Experimental and Theoretical Studies on Foam Flooding in Tight Reservoirs
Abstract
Enhanced oil recovery for tight reservoirs with extremely low permeability and porosity is
becoming the new routine for reservoir engineering research. Foam flooding has already been
proven as an effective and potential approach to enhance the oil recovery in conventional
reservoirs. However, limited research has been done on the phenomena and mechanism of foam
performance in tight porous media.
In this study, both experimental and theoretical approaches are utilized to study the foam
flooding process in tight reservoirs.
In the experimental part of this study, a series of core flooding tests are performed to
investigate foam performance in the absence and presence of oil in tight core samples with
different permeabilities, varying from 0.1mD to 3.3 mD. The foam resistance factor, mobility
reduction factor, and mobility of the displacing fluid are investigated by comparing the foam
flooding processes with waterflooding and the co-injection processes of brine and gas. The
effectiveness of applying foam flooding as a tertiary recovery method is studied by comparing
the production data, pressure drop data, and mobility of displacing fluid between foam flooding
and waterflooding. The fractional flow theory of the foam process is applied to study the relation
between the fractional flow of gas and water to present how gas is trapped in porous media by
foam.
The experimental results show the effectiveness of foam on reducing mobility compared with
waterflooding and the co-injection of brine and gas. An additional 15 to 22% oil recovery factor
is achieved by introducing foam flooding after waterflooding is completed. The foam mobility is
lowered by one order of magnitude compared with waterflooding in the presence of oil.
In the theoretical part of the study, a theoretical model is established to predict the dynamic
performance of surfactant-alternating-gas (SAG) flooding by considering the major mechanisms
in this process, such as gas channeling caused by an unfavorable mobility ratio, gravity
segregation, and the instability of foam.
Oil production estimated by the proposed theoretical model is compared with numerical
simulation and field production data collected from the Ganguyi project in China, and the growth
trend of oil production agrees well with them. The proposed model provides a fast approach to
predict the dynamic performance of surfactant-alternating-gas flooding, and it can be used as a
tool to optimize the operational parameters.