Formation mechanism and distribution law of remaining oil in fracture-cavity reservoir

摘要

Drilling and dewaxing methods are used to create the quantitative model and stochastic model for fracture-cavity reservoirs respectively, which are used to investigate oil displacement in full diameter cores and to study the formation mechanism and distribution law of remaining oil in fracture-cavity reservoirs. The density difference between displacing phase and displaced phase and the connection position between fractures and cavities determine the fluid distribution in the cave. After the first water flooding, the remaining oil is composed of the following parts: the “attic oil” caused by the density difference between oil and water, the “occlusion oil” formed because the oil-to-water replacement is not instantaneous, the “corner oil” caused by the irregularity of the cave, the “blind cavity oil” formed because of the complex connection or low connectivity of the fracture-cavity system, and the “oil film” caused by the wettability of rocks. When the connection is higher, the amount of the “attic oil” is less. When the injecting velocity is lower and the viscosity of crude oil is lower, the amount of “occlusion oil” is less. The content of “corner oil” will become less when the cave figure is more regular, and the amount of corner is less. The amount of “blind cavity oil” is less when the connection is simple or the connectivity is high. In addition, on the water-wet rock surface, the content of “oil film” is less.