We conducted a series of dynamic experiments in which liquid solvent (heptane) was injected into heavy-oilsaturated artificially fractured Berea sandstone samples with and without prethermal injection. To account for the effect of wettability on the process, experiments were repeated on the samples exposed to a wettability alteration (more oil-wet) process. Cores were saturated with heavy crude oil and placed inside a rubber sleeve. Next, the system was placed into an oven and maintained under constant temperature conditions. Then, either hot solvent (superheated to be in the vapor phase) or cold solvent was introduced into the system through the fracture at a constant rate. Pressure and temperature was continuously monitored at the inlet and center of the core. Properties of the oil and liquid condensate from the gas produced were measured and analyzed. This scheme was repeated for a wide range of temperature conditions. The retrieval of the solvent during the solvent injection phase and post-thermal method (steam or hot-water) injection performed for a wide range of temperature was monitored. Our results and observations indicate that the first requirement for a successful application is an effective solvent diffusion into matrix before it breaks through and improves the gravity drainage of oil by dilution. The second requirement is solvent retrieval. We also observed that a critical temperature and injection rate exists that yields a maximized oil recovery and solvent retrieval.

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Summary Our recent experimental studies on superheated solvent injection for heavy-oil recovery showed that when a solvent is injected into the reservoir, the process is highly sensitive to pressure and temperature. The effects of these parameters on the recovery factor (RF) are accentuated when the operating conditions are closer to the saturation curve of the solvent injected. This paper investigates this process and formulates the optimal field-scale application conditions that yield the maximum profit, as a continuation of previous work. To achieve this, a hypothetical field-scale numerical model was constructed, and the key parameters identified through the aforementioned sensitivity analysis were incorporated. Then, the injection process was simulated for a two-horizontal injection/production pattern. An optimization study was performed to identify the relative contributions of the effective parameters (pressure, temperature, and injection rate) and to propose an optimal application scheme with a genetic algorithm (GA). The critical pressure and temperature yielding maximum production and highest profit considering solvent retrieval were defined for different injection rates and application scenarios. Our results indicate that, at the end of the hot solvent-injection process, an important volume of solvent is left in the reservoir, and its volume depends on the injection–production scheme selected. Nevertheless, if the project is performed under appropriately selected operational parameters (obtained through the optimization processes) and followed by the proper process to retrieve the solvent from the reservoir (low-temperature steam or hot-water applications), it can make the hot solvent-injection process profitable.

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This paper presents an extensive analysis solvent injection at elevated temperatures to recover heavy- oil/bitumen from fractured carbonates. Three different solvents (propane, heptane and distillate oil - naphtha) were injected at different temperatures representing a wide range of carbon number. Indiana limestone (outcrop) and vuggy naturally fractured carbonate samples (outcrop core samples from a producing formation in Mexico) were selected as core samples. Hot solvent was injected continuously through artificially fractured cores followed by hot water (or steam injection) phase. The optimal temperatures for heavy oil recovery and solvent retrieval, in the subsequent hot water injection, for each kind of rock sample and type of solvent were determined. The results revealed that heavy oil recovery increase with the solvent carbon number used. Also, it was observed that when the temperature is higher than the saturation value for the given pressure curve, the recovery decreases and the lightest component of the heavy oil are dragged by the gas stream.