Method for improving single-well gas-lift oil production yield of oil reservoir with high gas-oil ratio

Abstract

The invention provides a method for improving the single-well gas-lift oil production yield of a high-gas-oil-ratio oil reservoir, and belongs to the technical field of oil reservoir development. The method comprises the steps that oil wells needing gas lift oil extraction are screened; the gas lift depth is determined by calculating the limit emptying depth; the obtained gas lift depth is compared with the safe emptying depth of the shaft, and a gas lift mode is determined; determining the designed gas lift displacement according to the earlier-stage production materials; compared with the prior art, the method has the advantages that the gas injection amount selection can be made according to the selected gas lift mode pipe column parameters and production parameters, the ground gas injection supercharger type selection is guided, the high gas-oil ratio lift oil production mode design method is formed, and the oil reservoir development efficiency can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of reservoir development, and particularly relates to a method for improving the oil recovery rate of single-well gas lift in high gas-oil ratio reservoirs. Background Art

[0002] Some existing fault-controlled fracture-cavity reservoirs are a special type of complex reservoir in the Ordovician system, which are characterized by deep burial, complex geological features, strong heterogeneity, and rapid decline of reservoir energy; exploration and development results show that the reservoir has rich reserves and great development potential, but the production gas-oil ratio is high.

[0003] The crude oil viscosity in high gas-oil ratio reservoirs is usually high, which means poor fluidity. During the exploitation process, higher pressure is required to overcome the formation pressure and keep the crude oil in a stable state; due to the high content of natural gas in high gas-oil ratio reservoirs and the influence of factors such as viscosity and fluidity, the recovery rate is usually low, and more complex and effective exploitation technologies and management measures need to be taken to improve the recovery rate. Conventional artificial lift is difficult to effectively improve the recovery rate of such reservoirs.

[0004] Gas lift oil production is an oil production method. When the energy supplied by the formation is not enough to lift the crude oil from the bottom of the well to the ground, the oil well stops flowing spontaneously. In order to make the oil well continue to produce oil, gas needs to be artificially injected into the bottom of the well to make the crude oil spray out of the ground. This method is the most adaptable to the production conditions of oil wells among mechanical oil production methods and is mostly used for high-production deep wells and oil wells with complex exploitation conditions. <U+

[0005] However, gas lift oil production still has problems inapplicable to some reservoirs with high development difficulty, such as the Shunbei fault-controlled body reservoir.

[0006] In the paper "Research and Application of Oilfield Gas Lift Technology" published by Su Guojun, the working system of gas lift oil production wells is adjusted according to the production change law of oil and gas wells. Through the analysis of factors such as the liquid production volume, liquid characteristics, working pressure in the well, liquid production index value, injection gas supply volume, lifting depth, well structure, injection gas working pressure, and production environment of oil and gas wells, the design of the working system of gas lift technology is carried out; the principle of gas lift technology is discussed, and then the gas lift product design is carried out according to the actual situation of a certain oilfield, and Well X is selected for experiments. It is found that after adopting the gas lift technology, the liquid production reaches more than 200m , ,

[0005] , 3 ,

[0007] , 3 , ,

[0006] , / d, and the gas production rises to 1440m 3 / d. Both the gas production volume and the liquid production volume have increased significantly, and the production effect is obvious, which can provide reference for peers.

[0007] The above paper has carried out a large number of analyses and examples on gas lift technology. However, it has not discussed the optimization method of adaptability parameters of gas lift lifting technology for high gas-oil ratio reservoirs with high recovery difficulty.

