Preferred resistance-reducing agent, method for evaluating performance thereof, and use thereof

Abstract

The application discloses a kind of preferred and performance evaluation method of resistance reducing agent, which comprises the following steps: obtaining polymer information, establishing resistance reducing agent optimization parameter model;Simplified molecular configuration I of CO2 and polymer is constructed, electrostatic potential distribution information is obtained, and resistance reducing agent polymer class I is optimized;Based on polymer class I, construct the mixed molecular configuration II of polymer in class I and SC-CO2, shear motion configuration III;Based on mixed molecular configuration II and shear motion configuration III, obtain molecular dynamics and shear motion calculation results, and optimize resistance reducing agent polymer II;For resistance reducing agent polymer II, indoor pipe flow resistance experiment is carried out, the optimization result of molecular simulation is verified, and the resistance reducing rate of the preferred resistance reducing agent is determined.The resistance reducing agent optimization and evaluation method provided by the application can quickly determine the SC-CO2 fracturing resistance reducing agent, reduce the burden of indoor experiment, and has high optimization efficiency and application reference value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resistance reducing agents, and particularly relates to a preferred resistance reducing agent and a performance evaluation method thereof and application thereof. BACKGROUND

[0002] Compared with conventional hydraulic fracturing technology, SC-CO2 has the characteristics of low viscosity, high permeability and high diffusion rate, so that SC-CO2 fracturing has the advantages of high-efficiency communication of reservoir cracks, reduction of fracture pressure, increase of methane desorption amount, water-free environmental protection and the like, and thus becomes a hot research topic at present and has great potential in the high-efficiency development industry of shale gas.

[0003] With the development of indoor research and field test of SC-CO2 fracturing, the problem of high friction resistance generated in the fracturing process is quickly found out. The shale gas reservoirs in China are generally buried deep, and the over-high construction friction resistance will cause over-high wellhead pressure, which not only requires higher construction equipment, but also causes greater safety hazards to the field construction. In the prior art, the above problem is generally solved by adding a resistance reducing agent.

[0004] At present, in the process of screening the resistance reducing agent, in order to more directly describe the friction resistance generated by the fluid flowing in the pipeline, various friction resistance testing devices are developed to carry out indoor experiments, and the friction resistance of the fluid flowing in the pipeline is obtained through physical experiments. However, through this method, the efficiency is low and the workload is large.

[0005] At present, it is an urgent problem for those skilled in the art to provide an efficient resistance reducing agent selection and performance evaluation method. SUMMARY

[0006] Therefore, the application provides a resistance reducing agent selection and performance evaluation method and application thereof, determines a chemical agent capable of effectively reducing the friction resistance of SC-CO2 fracturing, and determines a SC-CO2 fracturing resistance reducing agent formula with the best resistance reducing effect, which is an important guarantee for the stimulation and reconstruction of shale gas reservoirs.

[0007] In order to achieve the above purpose, the application adopts the following technical solutions:

[0008] A resistance reducing agent selection and performance evaluation method, wherein the method is a molecular simulation method combined with a pipe flow friction method.

[0009] Preferably, the molecular simulation method comprises the following specific steps:

[0010] (1) classifying polymers according to polymer information;

[0011] (2) constructing a simplified molecular configuration I of CO2 and the polymer, and selecting a resistance reducing agent polymer category I according to electrostatic potential distribution information;

[0012] (3) respectively construct polymer and SC-CO2 mixed molecular configuration II and shear motion configuration III in polymer large category I, and select the resistance reducing agent according to the settlement result.

[0013] In the prior art, there is no related chemical agent capable of reducing the CO2 friction resistance in the currently used industrial high molecular polymer. In order to quickly obtain the SC-CO2 resistance reducing agent, the preferred method of determining the specific resistance reducing agent is adopted after determining the polymer large category I.

[0014] Among them, the electrostatic potential distribution can describe the interaction energy between the unit positive charge at a certain point and the current system, determine whether the polymer molecules and CO2 molecules have the potential to interact, and further determine the polymer large category I of the resistance reducing agent.

[0015] In the preferred method of the specific resistance reducing agent, the mutual solubility and resistance reducing property between the chemical agent and SC-CO2 are considered. The solubility of the polymer in SC-CO2 is determined in the SC-CO2 mixed molecular configuration II, the resistance reducing property of the polymer to SC-CO2 is determined in the SC-CO2 shear motion configuration II, the evaluation parameters are used to select the typical chemical agent of different types of polymers, and the resistance reducing agent with resistance reducing property to SC-CO2 is determined.

[0016] Preferably, the polymer information in step (1) includes: polymer type, polymer molecular weight and polymer characteristic functional group.

