Productivity evaluation method for small-pressure-difference high-yield gas well

Abstract

The invention discloses a productivity evaluation method for a small-pressure-difference high-yield gas well, and belongs to the technical field of gas well development, correction coefficients beta corresponding to different alpha coefficients are calculated, and correction coefficient beta charts corresponding to the different alpha coefficients are drawn; the method comprises the following steps: collecting typical gas well productivity well test data, fitting to obtain a Darcy seepage item coefficient A and a non-Darcy seepage item coefficient B, and calculating open flow capacity and a stable empirical number alpha coefficient of a gas well; calculating gas production rates corresponding to different gamma on the basis of formation pressures of gas wells with different stable empirical number alpha coefficients, a Darcy seepage item coefficient A in a pressure square form and a non-Darcy seepage item coefficient B in a gas well pressure form, adding data into the chart, and drawing a'one-point method 'productivity evaluation comprehensive correction chart; and calculating gamma according to the oil testing yield, the formation pressure and the flowing bottomhole pressure of the well, inquiring a correction coefficient beta in the comprehensive correction chart, substituting the correction coefficient beta into a one-point method calculation formula containing the correction coefficient beta, and evaluating the productivity of the gas well.

Description

Technical Field

[0001] This invention belongs to the field of gas well development technology, specifically relating to a method for evaluating the production capacity of high-yield gas wells with small pressure differentials. Background Technology

[0002] In 1987, Chen Yuanqian, based on the binomial productivity equation in the form of pressure squares, and taking the average value of the stable empirical data (hereinafter referred to as "α") of 68 test points from 16 gas wells in 6 gas fields in my country as 0.25, derived the "one-point method" productivity evaluation calculation formula, which is generally referred to in the industry as the conventional "one-point method". Because the α coefficient can be determined, the conventional "one-point method" only requires one test regime to calculate the absolute unobstructed flow rate of the gas well (hereinafter referred to as "q"). AOF This method, which combines theoretical rigor, empirical experience, and convenience, is easy to apply and has acceptable error, and has therefore gradually become the main method for evaluating the single-point test productivity of gas wells.

[0003] Since the beginning of the 20th century, China National Petroleum Corporation's Southwest Oil & Gas Field Company has discovered a number of gas reservoirs with high permeability and high well production in the Sichuan Basin, such as the Feixianguan oolitic beach gas reservoir in northeastern Sichuan and the Longwangmiao Formation gas reservoir in Anyue, central Sichuan. The α coefficient of gas wells in these reservoirs is generally less than 0.25. Field application has revealed that high-yield gas wells with small production pressure differentials can be magnified several times using the conventional "single-point method" to achieve the desired gas well q. AOF If the α coefficient of the gas well is smaller, the evaluation error of the conventional "one-point method" will be greater. Taking the MX145 well as an example, the formation pressure is 74.5 MPa, the production pressure difference of the well completion and oil testing is 0.029~0.266 MPa, and the daily gas production is 22.58~82.84×104 m3 / d. The binomial q AOF The yield is 1077 × 10⁴ m³ / d, while the conventional "one-point method" yields 3139–7226 × 10⁴ m³ / d. Therefore, for this type of gas well, the conventional "one-point method" is chosen to evaluate the gas well's q. AOF Caution is advised. On the other hand, if the gas well's α coefficient is greater than 0.25, the conventional "one-point method" will underestimate the gas well's q to some extent. AOF The α coefficient in the original literature of Chen's "one-point method" ranges from 0.1374 to 0.3436. Therefore, if the α coefficient of the gas well is not in this range, it may produce a large calculation error, especially for high-permeability and high-yield gas wells with small α coefficients, where the calculation error of the conventional "one-point method" is unacceptable. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for evaluating the production capacity of high-yield gas wells with small pressure differentials. This invention can improve the accuracy of conventional "single-point method" production capacity evaluation, especially for high-yield wells with small pressure differentials.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for evaluating the production capacity of a high-yield gas well with a small pressure differential includes the following steps:

[0007] Step 1: Derive the theoretical expression for the correction coefficient β of the "one-point method" capacity evaluation;

[0008] Step 2: Calculate the correction coefficient β corresponding to different α coefficients, and plot the correction coefficient β corresponding to different α coefficients;

[0009] Step 3: Collect typical gas well productivity test data, fit the Darcy seepage term coefficient A in the form of pressure square and the non-Darcy seepage term coefficient B in the form of gas well pressure, and calculate the gas well's unobstructed flow rate and stability empirical number α coefficient.

[0010] Step 4: Based on the formation pressure, pressure square form of Darcy seepage term coefficient A, and gas well pressure form of non-Darcy seepage term coefficient B of gas wells with different stability empirical coefficients α in Step 3, calculate the gas production corresponding to different γ values, add the data to the chart in Step 2, and draw the "one-point method" production capacity evaluation comprehensive correction chart.

