] If the gas pressure in the casing is greater than zero and the bottomhole flowing pressure of the bottommost coal seam is greater than the gas pressure in the casing, the fluid state in the wellbore is determined as the mixed state of gas and liquid;

[0078] If the gas pressure in the casing is greater than zero and the bottomhole flowing pressure of the bottommost coal seam is equal to the gas pressure in the casing, the fluid state in the wellbore is determined as gas state.

[0079] In the present application, the fluid state of the multi-layer commingled well in different drainage processes is fully considered, and the corresponding bottomhole flowing pressure of the target coal seam is determined by determining the corresponding fluid.

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

[0081] In a case where the fluid state in the wellbore is judged to be a liquid state, the wellbore bottom flow pressure of each target coal seam = the wellbore bottom flow pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam x 0.01;

[0082] In a case where the fluid state in the wellbore is judged to be a mixed state of gas and liquid, the liquid level in the wellbore is first calculated by the following equation: liquid level = the vertical depth of the middle of the bottommost coal seam - (the wellbore bottom flow pressure of the bottommost coal seam - the gas pressure in the casing) x 100; then the positional relationship between the liquid level and each target coal seam is judged, and when the liquid level is above the target coal seam, the wellbore bottom flow pressure of each target coal seam = the wellbore bottom flow pressure of the bottommost coal seam - the vertical distance between each target coal seam and the bottommost coal seam x 0.01, and when the liquid level is below the target coal seam, the wellbore bottom flow pressure of each target coal seam = the gas pressure in the casing;

[0083] In a case where the fluid state in the wellbore is judged to be a gas state, the wellbore bottom flow pressure of each target coal seam = the gas pressure in the casing,

[0084] In the above equations, the wellbore bottom flow pressure of each target coal seam, the wellbore bottom flow pressure of the bottommost coal seam, and the gas pressure in the casing are all in units of MPa, the liquid level, the vertical depth of the middle of the bottommost coal seam, and the vertical distance are all in units of meters.

[0085] The present application fully considers the influence of the flow state on each coal seam in different drainage processes of a multilayer combined production well, and determines the wellbore bottom flow pressure of each target coal seam in different ways according to different fluid states.

[0086] As shown in Figure 2 The present application also provides a device 20 for determining the wellbore bottom flow pressure of each layer of a coalbed methane multilayer combined production well, comprising:

[0087] A first module 21 configured to acquire the wellbore bottom flow pressure of the bottommost coal seam;

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

[0089] A third module 23 configured to acquire the gas pressure in the casing;

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

[0091] A fifth module 25 configured to determine the wellbore bottom 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 wellbore bottom flow pressure of the bottommost coal seam, and the gas pressure in the casing.

[0092] The above technical solutions of the present application will be described below through specific embodiments.

[0093] Example 1

[0094] X well area has a well Z1-1, which is a multi-coal seam combined mining well. From top to bottom, the coal seams are 3 # coal seam, 9 # coal seam and 15 # coal seam combined mining well, and it is necessary to determine the bottom hole flowing pressure of 3 # coal seam. The steps are as follows:

[0095] (1) Obtain the bottom hole flowing pressure of 15 # coal seam. In the middle of 15 # coal seam, a bottom hole pressure gauge is lowered, and the reading of the bottom hole pressure gauge is 2 MPa, i.e. the bottom hole flowing pressure of 15 # coal seam is 2 MPa.

[0096] (2) Calculate the vertical distance between 3 # coal seam and 15 # coal seam. The logging data of the well shows that the well depth in the middle of 3 # coal seam is 654 meters, and the well depth in the middle of 15 # coal seam is 776 meters; and according to the deviation data, the vertical depth is calculated: the vertical depth in the middle of 3 # coal seam is 642 meters, and the vertical depth in the middle of 15 # coal seam is 756 meters; and the vertical distance between the two coal seams is calculated: 756 meters-642 meters = 114 meters, i.e. the vertical distance between 3 # coal seam and 15 # coal seam.

