Calculation method of gas well residual gas content

Abstract

The invention discloses a gas well residual gas content calculation method, and relates to the technical field of petroleum and natural gas industrial exploration and development, and the method comprises the following steps: S1, collecting and sorting the yield data of a gas well, and building a single well yield-time scatter diagram according to the production well yield data in the yield data; s2, fitting a function relationship between the gas production rate of the gas well and the production time by using the yield-time scatter diagram, and determining the total gas production rate of the single well by using the function relationship; s3, predicting a gas production curve of a single well according to the fitted function relationship, and predicting recoverable reserves of the single well through mathematical integration; and S4, according to the predicted single-well recoverable reserves, the single-well residual gas content is predicted in combination with the single-well total gas production rate. The calculation method provided by the invention does not depend on too many parameters such as formation pressure, only depends on single well yield data, can obtain the gas well residual gas content, can accurately indicate the gas well recovery degree in real time, and can timely and effectively guide and optimize a gas well production system and measures.

Description

Technical Field

[0001] The invention relates to the technical field of exploration and development of petroleum and natural gas industry, and more specifically to a method for calculating the gas content of residual gas in a gas well. Background Art

[0002] The residual gas content of a gas well is generally the ratio of natural gas reserves that have not been produced under the existing production technology and can be produced again through measures such as re-understanding the geology or improving the existing production technology to the total geological reserves. At different stages of gas well development, its reserves need to be evaluated. The residual gas content can help determine the reserve recovery degree and recoverable potential of the reservoir being developed, and help formulate effective production increase measures to increase reserves and increase revenue. Therefore, calculating the residual gas content of a gas well can effectively guide the efficient production of the gas well.

[0003] There is no method for calculating the gas content of gas wells at home and abroad. Usually, the distribution of residual gas is qualitatively described by formation pressure, and the recovery degree of recoverable reserves is combined with the formation pressure distribution to achieve a quantitative description of the distribution of residual gas. The more mature methods for calculating the recovery degree of recoverable reserves are material balance method, unstable well test analysis method and production accumulation method, but these methods require more parameters, and gas wells often cannot accurately obtain the required parameters, so the prediction results are not accurate, and these methods are not applicable to all stages of gas well development. 1) The material balance method is mostly used in the early stage of development, but this method has certain limitations for gas reservoirs with abnormal formation pressure, and this method is more dependent on formation pressure; 2) The unstable well test method can be applied in different stages of development, but the measured pressure curve is far from the ideal pressure curve; 3) The production accumulation method can only be used in the late stage of development.

[0004] In the prior art, the patent with publication number CN110617062A discloses a method for analyzing the distribution characteristics of residual gas in reservoirs, which includes the following steps: Step 1, collecting and collating the static and dynamic data of the research block; Step 2, calculating the reserves, water body energy, gas production rate, and permeability variation coefficient of a single well; Step 3, making an isovalue map of the calculation results of Step 2; Step 4, circling the area of ​​a single reservoir that meets a certain standard on the isovalue map in Step 3, and superimposing the area, dividing the research block into different small areas, and classifying and studying different residual gas distribution characteristics and their formation mechanisms. The advantage of the present invention is that it can combine field data to divide a large research block into small areas with different residual gas distribution characteristics, providing a basis for formulating mining countermeasures with different residual gas distribution characteristics, and is highly practical.

[0005] The patent with publication number CN115640484A discloses a method for calculating the residual gas distribution of a tight gas well with a fixed production. For a tight gas well with n (n≥1) layers, the residual gas distribution of the gas well is determined by the residual gas distribution of the production layer; the residual gas distribution of all production layers is calculated by the calculation formula of the residual gas distribution of the production layer, and the residual gas distribution of the gas well is calculated by the calculation formula of the residual gas distribution of the gas well. The method for calculating the residual gas distribution of a tight gas well with a fixed production established by the present invention can quickly evaluate the residual gas distribution of the production layer and the gas well. At the same time, the calculation steps are simple, which is convenient for on-site application in gas fields and has important value for the development of tight gas.

