Injection device and method of carbon dioxide composite nano-fracture displacement agent for oil fields

Abstract

The present invention relates to the technical field of oilfield exploitation, and in particular to an injection device and method for a carbon dioxide composite nano-fracture displacer for oilfields. The method comprises: determining an injection amount of the fracturing displacer according to an oil and gas-bearing area; uniformly mixing carbon dioxide with a liquid base fluid to obtain the fracturing displacer; injecting the fracturing displacer into a wellhead using an injection pump; when it is determined according to a reflux characteristic value that the injection of the fracturing displacer does not meet a preset standard, secondarily determining whether the injection of the fracturing displacer meets the preset standard according to a wellhead pressure evaluation value, or increasing the injection rate of the fracturing displacer; when it is determined according to the wellhead pressure evaluation value that the injection of the fracturing displacer does not meet the preset standard, determining the reason for the non-compliance according to the pressure fluctuation frequency; and completing the injection of the fracturing displacer under the condition that the injection of the fracturing displacer meets the preset standard, thereby improving the injection efficiency of the fracturing displacer.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield exploitation, and in particular to an injection device and method of a carbon dioxide composite nano-fracture displacement agent for oilfields. Background Art

[0002] In oilfield development, improving reservoir permeability and fluid mobility is the key to improving recovery. Although traditional water-based fracturing fluids can improve reservoir permeability to a certain extent, they have problems such as difficulty in fracturing fluid flowback, high waste fluid treatment costs, and high water resource consumption. In recent years, carbon dioxide fracturing technology has gradually become a research hotspot in the field of oil and gas reservoir development due to its significant advantages in energy enhancement and drainage, outstanding advantages in single-well production improvement, and environmental advantages of large-scale water conservation and carbon utilization. However, in order to effectively inject carbon dioxide composite nano-fracture displacement agents into the formation and control their distribution, special injection devices and methods are required. Existing injection devices and methods often have problems such as low injection efficiency, unstable pressure control, and easy leakage of injected fluids, which make it difficult to meet the needs of efficient and safe injection of carbon dioxide composite nano-fracture displacement agents. Therefore, the development of a carbon dioxide composite nano-fracture displacement agent injection device and method suitable for oil fields is of great significance for improving oil and gas reservoir development efficiency, reducing production costs, and reducing environmental impact.

[0003] Chinese patent publication number CN105986802B discloses a downhole fracturing method, comprising: lowering a downhole sand mixer into a fracturing interval via an oil pipe to form an oil pipe channel; injecting proppant into the fracturing interval via the oil pipe channel, and injecting slickwater into the fracturing interval via the oil casing annulus channel; and periodically controlling the flow rate of a high-sand-to-sand ratio sand-carrying fluid injected into the fracturing interval via the oil pipe channel and the flow rate of slickwater injected into the fracturing interval via the oil casing annulus channel, so that proppant bridges form in the fractures of the fracturing interval within a first preset time of a cycle and dissolve the proppant bridges within a second preset time of a cycle, wherein a cycle is the sum of the first preset time and the second preset time. However, the prior art lacks monitoring of wellbore pressure and backflow, resulting in low fracturing efficiency and the risk of downhole accidents. Summary of the Invention

[0004] To this end, the present invention provides an injection device and method for a carbon dioxide composite nano-fracture displacement agent for oil fields, so as to overcome the problems in the prior art of low fracturing efficiency and high accident risk due to the lack of monitoring of well pressure and backflow.

[0005] To achieve the above object, the present invention provides a method for injecting a carbon dioxide composite nano-fracture displacement agent for oil fields, comprising:

[0006] Determine the oil and gas containing area in the formation by seismic exploration method and determine the injection amount of the fracturing displacement agent according to the oil and gas containing area;

[0007] The carbon dioxide is mixed evenly with a liquid base fluid to obtain a fracturing displacement agent, wherein the liquid base fluid comprises water, sand, a nano-crosslinking agent, a nano-surfactant, a thickener, a gel breaker, a clay stabilizer, and a displacement aid;

[0008] Use an injection pump to inject the fracturing displacement agent into the wellhead;

[0009] Determining a reflux characteristic value through reflux information collected by a flow meter, and when determining that the injection of the fracturing displacement agent does not meet a preset standard based on the reflux characteristic value, re-determining whether the injection of the fracturing displacement agent meets the preset standard based on a wellhead pressure evaluation value obtained by a pressure sensor, or increasing the injection rate of the fracturing displacement agent;

[0010] When it is determined that the injection of the fracturing displacement agent does not meet the preset standard based on the wellhead pressure evaluation value, the reason why the injection of the fracturing displacement agent does not meet the standard is determined based on the pressure fluctuation frequency;

[0011] The injection of the fracturing displacement agent is completed under the condition that the injection of the fracturing displacement agent meets the preset standard.

