Equivalent evaluation method of dynamic reserves of whole gas reservoir

Abstract

The present invention discloses an equivalent evaluation method for dynamic reserves of the entire gas reservoir, and belongs to the technical field of gas reservoir engineering. The method comprises the following steps: based on the material balance principle, the production of oil and gas reservoirs in the same pressure system is equivalent to the production of a well, the production of the well satisfies the equal cumulative output at any time, the pressure drop of the entire formation is the same, and the simultaneous production of multiple wells in a short period of time is equivalent to the production of a single well for a long time, then the equivalent index of the entire gas reservoir is calculated; according to the equivalent index of the entire gas reservoir, the dynamic reserve evaluation index of the single well is corrected; the material balance pseudo-time and regularized production are iteratively calculated until convergence, and the allowable error of the single well controlled reserves is met. The present invention adopts the above-mentioned equivalent evaluation method for dynamic reserves of the entire gas reservoir, which has a better fitting effect and is more in line with actual production. In the initial stage, when there are few wells, the average formation pressure of the entire gas reservoir drops slowly. As the number of wells increases, the formation pressure of the entire gas reservoir drops faster. It is faster and more intuitive than the multi-well method in calculation, and has a wider range of applications.

Description

Technical Field

[0001] The invention relates to the technical field of gas reservoir engineering, and in particular to a method for evaluating the equivalent dynamic reserves of a whole gas reservoir. Background Art

[0002] With the continuous progress of gas well production, the determination of the dynamic reserves of the entire gas reservoir is becoming more and more important for the formulation of development plans, the design of development facilities and the evaluation of gas reservoir value. Therefore, the dynamic reserves evaluation of the entire gas reservoir is a very important and challenging task in the process of gas reservoir development, and it is also one of the key technologies for efficient development. Many experts, scholars and patents at home and abroad have done a lot of research work on the calculation of dynamic reserves of the entire gas reservoir, and have proposed a series of methods for predicting the dynamic reserves of gas reservoirs. The methods currently proposed mainly include material balance method, Blasingame method, modern production decline method (typical curve analysis method) and well test analysis method. Through a systematic analysis of these methods, it is found that some methods are suitable for the evaluation of dynamic reserves of the entire gas reservoir and the evaluation of dynamic reserves of a single well, and some methods are only suitable for the evaluation of dynamic reserves of a single well, but not for the evaluation of dynamic reserves of the entire gas reservoir.

[0003] At present, the main difference between the methods suitable for the dynamic reserves of the whole gas reservoir and the single well is whether the evaluation method depends on the bottom hole flowing pressure. If the dynamic reserves method must rely on the bottom hole flowing pressure to evaluate the dynamic reserves, it is only suitable for the evaluation of the dynamic reserves of a single well. If the evaluation method does not rely on the bottom hole flowing pressure, but relies on the formation pressure, it is suitable for the evaluation of the dynamic reserves of the whole gas reservoir and the evaluation method of the dynamic reserves of a single well. Among these methods, only the material balance equation does not rely on the bottom hole flowing pressure, while the Blasingame method, the modern production decline method (typical curve analysis method) and the well test analysis method all rely on the bottom hole flowing pressure, so they are only suitable for the evaluation of the dynamic reserves of a single well. Secondly, the multi-well simulation method based on a single well and the substantial numerical simulation method require more parameters to be adjusted, which is time-consuming, or each single well is evaluated separately and then summed. At present, there is no single well dynamic reserve evaluation method to solve the evaluation method of the dynamic reserves of the whole gas reservoir.

[0004] Therefore, the present invention proposes an equivalent evaluation method for dynamic reserves of the entire gas reservoir, and uses the single well dynamic reserves evaluation method to evaluate the dynamic reserves of the entire gas reservoir. Summary of the invention

[0005] The purpose of the present invention is to provide an equivalent evaluation method for dynamic reserves of the entire gas reservoir, which has a better fitting effect and is more in line with actual production. In the initial stage, when there are few wells, the average formation pressure of the entire gas reservoir decreases slowly. As the number of wells increases, the formation pressure of the entire gas reservoir decreases faster. The calculation is faster and more intuitive than the multi-well method, and has a wider range of applications.

