Thickened carbon dioxide fluid friction resistance testing system and method

Abstract

The invention relates to the technical field of oil and gas exploitation, and discloses a thickened carbon dioxide fluid flow friction resistance testing system and method. The method comprises the following steps: S1, liquefying carbon dioxide gas into liquid carbon dioxide; s2, preparing the liquid carbon dioxide, a cosolvent and a thickening agent into a thickened carbon dioxide fluid, and recording the density as shown in the specification; s3, the thickened carbon dioxide fluid is introduced into the testing pipeline, the flow speed of the thickened carbon dioxide fluid introduced into the testing pipeline is as follows, and the pressure difference of the thickened carbon dioxide fluid flowing through the inlet end and the outlet end of the testing pipeline is recorded; s4, calculating the friction resistance coefficient according to a formula (1), wherein D is the diameter of the test pipeline; l is the length of the test pipeline; s1 and S2 are the solubility of the cosolvent and the thickening agent in the liquid carbon dioxide. The invention creatively provides a friction coefficient calculation formula, and the numerical relationship between the friction of the thickened carbon dioxide fluid in the shaft and each parameter can be quickly calculated and evaluated according to the formula.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and specifically to a system and method for testing the friction of thickened carbon dioxide fluid. Background Technology

[0002] In the development of unconventional oil and gas reservoirs such as shale gas and tight oil and gas, CO2 fracturing technology has become one of the core development methods due to its advantages such as low damage, high flowback efficiency, and reservoir enhancement. The frictional resistance generated when fracturing fluid flows in the wellbore (including surface pipelines and downhole tubing) directly determines the selection of fracturing truck output pressure, the design of the fracturing displacement, and the safety of the operation. Therefore, accurate evaluation and rapid calculation of frictional resistance are key technical aspects of optimizing CO2 fracturing operation schemes. Currently, the evaluation and calculation of frictional resistance in thickened CO2 flow mainly relies on numerical simulation methods. This method, based on computational fluid dynamics (CFD) theory, establishes a numerical model of thickened CO2 flow, inputting parameters such as fracturing fluid density, chemical reagent solubility (affecting fluid viscosity and rheological properties), pipeline geometric parameters (length, diameter), and displacement velocity. It then simulates the flow process by solving the Navier-Stokes equations to calculate the frictional coefficient. This method requires extensive basic experimental data to calibrate the model parameters and consumes significant computational resources. Especially when faced with nonlinear changes in fluid rheological properties after the addition of thickeners, the model's prediction accuracy drops significantly, making it difficult to meet the precise requirements of frictional resistance evaluation in practical engineering applications. Besides numerical simulation, existing experimental testing techniques also have significant limitations. Traditional CO2 friction testing devices are mostly designed for unmodified pure CO2 fluids and lack the ability to adapt to the special rheological behavior of thickened CO2 fluids. Thickened CO2 fluids improve sand-carrying capacity by adding polymer thickeners, and their viscosity, shear dilution characteristics, and elastic modulus are fundamentally different from pure CO2. The dynamic process of the expansion, entanglement, and breakage of thickener molecular chains under high pressure and shear directly leads to a strong nonlinear response in the fluid friction characteristics. However, existing experimental devices have not established a linkage testing mechanism between rheological characteristics and friction parameters, making it impossible to achieve simultaneous characterization of the two. In addition, traditional testing devices mostly use atmospheric or near-atmospheric pressure environments and fixed roughness pipelines for simulation, making it difficult to reproduce the multi-field coupling effects of real working conditions. This results in a large deviation between the test results and the actual friction in the field, failing to provide reliable data support for optimizing construction parameters. Furthermore, existing testing methods generally suffer from high operational complexity and long testing cycles. Some experimental setups require segmented testing of fluid rheological parameters and pipeline pressure drop, followed by indirect derivation of the friction coefficient using empirical formulas. The accumulation of errors in these intermediate steps further reduces the reliability of the results. For variable-condition testing of key parameters such as thickener concentration and construction discharge rate, existing systems require rebuilding experimental loops and adjusting core components, making rapid iterative testing difficult and unable to adapt to the dynamic parameter adjustment needs during on-site construction. More importantly, thickened CO2 fluids may experience thickener precipitation and phase transitions during flow. Current technologies lack the ability to monitor and couple these complex physicochemical processes in real time, making it difficult to accurately pinpoint the causes of abnormal friction fluctuations, thus affecting construction safety. In summary, existing numerical simulation and experimental testing techniques are insufficient for accurate, efficient, and condition-adaptive evaluation of thickened CO2 fluid friction, becoming a core bottleneck restricting the large-scale promotion and improvement of CO2 fracturing technology. Therefore, developing a thickened CO2 fluid friction testing system and corresponding standardized testing methods that can reproduce real fracturing conditions, simultaneously characterize rheological properties and friction parameters, and balance testing accuracy and efficiency has significant engineering application value and academic significance.