[0012] Furthermore, it is determined whether the injection of the fracturing displacement agent meets the preset standard according to the backflow characteristic value, wherein:

[0013] If the backflow characteristic value is less than the first preset backflow characteristic value, it is determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters;

[0014] If the backflow characteristic value is greater than or equal to the first preset backflow characteristic value and less than the second preset backflow characteristic value, it is determined that the injection of the fracturing displacement agent does not meet the preset standard, and a secondary determination is made based on the wellhead pressure evaluation value whether the injection of the fracturing displacement agent meets the preset standard;

[0015] If the backflow characteristic value is greater than or equal to the second preset backflow characteristic value, it is determined that the injection of the fracturing displacing agent does not meet the preset standard, and the injection rate of the fracturing displacing agent is adjusted according to the difference between the backflow characteristic value and the second preset backflow characteristic value.

[0016] Furthermore, the reflux characteristic value is determined by the reflux velocity and the reflux amount.

[0017] Furthermore, the process of secondary determining whether the injection of the fracturing displacement agent meets the preset standard based on the wellhead pressure evaluation value includes:

[0018] Comparing the pressure evaluation value with a preset pressure value;

[0019] Based on the comparison result that the pressure evaluation value is less than the preset pressure value, it is secondarily determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters;

[0020] Based on the comparison result that the pressure evaluation value is greater than or equal to the preset pressure value, it is secondarily determined that the injection of the fracturing displacement agent does not meet the preset standard, and the reason why the injection of the fracturing displacement agent does not meet the standard is determined according to the pressure fluctuation frequency.

[0021] Furthermore, different adjustment modes are provided for the injection rate of the fracturing displacement agent, and each adjustment mode has a different adjustment range for the injection rate.

[0022] Furthermore, the reason why the injection of the fracturing displacement agent does not meet the standard is determined based on the pressure fluctuation frequency, wherein:

[0023] If the pressure fluctuation frequency is less than a preset pressure fluctuation frequency, it is determined that the reason why the injection of the fracturing displacement agent does not meet the standard is that the flow of the fracturing displacement agent in the formation is blocked, and the particle size of the sand particles in the fracturing displacement agent is reduced according to the formation permeability;

[0024] If the pressure fluctuation frequency is greater than or equal to the preset pressure fluctuation frequency, it is determined that the reason why the injection of the fracturing displacer does not meet the standard is that the flow of the fracturing displacer in the formation is uneven, and the carbon dioxide content in the fracturing displacer is increased according to the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency.

[0025] Furthermore, the adjustment range of the particle size of the sand particles in the fracturing displacement agent is positively correlated with the permeability of the formation.

[0026] Furthermore, the carbon dioxide content in the fracturing displacement agent is increased according to the pressure fluctuation frequency difference, wherein,

[0027] If the pressure fluctuation frequency difference is less than a preset pressure fluctuation frequency difference, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a first content adjustment coefficient;

[0028] If the pressure fluctuation frequency difference is greater than or equal to the preset pressure fluctuation frequency difference, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a second content adjustment coefficient;

[0029] The pressure fluctuation frequency difference is the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency.

[0030] Furthermore, the present invention also provides an injection device for a carbon dioxide composite nano-fracture displacement agent for oil fields, comprising: a liquid storage tank, a gas storage tank, a mixer, an injection pump, an injection pipeline, and a return pipeline;

[0031] The liquid storage tank is connected to the mixer via a first channel, and a first valve is provided on the first channel;

[0032] The gas storage tank is connected to the mixer via a second channel, and a second valve is provided on the second channel;

[0033] The injection pump is connected to the mixer via a third channel, and a third valve is provided on the third channel;

[0034] The injection pipe is connected to the injection pump, and a fourth valve and a pressure sensor are provided on the injection pipe;

[0035] The return pipe is connected to the injection pipe, and a fifth valve and a flow meter are provided on the return pipe.

