CN108612525A - A kind of gas reservoir protection Reserve Estimation Method - Google Patents

Abstract

The present invention aims at problems such as lack of data, harsh operating conditions or complex analysis process in the existing gas reservoir dynamic reserve calculation method, based on the advantages of the material balance method, combined with the gas seepage process, the vertical pipe flow model, the gas well productivity equation and the material balance equation are integrated , discloses a method for calculating dynamic reserves of gas reservoirs. The method includes the following steps: S1, preparing production dynamic data; S2, calculating the bottom hole flow pressure: calculating the gas well bottom hole flow pressure according to the sorted gas well production dynamic data; S3, calculating formation static pressure: using the gas well binomial productivity equation, Calculate the average formation pressure of the gas well; S4, divide the flow stage: determine the boundary control flow stage, the unstable flow stage, and the transition stage; S5, calculate the dynamic reserves: calculate the dynamic reserves after the end of the unstable flow stage of the gas well, and the The cumulative gas production is added to obtain the real dynamic reserves of the gas well.

Description

A Calculation Method for Dynamic Reserves of Gas Reservoirs

technical field

The invention relates to a method for calculating the dynamic reserves of a gas reservoir, in particular to a method for calculating the dynamic reserves of a gas reservoir.

Background technique

The dynamic reserves of a gas reservoir refer to the total gas volume participating in the flow in the reservoir. Accurate calculation of gas reservoir dynamic reserves is an important prerequisite for correctly evaluating gas reservoir development effects, accurately predicting gas reservoir development performance, and making a good gas reservoir development plan. At present, the methods for calculating the dynamic reserves of gas reservoirs mainly include material balance method (pressure drop method), flowing material balance method and production instability analysis method, etc. The material balance method is the most accurate and reliable method for calculating the dynamic reserves of gas reservoirs, but it requires regular and long-term shut-in and pressure measurement of the entire gas reservoir. The flow material balance method requires the gas well production to be stable and the initial formation pressure when the gas well is put into production must be known accurately. It is difficult to meet the application conditions of material balance method and flowing material balance method in actual gas reservoir development. The production instability analysis method is a kind of well testing analysis method based on production data. It has good adaptability to the changing situation of gas well production. It is currently recognized as a relatively accurate and reliable method for calculating the dynamic reserves of gas wells. However, its analysis The process is relatively complicated and needs to be analyzed with the help of professional software.

Contents of the invention

The present invention aims at problems such as lack of data, harsh conditions of use, or complicated analysis process in existing gas reservoir dynamic reserve calculation methods. Based on the advantages of the material balance method, combined with the gas seepage process, the vertical pipe flow model, the gas well productivity equation and the material balance equation are integrated. A method for calculating dynamic reserves of gas reservoirs is proposed.

The purpose of the present invention is achieved like this:

A method for calculating dynamic reserves of a gas reservoir, the method comprising the following steps:

S1. Prepare production dynamic data: obtain gas well production dynamic data, the gas well production dynamic data includes gas well daily gas production, exclude production dynamic data during well shut-in period, and convert gas wells with daily production time less than 24 hours into 24-hour daily gas production;

S2. Calculate the bottomhole flow pressure: according to the sorted gas well production dynamic data, select the vertical pipe flow model to calculate the bottomhole flow pressure of the gas well;

S3. Calculating the average formation pressure of the gas well: according to the daily gas production of the gas well obtained in S1 and the bottom hole flow pressure obtained in S2, the average formation pressure of the gas well is calculated by using the binomial productivity equation of the gas well;

S4. Divide the flow stage: calculate the cumulative gas production according to the cumulative sum of the daily gas production of the gas well, and the average formation pressure calculated in S3, draw the relationship curve between the apparent pressure of the average formation pressure of the gas well and the cumulative gas production, and determine the boundary control flow stage, not The transition stage from stable flow stage, unstable flow stage to boundary control flow stage;

S5. Calculation of dynamic reserves: According to the data in the boundary control flow stage, use linear regression analysis to determine the slope and intercept of the straight line, and then calculate the dynamic reserves of the gas well after the end of the unstable flow stage, which is comparable to the cumulative gas production in the unstable flow stage Added to get the real dynamic reserves of the gas well.

