Abstract: The Ordovician reservoir in Halahatang is a typical fractured-vuggy carbonate reservoir. The karst reservoir is well developed, and the reservoir permeability space is mainly composed of karst caves, dissolution holes and fractures of different sizes, which are discrete in general, locally continuous, multi-scaled in reservoir collective space, and complex in morphology and distribution. Water injection and displacement are the most important development methods for this type of reservoir. After 15 years of development, the number of single wells and units with water injection failure is increasing year by year. After water flooding failure, gas injection becomes the most important means of fractured-vuggy carbonate reservoir extraction. The gas injection extraction technology has been tested and applied in Halahatang. And the six-factor gas injection well selection standard has been established. The wells are selected from six aspects, including karst background, well-reservoir relationship, drilling depth, reserve scale, production dynamics, and remaining oil type. The gas injection parameters are designed according to five aspects, including gas injection timing, gas injection method, gas injection volume, stewing time, and indicator curve. Some preliminary understandings of gas injection well selection principles and gas injection parameters design have been obtained, which is hoped to provide reference for gas injection development of fractured-vuggy carbonate reservoir.

Key words: karst reservoir, locally continuous, water flooding failure, gas injection extraction, gas injection parameters