Analysis of typical gas injection well patterns and key control factors in the Tahe oilfield

After several rounds of water injection, the secondary oil-water interface in the fracture-vuggy reservoirs in the Tahe oil field is uplifted, resulting in the gradual deterioration of the effect of water injection on oil replacement, and it is beginning to be explored that the formation energy can be supplemented by gas injection to increase the synergy and improve the efficiency of replacement. Aiming at the problem of the unknown development strategy of late adjustment of typical gas injection wells in the Tahe oilfield, this paper establishes the criteria for judging different gas injection well patterns and proposes five typical gas injection well patterns: cave + side secondary, cave + penetrating deep and large fracture, fracture + cave reservoir, surface weathered crust + cave pattern, and dark river + upper hall cave pattern. Based on the grey correlation degree and group decision hierarchy analysis method, the main controlling factors analysis model was established, and the main controlling factors of the five models were analysed by numerical simulation. The results show that: in the cave + side secondary gas injection mode, the main controlling factors are the fracture distance and the permeability, with influence degrees of 26.98% and 26.75% respectively on the gas injection effect; in the cave + penetrating deep and large fracture gas injection mode, the main controlling factor are the permeability of the fracture and water size, with influence degrees of 29. 82% and 29.70%, respectively; in the fracture + cave reservoir gas injection mode, the main controlling factor is the permeability of the fracture, with an influence degree of 38.84%; the main controlling factor of the surface weathered crust + cave pattern gas injection well model is the permeability of the weathered crust, with a degree of influence of 35.65%; the main controlling factor of the dark river + upper hall cave pattern gas injection well model is the size of the water body, with a degree of influence of 39.45%. The main controlling factors and the dynamic and static characteristics of each different gas injection well pattern can provide guidance for the adaptive strategy of subsequent development of the same type of fracture-vuggy reservoirs.