Method for analyzing effectiveness of drainage, pressure reduction and gas production of coal-bed gas well based on drainage and production data

Abstract

The invention relates to the technical field of coal-bed gas well drainage, and discloses a coal-bed gas well drainage, pressure reduction and gas production effectiveness analysis method based on drainage and production data, which comprises the following steps of: extracting service data on the basis of dynamic analysis of a drainage and production curve; a drainage and mining effectiveness analysis curve; performing drainage-pressure reduction-gas production effectiveness analysis treatment; and splitting gas reservoir attribute parameters and water yield. According to the method, the coal bed gas drainage effectiveness analysis method based on relation curves of the accumulated water yield and the flowing bottomhole pressure, relation curves of the accumulated gas yield and the flowing bottomhole pressure and relation curves of the accumulated water yield and the accumulated gas yield is constructed, the water invasion phenomenon can be recognized according to curve forms and typical straight line segment fitting results, gas reservoir attribute parameters are obtained, and the gas reservoir drainage effectiveness is improved. The elastic water yield and the water invasion water yield are split, the drainage pressure reduction effectiveness and the pressure reduction gas production effectiveness are stripped, key restraining factors for the productivity of the coal-bed gas well are revealed, and optimization and adjustment of a development scheme are effectively promoted.

Description

Technical Field

[0001] The invention relates to the technical field of coalbed methane well drainage, and in particular to a method for analyzing the effectiveness of coalbed methane well drainage, pressure reduction and gas production based on drainage and production data. Background Art

[0002] Drainage and pressure reduction are the mainstream methods for the development of medium-shallow coalbed methane. The effectiveness of drainage-pressure reduction-gas production in coalbed methane wells determines whether high production can be achieved. There are two key links, namely whether drainage can induce pressure reduction and whether pressure reduction can induce gas production. The former involves issues such as drainage water source, water content of coal reservoirs and surrounding rocks, and groundwater dynamic conditions. The water source that can induce reservoir pressure reduction is elastic water, also known as effective water, and vice versa, water intrusion, also known as invalid water; the latter involves issues such as resource quantity and abundance, gas saturation, desorption efficiency, coal reservoir permeability, and fracturing transformation effect. For low-yield and low-efficiency wells, how to effectively separate these two links is the premise for finding the key factors that limit gas production and formulating targeted production improvement and transformation measures. On the other hand, the rich drainage data on site contain information on the effectiveness of drainage, pressure reduction, and gas production. Based on the drainage data, a relatively simple, highly operational, and highly practical method for diagnosing the drainage effect and identifying the water source of coalbed methane wells is constructed, and gas reservoir-related attribute parameters are obtained, which has important practical guiding significance.

[0003] Coalbed methane exploration and development has made important progress in recent years. In long-term follow-up research, based on the geochemical characteristics of produced water, it is proposed that surface water interference profoundly restricts the efficient development of coalbed methane in this area, resulting in high water production and low gas production in gas wells. The reason is that in areas where limestone is exposed over a large area and karst landforms are developed, if the rainfall is abundant, the circulation of surface water and shallow groundwater is alternating strongly, and the precipitation infiltration coefficient in karst areas can reach more than 0.8, which makes the upper coalbed methane system easily affected by shallow groundwater, limiting the reservoir depressurization effect, thereby reducing development efficiency; in view of this, we propose a coalbed methane well depressurization and gas production effectiveness analysis method based on drainage data. Summary of the invention

[0004] The purpose of the present invention is to provide a method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data, the analysis method comprising the following steps:

[0006] S1. Extract service data based on dynamic analysis of drainage curve;

[0007] S2, drainage effectiveness analysis curve;

[0008] S21, calculating the relationship curve between the cumulative water production and the bottom hole flowing pressure;

[0009] S22, calculating the relationship curve between the cumulative gas production and the bottom hole flowing pressure;

[0010] S23, calculating the relationship curve between the cumulative water production and the cumulative gas production;

[0011] S3, drainage-pressure reduction-gas production effectiveness analysis and processing;

[0012] S4. Splitting of gas reservoir attribute parameters and water production.

