Method for predicting single well recoverable reserves through pressure and yield composite decline

Abstract

The invention discloses a method for predicting single well recoverable reserves through pressure and yield composite decline. The method comprises the steps that production dynamic data such as wellhead pressure, daily gas production and cumulative gas production of a tight sandstone gas production well are collected and arranged; constructing a scatter diagram by using the accumulated gas production data as a horizontal coordinate and the daily gas production * wellhead pressure data as a vertical coordinate; fitting the relation curve of the cumulative gas production and the daily gas production * wellhead pressure by adopting a hyperbolic decline analysis method to obtain a regression relational expression; and substituting the wellhead pressure and the daily gas production under the waste condition to obtain the accumulated gas production under the corresponding waste pressure, namely the recoverable reserves of the production well under the corresponding waste pressure. The method provides a quantitative basis for the evaluation of the tight sandstone gas production well.

Description

Technical Field

[0001] The present invention relates to the field of tight sandstone gas reservoir development, and particularly to a method for predicting the recoverable reserves of a single well by using the composite decline of pressure and production. Background Art

[0002] The well-controlled recoverable reserves are an important reference index for evaluating gas wells. The gas production of tight sandstone gas wells usually starts to decline from the start of production, meeting the applicable requirements of the decline analysis method. Arps proposed three types of decline: exponential decline, hyperbolic decline, and harmonic decline. By comparing and selecting different decline types, the recoverable reserves of gas wells can be predicted more accurately. However, during the production process of tight sandstone gas production wells, due to the change of the working system, the production will fluctuate in local periods under the long-term declining trend. For example, when the production pressure difference is enlarged in a local period, the wellhead pressure drops significantly and the production increases significantly, resulting in fluctuations in the production curve or deviation from the original decline trend, which interferes with the conventional decline analysis.

[0003] For tight sandstone gas production wells, the current decline analysis methods for obtaining well-controlled recoverable reserves are roughly divided into three types:

[0004] (1) Hyperbolic decline method

[0005] First, collect and process the historical production data of the gas well, draw the curve of production changing with time, select the hyperbolic decline model, and fit the initial production, initial decline rate, and hyperbolic index model parameters through optimization algorithms such as the nonlinear least squares method. Predict the future production through the model and calculate the recoverable reserves of the gas well. The hyperbolic decline model is very sensitive to the hyperbolic index and decline rate parameters, and slight errors may lead to significant differences in long-term prediction results.

[0006] (2) Exponential decline method

[0007] First, collect and process the historical production data of the gas well, draw the curve of production changing with time, select the exponential decline model, fit the initial production and decline rate parameters through the nonlinear least squares method, use the fitted model to predict the future production, and calculate the recoverable reserves of the gas well. The exponential decline method is applicable to gas wells with a relatively fast decline and has a small applicable range.

[0008] (3) Harmonic decline method

[0009] First, collect and process the historical production data of the gas well, draw the curve of production changing with time, select the harmonic decline model, fit the initial production and decline rate parameters through the nonlinear least squares method, use the fitted model to predict the future production, and calculate the recoverable reserves of the gas well. The harmonic decline method is applicable to gas production wells with a relatively slow decline in the later stage of production and is not applicable to gas wells with normal or relatively fast decline in production.

[0010] The method of the present invention provides a new option and a reference for comparison in predicting the recoverable reserves of tight sand gas wells that meet the practical conditions of the method of the present invention. Summary of the Invention

[0011] The present invention provides a method for predicting the recoverable reserves of a single well by using the combined decline of pressure and production.

[0012] In order to achieve the above invention objectives, the technical solutions adopted by the present invention are as follows:

[0013] (1) Collect the production dynamic data of tight sand gas production wells, including production date, wellhead pressure (oil pressure or casing pressure), daily gas production, cumulative gas production, etc.

[0014] (2) Use the cumulative gas production data (abscissa) in step (1) and the (daily gas production × wellhead pressure) data (ordinate) to construct a scatter plot.

[0015] (3) Use the hyperbolic decline analysis method to fit the relationship curve between the cumulative gas production and (daily gas production × wellhead pressure) in step (2) to obtain a regression relationship formula:

[0016]

[0017] Where: Q is the daily gas production, with the unit of m 3 ;

[0018] P h is the wellhead pressure, with the unit of MPa;

[0019] n is a constant, dimensionless;

[0020] Q i is the daily gas production corresponding to the beginning of the decline of the daily gas production, with the unit of m 3 ;

[0021] P hi is the wellhead pressure corresponding to the beginning of the decline of the daily gas production, MPa;

[0022] D i is a constant, dimensionless;

[0023] G p is the cumulative gas production, with the unit of 10 4 m 3 .

