This book provides a systematical investigation on the reservoir characteristics and percolation mechanism of ultradeep carbonate gas reservoirs, including reservoir characteristics and classification, gas storage and percolation capacities, gas-phase and gas-water two-phase percolation mechanism, microscale complex gas-water relationship, reservoir sensitivity characteristics, and gas production characteristics of heterogeneous carbonate reservoirs. Some advanced and improved experimental techniques and analytical methods are introduced and applied, including comprehensive evaluation technique of storage and percolation capacities, ultra-high temperature and pressure physical simulation experiment technique, microscopic visualization technique based on CT scanning and microelectronics lithography, and physical simulation technique for heterogeneous reservoir development. In addition, it summarizes strategies for the efficient development of ultradeep carbonate gas reservoirs based on these theoretical research results. The key techniques and methods introduced in this monograph satisfy the need for efficient development of ultradeep carbonate gas reservoirs and provide theoretical basis and methodological value for investigations on similar gas reservoirs. This book serves as a reference for engineering technical professionals, researchers, and graduate students who are engaged in the exploration and development of carbonate gas reservoirs.