Alkali metal silicides have ability to enhance oil recovery in a variety of light, medium and heavy oil reservoirs. These chemicals, which include the silicides of sodium (Na), potassium (K) and lithium (Li), are free-flowing granules or very fine powders that are applied downhole in hydrocarbon dispersions. When introduced into a formation through an appropriate non-aqueous carrier fluid, these materials rapidly react with the water in the reservoir pore space, releasing hydrogen gas and heat, and converting into alkali silicates. The silicide-water reaction combined with the flooding process provides multiple mechanisms in the reservoir to enhance oil recovery. Enhanced oil recovery mechanisms include: energy addition through the generation of hydrogen; oil viscosity reductions due to hydrogen solubilization, temperature increase and solvent dilution from the carrier fluid; interfacial tension reduction due to in-situ surfactant generation from interaction of the crude oil organic acids in the reservoir oil with the alkalinity from the produced silicates; and potential improvement of water wettability in carbonate reservoirs. This one chemical combines the effects of thermal, drive energy and chemical mechanisms.
In this work, a field-scale numerical simulation study was conducted to investigate the feasibility of cyclically injecting an alkali metal silicide into the wormhole structures of a post CHOPS (cold heavy oil production with sand) reservoir. The Computer Modeling Group's (CMG) STARS simulator was used to perform the simulations; the model consists of six vertical wells with wormhole structures developed using proprietary wormhole growth models that are based on actual field production histories from a representative CHOPS field in Canada (the Lloydminster, Alberta and Saskatchewan region). Multiple simulation cases were run to investigate the effects of injected cycle volume, cycle time, injection rate and silicide concentration. A sensitivity analysis was performed on parameters affecting the slurry model and dispersion rates of the silicide in the reservoir. The preliminary economics of the process were calculated and used to identify an optimized and cost-effective injection strategy, which can subsequently be used as a basis to design a field trial application.
The study results showed that the cyclic injection of sodium silicide in a post CHOPS reservoir can in fact improve the recovery of oil in place. The study shows that the predominant recovery mechanism is likely the pressure maintenance of the reservoir that provides energy for continued oil production. This, coupled with secondary oil viscosity reductions, enable the cyclic injection of silicide to increase production for an additional 5 to 10 years, thereby adding 25 to 50% to recoverable reserves under favorable economics. This paper discusses the impacts of the in situ generation of heat, hydrogen and alkali silicate for post CHOPS augmentation and summarizes the key findings of the simulation study and economic modeling.