A method for calculating the gas-oil ratio of a condensate gas reservoir

Abstract

The present invention relates to the field of oil and gas field development, and in particular to a method for calculating the gas-oil ratio of a condensate gas reservoir, comprising the following steps: S1, calculating the bottom hole pressure P obtained by a static ladder test; ws Compared with the assumed relative density γ′ of the condensate phase G The calculated bottom hole pressure P′ is obtained ws Compare and obtain a reasonable relative density γ of the condensate gas phase G ; S2, using a reasonable relative density of condensate gas γ G , gas-oil ratio R go The calculation method of the gas-oil ratio of condensate gas reservoirs adopted by the present invention has a strict theoretical derivation basis, eliminates the influence of human interference and the disadvantages of the metering and separation devices themselves, has high reliability, fast calculation speed, true and reliable data, and can effectively guide production adjustments; it can solve the various disadvantages of the current ground metering method for determining the gas-oil ratio, the calculation method is simple, and the calculation results are accurate and reliable.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas field development, and particularly to a method for calculating the gas-oil ratio of a condensate gas reservoir. Background Art

[0002] A condensate gas reservoir is a special type of gas reservoir. It refers to a gas state under high temperature and high pressure deep in the formation. When the gas is produced to the ground, due to the decrease in temperature and pressure, liquid petroleum will condense from the gas. This liquid petroleum is called condensate oil, and the gas reservoir is called a condensate gas reservoir. The gas-oil ratio is a very important indicator during the exploitation of a condensate gas reservoir, which reflects the amount of natural gas (m 3 ) produced along with the production of 1 t of crude oil. The gas-oil ratio before the development of a condensate gas reservoir is called the initial gas-oil ratio, and the gas-oil ratio during the exploitation of the gas reservoir is called the production gas-oil ratio.

[0003] With the development of the gas reservoir, the condensate oil in the formation is continuously produced, and the content of condensate oil will gradually decrease, which means that more natural gas needs to be produced to produce 1 t of crude oil. That is, compared with the initial gas-oil ratio, the gas-oil ratio gradually increases. For a condensate gas reservoir developed by gas injection, due to the extraction effect of the injected dry gas on the heavy components in the condensate gas, the gas-oil ratio of the gas reservoir will also gradually increase. The size of the gas-oil ratio essentially reflects the remaining condensate oil volume and potential economic benefits in the condensate gas reservoir. Therefore, determining the change of the gas-oil ratio is crucial for the development of a condensate gas reservoir, which is conducive to timely adjusting the gas reservoir development policy. For example, when the gas-oil ratio of a condensate gas reservoir developed by gas injection decreases to a certain extent, if the gas injection development method is continued, the recovery rate of condensate oil will no longer increase significantly, but instead will greatly reduce the gas reservoir development benefit. Then the gas reservoir will be adjusted to depletion development.

[0004] For a condensate gas reservoir about to be developed or in the process of exploitation, the ground measurement method is usually used to verify the gas-oil ratio of the gas reservoir. Its working principle is that after the underground fluid is produced, the well stream is separated by a ground separator to obtain the oil and gas production respectively, and then the gas-oil ratio is calculated. However, this method is affected by the accuracy of the measurement equipment, incomplete separation of oil and gas by the separator (such as liquid carried in the gas phase, reducing the condensate oil production, or gas carried in the liquid phase, reducing the natural gas production), and the inability of the separator to deeply remove hydrocarbons. The obtained gas-oil ratio has a large deviation from the true value, resulting in inaccurate calculation of the gas reservoir reserves and deviation of the economic benefit evaluation from the actual situation.

