The development of ultra-deep fault-controlled fracture-cavity reservoirs is confronted with such issues as insufficient formation pressure，unclear reserve status，subpar water injection effects，and ambiguous direction for significant enhanced oil recovery（EOR）. This paper systematically summarizes the understanding of reservoir energy，reserve production，and water injection effects，while exploring technologies for substantially improving the recovery of such reservoirs. The research reveals that the static pressure measured by a single well in ultra-deep fault-controlled fracture-cavity reservoirs fails to represent the formation pressure in areas beyond the wellbore or at distant locations or reflect the overall energy level of the entire reservoir. When inter-well connectivity weakens，the energy-variation coefficient and inter-well dynamic connectivity-variation coefficient of the connected well-group both increase. Reserves must be activated before they can be produced. Some reserves become“quasi unproduced reserves”in the development，and dynamic reserves are consistent with activated reserves. It is one-sided to judge the effectiveness of water injection merely by comparing evaluation indices before and after water injection. Water-injection supplementation requires reasonable control of the injection-production ratio， along with dynamic adjustment and optimization. Three-dimensional development is an important technical direction for significantly improving the recovery of ultra-deep fault-controlled fracture-cavity reservoirs in the future.