Experimental study of permeability reduction and pore size distribution change due to asphaltene deposition during CO2 huff and puff injection in Eagle Ford shale

Many laboratory and simulation studies regarding gas injection enhanced oil recovery method in shale reservoir have been performed and shown good results. However, one problem not investigated is the asphaltene precipitation and deposition problem. In conventional reservoirs, the permeability reduction caused by asphaltene plugging and adsorption has been observed and well studied. In shale reservoirs, the deposition, if any, will be more critical. In this work, experimental studies were conducted to investigate the effect of asphaltene deposition on the pore size reduction and permeability reduction in shale core samples during the CO2 huff and puff injection process using a dead oil sample from a Wolfcamp shale reservoir. A decrement of pore with a diameter size in the range from 100 to 800 nm and an increment of pore with a diameter size smaller than 100 nm were observed after 6 cycles of CO2 huff and puff injection. The result indicates the existence of pore plugging and asphaltene adsorption during the gas injection process. The experimental results also showed a 47.5-nD permeability reduction after 6 cycles of CO2 huff and puff injection. Compared with the original permeability of the shale core, 126 nD, the permeability reduction is more than one-third of the original permeability. (C) 2017 Curtin University of Technology and John Wiley & Sons, Ltd.