Analysis of Impact of Pressure Gradient on Water Drive Recovery of Sandstone Reservoirs

Abstract The accurate assessment of water flooding recovery factor is of crucial importance for Realizing the unexploited possibilities of residual oil resources in medium and high permeability reservoirs. Based on key element of pressure gradient and by means of the combination of laboratory core displacement experiments, data statistical analysis and reservoir numerical simulation, a calculation model of water flooding recovery factor with pressure gradient as the core parameter is constructed. This model can capture the microscopic displacement details of oil and water and the macroscopic seepage laws more accurately. Through CT online displacement scanning, the microscopic utilization laws of residual oil under different pressure gradient conditions are revealed. Use the function of the relationship among pressure gradient, permeability and recovery factor to calculate the residual oil saturation under different injection-production pressure difference conditions, the impact of pressure gradient on recovery factor under different well pattern conditions can be clarified. oil displacement results under different displacement pressure difference conditions show that:Water flooding recovery factors of cores with different permeabilities and pressure gradients conform to the Langmuir equation. A larger pressure gradient helps to improve the distribution of the displacing phase and the displaced phase (oil) in pores, reducing the clustered and porous residual oil while increasing the columnar, droplet-shaped and film-like residual oil. In the reservoir with one injection well and one production well pattern, The gradient value of pressure at the corners is low and the residual oil is enriched. Increasing pressure at injection end and reducing pressure at production end can effectively enhance pressure gradient in corners of reservoir and efficiently exploit the remaining oil reserves. After the well network type with a single injection borehole accompanied by five output-generating wells is converted into well network type with one injection borehole and eight output-generating wells, The reservoir’s water flooding pressure gradient can be powerfully elevated. It brings important guiding implications for the adjustment of well pattern disposition, optimizing water injection methods and efficiently tapping potential of residual oil in oilfields at the late period of extremely high water cut ratio, helping sandstone reservoirs achieve better development benefits.