Polymer flooding method based on pressure pulse

Abstract

The present invention proposes a polymer displacement method based on pressure pulses, including: injecting polymer from a target well into a reservoir in a pressure pulse manner; generating a pressure pulse wave when injecting the polymer in a pressure pulse manner; when the injected polymer is within the effective range of the pressure pulse, the pressure pulse wave reduces the viscosity of the injected polymer, and the polymer with reduced viscosity is subjected to displacement; when the injected polymer is outside the effective range of the pressure pulse, the polymer viscosity is restored, and the polymer with restored viscosity is subjected to displacement. The present invention utilizes pressure pulse polymer injection to simultaneously achieve the purpose of improving the polymer injection capacity in the near-wellbore zone and polymer depth displacement. The present invention has low cost, can economically and practically achieve polymer depth displacement, and improve polymer displacement recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum engineering, relates to a pressure pulse oil recovery technology, and in particular to a polymer flooding method based on pressure pulse. Background Art

[0002] my country has abundant low permeability oil reservoir resources, but the water flooding recovery rate of low permeability oil reservoirs is usually only about 20%. The main reason is that low permeability oil reservoirs are often accompanied by a certain degree of heterogeneity, and the water flooding sweep efficiency is poor. my country usually uses polymer flooding to expand the sweep efficiency, but the flooding injection capacity of polymers in low permeability oil reservoirs is poor, and it is easy to stay in the near-well area, making it difficult to achieve deep flooding. Improving the injection capacity of polymers is of great significance for the promotion and application of polymer flooding technology in low permeability oil reservoirs. Therefore, a polymer flooding method that improves the near-well injection capacity and is low-cost is needed.

[0003] Specifically, with the development of physical oil recovery technology, low-frequency pressure pulse technology has gradually become a hot spot for domestic and foreign oil companies to compete for research and development due to its advantages such as convenient construction and economic reliability. Some scholars have studied the influence of pressure pulse waves on polymer viscosity: Johnston (1971) found that pressure pulse waves can reduce polymer viscosity; Gadiev (1977) used a viscometer to measure the flow changes of polyacrylamide solution under different excitation frequencies, and found that under the action of oscillating waves for 6 hours, the flow rate increased by 0.5-1 times, indicating that low-frequency waves can change the viscosity of polymer solutions during excitation. Existing studies have found that in the low-frequency vibration wave field, the molecular structure of polymers will undergo periodic arrangement and combination under the action of oscillation, thereby reducing the viscosity of polymer fluids. When the pressure pulse amplitude is reduced or stopped, the viscosity of the polymer fluid can be restored. Therefore, pressure pulse technology can effectively improve the injection capacity of polymers, while having relatively little effect on the molecular weight of polymers. Therefore, the present invention proposes a polymer adjustment and displacement method with strong injection capacity and low cost. Summary of the invention

[0004] The purpose of the present invention is to provide a polymer flooding method with good injection capability and low cost.

[0005] In order to achieve the above-mentioned object, the present invention provides a polymer displacement method based on pressure pulse, comprising: injecting a polymer from a target well into a reservoir in a pressure pulse manner; generating a pressure pulse wave when injecting the polymer in the pressure pulse manner; when the injected polymer is within an effective range of the pressure pulse, the pressure pulse wave reduces the viscosity of the injected polymer, and the polymer with reduced viscosity is subjected to displacement; when the injected polymer is outside the effective range of the pressure pulse, the viscosity of the polymer is restored, and the polymer with restored viscosity is subjected to displacement.

[0006] Optionally, the intensity of the pressure pulse wave gradually decreases as the propagation distance of the pressure pulse wave increases.

[0007] Optionally, the viscosity of the polymer is inversely proportional to the intensity of the pressure pulse wave.

[0008] Optionally, when the injected polymer is within the effective range of the pressure pulse, the viscosity of the injected polymer increases with increasing distance from the injection well; when the injected polymer is outside the effective range of the pressure pulse, the viscosity of the injected polymer recovers.

[0009] Optionally, the polymer is injected into the reservoir from the target well in a continuous injection manner or a slug manner.

[0010] Optionally, after the polymer is injected into the reservoir from the target well in a slug manner for a first preset period of time, water is injected into the reservoir from the target well in a pressure pulse manner.

[0011] Optionally, water is injected from the target well into the reservoir in a constant pressure manner, a constant flow manner or a regular cycle manner, and the injected water includes formation water, diluted formation water, fresh water, polymer dilution and aqueous solution.