[0011] Step 5: Calculate γ based on the well's test production, formation pressure, and bottom hole flowing pressure. Look up the correction coefficient β in the chart from Step 4, and substitute it into the "one-point method" calculation formula containing the correction coefficient β to evaluate the gas well's production capacity.

[0012] Preferably, in step one, the gas well correction coefficient β is only related to the stability empirical number α and the ratio of production pressure differential to formation pressure γ, and its expression is:

[0013]

[0014] In the formula: γ is the ratio of gas well production pressure differential to formation pressure;

[0015] p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf This represents the bottom hole flowing pressure, measured in MPa.

[0016] Preferably, the stability empirical number α is determined by the following formula:

[0017]

[0018] In the formula: A is the Darcy seepage term coefficient in the form of the square of the gas well pressure, in MPa. 2 ·(10 4 m 3 / d)-1; B is the non-Darcy seepage term coefficient in the gas well pressure form, MPa2 ·(10 4 m 3 / d)-2.

[0019] Preferably, the correction coefficient β is calculated based on the different γ and different α coefficients in step one.

[0020] Preferably, in step three, the gas well productivity test data includes formation pressure, gas production, and bottom hole flowing pressure corresponding to different gas production rates.

[0021] Preferably, in step three, the Darcy seepage term coefficient A in the form of the square of the gas well pressure and the non-Darcy seepage term coefficient B in the form of the gas well pressure are determined by the production capacity test fitting, and the production capacity equation when the gas well seepage enters the quasi-steady state is:

[0022]

[0023] The expressions for A are as follows:

[0024]

[0025] The expressions for B are as follows:

[0026]

[0027] In the formula: A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 K represents the gas reservoir permeability, 10 -3 μm 2 h is the reservoir thickness, in meters. Temperature, expressed in Kelvin (K). Where is the gas viscosity, mPa·s; The r represents the deviation factor, which is dimensionless. e r is the well radius of the venting zone, in meters. w ρ is the well radius, in meters; h is the reservoir thickness, in meters; S represents the skin factor, dimensionless; D represents the non-Darcy flow coefficient, in meters. 3 / d) -1 .

[0028] Preferably, in step three, the gas well production capacity is determined by A, B, and p. R Together, we determine that its expression is:

[0029]

[0030] Where: q g To test gas production, the unit is 10. 4 m 3 / d; A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 γ is the ratio of gas well production pressure differential to formation pressure; p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf This represents the bottom hole flowing pressure, measured in MPa.

[0031] Preferably, in step five, γ is first calculated from the well's oil test production, formation pressure, and bottom hole flowing pressure, and then the α coefficient of the gas well is looked up.

[0032] Preferably, in step five, the correction coefficient β is then looked up in the chart from step four based on the coefficients γ and α, and finally the gas well productivity is evaluated using the "one-point method" calculation formula containing the correction coefficient β.

[0033] Preferred, gas well q AOF The expression is:

[0034]

[0035] In the formula: p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf q is the bottom hole flowing pressure in MPa; β is the correction factor; g To test gas production, the unit is 10. 4 m 3 / d.

[0036] The beneficial effects of this technical solution are as follows:

[0037] I. This invention provides a method for evaluating the production capacity of high-yield gas wells with small pressure differentials, which can improve the accuracy of conventional "single-point method" production capacity evaluation, especially for high-yield wells with small pressure differentials. (39 gas wells q) AOF The average relative error decreased from 54.59% to 7.81%.

[0038] II. This invention provides a method for evaluating the production capacity of high-yield gas wells with small pressure differentials. It requires only one measurement point to accurately evaluate the well's production capacity. Compared to conventional methods, this significantly reduces the operational costs associated with specialized well testing (each production well test costs 600,000 yuan), effectively saving costs.

[0039] Third, the present invention provides a method for evaluating the production capacity of high-yield gas wells with small pressure differentials, which can reduce the waste of resources caused by releasing a large amount of sulfur-containing natural gas during production capacity testing of sulfur-containing gas wells, and reduce the risks of on-site testing operations and safety management.