[0017] Preferably, the selection method in step (2) is: according to the electrostatic potential distribution simulation result, selecting the resistance reducing agent polymer large category I which interacts with CO2; at the same time, the polymer large category I has obvious chemical characteristics, common in the market and economic and environmental protection characteristics.

[0018] Preferably, the ratio of the number of molecules of SC-CO2 to the number of molecules of the polymer in step (3) is 500-1000:1-10.

[0019] The number of atoms in the polymer molecule is large, and a large number of CO2 molecules are needed to systematically study the interaction between the polymer and CO2. However, a large number of system molecules will cause long molecular dynamics calculation time and large calculation resource requirement. In the comprehensive consideration of literature research and computer software calculation efficiency, the ratio of 500-1000:1-10 is set.

[0020] Preferably, the shear motion configuration III in step (3) adopts Build Layer construction; wherein the BOTTOMWALL layer and the TOPWALL layer are alloys, and the mixed molecular system of SC-CO2 and the polymer is used as an intermediate FLUID layer, and a vacuum layer of 20-30 nm is added above the TOPWALL layer.

[0021] In the shear motion configuration III, the BOTTOMWALL layer and the TOPWALL layer are alloys, and the intermediate FLUID layer is a mixed molecular system of SC-CO2 and the polymer, which can truly simulate the flow of the mixed system of SC-CO2 and the polymer in a metal pipeline and obtain a pipe wall friction coefficient. The pipe wall friction coefficient can describe the external friction caused by the metal pipe wall to the mixed system, directly reflect the friction between the fluid and the metal pipe wall, and the smaller the pipe wall friction coefficient, the smaller the friction loss in the flow process. The polymer with a drag reduction effect on the flow of SC-CO2 can be quickly optimized.

[0022] Preferably, the upper and lower boundary layers in the shear motion configuration III use stainless steel (0-3) Cr (13-30) Ni (3-10) Ti.

[0023] The stainless steel material can be selected from ferritic stainless steel, austenitic stainless steel, austenitic-ferritic duplex stainless steel, and martensitic stainless steel.

[0024] Preferably, in the shear motion configuration III in step (3), the drag reduction performance of the drag reducer is judged by the friction coefficient and the relative viscosity parameter simulation results, and is selected; and in the mixed molecular configuration II, the solubility of the drag reducer is judged by the radial distribution function, the interaction energy and the cohesive energy density parameter simulation results, and is selected.

[0025] Preferably, the pipe flow resistance method is to verify the performance of the drag reducer selected by the molecular simulation method through a carbon dioxide pipe flow resistance experiment; wherein the experiment takes water pipe flow resistance as a benchmark.

[0026] The preferred and performance evaluation method of the drag reducer as described above is applied to a supercritical carbon dioxide fracturing fluid drag reducer.

[0027] ​Compared with the prior art, the application has the following beneficial effects: a preferred and performance evaluation method of a resistance reducing agent, the application combines molecular simulation technology with indoor experimental research to realize the optimization of the SC-CO2 fracturing fluid resistance reducing agent formula; wherein, the molecular simulation method is used to optimize the resistance reducing agent polymer category and the resistance reducing agent candidate chemical agent, the computer chemical software is used to determine the SC-CO2 fracturing fluid resistance reducing agent candidate chemical agent, the type of the SC-CO2 fracturing fluid resistance reducing agent chemical agent is determined, the burden of the indoor experiment is reduced, the correctness of the molecular simulation optimization result is verified by combining the indoor experiment, the performance of the resistance reducing agent candidate chemical agent is evaluated, and the resistance reducing agent capable of effectively reducing the SC-CO2 fracturing pipe flow friction is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute the embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0029] Figure 1 The flow chart of the preferred and performance evaluation method of the resistance reducing agent in the embodiment of the application;

[0030] Figure 2 The CO2+ polymer mixed system molecular model schematic diagram after annealing optimization in the embodiment of the application;

[0031] Figure 3 The shearing motion simulation molecular configuration schematic diagram after annealing optimization in the embodiment of the application;

[0032] Wherein, 1-vacuum layer, 2-TOPWALL layer, 3-CO2+ polymer layer; 4-BOTTOMWALL layer;

[0033] Figure 4 The electrostatic potential distribution diagram of the fluorine-containing polymer-CO2 in the embodiment of the application;

[0034] Figure 5 The electrostatic potential distribution diagram of the amide polymer-CO2 in the embodiment of the application;

[0035] Figure 6 The electrostatic potential distribution diagram of the sulfur-containing polymer-CO2 in the embodiment of the application;