[0003] CN108709826A discloses a CO2 friction measurement device and method. The device includes a power unit, a flow meter, and a friction testing unit connected sequentially via pipelines to form a circulation loop. A liquid phase pipeline and a gas phase pipeline are connected in parallel on the pipeline between the friction testing unit and the power unit. The method simulates the flow of liquid CO2 under different pipe diameters, measures the flow friction, and quantitatively analyzes the vaporization of liquid CO2. A drawback of this patent is that it does not provide specific quantitative relationships, making it impossible to directly and quickly evaluate the flow friction of thickened CO2 fluid in a wellbore.

[0004] CN104007043B discloses a large-scale, multifunctional fracturing fluid experimental system for measuring the rheological properties, frictional properties, and proppant carrying capacity of gel fracturing fluid, water fracturing fluid, and CO2 foam fracturing fluid, or for studying the rheological properties, frictional properties, and proppant carrying capacity of CO2 dry fracturing fluid under different temperatures and pressures. The system allows observation of the proppant suspension state in the fracturing fluid through multi-level viewing windows. A drawback of this patent is that it cannot directly evaluate the flow friction of thickened CO2 fluid in the wellbore. Summary of the Invention

[0005] This invention provides a friction testing system and method for thickened carbon dioxide fluid. The system and method can quickly evaluate the friction coefficient of thickened carbon dioxide fluid in a wellbore based on the density of the thickened carbon dioxide fluid, the solubility of chemical reagents in the thickened carbon dioxide fluid, the pressure difference across the test pipeline, the displacement velocity in the thickened carbon dioxide fluid, and the length and diameter of the test pipeline. Furthermore, the friction coefficient can be adjusted by adjusting the aforementioned parameters, which has important guiding significance for subsequent construction.

[0006] To achieve the above objectives, the first aspect of the present invention provides a thickened carbon dioxide fluid friction testing system, the system comprising a carbon dioxide storage tank, a first temperature control device, a chemical reagent storage tank unit, a thickened carbon dioxide fluid preparation container, a flow meter, and at least one testing unit, wherein each testing unit includes a testing pipeline, the testing pipeline being equipped with a differential pressure sensor; Carbon dioxide gas from the carbon dioxide storage tank enters the temperature control device, where the temperature is adjusted to liquefy the carbon dioxide gas into liquid carbon dioxide. Chemical reagents and liquid carbon dioxide from the chemical reagent storage tank unit enter the thickened carbon dioxide fluid preparation container to prepare thickened carbon dioxide fluid. The thickened carbon dioxide fluid enters the test pipeline, and the flow rate of the thickened carbon dioxide fluid entering the test pipeline is measured by a flow meter. The differential pressure sensor is used to measure the pressure difference between the inlet and outlet of the test pipeline.

[0007] Preferably, the test pipeline is equipped with a viewing window.

[0008] Preferably, the temperature control range of the first temperature control device is -30~200℃.

[0009] Preferably, the flow meter has a measurement range of 0~1.8m. 3 / h.

[0010] Preferably, the differential pressure sensor has a range of 0~870 kPa.

[0011] Preferably, the chemical reagent storage tank unit includes a first chemical reagent storage tank and a second chemical reagent storage tank, wherein the first chemical reagent storage tank and the second chemical reagent storage tank are used to store a cosolvent and a thickener, respectively.

[0012] Preferably, the diameter of the test pipeline is 3~15mm and the length is 3~10m.

[0013] Preferably, the system further includes a second temperature control device for regulating the temperature of the thickened carbon dioxide fluid prepared in the thickened carbon dioxide fluid preparation container.

[0014] A second aspect of the present invention provides a method for testing the flow friction of thickened carbon dioxide fluid, which is implemented in the system described above and includes the following steps: S1. Liquefy carbon dioxide gas into liquid carbon dioxide; S2. Liquid carbon dioxide, a co-solvent, and a thickener are mixed to form a thickened carbon dioxide fluid, the density of which is denoted as . ; S3. The thickened carbon dioxide fluid is introduced into the test pipeline, and the flow rate of the thickened carbon dioxide fluid into the test pipeline is denoted as . Record the pressure difference between the inlet and outlet ends of the thickened carbon dioxide fluid flowing through the test pipeline. ; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline according to formula (1). , Equation (1) Where D is the diameter of the test pipeline in mm; L is the length of the test pipeline in m; S1 represents the density increase coefficient of the thickened carbon dioxide fluid flowing through the test pipeline; S2 represents the solubility of the co-solvent in liquid carbon dioxide, in mass%; and S3 represents the solubility of the thickener in liquid carbon dioxide, in mass%. The unit is g / cm³ 3 ; The unit is m / s; The unit is MPa.

[0015] Preferably, the co-solvent is at least one of ethanol, methanol, and N,N-dimethylformamide.

