Evaluation of Gas-Based EOR Methods in Gas-Invaded Zones of Fractured Carbonate Reservoir

Abstract

More than half of all recoverable oil reserves are found in carbonate rocks. Most of these fields are highly fractured and develop different zonations during primary and secondary recovery stages; therefore, they require a different developmental approach than conventional reservoirs. Experimental results for water-alternating gas injection [WAG] and foam-assisted water-alternating gas [FAWAG] injection under secondary and tertiary recovery conditions were used to investigate these enhanced oil recovery [EOR] methods in gas-invaded reservoirs. The relative permeability curves of the cores and the fitting foam parameters were derived from these experiments through history matching. These findings were then used in a quarter five-spot, cross-sectional, and a sector model of a carbonate reservoir where a double five-spot setup was implemented. The fracture and matrix properties’ impact on the recovery was illustrated through the cross-sectional model. The gas mobility reduction effect of the FAWAG was more noticeable than that of WAG. The apparent viscosity of the gas was increased due to the foam presence, which caused a diversion of the gas from the fractures into the matrix blocks. This greatly enhanced the sweep efficiency and led to higher oil recovery. The gas front was much sharper, and gravity overrides by the gas were much less of a concern. The properties of the fracture network also had a significant effect on the recovery. Oil recovery was found to be most sensitive to fracture permeability. At the same time, sweep efficiency increased substantially, improving the recovery rate in the early injection stages, and differed slightly at the ultimate recovery. However, a lower fracture permeability facilitated gas entry into the matrix blocks. The results of the reservoir sector model were similar to the core and pilot. However, the WAG injection recovered more of the uppermost layers, whereas significant portions of the lowest layer were not effectively recovered. In contrast, FAWAG was more effective in the lowest layer of the reservoir. The FAWAG was a beneficial aid in the recovery of gas-invaded fractured reservoirs, increasing the oil recovery factor with respect to WAG.

Introductory Chapter: Lithological Dynamics – CO2-EOR at the Forefront of Enhanced Oil Recovery Evolution

“…Hydrocarbon gas injection in onshore carbonate reservoirs has a marginal contribution to total oil recovery. Utilizing natural gas for pressure maintenance or in WAG and foam-assisted water-alternating gas (FAWAG) processes is considered practical, preserving reservoir energy and maximizing oil recovery [14]. CO2-EOR in carbonate formations relies on natural CO2 sources, especially in the United States Permian Basin, with expected growth unless more viable EOR strategies are developed [15].…”

Carbon Dioxide (CO2) Microbubble Suspension and Stabilization for Advancing Tertiary Oil Recovery

“…3 Gas injection methods for EOR utilize gases like CO 2 , nitrogen, lean gas, rich gas, and air injected into oil reservoirs to enhance oil recovery. 4 CO 2 injection is particularly favored due to its effectiveness in mobilizing trapped oil. Microbial EOR methods encompass both ex situ and in situ approaches.…”

“…EOR encompasses various methods, including miscible and immiscible gas flooding, polymer flooding, microbial injection, chemical flooding, and thermal methods, like steam flooding . Gas injection methods for EOR utilize gases like CO 2 , nitrogen, lean gas, rich gas, and air injected into oil reservoirs to enhance oil recovery . CO 2 injection is particularly favored due to its effectiveness in mobilizing trapped oil.…”

Assessing the Influence of Fracture Networks on Gas-Based Enhanced Oil Recovery Methods

“…Therefore proper fracture identification and characterization are essential for understanding fluid displacements, especially for improved and enhanced oil recovery [11,12]. Recent studies have focused on modeling and simulating fluid flow in fractured subsurface systems due to the potential hydrocarbon reserves in fractured reservoirs [13][14][15][16][17].…”