[0008] Therefore, how to provide a method for improving the oil recovery rate of single-well gas lift in high gas-oil ratio reservoirs is a key issue for those skilled in the art to study. Summary of the Invention

[0009] In view of the lack in the prior art of a gas lift oil production method that can be applied to high gas-oil ratio reservoirs and effectively improve the oil recovery rate, the present invention provides a method for improving the oil recovery rate of single-well gas lift in high gas-oil ratio reservoirs. For single wells with different wellbore conditions, different liquid production properties, and different liquid production capacities, the adaptability of different artificial lift methods is summarized and evaluated, an evaluation system for selecting wells suitable for single-well gas lift in high gas-oil ratio reservoirs is established, the gas lift process parameters are reasonably controlled, and the gas lift production is optimized to achieve the purpose of increasing the recovery rate.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for improving the oil recovery rate of single-well gas lift in high gas-oil ratio reservoirs, comprising the following steps:

[0012] S1. Screening the oil wells that need gas lift oil production;

[0013] S2. Determining the gas lift depth by calculating the ultimate drawdown depth;

[0014] S3. Comparing the gas lift depth obtained in step S2 with the safe drawdown depth of the wellbore to determine the gas lift method;

[0015] S4. Determining the designed gas lift displacement according to the previous production data.

[0016] Preferably, the screening method in step S1 is:

[0017] Determined based on the designed shut-in liquid level, liquid production per unit pressure drop, and gas-liquid ratio.

[0018] Further preferably, the range of the designed shut-in liquid level is 3000 - 5000 m;

[0019] The range of the liquid production per unit pressure drop is 1000 - 5000 m 3 / MPa;

[0020] The range of the gas-liquid ratio is 350 - 7000 m 3 / m 3 .

[0021] Preferably, the method for calculating the ultimate drawdown depth in step S2 includes: taking the smaller value between the maximum allowable drawdown depth of the casing and the maximum allowable drawdown depth of the formation.

[0022] Further preferably, the calculation method of the maximum allowable drawdown depth of the casing is:

[0023] P i ×1 / f i安全系数 =P 地层压力i -P i临界内压

[0024] P wi临界压力 =P i临界内压 +(H w -H i )×g 梯度

[0025] P w允许最低压力 =MAX(P wi临界压力 )

[0026] H max1 =H w -P w允许最低压力 ×g 梯度

[0027] In the formula, P i represents the external collapse pressure resistance of the i-th stage casing, f i安全系数 represents the safety factor of the i-th stage casing, which is a constant between 1.1 and 1.3 according to the metal loss value, P 地层压力i represents the formation pressure during drilling at the bottom boundary of the i-th stage casing, P i临界内压 represents the minimum allowable internal pressure value of the i-th stage casing, P wi临界压力 represents the minimum allowable flowing pressure value of the i-th stage casing, H w represents the wellbore depth, H i represents the setting depth of the i-th stage casing, g 梯度 represents the production gradient of the oil well, P w允许最低压力 represents the minimum formation pressure allowed under the safety of the casing, H max1 represents the maximum allowable emptying depth under the safety of the casing.

[0028] Further preferably, the calculation method of the maximum allowable emptying depth allowed by the formation safety is:

[0029] H max2 =(P - Δp)×g 梯度

[0030] In the formula, H max2 represents the maximum allowable emptying depth allowed by the formation safety, P represents the formation static pressure, and Δp takes a constant value of 25 MPa.

[0031] Preferably, the method for determining the gas lift depth in step S2 includes the steps of: calculating the gas gradient above the gas lift point using the ideal gas state equation, calculating the gas lift emptying pressure difference based on the original pressure and the flowing pressure after emptying, calculating the formation starting pressure difference with a starting pressure of 2 MPa, and requiring that the flowing pressure value calculated at the maximum gas lift depth and the starting emptying depth H q ≥P q -2, Pq Indicates the starting depletion depth H q of the static pressure below.

[0032] Further preferably, the method for determining the gas lift depth in step S2 further includes the steps: If the limit depletion depth is greater than the starting depletion depth, the limit depletion depth is the gas lift depth; if the limit depletion depth is less than the starting depletion depth, the starting depletion depth is the gas lift depth.

[0033] Preferably, the basis for determining the gas lift method in step S3 is: the magnitudes of the limit depletion depth and the starting depletion depth.

