Researchers have developed a groundbreaking model that can simulate the complex pressure dynamics of oil and gas flowing through fractured underground formations. This new model takes into account the unique properties of these dual-porosity systems, where natural fractures act as the main conduits for fluid flow while the surrounding rock matrix stores the bulk of the hydrocarbons. Importantly, the model also incorporates the sensitivity of the fracture permeability to changes in formation pressure, a phenomenon known as permeability-stress sensitivity. With this comprehensive approach, the researchers have shed new light on how the pressure behavior in these reservoirs is influenced by factors such as oil saturation, fracture development, and stress sensitivity. Their findings have significant implications for improving our understanding and management of oil and gas reservoirs.
Fractures and Matrices: The Dual Nature of Naturally Fractured Formations
Naturally fractured formations are complex geological systems that consist of both natural fractures and the surrounding rock matrix. These two components have vastly different properties: the fractures act as the primary flow channels, with much higher permeability than the matrix, while the matrix serves as the main storage for the hydrocarbons.
This dual-porosity nature of fractured formations has a profound impact on their pressure dynamics. As fluids are extracted from the well, the pressure changes in the fractures and the matrix are relatively independent, leading to a characteristic “V-shaped” response in the pressure derivative curve. This pattern reflects the interplay between the fluid flow from the matrix into the fractures and the overall depletion of the reservoir.
Incorporating Permeability-Stress Sensitivity
The researchers’ new model takes an important step forward by also accounting for the permeability-stress sensitivity effect. As formation pressure changes, the natural fractures can deform, leading to alterations in their permeability. This phenomenon can significantly influence the pressure dynamics, and the researchers’ model is the first to simultaneously consider both the dual-porosity nature of the system and the stress sensitivity of the fractures.
Insights into Pressure Behavior
By simulating the pressure dynamics under various conditions, the researchers have gained valuable insights:
– Oil Saturation: Higher oil saturation leads to higher pressure curves, as the total flow resistance for the oil-gas mixture is greater.
– Stress Sensitivity: Stronger stress sensitivity (higher permeability-stress sensitivity coefficient) results in higher pressure curves, with the influence becoming more pronounced over time.
– Fracture Development: The degree of fracture development, as represented by the elastic storage ratio of the fractures, affects the shape and depth of the characteristic V-shaped pressure derivative curve.
These findings have important implications for interpreting pressure data from well tests and improving the management of fractured oil and gas reservoirs.
Practical Applications and Future Directions
The researchers have validated their model by successfully fitting it to pressure data from a real condensate gas well in a fractured sandstone formation. This demonstrates the model’s potential as a valuable tool for practitioners in the oil and gas industry.
While the current model focuses on oil-gas two-phase flow, the researchers note that future work could explore the dynamics of three-phase flow (oil, gas, and water) and the pressure behavior associated with horizontal well production. By continuously expanding the capabilities of their model, the researchers aim to provide even deeper insights into the complex world of fractured hydrocarbon reservoirs.
Meta description: Researchers have developed a comprehensive model that can simulate the pressure behavior in fractured oil and gas reservoirs, shedding light on the interplay between dual-porosity systems and permeability-stress sensitivity.
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