Study On Microcosmic Mechanism Of Unsteady Water Flooding For Non-Homogeneity Reservoir

Reservoirs in China mainly belong to fluvial reservoirs, which show heterogeneity sharply. After long time waterflooding development, it have formed the relatively Injection-production relation underground. Injecting water always flow along the high permeability parts to oil wells, which made waterflooding efficiency low. With deepening of waterflooding degree, injection-production relation become more complex which made it difficult for reservoir exploitation. Unsteady waterflooding is a method aimed at heterogeneity reservoir exploitation. Unsteady waterflooding is a way of heterogeneous reservoirs exploitation. Without changing well distribution, it can increase water injection area, decrease water content ratio of the produced fluid and increase degree of reserve recovery though changing working system. However, research of unsteady waterflooding mechanism is just confined in oil field experiments, which hasn't formed a completed theory. Further research is needed to conduct the production.Degree of reservoir heterogeneity directly affects the effect of unsteady waterflooding. Capillary force and the reservoir elastic have relations with reservoir wettability, which play different roles in different step of unsteady waterflooding.According to unsteady waterflooding mechanism, microscopic model was built to simulate the relations between oil production and produced fluid at different step of injecting and non- injecting. Program of analysis is also design to verify the method. All the work provides a new analysis method to future unsteady waterflooding experiments.Bubble method threshold pressure gradient tested and single-phase seepage flow experiments have been done whose cores come from a low mobility reservoir of oilfield, which lies in the eastern of China. The results showed that the seepage flow of low mobility reservoir has threshold pressure gradient and nonlinear seepage flow feature. The lower mobility is, the higher threshold pressure gradient is. The threshold pressure gradient has high relativity power correlation with mobility. An equation is also got to calculate the threshold pressure gradient in nonlinear seepage flow by analyzing to the data got form the single-phase seepage flow experiments. Analyzing to the nonlinear seepage flow feather, minimum threshold pressure gradient and pseudo-threshold pressure gradient were got. Function of relation between threshold pressure gradient and displacement pressure gradient was also proposed. Based on mathematic expression for the area of nonlinear seepage flow, the lower mobility is, the wider nonlinear seepage flow area is.