Method for determining abandoned formation pressure considering influence of coalbed methane well water production

Abstract

The application discloses a kind of abandoned formation pressure determination method considering coalbed gas well water production influence.The method includes: obtaining the PVT experimental data and production data of target coalbed gas well, establishing the relationship table between the deviation factor and viscosity of coalbed gas and pressure;Determine the stable production liquid gas ratio of coalbed gas well according to production data;According to the production test data interpretation results of early stage, obtain the deliverability equation of gas well, and record the average formation pressure during corresponding production test;Deviation factor and viscosity corresponding to the average formation pressure during production test are obtained by using interpolation method;Determine the abandoned wellhead flowing pressure of coalbed gas well;Determine the abandoned daily gas production of coalbed gas well;Determine the abandoned daily water production of coalbed gas well;Determine the abandoned bottom hole flowing pressure of coalbed gas well;Abandoned formation pressure is determined by using iterative method based on deliverability equation.The method effectively overcomes the deficiencies of traditional analogy method and empirical formula method, such as poor targeting and large error.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane development research, and specifically relates to a method for determining the pressure of abandoned formations considering the impact of water production from coalbed methane wells. Background Technology

[0002] The abandoned formation pressure of coalbed methane wells is an essential parameter for calculating recoverable reserves, evaluating reservoir recovery rates, and developing development plans. It is also a crucial indicator and basis for surface engineering demonstrations and designs. Currently, the determination of abandoned formation pressure in gas wells typically employs analogy methods, empirical formula methods, and production capacity formula evaluation methods based on economic limit production. Among these, analogy methods and empirical formula methods, due to their inability to fully consider factors such as fluid characteristics and engineering processes, lack specificity and often lead to significant errors, primarily used in the early stages of gas field development evaluation. Furthermore, the production capacity formula evaluation method based on economic limit production fails to consider the impact of water production, resulting in an underestimation of the abandoned formation pressure for high-water-producing coalbed methane wells, which is detrimental to reliable decisions regarding profitable development. Therefore, this paper proposes a new method for determining abandoned formation pressure. Summary of the Invention

[0003] The purpose of this invention is to provide a method for determining the pressure of abandoned formations that takes into account the influence of water production in coalbed methane wells, in order to solve the technical problem of large errors in determining the pressure of abandoned formations in the prior art.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] Step 1: Obtain PVT experimental data of the target coalbed methane well and the original formation pressure P of the well in the middle and deep production layers. Ri In addition to the production tubing dimensions of the gas well; and based on PVT test data, establishing the deviation factor Z and viscosity u of coalbed methane. g Table showing the relationship between pressure P and pressure;

[0006] Step 2: Determine the stable production liquid-to-gas ratio R of the coalbed methane well based on historical production data. wg ;

[0007] Step 3: Interpret the results based on historical production test data to obtain the gas well's production capacity equation. And obtain the mean formation pressure P during the production test. Rref ;

[0008] Step 4, based on the deviation factor Z and viscosity u g The relationship table between pressure P and the average formation pressure P during the production test in step 3 was obtained by interpolation. Rref The corresponding deviation factor Z ref and viscosity u gref ;

[0009] Step 5: Determine the abandoned wellhead flowing pressure P of the coalbed methane well. wha The abandoned wellhead pressure of a self-flowing well is equal to the minimum gas transmission pressure, while the abandoned wellhead pressure of a booster well is equal to the minimum suction pressure required by the booster plus the pipeline pressure loss between the booster inlet and the wellhead.

