There are some challenges in chemical flooding, such as, gas finger problem usually occurred in field tests, potential scale problems of chemical slug caused by precipitation due to incompatibility between chemical solution and formation brine, and drawbacks of experimental designing of chemical flooding. In this work, three challenges are mainly discussed in following chapters. Chapter one focuses on optimization of designing single well test; chapter two discusses the feasibility of foam stabilized by nanoparticles in porous media; chapter three states that coacervates problems are occurred in preparation of chemical solutions. The summary of three topics is addressed below.

The first chapter, the single well chemical tracer test (SWCTT) has emerged in the past decades as a method for measuring oil saturation prior to and/or after EOR operations, to measure the recovery performance in-situ. To use this technology, the partition coefficients of the selected tracers are essential for estimating the level of residual oil at the targeted single well. Commonly, injection of short chain alcohols and ethyl acetate, a reactive tracer, is carried out for the tracer slug, mainly based on site-specific reservoir conditions, to accurately determine the level of oil saturation in-situ. However, injection of ethyl formate has been less common due to its fast hydrolysis rate under elevated temperature, which increases the challenges in data interpretation. Therefore, a systematic study for using ethyl formate under mid-range temperature (<60°C); -as commonly found in mature oil field in the U.S., show the potential to be applied for SWCTT.

As part of the design effort for a series of EOR field tests to manage the project risk, we particularly assessed the relationships between the partition coefficients of reactive tracers and subsurface conditions; -such as salinity, temperatures, type of electrolytes and the equivalent alkane carbon number (EACN) of the crude oil experiments were performed under various reservoir conditions as a function of actual site characteristics at the targeted high saline formations.

In brief, our data clearly show that the (oil/water) partition coefficient of ethyl formate increase steadily with increasing NaCl concentrations, ranging from 10,000mg/L (0.17M) to 250,000mg/L (4.28M). A similar upward trend was observed for increasing temperature between 25°C to 52°C; however, the partition coefficient decrease inversely with increasing the crude oil EACN over the range from 8 to 12, which are common for domestic oil samples. It was also showed that brine with high NaCl concentration yielded higher partition coefficients. In contrast, brine with high CaCl2 and BaCl2 concentration yielded lower values. And MgCl2 performed somewhat unusual trend in our tests. These results further indicate that the partition coefficient of the reactive tracer, ethyl formate, is sensitive to change in salinity, temperatures, type of electrolytes and EACN, as observed for other chemical tracers. In addition, based on the hydrolysis rate of ethyl formate under various reservoir conditions, the appropriate window of shut-in time can be pre-determined before initiating the field test. We believe that the ability of better understanding the partition coefficients and predicting the shut-in time beforehand could drastically reduce the risks of SWCTT operations. In second chapter, the application of nanoparticles dispersions in foam flooding has become an attractive chemical enhanced oil recovery (EOR) technique as compared to conventional surfactant only foaming system. This study is to expand our understanding of utilizing multi walled carbon nanotube (MWCNT) on foam stability in porous media. We developed several foaming agent formulations (surfactants and polymers) in the presence of MWNT in 3% salinity (NaCl, 2.4wt%, CaCl2, 0.6wt %). The dispersion stability of the MWCNT and the viscosity of the solutions were measured. Foam was generated in-situ, one-dimensional flow-through tests were performed by co-injecting air and foaming solution containing either the foaming agents-only or the foaming agents in the presence of MWCNT. During each experiment, the pressure drop (∆p) and the nanoparticles recovered across the sand-pack were monitored. Injection rate, gas fraction and the effect of MWCNT stabilized foams in porous media were investigated.

The results reveal that foams stabilized by nanoparticles are able to generate stronger foams leading to apparent higher ∆p by introducing MWCNT that total concentration is as low as 60ppm. ∆p profile varies with gas fraction which largely affects the foam texture. Also, our data indicate the viscosity of foaming agent solutions influences ∆p values. Adding MWNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorb to nanoparticles which facilitates surfactants partitioning to the G/L interface. Thus, addition of nanoparticles in the developed surfactant-polymer foam formulations can lead to formation of stronger high-quality foams in porous media, which improves the sweep efficiency and increases the oil recovery. In third chapter, large amounts of surfactant coacervation work were focused on complex coacervation, such as mixture of surfactant and polymer, or mixture of different species of surfactants, seldom on the simple coacervation of single conventional surfactant in aqueous phase. This study aims to investigate evolution of dioctyl sulfosuccinate (AOT) /sodium chloride coavervation in aqueous solution associated with change in counterion binding degree.

In this work, coacervation phase boundary of AOT in the presence of sodium chloride was obtained by spectrophotometer in terms of turbidity measurement. The activity of counterion was measured by sodium ion electrode probe. Electro kinetic parameters such as hydrodynamic aggregate size were investigated by dynamic lighting scattering (DLS).
A monotonic decreasing AOT coacervate boundary was observed with increase in NaCl concentration. The degree of counterion binding, calculated by modified Corrin-Harkins equations, revealed a 3-segment behavior of AOT in salt solution. Colloid size distribution was conducted with DLS.

Counterion binding degree plays an important role in the formation of surfactant aggregates. A further study of binding degree facilitates to understand coacervation.