Gas reservoir dynamic reserve calculation method
Technical Field
The invention relates to a gas reservoir dynamic reserve calculation method, in particular to a gas reservoir dynamic reserve calculation method.
Background
Gas reservoir dynamic reserve refers to the total amount of gas that participates in flow in a reservoir. The accurate calculation of the gas reservoir dynamic reserves is an important prerequisite for correctly evaluating the gas reservoir development effect, accurately predicting the gas reservoir development dynamics and making the gas reservoir development planning. At present, methods for calculating the dynamic reserves of gas reservoirs mainly comprise a material balance method (a pressure drop method), a flowing material balance method, a yield instability analysis method and the like. The material balance method is the most accurate and reliable method for calculating the dynamic reserve of the gas reservoir, but the whole gas reservoir shut-in pressure measurement needs to be carried out for a long time regularly. The mobile material balance method requires that the gas well production be stable and the initial formation pressure at which the gas well is put into production must be known accurately. It is difficult to satisfy the use conditions of the material balance method and the fluid material balance method in the gas reservoir development. The yield instability analysis method is a well testing analysis method based on production data, has good adaptability to the condition that the yield of a gas well constantly changes, is a method which is recognized at present and is more accurate and reliable in calculating the dynamic reserves of the gas well, but the analysis process is more complex, and the analysis needs to be carried out by means of professional software.
Disclosure of Invention
The invention provides a gas reservoir dynamic reserve calculation method aiming at the problems of insufficient data, harsh use conditions, complex analysis process and the like of the existing gas reservoir dynamic reserve calculation method, combining a gas seepage process and a vertical pipe flow model, a gas well productivity equation and a material balance equation based on the advantages of a material balance method.
The purpose of the invention is realized as follows:
a gas reservoir dynamic reserve calculation method comprises the following steps:
s1, preparing production dynamic data: acquiring gas well production dynamic data, wherein the gas well production dynamic data comprises gas well daily gas production rate, eliminating the production dynamic data during shut-in periods, and converting the gas well with daily gas production time less than 24 hours into 24-hour daily gas production rate;
s2, calculating the bottom hole flow pressure: selecting a vertical pipe flow model according to the sorted gas well production dynamic data, and calculating the bottom flow pressure of the gas well;
s3, calculating the average formation pressure of the gas well: calculating the average formation pressure of the gas well by adopting a binomial productivity equation of the gas well according to the daily gas yield of the gas well obtained in the step S1 and the bottom hole flowing pressure obtained in the step S2;
s4, flow stage division: according to the accumulated gas production rate of the gas well, the accumulated gas production rate is obtained through accumulated summation calculation, the average formation pressure is obtained through calculation of S3, a relation curve of the apparent pressure of the average formation pressure of the gas well and the accumulated gas production rate is drawn, and a boundary control flow stage, an unstable flow stage and a transition stage from the unstable flow stage to the boundary control flow stage are sequentially determined;
s5, calculating dynamic reserves: and determining the slope and intercept of a straight line by adopting linear regression analysis according to the data of the boundary control flow stage, further calculating the dynamic reserves of the gas well after the unstable flow stage of the gas well is finished, and adding the dynamic reserves of the gas well with the accumulated gas production of the unstable flow stage to obtain the real dynamic reserves of the gas well.
Preferably, in S1, the gas well production dynamic data further includes a wellhead pressure and a wellhead temperature.
Preferably, in S2, the bottom hole flow pressure is calculated as follows:
selecting a vertical pipe flow model to calculate the bottom hole flowing pressure of the gas well, wherein the general expression of a shaft pressure gradient calculation model in the vertical pipe flow model is as follows:
in the formula:
is the pressure gradient of the shaft, and the unit is MPa/m;
is friction pressure gradient, unitMPa/m;
The unit is a gravity pressure gradient and is MPa/m;
is the acceleration pressure gradient in MPa/m.
Preferably, in S3, the method for calculating the average formation pressure of the gas well is as follows:
calculating the average formation pressure of the gas well by adopting a binomial productivity equation determined by the gas well productivity test, wherein the calculated average formation pressure is the formation static pressure after the well closing recovery, and the binomial productivity equation of the gas well is as follows:
in the formula:
psi (p) is the average formation pressure of the gas well in MPa2/(mPa·s);
ψ(pwf) Is the pseudo pressure of the bottom hole flowing pressure in MPa2/(mPa·s);
qscThe daily gas production of the gas well is 10 units4m3/d;
and a and b are binomial productivity equation coefficients.