[0036] Furthermore, a control module is provided, which is respectively connected to the first valve, the second valve, the third valve, the injection pump, the fourth valve, the fifth valve, the pressure sensor and the flow meter, and is used to control the switches of the first valve, the second valve, the third valve, the fourth valve and the fifth valve respectively, to determine whether the injection of the fracturing displacer meets the preset standard according to the backflow characteristic value, to determine whether the injection of the fracturing displacer meets the preset standard according to the wellhead pressure evaluation value for the second time, and to determine the reason why the injection of the fracturing displacer does not meet the standard according to the pressure fluctuation frequency.

[0037] Compared with the prior art, the beneficial effect of the present invention lies in that the present invention determines whether the injection of the fracturing displacer meets the preset standard based on the backflow characteristic value. If it does not meet the preset standard, the present invention makes a secondary judgment on whether the injection of the fracturing displacer meets the preset standard based on the wellhead pressure evaluation value obtained by the pressure sensor, or increases the injection rate of the fracturing displacer. By setting different adjustment schemes for different backflow characteristic values, the risk of accidents is reduced while the injection efficiency is improved.

[0038] Furthermore, when the present invention secondary determines based on the wellhead pressure evaluation value that the injection of the fracturing displacer does not meet the preset standard, the reason why the injection of the fracturing displacer does not meet the standard is determined based on the pressure fluctuation frequency. Through the secondary determination, it is possible to more accurately determine whether the injection of the fracturing displacer meets the preset standard. At the same time, by determining the reason for not meeting the standard, an effective adjustment plan can be provided, so that the fracturing operation can better adapt to different formation conditions and improve the fracturing effect.

[0039] Furthermore, the present invention provides a variety of methods for adjusting the injection parameters of the fracturing displacer, including setting different adjustment methods for the injection rate of the fracturing displacer, reducing the particle size of the sand particles in the fracturing displacer according to the formation permeability, and increasing the carbon dioxide content in the fracturing displacer according to the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency. Through the comprehensive application of multiple adjustment methods, the injection parameters of the fracturing displacer can be flexibly controlled, the performance of the fracturing displacer can be optimized, and the fracturing efficiency can be improved.

[0040] Furthermore, the present invention implements intelligent control of the fracturing displacer injection process by providing a control module. Based on real-time monitoring data, the control module automatically determines whether the fracturing displacer injection meets preset standards and automatically adjusts injection parameters based on the judgment result, thereby improving the automation and accuracy of the fracturing operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of a method for injecting a carbon dioxide composite nano-fracture displacement agent for oil fields according to an embodiment of the present invention;

[0042] Figure 2 This is a flow chart of an embodiment of the present invention for determining whether the injection of a fracturing displacement agent meets preset standards;

[0043] Figure 3 A flow chart for determining why the injection of a fracturing displacement agent does not meet standards according to an embodiment of the present invention;

[0044] Figure 4 This is a schematic structural diagram of an injection device for a carbon dioxide composite nano-fracture displacement agent for oil fields according to an embodiment of the present invention;

[0045] In the figure: 1. Liquid storage tank; 11. First channel; 12. First valve; 2. Gas storage tank; 21. Second channel; 22. Second valve; 3. Mixer; 31. Third channel; 32. Third valve; 4. Injection pump; 5. Injection pipe; 51. Fourth valve; 52. Pressure sensor; 6. Return pipe; 61. Fifth valve; 62. Flow meter. DETAILED DESCRIPTION

[0046] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0047] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0048] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0049] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0050] See also Figures 1 to 4 As shown, they are respectively a flow chart of a method for injecting a carbon dioxide composite nano-fracture displacing agent for oil fields according to an embodiment of the present invention; a flow chart of determining whether the injection of a fracturing displacing agent meets a preset standard according to an embodiment of the present invention; a flow chart of determining the reason why the injection of a fracturing displacing agent does not meet the standard according to an embodiment of the present invention; and a structural schematic diagram of an injection device for a carbon dioxide composite nano-fracture displacing agent for oil fields according to an embodiment of the present invention.