[0016] Preferably, the thickener is at least one of perfluorohexyl acrylate-methyl methacrylate copolymer, polyfluoroether-polyoxyethylene block copolymer, and perfluoropolyether-nano silica composite system.

[0017] Preferably, when the temperature of the thickened carbon dioxide fluid is 15°C, the density growth coefficient of the thickened carbon dioxide fluid flowing through the test pipeline is... The value is 0.0015 to 0.003.

[0018] Preferably, The concentration ranges from 1.09 to 1.83 g / cm³.

[0019] Preferably, S1 is 2.5~3% by mass.

[0020] Preferably, S2 is 0.5~2% by mass.

[0021] Preferably, The speed is 1.5~5 m / s.

[0022] Preferably, The pressure ranges from 0.5 to 8 MPa.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Through research, this invention has discovered the relationship between the density of thickened carbon dioxide fluid, the solubility of chemical reagents in thickened carbon dioxide fluid, the pressure difference between the two ends of the test pipeline, the displacement velocity in thickened carbon dioxide fluid, and the length and diameter of the test pipeline and the friction coefficient. It creatively proposes the friction coefficient calculation formula shown in Equation (1). Based on this formula, the numerical relationship between the friction coefficient of thickened carbon dioxide fluid in the wellbore and various parameters can be quickly calculated and evaluated. Specifically, the friction coefficient of thickened carbon dioxide fluid in the wellbore can be quickly evaluated based on the density of thickened carbon dioxide fluid, the solubility of chemical reagents in thickened carbon dioxide fluid, the pressure difference between the two ends of the test pipeline, the displacement velocity in thickened carbon dioxide fluid, and the length and diameter of the test pipeline. Furthermore, the magnitude of the friction coefficient can be controlled by adjusting the aforementioned parameters, which has important guiding significance for subsequent construction.

[0024] (2) In a preferred embodiment, the system of the present invention is provided with a viewing window on the test pipeline. Through the viewing window, the dissolution of thickeners, cosolvents and other chemical agents in thickened carbon dioxide fluid can be observed in real time, and the micro-dynamic changes of thickened carbon dioxide fluid in different states and the phase change process of carbon dioxide can be monitored.

[0025] (3) Based on the temperature-friction relationship, optimize and adjust the type and concentration of thickener, reveal the behavior of thickened carbon dioxide fluid in complex temperature field, provide accurate parameters for subsequent construction, and improve the safety and economy of fracturing operation.

[0026] (4) The test pipeline is designed with a multi-hole flow channel, which can realistically simulate the flow state of fluid in the well. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the thickened carbon dioxide fluid friction testing system described in this invention.

[0028] Explanation of reference numerals in the attached figures 1 Carbon dioxide storage tank; 2 First temperature control device; 3 Chemical reagent storage tank unit; 4 Thickened carbon dioxide fluid preparation container; 5 Flow meter; 6 Test pipeline; 7 Differential pressure sensor; 8 Viewing window; 9 Second temperature control device; 31 First chemical reagent storage tank; 32 Second chemical reagent storage tank. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] The greatest innovation of this invention lies in the following: through research, the relationship between the density of thickened carbon dioxide fluid, the solubility of chemical reagents in thickened carbon dioxide fluid, the pressure difference across the test pipeline, the displacement velocity in thickened carbon dioxide fluid, and the length and diameter of the test pipeline and the friction coefficient was discovered. The relationship shown in equation (1) was creatively proposed, and a thickened carbon dioxide fluid friction testing system capable of testing the friction of thickened carbon dioxide fluid was constructed. In this invention, the thickened carbon dioxide fluid refers to a fluid with a viscosity of 5~100 mPa·s.

[0032] like Figure 1 As shown, the thickened carbon dioxide fluid friction test system provided by the present invention includes a carbon dioxide storage tank 1, a first temperature control device 2, a chemical reagent storage tank unit 3, a thickened carbon dioxide fluid preparation container 4, a flow meter 5, and at least one test unit, wherein each test unit includes a test pipeline 6, and the test pipeline 6 is equipped with a differential pressure sensor 7. Carbon dioxide gas from the carbon dioxide storage tank 1 enters the temperature control device 2, where the temperature is adjusted to liquefy the carbon dioxide gas into liquid carbon dioxide. Chemical reagents and liquid carbon dioxide from the chemical reagent storage tank unit 3 enter the thickened carbon dioxide fluid preparation container 4 to prepare thickened carbon dioxide fluid. The thickened carbon dioxide fluid enters the test pipeline 6, and the flow rate of the thickened carbon dioxide fluid entering the test pipeline 6 is measured by the flow meter 5. The differential pressure sensor 7 is used to measure the pressure difference between the inlet and outlet ends of the test pipeline 6.

