In all the enhanced oil recovery processes, flow of displacing and displaced fluids on a microscopic scale in a petroleum reservoir rock is affected by the wettability of the reservoir rock. Gaining proper knowledge of the dominant microscale multiphase flow mechanisms enables us to better predict the foremost prevailing macroscale flow behavior of the process. This research provides new insights into the effect of wettability on microscopic two-phase flow displacement mechanisms of dilute surfactant flooding using micromodel. It was inferred that the primary mechanisms of dilute surfactant flooding in the oil-wet medium were, intra-pore and inter-pore bridging of the surfactant solution, pore wall transportation of the oleic phase, formation of water-in-oil macroemulsion, and formation of partially continuous surfactant solution which enhanced the oil recovery. In water-wet medium, transportation of oil phase along pore body and neck walls, complete and incomplete inter-pore bridging, and deformation and stringing of the residual oil were the primary mechanisms of dilute surfactant flooding which made the residual oil entrapped in micromodel easily move forward and enhance oil recovery.

Post-primary recovery from some mobile heavy-oil reservoirs in Western Canada cannot be improved using thermal methods due to environmental concerns and technical difficulties. Moreover, miscible gas injection suffers from low initial production rates, premature breakthrough, and possible, formation damage. Low-tension polymer flooding (LTPF) can be an alternative in these reservoirs. However, a major technical challenge in LTPF is that a fingered displacement front may occur. This instability reduces displacement efficiency and may invalidate normal method of simulating LTPF performance based on relative permeability and capillary pressure concepts. Also, it introduces an additional scaling requirement for using results of experimental tests in larger scales. Therefore, it is important to predict the nature of instability, to avoid viscous fingering, or, where it is inevitable, to be capable to include it as an additional factor in modeling displacement. Previous experiments of viscous fingering in immiscible displacements have been conducted in presence of high single-phase permeabilities and linear displacement schemes. The question is whether previous findings are valid in displacement schemes similar to oil-field patterns (e.g., five-spot) in which one should deal with varying velocity profiles from injector(s) to producer(s). Hence, the effect of dispersion caused by varying velocity profiles has not been tested completely on viscous fingering. To help understand viscous fingering in LTPF in heavy oil reservoirs and to overcome the aforementioned limitations, we conducted experiments in low-permeability, one-quarter five-spot patterns. Foremost parameters including oil recoveries at different times to breakthrough, ultimate oil recovery, pressure drops, cumulative saturation profiles, mean local saturations, fingers length and width, dynamic level of bypassing, dynamic population of fingers, rate of growth of population of fingers and number frequency of the fingers were measured. We have correlated some of these parameters with displacement time and front position. Analysis of experimentally-observed fingering patterns of LTPF in this study is the most detailed interpretation performed to date, which provides new insights into the onset of fingering and fingers development. Results would help numerical simulation and stability theory to satisfactorily reproduce qualitative and quantitative features of finger growth.

Appropriate techniques have to be developed for improving heavy oil recovery from thin reservoirs in western Canada, where thermal methods suffer from heat loss to overburden/underburden and vapor extraction (VAPEX) is not effective because of the lack of efficient gravity drainage. Considering this, a hydrocarbon gas injection process in huff-n-puff mode, i.e., traditional hydrocarbon-based cyclic solvent process (CSP), has been tested to evaluate its applicability to such thin reservoirs. In the first part of this study, the behavior of methane huff-n-puff for heavy oil recovery is investigated by conducting a series of CSP cycles in a sandpack saturated with crude oil (with a viscosity of 1080.6 cP at 22 °C) and brine. The results of the six methane CSP cycles revealed that methane huff-n-puff is inefficient. The problem is that, during the production cycles, the reservoir pressure has to be greatly reduced to realize solvent gas drive. In doing this, the oil regains its high viscosity, because a large fraction of methane evolves out of the oil. To overcome this limitation and keep the oil viscosity low by maintaining most of the viscosity-reducing solvent in oil during the production period, we examined a new process, enhanced cyclic solvent process (ECSP). In ECSP, two types of hydrocarbon solvents are cyclically injected but in two separate slugs. One slug is more volatile (methane), and the other is more soluble (propane) in the heavy oil. A series of six ECSP cycles was conducted in the same sandpack used in the methane huff-n-puff tests. A total recovery of 34.30% original-oil-in-place (OOIP) was obtained through six ECSP cycles compared to 4.27% OOIP of six methane huff-n-puff cycles, indicating that ECSP improves the methane huff-n-puff for the heavy oil recovery in thin formations.

Low-tension polymer flooding (LTPF) can be an alternative for improving the recovery from some problematic heavy oil reservoirs, especially thin formations, where thermal methods face some challenges. A major technical challenge in LTPF is that a fingered displacement front may occur. Therefore, it is important to predict the nature of instability, to avoid viscous fingering, or, where it is inevitable, to be capable of including it as an additional factor in modeling displacement. Previous experiments of viscous fingering in immiscible displacements have been conducted in the presence of high permeabilities and linear displacement schemes. The question is whether previous findings are valid in displacement schemes similar to oil-field patterns (e.g., five-spot) in which one should deal with varying velocity profiles from injector(s) to producer(s). Hence, the effect of dispersion caused by varying velocity profiles has not been tested completely on viscous fingering. To help understand viscous fingering in LTPF in heavy oil reservoirs and to overcome the aforementioned limitations, we conducted experiments in relatively low-permeability, one-quarter, five-spot patterns. Foremost parameters, including oil recoveries at different times to breakthrough, pressure drops, cumulative saturation profiles, mean local saturations, finger lengths and widths, the dynamic level of bypassing, the dynamic population of fingers, the rate of growth of the population of fingers, and the number frequency of the fingers, were measured. We have correlated some of these parameters with the displacement time and front position. In summary, three distinct regions were identified for the viscous fingering patterns: onset of fingering, spreading phase, and end of sideways growth. The results also show that the finger width is comparable with the pore size and the fingerlike instabilities exist both in front of and behind the unstable front. Furthermore, the dynamic population of the macrofingers is well correlated with the square root of the time, and the profile of mean local oil saturation versus traveled distance is almost linear. Finally, the sharpest increase in the rate of growth of the finger population versus dimensionless pressure drop is accompanied with the sharpest pressure drop occurring at the onset of fingering and axial finger propagation during the early stages. A subsequent relatively uniform trend of the pressure drop versus time occurs during the spreading phase. Analysis of the experimentally observed fingering patterns of LTPF in this study is the most detailed interpretation performed to date, which provides new insight into the onset of fingering and finger development.