Micro-pore structure and oil displacement mechanism analysis for deep zone and low permeability reservoir in Mobei oilfield

The Mobei reservoir is a low-permeability-sandstone reservoir, due to differences in pore geometry, it can be divided into two independent reservoirs: A1 reservoir and A2 reservoir. For better understanding the water flooding development effects of Mobei reservoir, the mercury intrusion porosimetry, water flooding CT scanning and micro-CT scanning experiments are used in this study. The result shows that the reservoir has the strong heterogeneity which is weaken gradually from A1 reservoir to A2 reservoir. Reservoir pore radius is mainly distributed in the 100–200 microns, the throat radius is mainly distributed in the 1–3 micron. The water flooding core experiment in each reservoir shows a short water-free oil production period and rapid water cut after breakthrough. The A2 reservoir core flooding process is similar to piston displacement, the A1 reservoir core flooding process refers to the phenomenon (The fingering phenomenon in the process of core flooding in the A1 reservoir is obvious). The calculated water drive efficiency of the A2 reservoir is 61.2%, which is higher than 49.1% of the A1 reservoir. According to the CT scanning process, the Mobei oilfield has low micro displacement efficiency and the A1 reservoir has a smaller spread (sweep area) and higher residual oil saturation.