[0036] Figure 7 The electrostatic potential distribution diagram of the silicon-containing polymer-CO2 in the embodiment of the application;

[0037] Figure 8The electrostatic potential distribution diagram of the hydrocarbon polymer-CO2 of the embodiment of the present application;

[0038] Figure 9 The friction coefficient column diagram of the embodiment 1 of the present application adding different fluorine-containing polymer systems;

[0039] Figure 10 The relative viscosity column diagram of the embodiment 1 of the present application adding different fluorine-containing polymer systems;

[0040] Figure 11 The friction coefficient column diagram of the embodiment 2 of the present application adding different hydrocarbon polymer systems;

[0041] Figure 12 The relative viscosity column diagram of the embodiment 2 of the present application adding different hydrocarbon polymer systems. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0043] As Figure 1 , a preferred method for evaluating the performance of a resistance reducer, specifically comprising the following steps:

[0044] (1) classifying polymers according to polymer information;

[0045] (2) constructing a simplified molecular configuration I of CO2 and the polymer, and selecting a resistance reducer polymer category I according to electrostatic potential distribution information;

[0046] (3) respectively constructing a polymer in the polymer category I and a mixed molecular configuration II and a shearing motion configuration III of SC-CO2, and selecting a resistance reducer according to the calculation results;

[0047] (4) selecting a resistance reducer for step (3), performing an indoor pipe flow resistance experiment, verifying the molecular simulation optimization results, and determining the resistance reduction rate of the optimized resistance reducer.

[0048] Embodiment 1

[0049] A method for optimizing and evaluating the performance of a supercritical carbon dioxide fracturing fluid resistance reducer, mainly comprising the following steps:

[0050] (1) obtaining polymer information, and establishing a resistance reducer optimization parameter model;

[0051] The polymer selected according to the polymer type, polymer molecular weight and polymer characteristic functional group includes: fluorine-containing polymer, amide polymer, sulfur-containing polymer, silicon-containing polymer;

[0052] The preferred parameters of the friction reducer include: electrostatic potential distribution, radial distribution function, interaction energy, cohesive energy density, friction coefficient and relative viscosity;

[0053] (2) Construct a simplified molecular configuration I of CO2 and polymer, obtain electrostatic potential distribution information, and preferably select a large category I of friction reducer polymers;

[0054] Under the DMol3 module, the simplified molecular configuration of CO2 and the polymer selected in step (1) is calculated, after the simulation calculation is completed, the DMol3 electrostatic potential is selected, the electrostatic interaction between molecules is analyzed, and according to the electrostatic potential distribution simulation result (see Figures 4-7 ), the fluorine-containing polymer is preferably selected as the large category I of SC-CO2 friction reducer polymers;

[0055] (3) Based on the polymer large category I, construct the mixed molecular configuration II and the shear motion configuration III of the polymer in the large category I and SC-CO2, obtain the molecular dynamics and shear motion calculation results, and select the friction reducer;

[0056] Five fluorine-containing polymers with obvious chemical properties, common on the market, and economic and environmental protection characteristics are selected for chemical agent optimization, including: polyfluoroalkene A, polyfluoroalkene B, polyfluoroether, polyfluoroester A and polyfluoroester B;

[0057] The mixed molecular configuration II and the shear motion configuration III of SC-CO2 and the polymer are constructed, and the molecular number ratio of SC-CO2 and the polymer is 1000:4;

[0058] The shear motion configuration III of SC-CO2 and the polymer is constructed, and the single-phase austenitic stainless steel 1Cr18Ni9Ti is used for the upper and lower boundary layers, the shear motion configuration III is established by using Build Layer, the alloy is selected as the BOTTOMWALL layer and the TOPWALL layer, the mixed molecular system of SC-CO2 and the polymer is selected as the middle FLUID layer, a 30nm vacuum layer is added above the TOPWALL layer, and the molecular model schematic diagram is as shown in Figure 2 、 Figure 3 ;

[0059] The annealing process of the mixed molecular configuration II and the shear motion configuration III is carried out under the NVT ensemble, the temperature range is set to 300-500K, the cycle is 5 times, and the total simulation step is set to 50000 steps;

[0060] The molecular dynamics process is first carried out under NVT ensemble, the temperature is set to 308K, the simulation time is set to 500ps; under NPT ensemble, the temperature is set to 308K, the pressure is set to 25MPa, and the simulation time is set to 1500ps;

[0061] The shearing motion process is carried out under the condition of 500ps NVT equilibrium phase simulation at the temperature of 308K, the motion of the upper and lower metal layers in X, Y directions is limited, and the relative movement speed of the metal layers is set to The temperature is set to 308K, the pressure is set to 25MPa, and the simulation time is set to 1500ps;

