Demulsifier for separation of liquid obtained in chemical flooding of oil layers

Abstract

The development and use of a demulsifier for separation of the fluid obtained after flooding of an oil layer using ASP (alkaline surfactant polymer) are described. The mechanism of separation of the emulsion was investigated. As a result of laboratory studies and tests in the field, it was shown that the demulsifier produces excellent results in separation of such emulsions.Flooding with SF is used to increase oil recovery on industrial scales at the end of the life of a field. Oil recovery increases by more than 12% of the initial oil reserves with this method of flooding in comparison to ordinary flooding. In combined chemical flooding, defined as flooding with an alkali, SF, and a polymer, this increase is greater than 20%. Successful operation of the pilot chemical flooding unit at Daqing field provided a new method of development [1].Crude oil is rarely recovered alone; it is frequently mixed with water, which can create emulsions. These emulsions can be treated to remove dispersed water and associated inorganic salts to satisfy the requirements for transport, storage, and exportation of the crude and to reduce corrosion of equipment and poisoning of catalysts in refining it. Chemical flooding emulsions have higher stability and more complex properties than the emulsions formed in ordinary flooding, which creates difficulties in conducting subsequent processes, in particular, in separating the crude and the water. The increase in the stability of the emulsion in chemical flooding is due to the following reasons:• the fluid obtained in chemical flooding contains reagents that displace crude oil: alkali, SF, and polymer. The studies showed that sodium hydroxide reacts with the fatty acids in the crude, forming soapy surface-active components [2] which accumulate on the oil"water interface, strengthening the interface, and thus significantly increasing the stability of the oil "water emulsion. SF, which significantly reduce the surface tension between the crude and the water [3], also increase the stability of the oil"water emulsion in moving to the surface of the 113 oil -water interface. The sterically and electrostatically stable polymer [4] accumulates on the oil -water interface and makes its own contribution to stabilization of the emulsion.• The content of asphaltenes, resins, and aromatic compounds is higher in crude recovered in chemical flooding than in ordinary flooding [5]. The contribution of asphaltenes and resins to strengthening of the oil -water interface is greater than for the other components of crude oil. Both asphaltenes and resins are found on the oil -waterr phase interface, strengthening it.• The structure of the emulsion is more complex [6]: it includes water -oil and oil -water emulsions and multiemulsions (water -oil -water, oil -water-oil, etc.).In operating the pilot chemical flooding unit, we found that: the polyester demulsifiers usually used for separating the fluid obtained after flooding are ineffective; the emulsion layer between crude and water is thicker than necessary; the...