[0024] (4) Use the regression relationship formula in step (3), substitute the wellhead pressure and daily gas production under the abandonment conditions of the gas well production well on the left side, and the cumulative gas production corresponding to the abandonment pressure can be obtained, that is, the recoverable reserves of the production well under the corresponding abandonment pressure.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] The decline curve method is improved to eliminate the interference of gas production fluctuations caused by production regime changes on decline curve analysis, improve the accuracy of recoverable reserve calculation, and has a simple calculation process and strong practicability. Description of the Drawings

[0027] Figure 1 It is the production performance curve of the tight sandstone gas production well described in the embodiment;

[0028] Figure 2 It is the relationship diagram between (daily gas production × wellhead oil pressure) and cumulative production of the tight sandstone gas production well described in the embodiment;

[0029] Figure 3 It is the hyperbolic decline fitting diagram of (daily gas production × wellhead oil pressure) and cumulative production of the tight sandstone gas production well described in the embodiment. Detailed Embodiment

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in detail according to the drawings, schedules and by way of examples.

[0031] For the production performance of the tight sandstone gas production well as shown in Figure 1 A method for predicting the recoverable reserve of a single well by using the compound decline of pressure and production includes the following steps:

[0032] (1) Collect the production performance data of the tight sandstone gas production well, including production date, wellhead pressure (oil pressure or casing pressure), daily gas production, cumulative gas production, etc., to form a data table of wellhead pressure, daily gas production and cumulative gas production as shown in Table 1.

[0033] Table 1 Production performance data table of the tight sandstone gas well in the embodiment

[0034]

[0035] (2) Use the cumulative gas production data (abscissa) and (daily gas production × wellhead pressure) data (ordinate) in step (1) to construct a scatter plot, as shown in Figure 2 .

[0036] (3) Use the hyperbolic decline analysis method to fit the relationship curve between the cumulative gas production and (daily gas production × wellhead pressure) in step (2) ( Figure 3 ) to obtain the regression relation:

[0037]

[0038] Where: Q is the daily gas production, unit m 3 ;

[0039] P h is the wellhead pressure, with the unit of MPa;

[0040] n is a constant, dimensionless;

[0041] Q i is the gas production per day corresponding to the beginning of the decline of gas production per day, with the unit of m 3 ;

[0042] P hi is the wellhead pressure corresponding to the beginning of the decline of gas production per day, in MPa;

[0043] D i is a constant, dimensionless;

[0044] G p is the cumulative gas production, with the unit of 10 4 m 3 .

[0045] (4), Using the regression relation in step (3), substituting the wellhead pressure of 0.2 MPa and the gas production per day of 2000 m 3 under the abandonment condition, the cumulative gas production corresponding to the abandonment pressure can be obtained, that is, the recoverable reserve of this tight sandstone gas production well under the corresponding abandonment pressure is 9519×10 4 m 3 .

[0046] As can be seen from the embodiment Figure 3 , the curve fitting correlation coefficient reaches 0.9587, indicating that this recoverable reserve prediction method has good practicability and reliability.

[0047] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for predicting the recoverable reserves of a single well by using the compound decline of pressure and production, characterized in that, It includes the following steps: (1) Collect the production dynamic data of tight sand gas production wells, including production date, wellhead pressure, daily gas production, and cumulative gas production data; (2) Use the cumulative gas production data and the daily gas production × wellhead pressure data in step (1) to construct a scatter plot; (3) Fit the relationship curve between the cumulative gas production and the daily gas production × wellhead pressure in step (2) using the hyperbolic decline analysis method to obtain a regression equation; (4) Use the regression equation in step (3) to obtain the cumulative gas production corresponding to the abandonment pressure, that is, the recoverable reserves of the production well at the corresponding abandonment pressure.

2. The method for predicting the recoverable reserves of a single well by using the compound decline of pressure and production according to claim 1, characterized in that: In step (1), the wellhead pressure is the tubing pressure or the casing pressure.

3. A method for predicting the recoverable reserves of a single well by using the compound decline of pressure and production according to claim 1, characterized in that: In step (2), the cumulative gas production data is used as the abscissa, and the daily gas production × wellhead pressure data is used as the ordinate.

4. A method for predicting the recoverable reserves of a single well by using the composite decline of pressure and production according to claim 1, characterized in that: In step (3), for the scatter data in step (2), the regression equation obtained by fitting according to the hyperbolic decline analysis method is: Where: Q is the daily gas production, unit m 3 ; P h is the wellhead pressure, in MPa; n is a constant, dimensionless; Q i is the daily gas production corresponding to the initial decline of the daily gas production, with the unit of m 3 ; P hi is the wellhead pressure corresponding to the initial decline of the daily gas production, MPa; D i is a constant and dimensionless; G p is the cumulative gas production, with the unit of 10 4 m 3 .

5. A method for predicting the recoverable reserves of a single well by using the compound decline of pressure and production according to claim 4, characterized in that: In step (4), use the regression equation obtained in step (3), substitute the wellhead pressure and daily gas production under the abandonment conditions of the gas well production well on the left side, and calculate the corresponding cumulative gas production, which is the recoverable reserves of the production well at the corresponding abandonment pressure.

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