[0006] To achieve the above object, the present invention provides a method for evaluating the equivalent reserves of a gas reservoir, comprising the following steps:

[0007] S1. Based on the material balance principle, the production of oil and gas reservoirs in the same pressure system is equivalent to the production of a well. The production of the well satisfies the requirement that the cumulative output at any time is equal, the pressure drop of the entire formation is the same, and the simultaneous production of multiple wells in a short period of time is equivalent to the production of a single well for a longer period of time. Then calculate the equivalent index of the entire gas reservoir;

[0008] S2, according to the equivalent index of the whole gas reservoir calculated in step S1, correct the single well dynamic reserve evaluation index;

[0009] S3. Iterate the material balance pseudo-time and normalized production until convergence and the allowable error of the single well controlled reserves is met.

[0010] Preferably, in step S1, the equivalent indicators of the entire gas reservoir include equivalent production time, equivalent daily production, equivalent bottom hole flowing pressure, equivalent cumulative production, equivalent radius, and equivalent horizontal well length.

[0011] Preferably, the production time is equivalent to the production time of a well, as shown below:

[0012]

[0013] Among them, t p is the production time of a single well, in days; i represents the i-th well.

[0014] Preferably, the daily production equivalent includes oil production, gas production and water production; since the production output of each well is different and the corresponding production time is different, the equivalent daily production is calculated by weighted average of the production time, as shown below:

[0015]

[0016] Where q is the single well production, 10 4 m 3 / d.

[0017] Preferably, since the production output of each well is different and the corresponding flowing pressure is different, the equivalent bottom hole flowing pressure is calculated by using the output weighted average, as shown below:

[0018]

[0019]

[0020] Among them, p wf is the bottom hole flowing pressure of a single well, MPa; p t is the wellhead oil pressure of a single well, MPa.

[0021] Preferably, the equivalent cumulative production includes cumulative oil production, cumulative gas production and cumulative water production; when multiple wells are generated simultaneously, the volume of all fluids produced cumulatively by the equivalent wells at the same time is consistent, and the energy conservation residual force is satisfied, then the equivalent cumulative production of one well is as follows:

[0022]

[0023] Among them, N p is the cumulative oil production of a single well, 10 4 m 3 ; G p is the cumulative gas production of a single well, 10 8 m 3 .

[0024] Preferably, if all wells are vertical wells, their equivalent radius is the same as the single well radius, that is, r w ; If there are both vertical wells and horizontal wells in the entire oil and gas reservoir, the length of the horizontal well can be equivalent to:

[0025]

[0026] Wherein, L is the length of a single horizontal well, m.

[0027] Preferably, step S2 corrects the single well dynamic reserve evaluation index, and the specific process is as follows:

[0028] After the single-phase flow of the gas well enters the quasi-stable state, the pseudo-pressure solution is expressed as follows:

[0029]

[0030] The normalized pseudo-pressure is defined as:

[0031]

[0032] The material balance pseudo-time is defined as:

[0033]

[0034] Among them, C A is the shape factor; γ = e 0.57721.... =1.781.....; r w is the well radius, m; B g is the gas volume coefficient, dimensionless; is the normalized bottom hole flowing pressure, MPa;

[0035] The entire gas reservoir is equivalent to a single well production. The pseudo-pressure solution combined with the closed gas reservoir material balance equation can be obtained:

[0036]

[0037] make The dynamic reserves of the entire gas reservoir are as follows:

[0038]

[0039] in, With t ca It is a linear relationship, and the slope of the straight line is m a .