[0005] Before the development of a condensate gas reservoir, the wellbore static temperature and pressure gradient (abbreviated as static gradient) is usually recorded to obtain the formation pressure information. Especially after the gas reservoir is put into development, in order to understand the change of the formation pressure, a large amount of wellbore static temperature and pressure gradient data will be recorded. However, these pressure data are usually only used to convert the formation pressure at the middle depth of the gas reservoir, and their potential value has not been fully utilized. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention provides a method for calculating the gas-oil ratio of a condensate gas reservoir. By deeply mining and utilizing the existing dynamic monitoring data, parameters such as gas reservoir temperature, pressure, well depth, deviation coefficient, and fluid relative density are comprehensively considered, and a functional relationship between the static temperature and pressure in the wellbore and the gas-oil ratio is established. By solving the partial differential equation and performing cyclic iteration to obtain the gas-oil ratio value, various drawbacks of determining the gas-oil ratio by the current ground measurement method can be solved. The calculation method is simple, and the calculation result is accurate and reliable.

[0007] The present invention is realized through the following technical solutions:

[0008] A method for calculating the gas-oil ratio of a condensate gas reservoir, comprising the following steps:

[0009] S1, comparing the bottom-hole pressure obtained by using the static gradient test with the calculated bottom-hole pressure obtained by using the assumed relative density of the condensate gas phase to obtain a reasonable relative density of the condensate gas phase ; ;

[0010] S2, using the reasonable relative density of the condensate gas phase to calculate the gas-oil ratio R go , and the calculation formula is:

[0011]

[0012] In the formula, is the relative density of the condensate gas phase;

[0013] is the relative molecular weight of the condensate oil;

[0014] R go is the gas-oil ratio;

[0015] is the measured relative density of natural gas;

[0016] r o is the measured relative density of the condensate oil.

[0017] Preferably, the method for obtaining the reasonable relative density of the condensate gas phase is: comparing the absolute difference between the bottom-hole pressure obtained by the static gradient test P ws and the calculated bottom-hole pressure obtained by the assumed relative density of the condensate gas phase with the given error until the absolute difference is less than the given error ε ε ​, the assumed relative density of the condensate gas phase at this time is the reasonable relative density of the condensate gas phase .

[0018] Preferably, the value of the given error ε is 0.01 MPa.

[0019] Preferably, the steps for calculating the bottom-hole pressure are as follows:

[0020] S11, using the parameters at the wellhead or starting point and the assumed relative density of the condensate gas phase to calculate the pressure at the end of the upper section of the tubing P ms and the intermediate parameters at the end of the upper section of the tubing I ms ;

[0021] S12, using the pressure at the end of the upper section of the tubing P ms , the intermediate parameters at the end of the upper section of the tubing I ms and the assumed relative density of the condensate gas phase to calculate the pressure at the end of the lower section of the tubing P ws1 ; when the absolute difference between the bottom-hole pressure P ws and the calculated bottom-hole pressure is less than the given error ε , the pressure at the end of the lower section of the tubing P ws1 is equal to the calculated bottom-hole pressure obtained from the reasonable relative density of the condensate gas phase .

[0022] Preferably, in S11, the expression for the pressure at the end of the upper section of the tubing P ms is:

[0023]

[0024] In the formula, P ts —— the measured wellhead pressure or the pressure at a certain starting depth;

[0025] h —— the depth from the wellhead to the bottom hole or the depth from the starting point to the end point;

[0026] I ms —— represents the intermediate parameters at the end of the upper section of the tubing;

[0027] I ​ts —— Intermediate parameters representing the wellhead or the starting point.

[0028] Preferably, the intermediate parameters of the end point of the upper section of the tubing I ms The expression is:

[0029]

[0030] Wherein, Z ms —— Represents the condensate gas deviation factor;

[0031] T ms —— Represents the temperature at the end point of the upper section of the tubing;

[0032] P ms —— Represents the pressure at the end point of the upper section of the tubing.

[0033] Preferably, the intermediate parameters of the wellhead or the starting point I ts The expression is:

[0034] Wherein, Z ts —— Represents the condensate gas deviation factor;

[0035] T ts —— Represents the temperature of the wellhead or the starting point;

[0036] P ts —— Represents the pressure of the wellhead or the starting point.

[0037] Preferably, the pressure of the lower section of the tubing P ws1 The expression is:

[0038] Wherein, h —— Represents

[0039] I ws —— Represents the intermediate parameters of the end point of the lower section of the tubing.