[0033] In this invention, the carbon dioxide storage tank 1 is used to store carbon dioxide. Specifically, the carbon dioxide storage tank 1 is pressure-resistant to 40 MPa, temperature-resistant to 200°C, and has a volume of 200 L.

[0034] In one embodiment, the first temperature control device 2 has a cooling and heating unit, through which the temperature can be adjusted, with a temperature control range of -30~200℃. The first temperature control device 2 has a communication interface and is connected to a computer via a data cable. In this invention, the function of the first temperature control device 2 is to convert carbon dioxide gas into liquid carbon dioxide by regulating the temperature within the first temperature control device 2. Specifically, for example, regulating the temperature of the first temperature control device 2 to 15℃ can convert carbon dioxide gas into liquid carbon dioxide. The first temperature control device 2 can be a constant temperature chamber.

[0035] In this invention, one or more chemical reagent storage tank units 3 can be provided as needed. In one embodiment, when preparing thickened carbon dioxide fluid, it is necessary to add a co-solvent and a thickener to the liquid carbon dioxide, and two chemical reagent storage tanks can be provided.

[0036] Specifically, the chemical reagent storage tank unit 3 includes a first chemical reagent storage tank 31 and a second chemical reagent storage tank 32. The first chemical reagent storage tank 31 and the second chemical reagent storage tank 32 are used to store a co-solvent and a thickener, respectively. The thickening ability of the thickener in liquid carbon dioxide is key to improving the viscosity of thickened carbon dioxide fluid, while the co-solvent can significantly improve the solubility of the thickener in carbon dioxide. The coupled effect of the two can significantly improve the fracturing effect.

[0037] The function of the thickened carbon dioxide fluid preparation container 4 is to mix liquid carbon dioxide and chemical reagents in the chemical reagent storage tank unit 3 to prepare thickened carbon dioxide fluid.

[0038] In one embodiment, the system further includes a second temperature control device 9 for regulating the temperature of the thickened carbon dioxide fluid prepared in the thickened carbon dioxide fluid preparation container 4.

[0039] In this invention, the flow meter 5 is used to measure the displacement velocity, that is, the speed at which the thickened carbon dioxide fluid enters the test pipe 6. Specifically, the flow meter 5 has a measurement range of 0~1.8m. 3 The flow meter 5 has a flow rate of 0.01 mL / min and an accuracy of 0.01 mL / min. It is equipped with a communication interface and can be connected to a computer via a data cable.

[0040] In this invention, the test pipeline 6 is used to simulate a wellbore. By passing thickened carbon dioxide fluid into the test pipeline 6, the friction of the thickened carbon dioxide fluid in the test pipeline 6 is tested, thereby simulating the friction of the thickened carbon dioxide fluid when it enters the formation through the wellbore. This has important guiding significance for actual construction.

[0041] In a preferred embodiment, the test pipeline 6 is equipped with a viewing window 8. Through the viewing window 8, the dissolution of thickeners, co-solvents, and other chemical agents in the thickened carbon dioxide fluid can be observed in real time, and the microscopic dynamic changes of the thickened carbon dioxide fluid under different states and the phase change process of carbon dioxide can be monitored.

[0042] In this invention, the test unit can be one or more. In a specific embodiment, each test unit includes a test pipeline 6, and each test pipeline 6 is equipped with a differential pressure sensor 7 and a viewing window 8.

[0043] In one implementation, such as Figure 1 As shown, there can be three test units, arranged side by side. During friction testing, tests can be performed in one test unit at a time, or simultaneously in multiple test units. The length and diameter of the test conduit 6 in each test unit can be the same or different.

[0044] Furthermore, the test pipeline 6 is pressure resistant to 40MPa, and its diameter can be 3~15mm and its length can be 3~10m. In a preferred embodiment, when there are 3 test units, the diameters of the 3 test pipelines 6 can be 6mm, 8mm, and 10mm, respectively.

[0045] In some embodiments, the differential pressure sensor 7 has a range of 0~870 kPa and an accuracy of 0.01 kPa. The differential pressure sensor 7 is used to measure the pressure difference between the two ends of the test pipeline 6. Specifically, when thickened carbon dioxide fluid is introduced and flows through the test pipeline 6, the differential pressure sensor 7 can measure the pressure difference between the inlet and outlet ends of the test pipeline 6.

