Enhanced chemical injection

D. T. Wason. Enhanced oil recovery through in-situ generated surfactants augmented by chemical injection. US DOE Rep DOE/BC/10847-20, Inst Gas Technol, Chicago, IL, August 1990. 

ISCO In situ amendments to stimulate and enhance biodegradation Injection of chemicals such as ozone,... 

In this paper, a new technique for plugging fractures is also presented. Also, surfactant-enhanced alkall/polymer flood is alternated with water injection in order to optimize oil production. This technique uses a shorter sequence of chemical injection and therefore increases the possibility of plugging the fractures. 

There are two principal mechanisms of enhanced oil recovery increasing volumetric sweep efficiency of the injected fluid and increasing oil displacement efficiency by the injected fluid. In both, chemicals are used to modify the properties of an injected fluid whether water, steam, a miscible gas such as CO2 or natural gas, or an immiscible gas, usually nitrogen. Poor reservoir volumetric sweep efficiency is the greatest obstacle to increasing oil recovery (9). 

Microbial-enhanced oil recovery involves injection of carefully chosen microbes. Subsequent injection of a nutrient is sometimes employed to promote bacterial growth. Molasses is the nutrient of choice owing to its low (ca 100/t) cost. The main nutrient source for the microbes is often the cmde oil in the reservoir. A rapidly growing microbe population can reduce the permeabiHty of thief zones improving volumetric sweep efficiency. Microbes, particularly species of Clostridium and Bacillus, have also been used to produce surfactants, alcohols, solvents, and gases in situ (270). These chemicals improve waterflood oil displacement efficiency (see also Bioremediation (Supplement)). 

The in situ combustion method of enhanced oil recovery through air injection (28,273,274) is a chemically complex process. There are three types of in situ combustion dry, reverse, and wet. In the first, air injection results in ignition of cmde oil and continued air injection moves the combustion front toward production wells. Temperatures can reach 300—650°C. Ahead of the combustion front is a 90—180°C steam 2one, the temperature of which depends on pressure in the oil reservoir. Zones of hot water, hydrocarbon gases, and finally oil propagate ahead of the steam 2one to the production well. 

Secondary recovery, infill drilling, various pumping techniques, and workover actions may still leave oil, sometimes the majority of the oil, in the reservoir. There are further applications of technology to extract the oil that can be utilized if the economics justifies them. These more elaborate procedures are called enhanced oil recovery. They fall into three general categories thermal recoveiy, chemical processes, and miscible methods. All involve injections of some substance into the reservoir. Thermal recovery methods inject steam or hot water m order to improve the mobility of the oil. They work best for heavy nils. In one version the production crew maintains steam or hot water injection continuously in order to displace the oil toward the production wells. In another version, called steam soak or huff and puff, the crew injects steam for a time into a production well and then lets it soak while the heat from the steam transfers to the resei voir. After a period of a week or more, the crew reopens the well and produces the heated oil. This sequence can be repeated as long as it is effective. 

Manipulating a petroleum reservoir during enhanced oil recovery through remote sensing of proeess data, development and use of dynamic models of underground interactions, and selective injection of chemicals to improve efficiency of recovery ... 

Enhanced oil-recovery processes include chemical and gas floods, steam, combustion, and electric heating. Gas floods, including immiscible and miscible processes, are usually defined by injected fluids (carbon dioxide, flue gas, nitrogen, or hydrocarbon). Steam projects involve cyclic steam (huff and puff) or steam drive. Combustion technologies can be subdivided into those that autoignite and those that require a heat source at injectors [521]. 

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

Polar organic compounds such as amino acids normally do not polymerize in water because of dipole-dipole interactions. However, polymerization of amino acids to peptides may occur on clay surfaces. For example, Degens and Metheja51 found kaolinite to serve as a catalyst for the polymerization of amino acids to peptides. In natural systems, Cu2+ is not very likely to exist in significant concentrations. However, Fe3+ may be present in the deep-well environment in sufficient amounts to enhance the adsorption of phenol, benzene, and related aromatics. Wastes from resinmanufacturing facilities, food-processing plants, pharmaceutical plants, and other types of chemical plants occasionally contain resin-like materials that may polymerize to form solids at deep-well-injection pressures and temperatures. 

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