[0012] Optionally, the pressure pulse is generated by an excitation wave method, a fluid impact method and a rotational hydraulic oscillation method.

[0013] Optionally, the frequency of the pressure pulse is 0.002 Hz-200 Hz.

[0014] Optionally, the polymer is polyacrylamide, and the concentration of the polymer is 100 mg / L-10000 mg / L.

[0015] The beneficial effects of the present invention are as follows: the polymer flooding method based on pressure pulse of the present invention injects polymer into the reservoir in the form of pressure pulse, and improves the injection capacity of the polymer near the wellbore zone by using the pressure pulse wave. At the same time, as the polymer moves away from the injection well, the energy of the pressure pulse wave decays rapidly, and the viscosity of the polymer gradually recovers, thereby achieving the purpose of polymer deep flooding. The present invention has low cost, can economically and practically realize polymer deep flooding, and improve polymer flooding oil recovery.

[0016] The present invention has other features and advantages, which will be apparent from or will be described in detail in the accompanying drawings and the following specific embodiments incorporated herein, which together serve to explain the specific principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0018] Figure 1 A flow chart of a polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown.

[0019] Figure 2 A polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown, which schematically illustrates the attenuation of the amplitude of the pressure pulse with the propagation distance.

[0020] Figure 3 A polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown as a schematic diagram of how polymer viscosity changes with the amplitude of pressure pulses.

[0021] Figure 4 A continuous polymer flooding of a polymer flooding method based on pressure pulse according to an embodiment of the present invention shows a schematic diagram of the change of average pressure at different polymer injection rates.

[0022] Figure 5 A polymer flooding method based on pressure pulse according to an embodiment of the present invention includes water flooding after polymer injection, which shows a schematic diagram of the change of average pressure at different polymer injection rates. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0024] A polymer displacement method based on pressure pulses according to the present invention comprises: injecting a polymer from a target well into a reservoir in a pressure pulse manner; generating a pressure pulse wave when injecting the polymer in a pressure pulse manner; when the injected polymer is within an effective range of the pressure pulse, the pressure pulse wave reduces the viscosity of the injected polymer, and the polymer with reduced viscosity is subjected to displacement; when the injected polymer is outside the effective range of the pressure pulse, the polymer viscosity is restored, and the polymer with restored viscosity is subjected to displacement.

[0025] The polymer is injected into the reservoir in the form of pressure pulses. The pressure pulse wave can reduce the viscosity of the polymer, thereby improving the injection capacity of the polymer near the wellbore. The higher the amplitude of the pressure pulse, the faster the viscosity of the polymer decreases. Therefore, in the area near the injection well, the viscosity of the polymer decreases. The polymer with reduced viscosity is adjusted and driven, and the adjustment and drive effect is low. As the distance between the polymer and the injection well increases, the amplitude of the pressure pulse gradually decays with the propagation of distance. The energy of the pressure pulse wave received by the polymer decays rapidly, and the viscosity of the polymer gradually recovers. Therefore, in the area far from the injection well, the amplitude of the pressure pulse becomes smaller, and the viscosity of the polymer gradually recovers. The polymer with gradually recovered viscosity achieves the effect of profile adjustment and achieves the purpose of polymer adjustment and drive.

[0026] According to an exemplary embodiment, a polymer drive method based on pressure pulses improves the injection capacity of the polymer near the wellbore zone by utilizing pressure pulse waves. At the same time, as the distance from the injection well increases, the energy of the pressure pulse waves decays rapidly and the viscosity of the polymer gradually recovers, thereby achieving the purpose of deep polymer drive. The present invention has the effect of deep profile adjustment and is low in cost, and can improve the polymer sweep efficiency economically and practically.

[0027] As an alternative, the intensity of the pressure pulse wave gradually decreases as the propagation distance of the pressure pulse wave increases.

[0028] Alternatively, the viscosity of the polymer is inversely proportional to the intensity of the pressure pulse wave.

[0029] Alternatively, when the injected polymer is within the effective range of the pressure pulse, the viscosity of the injected polymer increases with increasing distance from the injection well; when the injected polymer is outside the effective range of the pressure pulse, the viscosity of the injected polymer recovers.

[0030] Specifically, the intensity of the pressure pulse gradually decays with increasing distance from the injection well, and the viscosity of the polymer gradually increases with increasing distance from the injection well. When the distance to the injection well is close, the intensity of the pressure pulse wave is high and the viscosity of the polymer is low. When the distance to the injection well is far, the intensity of the pressure pulse wave is low and the viscosity of the polymer gradually recovers.

