Optimized pressure drop method for calculating dynamic reserves of low-permeability gas reservoir

Abstract

The invention discloses an optimized pressure drop method for calculating dynamic reserves of a low-permeability gas reservoir, which relates to the technical field of oil-gas field development, and comprises the following steps: converting medium-depth original formation pressure of the gas reservoir and medium-depth formation pressure of the gas reservoir measured at different time nodes into apparent formation pressure, drawing the apparent formation pressure and corresponding accumulated gas production in a rectangular coordinate system, and calculating the dynamic reserves of the low-permeability gas reservoir. Calculating the accumulated gas production increment under unit apparent formation pressure according to the last two time node data, multiplying the accumulated gas production increment by the current apparent formation pressure to obtain the current residual dynamic reserves, and finally adding the current accumulated gas production to obtain the low-permeability gas reservoir pressure drop dynamic reserves. The problem that in the prior art, the dynamic reserves of the low-permeability gas reservoir obtained through a pressure drop method are large in deviation is solved, and the method is easy to operate and convenient to popularize.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to an optimized pressure drop method for calculating dynamic reserves of low-permeability gas reservoirs. Background Art

[0002] Reserves are the material basis for the development of oil and gas fields and are related to the adjustment and deployment of development well networks. Accurate calculation of dynamic reserves of gas reservoirs is of great significance to the preparation of gas reservoir trial production (development) plans, value assessment and dynamic analysis, and is a prerequisite for achieving long-term high and stable production of gas fields.

[0003] For low permeability gas reservoirs (permeability 0.1 ~ 5mD) and ultra-low permeability gas reservoirs (permeability ≤ 0.1mD), the pressure drop method is currently usually used to calculate the dynamic reserves of gas reservoirs. The original deep formation pressure of the gas reservoir is measured before production. After production, the deep formation pressure of no less than one gas reservoir is measured at different time points. The apparent formation pressure and the formation pressure at each time point are calculated. The apparent formation pressure is used as the Y variable, and the cumulative gas production of the gas reservoir at each time point is used as the X variable. In the rectangular coordinate system, linear regression is performed on the X and Y variables. The intersection value of the extended regression line and the horizontal coordinate is the dynamic reserves of the gas reservoir, or the regression formula is set equal to zero to calculate the dynamic reserves of the gas reservoir pressure drop. In actual applications, it is found that the results obtained by this method have a low consistency with the actual situation and a large deviation.

[0004] At the same time, numerical simulation methods can also be used to obtain the dynamic reserves of gas reservoirs. The dynamic reserves of gas reservoirs obtained by this method are relatively accurate, but this method requires first establishing a geological model based on the results of seismic, well logging and comprehensive geological research, and then establishing a numerical model based on formation pressure and temperature, PVT, oil test, VFP and other data to fit the historical production data of the gas reservoir. This process requires repeated adjustment and optimization of the model. This method is complex and takes a long time to process. It is difficult for ordinary personnel to master and is not convenient for dynamic reserve calculation of low permeability gas reservoirs. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an optimized pressure drop method for calculating the dynamic reserves of low permeability gas reservoirs. The present invention calculates the pressure drop dynamic reserves of low permeability and ultra-low permeability gas reservoirs by accumulating gas production and adding the remaining dynamic reserves. The operation is simple and the calculation results are highly consistent with the actual situation.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs, which converts the original deep-middle formation pressure of the gas reservoir and the deep-middle formation pressure of the gas reservoir measured at different time nodes into apparent formation pressure, then plots the apparent formation pressure and the corresponding cumulative gas production in a rectangular coordinate system, calculates the cumulative gas production increment under unit apparent formation pressure based on the data of the last two time nodes, multiplies the incremental gas production by the current apparent formation pressure to obtain the current remaining dynamic reserves, and finally adds the current cumulative gas production to obtain the pressure drop dynamic reserves of the low permeability gas reservoir.

