Macroscopic three-dimensional physical simulation of water flooding in multi-well fracture-cavity unit

A macroscopic three-dimensional physical simulating model of multi-well fracture-cavity units was designed and constructed based on similarity theory. The characteristics and the water breakthrough pattern of fracture-cavity reservoirs developed in bottom water depletion and water injection modes were investigated by the model. The results show that, in bottom water drive, under the effect of bottom water depletion and water breakthrough, the wells had high productivity in early stage and fast decline. After energy supplement by injecting water, the productivity rebounded in a short time and then began a slow decline. The bottom water tended to coning to the wells at the place of bottom water entry. The water breakthrough pattern is spot pattern and the water breakthrough time is controlled by the wellʹs connectivity to the bottom water; the water injection can inhibit coning and intrusion of bottom water, turning the spot pattern water breakthrough in bottom water drive period into planar line form, and the water breakthrough time in water injection period was mainly influenced by the well depth. The water cut of wells in water flooding multi-well fracture-cavity units changes in three patterns: slow rise, staircase rise and abrupt watered-out, which is influenced by the reservoir type and the coordination number. When the well encounters cavity, the water cut increasing rate slows down with the increase of the coordination number; when the well drilled fractures, the water cut changes in staircase pattern with the increase of coordination number.