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

Abstract

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-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.

The Application of X-ray Micro Computed Tomography (Micro-CT) of Core Sample for Estimation of Physicochemical Treatment Efficiency

“…To simulate the process of oil degassing in the bottom-hole formation zone, pumping of oil at a constant pressure, which is less than saturation pressure of the oil saturated by gas. As a result of this, asphaltenes contained in the oil, will be precipitated mainly within the pore space of the core sample [8,14,17,22,25,27,31,43]. 6.…”

“…For example, the use of various reagents and solvents to remove deposits of asphaltenes, resins and waxes, the application of surfactants, and special physical (e.g. wave) methods on reservoir [6][7][8][9][10]14,16,18,[26][27][28]31,37].…”

The Application of X-ray Micro Computed Tomography (Micro-CT) of Core Sample for Estimation of Physicochemical Treatment Efficiency (Russian)

“…При этом асфальтены, содержащиеся в нефти, выпадают в основном в поровом пространстве керна [8, 14,17,22,25,27,31,43]. Проводится процедура сканирования керна и реконструкция изображений по аналогии с приведенной выше в статье последовательностью.…”

“…Например, применение различных реагентоврастворителей для удаления отложений асфальтенов, смол и парафинов, применение поверхностно-активных веществ, специальное физическое (например, волновое) воздействие на породу-коллектор [6-10, 14,16,18,[26][27][28]31,37]. Для оценки степени повреждения пласта (кольматации его асфальтенами) производится повышение противодавления до исходного пластового и проводится измерение фазовой проницаемости по нефти с растворенным в ней газом.…”

The composition of acid/oil interface in acid oil emulsions

“…However, it is well known that these processes are greatly enhanced in the presence of ferric cations, the sources of which are the corroded surfaces of field equipment and iron-bearing minerals of the oil reservoir. On the one hand, it is assumed (O'Neil et al 2015) that Fe(III), especially in form of the complex HFeCl 4 facilitates acid transfer to the oil phase, increasing the acid concentration in the oil; this assumption is confirmed by an insignificant iron content in the precipitate (sludge) and by similar chemical structure of precipitates formed with and without participation of iron. On the other hand, it has been shown (Antipenko et al 1994) that Fe(III) participates in complexation with the aromatic cores of asphaltenes, causing them to flocculate into large asphaltene clusters that are unstable to deposition.…”