[0040] Fourth, the present invention provides a method for evaluating the production capacity of high-yield gas wells with small pressure differentials. The method has high accuracy in evaluating production capacity and can effectively reduce investment errors caused by inaccurate evaluation of gas well production capacity. Attached Figure Description

[0041] Figure 1 This is a chart showing the correction coefficient β corresponding to the coefficient α in this invention;

[0042] Figure 2 This is a comprehensive calibration diagram for the "one-point method" capacity evaluation in this invention. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0044] Example 1

[0045] like Figure 1 and Figure 2 As shown, a method for evaluating the production capacity of a high-yield gas well with a small pressure differential includes the following steps:

[0046] Step 1: Derive the theoretical expression for the correction coefficient β of the "one-point method" capacity evaluation;

[0047] Step 2: Calculate the correction coefficient β corresponding to different α coefficients, and plot the correction coefficient β corresponding to different α coefficients;

[0048] Step 3: Collect typical gas well productivity test data, fit the Darcy seepage term coefficient A in the form of pressure square and the non-Darcy seepage term coefficient B in the form of gas well pressure, and calculate the gas well's unobstructed flow rate and stability empirical number α coefficient.

[0049] Step 4: Based on the formation pressure, pressure square form of Darcy seepage term coefficient A, and gas well pressure form of non-Darcy seepage term coefficient B of gas wells with different stability empirical coefficients α in Step 3, calculate the gas production corresponding to different γ values, add the data to the chart in Step 2, and draw the "one-point method" production capacity evaluation comprehensive correction chart.

[0050] Step 5: Calculate γ based on the well's test production, formation pressure, and bottom hole flowing pressure. Look up the correction coefficient β in the chart from Step 4, and substitute it into the "one-point method" calculation formula containing the correction coefficient β to evaluate the gas well's production capacity.

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that, in step one, the gas well correction coefficient β is only related to the stability empirical number α and the ratio of production pressure differential to formation pressure γ, and its expression is:

[0053]

[0054] In the formula: γ is the ratio of gas well production pressure differential to formation pressure;

[0055] p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf This represents the bottom hole flowing pressure, measured in MPa.

[0056] The stability empirical number α is determined by the following formula:

[0057]

[0058] In the formula: A is the Darcy seepage term coefficient in the form of the square of the gas well pressure, in MPa. 2 ·(10 4 m 3 / d)-1; B is the non-Darcy seepage term coefficient in the gas well pressure form, MPa 2 ·(10 4 m 3 / d)-2.

[0059] In this step, the correction coefficient β is calculated based on the different γ and α coefficients from step one.

[0060] In step three, the gas well productivity test data includes formation pressure, gas production, and bottom hole flowing pressure corresponding to different gas production rates.

[0061] In step three, the Darcy seepage term coefficient A in the square form of gas well pressure and the non-Darcy seepage term coefficient B in the form of gas well pressure are determined by the production capacity test fitting. The production capacity equation when the gas well seepage enters the quasi-steady state is:

[0062]

[0063] The expressions for A are as follows:

[0064]

[0065] The expressions for B are as follows:

[0066]

[0067] In the formula: A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 K represents the gas reservoir permeability, 10 -3 μm 2 h is the reservoir thickness, in meters. Temperature, expressed in Kelvin (K). Where is the gas viscosity, mPa·s; The r represents the deviation factor, which is dimensionless. e r is the well radius of the venting zone, in meters. w ρ is the well radius, in meters; h is the reservoir thickness, in meters; S represents the skin factor, dimensionless; D represents the non-Darcy flow coefficient, in meters. 3 / d) -1 .

[0068] In step three, the gas well production capacity is determined by A, B, and p. R Together, we determine that its expression is:

[0069]

[0070] Where: q g To test gas production, the unit is 10. 4 m 3 / d; A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 γ is the ratio of gas well production pressure differential to formation pressure; p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf This represents the bottom hole flowing pressure, measured in MPa.

[0071] In step five, γ is first calculated from the well's oil test production, formation pressure, and bottom hole flowing pressure, and then the α coefficient of the gas well is looked up.

[0072] In step five, the correction coefficient β is then looked up in the chart from step four based on the coefficients γ and α. Finally, the gas well productivity is evaluated using the "one-point method" formula containing the correction coefficient β.

[0073] Among them, gas well q AOF The expression is:

[0074]

[0075] In the formula: p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf q is the bottom hole flowing pressure in MPa; β is the correction factor; g To test gas production, the unit is 10. 4 m 3 / d.

[0076] Example 3

[0077] This embodiment employs the production capacity evaluation method for high-yield gas wells with small pressure differentials described in Embodiment 2. Field data from 39 gas wells in China were selected to verify the comprehensive calibration chart. The α coefficients of the verified wells ranged from 0.0022 to 0.8655 (Table 1). Compared with the conventional "one-point method" where the α coefficient is set to 0.25, the α coefficients determined by the comprehensive calibration chart established in this paper are closer to the true α coefficients of the gas wells. As can be seen from Table 1, compared with the gas well q calculated by the binomial production capacity equation... AOF In comparison, the gas well q calculated by this method AOF The results are superior to those calculated using the conventional "one-point method" for 39 gas wells. AOF The average relative error decreased from 54.59% to 7.81%. Notably, for gas wells with an α coefficient less than 0.25, the productivity evaluation effect improved significantly, with the relative error decreasing from 2.92%–186.84% (average 72.82%) to 0.17%–52.17% (average 6.86%). For gas wells with an α coefficient greater than 0.25, the productivity evaluation effect also improved to some extent, with the relative error decreasing from 12.21%–76.33% (average 28.39%) to 0.29%–31.23% (average 9.17%).