[0010] Step 6: Determine the daily abandoned gas production q of the coalbed methane well. ga ;

[0011] Step 7, use the stable production liquid-gas ratio R of the coalbed methane well obtained in Step 2. wg Multiply by the daily abandoned gas production q of the coalbed methane well obtained in step 6. ga Obtain the daily wastewater production q wa , i.e. q wa =R wg ×q ga ;

[0012] Step 8: Determine the abandoned bottom flow pressure P of the coalbed methane well. wfa ;

[0013] Step 9: Determine the abandoned formation pressure P using an iterative method based on the production capacity equation. Ra The method for determining the abandoned formation pressure P based on the production capacity equation using an iterative approach. Ra The specific steps include:

[0014] Based on the original formation pressure P obtained in step 1 Ri And the abandoned wellbore bottom pressure P obtained in step 8 wfa Assume that the abandoned formation pressure P in the i-th iteration step ait =P wfa +i×ΔP, i=1, 2,…,n,ΔP=(P Ri -P wfa The iterative model is used to solve for the abandoned formation pressure, based on the deviation factor Z and the gas viscosity u. g The table showing the relationship between pressure and calculation, assuming the pressure P in abandoned formations. ait The corresponding deviation factor Z a and gas viscosity u ga And combined with A obtained in step 3 ref B ref The deviation factor Z obtained in step 4 ref and viscosity u gref Then use The calculated value of P is obtained from the iterative assumption of pressure in abandoned formations. ait The corresponding capacity equation coefficient A a and B a Subsequently, based on the daily waste gas production q obtained in step 6... gaAnd the abandoned wellbore bottom pressure P obtained in step 8 wfa ,use Calculate the pressure P in the abandoned formation Ra If the iteratively calculated value P of the abandoned formation pressure Ra The iterative assumption value P of the abandoned formation pressure ait The error between them meets the accuracy requirement, that is, Abs(P) Ra -P ait )≤Tol or Abs(P Ra -P ait ) / P Ra If the value is less than or equal to Tol, the iteration terminates, and the iteratively calculated value P is... Ra Tol represents the pressure of abandoned formations and is the error tolerance.

[0015] Further, in step 6, the daily abandoned gas production q of the coalbed methane well is determined. ga The steps are as follows:

[0016] First, determine the economic limit daily gas production q of the coalbed methane well. glim ;

[0017] Next, determine the critical fluid carrying capacity q of the coalbed methane well. gcr ;

[0018] The larger of the two values ​​is taken as the daily abandoned gas production q of the coalbed methane well. ga , i.e. q ga =max(q) glim ,q gcr );

[0019] Furthermore, in step 8, the steps for determining the abandoned bottom flow pressure of the coalbed methane well are as follows:

[0020] Based on the abandoned wellhead pressure P wha Daily waste gas production q ga Daily wastewater production q wa Based on the depth of the production formation and the size of the production tubing, the bottom flow pressure P of the abandoned well is calculated using a multiphase flow model in the wellbore. wfa ;

[0021] Alternatively, based on relevant test data during the production process, regression fitting can be used to obtain the bottom-hole and wellhead flowing pressure difference deltaP (the difference between the bottom-hole flowing pressure and the wellhead flowing pressure) and the wellhead flowing pressure P. wh Daily gas production q g and daily liquid production q w The relational expression is deltaP = f(P) wh ,q g ,q w Then, a fitting expression was used, combined with the abandoned wellhead flowing pressure P.wha Daily waste gas production q ga and daily wastewater production q wa The pressure difference deltaP at the bottom and wellhead of the abandoned well was calculated. a Using the abandoned wellhead flow pressure P wha Plus the pressure difference deltaP at the bottom and wellhead of the abandoned well a Then the bottom pressure value P of the abandoned well is obtained. wfa That is, P wfa =P wha +deltaP a .

[0022] Beneficial effects:

[0023] (1) The method of the present invention effectively overcomes the shortcomings of traditional analogy method and empirical formula method, such as weak pertinence and large error. At the same time, it can also consider the influence of coalbed methane well water production on the pressure of abandoned formation. The results obtained are more in line with the actual situation of the mine and are more conducive to reliable decision-making for efficient development. Moreover, the method is simple, easy to understand and implement, highly operable, effective and practical, and has great value for promotion and use.