[0040] Preferably, in step S3, the material balance pseudo-time and normalized production are iteratively calculated until convergence and the allowable error of the single well controlled reserves is satisfied. The specific process is as follows:

[0041] S31. Calculate the material balance pseudo time. The controlled reserves of a single well are G. The material balance pseudo time is calculated for each production data point as follows:

[0042]

[0043] Calculate the average formation pressure as follows:

[0044]

[0045] During the entire production process, the formation pressure meets the constraints: If the constraint condition is not met, return to step S31 to change the size of G;

[0046] S32. Calculate the normalized yield as follows:

[0047]

[0048] S33, drawing The relationship curve of the straight line is used to determine G according to the slope m, as shown below:

[0049]

[0050] Repeat steps S31-S33 to perform iterative calculation until convergence and the allowable error of G is met.

[0051] Therefore, the present invention adopts the above-mentioned whole gas reservoir dynamic reserve equivalent evaluation method, which has better fitting effect and is more in line with actual production. In the initial stage, when there are few wells, the average formation pressure of the whole gas reservoir drops slowly. As the number of wells increases, the formation pressure of the whole gas reservoir drops faster. It is faster and more intuitive than the multi-well method and has a wider range of applications.

[0052] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1It is an arbitrary distribution diagram of multiple wells in a closed rectangular oil and gas reservoir of the present invention;

[0054] Figure 2 The equivalent production indicator curve of the present invention;

[0055] Figure 3 The single-well Blasingame method analysis curve of the present invention;

[0056] Figure 4 Material balance analysis curve of the present invention;

[0057] Figure 5 The present invention corrects the flow-pressure fitting curve. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0059] The method for evaluating the equivalent reserves of the entire gas reservoir includes the following steps:

[0060] S1. Based on the material balance principle, the production of oil and gas reservoirs in the same pressure system is equivalent to the production of a well. The production of the well satisfies the requirement that the cumulative output at any time is equal, the pressure drop of the entire formation is the same, and the simultaneous production of multiple wells in a short period of time is equivalent to the production of a single well for a longer period of time. Then calculate the equivalent index of the entire gas reservoir;

[0061] S2, according to the equivalent index of the whole gas reservoir calculated in step S1, correct the single well dynamic reserve evaluation index;

[0062] S3. Iterate the material balance pseudo-time and normalized production until convergence and the allowable error of the single well controlled reserves is met.

[0063] Example

[0064] 1. Material balance method;

[0065] The material balance equation of a general gas reservoir is as follows:

[0066]

[0067] Where: G is dynamic reserves, 10 8 m 3 ; C e is the effective compression coefficient, C e =C w S wi +C p , MPa -1 ; ω is the water intrusion related parameter, G p is the cumulative gas production, 10 8 m 3 ;pi is the original formation pressure of the gas reservoir, MPa; p is the formation pressure of the gas reservoir at a certain production time, MPa; Δp is the formation pressure drop, MPa; p i / Z i For gas reservoir i p / Z is the apparent formation pressure under the gas reservoir p pressure, MPa; Z i For the original p i and gas reservoir temperature conditions; Z is the gas deviation coefficient under the current p and gas reservoir temperature conditions.

[0068] The application conditions of the material balance method are very harsh. The reasons are as follows: 1. It does not rely on the bottom flow pressure of a single well. It must satisfy the average formation pressure that represents the entire gas reservoir. The average formation pressure of the entire gas reservoir is a weighted average of the pressure obtained by well test analysis of representative single wells. The average formation pressure of a single well is very easy to obtain. It can be obtained through pressure recovery well testing. The dynamic control reserves of a single well can be obtained by material balance. Therefore, the single well test seepage model is the theoretical basis for the application of the material balance equation. 2. The test pressure of a representative single well is small and does not represent the average formation pressure of the entire gas reservoir. 3. There are many evaluation methods for the dynamic reserves of a single well, but none of them can be directly used for the evaluation of the dynamic reserves of the entire gas reservoir. 4. The evaluation method of the dynamic reserves of the entire gas reservoir can only be solved by using the multi-well method.

