Caili Dai

The structure effect on the surface and interfacial properties of zwitterionic sulfobetaine surfactants for enhanced oil recovery

The surface and interfacial properties of five zwitterionic surfactants, including three propyl sulfobetaines CSB (where the carbon atom number of the alkyl chain is 12, 14 and 16, respectively) and two hydroxypropyl sulfobetaine surfactants CHSB (where the carbon atom number of the alkyl chain is 12 and 14, respectively), were studied at both air–water and oil–water interfaces. The surface activity of these surfactants at the air–water interface in aqueous solutions was investigated by the Wilhelmy plate method at 30 °C and ambient pressure. The values of the critical micelle concentration (CMC) and surface tension at CMC (γCMC) were determined from the surface tension measurements. The obtained results indicate that CMC and surface tension strongly depend on the surfactant molecular structure. An increase in the alkyl chain length results in a decrease in the CMC and γCMC values. The presence of a hydroxyl group causes an increase in CMC values and a decrease in γCMC values. The hydroxypropyl sulfobetaine surfactants have better surfacial properties. In addition, the interfacial activity at the oil–water interface among the crude oil–reservoir water–surfactant systems was investigated by use of the spinning drop method under harsh reservoir conditions of high temperature (90 °C) and high salinity (11.52 × 104 ppm, including 7040 ppm Ca2+ and 614 ppm Mg2+). It is interesting that the transient minimum dynamic interfacial tension (DITmin) could be observed in a specific concentration range. The time to reach DITmin is different with different surfactant molecular structures and surfactant concentrations. The hydroxypropyl sulfobetaine surfactant C14HSB shows excellent interfacial properties: it can reduce interfacial tension (IFT) between oil and water to an ultralow level at a very low concentration, and the ultralow IFT phenomenon only occurs in a specific concentration range from 0.03 to 0.10 wt%. In this work, hydroxypropyl sulfobetaine surfactants exhibit remarkable ability and are good candidates for chemical agents to enhance oil recovery in harsh reservoirs.

Study on formation of gels formed by polymer and zirconium acetate

The gel system used in the preparation of dispersed particle gel for water shutoff treatments, which is composed of polyacrylamides and zirconium acetate, was investigated. The gelation process, the effects of various parameters on the gelation properties, the thermal stability, and the microstructure were addressed. The cross-linking reaction process is divided into three successive steps: induction, rapid cross-linking, and stabilization. High polymer and crosslinker concentrations reduce gelation time and increase gel strength. In addition, adding salts to the brine or increasing the temperature also decrease gelation time and increase gel strength. The optimum pH for the gel system is 7.49. In field applications, this gel system is recommended to be used within 130 °C using differential scanning calorimetry. The gel formed in a three-dimensional network structure was confirmed through environmental scanning electron microscopy.

Preparation of Dispersed Particle Gel (DPG) through a Simple High Speed Shearing Method

Dispersed particle gel (DPG) has been first successfully prepared using cross-linked gel systems through a simple high speed shearing method with the aid of a colloid mill at room temperature. The gel microstructure and particle size were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), and dynamic light scattering (DLS) measurements. The results clearly show that the prepared DPG particles have highly uniformly spherical structures with an average size of 2.5 μm. A possible mechanism for the formation of DPG has been put forward and discussed in details. The high speed shearing method is considered to be the simple and rapid method for the preparation of DPG.

Construction of Supramolecular Self‐Assembled Microfibers with Fluorescent Properties through a Modified Ionic Self‐Assembly (ISA) Strategy

Highly ordered supramolecular microfibers were constructed through a simple ionic self-assembly strategy from complexes of the N-tetradecyl-N-methylpyrrolidinium bromide (C(14)MPB) surface-active ionic liquid and the small methyl orange (MO) dye molecule, with the aid of patent blue VF sodium salt. By using scanning electron microscopy and polarized optical microscopy, the width of these self-assembled microfibers is observed to be about 1 to 5 μm and their length is from tens of micrometers to almost a millimeter. The (1)H NMR spectra of the microfibers indicates that the supramolecular complexes are composed of C(14)MPB and MO in equal molar ratio. The electrostatic, hydrophobic, and π-π stacking interactions are regarded as the main driving forces for the formation of microfibers. Furthermore, through characterization by using confocal fluorescence microscopy, the microfibers were observed to show strong fluorescent properties and may find potential applications in many fields.

Formation and rheological properties of wormlike micelles by N-hexadecyl-N-methylpiperidinium bromide and sodium salicylate

The formation and properties of wormlike micelles composed of a surface-active surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) and organic salt sodium salicylate (NaSal) at room temperature were studied. Rheological measurements and cryogenic transmission electron microscopy (cryo-TEM) were conducted to study the rheological properties and microstructures of wormlike micelles. Cryo-TEM image confirms the formation of wormlike micelles in aqueous solution. Rheological results show that wormlike micelles indicate linear viscoelasticity and follow the Maxwell model. The Cole–Cole plots agree well with the typical characteristic of the Maxwell model at low and middle frequencies. The contour length, mesh size, and entanglement length of wormlike micelles are estimated from the rheological measurements. In addition, the temperature effect on the rheological properties of wormlike micelles is also studied. Through comparison, the entanglement length and mesh size of wormlike micelles are nearly unchanged, while the contour length shows a sharp decrease tendency with the increase of temperature, indicating that the change of rheological properties with the temperature is due to the contour length change of wormlike micelles.