[0051] The method for injecting a carbon dioxide composite nano-fracture displacement agent for oil fields according to an embodiment of the present invention comprises:

[0052] Determine the oil and gas containing area in the formation by seismic exploration method and determine the injection amount of the fracturing displacement agent according to the oil and gas containing area;

[0053] The carbon dioxide is mixed evenly with a liquid base fluid to obtain a fracturing displacement agent, wherein the liquid base fluid comprises water, sand, a nano-crosslinking agent, a nano-surfactant, a thickener, a gel breaker, a clay stabilizer, and a displacement aid;

[0054] Use injection pump 4 to inject fracturing displacement agent into the wellhead;

[0055] Determine the reflux characteristic value by using the reflux information collected by the flow meter 62. When it is determined that the injection of the fracturing displacing agent does not meet the preset standard based on the reflux characteristic value, re-determine whether the injection of the fracturing displacing agent meets the preset standard based on the wellhead pressure evaluation value obtained by the pressure sensor 52, or increase the injection rate of the fracturing displacing agent;

[0056] When it is determined that the injection of the fracturing displacement agent does not meet the preset standard based on the wellhead pressure evaluation value, the reason why the injection of the fracturing displacement agent does not meet the standard is determined based on the pressure fluctuation frequency;

[0057] The injection of the fracturing displacement agent is completed under the condition that the injection of the fracturing displacement agent meets the preset standard.

[0058] Specifically, the seismic exploration methods include reflection seismic exploration, refraction seismic exploration and downhole seismic exploration, and the preferred method in the embodiment of the present invention is reflection seismic exploration.

[0059] Specifically, the nano cross-linking agent is such as boric acid, borax, etc., the nano surfactant is such as sodium dodecylbenzene sulfonate, polyoxyethylene ether, etc., the thickener is such as hydroxypropyl guar gum, xanthan gum, etc., the breaker is such as ammonium persulfate, hydrogen peroxide, etc., the clay stabilizer is such as potassium chloride, ammonium chloride, etc., the drainage agent is such as isopropyl alcohol, ethanol, etc., and there is no specific limitation.

[0060] Specifically, the weight percentages of carbon dioxide and liquid base fluid are as follows: carbon dioxide, 5% to 20%; liquid base fluid, 80% to 95%.

[0061] Specifically, the weight percentages of the components of the liquid base fluid are as follows: water 90% to 95%; sand 3% to 8%; nano cross-linking agent 0.1% to 0.5%; nano surfactant 0.05% to 0.2%; thickener 0.2% to 0.8%; breaker 0.01% to 0.1%; clay stabilizer 0.1% to 0.5%; and drainage aid 0.05% to 0.3%.

[0062] Specifically, the backflow characteristic value is used to determine whether the injection of the fracturing displacement agent meets the preset standard, wherein:

[0063] If the backflow characteristic value is less than the first preset backflow characteristic value of 0.85, it is determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters;

[0064] If the backflow characteristic value is greater than or equal to the first preset backflow characteristic value and less than the second preset backflow characteristic value of 0.92, it is determined that the injection of the fracturing displacement agent does not meet the preset standard, and a secondary determination is made based on the wellhead pressure evaluation value whether the injection of the fracturing displacement agent meets the preset standard;

[0065] If the backflow characteristic value is greater than or equal to the second preset backflow characteristic value, it is determined that the injection of the fracturing displacing agent does not meet the preset standard, and the injection rate of the fracturing displacing agent is adjusted according to the difference between the backflow characteristic value and the second preset backflow characteristic value.

[0066] In the embodiment of the present invention, the first preset reflux characteristic value is 0.85, and the second preset reflux characteristic value is 0.92, but the above values ​​are not limited thereto, and those skilled in the art may also adjust the values ​​according to actual needs.

[0067] Specifically, the reflux characteristic value is determined by the reflux velocity and the reflux amount, and is calculated by the following formula:

[0068]

[0069] In the formula, λ represents the reflux characteristic value, V represents the reflux velocity, Vy represents the reflux velocity threshold, and Vy is set to 500 L / min. α represents the first evaluation coefficient and α is set to 0.54. Q represents the reflux volume, Qy represents the reflux volume threshold, and Qy is set to 80t. β represents the second evaluation coefficient and β is set to 0.45.

