The Interaction Between Soluble Polymers With Low-molecular Weight And Their Environmental-Responsive Behavior

With the ongoing exploration of oil, the proportion of oil and gas resources in deep strata is becoming larger and larger. In order to meet the increasing demand for oil energy, the efficient exploration and exploitation of oil and gas resources in deep strata are of particular importance. Based on investigation of a large number of related literatures in detail, the water-soluble polymer with-SO3H,-NH2, or-OH groups are usually used to effectively regulate and control the rheology and filtration loss under high-temperature and high-salinity. Therefore, the investigation of the physical and chemical properties of the above polymer molecules in solution under high-temperature and high-salinity and their effects on the colloidal stability of montmorillonite suspensions is the key technology to design and produce the high-temperature resistant water-based drilling fluids. It is very important for the development of the ultra-deep drilling technology and the application of oil consumption in such a large demandent country. What is more, it could accelerate the speed of China’s oil and gas exploration and development, to ensure self-sufficiency ratio of oil and gas resources in China and the country’s energy security.Recently, researchers focus on the developing new drilling fluid additives with good performance through polymerization with molecular structure design. They also studied the effects of polymer concentration, pH, salt concentration and temperature on the physical and chemical properties of the above polymer molecules in solution at room temperature and their influences on the colloidal stability of montmorillonite suspensions. However, there are still some problems in the following aspects. Firstly, the adsorption mechanism of polyetheramine on montmorillonite particles and its influences on the colloidal stability of montmorillonite suspensions are not fully understood. Secondly, the effect of temperature on the rheology behaviors of aqueous solutions containing polytheramine and montmorillonite particles should be studied in detail. Thirdly, the influences of high-salinity on the properties of sulfonated polymers are not clear. Finally, more methods should be explored to investigate the effects of high-temperature and high-salinity on the properties of water-soluble polymer in solutions.Based on the above discussion, in this dissertation, two kinds of water-soluble polymers with low molecular weight, polyetheramine and styrene sulfonic acid maleic anhydride copolymer (PSSMA) are investigated. First, the adsorption mechanism of polyetheramines on montmorillonite particles and their effects on the colloidal stability of montmorillonite suspensions after high temperature treatments or in the presence of salts are studied. Second, by investigating the rheology behavior of montmorillonite dispersion with polyetheramine under different temperatures, thermogelling in polyetheramine/montmorillonite suspensions are studied in detail. In addition, the physical and chemical properties of PSSMA molecules in the presence of Ca2+ions are investigated systematically, including the aggregation of PSSMA molecules and the interfacial activity.The present dissertation includes three topics.1. Colloidal properties of montmorillonite suspensions modified with polyetheramineA systematical evaluation of a polyetheramine (Jeffamine M1000) and polyethylene oxide (PEO), which have a similar number of ethylene oxide units and molecular weight, on modulating colloidal stability of montmorillonite suspensions exposed to high temperature (120℃,16h) or salt conditions are performed. A varied of methods including measurement of adsorption, X-ray diffraction (XRD), zeta potential, transmission electron microscopy (TEM), settlement experiments and rheology measurements are used to illustrate the difference. Results indicate that M1000molecules adsorb onto the particles mainly through electrostatic interaction and adopt a densely packed mushroom configuration on the clay surface. Because of the adsorption properties of M1000, the salt tolerance is improved slightly (from10mmol/L to50mmol/L NaCl) and the colloidal stability of the high temperature treated suspensions is maintained. Meanwhile, PEO molecules adsorb onto clay via hydrogen bonding and take a compact conformation on the clay surface, which could not improve the salt tolerance effectively and leads to a weak bridging flocculation at high temperature. Thus, this finding not only provides some new guidance on modulating the colloidal stability of dispersion but also would be very useful in specific applications, such as drilling fluids and water treatment.2. Thermoreversible gelation in montmorillonite suspension containing polyetheramineMost types of structured complex fluids tend to decrease in viscosity with increasing temperature. However, in polyetheramine/montmorillonite mixed system the polymer-liquid affinity is strongly influenced by temperature, and as a result, unusual behaviors occur in the microstructure of dispersions upon heating. At low temperature (5℃), water is a good solvent for PEO and PPO chains of polyetheramine molecules adsorbed on montmorillonite particles, and the dispersion is a stable, low-viscosity sol. With the increase of temperature, water becomes a progressively worse solvent for PEO and PPO chains. Beyond a critical temperature (Tc), there is a sharp transition in microstructure from a stable sol to a volume-filling gel. The sol-gel transition is reversible, which requires each component to be present in certain percentage. Remarkably, the gelation occurs under significantly better than0temperature, which nearly equals the lower consolute solution temperature for PEO and PPO chains in water. Tc is strongly influenced by the chain length of PEO and PPO. The longer the PEO chains, the higher the Tc for gelation. We attribute the onset of thermogelling to the secondary minimum in the interparticle potential that can develop in the case of short stabilizing moieties and moderate solvent conditions. Owing to the modulating of the microstructure upon heating, this finding provides theoretical basis and guidance for filed application of the plugging principle and technology of gel sug.3. Ca2+ion responsive Pickering emulsions stabilized by PSSMA nanoaggregatesSulfonated polymers are a variety of strong water-soluble anionic polyelectrolytes with high charge density, good dispersion property in aqueous solution, without pH control and good surface and interfacial activities. They are often used in oil and gas drilling, whose dehydration and aggregation frequently brings about the difficulty of losing control of drilling fluid filtration at the elevated temperatures and salt concentrations. Therefore, the investigations of the physical and chemical properties of the sulfonated polymer molecules in solution under high-temperature and high-salinity are important. This topic is mainly focused on the interaction between Ca2+and Poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) molecules and its effect on the physical and chemical properties of PSSMA molecules. Results from dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM) indicate that the formation of PSSMA nanoaggregates is strongly dependent on Ca2+concentration. The PSSMA copolymer only aggregates above a critical Ca2+concentration (0.2mol/L) with an average diameter of10-40nm. After dilution with water, PSSMA nanoaggregates are rapidly redissolved again. Based on the properties of PSSMA nanoaggregates, Ca2+ion responsive Pickering emulsions were successfully prepared. At high Ca2+concentrations, the emulsions with high stability against coalescence can be prepared with the size in the submicrometer range as determined by DLS. Cryo-TEM and dynamic interfacial tension results confirm the adsorption of PSSMA nanoaggregates at the interface, which is the key to the stability of the emulsions. More importantly, rapid demulsification can be achieved by dilution with water on demand. It is because that upon dilution with water, PSSMA nanoaggregates undergo a transition from stable nanoaggregates to individual polymer chains, which leads to interfacial desorption of nanoaggregates and rapid demulsification of emulsions. Thus, this finding presents a new manipulation on emulsion stability and is expected to provide a useful guidance in the field of oil recovery, food science, environment protection and so on.