[0013] Optionally, the service data includes: extracted bottom hole flow pressure, cumulative water production, and cumulative gas production.

[0014] Optionally, pairwise relationship curves are drawn for the service data, the relationship curve between cumulative water production and bottom hole flow pressure reflects the drainage and pressure reduction efficiency, the relationship curve between cumulative gas production and bottom hole flow pressure reflects the pressure reduction and gas production efficiency, and the relationship curve between cumulative water production and cumulative gas production reflects the drainage and gas production efficiency, and a coupling analysis is performed.

[0015] Optionally, S21 includes plotting data of a relationship curve between the cumulative water production and the bottom hole pressure of the Z-2 well in two production stages, wherein the first stage of the relationship curve is concave downward, and the second stage of the relationship curve is concave upward;

[0016] The relationship curve between cumulative water production and bottom hole pressure is fitted by piecewise linear fitting.

[0017] Optionally, S3 includes a drainage pressure reduction effectiveness analysis:

[0018] The bottom flow pressure drop per unit water production in the initial stage of drainage can be 0.5MPa / 100m 3 , is regarded as the critical value of water invasion. If it is lower than this value, water invasion is very likely to occur. If this value is further reduced, it can be determined that water invasion has occurred. The identification mark of a well without water invasion is that the drop in bottom flow pressure per unit water production in the initial stage of drainage is greater than 0.5MPa / 100m 3 , and there is an increasing trend in the future.

[0019] Optionally, S4 includes: extracting gas reservoir attribute parameters for processing based on the drainage effectiveness analysis curve.

[0020] Compared with the prior art, the present invention provides a method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data, which has the following beneficial effects:

[0021] 1. The method for analyzing the effectiveness of drainage and pressure reduction in coalbed methane wells based on drainage data has constructed a method for analyzing the effectiveness of coalbed methane drainage based on the relationship curves of cumulative water production and bottom hole pressure, cumulative gas production and bottom hole pressure, and cumulative water production and cumulative gas production. According to the curve shape and the fitting results of typical straight line segments, it can identify water invasion, obtain gas reservoir attribute parameters, split elastic water production and water invasion production, and separate the effectiveness of drainage and pressure reduction and the effectiveness of pressure reduction and gas production. It can reveal the key constraints on the production capacity of coalbed methane wells and effectively promote the optimization and adjustment of development plans.

[0022] 2. This method of analyzing the effectiveness of drainage and pressure reduction in gas production in coalbed methane wells based on drainage and production data shows that when the relationship curve between cumulative water production and bottom hole pressure is concave, it indicates water invasion, corresponding to low-yield wells; concave means that no water invasion has occurred, and a large amount of gas is produced, causing the curve to be concave, corresponding to high-yield wells. The key to influencing gas production lies in how drainage induces pressure reduction, rather than how pressure reduction induces gas production.

[0023] 3. The analysis method of the effectiveness of drainage and depressurization of coalbed methane wells based on drainage and production data shows that water-invaded wells have the characteristics of low start-up pressure and high elastic water production index, while non-water-invaded wells are the opposite. The water-invaded water production of water-invaded wells is greater than the elastic water production, and the total water production is high; non-water-invaded wells mainly produce elastic water, and the total water production is low. There is no regular difference in well-controlled dynamic reserves between the two types of wells, and resource conditions are not the main limiting factor. Low start-up pressure can be used as an important identification mark for water-invaded wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the present invention;

[0025] Figure 2 A schematic diagram of a curve showing the relationship between the cumulative water production and the bottom hole pressure of the present invention;

[0026] Figure 3 A schematic diagram of a curve showing the relationship between the cumulative gas production and the bottom hole flow pressure calculated by the present invention;

[0027] Figure 4 A schematic diagram of a relationship curve between cumulative water production and cumulative gas production calculated by the present invention;

[0028] Figure 5 It is a schematic diagram of the drainage-pressure reduction-gas production relationship curve of the present invention. DETAILED DESCRIPTION

[0029] 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.