Preferably, in S1, the gas well production performance data also includes wellhead pressure and wellhead temperature.

Preferably, in S2, the calculation method of bottom hole pressure is as follows:

The vertical pipe flow model is selected to calculate the bottomhole flow pressure of gas wells. The wellbore pressure gradient calculation model in the vertical pipe flow model is generally expressed as follows:

In the formula:

is the wellbore pressure gradient, in MPa/m;

is the frictional pressure gradient, in MPa/m;

is gravity pressure gradient, unit MPa/m;

is the acceleration pressure gradient, in MPa/m.

Preferably, in S3, the calculation method of the average formation pressure of the gas well is as follows:

The binomial productivity equation determined by the gas well productivity test is used to calculate the average formation pressure of the gas well. The calculated average formation pressure is the formation static pressure after the well is shut down and restored. The binomial productivity equation of the gas well is as follows:

In the formula:

ψ(p) is the average formation pressure of the gas well, in MPa ² /(mPa·s);

ψ(p _wf ) is the pseudo pressure of bottomhole flowing pressure, unit MPa ² /(mPa·s);

q _sc is the daily gas production of the gas well, the unit is 10 ⁴ m ³ /d;

a, b are coefficients of binomial capacity equation.

Preferably, in S5, the dynamic reserves of the gas well after the unsteady flow of the gas well is calculated according to the gas reservoir material balance equation, and the gas reservoir material balance equation is as follows:

In the formula:

is the apparent pressure of the initial pressure when the gas well is put into production, in MPa;

is the apparent pressure of the average formation pressure, in MPa;

G _p is the cumulative gas production of the gas well, the unit is 10 ⁸ m ³ ;

G _bdf is the dynamic reserves of the gas well after the unsteady flow stage, and the unit is 10 ⁸ m ³ .

The formula for calculating the real dynamic reserves of gas wells is as follows:

In the formula:

t _trn is the unsteady flow time;

q _sc (t) is the instantaneous production of the gas well, the unit is 10 ⁴ m ³ /d;

G _trn is the cumulative gas production of the gas well in the unsteady flow stage, the unit is 10 ⁸ m ³ ;

G _bdf is the dynamic reserves of the gas well, the unit is 10 ⁸ m ³ .

Preferably, in S5, when the gas flow completely enters the boundary-controlled flow stage, the apparent pressure of the average formation pressure of the gas well shows a downward trend, and the relationship between the apparent pressure and the cumulative gas production of the average formation pressure of the gas well shows a linear relationship, while the apparent pressure of the average formation pressure of the gas well in the early stage of unstable flow The data will obviously deviate from this straight line, so as to determine the time when the gas flow enters the boundary control flow, and then remove the data of the early unstable flow stage from the regression analysis data.

Owing to adopting above-mentioned technical scheme, the present invention has following beneficial effect:

(1) The present invention determines the dynamic reserves of the gas well based on the flow data of the gas well, and does not need to regularly shut down the entire gas reservoir for a long time to measure the pressure of the gas well and restore the pressure, effectively solving the problem of lack of data in the application process of the material balance method. The new method essentially still uses the gas reservoir material balance equation to determine the dynamic reserves of gas wells, thus inheriting the advantages of accurate and reliable calculation results and simple calculation process of the material balance method, and also effectively overcomes the harsh conditions and unstable analysis of the flowing material balance method complex computational problems. The invention realizes the simple and accurate calculation of the dynamic reserve of the gas reservoir, which is of great significance for correctly evaluating the development effect of the gas reservoir, accurately predicting the development dynamics of the gas reservoir and making a good plan for the development of the gas reservoir.

(2) The calculation results of the example show that the maximum relative deviation between the calculation results of the method in this paper and the average value of the calculation results of the instability analysis method is 4.40%, the minimum relative deviation is -0.07%, and the relative deviation is within ±5.0%, which shows that the calculation of the method in this paper The results are accurate and reliable.