[0034] Further preferably, the method for determining the gas lift method in step S3 is:

[0035] If the starting depletion depth is less than the limit depletion depth, a single flow valve or perforated gas lift oil production method is adopted;

[0036] If the starting depletion depth is greater than the limit depletion depth, a concentric continuous tubing or concentric small tubing is lowered with a packer string in the original well.

[0037] Preferably, the designed gas lift displacement in step S4 is: the allowable minimum displacement plus 400 m 3 / h.

[0038] Further preferably, the allowable minimum displacement is determined by calculating the critical liquid-carrying minimum gas injection displacement using the Li Min ellipsoid model.

[0039] Even more preferably, the formula for calculating using the Li Min ellipsoid model is:

[0040]

[0041]

[0042] In the formula, v g - critical liquid-carrying flow velocity, m / s;

[0043] σ - gas-water interfacial tension, N / m;

[0044] ρ1 - formation water density, kg / m 3 ;

[0045] ρ g - natural gas density, kg / m 3 ;

[0046] C d - drag coefficient, taking 1.0;

[0047] q c - critical liquid-carrying flow rate, 10 4 m3 / d;

[0048] A - Cross - sectional area of tubing, m 2 ;

[0049] P - Bottom - hole flowing pressure, MPa;

[0050] Z - Gas deviation factor;

[0051] T - Bottom - hole temperature, K.

[0052] The present invention also provides an application of the above - mentioned method in gas - lift oil production.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] Based on the single - well gas - oil ratio, the mechanical - lift depth capacity and the liquid - supply capacity, and combined with the allowable depleted depth of the wellbore, the present invention formulates an optimized gas - lift oil - production method. The gas - injection volume selection can be determined according to the string parameters and production parameters of the selected gas - lift method, guiding the selection of surface gas - injection booster pumps, forming a design method for gas - lift oil - production with a high gas - oil ratio, which can improve the development efficiency of the oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a graph of the minimum gas - injection displacement for critical liquid - carrying in a single well in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] Embodiment A method for improving the recovery rate of single - well gas - lift oil production in high - gas - oil - ratio reservoirs

[0057] S1. Screening the oil wells that need gas - lift oil production

[0058] According to the production conditions of the previous sucker - rod pumped wells and electric - submersible pump wells in the Shunbei Oilfield, determine that the designed liquid level at which the well stops flowing is 3000 - 5000 m, the liquid production per unit pressure drop is 1000 - 5000 m 3 / MPa, and the gas - liquid ratio is 350 - 7000 m 3 / m 3 of the oil wells are selected for gas - lift oil production.

[0059] S2. Determining the gas - lift depth by calculating the ultimate depleted depth

[0060] Combining the liquid level at which the well stops flowing, casing damage and calculation, screening the weak points of the casing. Based on the liquid - drainage requirements of the oil reservoir and considering that the booster pump equipment can meet a maximum gas - injection pressure of more than 40 MPa, the gas - lift depth is set by calculating the ultimate depleted depth:

[0061] P i ×1 / f i安全系数 = P 地层压力i - P i临界内压

[0062] P wi临界压力 =P i临界内压 +(H w -H i )×g 梯度

[0063] P w允许最低压力 =MAX(P wi临界压力 )

[0064] H max1 =H w -P w允许最低压力 ×g 梯度

[0065] Where P i Indicates the external extrusion pressure of the i-th level casing, f i安全系数 It represents the safety factor of the i-th level casing, which is a constant between 1.1 and 1.3 according to the gold loss value. 地层压力i represents the formation pressure during drilling at the bottom of the i-th level casing, P i临界内压 Indicates the minimum allowable internal pressure value of the i-th level casing, P wi临界压力 Indicates the minimum allowable flow pressure value of the i-th level casing, H w Indicates the wellbore depth, H i Indicates the depth of the casing at level i, g 梯度 represents the oil well production gradient, P w允许最低压力 Indicates the minimum formation pressure allowed under casing safety, H max1 Indicates the maximum hollowing depth allowed for casing safety.