[0046] In a more specific implementation, such as Figure 1 As shown, the thickened carbon dioxide fluid friction test system includes a carbon dioxide storage tank 1, a first temperature control device 2, a chemical reagent storage tank unit 3, a thickened carbon dioxide fluid preparation container 4, a flow meter 5, at least one test unit, and a second temperature control device 9. Each test unit includes a test pipeline 6, which is equipped with a differential pressure sensor 7 and a viewing window 8. The chemical reagent storage tank unit 3 includes a first chemical reagent storage tank 31 and a second chemical reagent storage tank 32, which are used to store a cosolvent and a thickener, respectively. Carbon dioxide gas from the carbon dioxide storage tank 1 enters the temperature control device 2, where the temperature is adjusted to liquefy the carbon dioxide gas into liquid carbon dioxide. The co-solvent from the first chemical reagent storage tank 31, the thickener from the second chemical reagent storage tank 32, and the liquid carbon dioxide all enter the thickened carbon dioxide fluid preparation container 4 to prepare thickened carbon dioxide fluid. The temperature of the thickened carbon dioxide fluid is adjusted to a suitable range by the second temperature control device 9 before entering the test pipeline 6. The flow rate of the thickened carbon dioxide fluid entering the test pipeline 6 is measured by the flow meter 5. The differential pressure sensor 7 is used to measure the pressure difference between the inlet and outlet of the test pipeline 6. The viewing window 8 can observe the dissolution of thickener, co-solvent, and other chemical agents in the thickened carbon dioxide fluid in real time, and monitor the microscopic dynamic changes of the thickened carbon dioxide fluid under different states and the phase change process of carbon dioxide.

[0047] The present invention also provides a method for testing the friction resistance of thickened carbon dioxide fluid, which is implemented in the system described above and includes the following steps: S1. Liquefy carbon dioxide gas into liquid carbon dioxide; S2. Liquid carbon dioxide, a co-solvent, and a thickener are mixed to form a thickened carbon dioxide fluid, the density of which is denoted as . ; S3. The thickened carbon dioxide fluid is introduced into the test line 6, and the flow rate of the thickened carbon dioxide fluid into the test line 6 is denoted as . Record the pressure difference between the inlet and outlet ends of the thickened carbon dioxide fluid flowing through the test pipeline 6. ; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline 6 according to formula (1). , Equation (1) Where D is the diameter of test pipe 6 in mm; L is the length of test pipe 6 in m; S1 represents the density increase coefficient of the thickened carbon dioxide fluid flowing through test pipe 6; S2 represents the solubility of the cosolvent in liquid carbon dioxide, in mass%; and S3 represents the solubility of the thickener in liquid carbon dioxide, in mass%. The unit is g / cm3; The unit is m / s; The unit is MPa.

[0048] The thickening ability of thickeners in liquid carbon dioxide is key to improving the viscosity of thickened carbon dioxide fluid. Cosolvents can significantly improve the solubility of thickeners in carbon dioxide, and the combined effect of the two can significantly improve the fracturing effect.

[0049] In some embodiments, the cosolvent can be a conventional choice in the art, such as at least one of ethanol, methanol, and N,N-dimethylformamide (DMF).

[0050] In this invention, the thickener can be a common additive in the art capable of increasing the viscosity of thickened carbon dioxide fluid to 5-100 mPa·s. In some embodiments, the thickener can be at least one of perfluorohexyl acrylate-methyl methacrylate copolymer, polyfluoroether-polyoxyethylene block copolymer, and perfluoropolyether-nano silica composite system.

[0051] Specifically, the perfluorohexyl acrylate-methyl methacrylate copolymer is composed of perfluorohexyl acrylate monomer ( C 11 H 7 F 13 O 2) and methyl methacrylate monomer ( C 5 H 8 O 2) It is copolymerized, and its number-average molecular weight is 30,000 g / mol, and its degree of polymerization n is 209.

[0052] Specifically, the polyfluoroether-polyoxyethylene block copolymer is a combination of repeating block structures. The repeating units of the polyfluoroether structure are (C3F6O) and (CF2O), and the repeating unit of the polyoxyethylene structure is (C2H4O). The overall block structure can be represented as C3F7O[C3F6O]. n [C2H4O] m OCH3, with a number-average molecular weight of 10,000~500,000 g / mol, n of 100~300, and m of 300~1,000.

[0053] Specifically, the perfluoropolyether-nano silica composite system uses nano-SiO2 particles as raw material. The nano-SiO2 particles are surface-modified with a silane coupling agent (e.g., KH550 or KH560) in a toluene / ethanol solvent. Through hydrolysis-condensation reactions, functional groups such as amino (-NH2) or epoxy groups are grafted onto the SiO2 surface, eliminating particle agglomeration and introducing active sites for reaction with perfluoropolyether (PFPE). Using anhydrous DMF as solvent, hydroxyl-terminated PFPE (PFPE-OH) is mixed with the surface-modified nano-SiO2, and a crosslinking aid is added. A three-dimensional crosslinked network of "PFPE molecular chains-nano-SiO2" is formed through chemical bonding or strong physical adsorption, ultimately obtaining a uniformly dispersed composite system. The perfluoropolyether has a fluorine content of 43% and a number-average molecular weight (Mn) of 5 × 10⁻⁶. 5The nano-SiO2 particles have a particle size of 15nm (hydroxylated, moisture ≤0.1%), and the mass ratio of perfluoropolyether to nano-SiO2 particles is 7:3, wherein the perfluoropolyether is CF3O (C3F6O). a (CF2O) b CF3 has a number-average molecular weight of 20,000 to 100,000 g / mol, a main chain repeating unit number a of 10 to 500, and a branch or terminal repeating unit number b of 5 to 200.

