Feasibility Study of Applying Modified Nano-SiO2 Hyperbranched Copolymers for Enhanced Oil Recovery in Low-Mid Permeability Reservoirs

Study on the Shale Hydration Inhibition Performance of Triethylammonium Acetate

Shale inhibitor is an additive for drilling fluids that can be used to inhibit shale hydration expansion and dispersion, and prevent wellbore collapse. Small molecular quaternary ammonium salt can enter the interlayer of clay crystal, and enables an excellent shale inhibition performance. In this paper, a novel ionic shale inhibitor, triethylammonium acetate (TEYA), was obtained by solvent-free synthesis by using acetic acid and triethylamine as raw materials. The final product was identified as the target product by Fourier transform infrared spectroscopy (FT-IR). The inhibition performance of TEYA was studied by the mud ball immersion test, linear expansion test, rolling recovery test and particle size distribution test. The results demonstrated that the shale inhibitor shows a good shale hydration inhibition performance. The inhibition mechanism was studied by FT-IR and X-ray diffraction (XRD), respectively; the results showed that triethylammonium acetate TEYA could enter the crystal layer of clay and inhibit it through physical adsorption.

Experimental Research on Seepage Law and Migration Characteristics of Core-Shell Polymeric Nanoparticles Dispersion System in Porous Media

The nanoparticles dispersion system has complex migration characteristics and percolation law in porous media due to the interaction between the nanoparticles and porous media. In this paper, lab experiments were carried out to characterize the morphology, particle size distributions, and apparent viscosities of SiO2/P(MBAAm-co-AM) polymeric nanoparticle solution, investigate its migration characteristics in porous media, and probe its capability of enhanced oil recovery (EOR) in the reservoirs. Quartz microtubule, sand pack, and etched glass micromodels were used as the porous media in the flow and flooding experiments. Gray image-processing technology was applied to achieve oil saturation at different flooding stages in the micromodel for calculating the EOR of the SiO2/P(MBAAm-co-AM) polymeric nanoparticle solution. The results show that The SiO2/P(MBAAm-co-AM) polymeric nanoparticles are spherical with diameters ranging from 260 to 300 nm, and the thicknesses of the polymeric layers are in the range of 30-50 nm. As the swelling time increases from 24 to 120 h, the medium sizes of the SiO2/P(MBAAm-co-AM) polymeric nanoparticles increase from 584.45 to 1142.61 nm. The flow of the SiO2/P(MBAAm-co-AM) polymeric nanoparticles has obvious nonlinear characteristics and a prominent scale effect at a low-pressure gradient, and there should be an optimal matching relationship between its injection mass concentration and the channel size. The flow tests in the sand packs demonstrate that the SiO2/P(MBAAm-co-AM) polymeric nanoparticles can form effective plugging in the main flow channels at different permeability areas and can break through at the throat to fulfill the step-by-step profile control. Moreover, the profile control of the SiO2/P(MBAAm-co-AM) polymeric nanoparticles strengthens with an increase in their swelling time. The microscopic flooding experiment in the etched glass micromodel confirms that the SiO2/P(MBAAm-co-AM) polymeric nanoparticles can block dynamically and alternatively the channels of different sizes with the form of loose or dense networks to adjust the fluid flow diversion, improve the sweep efficiency, and recover more residual oil. The SiO2/P(MBAAm-co-AM) polymeric nanoparticles can achieve an enhanced oil recovery of 20.71% in the micromodel.

Synthesis and Solution Properties of a Novel Hyperbranched Polymer Based on Chitosan for Enhanced Oil Recovery

A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.

CO2/N2-Responsive Nanoparticles for Enhanced Oil Recovery During CO2 Flooding

During CO₂ flooding, serious gas channeling occurs in ultra-low permeability reservoirs due to the high mobility of CO₂. The chief end of this work was to research the application of responsive nanoparticles for mobility control to enhance oil recovery. Responsive nanoparticles were developed based on the modification of nano-silica (SiO₂) by 3-aminopropyltrimethoxysilane (KH540) via the Eschweiler-Clark reaction. The proof of concept for responsive nanoparticles was investigated by FT-IR, ¹H-NMR, TEM, DLS, CO₂/N₂ response, wettability, plugging performance, and core flooding experiments. The results indicated that responsive nanoparticles exhibited a good response to control nanoparticle dispersity due to electrostatic interaction. Subsequently, responsive nanoparticles showed a better plugging capacity of 93.3% to control CO₂ mobility, and more than 26% of the original oil was recovered. Moreover, the proposed responsive nanoparticles could revert oil-wet surfaces to water-wet, depending on surface adsorption to remove the oil from the surface of the rocks. The results of this work indicated that responsive nanoparticles might have potential applications for improved oil recovery in ultra-low permeability reservoirs.

The Inhibition Property and Mechanism of a Novel Low Molecular Weight Zwitterionic Copolymer for Improving Wellbore Stability

In this work, a novel low molecular weight zwitterionic copolymer for improving wellbore stability, which is expected to be an alternative to the current shale inhibitors, was obtained by copolymerization of tris hydroxyethyl allyl ammonium bromide (THAAB), 2-acrylamido-2- methyl propane sulfonic acid (AMPS) and acrylamide (AM), initiated by a redox initiation system in an aqueous solution. The copolymer, denoted as SX-1, was characterized by FT-IR, TGA-DSC, and GPC. Results demonstrated that the molecular weight of SX-1 was approximately 13,683 g/mol and it displayed temperature resistance up to 225 °C. Regarding the inhibition performance, evaluation experiments showed the hot rolling recovery of a Longmaxi shale sample in 2.0 wt % SX-1 solutions was up to 90.31% after hot rolling for 16 h at 120 °C. The Linear swelling height of Na-MMT artificial core in 2.0 wt % SX-1 solution was just 4.74 mm after 16 h. Methods including particle size analysis, FTIR, XRD, and SEM were utilized to study the inhibition mechanism of SX-1; results demonstrated that SX-1 had entered into the inner layer of sodium montmorillonite (Na-MMT) and adsorbed on the inner surface, and the micro-structure of Na-MMT was successfully changed by SX-1. The particle size of Na-MMT in distilled water was 8.05 μm, and it was observed that its size had increased to 603 μm after the addition of 2.0 wt % of SX-1. Its superior properties make this novel low molecular weight copolymer promising for ensuring wellbore stability, particularly for high temperature wells.

CO2 Capture With Absorbents of Tertiary Amine Functionalized Nano-SiO2

To improve CO2 adsorption performance of nanoparticle absorbents, a novel tertiary amine functionalized nano-SiO2 (NS-NR2) was synthesized based on the 3-aminopropyltrimethoxysilane (KH540) modified nano-SiO2 (NS-NH2) via methylation. The chemical structure and performances of the NS-NR2 were characterized through a series of experiments, which revealed that NS-NR2 can react with CO2 in water and nanofluid with low viscosity revealed better CO2 capture. The CO2 capture mechanism of NS-NR2 was studied by kinetic models. From the correlation coefficient, the pseudo second order model was found to fit well with the experiment data. The influencing factors were investigated, including temperature, dispersants, and cycling numbers. Results has shown the additional surfactant to greatly promote the CO2 adsorption performance of NS-NR2 because of the better dispersity of nanoparticles. This work proved that NS-NR2 yields low viscosity, high capacity for CO2 capture, and good regenerability in water. NS-NR2 with high CO2 capture will play a role in storing CO2 to enhanced oil recovery in CO2 flooding.