[0030] like Figure 1-Figure 5 As shown, the present invention provides a technical solution: a method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data, comprising the following steps:

[0031] S1. Based on the dynamic analysis of the production curve, service data is extracted.

[0032] The service data include: extracting bottom hole flow pressure, cumulative water production, cumulative gas production, and drawing pairwise relationship curves; the relationship curve between cumulative water production and bottom hole flow pressure can reflect the drainage and pressure reduction efficiency, the relationship curve between cumulative gas production and bottom hole flow pressure can reflect the pressure reduction and gas production efficiency, and the relationship curve between cumulative water production and cumulative gas production can reflect the drainage and gas production efficiency, which is a comprehensive reflection of the effects of the first two aspects. The above three curves are collectively referred to as the drainage and production effectiveness analysis curves, and through their coupling analysis, they provide a basis for stripping the key factors affecting gas production efficiency;

[0033] S2, drainage effectiveness analysis curve;

[0034] S21, calculating the relationship curve between the cumulative water production and the bottom hole flowing pressure;

[0035] like Figure 2 As shown in Figure 2, the relationship curves between the cumulative water production and bottom hole pressure in the two production stages of Well Z-2 show different characteristics. The first stage is concave ( Figure 2 a), the second stage is concave upward ( Figure 2 b). The former reflects that drainage can continuously induce reservoir pressure drop, which belongs to the elastic water production of coal reservoir; the latter reflects that drainage cannot effectively induce reservoir pressure drop in the later stage (after 480 days of drainage), and the bottom hole pressure remains basically stable with the increase of cumulative water production, indicating that water invasion has occurred. Specifically, after the first reduction flush, the supply volume and water production are basically balanced, the daily water production is maintained at about 3.5m3 / d, and the dynamic liquid level is stable at about 350m. The effectiveness of drainage and pressure reduction can be judged based on the shape of the relationship curve between cumulative water production and bottom hole pressure.

[0036] The relationship curve between cumulative water production and bottom hole pressure was fitted by piecewise linear fitting. Since the bottom hole pressure generally decreases with the increase of cumulative water production, the negative sign was ignored when discussing the slope of the fitting line, and the absolute value of the slope was analyzed. The slope of the first straight line segment of the first stage of Well Z-2 was 0.0192, and the slope of the second straight line segment was 0.1018, which means that for every 100m3 of water produced, the bottom hole pressure decreased by 1.92MPa and 10.18MPa, respectively. The drainage and pressure reduction efficiency after gas production was significantly higher than that before gas production. The overall curve showed a concave shape with a gradually increasing slope, and the drainage effectiveness gradually increased ( Figure 2 a).

[0037] The slopes of the three straight line segments in the second stage of Well Z-2 are 0.0043, 0.0001 and 0.0002, respectively, which means that for every 100m3 of water produced, the bottom flow pressure decreases by 0.43MPa, 0.01MPa and 0.02MPa, respectively. The curve as a whole presents an upward concave shape with a gradually decreasing slope. The water invasion leads to a gradual weakening of the drainage and pressure reduction effect ( Figure 2 b).

[0038] The relationship curve of Well Z-1 is generally concave, indicating water invasion. For every 100m3 of water discharged in the first straight line segment, the bottomhole pressure drops by 0.42MPa. In this interval, there is no significant change in the pressure reduction efficiency before and after gas is seen. After reducing the number of flushing, the curve turns, and the bottomhole pressure no longer decreases with the increase of cumulative water production and tends to be stable. The second straight line segment shows a horizontal trend. After stopping pumping, the fast drainage caused the bottomhole pressure to drop rapidly, and then remained stable. The drainage of the second and third straight line segments failed to form an effective pressure drop, indicating that the external water supply and water production have reached a balance, and the gas well has been in a low-yield and low-efficiency state for a long time ( Figure 2 c).

[0039] The relationship curve of Well Z-3 has a concave characteristic, showing a good pressure reduction effect. Specifically, before casing was exposed, the cumulative water production had a significant linear relationship with the bottom hole pressure. For every 100m3 of water produced, the bottom hole pressure decreased by 2.75MPa. After gas was exposed, the curve became curved and concave, the slope of the second straight line segment increased, and the bottom hole pressure decreased by 6.45MPa for every 100m3 of water produced. The increase in the slope after gas was exposed is due to the additional pressure reduction effect of gas production during the gas and water co-production stage, as well as the obstruction effect on water production after gas production ( Figure 2 d).