[0008] Furthermore, the method specifically comprises the following steps:

[0009] S1. Converting the original deep-middle formation pressure of the gas reservoir measured before production and the deep-middle formation pressure of the gas reservoir measured at different time points after production into apparent formation pressure;

[0010] S2. Sorting out the cumulative gas production when the formation pressure is measured at different time nodes, and plotting the apparent formation pressure as the Y variable and the corresponding cumulative gas production as the X variable in the same rectangular coordinate system;

[0011] S3, calculating the cumulative gas production increment per unit apparent formation pressure according to the last two time node data (X, Y);

[0012] S4. Multiply the cumulative gas production increment per unit apparent formation pressure by the current apparent formation pressure to obtain the current remaining dynamic reserves;

[0013] S5. Add the current remaining dynamic reserves to the current cumulative gas production to obtain the low-permeability gas reservoir pressure drop dynamic reserves.

[0014] Furthermore, the apparent formation pressure is the ratio of the deep formation pressure of the gas reservoir measured at different time nodes to the deviation factor Z at the corresponding time node.

[0015] Furthermore, the calculation method of the cumulative gas production increment per unit apparent formation pressure involved in S3 is:

[0016]

[0017] Where, Ω is the cumulative gas production increment per unit apparent formation pressure, 10 8 m 3 / MPa;

[0018] G pn is the cumulative gas production at time node n or the current cumulative gas production, 10 8 m 3 ;

[0019] G pn-1 is the cumulative gas production at time node n-1, 10 8 m 3 ;

[0020] p n-1 / Z n-1 is the apparent formation pressure at time node n-1, MPa;

[0021] p n / Z n is the apparent formation pressure at time node n or the current apparent formation pressure, MPa.

[0022] Furthermore, the calculation formula for the current remaining dynamic reserves involved in S4 is:

[0023] G s =Ω×p n / Z n (2)

[0024] In the formula, G s is the current remaining dynamic reserves, 10 8 m 3 .

[0025] Furthermore, the calculation formula for the dynamic reserve of low-permeability and ultra-low-permeability pressure drop involved in S5 is:

[0026] G= G s + G pn (3)

[0027] Where G is the pressure drop dynamic reserve of low permeability gas reservoir, 10 8 m 3 .

[0028] Furthermore, the target area applicable to the optimized pressure drop method is a general low permeability gas reservoir or an ultra-low permeability gas reservoir.

[0029] A device for calculating dynamic reserves of a low-permeability gas reservoir, comprising:

[0030] An information collection unit is used to input and confirm the aforementioned deep original formation pressure, the deep formation pressure of the gas reservoir measured at different time points, and the cumulative gas production corresponding to different time points;

[0031] A drawing unit is used to draw a dynamic reserve curve of a low-permeability gas reservoir based on the results of statistics, analysis and calculation;

[0032] The calculation unit is used to calculate the cumulative gas production increment per unit apparent formation pressure, the remaining dynamic reserves, and the pressure drop dynamic reserves of the low permeability gas reservoir in the area to be measured according to the input parameters and / or formulas.

[0033] Furthermore, the information acquisition unit also includes a pressure determination module.

[0034] Furthermore, the information collection unit also includes a time determination module

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] 1. The present invention further improves the existing pressure drop method. The cumulative gas production increment per unit apparent formation pressure is calculated based on the data of the last two time nodes. The increment is multiplied by the current apparent formation pressure to obtain the current remaining dynamic reserves. The remaining dynamic reserves are added to the current cumulative gas production to obtain the pressure drop dynamic reserves of the low permeability gas reservoir. This value is closer to the actual value than the dynamic reserve value obtained by the pressure drop method and has more analytical and evaluation significance.

[0037] Second, during the development of low-permeability and ultra-low-permeability gas reservoirs or gas wells, the peripheral formation energy is slowly replenished to the gas well, and the pressure drop curve will deviate from the original downward trend and gradually rise, so the last data point can better reflect the size of the formation energy (dynamic reserves). In the present invention, the cumulative gas production increment of the unit apparent formation pressure is calculated by the last two time node data, and the current remaining dynamic reserves are obtained by multiplying this by the current apparent formation pressure, and the current cumulative gas production is added to obtain the dynamic reserves of the pressure drop of the low-permeability and ultra-low-permeability gas reservoir. This method is simple to operate, and the calculation results are more consistent with the actual situation.