Preferably, in S5, the dynamic reserve after the unstable flow of the gas well is ended is calculated according to a gas reservoir material balance equation, where the gas reservoir material balance equation is as follows:
in the formula:
apparent pressure of initial pressure for gas well productionBit MPa;
apparent pressure, in MPa, which is the average formation pressure;
Gpcumulative gas production for gas wells, unit 108m3;
GbdfDynamic reserves of the well at the end of the unstable flow phase, in 10 units8m3。
The real dynamic reserves of the gas well are calculated as follows:
in the formula:
ttrnan unstable flow time;
qsc(t) is the instantaneous gas well production in 10 units4m3/d;
GtrnCumulative gas production for gas wells in unstable flow phase, unit 108m3;
GbdfIs the dynamic reserve of the gas well, unit 108m3。
Preferably, in S5, after the gas flow completely enters the boundary control flow stage, the average formation pressure apparent pressure of the gas well is in a descending trend and the relationship curve of the average formation pressure apparent pressure of the gas well and the accumulated gas production rate is in a straight line relationship, and the data in the early unstable flow stage obviously deviates from the straight line, so as to determine the time for the gas flow to enter the boundary control flow stage, and further remove the data in the early unstable flow stage from the regression analysis data.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
(1) the method determines the dynamic reserve capacity of the gas well based on the flowing data of the gas well, does not need to carry out long-time full gas reservoir shut-in well logging to recover the pressure of the gas well periodically, and effectively solves the problem that the material balance method has short data in the application process. The new method essentially still uses the gas reservoir material balance equation to determine the dynamic reserves of the gas well, thereby inheriting the advantages of accurate and reliable calculation results and simple calculation process of the material balance method, and simultaneously effectively overcoming the problems of harsh use conditions of the flowing material balance method and complex calculation process of the unstable analysis method. The invention realizes simple, convenient and accurate calculation of the gas reservoir dynamic reserves, and has important significance for correctly evaluating the gas reservoir development effect, accurately predicting the gas reservoir development dynamics and making the gas reservoir development planning.
(2) The example calculation results show that the maximum relative deviation between the calculation results of the method and the average values of the calculation results of the instability analysis method is 4.40 percent, the minimum relative deviation is-0.07 percent, and the relative deviation is within +/-5.0 percent, so that the calculation results of the method are accurate and reliable.
Drawings
FIG. 1 is a graph of mean formation pressure versus cumulative gas production for a P2011-3 well;
FIG. 2 shows typical curve plate fitting results for P2011-3 well Blasinname;
FIG. 3 shows the fitting results of a typical P2011-3 well AG plate;
FIG. 4 shows typical fitting results of a P2011-3 well NPI curve plate.
Detailed Description
A gas reservoir dynamic reserve calculation method comprises the following steps:
s1, preparing production dynamic data: and acquiring gas well production dynamic data, wherein the gas well production dynamic data comprises gas well daily gas production, well head pressure and well head temperature, and is used for eliminating the production dynamic data during the well shut-in period according to the requirements of vertical pipe flow model calculation, and converting the gas well with daily production time less than 24 hours into 24-hour daily gas production so as to ensure the accuracy of the calculation result.
S2, calculating the bottom hole flow pressure: selecting a proper vertical pipe flow equation according to the sorted gas well production dynamic data, and calculating the bottom flow pressure of the gas well;
in this embodiment, the bottom hole flowing pressure is calculated as follows:
selecting a vertical pipe flow model to calculate the bottom hole flowing pressure of the gas well, wherein the general expression of a shaft pressure gradient calculation model in the vertical pipe flow model is as follows:
in the formula:
is the pressure gradient of the shaft, and the unit is MPa/m;
is friction resistance pressure gradient with unit of MPa/m;
the unit is a gravity pressure gradient and is MPa/m;
is the acceleration pressure gradient in MPa/m.
S3, calculating the average formation pressure of the gas well: calculating the average formation pressure (namely the well closing recovery static pressure) of the gas well by adopting a binomial productivity equation of the gas well according to the daily gas production rate of the gas well obtained from S1 and the bottom hole flow pressure obtained from S2;
the method for calculating the static pressure of the stratum comprises the following steps:
calculating the average formation pressure of the gas well by adopting a binomial productivity equation determined by the gas well productivity test, wherein the calculated average formation pressure is the formation static pressure after the well closing recovery, and the binomial productivity equation of the gas well is as follows:
in the formula:
psi (p) is the average formation pressure of the gas well in MPa2/(mPa·s);
ψ(pwf) Is the pseudo pressure of the bottom hole flowing pressure in MPa2/(mPa·s);
qscThe daily gas production of the gas well is 10 units4m3/d;
and a and b are binomial productivity equation coefficients.
S4, flow stage division: calculating to obtain accumulated gas production according to the daily gas production of the gas well, drawing a relation curve of the apparent pressure of the average formation pressure of the gas well and the accumulated gas production, and sequentially determining a boundary control flow stage, an unstable flow stage and a transition stage from the unstable flow stage to the boundary control flow stage;
s5, calculating dynamic reserves: and determining the slope and intercept of a straight line by adopting linear regression analysis according to the data of the boundary control flow stage, further calculating the dynamic reserves after the unstable flow stage of the gas well is finished, and adding the dynamic reserves to the accumulated gas production of the unstable flow stage to obtain the real dynamic reserves of the gas well.