[0006] In the above patent, the use of a large amount of adjacent well data can only qualitatively describe the distribution of the remaining gas in the reservoir. Gas itself has certain limitations and is greatly affected by the richness of the data. In addition, the calculation of the remaining gas distribution in the gas well is only for the tight gas well with a fixed production, and the calculation result is greatly affected by the number of producing layers. Summary of the invention

[0007] In order to overcome the defects in the above-mentioned prior art, the present invention discloses a method for calculating the residual gas content of a gas well. The present invention does not rely on formation pressure, but only relies on single well production data to obtain the residual gas content of a gas well, can accurately indicate the degree of gas well production in real time, and can timely and effectively guide the optimization of gas well production systems and measures.

[0008] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0009] A method for calculating the residual gas content of a gas well comprises the following steps:

[0010] 1. Establishment of single well production-time scatter plot

[0011] S1. Collect and organize the production data of gas wells, and establish a single well production-time scatter plot based on the production data of production wells in the production data;

[0012] In the above steps, the purpose of establishing a single well production-time scatter plot is to facilitate the subsequent determination of the functional relationship between the gas production of the gas well and the production time.

[0013] Preferably, in the step S1, when collecting and collating the production data of the production wells, the production data after the gas wells have been put into production for a period of time without frequent replacement of nozzles and without large-scale fluctuations are selected.

[0014] In the above steps, when selecting production well production data, it is necessary to select production data after the gas well has been put into production for a period of time, without frequent nozzle changes and large fluctuations, so as to avoid the production well production data affecting subsequent calculations.

[0015] 2. Fitting Function Relationship

[0016] S2. Fitting the functional relationship between the gas production of the gas well and the production time by using the production-time scatter plot, and determining the total gas production of the single well by using the functional relationship;

[0017] Preferably, in step S2, fitting the functional relationship between the gas production of the gas well and the production time comprises the following steps:

[0018] S21. Determine the initial output q i , this point is the peak value of the output. When there are multiple peak values, select the last peak point or the peak point before the output shows a clear downward trend;

[0019] S22, production time from initial output to current production t 1 ;

[0020] S23, using Arps hyperbolic decreasing relation, according to q i and t 1 , draw the production-time curve, and by continuously adjusting the decline parameter in the Arps hyperbolic decline relationship, make the drawn scatter plot have the strongest correlation with the actual production-time curve. At this time, the hyperbolic decline relationship is the fitting function of the well.

[0021] Preferably, in step S2, determining the total gas production of a single well includes:

[0022] Assume f(i) is the daily gas production of the gas well on the i-th day of production. When the gas well is put into production at time t, the total gas production Qt of the well is:

[0023]

[0024] Where Qt is the total gas production of the gas well when the well is put into production at time t, 10 4 m 3 .

[0025] 3. Prediction of recoverable reserves of a single well

[0026] S3. Predict the gas production curve of a single well based on the fitted functional relationship, and predict the recoverable reserves of a single well through mathematical integration;

[0027] Preferably, in the step S3, predicting the single well gas production curve according to the fitted functional relationship comprises the following steps:

[0028] S31. Determine the time point t you want to predict n ;

[0029] S32, determine the time interval, and set t according to the time interval 1 to n The time period is divided into n-1 time points;

[0030] S33, substituting the time point into the fitting function to calculate t2, t3, ..., t n-1 The output at the moment, connect the output of each point, and draw the current time point t 1 After t n Predicted gas production curve at the time.

[0031] Preferably, in step S3, the recoverable reserves of a single well Q z for:

[0032]

[0033] In the formula, Q z is the recoverable reserves of the gas well, 10 4 m 3 ; f(i) is the daily gas production of the gas well on the i-th day of production.

[0034] 4. Prediction of Remaining Gas Content in a Single Well

[0035] S4. Based on the predicted recoverable reserves of a single well and the total gas production of the single well, predict the remaining gas content of the single well.

[0036] Preferably, the S4 step comprises:

[0037] Assume that the single well is put into production at a time t, and the total gas production of the single well is Q t , the remaining gas volume at this time is Q s , the residual gas content is A, then:

[0038]

[0039] Q s =Q z -Q t ;

[0040]

[0041] Where: A is the residual gas content, %; Qs is the residual gas volume of the gas well, 10 4 m 3 ; Qz is the recoverable reserves of the gas well, 10 4 m 3 ;Q t is the total gas production of the gas well at time t, 10 4 m 3 .

[0042] Preferably, different gas well residual gas content ratios are calculated using different production start times, and the residual gas content ratios calculated at different production start times are mutually verified.

[0043] In the present invention, as the gas well continues to be produced, different residual gas content ratios of the gas well can be calculated at different production times, and these calculated residual gas content ratios can be mutually verified.

