Kelasu Gas Field is a complicatedly structured, ultra-deep buried, ultra pressurized gas reservoir, with ultra-thick pay-zones, tight matrix and has a complex structure of WOC as well as fracture developments, which is very rare in the world and has no development precedents around the world. Meanwhile, fast and safe drilling of ultra-deep wells, safe drilling involving low pressure gradient and layered, differently pressured horizons, as well as high temperature, high salinity, anti-composite salt gel drilling fluids have remained worldwide drilling challenges. This set of technologies overcame a series of technical obstacles through systematic studies and optimization, including thermal-resistant, high gravity frac fluids and thermal dissolution plugging agents, which represent cutting edge researching and engineering abilities on a global stage. Overall, this set of technologies holds leading status at an international advanced level, represents a breakthrough in developing this type of reservoirs, and promoted production in associated fields, and recommended for further implementation.