[0066] H max2 =(P-Δp)×g 梯度

[0067] Where H max2 It represents the maximum allowable hollowing depth of the formation for safety, P represents the static pressure of the formation, and Δp represents the maximum allowable production pressure difference. Previous studies have shown that the pressure difference value to ensure stable production of the formation should not exceed 25MPa, so Δp is taken as a constant of 25MPa.

[0068] Maximum hollowing depth H max H max1 With H max2 The smaller value.

[0069] The ideal gas state equation PV = nRT is used to calculate the gas gradient above the gas lift point. The gas lift hollowing pressure difference is calculated based on the original pressure and the flow pressure after hollowing. The formation starting pressure difference is calculated with a starting pressure of 2 MPa. The hollowing depth H is required to be started at the maximum gas lift depth. q Calculated flow pressure value ≥ P q -2, P q Indicates the starting hollowing depth H q The static pressure under.

[0070] Calculate the ultimate hollowing depth H based on wellbore integrity max Starting hollowing depth H t Set gas lift depth: If H q <H max , then the gas lift depth is H max , if H q <H max , then the gas lift depth is H q .

[0071] S3. Determine the gas lift method

[0072] If H q <H max , that is, the gas lift startup hollowing depth is less than the wellbore safety limit hollowing depth. At this time, there is no risk to the wellbore integrity when the gas lift injection point is hollowed out, and the check valve / perforation gas lift oil production method can be used.

[0073] If H q >H max That is, the gas lift starting hollowing depth is greater than the wellbore safety limit hollowing depth. At this time, if a check valve is used, it is easy to cause casing damage or wellbore instability. The original well should be equipped with a packer string and run into a concentric continuous tubing or a concentric small tubing for gas lift.

[0074] S4. Determine the designed gas lift displacement based on previous production data

[0075] According to the Li Min ellipsoid model, the critical liquid-carrying gas volume of a gas well is calculated as follows:

[0076]

[0077]

[0078] Where, v g -critical liquid carrying velocity, m / s;

[0079] σ-air-water interfacial tension, N / m;

[0080] ρ1-formation water density, kg / m 3 ;

[0081] ρ g -Natural gas density, kg / m 3 ;

[0082] C d -Drag coefficient, take 1.0;

[0083] q c - Critical liquid carrying capacity, 10 4 m 3 / d;

[0084] A - Cross - sectional area of tubing, m 2 ;

[0085] P - Bottom - hole flowing pressure, MPa;

[0086] Z - Gas deviation factor;

[0087] T - Bottom - hole temperature, K;

[0088] The minimum gas injection displacement for critical liquid - carrying of different single wells is calculated according to the formula and a chart is formed, as Figure 1 shown.

[0089] On the basis of Figure 1 this, the highest point of the designed chart is taken as the allowable minimum gas injection displacement, and the designed gas injection displacement is an additional 400 m 3 / h on the basis of the allowable minimum displacement, which is used as the selection standard for surface compressors.

[0090] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Simple modifications or equivalent replacements made by those of ordinary skill in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for improving the gas lift oil recovery rate of a single well in a high gas-oil ratio oil reservoir, characterized in that: The following steps are involved: S1. Screening of oil wells requiring gas lift production; S2. Determine the gas lift depth by calculating the ultimate hollowing depth; S3. Compare the gas lift depth obtained in step S2 with the safe hollowing depth of the wellbore to determine the gas lift method; S4. Determine the designed gas lift displacement based on previous production data.

2. The method according to claim 1, characterized in that The screening method in step S1 is: It is determined based on the designed stop-spray liquid level, liquid production per unit pressure drop and gas-liquid ratio.

3. The method according to claim 2, characterized in that The designed stop-spraying liquid level range is 3000-5000m; The unit pressure drop liquid production range is 1000-5000m 3 / MPa; The gas-liquid ratio range is 350-7000m 3 / m 3 .