[0031] Alternatively, the polymer may be injected into the reservoir from the target wellbore in a continuous injection or slug manner.

[0032] Specifically, the polymer is injected into the reservoir of the target well in a continuous injection manner or in a polymer plug manner in a pressure pulse manner; when the distance between the injected polymer and the target well is small, the viscosity of the polymer decreases and the injection capacity of the polymer increases; when the distance between the polymer and the target well increases, the energy of the pressure pulse wave received by the polymer decays rapidly and the viscosity of the polymer gradually recovers.

[0033] As an alternative, after the polymer is injected into the reservoir from the target well in a slug manner for a first preset period of time, water is injected into the reservoir from the target well in a pressure pulse manner.

[0034] Specifically, the amount of polymer required to adjust the water absorption profile and polymer displacement of crude oil by continuous polymer injection is large and the cost is relatively expensive. Therefore, the polymer slug is injected into the reservoir from the target well in a pressure pulse manner. After a period of time, water is then injected into the reservoir from the target well in a pressure pulse manner. After the polymer is gradually moved away from the injection well by water drive, the viscosity of the polymer gradually recovers as the energy of the pressure pulse wave decays rapidly, thereby achieving the purpose of polymer depth adjustment and displacement. Preferably, the amount of the polymer slug is greater than 0.1PV.

[0035] Specifically, after the polymer is injected into the reservoir in the form of a slug from the target well by pressure pulse for a period of time, water is then injected into the reservoir from the target well by pressure pulse. When the polymer slug reaches a specific position, that is, when the polymer reaches the target area of ​​deep drive, the pressure pulse displacement is stopped to further quickly restore the polymer viscosity, and water is injected into the reservoir from the target well by any conventional water injection method to achieve the effect of fixed-point profile control.

[0036] Subsequent water injection by pressure pulse still has a certain effect of reducing polymer viscosity. If the pressure pulse displacement is stopped after polymer displacement, the polymer viscosity will increase rapidly in the vicinity of the injection well, thereby blocking the formation. Therefore, after polymer displacement, it is impossible to directly inject water from the target well into the reservoir by any conventional water injection method.

[0037] As an alternative, the pressure pulse based polymer flooding method further includes injecting water into the reservoir in a constant pressure mode, a constant flow mode or a conventional cycle mode.

[0038] Specifically, water flooding is performed after the polymer is injected, and water can be injected by pressure pulse mode or by conventional water injection mode.

[0039] As an option, the injected water includes formation water, diluted formation water, fresh water, polymer dilution and aqueous solution.

[0040] As an optional solution, the pressure pulse generation method includes an excitation wave method, a fluid impact method and a rotational hydraulic oscillation method.

[0041] Specifically, common ways to generate pressure pulses include excitation waves, fluid impact, rotary hydraulic oscillation, etc. Preferably, a fluid impact device is used to achieve pressure pulse displacement to reduce the effect of shearing on the molecular weight of the polymer.

[0042] As an option, the frequency of the pressure pulses is 0.002 Hz - 200 Hz.

[0043] Specifically, the pressure pulse is a low-frequency pressure pulse, preferably 0.002 Hz-200 Hz.

[0044] Alternatively, the polymer is polyacrylamide.

[0045] Alternatively, the concentration of the polymer is 100 mg / L to 10000 mg / L.

[0046] Specifically, the polymer is polyacrylamide, the concentration is generally 100-10000 mg / L, the polymer molecular weight is 500,000-50 million, and the polymer slug injection volume is 0.1-0.9 PV.

[0047] Example

[0048] Figure 1 A flow chart of a polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown. Figure 2 A polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown, which schematically illustrates the attenuation of the amplitude of the pressure pulse with the propagation distance.

[0049] Figure 3 A polymer displacement method based on pressure pulses according to an embodiment of the present invention is shown as a schematic diagram of how polymer viscosity changes with the amplitude of pressure pulses. Figure 4 A continuous polymer flooding of a polymer flooding method based on pressure pulse according to an embodiment of the present invention shows a schematic diagram of the change of average pressure at different polymer injection rates. Figure 5 A polymer flooding method based on pressure pulse according to an embodiment of the present invention includes water flooding after polymer injection, which shows a schematic diagram of the change of average pressure at different polymer injection rates.

