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How to enhance heavy oil recovery to meet the oil consumption is a popular issue around the world, and it has attracted widespread attention. A two-dimensional visualized model was adopted to study the pore-scale mechanisms and development effects of foam for enhancing oil recovery in steam injection processes for heavy oil. Experimental images visually presented that small bubbles gather together to form bigger foams, thus blocking the small pores and throats and leading to fluid diversion in porous media. As a result, the sweep efficiency was improved from 46.18% to 77.93% after foam injection. Foams could effectively improve the mobility ratio between oil and water and decreased water cut after foam injection, which was significant for decaying the decline of oil production. As for the pore-scale level, after foams were injected into the visualized model, the residual oil caused by steam flooding entered into the main streamline under the disturbance of foams and was carried out by the following displacement fluid. The heavy oil was emulsified into O/W emulsions that had lower viscosity under the action of foams; hence, more trapped oil was mobilized and displaced. As a result, the micro oil displacement efficiency increased from 72.76% to 84.01%. In order to provide a reference for the choice of foam injection, experiments that investigated development effects of cold foam and hot foam were also conducted. Compared with the incremental of oil recovery caused by cold foam, that induced by hot foam was 41.51% higher, demonstrating that the coinjection of steam and foam was more advantageous to heavy oil production.

As a temperature-sensitive non-Newtonian fluid, the seepage of heavy crude oil in porous media shows the non-linear characteristics. The flowing behavior of three heavy oils through porous media is experimentally investigated, and the influence of temperature and pressure-drop on this flowing process is also described. Thereafter, based on the flowing behavior of heavy crude oil, the new models of productivity of the thermal producers (including vertical well and horizontal well) are proposed. In these models, both the threshold pressure gradient (TPG) and thermal effect are taken into account. The flowing experiments of heavy oil in porous media indicate that the pressure gradient and temperature have the significant influence on the flowing process because of the existence of threshold temperature and TPG. Heavy crude oil begins to flow only when the pressure gradient is in excess of TPG, and there dose not actually exist TPG above the threshold temperature. The viscosity-temperature curves demonstrate that the viscosity of heavy crude oil has an obvious feature of two straight-lines on semilog coordinate. On account of the damage of overlapping phenomena of asphaltenes in crude oil, when temperature is higher than the critical temperature, the reducing trend of TPG (with the increase of temperature) will be lessened. Furthermore, on the basis of flowing process of heavy crude oil, the concepts of threshold temperature and certain production temperature of thermal wells are introduced. That heavy oil with a higher viscosity would have a higher threshold temperature, as well as the certain production temperature. The application of horizontal wells tremendously increases the oil recovery rate in comparison with the vertical wells. This investigation could be used as a tool to study the flowing process of heavy oil and productivity calculation of thermal wells in heavy oil reservoirs.

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Foam flow experiments were carried out to study the influence factors such as surfactant concentration, foam quality, injection rate of liquid and gas, permeability of porous media, temperature, and oil saturation on blocking ability and flowing characteristics of steady foams in porous media. Foam blocking mechanisms and flowing characteristics were summarized according to the experimental results and foam migration behavior. The results showed that the pressure distribution of flowing foams was linearly descending in porous media at steady state. The results further showed that the foam size and quality in pores along the sand pack were almost uniform, that is, foam generation and destruction gradually reached dynamic equilibrium at steady state. In porous media, the blocking ability of steady foams increased with the concentration of the foaming agent and the increase in the permeability of porous media, but the blocking ability decreased with the increase in the temperature, the shearing rate, and the oil saturation of the porous media. Foam resistance factor reached maximal value at the foam quality of 85% in porous media. List of symbols CMC Critical micelle concentration of surfactant in solution, wt% AOSAlpha olefin sulfonate, which is a kind of surfactant BS-12 Dodecyl dimethyl betaine, which is a kind of surfactant SDS Sodium dodecyl sulfate, which is a kind of surfactant V fm Foaming volume of foaming agent, ml