Abstract
To improve in-depth profile control in a low-permeability reservoir, polymeric microspheres were used. A distillation–precipitation polymerization method was adopted to prepare nanometer-sized polymeric microspheres, whose structure, apparent pattern, thermal endurance, particle size, hydration, and swelling capacity were tested and analyzed by a series of techniques, including infrared spectroscopy, scanning electron microscopy, thermogravimetry, high-pressure and high-temperature rheometry, and dynamic light scattering. The prepared polymeric microspheres were copolymerization products of acrylamide, acrylic acid, and methyl methacrylate that were uniformly round with a centralized size distribution. The nanometer-sized microspheres had satisfactory hydration/swelling performance, indicating that they could act as oil displacement profile control agents. With the increase of shear rate, the apparent viscosity of the polymeric microspheres was significantly reduced, and the fluid possessed a pseudoplastic behavior. When the shear rate was 100–1000 s−1, the fluid demonstrated a Newtonian fluid behavior. After the polymeric microspheres were hydrated, the particle size distribution curve shows a normal distribution, reaching a maximum swelling size of 21.3 times that of the original microspheres. The plugging performance and deformability of the polymeric microspheres gradually enhanced with swelling time, which makes the microspheres effective pore channel plugging agents for delivering a better in-depth profile control effect in rock cores with lower permeability. The core flooding test showed that, for the heterogeneous core with a permeability of 10 μm2, polymer microspheres have good plugging effect.
Highlights
As oil fields are continuously expanding, a heterogeneous reservoir has stronger heterogeneity and offers better distribution of the remaining oil, leading to severe water logging and water channeling
Preparation of the Polymeric Microspheres. e polymeric microspheres were prepared according to the literature [17, 18]: AM and acrylic acid (AA) served as the monomers, MBA served as the cross-linking agent, AIBN served as the radical initiator, and the distillation–precipitation polymerization reaction occurred in acetonitrile at 90°C. e state of ebullience was maintained for 15 min to wait for the reactant liquor to turn light blue and become milky. e temperature of the oil bath was adjusted to 115°C, and its reflux ratio was kept at about 2. e reaction lasted for 2 h, almost to dryness. e white solid powder precipitate was dispersed by ethanol, washed, centrifugated, and dried in vacuum at room temperature for 12 h to obtain the polymeric microspheres
Different volumetric flasks were used to formulate solutions whose concentration of AM/AA/methyl methacrylate (MMA) polymeric microspheres was 1.5 g/L with NaCl mass concentrations of 5, 10, 15, and 20 g/L. e solutions were placed in an incubating shaker at 60°C for hydration and swelling. e AM/AA/ MMA polymeric microsphere solutions were subjected to dynamic light scattering characterization at various time points to monitor the swelling size distributions
Summary
As oil fields are continuously expanding, a heterogeneous reservoir has stronger heterogeneity and offers better distribution of the remaining oil, leading to severe water logging and water channeling. E microspheres can plug and migrate vigorously in highpermeability zones to deliver the effect of plugging by grade and in-depth profile control. Related laboratory experiments proved that polymeric microspheres can expand, physically adsorb and cross-link, and demonstrate salinity and shear resistance [15, 16]. Erefore, they are able to enter plug formation depths to change the existing flow direction of injected water and enlarge swept volume, thereby improving water drive development. To eliminate the technological drawbacks of existing polymeric microspheres used for low-permeability reservoir control and provide microspheres with stronger in-depth profile control capacity, the authors adopted a distillation–precipitation polymerization method to prepare micrometer-sized polymeric microspheres. To eliminate the technological drawbacks of existing polymeric microspheres used for low-permeability reservoir control and provide microspheres with stronger in-depth profile control capacity, the authors adopted a distillation–precipitation polymerization method to prepare micrometer-sized polymeric microspheres. e resulting particles were studied using infrared analysis, scanning electron microscopy, and dynamic light scattering to study the pattern, particle size distribution, hydration/swelling properties, and rheological properties of the micrometersized polymeric microspheres
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