[0062] Both use Velocity-Scale heat bath control system temperature, and use Parrinello-Rahman pressure bath control system pressure;

[0063] Through the analysis and evaluation of radial distribution function, interaction energy, cohesive energy density, friction coefficient and relative viscosity parameters, the results are shown in Tables 1-2 and Figures 9-10 , preferably, polyurethane A can be dissolved with SC-CO2 and has resistance reduction and viscosity increasing properties, and can be used as a candidate resistance reducer for SC-CO2;

[0064] Table 1 Interaction energy between polymer-CO2 (unit: KJ / mol)

[0065]

[0066] Table 2 Polymer cohesive energy density, solubility parameter calculation results

[0067]

[0068]

[0069] (4) For the resistance reducer polyurethane A, indoor pipe flow friction experiment is carried out to verify the molecular simulation optimization result, taking the pipe flow friction of clear water as the benchmark, the resistance reduction rate of the optimized resistance reducer is determined, and the specific steps are as follows: under the conditions of displacement of 9L / min, pressure of 10MPa, temperature of 40℃ and concentration of 1-6wt%, SC-CO2 friction experiment and resistance reducer resistance reduction performance test experiment are carried out on polyurethane A, the molecular simulation optimization result is verified, the resistance reduction rate of polyurethane A resistance reducer is measured, and the test results are shown in Table 5.

[0070] Example 2

[0071] A method for optimizing and evaluating the resistance reduction performance of a supercritical carbon dioxide fracturing fluid resistance reducer, the main steps of which include:

[0072] (1) Obtain polymer information and establish resistance reducer optimization parameter model;

[0073] wherein the polymers selected according to the polymer category, polymer molecular weight and polymer characteristic functional group include: hydrocarbon-based polymers, amide-based polymers, sulfur-containing polymers, silicon-containing polymers;

[0074] The preferred parameters of the friction reducer include: electrostatic potential distribution, radial distribution function, interaction energy, cohesive energy density, friction coefficient and relative viscosity;

[0075] (2) Construct a simplified molecular configuration I of CO2 and polymers, obtain electrostatic potential distribution information, and preferably select a large category I of friction reducer polymers;

[0076] Under the DMol3 module, the simplified molecular configuration of CO2 and the polymer selected in step (1) is calculated, after the simulation calculation is completed, the DMol3 electrostatic potential is selected, the electrostatic interaction between molecules is analyzed, and according to the electrostatic potential distribution simulation result (see Figures 5-8 ), the hydrocarbon-based polymer is preferably selected as the large category I of SC-CO2 friction reducer polymers;

[0077] (3) Based on the polymer large category I, construct the mixed molecular configuration II and the shear motion configuration III of the polymer in the large category I and SC-CO2, obtain the molecular dynamics and shear motion calculation results, and select the friction reducer;

[0078] Five hydrocarbon-based polymers with obvious chemical properties, common on the market, and economic and environmental protection characteristics are selected for chemical agent optimization, including: polyolefin ester, polyolefin ether, polylactic acid, polyolefin ester A and polyolefin ester B;

[0079] The mixed molecular configuration II and the shear motion configuration III of SC-CO2 and the polymer are constructed, and the molecular number ratio of SC-CO2 and the polymer is 1000:4;

[0080] The shear motion configuration III of SC-CO2 and the polymer is constructed, and the single-phase austenitic stainless steel 1Cr18Ni9Ti is used for the upper and lower boundary layers; The shear motion configuration III is established by using Build Layer, the alloy is selected as the BOTTOMWALL layer and the TOPWALL layer, the mixed molecular system of SC-CO2 and the polymer is selected as the middle FLUID layer, a 30nm vacuum layer is added above the TOPWALL layer, and the molecular model schematic diagram is shown in Figure 2 、 Figure 3 ;

[0081] Wherein, the annealing process of the mixed molecular configuration II and the shear motion configuration III is carried out under the NVT ensemble, the temperature range is set to 300-500K, the cycle is 5 times, and the total simulation step is set to 50000 steps;

[0082] The molecular dynamics process is first carried out under NVT ensemble, the temperature is set to 308K, the simulation time is set to 500ps; under NPT ensemble, the temperature is set to 308K, the pressure is set to 25MPa, and the simulation time is set to 1500ps;

[0083] The shearing motion process is carried out under the condition of 500ps NVT equilibrium phase simulation with the temperature of 308K, the movement of the upper and lower metal layers in X, Y direction is limited, and the relative movement speed of the metal layers is set to The temperature is set to 308K, the pressure is set to 25MPa, and the simulation time is set to 1500ps;