Description of drawings

Fig. 1 is the relationship curve between the apparent pressure of the average formation pressure and the cumulative gas production in Well P2011-3;

Fig. 2 is the fitting result of a typical curve of Blasingame in Well P2011-3;

Fig. 3 is the fitting result of the AG typical curve of Well P2011-3;

Fig. 4 is the fitting result of the typical curve of NPI in Well P2011-3.

Detailed ways

A method for calculating dynamic reserves of a gas reservoir, the method comprising the following steps:

S1. Prepare production dynamic data: obtain gas well production dynamic data, the gas well production dynamic data includes gas well daily gas production, wellhead pressure and wellhead temperature, for the needs of vertical pipe flow model calculation, eliminate production dynamic data during well shut-in period, and The gas wells whose daily production time is less than 24 hours are converted into 24-hour daily gas production to ensure the accuracy of the calculation results.

S2. Calculating the bottomhole flow pressure: according to the compiled gas well production dynamic data, select the appropriate vertical pipe flow equation to calculate the bottomhole flow pressure of the gas well;

In this embodiment, the calculation method of the bottom hole pressure is as follows:

The vertical pipe flow model is selected to calculate the bottomhole flow pressure of gas wells. The wellbore pressure gradient calculation model in the vertical pipe flow model is generally expressed as follows:

In the formula:

is the wellbore pressure gradient, in MPa/m;

is the frictional pressure gradient, in MPa/m;

is gravity pressure gradient, unit MPa/m;

is the acceleration pressure gradient, in MPa/m.

S3. Calculating the average formation pressure of the gas well: according to the daily gas production of the gas well obtained in S1 and the bottom hole flow pressure obtained in S2, the average formation pressure of the gas well is calculated by using the binomial productivity equation of the gas well (that is, the static pressure is restored after shutting down the well);

The calculation method of formation static pressure is as follows:

The binomial productivity equation determined by the gas well productivity test is used to calculate the average formation pressure of the gas well. The calculated average formation pressure is the formation static pressure after the well is shut down and restored. The binomial productivity equation of the gas well is as follows:

In the formula:

ψ(p) is the average formation pressure of the gas well, in MPa ² /(mPa·s);

ψ(p _wf ) is the pseudo pressure of bottomhole flowing pressure, unit MPa ² /(mPa·s);

q _sc is the daily gas production of the gas well, the unit is 10 ⁴ m ³ /d;

a, b are coefficients of binomial capacity equation.

S4. Divide the flow stage: Calculate the cumulative gas production and the calculated average formation pressure according to the daily gas production of the gas well, draw the relationship curve between the apparent pressure of the average formation pressure of the gas well and the cumulative gas production, and determine the boundary control flow stage, the unstable flow stage, and the unsteady flow stage in sequence. Transition stage from stable flow stage to boundary controlled flow stage;

S5. Calculation of dynamic reserves: According to the data in the boundary control flow stage, use linear regression analysis to determine the slope and intercept of the line, and then calculate the dynamic reserves of the gas well after the end of the unstable flow stage, and add it to the cumulative gas production in the unstable flow stage , to get the real dynamic reserves of the gas well.

When the gas flow completely enters the boundary-controlled flow stage, according to the gas reservoir material balance equation, the relationship curve is a straight line. According to the slope and intercept of the straight line, the dynamic reserves of the gas well after the unsteady flow ends are calculated. The gas reservoir material balance equation is as follows:

In the formula:

is the apparent pressure of the initial pressure when the gas well is put into production, in MPa;

is the apparent pressure of the average formation pressure, in MPa;

G _p is the cumulative gas production of the gas well, the unit is 10 ⁸ m ³ ;

G _bdf is the dynamic reserves of the gas well after the unsteady flow stage, and the unit is 10 ⁸ m ³ .

Since the gas well binomial productivity equation is determined by the productivity test, the bottomhole flow pressure is required to be stable during the productivity test, and the gas well binomial productivity equation determined by the productivity test represents the average formation pressure, bottomhole flow pressure and gas well production during the boundary control flow stage the mathematical relationship between them. Therefore, only the dynamic reserves determined according to the production dynamic monitoring data that have entered the boundary control flow stage are reliable.

