Fracture effect limitation on residual oil saturation & visualization by computer tomography

Canbolat, Serhat
Recovery estimations of fractured reservoirs are considered to be extremely challenging due to complexity and heterogeneity of the geological patterns. Most reservoirs consist of natural and artificial fractures, including isolated microscopic fissures. These fractures form complicated paths for reservoir characterization and fluid movement that ultimately impacts production performance and ultimate recovery. In naturally fractured reservoirs, the matrix is the dominant storage area, while the main flowing channels are fractures. Oil production from fractured reservoirs results in varying saturation values throughout the reservoir. This is due to the microscopic fissures and heterogeneity of the fracture environment, which could not be swept thoroughly. Higher production / injection ratios also enhance the fingering effect by passing oil through the reservoir. To get rid off fingering or minimize, a polymer gel application is applied to the fractured cores to reduce residual oil saturation and to increase oil production. In this study, naturally and artificially fractured cores were used. Analytical and experimental calculations were performed in order to understand the physical vi structure of the cores. After the characteriztion of the fractured cores a polymer gel application is done to limit the fracture effect and increase oil recovery. Equivalent fracture aperture measurements were done by microscope and compared with the analytical calculations with cubic law. Using CT scanner images, matrix porosity and saturation calculations were done. Matrix permeability and fracture permeability values were found before and after the polymer gel injection application. Measurements of the fractures were completed by using microscope to verify the analytical calculations. Laboratory results were defined by the equation developed for predicting equivalent fracture apertures with and without polymer gel as Improved Cubic Law (ICL). Shrinkage in equivalent fracture aperture was also defined by ICL observed by microscope. Using ICL, analytical calculations were done in different environments. Equivalent fracture apertures were calculated for all the experimental flow rates under laminar flow. ICL has worked with the fractured cores flow definition whereas not for homogeneous cores. There is a direct relation between fracture permeability with equivalent fracture aperture. The experiments with different environments (initially oil saturated and water saturated) in the cores, with calculations of equivalent fracture aperture and fracture permeability, showed similar results. The effect of polymer gel conformance to increase recovery by decreasing equivalent fracture aperture plugging was proven. Moreover, the decrese in equivalent fracture aperture in the cores were resulted in decreasing fracture permeability respectively.
Citation Formats
S. Canbolat, “Fracture effect limitation on residual oil saturation & visualization by computer tomography,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.