Laboratory research of wettability and heterogeneity effect on microscopic residual oil distribution in tight sandstone cores during CO2 flooding

Abstract

Based on physical simulation experiment and nuclear magnetic resonance (NMR) measurements, the effect of wettability and pore throat heterogeneity upon oil recovery efficiency during CO2 flooding, were conducted to investigate how crude oil residing in different sized pore are produced by immiscible CO2 flooding schemes in tight sandstone cores. Experimental results indicate that water wet cores lead to the highest final recovery factor in comparison with intermediate wet cores and weak oil wet cores. The recovery factor difference in clay micro pore is mainly because of the heterogeneity, while the difference in medium pore and large pore is affected by asphaltene precipitation phenomenon. Therefore, it is important to enhance the recovery in the clay micro pores, and focus on the cores permeability reduction caused by asphaltene precipitation. Based on this investigation on the residual oil saturation in pore throats subjected to immiscible CO2 flooding, it is possible to design an optimum flood scheme which suits for the microscope pore throat characteristics for a given tight oil reservoir.