When the gas flow completely enters the boundary-controlled flow stage, the apparent pressure of the average formation pressure of the gas well shows a downward trend, and the relationship between the apparent pressure of the average formation pressure of the gas well and the cumulative gas production is linear, while the data in the early unstable flow stage will obviously deviate from this. A straight line can be used to determine the time when the gas flow enters the boundary control flow, which can help to remove the data of the early unstable flow stage from the regression analysis data.

The intercept obtained from the regression analysis of the boundary-controlled flow stage data reflects the average formation pressure when the gas flow begins to transition from the unstable flow to the boundary-controlled flow, not the initial formation pressure when the gas well is put into production. Therefore, the dynamic reserves determined by regression analysis using the above method are only the dynamic reserves after the unsteady flow of the gas well ends. The real dynamic reserves of a gas well should also include the cumulative gas production of the gas well in the unsteady flow stage, namely:

In the formula:

t _trn is the unsteady flow time;

q _sc (t) is the instantaneous production of the gas well, the unit is 10 ⁴ m ³ /d;

G _trn is the cumulative gas production of the gas well in the unsteady flow stage, the unit is 10 ⁸ m ³ ;

G _bdf is the dynamic reserves of the gas well, the unit is 10 ⁸ m ³ .

According to the production dynamic monitoring data of Well P2011-3 in the main gas reservoir of the Puguang Gas Field, the relationship curve between the apparent pressure of the average formation pressure and the cumulative gas production was calculated and drawn (Fig. 1). According to the relationship curve of average formation pressure, apparent pressure and cumulative gas production, after March 2, 2011, the gas flow completely entered the boundary-controlled flow stage, before August 14, 2010, it was an unstable flow stage, and from August 14, 2010 to The period of March 2, 2011 was the transition period from unstable flow to border-controlled flow. According to the data in the boundary-controlled flow stage, linear regression analysis was used to determine the slope and intercept of the straight line, and the calculated dynamic reserves after the end of the unsteady flow of the gas well were 27.22×10 ⁸ m ³ , and the cumulative gas production during the unsteady flow stage of the gas well was 0.44×10 ⁸ m ³ , so it is determined that the dynamic reserves of Well P2011-3 are 27.66×10 ⁸ m ³ . The dynamic reserves of the P2011-3 well mentioned above were calculated by using Blasingame method, AG method, NPI method and other production instability analysis methods (Fig. 2-4). The calculated dynamic reserves of gas wells are 27.59×10 ⁸ m ³ and 28.05×10 ⁸ respectively. m ³ and 28.28×10 ⁸ m ³ , with an average dynamic reserve of 27.97×10 ⁸ m ³ .

From the fitting results of typical curves and plates of Blasingame method, AG method and NPI method, the gas well flow has completely entered the boundary control flow stage, and the calculation results of production instability analysis method are reliable. The new method is similar to the dynamic reserves of well P2011-3 determined by the production instability analysis method, with a relative deviation of -1.11%, which shows that the calculation results of the new method are accurate and reliable.

In order to further verify the accuracy and reliability of the calculation results of the method in this paper, the same analysis and calculation process was used to analyze and calculate the dynamic reserves of 9 gas wells including P201-4 in the main gas reservoir of the Puguang Gas Field (Table 1). From the calculation results of gas well dynamic reserves, the maximum relative deviation between the calculation results of the method in this paper and the average value of the calculation results of the instability analysis method is 4.40%, the minimum relative deviation is -0.07%, and the relative deviation is within ±5.0%. The calculation results are accurate and reliable.

Table 1 Calculation results of gas well dynamic reserves

Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that it can be described in terms of form and Various changes may be made in the details without departing from the scope of the invention defined by the claims.