[0054] In this invention, the density of the thickened carbon dioxide fluid and the solubility of the cosolvent and thickener in the thickened carbon dioxide fluid can be tested using conventional methods.

[0055] In this invention, the density growth coefficient in equation (1) This is an empirical constant, related to the temperature of the thickened carbon dioxide fluid. Specifically, when the temperature of the thickened carbon dioxide fluid is 15°C, the density growth coefficient of the thickened carbon dioxide fluid flowing through test pipe 6 is... The value is 0.0015 to 0.003.

[0056] In some implementations... It can be 1.09~1.83 g / cm3.

[0057] In some implementations, S1 can be 2.5 to 3 units of mass.

[0058] In some implementations, S2 is 0.5 to 2% by mass.

[0059] In some implementations... It can be 1.5~5m / s.

[0060] In some implementations... It can be 0.5~8MPa.

[0061] The method of this invention can accurately measure the friction coefficient of thickened carbon dioxide fluid in test pipeline 6, and can simulate the friction situation when thickened carbon dioxide fluid enters the formation through the wellbore. Furthermore, equation (1) reveals the relationship between the density of thickened carbon dioxide fluid, the solubility of chemical reagents in thickened carbon dioxide fluid, the pressure difference between the two ends of the test pipeline, the displacement velocity in thickened carbon dioxide fluid, and the length and diameter of the test pipeline and the friction coefficient. During construction, the parameters in equation (1) can be adjusted according to the construction situation to achieve the effect of controlling the friction coefficient.

[0062] The following examples further illustrate the thickened carbon dioxide fluid friction testing system and method of the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0063] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0064] In the following embodiments: Perfluorohexyl acrylate-methyl methacrylate copolymer is composed of perfluorohexyl acrylate monomer ( C 11 H 7 F 13 O 2) and methyl methacrylate monomer ( C 5 H 8 O 2) It is copolymerized, and its number-average molecular weight is 30,000 g / mol, and its degree of polymerization n is 209.

[0065] The polyfluoroether-polyoxyethylene block copolymer is a combination of repeating block structures. The repeating units of the polyfluoroether structure are (C3F6O) and (CF2O), and the repeating unit of the polyoxyethylene structure is (C2H4O). The overall block structure can be represented as C3F7O[C3F6O]. n [C2H4O] m OCH3, with a number-average molecular weight of 10,000~500,000 g / mol, n of 100~300, and m of 300~1000.

[0066] The perfluoropolyether-nano silica composite system uses nano-SiO2 particles as raw material. The nano-SiO2 particles are surface-modified with a silane coupling agent (e.g., KH550) in a toluene / ethanol solvent. Through hydrolysis-condensation reaction, amino (-NH2) functional groups are grafted onto the SiO2 surface, eliminating particle agglomeration and introducing active sites for reaction with perfluoropolyether (PFPE). Using anhydrous DMF as solvent, hydroxyl-terminated PFPE (PFPE-OH) is mixed with the surface-modified nano-SiO2, and a crosslinking aid is added. A three-dimensional crosslinked network of "PFPE molecular chains-nano-SiO2" is formed through chemical bonding or strong physical adsorption, ultimately obtaining a uniformly dispersed composite system. The perfluoropolyether contains 43% fluorine and has a number-average molecular weight (Mn) of 5 × 10⁻⁶. 5 The nano-SiO2 particles have a particle size of 15nm (hydroxylated, moisture ≤0.1%), and the mass ratio of perfluoropolyether to nano-SiO2 particles is 7:3, wherein the perfluoropolyether is CF3O (C3F6O). a(CF2O) b CF3 has a number-average molecular weight of 20,000 to 100,000 g / mol, a main chain repeating unit number a of 10 to 500, and a branch or terminal repeating unit number b of 5 to 200.