[0044] Preferably, when the remaining gas content of the well is calculated at a certain time point, the remaining gas content is used to indicate the current recovery degree of the well:

[0045] When the residual gas content of a gas well is greater than 80%, it indicates that the gas well has a low recovery rate;

[0046] When the residual gas content of a gas well is between 20% and 80%, it indicates that the gas well has a normal recovery rate.

[0047] When the residual gas content of a gas well is less than 20%, it indicates that the gas well has a high degree of recovery.

[0048] Preferably, after obtaining the single well residual gas content, the single well residual gas content is used to guide the optimization of gas well production:

[0049] When the residual gas content of a gas well is greater than 80%, it indicates that the gas well has a low recovery rate. At this time, the gas production of the gas well is spontaneous, and it is produced in a natural exhaustion manner.

[0050] When the residual gas content of a gas well is between 20% and 80%, it indicates that the gas well has a general recovery rate. If the gas well encounters a complex situation at this time, corresponding measures should be implemented according to the actual situation of the gas well.

[0051] When the residual gas content of a gas well is less than 20%, it indicates that the well has a high degree of recovery. If the gas well encounters a complex situation at this time, the relationship between the gas well output and the production increase cost should be comprehensively considered and corresponding adjustments should be made.

[0052] Beneficial effects of the present invention:

[0053] 1. The present invention uses mathematical methods to quantitatively predict the recovery rate of gas wells, which has the advantages of simple calculation process, low calculation difficulty, high prediction efficiency, low prediction cost, etc. The calculation formula proposed in the present invention can be applied to the prediction of the recovery rate of gas wells.

[0054] 2. The calculation method proposed in the present invention does not rely on too many parameters such as formation pressure, but only relies on single well production data to obtain the gas content of the remaining gas in the gas well. It can accurately indicate the degree of gas well production in real time and can timely and effectively guide the optimization of gas well production systems and measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is the fitted production curve of a shale gas produced 400 days after it was put into production. DETAILED DESCRIPTION

[0056] The concept, specific structure and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments and drawings to fully understand the purpose, characteristics and effects of the present invention.

[0057] Example 1

[0058] A method for calculating the residual gas content of a gas well comprises the following steps:

[0059] S1. Collect and organize the production data of gas wells, and establish a single well production-time scatter plot based on the production data of production wells in the production data;

[0060] In the above steps, when selecting production well production data, it is necessary to select production data after the gas well has been put into production for a period of time, without frequent nozzle changes and large fluctuations, so as to avoid the production well production data affecting subsequent calculations.

[0061] S2. Fitting the functional relationship between the gas production of the gas well and the production time by using the production-time scatter plot, and determining the total gas production of the single well by using the functional relationship;

[0062] In the step S2, fitting the functional relationship between the gas production of the gas well and the production time includes the following steps:

[0063] S21. Determine the initial output q i , this point is generally the peak of production. When there are multiple peaks, the last peak or the peak point before the production shows a clear downward trend should be selected;

[0064] S22, determine time t 1 , that is, the production time from the initial output to the present;

[0065] S23, using Arps hyperbolic decreasing relation, according to q i and t 1 , draw the production-time curve, and by continuously adjusting the decline parameter in the Arps hyperbolic decline relationship, make the drawn scatter plot have the strongest correlation with the actual production-time curve. At this time, the hyperbolic decline relationship is the fitting function of the well.

[0066] In the step S2, determining the total gas production of a single well includes:

[0067] Assume f(i) is the daily gas production of the gas well on the i-th day of production. When the gas well is put into production at time t, the total gas production Qt of the well is:

[0068]

[0069] Where Qt is the total gas production of the gas well when the well is put into production at time t, 10 4 m 3 .

[0070] S3. Predict the gas production curve of a single well based on the fitted functional relationship, and predict the recoverable reserves of a single well through mathematical integration;

[0071] In the step S3, predicting the single well gas production curve according to the fitted functional relationship includes the following steps:

[0072] S31. Determine the time point t you want to predict n ;

[0073] S32, determine the time interval, and set t according to the time interval 1 to n The time period is divided into n-1 time points;

[0074] S33, substituting the time point into the fitting function to calculate t2, t3, ..., t n-1 The output at the moment, by connecting the outputs of each point, can be plotted at the current time point t 1 After t n Predicted gas production curve at the time.