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

[0098] (4) Determine the fluid state in the wellbore. At present, the bottom hole flowing pressure of 15 # coal seam is greater than the gas pressure in the casing, indicating that the fluid in the wellbore is in a mixed state of gas and liquid.

[0099] (5) Determine the bottom hole flowing pressure of 3 # coal seam according to the fluid state. At present, the fluid in the wellbore is a mixture of gas and liquid, and the liquid level in the wellbore is calculated first: liquid level = 756 m-(2 MPa-0.5 MPa) x 100 = 606 m, which is located above 3# coal seam, and the bottom hole flowing pressure of 3# coal seam = 2 MPa-114 x 0.01 = 0.86 MPa.

[0100] Example 2

[0101] X well area has a well Z1-1, which is a multi-coal seam combined mining well. The coal seams from top to bottom are 3 # coal seam, 9 # coal seam and 15 # coal seam combined mining well, now need to determine the bottom hole flowing pressure of 9 # coal seam.

[0102] (1) Obtain the bottom hole flowing pressure of 15 # coal seam. In 15 # coal seam, a bottom hole pressure gauge is lowered in the middle, the reading of which is 2Mpa, i.e. the bottom hole flowing pressure of 15 # coal seam is 2Mpa.

[0103] (2) Calculate the vertical distance between 9 # coal seam and 15 # coal seam. The logging data of this well shows that the well depth of 9 # coal seam is 410 meters, and the well depth of 15 # coal seam is 510 meters; according to the deviation data, the vertical depth is calculated as follows: the vertical depth of 9 # coal seam is 402 meters, and the vertical depth of 15 # coal seam is 480 meters; the vertical distance between the two coal seams is calculated as 78 meters, i.e. the vertical distance between 9 # coal seam and 15 # coal seam.

[0104] (3) Obtain the gas pressure in the casing of Z1-1 well. The casing pressure gauge installed at the wellhead reads 2Mpa, i.e. the gas pressure in the casing is 2Mpa.

[0105] (4) Determine the fluid state in the wellbore. At present, the bottom hole flowing pressure of 15 # coal seam is equal to the gas pressure in the casing, which indicates that the fluid in the wellbore is all gas.

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

[0107] Example 3

[0108] X well area has a well Z2-1, which is a multi-coal seam combined mining well. The coal seams from top to bottom are 4 # coal seam, 8 # coal seam and 16 # coal seam combined mining well, now need to determine the bottom hole flowing pressure of 4 # coal seam.

[0109] (1) Obtain the bottom hole flowing pressure of the 16 # coal seam. In the 16 # coal seam, a bottom hole pressure gauge is lowered, and the reading of the bottom hole pressure gauge is 1.5 MPa, that is, the bottom hole flowing pressure of the 16 # coal seam is 1.5 MPa.

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

[0111] (3) Obtain the gas pressure in the casing of the Z2-1 well. The casing pressure gauge installed at the wellhead shows that the reading is 0 MPa, that is, the gas pressure in the casing is 0 MPa.

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

[0113] (5) Determine the bottom hole flowing pressure of the 4 # coal seam according to the fluid state. At present, the fluid in the wellbore is all liquid, so the bottom hole flowing pressure of the 4 # coal seam is 1.5 MPa-106*0.01 = 0.44 MPa.

[0114] Through the above examples 1-3, it can be seen that, by obtaining the bottom hole flowing pressure of the lowest coal seam, the casing pressure, the inclination data, the liquid level data and the vertical depth of the coal seam, the bottom hole flowing pressure of each target coal seam can be calculated. The data of the present application is easy to obtain, and has strong practicability, greatly shortens the calculation time, and improves the accuracy. The method for determining the bottom hole flowing pressure of the coal seam gas multi-layer commingling well provided by the present application can quickly and accurately calculate the bottom hole flowing pressure of the target coal seam in the commingling well, and provides a reasonable basis for the determination of the later production capacity and the formulation of the production and mining system, and has a certain significance for the reservoir productivity evaluation and the production capacity improvement.

[0115] The above only describes the preferred embodiments of the present application, and is not intended to limit the scope of the present application; if the present application is modified or replaced without departing from the spirit and scope of the present application, it should be covered in the protection scope of the claims of the present application.