4. The method according to claim 1, wherein The method for calculating the ultimate hollowing depth in step S2 includes: taking the smaller value of the maximum hollowing depth allowed by casing safety and the maximum hollowing depth allowed by formation safety.

5. The method according to claim 4, characterized in that The calculation method of the maximum hollowing depth allowed for casing safety is: P i ×1 / f i安全系数 =P 地层压力i -P i临界内压 P wi临界压力 =P i临界内压 +(H w -H i )×g 梯度 P w允许最低压力 =MAX(P wi临界压力 ) H max1 =H w -P w允许最低压力 ×g 梯度 Where P i Indicates the external extrusion pressure of the i-th level casing, f i安全系数 It represents the safety factor of the i-th level casing, which is a constant between 1.1 and 1.3 according to the gold loss value. 地层压力i represents the formation pressure during drilling at the bottom of the i-th level casing, P i临界内压 Indicates the minimum allowable internal pressure value of the i-th level casing, P wi临界压力 Indicates the minimum allowable flow pressure value of the i-th level casing, H w Indicates the wellbore depth, H i Indicates the depth of the casing at level i, g 梯度 represents the oil well production gradient, P w允许最低压力 Indicates the minimum formation pressure allowed under casing safety, H max1 Indicates the maximum hollowing depth allowed for casing safety.

6. The method according to claim 5, characterized in that The calculation method of the maximum hollowing depth allowed by the stratum safety is: H max2 =(P-Δp)×g 梯度 Where H max2 It represents the maximum hollowing depth allowed for stratum safety, P represents the static pressure of stratum, and Δp is taken as a constant of 25 MPa.

7. The method according to claim 1, characterized in that The method for determining the gas lift start-up hollowing depth in step S2 comprises the following steps: using the ideal gas state equation to calculate the gas gradient above the gas lift point; calculating the gas lift hollowing pressure difference based on the original pressure and the flow pressure after hollowing; calculating the formation start-up pressure difference with a starting pressure of 2 MPa; requiring the calculated flow pressure value at the start-up hollowing depth at the maximum gas lift depth to be ≥ P q -2, P q Indicates the starting hollowing depth H q The static pressure below.

8. The method according to claim 7, characterized in that The method for determining the gas lift depth in step S2 further includes the following steps: if the limit hollowing depth is greater than the starting hollowing depth, the limit hollowing depth is the gas lift depth; if the limit hollowing depth is less than the starting hollowing depth, the starting hollowing depth is the gas lift depth.

9. The method according to claim 1, characterized in that The basis for determining the gas lift mode in step S3 is: the size of the limit hollowing depth and the starting hollowing depth.

10. The method according to claim 1, characterized in that The method for determining the gas lift mode in step S3 is: If the starting hollowing depth is less than the limit hollowing depth, a check valve or perforation gas lift oil recovery method is used; If the starting hollowing depth is greater than the limit hollowing depth, the original well with a packer string is run into the concentric coiled tubing or concentric small tubing.

11. The method according to claim 1, wherein The designed gas lift displacement in step S4 is: the minimum displacement is allowed to be increased by 400m 3 / h.

12. The method according to claim 11, characterized in that The allowable minimum displacement is determined by calculating the critical liquid-carrying minimum gas injection displacement using the Li Min ellipsoid model.

13. The method according to claim 12, characterized in that The formula for calculating using the Li Min ellipsoid model is: Where, v g -critical liquid-carrying velocity, m / s; σ-gas-water interfacial tension, N / m; ρ1-formation water density, kg / m 3 ; ρ g -Natural gas density, kg / m 3 ; C d -Drag coefficient, take 1.0; q c - Critical liquid carrying capacity, 10 4 m 3 / d; A-oil pipe cross-sectional area, m 2 ; P-bottomhole flowing pressure, MPa; Z-natural gas deviation factor; T-bottomhole temperature, K.

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