[0075] In the step S3, the recoverable reserves of a single well are Q z for:

[0076]

[0077] In the formula, Q z is the recoverable reserves of the gas well, 10 4 m 3 ; f(i) is the daily gas production of the gas well on the i-th day of production.

[0078] S4. Based on the predicted recoverable reserves of a single well and the total gas production of the single well, predict the remaining gas content of the single well.

[0079] The S4 step includes:

[0080] Assume that the single well is put into production at a time t, and the total gas production of the single well is Q t , the remaining gas volume at this time is Q s , the residual gas content is A, then:

[0081]

[0082] Q s =Q z -Q t ;

[0083]

[0084] Where: A is the residual gas content, %; Qs is the residual gas volume of the gas well, 10 4 m3 ; Qz is the recoverable reserves of the gas well, 10 4 m 3 ;Q t is the total gas production of the gas well at time t, 10 4 m 3 .

[0085] In the present invention, as the gas well continues to be produced, different residual gas content ratios of the gas well can be calculated at different production times, and these calculated residual gas content ratios can be mutually verified.

[0086] In the present invention, when the remaining gas content of the well is calculated at a certain time point, the remaining gas content is used to indicate the current recovery degree of the well:

[0087] When the residual gas content of a gas well is greater than 80%, it indicates that the gas well has a low recovery rate;

[0088] When the residual gas content of a gas well is between 20% and 80%, it indicates that the gas well has a normal recovery rate.

[0089] When the residual gas content of a gas well is less than 20%, it indicates that the gas well has a high degree of recovery.

[0090] In the present invention, after obtaining the gas content ratio of the remaining gas in a single well, the gas content ratio of the remaining gas in a single well is used to guide and optimize the production of the gas well:

[0091] When the residual gas content of a gas well is greater than 80%, it indicates that the gas well has a low recovery rate. At this time, the gas production of the gas well is generally spontaneous, and is produced in a natural depletion manner.

[0092] When the residual gas content of a gas well is between 20% and 80%, it indicates that the gas well has a general recovery rate. If the gas well encounters complex situations such as flooding, corresponding measures can be implemented according to the actual situation of the gas well.

[0093] When the residual gas content of a gas well is less than 20%, it indicates that the well has a high degree of recovery. If the gas well encounters a complex situation at this time, it is necessary to comprehensively consider the relationship between the gas well output and the production increase cost and make corresponding adjustments.

[0094] Example 2

[0095] In this embodiment, the remaining gas content of a production well in the Luzhou shale gas field in southern Sichuan is predicted, including the following steps:

[0096] Step 1: Collect and organize the production data of gas wells, and establish a single well production-time scatter plot based on the production data of production wells ( Figure 1 ).

[0097] Step 2: Fit the functional relationship between gas well production and production time according to the production-time scatter plot in step 1 ( Figure 1 );

[0098] The fitted function relationship is:

[0099] Step 3: According to the functional relationship fitted in step 2, predict the gas production curve of a single well, and predict the recoverable reserves of a single well through mathematical integration;

[0100] Predict the recoverable reserves of the well Q z It is 122.63 million square meters.

[0101]

[0102] Step 4: Based on the recoverable reserves predicted in step 3 and the produced reserves of the single well, predict the remaining gas content of the well when the well is put into production for 400 days;

[0103]

[0104]

[0105] Q s =Q z -Q t =12263-3249=9014 (ten thousand square meters)

[0106]

[0107] When the well was put into production for 400 days, the predicted recoverable reserves were 123 million cubic meters, the recovered reserves were 32.49 million cubic meters, and the predicted remaining gas content was 73%.

[0108] In the prior art patents CN110617062A and CN115640484A, a large amount of adjacent well data can only be used to qualitatively describe the distribution of residual gas in the reservoir. Gas itself has certain limitations and is greatly affected by the richness of the data. Moreover, the calculation of the residual gas distribution in gas wells is only for fixed-yield tight gas wells, and the calculation results are greatly affected by the number of production layers. This embodiment proposes a quantitative calculation method for the residual gas content based on the gas well production, which does not rely on formation pressure data, and can only rely on single well production data to obtain the residual gas content of the gas well. It can indicate the degree of gas well production in real time and accurately, and can timely and effectively guide the optimization of gas well production systems and measures.

[0109] The above is a specific description of the implementation mode of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalents or substitutions are all included in the scope defined by the claims of the present invention.

