Preparation and Properties of Polymer Compound Profile Control Agent

1.1 Raw materials and reagents Propylamine: Henan Jiaozuo (biochemical method) is greater than 98%; Acrylic acid: Beijing Dongfang Chemical Plant (first grade); Montmorillonite: Liaoning Heishan (industrial grade); Sodium hydroxide: Qiqihar Reagent Factory (industrial Grade); Ammonium persulfate: (Analytical); Sodium bisulfite: (Analytical); N,N-Bisacrylamide: Tianjin Chemical Reagent Factory (Analytical Pure); Polyethylene Glycol (PEG): Degree of Polymerization 1500; Additives: Other organic reagents, inorganic salts are of analytical grade.

1.2 Experimental Methods According to the method of orthogonal test design, prepare a mixed solution of acrylamide (or acrylate) and montmorillonite separately, add appropriate amount of free radical initiator, cross-linking agent and additives, and fill in the PE bag. After deoxygenation of nitrogen for 1-20 min, polymerization was carried out in a water bath at a constant temperature to prepare a polymer gel. After granulation, drying, and crushing into a dry powder sample, the test performance was analyzed. A number of factors affecting product performance (initiator concentration, polymerization time, reaction temperature, system concentration, raw material ratio, cross-linker concentration, additives, etc.) were studied to optimize the reaction conditions.

1.3 Performance Test Methods 1.3.1 Determination of Water Absorption Factor Accurately weigh a certain amount of profile control agent sample in a beaker, add a large amount of distilled water, after full swelling, use a mesh sieve to remove excess water, and then weigh out FRC The weight of the water-absorbing gel. The following formula is used to calculate the water absorption factor.

Fund Project: Key Project of Heilongjiang Academy of Sciences (01CFBALYG05) 1.3.2 Determination of water absorption rate The vortex observation method: The specific process is as follows. Add 50 ml of physiological saline (0.9% NaCl) solution to a 1 ml beaker and put it on an electric magnetic stirrer. One of the rotors was thrown into it, and the rotor speed was adjusted so that the rotor did not touch the cup wall, and the top of the vortex crossed the bottom of the cup. Then add 2 g of the accurately weighed FRC sample to the beaker while pressing the stopwatch. As it absorbs water, the viscosity of the system gradually increases and the rotational speed of the rotor decreases.

Until the vortex disappears, stop timing. The recorded time tv indicates the rate of absorption of the FRC resin.

1.3.3 Determination of water retention capacity The size of water retention capacity is measured by the water retention rate. The determination method is divided into the water holding capacity under heat drying, under pressure, or under centrifugal conditions, and the water retention rate is calculated using the following formula: the water retention rate under the conditions of heating, pressurization, and centrifugation.

1.3.4 Determination of material particle size.

1.3.5 Determination of Condensation Fraction A certain amount of FRC sample (G,) is accurately weighed. After soaking in distilled water for 24 h, the water-absorbing gel is wrapped with filter paper and transferred to a Soxhlet extractor and extracted with a methanol-water solution. After 24 h, remove, 105 T dry, and weigh (G, calculate the gel fraction 2 results and discussion) Molecular structure compound profile control agent (FRC) is a lightly cross-linked spatial network structure, free Initiating polymerization and simultaneous cross-linking of the intercalated monomeric molecular chains and montmorillonite are intertwined with each other. Before water absorption, the polymer chains and the montmorillonite layer sheets are closely packed and mutually entangled and crosslinked to form a network structure. In addition, the polymer compound profile control agent can also be regarded as an ion network composed of a polymer electrolyte and cations adsorbed between layers in the montmorillonite structure, and there are a large number of mobile ions such as IT in the ion network. When the material and the solution meet, an ion concentration gradient is formed at the interface, and the prerequisite for osmotic pressure generation is> 81. The most important application performance of FRC is the volume expansion capacity (ie, the expansion ratio), and its expansion performance depends on the composition of the material. and Fine crosslinked structure, and depending on the environmental factors of the external medium will now be discussed parameters affecting the synthesis conditions simulations and field application of material properties.

