2001 Technology for a Sustainable Environment: An Environmentally Sustainable Approach to Crude Oil Production and Processing: Compressed Gas Demulsification

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AbstractCTS-0124760Kilpatrick, PNorth Carolina State UThe management of emulsions during the production, transportation, and processing of crude petroleum fluids is one of the most persistent challenges which faces the petroleum industry. Annually, tens of millions of tons of emulsions are produced during production of petroleum and this figure is likely to rise annually with the increased production of heavy oils. A substantial percentage of these emulsions are stabilized by elastic films of adsorbed asphaltenes. It is common to treat these emulsions with chemical demulsifiers, typically nonionic polymers containing substantial proportions of ethylene oxide (EO) and propylene oxide (PO). Other methods employed to a lesser extent include thermal pressurization and rapid depressurization, electrostatic droplet shattering and coalescence, and ultrasonication of emulsions. Among the most effective chemical demulsifiers are oxyalkylated phenol resins, phenol-formaldehyde glycidyl ethers, and other polymers based on EO, PO, phenol, and formaldehyde. There is considerable concern in that many of these demulsifier chemicals persist in the environment, are nonbiodegradable, and may have adverse human health effects, including being suspected endocrine disruptors. Moreover, the costs associated with demulsifiers in particularly heavy and troublesome fields can be substantial. This project describes a novel method for demulsifying water-petroleum emulsions using compressed gases; the specific example which has been reduced to practice is the use of compressed carbon dioxide (CO2). The project describes the further development of this method and the possible use of mixed compressed gases, including methane (CH4), ethane (C2H6), propane (C3H8), and CO2. The method is based on the alteration of the solvent properties of petroleum for asphaltenes upon dissolution of dissolved gas. It is well known that dissolution of appreciable amounts of propane in petroleum fluids can precipitate asphaltenes, a process known as propane de-asphalting. CO2 is also highly effective and the precipitation is of sufficient magnitude to demulsify extremely stable petroleum emulsions. Should the method be plausible with compressed gases commonly found in contact and coproduced with petroleum - e.g. CH4, C2H6, C3H8, and CO2 - the possibility exists for demulsifying produced emulsions at the source and, perhaps, perform preliminary unit operations on the crude, such as downhole deasphalting. The impact of such a technology, if successfully reduced to economical practice, would be difficult to overestimate. Based on the somewhat reduced scope due to the revised budget reductions, the mixed gas demulsifications will be performed with methane (CH4) and CO2 only.