Use of Nickel Nanoparticles for Promoting Aquathermolysis Reaction During Cyclic Steam Stimulation

Late cycles of cyclic steam stimulation (CSS) are characterized by a decreasing heavy-oil recovery and an increasing water cut. Nickel nanoparticles can be used to promote aquathermolysis reactions between water and heavy oil in steam-injection processes, thereby increasing the recovery factor (RF). In this paper, detailed investigations were performed to determine the optimal operational parameters and answers to the following questions: What is the optimal concentration of nickel nanoparticles for promoting aquathermolysis under high steam temperature? Can we improve oil recovery at lower steam temperatures with the presence of nickel nanoparticles? What effect does the penetration depth of nickel nanoparticles have on the final oil recovery? CSS experiments were conducted between temperatures of 150 and 220 degrees C. Steam generated under these temperatures was injected into sandpacks saturated with Mexican heavy oil. Powder-form nickel nanoparticle was introduced into this process to boost the oil production. In an attempt to obtain the optimal concentration, different concentrations were tested. Next, oil sands without any nanoparticle additives were first added into the cylinder. Then, only one-third of the sandpack was mixed with nickel nanoparticles near the injection port. Experiments were executed to study the effects of temperature, nickel concentrations, and nanoparticle-penetration depth on the ultimate oil recovery and produced oil/water ratios after each cycle. Produced-oil quality and emulsion formation were evaluated with gas-chromatography (GC) analysis, viscosity measurements, saturates/asphaltenes/resins/aromatics (SARA) tests, and microscopic analysis of the effluents. Experimental results show that the best concentration of nickel nanoparticles, which gives the highest ultimate oil RF, is 0.20 wt% of initial oil in place (IOIP) under 220 degrees C, whereas the nickel concentration of 0.05 wt% provides the highest RFs at the early stages. A lower temperature of 150 degrees C provides a much-lower RF than 220 degrees C, which is mainly because of a lower level of aquathermolysis reactions at 150 degrees C. By analyzing the compositions of produced oil and gas samples with GC and SARA tests, we confirm that the major reaction mechanism during the aquathermolysis reaction is the breakage of the carbon/sulfur (C/S) bond; the nickel nanoparticles can act as catalyst for the aquathermolysis reaction; and the catalytic effect becomes less remarkable from cycle to cycle. One run of the experiment to test the effect of particle-penetration depth revealed that the nickel nanoparticles distributed near the injection port greatly contributed to the ultimate RF.