[0038] 3. Compared with the numerical simulation method, the method of the present invention avoids complicated model optimization and adjustment, and at the same time reduces the requirements for data, and does not require a large amount of various data to be collated and entered. The present invention can obtain more accurate dynamic reserves of pressure drop of low-permeability gas reservoirs based on simpler and easier-to-obtain data. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the formation pressure and the cumulative gas production data points in Example 1.

[0040] Figure 2 This is a schematic diagram of data selection for the last two time nodes in the present invention.

[0041] Figure 3 It is a plot of formation pressure and cumulative gas production data points in an embodiment of the present invention.

[0042] Figure 4 The data in Example 1 are obtained by using the existing pressure drop method. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0044] The following examples further illustrate an optimized pressure drop method and device for calculating dynamic reserves of low permeability gas reservoirs provided by the present invention. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above invention content and implement them specifically, which still falls within the scope of protection of the present invention.

[0045] The method of the present invention is further described below.

[0046] The original deep-mid-depth formation pressure p of a low-permeability gas reservoir before production was 25.72 MPa, the formation temperature was 87 °C, and the relative density of gas was 0.63. The deep-mid-depth formation pressure, cumulative gas production, gas deviation factor and other data measured at each time point after production are shown in Table 1. The data points involved are shown in the attached figure. Figure 3 According to the numerical model production history fitting, the dynamic reserves of the gas reservoir are 27.02×10 8 m 3 .

[0047] Table 1

[0048]

[0049] Example 1

[0050] An optimized pressure drop method for calculating dynamic reserves of a low-permeability gas reservoir relates to the technical field of oil and gas field development. The method converts the original deep-middle formation pressure of a gas reservoir and the deep-middle formation pressure of a gas reservoir measured at different time nodes into an apparent formation pressure. The apparent formation pressure and the corresponding cumulative gas production are then plotted in the same rectangular coordinate system. The cumulative gas production increment under the unit apparent formation pressure is calculated based on the data of the last two time nodes. The current remaining dynamic reserves are obtained by multiplying the increment by the current apparent formation pressure. Finally, the current cumulative gas production is added to obtain the dynamic reserves of the low-permeability gas reservoir by pressure drop.

[0051] The specific steps are as follows:

[0052] Step 1: convert the original deep formation pressure p of the gas reservoir measured before production and the deep formation pressure of the gas reservoir measured at different time nodes after production into apparent formation pressure, wherein the apparent formation pressure is the ratio of the deep formation pressure of the gas reservoir measured at different time nodes to the deviation factor Z at the corresponding time node, and the deviation factor Z can be calculated by an empirical formula.

[0053] Step 2: Sort out the cumulative gas production when measuring formation pressure at different time nodes, and plot the apparent formation pressure as the Y variable and the corresponding cumulative gas production as the X variable in the same rectangular coordinate system; see the attached diagram for the plotting of the data points involving the apparent formation pressure and the cumulative gas production. Figure 1 ;

[0054] The cumulative gas production refers to the sum of the daily gas production from the time of commissioning to the nth time point; the calculation formula involved is shown in formula (1):

[0055]

[0056] In the formula, G pn —The cumulative gas production at time n or the current cumulative gas production, 10 8 m 3 ;

[0057] q i —Gas production on day i, 10 8 m 3 .

