Water-oil displacement is an important process that occurs in a shale matrix after hydraulic fracturing and in water-based enhanced oil recovery. This process and its controlling factors are investigated through a comparative study of three shale samples that have different types of pore systems and wettability. An integrated method of imbibition and multiscale imaging was applied, and a modified oleic tracer that can better represent oil flow was used in imbibition testing and micro-CT imaging. SEM pore characterization was then performed under high magnification with guidance from the micro-CT images showing the changes due to oil or water imbibition. New insights were obtained on the importance of both wettability and pore size effect on oil recovery and the distribution of residual oil after water-oil displacement. Connectivity of pores with different wettability is also discussed on the basis of 3D analysis and SEM pore characterization.
Collectively, these new findings improve the understanding of the complicated process of water-oil displacement and the role of influencing factors including wettability and pore aspect ratio. Important implications for improved oil recovery strategy in shale are discussed for different types of reservoir rocks. The integrated imaging and imbibition technique provides a new path for further investigation of improved oil recovery in shale.
Oil recovery by water imbibition can be quantified through image analysis. Figure in the right shows the residual oil factor map (B) in water-imbibed and residual oil areas (A). Red and green in (A) denote the residual oil and water-imbibed areas, respectively. Scale bar in (B) is the residual oil factor after water imbibition from 0 to 1.0.
Representative publications
Peng, S., Shevchenko, P., Periwal, P. et al. 2021. Water-Oil Displacement in Shale: New Insights from a Comparative Study Integrating Imbibition Tests and Multiscale Imaging. SPE J. SPE-205515-PA. https://doi.org/10.2118/205515-PA. Also presented in URTeC 2021.
Peng, S., Y. Liu, L. Ko, W. Ambrose, 2019. Water/Oil Displacement by Spontaneous Imbibition Through Multiscale Imaging and Implication on Wettability in Wolfcamp Shale, Unconventional Resources Technology Conference, July 22–24, 2019, Denver, Colorado, doi:10.15530/urtec-2019-194.
Peng, S, and X. Xiao, 2017. Investigation of multiphase fluid imbibition in shale through synchrotron-based dynamic micro-CT imaging, J. Geophys. Res. Solid Earth, vol. 122, doi:10.1002/2017JB014253.
