Abstract:

After nearly 30 years of waterflooding development, the reservoir in Block WX-3 of Wenmi oilfield has changed in porosity, permeability and microscopic pore structure, resulting in variations of fluid flow behaviors in the reservoir. In order to further quantify the variations of flow behaviors during waterflooding in the reservoir in Block WX-3, using the experimental data of oil-water relative permeability before and after waterflooding at different watered-out levels, a mathematical model for oil-water relative permeability and a prediction model for water cut changes during the whole process of waterflooding development were constructed by virtue of waterflood analytical method and Newton iteration method. The results show that the actual water cut during production in Block WX-3 changes in a consistent pattern with the model prediction result. The main problems in the development of Block WX-3 are relatively high displacement rate in waterflooding, and the migration, expansion and blockage of clay particles caused by injected water, which alter the pore structure and wettability of the reservoir. Along with extension of water injection, the irreducible water saturation and residual oil saturation gradually increase, and the oil displacement efficiency gradually decreases. Specifically, on average, the irreducible water saturation increases by 0.067 7, the residual oil saturation increases by 0.053 1, and the oil displacement efficiency decreases by 0.142 8.

Key words: Block WX-3, waterflooding, displacement characteristic, oil-water relatively permeability, waterflood analytical method, Newton iteration method, water cut variation