A systematic study of the transition in silicate solutions from a solution containing a highly complex mixture of silicate species to one dominated by a single symmetric cubic octamer has been completed. Infrared and NMR results have been analyzed and compared with each other and literature values. The FT-IR band locations are dependent on many factors, particularly the dominant band near 1000 cm(-1). The analysis supports Dent Glasser's hypothesis that silica polymerization results from changes in distribution between the larger colloidal silica and intermediate sized anionic fraction rather than the continuous stepwise growth seen with organic polymerization. A constant value of silica monomer seen in all solutions independent of the complexity of the species or their distribution suggests equilibrium between the monomeric form and larger anions and polymers that is independent of their structure. No evidence is uncovered for specific silicate species dependent IR band assignments.

This paper examines the effects of alkaline additives on dilute surfactant systems for improved oil recovery. The study was limited to the determination of the effects of alkaline additives on interfacial tension (IFT), surfactant adsorption or retention in Berea cores, and improvement in oil recovery. The alkaline chemicals studied were sodium silicates, sodium phosphates, sodium carbonate, and sodium hydroxide. In addition, optimal salinities and surfactant average equivalent molecular weight for the recovery of two midcontinent crude oils were determined through a combination of IFT determinations and oil displacement tests. The laboratory results show that the alkaline chemicals have two major effects. First, IFT is reduced further by the high pH surfactant/alkali solution combinations, and second, certain alkaline species significantly reduce surfactant retention. This leads to recoveries of residual oil from 40 to 70% with surfactant solutions containing only 0.25 wt% surfactant. Introduction The use of dilute aqueous surfactant systems for enhanced oil recovery has been documented for several decades, but the more pertinent work has been performed in the past 15 years. Gogarty, and Tosch outlined Marathon's early studies on the Maraflood TM process, which employs what is commonly known as a micellar/polymer system for enhanced recovery. In the area of dilute surfactant systems, a considerable body of work has been published in which alkaline chemicals have been added to improve recovery efficiency. A number of processes have been patented in which excess alkaline chemicals have been injected following the initial injection of organic acids. Other systems in which an alkaline preflush preceded the injection of the surfactant slugs have been reported. Similar processes, which can be summarized in a general manner have been reported by several research teams. All these systems are individually different but employ the same general principles in their operation. These principles are as follows.Injection of a sacrificial alkaline chemical, such as sodium carbonate or sodium tripolyphosphate, in a saline solutionto reduce the hardness ion level,to reduce surfactant adsorption or retention, andto provide an optimal salinity for the surfactant slug.Injection of a dilute surfactant slug containing alkaline chemicals, such as sodium carbonate and/or sodium tripolyphosphate, with the proper concentration of sodium chloride added to provide the minimal IFT for optimal oil recovery.Injection of a drive fluid that may or may not contain a polymer additive for increased mobility control. Several field trials of low-tension waterfloods have been reported. In most cases, increased production was observed from watered-out areas. The tests were considered to be technologically successful but not necessarily economically feasible at the time of the test. Some of the disadvantages of dilute surfactant systems can be traced to complex and, in most cases, deleterious effects of hardness ions, mineral surfaces, and highly saline reservoir fluids on the effectiveness of the surfactant in mobilizing the oil phase. Some of these disadvantages can be overcome by proper selection of surfactants that are less sensitive to hardness ions and more tolerant of high salinities. However, most of these surfactant systems are much more expensive than the petroleum sulfonates and still would be subjected to considerable adsorption or retention by the reservoir substrate. Thus, the addition of alkaline chemicals to the surfactant system provides an economical solution that overcomes the adverse conditions mentioned previously. SPEJ P. 503^

Surfactants, polymers and alkaline chemicals are the major components of any chemical flooding process. Interactions of these chemicals can be extremely important to the final outcome of field trials, since the desired effect of each chemical may be enhanced or degraded as the various chemical slugs become mixed in the reservoir. In some instances it may be desirable to inject these various chemicals together in the same slug because of synergistic effects or to shorten the duration thereby improving the economics for the project. It is important to understand and anticipate the nature of these interactions to optimize flood design and recovery performance. Specific interactions among these chemicals have been examined by interfacial tension (IFT) and viscosity measurements and core displacement studies. Many polymers contain small amounts of surfactant which contribute to IFT reduction, and also polymers slow diffusion and mass transfer to and from the oil and water phases thereby affecting consumption and adsorption phenomena. Certain alkalis have a dramatic effect on the ionic environment which affects both surfactant activity and optimal partioning between phases and polymer hydrolysis, stability, and viscosity. Also alkalis can modify mineral surfaces leading to reduced adsorption of the more expensive chemical components. These observations correlate well with core flood performance where the various chemicals are used either together or in successive slugs of various combination. In general at low concentrations most of these chemicals are compatible with each other and appear to enhance overall performance when used together.

A procedure that measures both the silica concentration and the ratio of silica to alkali content of the commercially important sodium silicate solutions using an ATR FT-IR spectrophotomer has been developed. The accuracy and precision have been found to be equal to or better than the commonly used measures via titrimetry and density determination.