2.1 Effect of Crosslinker Concentration on Water Absorption of FRC FRC is a low cross-link density, P, and water-swellable polymer material. According to the theory of Flory-Huggins, the main factors affecting water swelling are the cross-linking density of the material and the hydrophilic groups contained in the material structure. By regulating the concentration of the cross-linking agent, the density of cross-linking points in the polymer network can be changed, thereby changing the size of the water-absorbing network and achieving the purpose of controlling the water-absorbing multiple. If the concentration of the cross-linking agent is too high, the cross-linking density of the polymer is too large, the network chain between the cross-linking points becomes shorter, the pore volume in the network structure is too small, and the water-absorbing multiple decreases. If the cross-linking agent concentration is too low, the three-dimensional network structure cannot be effectively cross-linked between the hydrazine molecular chains, the cross-linking density of the polymer is too small, the gel strength is poor, and the macroscopically water-soluble property shows that the material does not have the use performance.

The range of cross-linking agent concentration is preferably 8x10'2.5xHTVoI/L (see 2.2 Effect of montmorillonite content on the water absorption of FRC) The content of montmorillonite has a great influence on the water absorption of FRC. On the one hand, the main montmorillonite The component is aluminosilicate' with a multi-functional layered sheet structure, which is embedded with the monomer and has a cross-linking effect to a certain extent. It acts synergistically with the bifunctional chemical cross-linking agent to promote the composite material The increase of the link density, thus affecting the water absorption performance of FRC and the effect of montmorillonite content on the water absorption (see below).When the content of montmorillonite is below 15%, FRC has a higher water-absorption multiple, and when the content of montmorillonite is At 5% or less, the water-absorption ratio of FRC is higher than that of pure organic monomer copolymers, which is a function that montmorillonite, as an embedded receptor for organic monomers, has a cross-linking point during the polymerization process, and a certain amount of a certain concentration is added. The montmorillonite contributes to the formation of the crosslinked structure of the material; but when the content of the montmorillonite is too large, the proportion of the embedded organic monomer is relatively reduced, and the montmorillonite fills most of the space of the crosslinked network structure space and hinders the water. The absorption of molecules makes the material Reduced water absorption.

Table 1 Effects of montmorillonite content on water absorption of FRC Crosslinking (NN) Water absorption (g/g) Montmorillonite (Montmorillonite (5%) Montmorillonite (30%)) Same crosslinker concentration Under the conditions, the composite material partially filled with montmorillonite is compared with the pure organic monomer copolymer (see Table 1).When the content of montmorillonite is less than 5%, the water absorption capacity of FRC is higher than that of pure polymer. high.

2.3 The influence of degree of hydrolysis on the water absorption of FRC Because the hydrophilicity of -CONH2 and -COONa groups in the molecular chain structure of FRC is different, the method of adjusting the proportion of acrylamide and sodium acrylate monomer can be used to prepare different degrees of hydrolysis. FRC. When the degree of hydrolysis (DH%) is that sodium acrylate accounts for 70% of the total combined monomers of acrylamide and sodium acrylate, the FRC has the highest water absorption (see). When the degree of hydrolysis is higher or lower than 70%, the water-absorbency is reduced.

This is because, on the one hand, COONa is more polar and hydrophilic than that of -C0NH2. As the degree of hydrolysis increases, the content of -COONa groups in the material structure increases, which is beneficial to the improvement of the water absorption performance of the material; but on the other hand, -COONa is an ionizable ionic group that can be dissociated into -C00 and ions in aqueous solution. The degree of hydrolysis is too large. The electrostatic repulsion of the -C0CT group on the polymer chain increases, making the crosslinked network system unstable. , The material's ability to absorb water decreases.

In summary, controlling the degree of hydrolysis not only adjusts the proportion of acrylamide and sodium acrylate in the comonomer component, but also controls the proportion of -COONa and -CONH2 groups in the material structure to make the electrically neutral molecular group -CONH2 ( The electrostatic repulsion between the groups is small) and the -COONa ionic group (larger electrostatic interaction between the groups) is arranged rationally on the polymer chain. The synergistic effect of each group makes the water absorption of the FRC higher than that of montmorillonite. - Water absorption properties of acrylamide and montmorillonite-sodium acrylate polymers.

