Effect of surfactant composition on reservoir wettability and scale inhibitor squeeze lifetime in oil wet carbonate reservoir

In the oil industry, scale inhibitor (SI) squeeze treatment is an established method to prevent deposition of inorganic scales in the wellbore and near wellbore formation. Most scale inhibitor chemicals are water soluble and therefore typically deployed as an aqueous solution. However, most carbonate reservoirs being preferentially oil-wet, SI squeeze treatment could be short lived, because of the competition for adsorption surface between the native oil and the SI. Although several authors studied surfactant activities on reservoir rock and fluid properties in relation to enhanced oil recovery, the literature lacks information on the effect of surfactant based preflush treatment on rock characteristics in relation to SI squeeze lifetime. It is obvious that a proper design of preflush, based on a detailed understanding of rock-fluid properties, could be as important as designing the main treatment (SI) itself. The objective of this study was to develop an understanding of surfactant composition and pH in altering carbonate rock wettability, and its impact on scale inhibitor squeeze performance. A set of carbonate core plugs with oil wet characteristics, crude oil and treatment chemicals (anionic surfactant and SI) were collected from an offshore oilfield. Surfactant preflush compositions with and without alkalis were evaluated for their ability to minimize oil-brine IFT and the extent of rock wettability alteration. A series of coreflood studies were conducted with selected preflush compositions and SI, followed by injecting incompatible brines. SI squeeze lifetimes were determined through observation of core permeability damage. The scale inhibitor and strontium return profile analyzed through ICP-MS studies also validated the onset of permeability damage. The study clearly established a correlation between rock wettability and scale inhibitor lifecycle. Extended SI lifecycle is evidenced in the core with a strongly water wet core and vice versa. The importance of proper preflush design based on rock-fluid characteristics and the role of alkali in changing wettability characteristics, surfactant adsorption and inhibitor lifecycle are discussed with experimental evidence. (C) 2013 Elsevier B.V. All rights reserved.