[0024] (2) The abandoned formation pressure of coalbed methane wells is an essential parameter for calculating the recoverable reserves of gas wells, evaluating the recovery rate of gas reservoirs and preparing development plans. It is also an important indicator and basis for the demonstration and design of relevant surface engineering, and therefore has very important practical value in the mine. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating an embodiment of a method for determining abandoned formation pressure considering the impact of water production from coalbed methane wells according to the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be illustrated by specific examples below, but the scope of protection of the present invention is not limited thereto.

[0027] See Figure 1 This invention provides a flowchart illustrating an embodiment of a method for determining abandoned formation pressure considering the impact of water production from coalbed methane wells. The specific implementation is as follows:

[0028] Step 1: Obtain PVT experimental data of the target coalbed methane well and the original formation pressure P of the well in the middle and deep production layers. Ri In addition to the production tubing dimensions of the gas well; and based on PVT test data, establishing the deviation factor Z and viscosity u of coalbed methane. g Table showing the relationship between pressure P and pressure.

[0029] Step 2: Determine the stable production liquid-to-gas ratio R of the coalbed methane well based on historical production data. wgGenerally, the average ratio of daily water production to daily gas production is taken after the fracturing fluid flowback rate of a coalbed methane well exceeds 100%.

[0030] Step 3: Interpret the results based on historical production test data to obtain the gas well's production capacity equation. And obtain the mean formation pressure P during the corresponding production test period. Rref ;

[0031] Step 4, based on the deviation factor Z and viscosity u g The relationship table between pressure P and the average formation pressure P during the production test in step 3 was obtained by interpolation. Rref The corresponding deviation factor Z ref and viscosity u gref ;

[0032] Step 5: Determine the abandoned wellhead flowing pressure P of the coalbed methane well. wha Specifically, the abandoned wellhead pressure of a self-flowing production well is equal to the minimum gas transmission pressure, while the abandoned wellhead pressure of a booster production well is equal to the minimum suction pressure required by the booster plus the pipeline pressure loss between the booster inlet and the wellhead.

[0033] Step 6: Determine the daily abandoned gas production q of the coalbed methane well. ga Specifically, the economic limit daily gas production q of the coalbed methane well is first determined. glim Secondly, determine the critical fluid-carrying flow rate q of the coalbed methane well. gcr The larger of the two values ​​is taken as the daily abandoned gas production q of the coalbed methane well. ga , i.e. q ga =max(q) glim ,q gcr ).

[0034] Step 7, use the stable production liquid-gas ratio R of the coalbed methane well obtained in Step 2. wg Multiply by the daily abandoned gas production q of the coalbed methane well obtained in step 6. ga Obtain the daily wastewater production q wa , i.e. q wa =R wg ×q ga ;

[0035] Step 8: Determine the abandoned bottom flow pressure P of the coalbed methane well. wfa ;

[0036] Specifically, based on the abandoned wellhead pressure P wha Daily waste gas production q ga Daily wastewater production q wa Based on the depth of the production formation and the size of the production tubing, the bottom flow pressure P of the abandoned well is calculated using a multiphase flow model in the wellbore. wfa ;

[0037] Alternatively, based on relevant test data from historical production processes, regression fitting can be used to obtain the bottom-hole and wellhead flowing pressure difference deltaP (the difference between the bottom-hole flowing pressure and the wellhead flowing pressure) and the wellhead flowing pressure P. wh Daily gas production q g and daily liquid production q w The relational expression is deltaP = f(P) wh ,q g ,q w Then, the fitted expression is used in conjunction with the abandoned wellhead flowing pressure P. wha Daily waste gas production q ga and daily wastewater production q wa The pressure difference deltaP at the bottom and wellhead of the abandoned well was calculated. a Using the abandoned wellhead flow pressure P wha Plus the pressure difference deltaP at the bottom and wellhead of the abandoned well a Then the bottom pressure value P of the abandoned well is obtained. wfa That is, P wfa =P wha +deltaP a .