[0069] 2. Multi-well method;

[0070] Based on the production between multiple wells, using the superposition principle, the multi-well method mainly refers to a closed oil and gas reservoir with multiple wells, each well produces at an arbitrary fixed rate, such as Figure 1 As shown, the well is located anywhere in the oil and gas reservoir and is defined as follows:

[0071]

[0072] The above formula (2) is written in dimensionless form as follows:

[0073]

[0074] in, μ is the fluid viscosity, mPa.s; B is the fluid volume coefficient, dimensionless; subscript D indicates dimensionless; A is the single well control area, m 2 ; t is the production time, ks; q is the daily production of a single well, m 3 / ks; k is the reservoir permeability, μm 2 ; h is the effective thickness of the reservoir, m; c t is the comprehensive compression coefficient, 1 / MPa, ct=cp+cgi·(1-swc)+cwswc.

[0075] Considering the influence of the near-well skin coefficient s on well k, the bottom hole pressure of well k is as follows:

[0076]

[0077] The solution for the constant production at any point in a closed rectangular oil and gas reservoir is as follows:

[0078]

[0079] According to formula (5), theoretically, fitting the bottom hole pressure is very complicated. If the reservoir heterogeneity is strong, the reservoir physical properties near each well are quite different, there are more fitting parameters and the production history fitting is more difficult. Therefore, a new method for evaluating the dynamic reserves of the entire oil and gas reservoir is proposed based on an "equivalent method" based on the single well seepage theory.

[0080] How to use the single-well seepage model to analyze the material balance of the entire gas reservoir is more important. Only with the single-well seepage model can there be a multi-well model, and the calculation of the multi-well model is relatively complicated. Therefore, how to make the multi-well seepage model equivalent to the single-well seepage model is more practical for production.

[0081] S1. Based on the material balance principle, the production of oil and gas reservoirs in the same pressure system is equivalent to the production of a well. The production of the well satisfies the requirement that the cumulative output at any time is equal, the pressure drop of the entire formation is the same, and the simultaneous production of multiple wells in a short period of time is equivalent to the production of a single well for a longer period of time. Then calculate the equivalent index of the entire gas reservoir;

[0082] S11, production time is equivalent to the production time of a well, as shown below:

[0083]

[0084] Among them, t p is the production time of a single well, in days; i represents the i-th well.

[0085] S12. Daily production equivalent includes oil, gas and water production. Since the production output of each well is different and the corresponding production time is different, the equivalent daily production is calculated by weighted average of production time, as shown below:

[0086]

[0087] Where q is the single well production, 10 4 m 3 / d.

[0088] S12. Since the production output of each well is different, the corresponding flowing pressure is different. The equivalent bottom hole flowing pressure adopts the weighted average of the production output, or the wellhead oil pressure of the equivalent well adopts the weighted average of the production output, and then the equivalent bottom hole flowing pressure is calculated from the oil pressure, as shown below:

[0089]

[0090]

[0091] Among them, p wf is the bottom hole flowing pressure of a single well, MPa; p t is the wellhead oil pressure of a single well, MPa.

[0092] S14. Cumulative production equivalence includes cumulative oil production, cumulative gas production and cumulative water production. If the volume of all fluids produced by multiple wells at the same time is consistent with that of equivalent wells, and the residual force of energy conservation is satisfied, then the cumulative production of one well is equivalent to that of the production, as shown below:

[0093]

[0094] Among them, N p is the cumulative oil production of a single well, 10 4 m 3 ; G p is the cumulative gas production of a single well, 10 8 m 3 .

[0095] S15. Equivalence of well radius: If all wells are vertical wells, their equivalent radius is the same as the single well radius, that is, r w ; If there are both vertical wells and horizontal wells in the entire oil and gas reservoir, the length of the horizontal well can be equivalent to:

[0096]

[0097] Wherein, L is the length of a single horizontal well, m.

[0098] According to the principle of material balance, the reserves of the entire oil and gas reservoir are certain, the cumulative production is the same, the formation pressure changes are also the same, but the production time in between and the daily output of a single well are different. The dynamic reserves method of a single well can be used to evaluate the dynamic reserves of the entire oil and gas reservoir. The evaluation method of the dynamic reserves of a single well is based on the seepage theory of a single well. The theory is relatively mature and very convenient to apply.