[0084] Both use Velocity-Scale heat bath control system temperature, and use Parrinello-Rahman pressure bath control system pressure;

[0085] Through the analysis and evaluation of radial distribution function, interaction energy, cohesive energy density, friction coefficient and relative viscosity parameters, the results are shown in Tables 3-4 and Figures 11-12 , preferably, polyolefin ester B can be miscible with SC-CO2 and has drag reduction and viscosity increasing, and can be used as a candidate drag reducer for SC-CO2;

[0086] Table 3 Interaction energy between polymer-CO2 (unit: KJ / mol)

[0087]

[0088] Table 4 Calculation results of polymer cohesive energy density and solubility parameter

[0089]

[0090] (4) For the drag reducer polyolefin ester B, indoor pipe flow friction experiment is carried out to verify the molecular simulation optimization result, taking the water pipe flow friction as the benchmark, the drag reduction rate of the optimized drag reducer is determined, and the steps are as follows: under the conditions of displacement of 9L / min, pressure of 10MPa, temperature of 40℃, and concentration of 1-6wt%, SC-CO2 friction experiment and drag reducer drag reduction performance test experiment are carried out on polyolefin ester B, the molecular simulation optimization result is verified, the drag reduction rate of polyolefin ester B is measured, and the test results are shown in Table 5.

[0091] Table 5 Drag reduction rate results of polyfluoroester A and polyolefin ester B

[0092]

[0093]

[0094] The various embodiments are described in a progressive manner, each embodiment focusing on the differences from the other embodiments, with the same or similar parts between the embodiments referring to each other.

[0095] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to those skilled in the art, and all such modifications are within the scope of the present application as defined by the appended claims. The devices and processes of aspects of the application are not limited to the embodiments described herein but can be practiced with modification and alteration within the scope of the appended claims, given the benefit of the teachings of the preceding description of the embodiments. The devices and processes of aspects of the application are not limited to the specific embodiments described herein but can be practiced with modification and alteration, given the benefit of the teachings of the preceding description of the embodiments. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature rather than restrictive.

Claims

1. A method for selecting and evaluating the performance of a drag-reducing agent, characterized in that, The method described is a combination of molecular simulation and pipe flow friction method; The molecular simulation method includes the following specific steps: (1) Classify polymers based on polymer information; (2) Construct a simplified molecular configuration I of CO2 and the polymer, and select drag-reducing polymer category I based on electrostatic potential distribution information; the polymer information includes: polymer type, polymer molecular weight and polymer characteristic functional groups; the selection method is: select drag-reducing polymer category I that interacts with CO2 based on electrostatic potential distribution simulation results; at the same time, the polymer category I has obvious chemical properties, is commonly available on the market and is economical and environmentally friendly; (3) Construct the polymer-SC-CO2 mixed molecular configuration II and shear motion configuration III of the polymer category I respectively, and select drag-reducing agents according to the calculation results; for the shear motion configuration III, the drag-reducing properties of the drag-reducing agent are determined by the simulation results of friction coefficient and relative viscosity parameters, and the drag-reducing agent is selected; for the mixed molecular configuration II, the solubility of the drag-reducing agent is determined by the simulation results of radial distribution function, interaction energy and cohesive energy density parameters, and the drag-reducing agent is selected.

2. The preferred method and performance evaluation method for a drag-reducing agent according to claim 1, characterized in that, The molecular ratio of SC-CO2 to the polymer in step (3) is 500-1000:1-10.

3. The preferred method and performance evaluation method for a drag-reducing agent according to claim 1, characterized in that, The shear motion configuration III described in step (3) is constructed using a Build Layer; wherein, the BOTTOMWALL layer and the TOPWALL layer are alloys, the mixed molecular system of SC-CO2 and the polymer serves as an intermediate FLUID layer, and a vacuum layer of 20-30 nm is added above the TOPWALL layer.

4. The preferred method and performance evaluation method of the drag-reducing agent according to claim 3, characterized in that, The upper and lower boundary layers in the shear motion configuration III use The stainless steel is (0-3)Cr(13-30)Ni(3-10)Ti.

5. The preferred method and performance evaluation method of the drag-reducing agent according to claim 1, characterized in that, The method for reducing pipe flow friction involves conducting an indoor carbon dioxide pipe flow friction experiment to verify the performance of the drag-reducing agent selected by the molecular simulation method; wherein, the experiment uses the flow friction of clean water pipes as a benchmark.

6. The application of the preferred drag-reducing agent and performance evaluation method as described in any one of claims 1-5 in drag-reducing agents for supercritical carbon dioxide fracturing fluid.

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