[0058] Step 3: Calculate the cumulative gas production increment per unit apparent formation pressure based on the data of the last two time nodes (X, Y); the calculation formula for the cumulative gas production increment per unit apparent formation pressure is shown in formula (2):

[0059]

[0060] Where, Ω is the cumulative gas production increment per unit apparent formation pressure, 10 8 m 3 / MPa;

[0061] G pn —The cumulative gas production at time n or the current cumulative gas production, 10 8 m 3 ;

[0062] G pn-1 —n-1 cumulative gas production at time node, 10 8 m 3 ;

[0063] p n-1 / Z n-1 —apparent formation pressure at time node n-1, MPa;

[0064] p n / Z n —N time node apparent formation pressure or current apparent formation pressure, MPa;

[0065] See the attached diagram for the data selection of the last two time nodes involved. Figure 2 .

[0066] In this example, based on the data of the last two time nodes (10.02, 13.73) and (12.81, 11.41), the cumulative gas production increment per unit apparent formation pressure is calculated to be 1.20×10 8 m 3 / MPa.

[0067] Step 4: Multiply the cumulative gas production increment per unit apparent formation pressure by the current apparent formation pressure to obtain the current remaining dynamic reserves; the calculation formula for the current remaining dynamic reserves involved is shown in formula (3):

[0068] G s =Ω×p n / Z n (3)

[0069] In the formula, G s - Current remaining dynamic reserves, 10 8 m 3 ;

[0070] The cumulative gas production increment per unit apparent formation pressure is 1.2×10 8 m 3 / MPa multiplied by the current apparent formation pressure of 11.41MPa, the remaining dynamic reserves of the low permeability gas reservoir are 13.72×10 8 m 3 .

[0071] Step 5: Add the current remaining dynamic reserves to the current cumulative gas production to obtain the pressure drop dynamic reserves of the low-permeability and ultra-low-permeability gas reservoir; the calculation formula for the pressure drop dynamic reserves of the gas reservoir involved is shown in formula (4):

[0072] G= G s + G pn (4)

[0073] G—pressure drop dynamic reserves of low-permeability and ultra-low-permeability gas reservoirs, 10 8 m 3 .

[0074] The current remaining dynamic reserves are 13.72×10 8 m 3 Plus the current cumulative gas production of 12.81×10 8 m 3 The pressure drop dynamic reserves of low permeability gas reservoirs are 26.53×10 8 m 3 The result is consistent with the actual situation by 1-(|26.53-27.02|) / 27.02=98.2%. The existing pressure drop method is used to obtain the pressure drop dynamic reserves G' of low permeability gas reservoirs. Figure 4 , and G' is 28.6323×10 8 m 3 The result is consistent with the actual situation by 1-(|28.6323-27.02|) / 27.02=94.03%. It can be seen that the result obtained by the calculation scheme of the present invention is closer to the actual value, and the result obtained by the calculation method of the present invention is more meaningful for analysis and evaluation.

[0075] The target area applicable to the optimized pressure drop method for calculating the dynamic reserves of low-permeability gas reservoirs of the present invention is a general low-permeability gas reservoir or an ultra-low-permeability gas reservoir.

[0076] At the same time, the present invention also discloses a low permeability gas reservoir dynamic reserve calculation system applicable to the method to obtain the low permeability gas reservoir dynamic reserve value, the low permeability gas reservoir dynamic reserve calculation system comprises an information acquisition unit, a drawing unit and a calculation unit:

[0077] The information acquisition unit is used to input and confirm the aforementioned deep and medium original formation pressure of the gas reservoir, the deep and medium formation pressure of the gas reservoir measured at different time points, and the accumulated gas production corresponding to different time points;

[0078] The drawing unit is used to draw a dynamic reserve curve of a low-permeability gas reservoir according to the results of statistics, analysis and calculation;

[0079] The calculation unit is used to calculate the cumulative gas production increment per unit apparent formation pressure, the remaining dynamic reserves, and the pressure drop dynamic reserves of the low permeability gas reservoir in the area to be measured according to the input parameters and / or formulas.

[0080] Furthermore, the information collection unit also includes a pressure determination module.

[0081] Furthermore, the information collection unit also includes a time determination module.

[0082] To ensure that the data obtained by the method of the present invention is accurate and the calculation results are reliable.