[0099] S2, according to the equivalent index of the whole gas reservoir calculated in step S1, correct the single well dynamic reserve evaluation index;

[0100] After the single-phase flow of the gas well enters the quasi-stable state, the pseudo-pressure solution is expressed as follows:

[0101]

[0102] The normalized pseudo-pressure is defined as:

[0103]

[0104] The material balance pseudo-time is defined as:

[0105]

[0106] Among them, C A is the shape factor; γ = e 0.57721.... =1.781.....; r w is the well radius, m; B g is the gas volume coefficient, dimensionless; is the normalized bottom hole flowing pressure, MPa.

[0107] The whole gas reservoir is equivalent to the production of a single well. The single well is regarded as a closed gas reservoir. Formula (12) combined with the material balance equation of the closed gas reservoir gives:

[0108]

[0109] make The dynamic reserves of the entire gas reservoir are as follows:

[0110]

[0111] in, With t ca It is a linear relationship, and the slope of the straight line is m a .

[0112] S3. Iterate the material balance pseudo-time and normalized production until convergence and the allowable error of the single well controlled reserves is met. The specific process is as follows:

[0113] S31. Calculate material balance pseudo time

[0114] Assuming a single well controlled reserve G, calculate the material balance time for each production data point, we have:

[0115]

[0116] The average formation pressure is calculated by the following formula:

[0117]

[0118] During the entire production process, the formation pressure must meet the constraints: If the constraint condition is not met, return to step S31 to change the size of G.

[0119] S32. Calculate the normalized yield as follows:

[0120]

[0121] S33, drawing The relationship curve of G is determined according to the slope m of the straight line, as shown below:

[0122]

[0123] Repeat steps S31-S33 to perform iterative calculation until convergence and the allowable error of G is met.

[0124] Example 2

[0125] A gas reservoir started production on September 23, 2012, with production from one well at the beginning to 34 vertical wells at the highest. The production of 34 wells is equivalent to the production of one well. The production curve is as follows: Figure 2 As shown in the figure, the single well method is used to analyze the equivalent and obtain the dynamic geological reserves of the entire gas reservoir as 51.0204 billion cubic meters (G = 1 / (0.00002*0.0098) / 10000). The single well analysis curve is shown in Figure 3 As shown, the material balance equation is iterated and the curve is analyzed as follows Figure 4 As shown in the figure, the dynamic reserves of the entire gas reservoir are 51.039 billion cubic meters, which meets the convergence conditions. The flow pressure fitting curve of its constraint condition is as follows: Figure 5 As shown in the figure, from the analysis of these fitting curves, the fitting effect is better in the production process and is more in line with the actual production. In the initial stage with few wells, the average formation pressure of the whole gas reservoir drops slowly. As the number of wells increases, the formation pressure of the whole gas reservoir drops faster. It is faster and more intuitive than the multi-well method.

[0126] Therefore, the present invention adopts the above-mentioned whole gas reservoir dynamic reserve equivalent evaluation method, which has better fitting effect and is more in line with actual production. In the initial stage, when there are few wells, the average formation pressure of the whole gas reservoir drops slowly. As the number of wells increases, the formation pressure of the whole gas reservoir drops faster. It is faster and more intuitive than the multi-well method and has a wider range of applications.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. The method for evaluating the equivalent reserves of the entire gas reservoir is characterized by: The following steps are involved: S1. Based on the material balance principle, the production of oil and gas reservoirs in the same pressure system is equivalent to the production of a well. The production of the well satisfies the requirement that the cumulative output at any time is equal, the pressure drop of the entire formation is the same, and the simultaneous production of multiple wells in a short period of time is equivalent to the production of a single well for a longer period of time. Then calculate the equivalent index of the entire gas reservoir; S2, according to the equivalent index of the whole gas reservoir calculated in step S1, correct the single well dynamic reserve evaluation index; S3. Iterate the material balance pseudo-time and normalized production until convergence and the allowable error of the single well controlled reserves is met. The specific process is as follows: S31. Calculate the material balance pseudo time. The controlled reserves of a single well are G. The material balance pseudo time is calculated for each production data point as follows: ； in, is the fluid viscosity, mPa.s; is the comprehensive compression coefficient, 1 / MPa; is the daily production of a single well; during the entire production process, the formation pressure satisfies the constraint conditions: , is the normalized pseudo-pressure, is the normalized bottom hole pressure, MPa; if the constraint condition is not met, return to step S31 to change the size of G; subscript Indicates well; Calculate the average formation pressure as follows: ； in, For gas reservoir p Apparent formation pressure under pressure, MPa; Indicates that at present p and gas deviation coefficient under reservoir temperature conditions; is the effective compression factor; is the formation pressure drop, MPa; For gas reservoir Apparent formation pressure under pressure, MPa; For the original and gas deviation coefficient under reservoir temperature conditions; is the cumulative gas production of a single well, 10 8 m 3 ; S32. Calculate the normalized yield as follows: ； S33, drawing The relationship curve of the straight line is used to determine G according to the slope m, as shown below: ； Repeat steps S31-S33 to perform iterative calculation until convergence and the allowable error of G is met.