[0038] Step 9: Determine the abandoned formation pressure P using an iterative method based on the production capacity equation. Ra ;

[0039] Specifically, based on the original formation pressure P obtained in step 1 Ri And the abandoned wellbore bottom pressure P obtained in step 8 wfa Assume that the abandoned formation pressure P in the i-th iteration step ait =P wfa +i×ΔP, i=1, 2,…,n,ΔP=(P Ri -P wfa The iterative model is used to solve for the abandoned formation pressure, based on the deviation factor Z and the gas viscosity u. g The table showing the relationship between pressure and calculation, assuming the pressure P in abandoned formations. ait The corresponding deviation factor Z a and gas viscosity u ga And combined with A obtained in step 3 ref B ref The deviation factor Z obtained in step 4 ref and viscosity u gref Then use The calculated value of P is obtained from the iterative assumption of pressure in abandoned formations. ait The corresponding capacity equation coefficient A a and B a ;

[0040] Based on the daily waste gas production q obtained in step 6 ga And the abandoned wellbore bottom pressure P obtained in step 8 wfa ,use Calculate the pressure P in the abandoned formation Ra ;

[0041] If the iterative calculation value P of the abandoned formation pressure Ra The iterative assumption value P of the abandoned formation pressure ait The error between them meets the accuracy requirement, that is, Abs(P) Ra -P ait )≤Tol or Abs(P Ra -P ait ) / P Ra If the value is less than or equal to Tol, the iteration terminates, and the iteratively calculated value P is... Ra Tol represents the pressure of abandoned formations and is the error tolerance.

[0042] This embodiment establishes a table showing the relationship between the deviation factor and viscosity and pressure of coalbed methane by collecting PVT experimental data and production data of relevant coalbed methane reservoirs. Based on the production data, the stable production liquid-to-gas ratio of coalbed methane wells is determined. The production capacity equation of the gas wells is obtained by interpreting the results of previous production test data, and the average formation pressure during the corresponding production test period is recorded. The deviation factor and viscosity corresponding to the average formation pressure during the production test period are calculated using an interpolation method. The abandoned wellhead flowing pressure of the coalbed methane well is determined. The abandoned daily gas production of the coalbed methane well is determined. The abandoned daily water production of the coalbed methane well is determined. The abandoned bottomhole flowing pressure of the coalbed methane well is determined. Based on the production capacity equation, an iterative method is used to calculate and determine the abandoned formation pressure. This invention effectively overcomes the shortcomings of traditional analogy methods and empirical formula methods, such as weak specificity and large errors. It also considers the impact of coalbed methane well water production on abandoned formation pressure. The results obtained are more consistent with the actual situation of the mine, more conducive to reliable decision-making for efficient development, and the method is simple, highly operable, effective, and practical, with great value for widespread application.

[0043] Furthermore, to better illustrate the effects of the present invention, a coalbed methane well is used as an example below to verify the method for determining abandoned formation pressure that takes into account the impact of coalbed methane well water production proposed in this invention.

[0044] Example 1

[0045] The gas well is as follows:

[0046] The coalbed methane well has a vertical depth of 2850m in the middle of the formation, an original formation pressure of 28MPa, a wellhead temperature of 15℃, and a formation temperature of 81.3℃. It employs... In the later stages of oil pipeline production, centralized pressurization extraction will be carried out using gas gathering stations, with a minimum intake pressure of 0.3 MPa for the pressurizer.

[0047] The method for determining abandoned formation pressure considering the impact of water production from coalbed methane wells according to this embodiment is detailed below:

[0048] (1) The gas well's production layer is at a depth of 2850m, and the original formation pressure P of the gas well is... Ri =28MPa, using Pipeline production; Based on collected PVT experimental data from relevant coalbed methane reservoirs, the deviation factor Z and viscosity u of the coalbed methane were obtained. g The relationship between pressure P and pressure is shown in Table 1.

[0049] Table 1. Relationship between pressure, deviation factor, and viscosity.