Claims

1. A calculation method for the gas content rate of residual gas in a gas well, characterized in that, it includes the following steps: S1. Collect and organize the production data of the gas well, and establish a scatter plot of single-well production vs. time based on the production data of the production well; S2. Use the scatter plot of production vs. time to fit the functional relationship between the gas production of the gas well and the production start time, and use the functional relationship to determine the total gas production already recovered by the single well; S3. According to the fitted functional relationship, predict the gas production curve of the single well, and predict the recoverable reserves of the single well through mathematical integration; S4. According to the predicted recoverable reserves of the single well, combined with the total gas production already recovered by the single well, predict the gas content rate of residual gas in the single well.

2. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, in the step S1, when collecting and organizing the production data of the production well, after a period of production start of the gas well, select the production data without frequent nozzle replacement and without large-scale fluctuations.

3. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, in the step S2, the steps for fitting the functional relationship between the gas production of the gas well and the production start time include: S21. Determine the initial output q i , this point is the peak value of the output. When there are multiple peak values, select the last peak point or the peak point before the output shows a clear downward trend; S22, production time from initial output to current production t 1 ; S23, using Arps hyperbolic decreasing relation, according to q i and t 1 , draw the production-time curve, and by continuously adjusting the decline parameter in the Arps hyperbolic decline relationship, make the drawn scatter plot have the strongest correlation with the actual production-time curve. At this time, the hyperbolic decline relationship is the fitting function of the well.

4. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, in the step S2, determining the total gas production already recovered by the single well includes: Let f(i) be the daily gas production of the gas well on the i-th day of production start, then when the production start time of the gas well is t, the total gas production already recovered by this well Qt is: Where Qt is the total gas production of the gas well when the well is put into production at time t, 10 4 m 3 .

5. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, in the step S3, according to the fitted functional relationship, the steps for predicting the gas production curve of the single well include: S31. Determine the time point t you want to predict n ; S32, determine the time interval, and set t according to the time interval 1 to n The time period is divided into n-1 time points; S33, substituting the time point into the fitting function to calculate t2, t3, ..., t n-1 The output at the moment, connect the output of each point, and draw the current time point t 1 After t n Predicted gas production curve at the time.

6. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, In the step S3, the recoverable reserves of a single well are Q z for: In the formula, Q z is the recoverable reserves of the gas well, 10 4 m 3 ; f(i) is the daily gas production of the gas well on the i-th day of production.

7. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, the step S4 includes: Assume that the single well is put into production at a time t, and the total gas production of the single well is Q t , the remaining gas volume at this time is Q s , the residual gas content is A, then: Q s =Q z -Q t ; Where: A is the residual gas content, %; Qs is the residual gas volume of the gas well, 10 4 m 3 ; Qz is the recoverable reserves of the gas well, 10 4 m 3 ;Q t is the total gas production of the gas well at time t, 10 4 m 3 .

8. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, it further includes: Calculate the gas content rate of residual gas in the gas well with different production start times, and verify the gas content rates calculated at different production start times with each other.

9. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, it further includes: When the gas content rate of residual gas in the well is calculated at a certain time point, use this gas content rate to indicate the current production degree of this well: When the gas content rate of residual gas in the gas well is greater than 80%, it indicates that the production degree of this gas well is relatively low; When the gas content rate of residual gas in the gas well is between 20% - 80%, it indicates that the production degree of this gas well is average; When the gas content rate of residual gas in the gas well is less than 20%, it indicates that the production degree of this gas well is relatively high.

10. The calculation method for the gas content rate of residual gas in a gas well according to claim 1, characterized in that, it further includes: After obtaining the gas content rate of residual gas in the single well, use the gas content rate of residual gas in the single well to guide the optimization of gas well production: When the gas content rate of residual gas in the gas well is greater than 80%, it indicates that the production degree of this gas well is relatively low. At this time, the gas production of the gas well is spontaneous, and it is exploited in a natural depletion mode; When the residual gas content of a gas well is between 20% and 80%, it indicates that the gas well has a general recovery rate. If the gas well encounters a complex situation at this time, corresponding measures should be implemented according to the actual situation of the gas well. When the residual gas content of a gas well is less than 20%, it indicates that the well has a high degree of recovery. If the gas well encounters a complex situation at this time, the relationship between the gas well output and the production increase cost should be comprehensively considered and corresponding adjustments should be made.

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