Claims (6)

1. A gas reservoir dynamic reserve calculation method is characterized in that the method may further comprise the steps: S1. Prepare production dynamic data: obtain gas well production dynamic data, the gas well production dynamic data includes gas well daily gas production, exclude production dynamic data during well shut-in period, and convert gas wells with daily production time less than 24 hours into 24-hour daily gas production; S2. Calculate the bottomhole flow pressure: according to the sorted gas well production dynamic data, select the vertical pipe flow model to calculate the bottomhole flow pressure of the gas well; S3. Calculating the average formation pressure of the gas well: according to the daily gas production of the gas well obtained in S1 and the bottom hole flow pressure obtained in S2, the average formation pressure of the gas well is calculated by using the binomial productivity equation of the gas well; S4. Divide the flow stage: calculate the cumulative gas production according to the cumulative sum of the daily gas production of the gas well, and the average formation pressure calculated in S3, draw the relationship curve between the apparent pressure of the average formation pressure of the gas well and the cumulative gas production, and determine the boundary control flow stage, not The transition stage from stable flow stage, unstable flow stage to boundary control flow stage; S5. Calculation of dynamic reserves: According to the data in the boundary control flow stage, use linear regression analysis to determine the slope and intercept of the straight line, and then calculate the dynamic reserves of the gas well after the end of the unstable flow stage, which is comparable to the cumulative gas production in the unstable flow stage plus, to get the real dynamic reserves of the gas well. 2. The method for calculating the dynamic reserves of gas reservoirs according to claim 1, characterized in that, in S1, the gas well production dynamic data also includes wellhead pressure and wellhead temperature. 3. according to claim 1 and 2 described gas reservoir dynamic reserve calculation methods, it is characterized in that, in S2, the calculation method of bottom hole flowing pressure is as follows: The vertical pipe flow model is selected to calculate the bottomhole flow pressure of gas wells. The wellbore pressure gradient calculation model in the vertical pipe flow model is generally expressed as follows: In the formula: is the wellbore pressure gradient, in MPa/m; is the frictional pressure gradient, in MPa/m; is gravity pressure gradient, unit MPa/m; is the acceleration pressure gradient, in MPa/m. 4. the gas reservoir dynamic reserve calculation method according to claim 1, is characterized in that, in S3, the calculation method of gas well average formation pressure is as follows: The binomial productivity equation determined by the gas well productivity test is used to calculate the average formation pressure of the gas well. The calculated average formation pressure is the formation static pressure after the well is shut down and restored. The binomial productivity equation of the gas well is as follows: In the formula: ψ(p) is the average formation pressure of the gas well, in MPa ² /(mPa·s); ψ(p _wf ) is the pseudo pressure of bottomhole flowing pressure, unit MPa ² /(mPa·s); q _sc is the daily gas production of the gas well, the unit is 10 ⁴ m ³ /d; a, b are coefficients of binomial capacity equation. 5. The gas reservoir dynamic reserve calculation method according to claim 1, characterized in that, in S5, according to the gas reservoir material balance equation, calculate the dynamic reserves after the unsteady flow of the gas well ends, and the gas reservoir material balance equation is as follows: In the formula: is the apparent pressure of the initial pressure when the gas well is put into production, in MPa; is the apparent pressure of the average formation pressure, in MPa; G _p is the cumulative gas production of the gas well, the unit is 10 ⁸ m ³ ; G _bdf is the dynamic reserves of the gas well after the unsteady flow stage, and the unit is 10 ⁸ m ³ . The formula for calculating the real dynamic reserves of gas wells is as follows: In the formula: t _trn is the unsteady flow time; q _sc (t) is the instantaneous production of the gas well, the unit is 10 ⁴ m ³ /d; G _trn is the cumulative gas production of the gas well in the unsteady flow stage, the unit is 10 ⁸ m ³ ; G _bdf is the dynamic reserves of the gas well, the unit is 10 ⁸ m ³ . 6. The gas reservoir dynamic reserve calculation method according to claim 5, characterized in that, in S5, after the gas flow completely enters the boundary control flow stage, the apparent pressure of the average formation pressure of the gas well shows a downward trend and the apparent pressure of the average formation pressure of the gas well The relationship curve with the cumulative gas production is in a straight line, and the data in the early unstable flow stage will deviate from this straight line, so as to determine the time when the gas flow enters the boundary control flow, and then use the data in the early unstable flow stage from the regression analysis removed from the data.