[0040] Preferably, the intermediate parameters of the end point of the lower section of the tubing I ws The expression is:

[0041]

[0042] In the formula, Z ws —— represents the deviation factor of condensate gas;

[0043] T ws —— represents the temperature at the end point of the lower section of the tubing;

[0044] P ws —— represents the pressure at the end point of the lower section of the tubing.

[0045] Preferably, the relative molecular weight of the condensate oil has the following calculation formula:

[0046] .

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The calculation method of the gas-oil ratio of the condensate gas reservoir adopted by the present invention has a strict theoretical derivation basis, eliminates the interference of human factors and the disadvantages of metering and separation devices, etc., has high reliability, fast calculation speed, true and reliable data, and can effectively guide production adjustment; it can solve various disadvantages of the current method of determining the gas-oil ratio by ground metering, the calculation method is simple, and the calculation result is accurate and reliable.

[0049] Through in-depth excavation of the static gradient, the present invention comprehensively considers parameters such as gas reservoir temperature, pressure, well depth, deviation coefficient, and fluid relative density, establishes the functional relationship between the static temperature and pressure in the wellbore and the gas-oil ratio, and obtains the gas-oil ratio value by solving partial differential equations and cyclic iteration. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is the design idea diagram of a calculation method of the gas-oil ratio of a condensate gas reservoir of the present invention;

[0051] Figure 2 is the calculation schematic diagram of a calculation method of the gas-oil ratio of a condensate gas reservoir of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0052] The following further describes the present invention in detail with specific embodiments, which are explanations rather than limitations of the present invention.

[0053] Referring to Figure 1 , the magnitude of the gas-oil ratio reflects the condensate oil content in the gas phase, the condensate oil content reflects the gas density, and the density reflects the pressure. Therefore, there is a specific functional relationship between the pressure and the gas-oil ratio.

[0054] A calculation method of the gas-oil ratio of a condensate gas reservoir includes the following steps:

[0055] S1. Compare the absolute difference between the bottom-hole pressure obtained from the static ladder test and the calculated bottom-hole pressure obtained with the assumed relative density of the condensate gas phase with the given error until the absolute difference is less than the given error. The value of the given error is 0.01 MPa, i.e., a reasonable relative density of the condensate gas phase is obtained. P ws with the assumed relative density of the condensate gas phase to obtain the calculated bottom-hole pressure and compare it with the given error ε until the absolute difference is less than the given error ε The given error ε is set to 0.01 MPa, that is, a reasonable relative density of the condensate gas phase is obtained. .

[0056] S2. Use the reasonable relative density of the condensate gas phase to calculate the gas-oil ratio. The calculation formula is as follows: in which R go is the relative density of the condensate gas phase, generally ranging between 0.5 and 0.8;

[0057]

[0058] In the formula, is the relative density of the condensate gas phase, generally between 0.5 and 0.8;

[0059] is the relative molecular mass of the condensate oil;

[0060] R go is the gas-oil ratio, with the unit of m 3 / t;

[0061] is the measured relative density of natural gas;

[0062] r o is the measured relative density of condensate oil.

[0063] Refer to Figure 2 to calculate the bottom-hole pressure The steps are as follows:

[0064] S11. Use the parameters at the wellhead or starting point and the assumed relative density of the condensate gas phase to calculate the pressure at the end of the upper section of the tubing and the intermediate parameters at the end of the upper section of the tubing P ms ; I ms ;

[0065] S12. Use the pressure at the end of the upper section of the tubing P ms and the intermediate parameters at the end of the upper section of the tubing I ms to calculate the pressure at the end of the lower section of the tubing P ws1, the pressure at the end point of the lower section of the tubing P ws1 equals the reasonable relative density of the condensate gas phase The calculated bottom hole pressure .

