(201b) A Microfluidics Based Study on the Effect of Immiscible Huff-n-Puff Process on Residual Oil Saturation in Hydrophilic and Hydrophobic Porous Media

Authors: 
Pradhan, S., Oklahoma State University
Kone, G., Oklahoma State University
Antle, R., Baker Hughes, a GE Company
Aichele, C., Oklahoma State University
Jiang, H., Baker Hughes, a GE Company
Bikkina, P., Oklahoma State University
Cyclic gas injection or “Huff-n-Puff” method is a widely applied enhanced oil recovery (EOR) method in depleted reservoirs. It extracts additional oil by reducing oil viscosity from gas diffusions. In this work, microfluidic experiments were conducted to investigate the performance of immiscible “Huff-n-Puff” process using a novel laboratory setup. Residual oil saturation (Sor) in each Huff-n-Puff cycle was studied after water and gas flooding, together with the effects of aspect ratio and wettability.

Uniform pore network chips with hydrophilic and hydrophobic wetting surfaces and aspect ratios ranging from 1.97 to 23.94 were used. In this study, the aspect ratio was defined as the ratio of the maximum cross-sectional area of the pore and that of the throat, both measured perpendicular to the flow direction. Water, n-decane, and CH4 were used as aqueous, oil, and gas phases, respectively. The aqueous and oil phases were dyed with methyl blue and Sudan red, separately to increase visual contrast for enhanced fluid saturation measurements.

In each experiment, a microfluidics chip was first saturated with water then oil to achieve the initial saturations. It was then flooded with water and gas to achieve residual fluid saturations before pressure reduction steps in “Huff-n-Puff”. Water and gas injection rates were adjusted to maintain capillary numbers in the range of 10-7 to 10-5, to match values of reservoirs. A constant back pressure of 100 psig was maintained before “Huff-n-Puff” started. Four pressure reduction steps were performed by reducing the back pressure by 25 psig in each step. Chip and pore scale images were taken, and analyzed using ImageJ software to measure the residual fluid saturations.

For the continuous gas flooding prior to “Huff-n-Puff”, the results show that the oil saturation increases semi-logarithmically with aspect ratio (log AR vs. Sorg) for both hydrophilic and hydrophobic chips. During the four “Huff-n-Puff” steps, up to 20 %PV oil was produced in hydrophilic chips, whereas less than 5 %PV of oil was produced in hydrophobic chips.