A dispersed low-elastic microsphere system, consisting of low-viscoelastic microspheres and polymers, is a novel suspension system for enhanced oil recovery in heterogeneous reservoirs. In this study, experiments were performed to characterize the morphology, viscoelasticity, and swelling performance of the synthetic low-elastic microspheres. The stability and rheological property of the dispersed low-elastic microsphere system was investigated using a Turbiscan Lab Expert stability analyzer and an MCR301 rheometer. In the flow and displacement experiments, the parallel-sandpacks model and microscopic visualization models were used to study the oil-displacement effect and micromigration mechanism of the low-elastic microspheres. The experimental results showed that the storage modulus (G′) of the synthetic low-elastic microspheres was only 23.6 Pa and they also had a good swelling property in the simulated formation water. The parallel-sandpacks test and micromodel test indicated that the dispersed low-elastic microsphere system was a promising agent for both conformance control and improved oil recovery in heterogeneous reservoirs. Moreover, the low-elastic microspheres had good deformation and shear resistance performances. Five transport behaviors, such as deformable passing through, partition passing through, blockage, adhesion, and directly passing through, of low-elastic microspheres in a porous medium have been put forward. This study not only provides an understanding of the properties of the dispersed low-elastic microsphere system but also supplies theoretical support for the mechanism of improving oil recovery for the dispersed low-elastic microsphere system.

Responsive wormlike micelles (WLMs) constructed by different carboxylic acids are fascinating. However, it is unknown how the position of the carboxylic groups alters the stimuli-response of wormlike micellar systems. Herein, three pH-responsive WLMs based on Gemini-like surfactants (named o-EAPA, m-EAPA, and p-EAPA) were formed and studied through the complexation of N-erucamidopropyl-N,N-dimethylamine (UC₂₂AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA) at the molar ratio of 2 : 1. The viscoelasticity, phase behavior and aggregate microstructure were separately explored by rheological, appearance observation and cryo-TEM methods. The results show that all phthalic acids can protonate UC₂₂AMPM, thereby forming WLMs. However, with the shorter spacer distance between two carboxyl groups in phthalic acid, o-EAPA exhibits the longer length scale of aggregates and a more efficient thickening ability compared to the other two systems. Similar results in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, and p-PA systems further verify the applicability of this mechanism. Furthermore, the phthalic acid based WLMs are found to exhibit intriguing reversible pH-responsive behaviors, which include promptly switching between a high elastic system and a low viscosity fluid by pH control. The o-EAPA system possesses a larger viscosity maximum, which produces more precipitous viscosity changes as the pH varies. This study is beneficial for the formation of pH-responsive WLMs and to determine their advantages for applications.