[0078] Table 1. Verification and Comparison of Capacity Evaluation Results

[0079]

[0080]

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for evaluating the production capacity of a high-yield gas well with a small pressure differential, characterized in that, Includes the following steps: Step 1: Derive the theoretical expression for the correction coefficient β of the "one-point method" capacity evaluation; Step 2: Calculate the correction coefficient β corresponding to different α coefficients, and plot the correction coefficient β corresponding to different α coefficients; Step 3: Collect typical gas well productivity test data, fit the Darcy seepage term coefficient A in the form of pressure square and the non-Darcy seepage term coefficient B in the form of gas well pressure, and calculate the gas well's unobstructed flow rate and stability empirical number α coefficient. Step 4: Based on the formation pressure, pressure square form of Darcy seepage term coefficient A, and gas well pressure form of non-Darcy seepage term coefficient B of gas wells with different stability empirical coefficients α in Step 3, calculate the gas production corresponding to different γ values, add the data to the chart in Step 2, and draw the "one-point method" production capacity evaluation comprehensive correction chart. Step 5: Calculate γ based on the well's test production, formation pressure, and bottom hole flowing pressure. Look up the correction coefficient β in the chart from Step 4, and substitute it into the "one-point method" calculation formula containing the correction coefficient β to evaluate the gas well's productivity.

2. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 1, characterized in that: In step one, the gas well correction coefficient β is only related to the stability empirical number α and the ratio of production pressure differential to formation pressure γ, and its expression is: In the formula: γ is the ratio of gas well production pressure differential to formation pressure; p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf This represents the bottom hole flowing pressure, measured in MPa.

3. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 2, characterized in that: The stability empirical number α is determined by the following formula: In the formula: A is the Darcy seepage term coefficient in the form of the square of the gas well pressure, in MPa. 2 ·(10 4 m 3 / d)-1; B is the non-Darcy seepage term coefficient in the gas well pressure form, MPa 2 ·(10 4 m 3 / d)-2.

4. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 3, characterized in that: Calculate the correction coefficient β based on the different γ and α coefficients in step one.

5. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 4, characterized in that: In step three, the gas well productivity test data includes formation pressure, gas production, and bottom hole flowing pressure corresponding to different gas production rates.

6. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 5, characterized in that: In step three, the Darcy seepage term coefficient A in the square form of gas well pressure and the non-Darcy seepage term coefficient B in the form of gas well pressure are determined by the production capacity test fitting. The production capacity equation when the gas well seepage enters the quasi-steady state is: The expressions for A are as follows: The expressions for B are as follows: In the formula: A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 K represents the gas reservoir permeability, 10 -3 μm 2 h is the reservoir thickness, in meters. Temperature, expressed in Kelvin (K). Where is the gas viscosity, mPa·s; The r represents the deviation factor, which is dimensionless. e r is the well radius of the venting zone, in meters. w _h_ is the well radius (m); h_ is the reservoir thickness (m); S_ represents the skin factor (dimensionless); D_ represents the non-Darcy flow coefficient (m). 3 / d) -1 .

7. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 6, characterized in that: In step three, the gas well production capacity is determined by A, B, and p. R Together, we determine that its expression is: Where: q g To test gas production, the unit is 10. 4 m 3 / d; A represents the Darcy seepage term coefficient for stable gas wells, in MPa 2 / (10 4 m 3 / d); B represents the coefficient of the stable non-Darcy seepage term of the gas well, MPa 2 / (10 4 m 3 / d) 2 γ is the ratio of gas well production pressure differential to formation pressure; p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. w f is the bottom hole flowing pressure, in MPa.

8. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 7, characterized in that: In step five, γ is first calculated from the well's oil test production, formation pressure, and bottom hole flowing pressure, and then the α coefficient of the gas well is looked up.

9. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 8, characterized in that: Next, based on the coefficients γ and α, the correction coefficient β is looked up in the chart in step four. Finally, the gas well productivity is evaluated using the "one-point method" formula containing the correction coefficient β.

10. The method for evaluating the production capacity of a high-yield gas well with a small pressure differential according to claim 9, characterized in that: gas well q AOF The expression is: In the formula: p R p represents the formation pressure under a specific regime during production testing, expressed in MPa. wf q is the bottom hole flowing pressure in MPa; β is the correction factor; g To test gas production, the unit is 10. 4 m 3 / d.

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