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Cyclic steam stimulation (CSS) has recently re-gaining attention as an alternative to the current applications, such as SAGD or CHOPS. However, low recovery factor and excessive water production are critical problems to tackle. These late-stage experiences require a revisit to the options of recovery improvement and reduction of water production at the mid- and late-stages of the cycles. This research proposes a new approach for this purpose and investigates the effects of nano-metal particles introduced into the reservoir on the recovery factor after several cycles of steam injection. We begin with CSS experiments on heavy-oil saturated sandpacks studying and clarifying the influence of the nanoparticle presence on the efficiency of the process. It is confirmed that the use of nanoparticle in the first place increases the oil recovery factor along with a higher water production. Then, one run of experiment is performed by introducing the nanoparticle in the sixth cycle of CSS treatment. It is found that a substantial increase in the recovery factor is achieved in such a simulated CSS experiment, which cannot be achieved by injecting steam alone. This experimental study on the addition of nickel particles to improve the recovery factor and extend the life of CSS process will not only add value to nano-technology use in the oil industry from a physics point of view, but will also provide insight into the operating parameters for better late- stage CSS project development.

Steam assisted gravity drainage (SAGD) is the main commercial technology used for in-situ recovery of bitumen in Canada. Solvent-assisted SAGD processes are being pursued to take advantage of heat transfer (steam) and mass transfer (solvent) mechanisms to reduce the bitumen viscosity, swell the bitumen and enhance the mobility of bitumen in an energy efficient way. In the steam-chamber boundary, multiple fluids comprising of solvent, steam and bitumen come in contact with each other, and may exhibit multiphase equilibria depending on the location in the boundary and bulk composition in the pores. These multiphase equilibria can significantly affect the drainage behavior of fluids inside the steam-chamber boundary. Therefore, it is of critical importance to study the phase behavior of these fluids at steam-chamber boundary to obtain a more insightful understanding of the mechanisms of solvent-assisted SAGD process. In this paper, the phase behavior of solvent-steam-Athabasca bitumen is analyzed with a Peng-Robison equation of state (PR EOS) model at the boundary of steam chamber under typical operating conditions in a SAGD process. The Athabasca bitumen is characterized with six pseudo-components as such characterization of bitumen provides satisfactory matches for experimental gas solubility data in the literature (Kariznovi et al., 2009). The EOS model has been validated with the recently published experimental data on phase behaviour of solvent-steam-bitumen system (where toluene is used as solvent) (Amani et al., 2014). The PR EOS model is able to provide a good representation of the phase behaviour of the water-Athabasca bitumen system and toluene-water-Athabasca bitumen system at temperatures below 317°C. The PR EOS model is used to perform the phase behaviour simulations at a constant pressure of 2.6 MPa and temperatures from 60°C to 250°C. Multiphase equilibria calculations with the PR EOS model indicate that the possible phase equilibria that can occur in the steam-chamber boundary include liquid-liquid-liquid (L1/L2/L3), liquid-liquid-vapor (L1/L3/V), liquid-liquid (L1/L3) and liquid-vapor (L3/V) equilibria. Significant water solubility in bitumen-rich liquid phase can exist at high temperatures, which is consistent with experimental observation in the literature, while a relatively large solvent solubility in bitumen-rich liquid phase is found to exist at low temperatures. The constant flash calculations for a given feed at different temperatures show that: the solvent commences to vaporize drastically from liquid phase and does not play any significant role in viscosity reduction of bitumen when the system switches from L1/L3 to L3/V equilibrium, or from L1/L3/V to L3/V equilibrium. Similarly, the swelling factor of the bitumen-rich liquid phase keeps increasing as a function of temperature until the L1/L3/V- L3/V boundary or L1/L3-L3/V boundary is reached. Viscosity reduction and swelling effect of the bitumen-rich liquid phase L3 due to heating from steam and dissolution of toluene and water can significantly enhance the mobility of bitumen, thus resulting in highly reduced residual bitumen saturation within the SAGD steam-chamber boundary.

Hydraulic fracturing can be used in low-permeability heavy oil reservoirs for improving the production rate. It is challenging to achieve a high degree of fracturing fluid flow-back in low-permeability heavy oil reservoirs. This research investigates the application of a novel hyper-branched polymer fracturing fluid in low-permeability heavy oil reservoirs. A hyper-branched polymer, which has numerous end groups and possesses a special highly branched three-dimensional spherical molecular structure, is characterized by Fourier Transform Infrared (FTIR) spectrophotometer. Laboratory tests are conducted to evaluate the stability of viscosity at a given shear rate, temperature and shearing resistance, reversible cross-linking property, filtration property, and proppant-carrying performance of this hyper-branched polymer fracturing fluid. The degrees of core's formation damage are compared through conducting coreflood experiments, where the cores are treated with two fluids: the hyper-branched polymer fracturing fluid and guanidine gel fracturing fluid. The laboratory evaluation shows that the hyper-branched polymer fracturing fluid has good rheological characteristics, a high solubility in water, as well as good temperature and anti-shearing resistance. After being sheared for 90 minutes with the shear rate of 170 s−1 at 150°C, it can still be reversed to gel with high strength because of its reversible cross-linking effect. This fracturing fluid has a good antioxidant ability, which allows its basic fluid to be exposed to air for 48 h without viscosity reduction. Therefore, the basic fluid can be prepared as spare fluid in a large amount, significantly improving job efficiency on site. Meanwhile, field applications in some wells in China show that: the friction of this fracturing fluid during fracturing is about 30%-50% to that of the normal guanidine gum fracturing fluid. Thus it has an ultra-low friction feature. The flow-back rate of the fracturing fluid can reach as high as 80%. Besides, its cost is about 75% to that of the normal guanidine gum fracturing fluid, making it a clean and cost-effective system. The fracturing fluid prepared with hyper-branched polymer possesses outstanding technical advantages as well as good cost effectiveness, implying a promising application in the large-scale fracturing stimulation of low-permeability heavy oil reservoirs.