[0070] Specifically, the process of secondary determination of whether the injection of the fracturing displacement agent meets the preset standards based on the wellhead pressure evaluation value includes:

[0071] Compare the pressure evaluation value with the preset pressure value of 50 MPa;

[0072] Based on the comparison result that the pressure evaluation value is less than the preset pressure value, it is secondarily determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters;

[0073] Based on the comparison result that the pressure evaluation value is greater than or equal to the preset pressure value, it is secondarily determined that the injection of the fracturing displacement agent does not meet the preset standard, and the reason why the injection of the fracturing displacement agent does not meet the standard is determined according to the pressure fluctuation frequency.

[0074] Specifically, the pressure evaluation value is the average pressure in the wellhead within a first preset time period of 10 minutes, which is monitored and obtained by the pressure sensor 52 .

[0075] In the embodiment of the present invention, the preset pressure value is 50 MPa, but the above value is not limited thereto, and those skilled in the art can also adjust the value according to actual needs.

[0076] Specifically, different adjustment modes are provided for the injection rate of the fracturing displacement agent, and each adjustment mode has a different adjustment range for the injection rate, wherein:

[0077] If the reflux characteristic difference is less than the preset reflux characteristic difference of 0.03, the injection rate is adjusted to the corresponding value using the first rate adjustment coefficient of 1.01;

[0078] If the reflux characteristic difference is greater than or equal to the preset reflux characteristic difference, adjusting the injection rate to a corresponding value using a second rate adjustment coefficient of 1.03;

[0079] The reflux characteristic difference is the difference between the reflux characteristic value and the second preset reflux characteristic value.

[0080] Specifically, the injection rate is adjusted by regulating the power of the injection pump 4 .

[0081] Specifically, the reasons why the injection of the fracturing displacement agent does not meet the standards are determined based on the pressure fluctuation frequency, among which:

[0082] If the pressure fluctuation frequency is less than a preset pressure fluctuation frequency of 40 Hz, it is determined that the reason why the injection of the fracturing displacement agent does not meet the standard is that the flow of the fracturing displacement agent in the formation is obstructed, and the particle size of the sand particles in the fracturing displacement agent is reduced according to the formation permeability;

[0083] If the pressure fluctuation frequency is greater than or equal to the preset pressure fluctuation frequency, it is determined that the reason why the injection of the fracturing displacer does not meet the standard is that the flow of the fracturing displacer in the formation is uneven, and the carbon dioxide content in the fracturing displacer is increased according to the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency.

[0084] In the embodiment of the present invention, the preset pressure fluctuation frequency is set to 40 Hz, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0085] Specifically, the pressure fluctuation frequency is monitored and acquired by the pressure sensor 52 .

[0086] Specifically, the formation permeability is determined by the reflux rate within the second preset time period of 5 minutes. The reflux rate is the reflux flow rate per unit time, and the reflux rate is monitored and obtained by the flow meter 62.

[0087] Specifically, the adjustment range of the particle size of the sand particles in the fracturing displacement agent is positively correlated with the permeability of the formation, wherein,

[0088] If the formation permeability is less than the preset formation permeability of 5 L / s, the particle size of the sand particles is adjusted to a corresponding value using a first particle size adjustment coefficient of 0.99;

[0089] If the formation permeability is greater than or equal to the preset formation permeability, the particle size of the sand particles is adjusted to a corresponding value using a second particle size adjustment coefficient of 0.97.

[0090] In the embodiment of the present invention, the preset formation permeability is 5 L / s, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0091] Specifically, the carbon dioxide content in the fracturing displacement agent is increased according to the pressure fluctuation frequency difference, wherein:

[0092] If the pressure fluctuation frequency difference is less than the preset pressure fluctuation frequency difference of 5 Hz, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a first content adjustment coefficient of 1.02;

[0093] If the pressure fluctuation frequency difference is greater than or equal to the preset pressure fluctuation frequency difference, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a second content adjustment coefficient of 1.05;

[0094] The pressure fluctuation frequency difference is the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency.

