Prevention of Acid-Induced Asphaltene Precipitation: A Comparison of Anionic Vs. Cationic Surfactants

With the recent proliferation of horizontal drilling specifically targeting oil-bearing reservoirs, high-strength-acid-fracturing treatments in the Beaverhill Lake formation in northern Alberta have increased dramatically in both product volume and number of treatments. The Beaverhill Lake formation is a limestone/calcareous shale that produces a desirable mid-to high-(O)API sweet crude oil. Although the crude oil typically has a low concentration of asphaltenes, the oil is sensitive to acid and/or iron-induced asphaltene precipitation. As the acid strength increases and ferric iron is dissolved into solution, it becomes increasingly difficult to chemically prevent the asphaltenes from precipitating. Acid blends designed to prevent asphaltene precipitation also tend to be emulsifying with the crude oil; therefore, a careful balance between antisludge additives and nonemulsifiers must be found. The objective of this study is to compare anionic and cationic antisludge agents, and to determine if there was an observable benefit in production when using a specific type of antisludge agent in the Beaverhill Lake formation.