Oil Displacement Efficiency of High-Power Water Flooding Displacement Core Experiment and Transformation Method of Reservoir Scale in Different Well Patterns

In this paper, mechanism for enhancing oil displacement efficiency by high-power water flooding displacement from pore-throat scale were studied by high-power water flooding and nuclear magnetic resonance (NMR) experiments. Transformation method from core scale to reservoir scale was established by high-power water flooding displacement law of core experiment and seepage characteristics in different well patterns. The results indicated that there is a logarithmic function between oil displacement efficiency and displacement multiple in the process of high-power water flooding. After water flooding 2000 times pore volume, the relaxation time peak region was moved right and enlarged, the short relaxation time signal intensity peak was decreased, the average pore-throat radius was increased, and the ratio of pore radius to throat radius was decreased, so cluster-like residual oil, stuck-like residual oil, and island-like residual oil could be mobilized. After high-power water flooding, core wettability changed from weak-lipophilic to weak-hydrophilic active, so film-like residual oil could be mobilized. And oil displacement efficiency computing model of reservoir scale for inverted nine-spot well pattern, line well pattern, and five-spot well pattern was established. Oil displacement efficiency of reservoir scale increases with the increase of injection volume and decreases with the increase of well spacing. Oil displacement efficiency of reservoir scale in line well pattern and five-spot well pattern is higher than that in inverted nine-spot well pattern with the same injection volume and well spacing. In 2008, an inter-well infill scheme was implemented in Bohai S oil field, well pattern was adjusted from an inverted nine-spot to a line well pattern. By the end of 2020, the displacement multiple of the whole reservoir increased from 0.21 to 1.28, oil displacement efficiency of the reservoir scale increased from 38.9% to 47%, with an increase of 8.1%, which is 3.5% higher than the continued maintain the development of the inverted nine-spot well pattern. The results of the study are of great significance in guiding the actual development of the oil field.