[0095] In the embodiment of the present invention, the preset pressure fluctuation frequency difference is 5 Hz, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0096] The injection device of the carbon dioxide composite nano-fracture displacement agent for oil fields according to the embodiment of the present invention comprises: a liquid storage tank 1, a gas storage tank 2, a mixer 3, an injection pump 4, an injection pipeline 5 and a return pipeline 6;

[0097] The liquid storage tank 1 is connected to the mixer 3 via a first channel 11, and a first valve 12 is provided on the first channel 11;

[0098] The gas storage tank 2 is connected to the mixer 3 via a second channel 21 , and a second valve 22 is provided on the second channel 21 ;

[0099] The injection pump 4 is connected to the mixer 3 via a third channel 31 , and a third valve 32 is provided on the third channel 31 ;

[0100] The injection pipe 5 is connected to the injection pump 4, and a fourth valve 51 and a pressure sensor 52 are provided on the injection pipe 5;

[0101] The return pipe 6 is connected to the injection pipe 5 , and a fifth valve 61 and a flow meter 62 are provided on the return pipe 6 .

[0102] Specifically, a control module is also provided, which is respectively connected to the first valve 12, the second valve 22, the third valve 32, the injection pump 4, the fourth valve 51, the fifth valve 61, the pressure sensor 52 and the flow meter 62, and is used to control the switches of the first valve 12, the second valve 22, the third valve 32, the fourth valve 51 and the fifth valve 61 respectively, to determine whether the injection of the fracturing displacement agent meets the preset standard according to the reflux characteristic value, to determine whether the injection of the fracturing displacement agent meets the preset standard according to the wellhead pressure evaluation value for the second time, and to determine the reason why the injection of the fracturing displacement agent does not meet the standard according to the pressure fluctuation frequency.

[0103] Specifically, the working process of the injection device of the carbon dioxide composite nano-fracture displacement agent for oil fields includes:

[0104] The control module opens the first valve 12 and the second valve 22, and passes the liquid in the liquid storage tank 1 and the gas in the gas storage tank 2 into the mixer 3 for mixing to obtain a fracturing displacement agent. After the mixing is completed, the third valve 32 and the fourth valve 51 are opened, and the fracturing displacement agent is passed into the injection pipeline 5 through the injection pump 4. After the injection is completed, the fourth valve 51 is closed, and the fifth valve 61 is opened to pass the reflux liquid into the reflux pipeline 6.

[0105] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0106] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for injecting a carbon dioxide composite nano-fracture displacement agent for oil fields, characterized in that: include: Determine the oil and gas containing area in the formation by seismic exploration method and determine the injection amount of the fracturing displacement agent according to the oil and gas containing area; The carbon dioxide is mixed evenly with a liquid base fluid to obtain a fracturing displacement agent, wherein the liquid base fluid comprises water, sand, a nano-crosslinking agent, a nano-surfactant, a thickener, a gel breaker, a clay stabilizer, and a displacement aid; Using an injection pump to inject the fracturing displacement agent into the wellhead; Determine the reflux characteristic value by using the reflux information collected by the flow meter; The injection of the fracturing displacement agent is determined according to the backflow characteristic value to determine whether it meets the preset standard, wherein: If the backflow characteristic value is less than the first preset backflow characteristic value, it is determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters; If the backflow characteristic value is greater than or equal to the first preset backflow characteristic value and less than the second preset backflow characteristic value, it is determined that the injection of the fracturing displacement agent does not meet the preset standard, and a secondary determination is made based on the wellhead pressure evaluation value whether the injection of the fracturing displacement agent meets the preset standard; If the backflow characteristic value is greater than or equal to the second preset backflow characteristic value, it is determined that the injection of the fracturing displacing agent does not meet the preset standard, and the injection rate of the fracturing displacing agent is adjusted according to the difference between the backflow characteristic value and the second preset backflow characteristic value; The process of secondary determining whether the injection of the fracturing displacement agent meets the preset standards based on the wellhead pressure evaluation value obtained by the pressure sensor includes: Comparing the pressure evaluation value with a preset pressure value; Based on the comparison result that the pressure evaluation value is less than the preset pressure value, it is secondarily determined that the injection of the fracturing displacement agent meets the preset standard, and the injection is continued according to the current parameters; Secondarily determining that the injection of the fracturing displacement agent does not meet the preset standard based on the comparison result that the pressure evaluation value is greater than or equal to the preset pressure value, and determining the reason why the injection of the fracturing displacement agent does not meet the standard based on the pressure fluctuation frequency; The reasons why the injection of the fracturing displacement agent does not meet the standards are determined based on the pressure fluctuation frequency, among which: If the pressure fluctuation frequency is less than a preset pressure fluctuation frequency, it is determined that the reason why the injection of the fracturing displacement agent does not meet the standard is that the flow of the fracturing displacement agent in the formation is blocked, and the particle size of the sand particles in the fracturing displacement agent is reduced according to the formation permeability; If the pressure fluctuation frequency is greater than or equal to the preset pressure fluctuation frequency, determining that the reason why the injection of the fracturing displacing agent does not meet the standard is that the flow of the fracturing displacing agent in the formation is uneven, and increasing the carbon dioxide content in the fracturing displacing agent according to the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency; completing the injection of the fracturing displacement agent under the condition that the injection of the fracturing displacement agent meets the preset standard; The reflux characteristic value In the formula, λ represents the reflux characteristic value, V represents the reflux velocity, Vy represents the reflux velocity threshold, α represents the first evaluation coefficient, Q represents the reflux volume, Qy represents the reflux volume threshold, and β represents the second evaluation coefficient.