After the gas flow completely enters the boundary control flow stage, according to a gas reservoir matter balance equation, a relation curve is a straight line, and the dynamic reserve after the unstable flow of the gas well is finished is calculated according to the slope and intercept of the straight line, wherein the gas reservoir matter balance equation is as follows:
in the formula:
the apparent pressure of the initial pressure in unit MPa during the production of the gas well;
apparent pressure, in MPa, which is the average formation pressure;
Gpcumulative gas production for gas wells, unit 108m3;
GbdfDynamic reserves of the well at the end of the unstable flow phase, in 10 units8m3。
Because the gas well binomial productivity equation is determined by the productivity test, the bottom hole flowing pressure is required to be stable during the productivity test, and the gas well binomial productivity equation determined by the productivity test represents the mathematical relationship among the average formation pressure, the bottom hole flowing pressure and the gas well yield in the boundary control flowing stage. Thus, only the dynamic reserves determined from the production dynamic monitoring data that have entered the boundary control flow phase are reliable.
When the gas flow completely enters the boundary control flow stage, the average formation pressure apparent pressure of the gas well is in a descending trend, the relation curve of the average formation pressure apparent pressure of the gas well and the accumulated gas production rate is in a linear relation, and the data in the early unstable flow stage obviously deviates from the straight line, so that the time for the gas flow to enter the boundary control flow can be determined, and the data in the early unstable flow stage can be removed from the regression analysis data.
The intercept obtained from the regression analysis of the data of the boundary control flow phase reflects the average formation pressure when the gas flow starts to transit from the unstable flow to the boundary control flow, and is not the initial formation pressure when the gas well is put into production. Therefore, the dynamic reserves determined by regression analysis by the method are only the dynamic reserves after the unstable flow of the gas well is finished. The true dynamic reserves of a gas well should also include the cumulative gas production of the gas well during periods of unsteady flow, i.e.:
in the formula:
ttrnan unstable flow time;
qsc(t) is the instantaneous gas well production in 10 units4m3/d;
GtrnCumulative gas production for gas wells in unstable flow phase, unit 108m3;
GbdfIs the dynamic reserve of the gas well, unit 108m3。
And (3) calculating and drawing a relation curve of the apparent pressure of the average formation pressure and the accumulated gas production according to the dynamic monitoring data of the main gas reservoir P2011-3 well production of the plain gas field (figure 1). And determining that the gas flow completely enters a boundary control flow stage after 3, month and 2 days 2011 according to a relation curve of the average formation pressure apparent pressure and the accumulated gas production rate, wherein the gas flow completely enters an unstable flow stage before 8, month and 14 days 2010, and the gas flow completely enters a transition stage of the unstable flow to the boundary control flow during the period from 14 days 2010, month and 14 days to 3, month and 2 days 2011. Determining the slope and intercept of a straight line by linear regression analysis according to the data of the boundary control flow stage, and calculating the dynamic reserve of the gas well after the unstable flow is finished to be 27.22 multiplied by 108m3The gas well has an unstable flow stage with a cumulative gas production of 0.44 multiplied by 108m3Thus, the dynamic reserve of the P2011-3 well is determined to be 27.66 multiplied by 108m3. The dynamic reserves of the P2011-3 well are calculated by adopting yield instability analysis methods such as a Blasingeam method, an AG method, an NPI method and the like (figures 2 to 4), and the calculation results of the dynamic reserves of the gas well are 27.59 multiplied by 10 respectively8m3,28.05×108m3And 28.28X 108m3Average dynamic reserve 27.97 × 108m3。
From typical curve plate fitting results of the Blasinname method, the AG method and the NPI method, the gas well flow completely enters a boundary control flow stage, and the calculation result of the yield instability analysis method is reliable. The dynamic reserves of the P2011-3 well determined by the new method and a yield instability analysis method are similar, and the relative deviation is-1.11%, which shows that the calculation result of the new method is accurate and reliable.
In order to further verify the accuracy and reliability of the calculation result of the method, the dynamic reserves of 9 gas wells such as a body gas reservoir P201-4 of the Puguang gas field are analyzed and calculated by adopting the same analysis and calculation process (Table 1). From the calculation result of the dynamic reserves of the gas wells, the maximum relative deviation between the calculation result of the method and the average value of the calculation result of the instability analysis method is 4.40 percent, the minimum relative deviation is-0.07 percent, and the relative deviation is within +/-5.0 percent, so that the calculation result of the method is accurate and reliable.
TABLE 1 gas well dynamic reserves calculation results
Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.