Experimental study on natural gas migration and accumulation mechanism in sweet spots of tight sandstones

Although sweet spots play a significant role in the exploration and exploitation of tight gas reservoirs, the research on the mechanisms of gas transport in sweet spots has been relatively sparse. In this work, two-dimensional physical experiments are designed and implemented to simulate the process of gas migration and accumulation in sweet spots. Combined with one-dimensional gas injection experiments, the mechanisms of gas migration and accumulation in sweet spots are discussed. The results indicate that the migration and accumulation of gas are two distinguishing processes. The condition of gas migration is mostly determined by the permeability of sands, and the critical condition of gas accumulation in sweet spots is that the permeability ratio between the inner and exterior area of the sweet spot is 2.6; values higher than this value represents more favorable conditions for gas accumulation. The gas saturation of sweet spot correlates well with permeability, i.e., gas saturation increases as permeability increases. The internal heterogeneity of sweet spots also affects the gas accumulation, i.e., a high permeability zone promotes the accumulation of gas in an adjacent mid-high permeability zone in the same sweet spot.