Improve Plugging Efficiency in Fractured Sandstone Reservoirs by Mixing Different Preformed Particles Gel Size

摘要

The oil recovery from fractured reservoirs is usually low, which is usually caused by the existence of areal formation heterogeneity. Preformed particle gel PPG has been used successfully use to reduce Heterogeneity and improve sweep efficiency. Low salinity waterflooding (LSWF) was recognized by the oil industry to increase displacement efficiency. The main objective of this study is to test the effectiveness of coupling these two technologies to increase oil recovery. Additionally, this study will determine the optimum PPG size to use with LSW to improve conformance control in the fractured sandstone cores. Semi-transparent five-spot model made of sandstone cores and acrylic plates were built to visualize the sweep efficiency from the coupled methods. Sandstone cores were saturated by 1.0% NaCl and then light oil was injected to simulate initial water saturation before the fracture was made. Brine at different salinities was injected initially into the fracture model to determine oil recovery. PPG with different sizes was injected later to reduce the fracture conductivity and increase sweep efficiency. Brine was injected again after gel treatment to determine the oil recovery improve after the gel injection. Laboratory experiments showed that the oil recovery factor and the water residual resistance factor (Frrw) increased when the low-salinity water was used for injection. However, the PPG extruded pressure decreased when the PPG swelled in a low-salinity water. Additionally, mixing different PPG size resulted in higher plugging efficiency than uniform PPG size and Frrw decreased as increased flow rate. Combining two different preformed particle gel sizes can improve plugging efficiency and, in turn, improve sweep efficiency and enhance conformance control.