2. The method for injecting carbon dioxide composite nano-fracture displacement agent for oil fields according to claim 1, characterized in that: The reflux characteristic value is determined by the reflux velocity and the reflux amount.

3. The method for injecting carbon dioxide composite nano-fracture displacement agent for oil fields according to claim 2, characterized in that: Different adjustment modes are provided for the injection rate of the fracturing displacement agent, and each adjustment mode has a different adjustment range for the injection rate.

4. The method for injecting carbon dioxide composite nano-fracture displacement agent for oil fields according to claim 3, characterized in that: The adjustment range of the particle size of the sand particles in the fracturing displacement agent is positively correlated with the permeability of the formation.

5. The method for injecting carbon dioxide composite nano-fracture displacement agent for oil fields according to claim 4, characterized in that: The carbon dioxide content in the fracturing displacement agent is increased according to the pressure fluctuation frequency difference, wherein: If the pressure fluctuation frequency difference is less than a preset pressure fluctuation frequency difference, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a first content adjustment coefficient; If the pressure fluctuation frequency difference is greater than or equal to the preset pressure fluctuation frequency difference, the carbon dioxide content in the fracturing displacement agent is increased to a corresponding value using a second content adjustment coefficient; The pressure fluctuation frequency difference is the difference between the pressure fluctuation frequency and the preset pressure fluctuation frequency.

6. The device for use in the method for injecting carbon dioxide composite nano-fracture displacement agent for oil fields according to any one of claims 1 to 5, characterized in that: include: Liquid storage tanks, gas storage tanks, mixers, injection pumps, injection pipes and return pipes; The liquid storage tank is connected to the mixer via a first channel, and a first valve is provided on the first channel; The gas storage tank is connected to the mixer via a second channel, and a second valve is provided on the second channel; The injection pump is connected to the mixer via a third channel, and a third valve is provided on the third channel; The injection pipe is connected to the injection pump, and a fourth valve and a pressure sensor are provided on the injection pipe; The return pipe is connected to the injection pipe, and a fifth valve and a flow meter are provided on the return pipe; A control module is also provided, which is used to execute the injection method of the carbon dioxide composite nano-fracture displacement agent for oil fields according to any one of claims 1 to 5. The control module is respectively connected to the first valve, the second valve, the third valve, the injection pump, the fourth valve, the fifth valve, the pressure sensor and the flow meter, and is used to control the switches of the first valve, the second valve, the third valve, the fourth valve and the fifth valve respectively, to determine whether the injection of the fracturing displacement agent meets the preset standard according to the reflux characteristic value, to determine whether the injection of the fracturing displacement agent meets the preset standard according to the wellhead pressure evaluation value for the second time, and to determine the reason why the injection of the fracturing displacement agent does not meet the standard according to the pressure fluctuation frequency.

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