[0050] like Figure 1 As shown, the polymer flooding method based on pressure pulse comprises:

[0051] S102: injecting polymer from the target well into the reservoir in a pressure pulse manner;

[0052] S104: generating a pressure pulse wave when injecting the polymer in a pressure pulse manner;

[0053] S106: When the injected polymer is within the effective range of the pressure pulse, the pressure pulse wave reduces the viscosity of the injected polymer, and the polymer with reduced viscosity is subjected to drive adjustment;

[0054] S108: When the injected polymer is outside the effective range of the pressure pulse, the polymer viscosity is restored, and the polymer with restored viscosity is adjusted and driven.

[0055] Among them, the intensity of the pressure pulse wave gradually decreases as the propagation distance of the pressure pulse wave increases.

[0056] Among them, the viscosity of the polymer is inversely proportional to the intensity of the pressure pulse wave.

[0057] When the injected polymer is within the effective range of the pressure pulse, the viscosity of the injected polymer increases with the increase of the distance from the injection well; when the injected polymer is outside the effective range of the pressure pulse, the viscosity of the injected polymer recovers.

[0058] The polymer is injected into the reservoir from the target well in a continuous injection mode or a slug mode.

[0059] Wherein, after the polymer is injected into the reservoir from the target well in a plug manner for a first preset period of time, water is injected into the reservoir from the target well in a pressure pulse manner.

[0060] Wherein, water is injected into the reservoir from the target well in a constant pressure mode, a constant flow mode or a conventional cycle mode, and the injected water includes formation water, diluted formation water, fresh water, polymer dilution liquid and aqueous solution.

[0061] Among them, the generation methods of pressure pulses include excitation wave method, fluid impact method and rotational hydraulic oscillation method.

[0062] Among them, the frequency of the pressure pulse is 0.002Hz-200Hz.

[0063] The polymer is polyacrylamide, and the concentration of the polymer is 100 mg / L-10000 mg / L.

[0064] When the distance between the injected polymer and the target well is close, the viscosity of the polymer decreases under the action of the pressure pulse wave and the injection capacity is enhanced; when the polymer is far away from the injection well, the viscosity of the polymer gradually recovers, thereby achieving the purpose of polymer profile control.

[0065] Specifically, a sand filling pipe experiment was conducted to verify the polymer displacement method based on pressure pulses based on the conditions of a low permeability oil reservoir in China. The average formation permeability of the target reservoir is 35mD, the average porosity is 17.5%, the formation pressure is 10.4MPa, the formation temperature is 65℃, and the average formation water mineralization is 6000mg / L.

[0066] The polymer is continuously injected into the sand filling pipe in the form of pressure pulses. The pressure pulse wave can reduce the viscosity of the polymer and improve the injection capacity of the polymer in the near-wellbore area. When the polymer is continuously injected and gradually moves away from the injection well, the energy of the pressure pulse wave decays rapidly and the viscosity of the polymer gradually recovers, thereby achieving the effect of depth profile adjustment and expansion of swept volume.

[0067] The pressure pulse is generated by a piston pressure pulse pump. The displacement of the pressure pulse is 0.1mL / min, and the displacement pressure difference is 3.8-4.5MPa. The frequency of the pressure pulse is 20Hz, and the working pressure is 3-35MPa. The amplitude of the pressure pulse attenuates with the propagation distance, such as Figure 2 As shown in the figure, the increase is the change in the instantaneous flow rate relative to the average flow rate in this experiment.

[0068] The polymer is polyacrylamide with a molecular weight of 8 million and a polymer concentration of 1500 mg / L. The change of polymer viscosity with the amplitude of pressure pulse wave was measured by capillary viscometer. The results are as follows: Figure 3 As shown in Figure 2, with the increase of pressure pulse amplitude, the shear rate of the polymer increases rapidly and the viscosity of the polymer decreases significantly.

[0069] The sand filling pipe is 1m long, 25mm in diameter, filled with 200-mesh quartz sand, and has a permeability of 10-100mD. There are three pressure measuring points on the sand filling pipe, which divides the sand filling pipe into four equal sections.

[0070] During continuous polymer flooding, at different polymer injection rates, the average pressure recorded at each pressure measuring point is as follows: Figure 4 So, by Figure 4 It can be seen that the closer to the outlet, the greater the pressure change, indicating that after the polymer moves away from the injection well, the viscosity gradually increases as the pressure pulse intensity decreases, which proves that polymer flooding based on pressure pulses can achieve deep profile control of polymers.