[0066] For the upper section of the tubing:

[0067] a) Using the parameters at the wellhead or the starting point, calculate the starting point I ts = Z ts * T ts / P ts

[0068] b) Assign I ts to the end point of the upper section of the tubing I ms = I ts , assume a value, and calculate the pressure at the end point of the upper section of the tubing P ms0 = P ts +0.03415* * h / ( I ms + I ts )

[0069] c) Calculate the end point of the upper section of the tubing I ms1 = Z ms1 * T ms / P ms0 and P ms1 = P ts +0.03415* * h / ( I ms1 + I ts ), where T ms = T ts / 2+ T ws / 2

[0070] d) Compare P ms1 andP ms0 The absolute difference, if greater than the given error ε , then P ms1 is assigned to P ms0 = P ms1 , and the above calculation is repeated until ABS ( P ms1 -P ms0 )< ε , the pressure at the end point of the upper section of the tubing is obtained P ms1 and the corresponding I ms1 .

[0071] For the lower section of the tubing:

[0072] a) First, assign the P ms1 and I ms1 calculated in the previous step to the end point of the lower section of the tubing P ws0 = P ms1 , I ws0 = I ms1 ;

[0073] b) Calculate the end point of the lower section of the tubing P ws1 = P ms1 + 0.03415 * * h / ( I ws0 + I ms1 );

[0074] c) Calculate I ws1 = Z ws1 * T ws / P ws1 , and calculate P ws2 = P ts + 0.2049 * γ G * h / ( I ts+4* I ms1 + I ws1 )

[0075] d) Compare simultaneously P ws2 and P ws1 for the absolute difference, and P ws2 and P ws for the absolute difference. If any one of them is greater than the given error ε , then assign P ws2 to P ws1 = P ws2 , and repeat the above calculations until ABS ( P ws2 -P ws1 ) < ε and ABS ( P ws2 -P ws ) < ε ， the accurate bottom pressure of the lower tubing string is obtained, and at this time P ws2 is the formation pressure that meets the current conditions.

[0076] e) Finally, use the formula , and calculate reversely to obtain the gas-oil ratio.

[0077] Taking the Dina 2 condensate gas field in the Tarim Basin as an example, the static gradients measured at three wells with different years were first taken for calculation.

[0078] The first well: The static temperature and static pressure gradient parameters measured in July 2015 were P ts = 72.24 MPa, T ts = 331.77 K, P ws = 86.13 MPa, T ws = 406.0 K, h = 4200 m, γ o = 0.810, γ g = 0.62, γ G = 0.675,Z is related to P the experimental data has a linear relationship Z = 0.01125 * P + 0.62866. Through the above calculations, after 3 iterations of cyclic iteration, the gas-oil ratio obtained is R go = 11502 m 3 / t. By comparing the actual oil and gas production in the gas reservoir in the current month (reducing the oil and gas production fluctuation errors caused by daily comparison), the calculated gas-oil ratio is 11574 m 3 / / t, and the absolute error between the two is 72 m 3 / t, and the relative error is 0.6%.

[0079] The second well: The static temperature and static pressure gradient parameters measured in June 2016 are P ts = 70.18 MPa, T ts = 333.55 K, P ws = 85.16 MPa, T ws = 409.2 K, h = 4700 m, γ o = 0.810, γ g = 0.62, γ G = 0.672, Z is related to P the experimental data has a linear relationship Z = 0.01125 * P + 0.62866. Through the above calculations, after 4 iterations of cyclic iteration, the gas-oil ratio obtained is R go = 11698 m 3 / t. By comparing the actual oil and gas production in the gas reservoir in the current month (reducing the oil and gas production fluctuation errors caused by daily comparison), the calculated gas-oil ratio is 11614 m 3 / t, and the absolute error between the two is 84 m 3 / t, and the relative error is 0.7%.

[0080] The third well: The static temperature and static pressure gradient parameters measured in April 2017 are P ts = 68.92 MPa, T ts = 325.85 K, P ws = 82.19 MPa, T ws=397.82K ，h =4100m, γ o =0.801, γ g =0.61, γ G =0.671, Z and P there is a linear relationship with the experimental data Z =0.01125 * P +0.62866. Through the above calculations, after 3 iterations of loop, the gas-oil ratio is obtained as R go =11758m 3 / t. By comparing the actually produced oil and gas volumes of the gas reservoir in the current month (reducing the oil and gas production fluctuation errors caused by daily comparison), the calculated gas-oil ratio is 11670 m 3 / t, and the absolute error between the two is 88 m 3 / t, and the relative error is 0.7%.