[0050]

[0051]

[0052] (2) Determine the stable production fluid-to-gas ratio of the gas well; according to the historical production data of this well, the stable production fluid-to-gas ratio after the fracturing fluid flowback rate reaches 100% is R. wg = 6.3993 cubic meters per 10,000 cubic meters.

[0053] (3) The production capacity equation of the gas well is obtained based on the interpretation results of historical production test data. That is, A ref =2.7698, B ref =9.4022, mean formation pressure P during production testing Rref =

[0054] 25.3256 MPa.

[0055] (4) Based on deviation factor Z and viscosity u g The table showing the relationship between pressure P and the average formation pressure P during the productivity testing period was obtained using interpolation. Rref =25.3256MPa, corresponding deviation factor Z ref =0.8731 and viscosity u gref =

[0056] 0.0212 mPa.

[0057] (5) Determine the abandoned wellhead flowing pressure P of the coalbed methane well. wha The gas well later adopted centralized booster extraction. The minimum suction pressure of the booster was approximately 0.15 MPa. Adding the pipeline pressure loss between the wellhead and the booster inlet, the abandoned wellhead flowing pressure was approximately P. wha =0.3MPa.

[0058] (6) Determine the daily abandoned gas production q of the coalbed methane well. ga ;

[0059] First, based on production and operation data and gas prices, a model is used. The economic limit of daily gas production for this coalbed methane well is determined to be q. glim = 0.1065 million cubic meters / day; where q glim C: Economic limit daily gas production, 10,000 cubic meters / day; P: Annual direct operating cost of the gas well, 10,000 yuan; T: Gas price, yuan / cubic meter; η: Commodity rate, decimal; λ: Gas well production hour rate, decimal.

[0060] Secondly, based on a wellhead temperature of 15℃, a production pipe diameter of 0.062m, and an abandoned wellhead pressure of 0.3MPa, the Turner model was used to determine the critical fluid-carrying flow rate q of the coalbed methane well. gcr = 0.8635 million cubic meters / day;

[0061] The larger of the economically limited daily production and the critical liquid-carrying flow rate is taken as the abandoned daily gas production q of the coalbed methane well. ga , i.e. q ga = max(0.1065 million cubic meters / day, 0.8635 million cubic meters / day), therefore q ga = 0.8635 million cubic meters / day.

[0062] (7) Use the stable production liquid-gas ratio R of the coalbed methane well obtained in step (2) wg Multiply by the daily abandoned gas production q of the coalbed methane well obtained in step (6). ga Obtain the daily wastewater production q wa , i.e. q wa =R wg ×q ga =6.3993 × 0.8635 = 5.5258, therefore the daily wastewater production q wa = 5.5258 cubic meters / day.

[0063] (8) Determine the abandoned bottom flow pressure P of the coalbed methane well. wfa ;

[0064] This embodiment uses regression fitting to obtain the abandoned bottomhole flowing pressure P of the gas well. wfa Based on relevant test data during the production process, the bottom-hole and wellhead flowing pressure differential deltaP and the wellhead flowing pressure P of the gas well were obtained. wh Daily gas production q g and daily liquid production q w The correspondence between them is shown in Table 2.

[0065] Table 2. Bottom-of-wellhead flowing pressure difference and related parameters

[0066]

[0067] Using the regression analysis function in EXEL software, regression fitting was used to obtain the bottom hole and wellhead flowing pressure difference deltaP (the difference between the bottom hole flowing pressure and the wellhead flowing pressure) and the wellhead flowing pressure P. wh Daily gas production q g and daily liquid production q w The relationship between them is expressed as deltaP = 5.9863 - 0.7325 × P wh +0.1511×q g +0.0086×q w Then, the fitted expression is used in conjunction with the abandoned wellhead flowing pressure P. wha =0.3MPa and daily waste gas production q ga =0.8635 million cubic meters / day and daily wastewater production q wa =5.5258 cubic meters / day, the calculated pressure difference deltaP at the bottom and top of the abandoned well. a = 5.9445 MPa, using the abandoned wellhead flowing pressure P wha =0.3MPa plus the differential pressure deltaP at the bottom and top of the abandoned well a =5.9445MPa, then the bottom pressure value P of the abandoned well is obtained. wfa That is, P wfa =P wha +deltaP a =0.3+5.9445=6.2445(MPa).

