Does Perforated Completion Strategy Aid Water-Based Chemical Flooding to Mitigate Gravity Segregation?

Abstract

Chemical flooding is a widely used enhanced oil recovery (EOR) method that involves injecting water-based chemicals into the reservoir. These chemicals are typically denser than oil, leading to gravity segregation, wherein the denser fluid underruns the oil, reducing sweep efficiency and overall recovery. This study evaluates the effectiveness of perforated completion versus open-hole completion in mitigating gravity segregation during surfactant and polymer flooding, two common chemical flooding techniques. While surfactant and polymer solutions have similar densities (1 g/cc), they differ significantly in viscosity and interfacial tension (IFT). Simulations using commercial software were conducted for a quarter of a five-spot pattern with varying reservoir properties, including anisotropy (0.1–0.75), oil viscosity (10–100 cP), and thickness (50–200 ft). Flooding durations of 5 months and 5 years were examined. Recovery and profitability served as metrics for evaluating completion strategies. Results indicate that polymer flooding, due to its higher viscosity, mitigates gravity segregation effectively with both open-hole and perforated completions, rendering the additional cost of perforation ($80,000 per operation) unjustified. Conversely, surfactant flooding benefits significantly from perforated completion under specific conditions. For short flooding periods, perforated completions increased recovery by 1,500–2,000 barrels in reservoirs with lower anisotropy (0.1), higher oil viscosity (100 cP), and greater thickness. This improvement is attributed to the selective slowing of surfactant movement, which enhances vertical sweep efficiency. Economically, perforated completions generate additional revenue ranging from $20,000 to $225,000, justifying their use in short-term surfactant floods but not in polymer floods if the objective is to prevent gravity segregation. The findings suggest that perforated completions are particularly advantageous for flooding with low-viscosity injection fluids (e.g., water or surfactant) in reservoirs characterized by high oil viscosity, significant thickness, and moderate anisotropy. In summary, while polymer floods mitigate gravity segregation well regardless of completion strategy for the studied conditions, surfactant flooding benefits from perforated completions in specific scenarios, emphasizing the importance of tailoring EOR strategies to reservoir characteristics and project duration.