2.4 Influence of Initiator Concentration on FPC Water Absorption Factor The initiator concentration has an effect on the size of the molecular chain between crosslinks. In the case of a certain concentration of cross-linking agent, the size of the molecular chain will directly affect the size of the cross-linked network, thus affecting the FPC's water absorption (see). The water-absorbing multiple of FRC began to increase significantly with the increase of the bowel hair spray concentration, whereas when the initiator concentration was greater than 7.88xl4 ml/L, the water-absorption fold decreased. This is because when the amount of initiator is small, the generated free radical concentration is low, the reaction rate of the initiated monomer is also low, and the entire polymerization reaction rate is very slow. At this time, the organic monomer and montmorillonite cannot be effectively embedded in the polymerization. The formation of composite polymer; if the amount of initiator is too much, it is easy to burst polymerization, organic monomers due to the formation of polymerization centers and the formation of homopolymer precipitation, and cross-linking density is too high, the water absorption fold.

2.5 Influence of Reaction System Concentration The concentration of the reaction system directly affects the polymerization kinetics, product performance, and economics of the production process. In the aqueous solution polymerization system, the reactant concentration has a great influence on the utilization rate of the polymerization apparatus. From the viewpoint of continuous production, the concentration is high, although the utilization rate of the polymerization apparatus can be increased, the reaction heat in the polymerization process is difficult to control, and If the concentration is too high, the fluidity of the system becomes worse, and continuous production is difficult. The concentration is low. Although the heat of polymerization is easily controlled, the utilization rate of the device is also low. According to the ratio of different raw materials, the suitable concentration range of the reaction system is 25% 37%. Influence of the degree of hydrolysis on the water absorption of the FRC The effect of the initiator concentration on the water absorption of the FRC 2.6 The relationship between the particle size and the water absorption rate For FRC samples with different particle sizes, the sample with water absorption rate (tv ~30 mesh) determined by vortex observation requires tv = 65 min to reach saturation; the larger the particle size of FRC, the slower the water absorption rate (see Table 2). This is because the water absorption rate is determined by the radial diffusion rate of water molecules from the surface of the material particles to its interior. The smaller the particle size, the larger the specific surface area, the shorter the water molecule's diffusion path to the interior and the faster the water absorption rate, and vice versa. .

Table 2 Relationship between FRC Particle Size and Water Absorption Rate Granularity (mm) Water Absorption Rate tv 2.7 Blockage Migration Characteristics of FRC Gel Particles in Porous Media 2.7.1 Influence of Core Permeability on Gel Blocking Effect Penetration rates of 8225 and 2007 md were used respectively. The core, the pump displacement of 2ml/min, after the oil injection reverse blocking agent 丨/3 void volume, and then water for positive displacement experiments. As the injection volume increases, the lower the permeability of the core, the smaller the outlet flow (see).

2.7.2 The flowability of FRC gel particles can be used to evaluate the sealing and migration of FRC gel particles by detecting pressure changes during different injection phases. The first stage is to adjust the front waterflood, the pressure remains basically stable; the second stage is to note the FRC grain stage, the general trend is that the pressure keeps rising, but there is a large fluctuation, and the fluctuation is the migration of particles in the pore and throat. To the extent that particles flow out of the core is the cause of the pressure drop, gel particles are observed from the effluent. Experiments show that the gel particles have plugging and migration effects in the pores of the core (see) Changes in pressure during different injection phases. 2.8 FRC Gel Particle Displacement Performance Measurement of Gel Particle Displacement Performance Using Sand Filling Tubes Before the Experiment Saturate the core with oil beforehand, and then perform water flooding. When the water flooded to a water content of 98%, reinject the FRC particles with a concentration of 1000 mg/L to perform flooding experiments (see Table 3).

The results show that the use of gel particle displacement can significantly reduce the residual oil saturation and improve recovery.

Table 3 Comparison of water flooding and FRC gel control and flooding effect Core number No. of water production after water flooding Recovery degree after gel flooding Production of gel flooding increments 3 Conclusions Polymer composite profile control agent was prepared by chemically initiated polymerization method ( FRC). The main technical parameters in the synthesis process such as raw material selection and group distribution ratio, polymerization conditions, additive concentration were optimized. By controlling the FRC performance through the structural parameters, the expansion ratio and the expansion rate of the profile control agent can be controlled. The conversion of field operations from high-pressure pumping to atmospheric injection has been realized, and oil recovery can be significantly improved in applications.

The research conclusions can also provide theoretical basis and technical guarantee for the large-scale production of FRC.