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 bottomhole flow pressure of the bottommost coal seam; Calculate the vertical distance between each target coal seam and the bottom coal seam; Obtain the gas pressure at the wellhead inside the casing; The fluid state in the wellbore is determined based on the bottomhole flow pressure of the lowest coal seam and the gas pressure at the wellhead in the casing; The bottomhole flow pressure of each target coal seam is determined based on the fluid state in the wellbore, the vertical distance between each target coal seam and the bottommost coal seam, the bottomhole flow pressure of the bottommost coal seam, and the gas pressure at the wellhead in the casing, including: When the fluid state in the wellbore is determined to be liquid, the bottomhole flow pressure of each target coal seam = the bottomhole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01; If the fluid state in the wellbore is determined to be a mixture of gas and liquid, the liquid level in the wellbore is first calculated using 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 at the wellhead in the casing) × 100. The positional relationship between the liquid level and each target coal seam is then determined. When the liquid level is above the target coal seam, the bottomhole flow pressure of each target coal seam is calculated as: bottomhole flow pressure of the bottommost coal seam - 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 is calculated as: gas pressure at the wellhead in the casing. 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 at the wellhead in the casing. Among them, the bottomhole flow pressure of each target coal seam, the bottomhole flow pressure of the bottommost coal seam and the gas pressure at the wellhead in the casing are all in MPa, and the liquid level height, the vertical depth and vertical distance of the middle of the bottommost coal seam are all in meters.

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 bottommost coal seam includes: A pressure measuring device is lowered into the middle of the bottom coal seam; Read the pressure gauge; The reading of the pressure measuring device is taken as the bottom hole flowing pressure of the bottommost 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 of the middle of each target coal seam and the well depth of 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 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 at the wellhead 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 at the wellhead inside 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 determining the fluid state in the wellbore based on the bottom hole flow pressure of the bottommost coal seam and the gas pressure at the wellhead in the casing comprises: If the gas pressure at the wellhead in the casing is zero, the fluid state in the wellbore is judged to be liquid; If the gas pressure at the wellhead in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is greater than the gas pressure at the wellhead in the casing, then the fluid state in the wellbore is determined to be a mixed state of gas and liquid; If the gas pressure at the wellhead in the casing is greater than zero and the bottomhole flow pressure of the bottommost coal seam is equal to the gas pressure at the wellhead in the casing, the fluid state in the wellbore is determined to be a gas state.

7. 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 configured to obtain a bottomhole flow pressure of a bottommost coal seam; a second module configured to calculate a vertical distance between each target coal seam and a bottommost coal seam; a third module configured to obtain a gas pressure at a wellhead in the casing; a fourth module configured to determine a fluid state in the wellbore based on a bottomhole flow pressure of the bottommost coal seam and a gas pressure at a wellhead in the casing; as well as The fifth module is configured to determine the bottomhole flow pressure of each target coal seam based on the fluid state in the wellbore, the vertical distance between each target coal seam and the bottommost coal seam, the bottomhole flow pressure of the bottommost coal seam, and the gas pressure at the wellhead in the casing, including: When the fluid state in the wellbore is determined to be liquid, the bottomhole flow pressure of each target coal seam = the bottomhole flow pressure of the bottom coal seam - the vertical distance between each target coal seam and the bottom coal seam × 0.01; If the fluid state in the wellbore is determined to be a mixture of gas and liquid, the liquid level in the wellbore is first calculated using 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 at the wellhead in the casing) × 100. The positional relationship between the liquid level and each target coal seam is then determined. When the liquid level is above the target coal seam, the bottomhole flow pressure of each target coal seam is calculated as: bottomhole flow pressure of the bottommost coal seam - 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 is calculated as: gas pressure at the wellhead in the casing. 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 at the wellhead in the casing. Among them, the bottomhole flow pressure of each target coal seam, the bottomhole flow pressure of the bottommost coal seam and the gas pressure at the wellhead in the casing are all in MPa, and the liquid level height, the vertical depth and vertical distance of the middle of the bottommost coal seam are all in meters.

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