[0040] The relationship curve between the cumulative water production and bottom hole pressure of Well Z-4 is not clear enough. According to the gas (casing) point and the gas production peak point, three typical straight line segments can be identified for fitting. The slope of the fitting straight line gradually increases, and the bottom hole pressure decreases by 0.43MPa, 0.92MPa and 1.83MPa for every 100m3 of water produced. The phenomenon of bottom hole pressure rebound caused by the peak of gas production is related to the casing pressure after the gas production is greatly increased. During this stage, the casing pressure increased from 0.6MPa to 1.5MPa, an increase of 0.9MPa, and the bottom hole pressure increased from 3.0MPa to 3.8MPa, an increase of 0.8MPa, which are basically consistent. As mentioned above, this well has the characteristics of a dual gas production system. After the lower system takes over the gas production, it ushers in the gas production peak, and the slope of the straight line further increases during the stage of bottom hole pressure decline. This shows that the curve is generally concave, which represents a better pressure reduction effect ( Figure 2 e).

[0041] The relationship curve between the cumulative water production and the bottom flow pressure of the Z-5 well has a concave characteristic. The first straight line segment is located before the gas is produced. The bottom flow pressure of the well decreases by 1.12MPa for every 100m3 of water produced. The second fitting straight line segment occurs after the gas is produced, before the peak of gas production, and the bottom flow pressure of the well decreases by 0.80MPa for every 100m3 of water produced. The third fitting straight line segment corresponds to the high-production stage, and the slope increases significantly. The bottom flow pressure of the well decreases by 4.07MPa for every 100m3 of water produced. The average daily gas production in this stage is 1885m3 / d, and the peak daily gas production is 2806m3 / d ( Figure 2 f).

[0042] The drainage and production of Well Z-S1 involved two pumping stops, two downdrafts, and two gas productions (extremely inefficient gas production), resulting in a relatively complex curve of the relationship between cumulative water production and bottom hole pressure. However, during the normal drainage and production phase, there are still three relatively obvious straight line segments. The fitting results show that the three straight line segments reduce the pressure by 0.10MPa, 0.06MPa, and 0.12MPa for every 100m3 of water produced, respectively. The pressure reduction efficiency is extremely low, and the bottom hole pressure can be quickly restored after stopping the pumping, reflecting the strong water invasion ( Figure 2 g).

[0043] S22, calculating the relationship curve between the cumulative gas production and the bottom hole flowing pressure;

[0044] like Figure 3 As shown in the first stage fitting results of Well Z-2, the inverse of the slope indicates that the gas production is 684932m for every 1MPa decrease in bottom hole flowing pressure. 3 ( Figure 3 a). The second phase linear fitting result of Well Z-2 is 925926m3( Figure 3 b) Under the unit bottom hole pressure drop, the gas production of Well Z-2 in the second stage is greater than that in the first stage.

[0045] The typical straight line fitting results of Well Z-1 and Well Z-3 show that the gas production per unit pressure drop is 1259450m3 and 649351m3 respectively. Figure 3 c, d). The two gas production systems of Well Z-4 formed two typical straight line segments, and the gas production per unit bottom flow pressure drop was 124378m3 and 246305m3 respectively, the latter being roughly twice the former ( Figure 3 e). Well Z-5 has two typical straight line segments, indicating that the gas production per unit bottom flow pressure drop is 232558m3 and 1257862m3, respectively, showing an increasing trend, reflecting a good gas supply potential ( Figure 3 f). Well Z-S1 has extremely low gas production and few gas production days, which does not meet the segment fitting criteria and is not further analyzed.

[0046] In summary, the depressurization gas production efficiency of Well Z-1 and Well Z-5 is the highest, but the actual gas production effects and water invasion degrees of these two wells vary greatly, indicating that the efficiency of depressurization-induced gas production is not the key constraint factor.

