With urgent need of greenhouse gas sequestration and booming oil prices, underground oil/gas reservoirs seem the only value added choice for CO₂ storage. A great portion of current CO₂ injection projects in the world is in naturally fractured reservoir. It is our aim to show that the matrix part of these reservoirs could be used as a permanent CO₂ storage unit while recovering oil from it.

This dissertation presents a different approach to die problem following a multistage research work. Initially, a series of laboratory experiments were performed at ambient conditions using artificially fractured (single) sandstone rocks to mimic fully miscible CO₂ injection. Different injection rates were tested and the efficiency of the process was analyzed in terms of maximized oil recovery. Next, CO₂ injection experiments at different miscible conditions were conducted to analyze the dominant transport mechanisms and to quantify enhanced oil recovery (EOR) / storage potential. CO₂ diffusion and other effective oil recovery mechanisms were studied during continuous injection at different rates into the fracture. After the continuous injection of CO₂, a soaking period was allowed following a blowdown period to produce the oil recovered by back-diffusion. The CO₂ storage and EOR capacity during the blowdown period were analyzed. Using dimensionless analysis and matrix-fracture diffusion groups, a critical number for optimal recovery/sequestration was obtained.

The pressure decay behavior during the shutdown was analyzed in conjunction with the gas chromatograph analysis of the produced oil sample collected during blowdown after the quasi-equilibrium reached during pressure decay. This gave insights into the governing mechanism of extraction/condensation and miscibility for recovering lighter to heavier hydrocarbons during pressure depletion from fractured reservoirs.

The importance of miscible recovery from fractured reservoirs in current petroleum industry makes its comprehensive understanding, characterization, and quantitative prediction very critical. Therefore, as a final step, a universal procedure of inspectional analysis followed by a numerical sensitivity was performed for the scaling of fractured porous media. A new dimensionless group introduced by combining the effects of major governing groups will improve the understanding of pore scale mechanisms also it can be further used for the improvement of fractured reservoir models and upscaling laboratory results.