2. The method for evaluating the equivalent reserves of a gas reservoir according to claim 1, characterized in that: In step S1, the equivalent indicators of the entire gas reservoir include equivalent production time, equivalent daily production, equivalent bottom hole flowing pressure, equivalent cumulative production, equivalent radius, and equivalent horizontal well length.

3. The method for evaluating the equivalent reserves of a gas reservoir according to claim 2, characterized in that: The production time is equivalent to the production time of a well, as shown below: ； in, is the production time of a single well, days; Indicates A well.

4. The method for evaluating the equivalent reserves of the entire gas reservoir according to claim 2, characterized in that: The daily production equivalent includes oil production, gas production and water production. Since the production output of each well is different and the corresponding production time is different, the equivalent daily production is calculated by weighted average of production time, as shown below: ； in, q is the single well production, 10 4 m 3 / d.

5. The method for evaluating the equivalent reserves of a gas reservoir according to claim 2, characterized in that: Since the production output of each well is different, the corresponding flowing pressure is different. The equivalent bottom hole flowing pressure is calculated by using the production weighted average, as shown below: ； ； in, is the bottom hole flowing pressure of a single well, MPa; is the wellhead oil pressure of a single well, MPa.

6. The method for evaluating the equivalent reserves of a gas reservoir according to claim 2, characterized in that: The equivalent cumulative production includes the cumulative oil production, cumulative gas production and cumulative water production. If the volumes of all fluids produced by multiple wells at the same time are consistent with the cumulative production of equivalent wells at the same time, and the energy conservation principle is satisfied, then the equivalent cumulative production of one well is as follows: ， ； in, is the cumulative oil production of a single well, 10 4 m 3 ; is the cumulative gas production of a single well, 10 8 m 3 .

7. The method for evaluating the equivalent reserves of a gas reservoir according to claim 2, characterized in that: If all wells are vertical wells, their equivalent radius is the same as the single well radius, which is ; If there are both vertical wells and horizontal wells in the entire oil and gas reservoir, the length of the horizontal well can be equivalent to: ； in, is the single well horizontal well length, m.

8. The method for equivalent evaluation of dynamic reserves of a gas reservoir according to claim 1, characterized in that: In step S2, the single well dynamic reserve evaluation index is corrected according to the equivalent index of the entire gas reservoir. The specific process is as follows: After the single-phase flow of the gas well enters the quasi-stable state, the pseudo-pressure solution is expressed as follows: ； in, is the gas volume coefficient, dimensionless; is the reservoir permeability, ; is the effective thickness of the reservoir, ; is the single well control area, m 2 ; is the shape factor; ; is the well radius, m; The normalized pseudo-pressure is defined as: ； The material balance pseudo-time is defined as: ； The entire gas reservoir is equivalent to a single well production. The pseudo-pressure solution combined with the closed gas reservoir material balance equation can be obtained: ； make , , then the dynamic reserves of the entire gas reservoir are as follows: ； in, It is a linear relationship, and the slope of the straight line is .

Images