[0047] S23, calculating the relationship curve between the cumulative water production and the cumulative gas production;

[0048] like Figure 4 As shown in the figure, except for the transitional stage at the beginning of gas production, the relationship curve between the cumulative water production and the cumulative gas production of Well Z-2 is generally linear. The two production stages are significantly different. In the first stage, 14207m3 of coalbed methane can be produced for every 1m3 of water produced, while in the second stage, only 122m3 of coalbed methane can be produced, which is 0.86% of the former, reflecting the limited gas production caused by water invasion ( Figure 4 a).

[0049] The linear fitting of the cumulative water production and cumulative gas production of Well Z-1, Well Z-3, and Well Z-5 shows that the gas production per 1m3 of water is 91m3, 7352m3, and 12043m3, respectively. The former has obvious water invasion interference, while the latter two have high gas production efficiency and no obvious water invasion characteristics ( Figure 4 b, c, e).

[0050] There are two obvious straight line segments in the cumulative water production and cumulative gas production curves of Well Z-4, corresponding to two gas production systems, which verifies the previous discussion on the dual gas production system. For every 1m3 of water produced, the first straight line segment produces 445m3 of gas, and the second straight line segment produces 4160m3 of gas, the latter being 9.35 times the former. There is no obvious water intrusion in the lower gas production system, and the gas production efficiency is high ( Figure 4 d).

[0051] The two straight lines of Well Z-S1 show that the gas production efficiency is extremely low, with 0.12m3 and 1.09m3 of gas produced for every 1m3 of water produced. The gas well has become a water well, and water invasion is serious ( Figure 4 f).

[0052] S3, drainage-pressure reduction-gas production effectiveness analysis and processing;

[0053] Effectiveness of drainage and pressure reduction: The bottom flow pressure drop per unit water production is higher in Z-2-1, Z-3, Z-4, and Z-5 wells, and the pressure reduction efficiency of these wells at different stages shows a trend of gradual increase (concave type), which is related to the large amount of gas production. They can be identified as non-water-invaded wells with high production potential. The bottom flow pressure drop per unit water production of Z-1, Z-2-2, and Z-S1 wells is very low, all below 0.5MPa / 100m 3 , and it shows a gradually decreasing trend (upward concave), which is a water invasion well ( Figure 5 a). Based on this, the bottom flow pressure drop per unit water production in the initial stage of drainage (before gas is produced) can be 0.5MPa / 100m 3, is regarded as the critical value of water invasion. If it is lower than this value, water invasion is very likely to occur. If this value is further reduced, it can be determined that water invasion has occurred. The identification mark of a well without water invasion is that the drop in bottom flow pressure per unit water production in the initial stage of drainage is greater than 0.5MPa / 100m 3 , and there is an increasing trend in the future.

[0054] Effectiveness of gas production by pressure reduction: The gas production per unit of bottom flow pressure reduction is generally at a high level. Except for Well Z-S1, the other wells are all higher than 100,000 m3 / MPa, especially Well Z-1 and Well Z-5, which exceed 1 million m3 / MPa. Well Z-2-2 is close to 1 million m3 / MPa ( Figure 5 b) Well Z-1 and Well Z-2-2 are both water-invaded wells with low gas production efficiency, but the gas production per unit of bottom flow pressure drop is the highest, indicating that the key to limiting gas production lies in how drainage induces pressure drop, rather than how pressure drop induces gas production.

[0055] Furthermore, inefficient pressure reduction caused by water intrusion is the key factor restricting the efficient development of coalbed methane in the region. Once the pressure can be effectively reduced, the potential for high production will be great, which is closely related to the higher gas content and gas saturation and shorter adsorption time of the regional coal seams [8,21].

[0056] The inter-well differences in gas production per unit of water production are highly consistent with the inter-well differences in bottom hole pressure drop per unit of water production ( Figure 5 c).