[0071] Based on the conditions of another domestic low-permeability reservoir, a 1m sand-filled pipe experiment was conducted to verify the polymer flooding method based on pressure pulse. The average formation permeability of the target reservoir is 35mD, the average porosity is 17.5%, the formation pressure is 10.4MPa, the formation temperature is 65℃, and the average formation water mineralization is 6000mg / L.

[0072] A 0.3PV polymer plug is injected into a sand-filled pipe filled with 200 mesh quartz sand by pressure pulse. The pressure pulse wave can reduce the viscosity of the polymer and improve the injection capacity of the polymer in the near-wellbore area. Subsequently, pressure pulse water injection is performed. When the injected polymer gradually moves away from the injection well, the energy of the pressure pulse wave decays rapidly, and the viscosity of the polymer gradually recovers. When the polymer approaches the target area of ​​deep profile adjustment, conventional water drive is used instead. At this time, the viscosity of the polymer recovers rapidly, achieving the effect of deep profile adjustment and expanding the swept volume.

[0073] The pressure pulse wave is generated by a piston pressure pulse pump, the displacement of the pressure pulse is 0.1mL / min, and the displacement pressure difference is 3.8-4.5MPa. The frequency of the pressure pulse wave is 20Hz, and the working pressure is 3-35MPa. The attenuation of the pressure pulse amplitude with the propagation distance is as follows: Figure 2 As shown in the figure, the increase is the change in the instantaneous flow rate relative to the average flow rate in this experiment.

[0074] The polymer is polyacrylamide with a molecular weight of 8 million and a polymer concentration of 1500 mg / L. The change of polymer viscosity with the amplitude of pressure pulse wave was measured by capillary viscometer. The results are as follows: Figure 3 As shown in Figure 2, with the increase of pressure pulse amplitude, the shear rate of the polymer increases rapidly and the viscosity of the polymer decreases significantly.

[0075] The sand filling pipe is 1m long, 25mm in diameter, filled with 200-mesh quartz sand, and has a permeability of 10-100mD. There are three pressure measuring points on the sand filling pipe, which divides the sand filling pipe into four equal sections.

[0076] During the water flooding process after polymer injection, the average pressure recorded at each pressure measuring point at different polymer injection rates is shown in Figure 2. Figure 4 As shown. Figure 4 It can be seen that the closer the polymer is to the outlet, the greater the pressure gradient generated by the polymer, which means that after the polymer moves away from the injection well, the viscosity gradually increases as the pressure pulse intensity decreases, thus proving that polymer flooding based on pressure pulses can achieve deep profile control of the polymer.

[0077] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A polymer displacement method based on pressure pulse, characterized in that: include: The polymer is injected into the reservoir from the target well in a pressure pulse manner; When the polymer is injected in the pressure pulse manner, a pressure pulse wave is generated; When the injected polymer is within the effective range of the pressure pulse, the pressure pulse wave reduces the viscosity of the injected polymer, and the polymer with reduced viscosity is adjusted and driven; When the injected polymer is outside the effective range of the pressure pulse, the viscosity of the polymer is restored, and the polymer after the viscosity is restored is subjected to drive adjustment; The intensity of the pressure pulse wave gradually decreases as the propagation distance of the pressure pulse wave increases; The viscosity of the polymer is inversely proportional to the intensity of the pressure pulse wave; When the injected polymer is within the effective range of the pressure pulse, the viscosity of the injected polymer increases with the distance from the injection well; When the injected polymer is outside the effective range of the pressure pulse, the viscosity of the injected polymer is restored; The frequency of the pressure pulse is 0.002Hz-200Hz; The polymer is polyacrylamide, and the concentration of the polymer is 100 mg / L-10000 mg / L.

2. The polymer displacement method based on pressure pulse according to claim 1, characterized in that: The polymer is injected into the reservoir from the target well in a continuous injection mode or a slug mode.

3. The polymer displacement method based on pressure pulse according to claim 2, characterized in that: After the polymer is injected into the reservoir from the target well in a slug manner for a first preset period of time, water is injected into the reservoir from the target well in a pressure pulse manner.

4. The polymer displacement method based on pressure pulse according to claim 3, characterized in that: Water is injected from the target well into the reservoir in a constant pressure mode, a constant flow mode or a conventional cycle mode, and the injected water includes formation water, diluted formation water, fresh water, polymer dilution solution and aqueous solution.

5. The polymer displacement method based on pressure pulse according to claim 1, characterized in that: The generation methods of the pressure pulses include an excitation wave method, a fluid impact method and a rotational hydraulic oscillation method.

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