Well pattern selection and gas injection strategy optimization for the fire flooding of thin reservoirs

In-situ combustion is one of the effective technologies for the development of thin reservoirs. In this paper, the influences of different factors on the fire flooding of low-permeability thin reservoir were discussed by means of numerical simulation, based on the actual formation conditions in one certain low-permeability thin layer block. In addition, the scheme for discriminating the moment when the oil bank sweeps past the production well was prepared, and the optimal production parameters were determined. It is indicated that compared with nine-spot well pattern and inverted nine-spot well pattern, row well pattern provides higher recovery factor and more stable production, but its thermal communication is slower. When the well spacing is in the range of 70-141 m, the recovery factor decreases with the increase of well spacing. When the number of production wells on one side is greater than that in one row, it is more rational to shut down the well the moment the oxygen content of produced gas of production well rises suddenly. For low-permeability thin reservoirs, the recovery factor is less influenced by the hole opening position of gas injection. After the gas injection rate reaches 25 000 m³/d, the recovery factor will not be improved greatly with the further increase of gas injection rate. The optimal production parameters are recommended as 70 m central row well pattern, hole opening in the upper part of gas injection well and gas injection rate of 25 000 m³/d.