[0057] S4, splitting processing of gas reservoir attribute parameters and water production;

[0058] Based on the extraction of gas reservoir attribute parameters based on the drainage effectiveness analysis curve, the three water-invaded wells all have the characteristics of low start-up pressure (<3MPa) and high elastic water production index (>200m3 / MPa). Considering that the water-invaded wells have opened the upper gas production system, it means that the upper system is highly water-rich, the hydrodynamic system is open, and the fracturing connects the aquifer, resulting in reservoir decompression. The non-water-invaded wells have high start-up pressure (>4MPa) and low elastic water production index (<100m3 / MPa). The elastic water production index of the Z-4 ​​well is 233m3 / MPa, but the subsequent connection of the gas production system effectively inhibited water invasion. The main production layer of the non-water-invaded well belongs to the lower gas production system. It can be seen that the lower system is weakly water-rich, the hydrogeological opening degree is low, and water invasion is not easy to occur during the development process, which can ensure the pressure reduction effect.

[0059] In terms of well-controlled dynamic reserves, Well Z-4 has the highest, indicating that it has the highest development potential after the gas production system is connected. The well-controlled dynamic reserves of water-invaded wells are not significantly lower than those of non-water-invaded wells, indicating that resource conditions are not the key limiting factor, which is consistent with the characteristics of large coalbed methane resources and high resource abundance in Qianxi area.

[0060] The results of water production splitting show that the water production of water-invaded wells is greater than the elastic water production, and the total water production reaches or exceeds 2000m3; non-water-invaded wells mainly produce elastic water, and the total water production is less than 700m3. The water production energy driving type of the two types of wells is significantly different. The higher the water invasion energy, the worse the pressure reduction and gas production effect. Z-S1 well is a strong water invasion well, with great production fluctuations and extremely unstable curves. Water production splitting is no longer performed. The results of gas reservoir attribute parameter extraction and water production splitting are shown in the following table:

[0061]

[0062] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data, characterized by: The analytical method comprises the following steps: S1. Extract service data based on dynamic analysis of drainage curve; S2, drainage effectiveness analysis curve; S21, calculating the relationship curve between the cumulative water production and the bottom hole flowing pressure; S22, calculating the relationship curve between the cumulative gas production and the bottom hole flowing pressure; S23, calculating the relationship curve between the cumulative water production and the cumulative gas production; S3, drainage-pressure reduction-gas production effectiveness analysis and processing; S4. Splitting of gas reservoir attribute parameters and water production.

2. The method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data according to claim 1, characterized in that: The service data include: extraction of bottom hole flow pressure, cumulative water production, and cumulative gas production.

3. The method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data according to claim 2, characterized in that: Pairwise relationship curves are drawn for the service data. The relationship curve between cumulative water production and bottom hole flowing pressure reflects the drainage and pressure reduction efficiency, the relationship curve between cumulative gas production and bottom hole flowing pressure reflects the pressure reduction and gas production efficiency, and the relationship curve between cumulative water production and cumulative gas production reflects the drainage and gas production efficiency, and a coupling analysis is performed.

4. The method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data according to claim 1, characterized in that: S21 includes drawing data of the relationship curve between the cumulative water production and the bottom hole pressure of the Z-2 well in two production stages, wherein the first stage of the relationship curve is concave downward, and the second stage of the relationship curve is concave upward; The relationship curve between cumulative water production and bottom hole pressure is fitted by piecewise linear fitting.

5. The method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data according to claim 1, characterized in that: The S3 includes the drainage pressure reduction effectiveness analysis: The bottom flow pressure drop per unit water production in the initial stage of drainage can be reduced by 0.5MPa / 100m 3 , is regarded as the critical value of water invasion. If it is lower than this value, water invasion is very likely to occur. If this value is further reduced in the future, it can be determined that water invasion has occurred. The identification mark of wells without water invasion is that the drop in bottom flow pressure per unit water production in the initial stage of drainage is greater than 0.5MPa / 100m 3 , and there is an increasing trend in the future.

6. The method for analyzing the effectiveness of drainage, pressure reduction and gas production in coalbed methane wells based on drainage data according to claim 1, characterized in that: The S4 includes: extracting gas reservoir attribute parameters based on the drainage effectiveness analysis curve for processing.

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