Role of Bitumen-Water Interfacial Tension in Steam Assisted Bitumen and Heavy Oil Production; Solvent versus Surfactant Coinjection with Steam Processes

S. Arnipally, A. Tang, B. Ozum

Dans les comptes rendus d’articles de la conférence: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Shallow Geothermal Energy Exchange

ABSTRACT: Over 80% of Athabasca, Alberta, Canada oil sands deposits are suitable for bitumen production by thermal in-situ recovery processes, such as SAGD and CSS processes; by which bitumen is produced over 1,500,000 barrels/day capacity. Oil industry needs novel methods to improve thermal efficiency, improve profitability and reduce environmental footprints of these processes. For this purpose, solvent (light hydrocarbons) co-injection with steam is studied by oil industry, speculating that it would reduce bitumen viscosity and increase bitumen mobility as predicted solvent on bitumen-water interfacial tension. At our laboratory, surfactant, such as biodiesel (fatty acid methyl esters) co-injection with steam is being developed as an alternative method to solvent co-injection with steam process. Steam assisted bitumen recovery tests were operated in continuous and batch (pressure cooker) modes, and high temperature-high pressure bitumen-water interfacial tension measurements were performed using pending drop method. Core samples from SAGD reservoirs, bitumen and process affected water recovered from bitumen-water emulsions produced by SAGD processes which were untreated with any chemical additive, were used in these tests. Bitumen recovery tests were made by operating the test unit as a pressure cooker, and showed that pentane addition into steam, at 5% and 15% of bitumen mass, reduced bitumen recovery efficiency by 39% and 61%, respectively, which contradicts expectations of solvent co-injection EOR methods. Our research findings suggest that solvent co-injection with steam further decreases bitumen viscosity, which is already reduced by thermal heating, but increases bitumen-water interfacial tension and causes slip of water at bitumen-water interface; which results in increase in water and decrease in bitumen mobilities. Experimental data on surfactant behavior of biodiesel and mathematical analysis of two phase immiscible fluids flow with slip boundary condition at bitumen-water interface will be discussed. Key Words: Surfactant and solvent co-injection with steam, interfacial tension, bitumen recovery efficiency. 1 BACKGROUND The Northern Alberta, Canada oil sands resources which extend over 77,000 km2, distributed in three principle regions: Athabasca, Cold Lake and Peace River. The estimated crude bitumen in-place volume and ultimate potentials for recovery are 270x109 m3 (1.6x1012 bbl) and 50x109 m3 (300x109 bbl), respectively. About 85% of these resources are in deeper formations, where the crude bitumen is not mobile because of high viscosity, over 104 mPa.s. Thermal in-situ production methods, such as Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) methods are commercially used for bitumen production. Existing bitumen production capacity by thermal in-situ methods is over 1.5x106 barrels/day, which is projected to exceed 3.5x106 in the next decade. Efficiency and profitability of the steam assisted bitumen production processes are measured by the steam-to-bitumen S/B (by mass). Commercial experience of bitumen production in Alberta, Canada by steam assisted production methods showed that S/B are in the range of 2.3 to 5, even higher, depending on the reservoir characteristics. To reduce S/B ratio, enhanced oil recovery (EOR) methods are being developed based on different physical-chemical methods and principles. The main obstacles to produce bitumen from deep formations are low reservoir permeability, in the order of 0.1 to 1.0 Darcy, and high bitumen viscosity, over 104 mPa.s. Viscosity of bitumen could be reduced by heating the reservoir by steam injection, in-situ combustion of bitumen, electrical or electro-magnetic heating methods. Another method to reduce bitumen viscosity is co-injection of solvents, such as light hydrocarbons, with steam. Based on these principles, several EOR processes, such as Steam Assisted Gravity Drainage (SAGD), Expanding Solvent-Steam Assisted Gravity Drainage (ES-SAGD), Cyclical Steam Stimulation (CSS), Toe to Heel Air Injection (THAI), Vapour Extraction (VAPEX), and N-Solv processes, were studied (Al-Bahlani & Babadagli 2009; Nenninger & Gunnewiek 2009; Butler & Mokrys, 1989). Among these processes, SAGD and CSS methods have proven to be reliable processes for commercial applications (Butler, 1998, 1991). Commercial experience over three decades showed that SAGD process is the most efficient and economical process to produce bitumen. In this process a pair of parallel injector and producer wellbores, five meters apart, with 20 to 50 centimeters in diameter and 1,000 to 1,500 meters long is drilled into the oil sands reservoir of 150 to 700 meters deep. High pressure and temperature steam at above 90% saturation is injected into upper wellbore which results in the formation of a steam chamber.

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