[0083] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs, characterized in that: The original deep-middle original formation pressure of the gas reservoir and the deep-middle formation pressure of the gas reservoir measured at different time nodes are converted into apparent formation pressure. The apparent formation pressure and the corresponding cumulative gas production are plotted in a rectangular coordinate system. The cumulative gas production increment under unit apparent formation pressure is calculated according to the data of the last two time nodes. The current remaining dynamic reserves are obtained by multiplying it by the current apparent formation pressure. Finally, the current cumulative gas production is added to obtain the dynamic reserves of the pressure drop of the low-permeability gas reservoir.

2. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 1, characterized in that: The method specifically comprises the following steps: S1. Converting the original deep-middle formation pressure of the gas reservoir measured before production and the deep-middle formation pressure of the gas reservoir measured at different time points after production into apparent formation pressure; S2. Sorting out the cumulative gas production when the formation pressure is measured at different time nodes, and plotting the apparent formation pressure as the Y variable and the corresponding cumulative gas production as the X variable in the same rectangular coordinate system; S3, calculating the cumulative gas production increment per unit apparent formation pressure according to the last two time node data (X, Y); S4. Multiply the cumulative gas production increment per unit apparent formation pressure by the current apparent formation pressure to obtain the current remaining dynamic reserves; S5. Add the current remaining dynamic reserves to the current cumulative gas production to obtain the pressure drop dynamic reserves of the low permeability gas reservoir.

3. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 2, characterized in that: The apparent formation pressure is the ratio of the deep formation pressure of the gas reservoir measured at different time nodes to the deviation factor Z at the corresponding time node.

4. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 3, characterized in that: The calculation method of the cumulative gas production increment per unit apparent formation pressure involved in S3 is: Where Ω is the cumulative gas production increment per unit apparent formation pressure, 10 8 m 3 / MPa; G pn is the cumulative gas production at time node n or the current cumulative gas production, 10 8 m 3 ; G pn-1 is the cumulative gas production at time node n-1, 10 8 m 3 ; p n-1 / Z n-1 is the apparent formation pressure at time node n-1, MPa; p n / Z n is the apparent formation pressure at time node n or the current apparent formation pressure, MPa.

5. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 4, characterized in that: The calculation formula for the current remaining dynamic reserves involved in S4 is: G s =Ω×p n / Z n (2), In the formula, G s is the current remaining dynamic reserves, 10 8 m 3 .

6. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 5, characterized in that: The calculation formula of the dynamic reserve of low osmotic pressure drop involved in S5 is: G=G s + G pn (3), Where G is the pressure drop dynamic reserve of low permeability gas reservoir, 10 8 m 3 .

7. An optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to any one of claims 1 to 6, characterized in that: The target area applicable to the optimized pressure drop method is a general low permeability gas reservoir or an ultra-low permeability gas reservoir.

8. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 2, characterized in that: The dynamic reserve value of a low permeability gas reservoir is obtained by using a system for calculating the dynamic reserve of a low permeability gas reservoir. The system for calculating the dynamic reserve of a low permeability gas reservoir includes an information collection unit, a drawing unit and a calculation unit: The information collection unit is used to input and confirm the original deep-middle formation pressure of the gas reservoir as claimed in claim 2, the deep-middle formation pressure of the gas reservoir measured at different time points, and the accumulated gas production corresponding to different time points; The drawing unit is used to draw a dynamic reserve curve of a low-permeability gas reservoir according to the results of statistics, analysis and calculation; The calculation unit is used to calculate the cumulative gas production increment per unit apparent formation pressure, the remaining dynamic reserves, and the pressure drop dynamic reserves of the low permeability gas reservoir in the area to be measured according to the input parameters and / or formulas.

9. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 8, characterized in that: The information acquisition unit also includes a pressure determination module.

10. The optimized pressure drop method for calculating dynamic reserves of low permeability gas reservoirs according to claim 8, characterized in that: The information collection unit also includes a time determination module.

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