[0081] From the above three examples, it can be seen that the gas-oil ratio calculated by the method of the present invention is consistent with the actual production data of the gas reservoir, and the change trend is also consistent with the dynamic characteristics of the gas reservoir production, indicating that the method of the present invention is reliable.

Claims

1. A method for calculating the gas-oil ratio of a condensate gas reservoir, characterized in that, Including the following steps: S1, compare the bottom hole pressure obtained by static ladder test with the calculated bottom hole pressure obtained using the assumed relative density of condensate gas phase to obtain a reasonable relative density of condensate gas phase ; ; S2, using the reasonable relative density of condensate gas phase , to calculate the gas-oil ratio R go . The calculation formula is as follows: In the formula, is the relative density of the condensate gas phase; is the relative molecular weight of condensate oil; R go is the gas-oil ratio; is the measured relative density of natural gas; r o For the measured relative density of condensate oil.

2. The gas-oil ratio calculation method for condensate gas reservoirs according to claim 1, characterized in that The method for obtaining the reasonable relative density of the condensate gas phase is as follows: Compare the absolute difference between the bottom-hole pressure P ws and the calculated bottom-hole pressure with the given error ε until the absolute difference is less than the given error ε . The assumed relative density of the condensate gas phase at this time is the reasonable relative density of the condensate gas phase .

3. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 2, wherein The given error ε is 0.01 MPa.

4. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 2, wherein The steps for calculating the bottom hole pressure are as follows: S11, using the parameters at the wellhead or starting point and the assumed relative density of the condensate gas phase to calculate the pressure at the end point of the upper section of the tubing P ms and the intermediate parameters at the end point of the upper section of the tubing I ms ; S12, using the pressure at the end point of the upper tubing P ms , the intermediate parameters at the end point of the upper tubing I ms and the assumed relative density of the condensate gas phase to calculate the pressure at the end point of the lower tubing P ws1 ; when the bottom hole pressure P ws and the calculated bottom hole pressure have an absolute difference less than the given error ε , the pressure at the end point of the lower tubing P ws1 is equal to the calculated bottom hole pressure .

5. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 4, wherein In S11, the pressure at the end point of the upper tubing P ms has the following expression: In the formula, P ts —— the measured wellhead pressure or the pressure at a certain starting depth; h —— the depth from the wellhead to the bottom of the well or the depth from the starting point to the ending point; I ms —— Indicate the intermediate parameter of the end point of the upper tubing section; I ts —— Indicate intermediate parameters of the wellhead or starting point.

6. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 5, characterized in that, The intermediate parameters of the end point of the upper tubing I ms The expression is: In the formula, Z ms —— represents the deviation factor of condensate gas; T ms —— represents the temperature at the end point of the upper tubing section; P ms —— Indicates the pressure at the end point of the upper tubing section.

7. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 5, characterized in that, The intermediate parameters at the wellhead or starting point I ts The expression is: In the formula, Z ts —— represents the deviation factor of condensate gas; T ts —— represents the temperature at the wellhead or the starting point; P ts —— Indicates the pressure at the wellhead or starting point.

8. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 5, wherein The pressure at the end point of the lower section of the tubing P ws1 is expressed as: wherein, I ws —— represents the intermediate parameter of the end point of the lower tubing string.

9. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 8, wherein The intermediate parameters of the end point of the lower section of the tubing I ws The expression is as follows: In the formula, Z ws —— represents the deviation factor of condensate gas; T ws —— represents the temperature at the end point of the lower section of the tubing. P ws —— Indicates the pressure at the end point of the lower tubing string.

10. The method for calculating the gas-oil ratio of a condensate gas reservoir according to claim 1, wherein The relative molecular weight of the condensate oil The calculation formula is as follows: 。

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