[0068] (9) Determine the pressure P of abandoned formations using an iterative method based on the productivity equation. Ra ;

[0069] Specifically, based on the original formation pressure P obtained in step (1) Ri =28MPa and the abandoned well bottom flow pressure P obtained in step (8) wfa =6.2445MPa, using P ait =P wfa The iterative mode of +i×0.02 is used to solve for the abandoned formation pressure, where i = 1, 2, ..., 1088; when the 31st iteration is performed, the iterative assumption is that the abandoned formation pressure P... ait =6.8645;

[0070] Based on the deviation factor Z and the gas viscosity u g The table shows the relationship between pressure and calculation, assuming the pressure P in the abandoned formation. ait The corresponding deviation factor Z a =0.8976 and gas viscosity u ga =0.0142, and combined with A obtained in step (3)ref =2.7698, P ref =9.4022 and the deviation factor Z obtained in step (4) ref =0.8731 and viscosity u gref =0.0212 mPa·s, and then use The calculated value of B is obtained from the iterative assumption of pressure in the abandoned formation. ait The corresponding capacity equation coefficient A a =1.9116 and B a =9.6663;

[0071] Then, based on the daily waste gas production q obtained in step (6) ga = 0.8635 million cubic meters / day and the abandoned well bottom flowing pressure P obtained in step (8) wfa =6.2445MPa, using Calculate the pressure P in the abandoned formation Ra =6.9175MPa;

[0072] Iterative calculation of the pressure in abandoned formations, P Ra The iterative assumption value P of the abandoned formation pressure ait The relative error between P and 6.8645 is 0.0077, which meets the accuracy requirements for engineering applications. Moreover, this result is consistent with the understanding gained from practical experience in the mine. Therefore, the iteratively calculated value P can be used. Ra =6.9175 MPa as the abandoned formation pressure.

[0073] It should be noted that when using the Meck empirical formula P Ra =2.149×10 -3 When calculating the abandoned formation pressure of a gas well, the abandoned formation pressure P is obtained. Ra =2.149×10 -3 D = 2.149 × 10 -3 ×2850=6.1246MPa.

[0074] The relative error between the abandoned formation pressure of 6.9175 MPa obtained by the method of the present invention and the abandoned formation pressure value obtained by the empirical formula is 12.95%.