[0067] The following examples are as follows Figure 1 The thickened carbon dioxide fluid friction test system shown is implemented. The system includes a carbon dioxide storage tank 1, a first temperature control device 2, a chemical reagent storage tank unit 3, a thickened carbon dioxide fluid preparation container 4, a flow meter 5, three test units, and a second temperature control device 9. Each test unit includes a test pipeline 6, which is equipped with a differential pressure sensor 7 and a viewing window 8. The chemical reagent storage tank unit 3 includes a first chemical reagent storage tank 31 and a second chemical reagent storage tank 32. The first chemical reagent storage tank 31 and the second chemical reagent storage tank 32 are used to store a cosolvent and a thickener, respectively. The length of the three test pipelines 6 is 5m, and the diameters of the three test pipelines 6 are 6mm, 8mm, and 10mm, respectively. Carbon dioxide gas from the carbon dioxide storage tank 1 enters the temperature control device 2, where the temperature is adjusted to liquefy the carbon dioxide gas into liquid carbon dioxide. The co-solvent from the first chemical reagent storage tank 31, the thickener from the second chemical reagent storage tank 32, and the liquid carbon dioxide all enter the thickened carbon dioxide fluid preparation container 4 to prepare thickened carbon dioxide fluid. The temperature of the thickened carbon dioxide fluid is adjusted to a suitable range by the second temperature control device 9 before entering the test pipeline 6. The flow rate of the thickened carbon dioxide fluid entering the test pipeline 6 is measured by the flow meter 5. The differential pressure sensor 7 is used to measure the pressure difference between the inlet and outlet of the test pipeline 6. The viewing window 8 can observe the dissolution of thickener, co-solvent, and other chemical agents in the thickened carbon dioxide fluid in real time, and monitor the microscopic dynamic changes of the thickened carbon dioxide fluid under different states and the phase change process of carbon dioxide.

[0068] Example 1 S1. Carbon dioxide gas in carbon dioxide storage tank 1 is introduced into first temperature control device 2, and carbon dioxide gas is liquefied into liquid carbon dioxide at 15°C. S2. Liquid carbon dioxide, co-solvent (methanol), and thickener (perfluorohexyl acrylate-methyl methacrylate copolymer) are introduced into the thickened carbon dioxide fluid preparation container 4 to prepare a thickened carbon dioxide fluid with a viscosity of 5.2 mPa·s. The temperature of the thickened carbon dioxide fluid is adjusted to 15°C by the second temperature control device 9. The density of the thickened carbon dioxide fluid is... It is 1.1 g / cm3; S3. The thickened carbon dioxide fluid is introduced into a test pipe 6 with a length of 5m and a diameter of 6mm. The flow rate of the thickened carbon dioxide fluid into the test pipe 6 is... The velocity is 3.6 m / s. The differential pressure sensor 7 records the pressure difference between the inlet and outlet ends of the thickened carbon dioxide fluid flowing through the test pipeline 6. It is 4.35 MPa; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline 6 according to formula (1). It is 7.3×10 -7 , Equation (1), where the density growth coefficient of the thickened carbon dioxide fluid flowing through test pipe 6 is... The solubility of the cosolvent and thickener in liquid carbon dioxide at 15°C is 0.003, and the solubilities S1 and S2 are 2.82% by mass and 1.64% by mass, respectively.

[0069] Example 2 S1. Carbon dioxide gas in carbon dioxide storage tank 1 is introduced into first temperature control device 2, and carbon dioxide gas is liquefied into liquid carbon dioxide at 15°C. S2. Liquid carbon dioxide, co-solvent (ethanol), and thickener (polyfluoroether-polyoxyethylene block copolymer) are introduced into the thickened carbon dioxide fluid preparation container 4 to prepare a thickened carbon dioxide fluid with a viscosity of 51 mPa·s. The temperature of the thickened carbon dioxide fluid is adjusted to 15°C by the second temperature control device 9. The density of the thickened carbon dioxide fluid is... It is 1.09 g / cm³ 3 ; S3. The thickened carbon dioxide fluid is introduced into a test pipe 6 with a length of 5m and a diameter of 8mm. The flow rate of the thickened carbon dioxide fluid into the test pipe 6 is... The velocity is 4.2 m / s. The differential pressure sensor 7 records the pressure difference between the inlet and outlet of the thickened carbon dioxide fluid flowing through the test pipeline 6. It is 6.64 MPa; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline 6 according to formula (1). 1.1×10 -6 , Equation (1), where the density growth coefficient of the thickened carbon dioxide fluid flowing through test pipe 6 is... The solubility of the cosolvent and thickener in liquid carbon dioxide at 15°C is 0.0028, and the solubility S1 and S2 are 2.82% by mass and 0.86% by mass, respectively.

[0070] Example 3 S1. Carbon dioxide gas in carbon dioxide storage tank 1 is introduced into first temperature control device 2, and carbon dioxide gas is liquefied into liquid carbon dioxide at 15°C. S2. Liquid carbon dioxide, a co-solvent (N,N-dimethylformamide), and a thickener (perfluoropolyether-nano silica composite system) are introduced into the thickened carbon dioxide fluid preparation container 4 to prepare a thickened carbon dioxide fluid with a viscosity of 102 mPa·s. The temperature of the thickened carbon dioxide fluid is adjusted to 15°C using the second temperature control device 9. The density of the thickened carbon dioxide fluid is... It is 1.08 g / cm³ 3 ; S3. The thickened carbon dioxide fluid is introduced into a test pipe 6 with a length of 5m and a diameter of 10mm. The flow rate of the thickened carbon dioxide fluid into the test pipe 6 is... The velocity is 3.8 m / s. The differential pressure sensor 7 records the pressure difference between the inlet and outlet ends of the thickened carbon dioxide fluid flowing through the test pipeline 6. It is 5.18 MPa; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline 6 according to formula (1). 1.32×10 -6 , Equation (1), where the density growth coefficient of the thickened carbon dioxide fluid flowing through test pipe 6 is... The solubility of the cosolvent and thickener in liquid carbon dioxide at 15°C is 0.0015, and the solubility S1 and S2 are 2.82% by mass and 1.26% by mass, respectively.

