linear viscoelastic

Hypothesis: 

Sand production from oil reservoirs is marked by many problems, such as well productivity reduction, operating equipment corrosion, and an increase in production costs; therefore, sand control in unconsolidated reservoirs is crucial for operating companies. Chemical injection into the production vessel, in order to strengthen and reduce sand formation, would be one of the most important methods of sand control.

In this study the effectiveness of a Co[AM-AMPS-AAC]/PEI-MBA(CO) hydrogel nanocomposite in sand control was investigated. The acrylamide-based nanocomposite is strengthened structurally and thermally by the addition of double crosslinkers and nanoparticles. Structural, morphological, thermal, rheological, compressive strength and flooding tests were carried out to define and assess its efficacy.

According to X-ray diffraction test findings, nanoparticles are evenly distributed throughout the structure. Morphological tests demonstrated the production of a dense, homogenous, and porous structure and validated the presence of nanoparticles in the structure. According to the thermal gravimetric test, adding nanoparticles increased the starting temperature of degradation from 80 to 195°C. The strain and frequency sweep rheological tests investigated the behavior of the material under different strains and stresses; they confirmed the preservation of the strong structure and linear viscoelastic behavior at a temperature of 90°C, strains between 0.1 and 20%, and frequencies between 0.1 and 10 Hz. The injection of 0.5 PV (pore volume) of 1% (by wt) nanocomposite to the sand pack resulted in a 730% increase in the axial strength of the sand pack according to the compressive strength test and 90% reduction in sand production measured by the chemical flooding test. Considering the stability and proper efficiency in the reservoir's harsh conditions, having linear viscoelastic properties, increasing compressive strength, and reducing sand production, the hydrogel nanocomposite designed in this research is proposed as a new and optimal product to control sand production and migration.

Considering the important economic and environmental benefits of low energy asphalt mixture and the need to know and study more about this asphalt due to little research, in this article, the linear viscoelastic properties of this type of asphalt are evaluated using dynamic modulus test. Due to the mechanical weakness of this asphalt mixture and considering its environmental nature, an additive compatible with the environment was selected to modify it. Therefore, crumb rubber in three levels of 10, 15 and 20% by weight of asphalt binder was used to modify the samples. Controlled and modified asphalt samples were designed and compacted according to the superpave method and were tested to determine the dynamic modulus and their viscoelastic properties at different temperatures and frequencies. The master curve of asphalt mixtures showed that at high temperature (low frequency) the highest dynamic modulus belongs to low energy asphalt mixtures with 15% rubber powder. Therefore, this mixture has the highest rutting strength compared to other mixtures. On the other hand, comparison of the master curve of asphalt mixtures at low temperature (high frequency) showed low stiffness of low energy asphalt samples without additive and low energy asphalt with 15% additive and their resistance to cracking, respectively. Evaluation of the viscoelastic properties of the test specimens also confirmed the fact that the highest elasticity belonged to the low-energy asphalt sample modified with 15% crumb rubber and the most viscous mixture was the hot asphalt sample.

In this work, an analytical micromechanical model based on unit-cell approach is used to study the effect of interphase on the non-linear viscoelastic response of multiphase polymer composites. The representative volume element of composite consists of three phases including unidirectional fibers, polymer matrix and fiber/matrix interphase. Perfect bonding conditions are applied between the constituents of composites. The Schapery viscoelastic constitutive equation is used to model the nonlinear viscoelastic matrix. Prediction of the presented micromechanical model for the creep response of polymer material and two-phase composites shows good agreement with available experimental data. Furthermore, the predicted overall elastic behavior of three-phase composites demonstrates close agreement with other numerical results available. The effects of material and thickness of interphase on the creep-recovery strain curves of three-phase composites are studied in details. Results show that the interphase thickness and material properties have significant effect on the creep-recovery strain responses of the three-phase composites under transverse loading. According to micromechanical modeling results, it is found that the interphase negligibly affects the nano-linear viscoelastic behavior of three-phase composites under axial loading. Effects of the different stress levels and the variation of fiber volume fraction on the creep-recovery strain curves of three-phase composites are also investigated.