[0075] When the production capacity evaluation method based on the economic limit output in the literature is adopted, the calculated pressure of the abandoned formation is about 0.6697 MPa. This value is much lower than the results obtained by the empirical formula method and the method of this invention, and there is a huge gap with the understanding of mine practice, so the reliability is extremely low.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes made without departing from the present invention should be considered as equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for determining abandoned formation pressure considering the impact of water production from coalbed methane wells, characterized in that, The steps of the method are as follows: Step 1: Obtain PVT experimental data of the target coalbed methane well and the original formation pressure P of the well in the middle and deep production layers. Ri And the production tubing dimensions of the gas well; Based on PVT test data, the deviation factor Z and viscosity u of coalbed methane were established. g Table showing the relationship between pressure P and pressure; Step 2: Determine the stable production liquid-to-gas ratio R of the coalbed methane well based on historical production data. wg ; Step 3: Interpret the results based on historical production test data to obtain the gas well's production capacity equation. And obtain the mean formation pressure P during the corresponding production test period. Rref ; Step 4, based on the deviation factor Z and viscosity u g The relationship table between pressure P and the average formation pressure P during the production test in step 3 was obtained by interpolation. Rref The corresponding deviation factor Z ref and viscosity u gref ; Step 5: Determine the abandoned wellhead flowing pressure P of the coalbed methane well. wha ; Step 6: Determine the daily abandoned gas production q of the coalbed methane well. ga ; Step 7, use the stable production liquid-gas ratio R of the coalbed methane well obtained in Step 2. wg Multiply by the daily abandoned gas production q of the coalbed methane well obtained in step 6. ga Obtain the daily wastewater production q wa , i.e. q wa =R wg ×q ga ; Step 8: Determine the abandoned bottom flow pressure P of the coalbed methane well. wfa ; Step 9: Determine the abandoned formation pressure P using an iterative method based on the production capacity equation. Ra The method for determining the abandoned formation pressure P based on the production capacity equation using an iterative approach. Ra The specific steps include: Based on the original formation pressure P obtained in step 1 Ri And the abandoned wellbore bottom pressure P obtained in step 8 wfa Assume that the abandoned formation pressure P in the i-th iteration step ait =P wfa +i×Δp, i=1, 2,...,n, Δp=(P Ri -P wfa The pressure in abandoned formations is solved using an iterative approach () / n. Based on the deviation factor Z and the gas viscosity u g The table showing the relationship between pressure and calculation, assuming the pressure P in abandoned formations. ait The corresponding deviation factor Z a and gas viscosity u ga And combined with A obtained in step 3 ref B ref The deviation factor Z obtained in step 4 ref and viscosity u gref Then use The calculated value of P is obtained from the iterative assumption of pressure in abandoned formations. ait The corresponding capacity equation coefficient A a and B a ; Based on the daily waste gas production q obtained in step 6 ga And the abandoned wellbore bottom pressure P obtained in step 8 wfa ,use Calculate the pressure P in the abandoned formation Ra ; If the iterative calculation value P of the abandoned formation pressure Ra The iterative assumption value P of the abandoned formation pressure ait The error between them meets the accuracy requirement, that is, Abs(P) Ra -P ait )≤Tol or Abs(P Ra -P ait ) / P Ra If the value is less than or equal to Tol, the iteration terminates, and the iteratively calculated value P is... Ra Tol represents the pressure of abandoned formations and is the error tolerance.

2. The method for determining abandoned formation pressure considering the impact of coalbed methane well water production according to claim 1, characterized in that, In step 6, the daily abandoned gas production q of the coalbed methane well is determined. ga The steps are as follows: First, determine the economic limit daily gas production q of the coalbed methane well. glim ; Next, determine the critical fluid carrying capacity q of the coalbed methane well. gcr ; The larger of the two values ​​is taken as the daily abandoned gas production q of the coalbed methane well. ga , i.e. q ga =max(q) glim q gcr ).

3. The method for determining abandoned formation pressure considering the impact of water production from coalbed methane wells according to claim 1, characterized in that, In step 8, the steps for determining the abandoned bottom flow pressure of the coalbed methane well are as follows: Based on the abandoned wellhead pressure P wha Daily waste gas production q ga Daily wastewater production q wa Based on the depth of the production formation and the size of the production tubing, the bottom flow pressure P of the abandoned well is calculated using a multiphase flow model in the wellbore. wfa ; Alternatively, based on relevant test data from historical production processes, regression fitting can be used to obtain the bottom-hole and wellhead flowing pressure difference deltaP and the wellhead flowing pressure P. wh Daily gas production q g and daily liquid production q w The relational expression is deltaP = f(P) wh q g q w Then, a fitting expression was used, combined with the abandoned wellhead flowing pressure P. wha Daily waste gas production q ga and daily wastewater production q wa The pressure difference deltaP at the bottom and wellhead of the abandoned well was calculated. a Using the abandoned wellhead flow pressure P wha Plus the pressure difference deltaP at the bottom and wellhead of the abandoned well a Then the bottom pressure value P of the abandoned well is obtained. wfa That is, P wfa =P wha +deltaP a .

Images