[0071] As can be seen from the examples, the system and method described in this invention can quickly calculate the friction coefficient of thickened carbon dioxide fluid in the wellbore.

[0072] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0073] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A system for testing the flow friction of thickened carbon dioxide fluid, characterized in that, The system includes a carbon dioxide storage tank (1), a first temperature control device (2), a chemical reagent storage tank unit (3), a thickened carbon dioxide fluid preparation container (4), a flow meter (5), and at least one test unit, wherein each test unit includes a test pipeline (6), and the test pipeline (6) is equipped with a differential pressure sensor (7). Carbon dioxide gas from the carbon dioxide storage tank (1) enters the temperature control device (2) and the carbon dioxide gas is liquefied into liquid carbon dioxide by adjusting the temperature. Chemical reagents and liquid carbon dioxide from the chemical reagent storage tank unit (3) enter the thickened carbon dioxide fluid preparation container (4) to prepare thickened carbon dioxide fluid. The thickened carbon dioxide fluid enters the test pipeline (6) and the flow rate of the thickened carbon dioxide fluid entering the test pipeline (6) is tested by the flow meter (5). The differential pressure sensor (7) is used to test the pressure difference between the inlet and outlet of the test pipeline (6).

2. The system according to claim 1, characterized in that, The test pipeline (6) is equipped with a viewing window (8).

3. The system according to claim 1 or 2, characterized in that, The temperature control range of the first temperature control device (2) is -30~200℃; And / or, the flow meter (5) has a metering range of 0~1.8m. 3 / h; And / or, the range of the differential pressure sensor (7) is 0~870kPa.

4. The system according to any one of claims 1-3, characterized in that, The chemical reagent storage tank unit (3) includes a first chemical reagent storage tank (31) and a second chemical reagent storage tank (32), which are used to store cosolvents and thickeners, respectively.

5. The system according to any one of claims 1-4, characterized in that, The diameter of the test pipeline (6) is 3~15mm and the length is 3~10m.

6. The system according to any one of claims 1-5, characterized in that, The system also includes a second temperature control device (9) for regulating the temperature of the thickened carbon dioxide fluid prepared in the thickened carbon dioxide fluid preparation container (4).

7. A method for testing the flow friction of thickened carbon dioxide fluid, wherein the method is implemented in the system described in any one of claims 1-6, characterized in that, The method includes the following steps: S1. Liquefy carbon dioxide gas into liquid carbon dioxide; S2. Liquid carbon dioxide, a co-solvent, and a thickener are mixed to form a thickened carbon dioxide fluid, the density of which is denoted as . ; S3. Thickened carbon dioxide fluid is introduced into the test pipeline (6), and the flow rate of the thickened carbon dioxide fluid into the test pipeline (6) is denoted as . Record the pressure difference between the inlet and outlet of the thickened carbon dioxide fluid flowing through the test pipeline (6). ; S4. Calculate the friction coefficient of the thickened carbon dioxide fluid flowing through the test pipeline (6) according to formula (1). , Equation (1) Where D is the diameter of the test pipe (6) in mm; L is the length of the test pipe (6) in m; The density growth coefficient of the thickened carbon dioxide fluid flowing through the test pipe (6); S1 is the solubility of the cosolvent in liquid carbon dioxide, in mass%; S2 is the solubility of the thickener in liquid carbon dioxide, in mass% The unit is g / cm³ 3 ; The unit is m / s; The unit is MPa.

8. The method according to claim 7, characterized in that, The co-solvent is selected from at least one of ethanol, methanol and N,N-dimethylformamide; And / or, the thickener is at least one of perfluorohexyl acrylate-methyl methacrylate copolymer, polyfluoroether-polyoxyethylene block copolymer, and perfluoropolyether-nano silica composite system.

9. The method according to claim 7 or 8, characterized in that, When the temperature of the thickened carbon dioxide fluid is 15°C, the density growth coefficient of the thickened carbon dioxide fluid flowing through the test pipe (6) The value is 0.0015 to 0.

003.

10. The method according to any one of claims 7-9, characterized in that, The concentration ranges from 1.09 to 1.83 g / cm³. 3 ; And / or, S1 is 2.5~3% by mass; And / or, S2 is 0.5~2% by mass; And / or, The speed is 1.5~5 m / s; And / or, The pressure ranges from 0.5 to 8 MPa.

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