Investigation of Preparation and Mechanisms of a Dispersed Particle Gel Formed from a Polymer Gel at Room Temperature

A dispersed particle gel (DPG) was successfully prepared from a polymer gel at room temperature. The polymer gel system, morphology, viscosity changes, size distribution, and zeta potential of DPG particles were investigated. The results showed that zirconium gel systems with different strengths can be cross-linked within 2.5 h at low temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) results showed that the particles were polygonal particles with nano-size distribution. According to the viscosity changes, the whole preparation process can be divided into two major stages: the bulk gel cross-linking reaction period and the DPG particle preparation period. A polymer gel with a 3-dimensional network was formed in the bulk gel cross-linking reaction period whereas shearing force and frictional force were the main driving forces for the preparation of DPG particles, and thus affected the morphology of DPG particles. High shearing force and frictional force reduced the particle size distribution, and then decreased the zeta potential (absolute value). The whole preparation process could be completed within 3 h at room temperature. It could be an efficient and energy-saving technology for preparation of DPG particles.

Investigation of the profile control mechanisms of dispersed particle gel.

Dispersed particle gel (DPG) particles of nano- to micron- to mm-size have been prepared successfully and will be used for profile control treatment in mature oilfields. The profile control and enhanced oil recovery mechanisms of DPG particles have been investigated using core flow tests and visual simulation experiments. Core flow test results show that DPG particles can easily be injected into deep formations and can effectively plug the high permeability zones. The high profile improvement rate improves reservoir heterogeneity and diverts fluid into the low permeability zone. Both water and oil permeability were reduced when DPG particles were injected, but the disproportionate permeability reduction effect was significant. Water permeability decreases more than the oil permeability to ensure that oil flows in its own pathways and can easily be driven out. Visual simulation experiments demonstrate that DPG particles can pass directly or by deformation through porous media and enter deep formations. By retention, adsorption, trapping and bridging, DPG particles can effectively reduce the permeability of porous media in high permeability zones and divert fluid into a low permeability zone, thus improving formation profiles and enhancing oil recovery.

A Study on the Morphology of a Dispersed Particle Gel Used as a Profile Control Agent for Improved Oil Recovery

To achieve in-depth profile control of injection water and improve oil recovery, a new profile control agent, termed as dispersed particle gel (DPG), has been developed and reported. In this paper, the morphology of DPG and the factors that influence its morphology are systematically investigated using atomic force microscopy (AFM). The AFM studies show that DPG is composed of small pseudospherical particles and that their sizes can be controlled by adjusting the shearing rate, the initial polymer mass concentration, and the salinity. Dynamic light scattering (DLS) is used to study the effects of the initial polymer mass concentration, the shearing rate, the salinity, and the high-temperature aging on the particle size of DPG. The aggregation ability of DPG is explained using the DLVO theory and space stability theory. This work provides a scientific basis and technical support for the formula design of DPG and its application in the oil and gas field.

Investigation of Novel Triple-Responsive Wormlike Micelles

Smart wormlike micelles with stimuli-tunable rheological properties may be useful in a variety of applications, such as in molecular devices and sensors. The formation of triplestimuli-responsive systems so far has been a challenging and important issue. In this work, a novel triplestimuli (photo-, pH-, and thermoresponsive) wormlike micelle is constructed with N-cetyl-N-methylmorpholinium bromide and trans-cinnamic acid (CA). The corresponding multiresponsive behaviors of wormlike micellar system were revealed using cryogenic transmission electron microscopy, a rheometer, and 1H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed by 1H NMR, chemical structure of a CA molecule can be altered by the multiple stimulation from an exotic environment. We expect it to be a good model for triple-responsive wormlike micelles, which is helpful to understand the mechanism of triple-responsiveness and widen their applications.

The first study of surface modified silica nanoparticles in pressure-decreasing application

In this study, hydrophobic silica nanoparticles were prepared by the surface modification of silica nanoparticles using dimethyldichlorosilane. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy were employed for the characterization of the raw silica nanoparticles and modified silica nanoparticles. The results showed that methyl groups are successfully grafted on the surface of silica nanoparticles. The titration method was employed to quantitatively determine the surface hydroxyl number of silica nanoparticles; the result demonstrated that the surface hydroxyl number of silica nanoparticles significantly decreases after modification. The modified silica nanoparticles was dispersed in water using TX-100 as the dispersant and NaOH to adjust the pH. The dispersion was injected into an oil-treated artificial core, the injecting pressure of the NaCl solution (5 wt%) before and after injection was measured. The result showed that the hydrophobic silica nanoparticles exhibit a good pressure-decreasing ability. The contact angle of the slabbed core was measured, the contact angle increased from 36° to 134° after it was treated by the modified silica nanoparticle dispersion. Transmission electron microscopy was employed for the characterization of the modified silica nanoparticles. Scanning electron microscopy was employed for the characterization of the treated core; the result showed that the modified silica nanoparticles are adsorbed on the surface of the core and forms a hydrophobic layer, changing the wettability of the sand surface from water wet to oil wet, thereby decreasing the flowing pressure.