Fractal characteristics of tight sandstone reservoirs: A case from the Upper Triassic Yanchang Formation, Ordos Basin, China

Sandstone samples of the Upper Triassic Yanchang Formation were collected from different wells, and then fractal dimension was calculated for each of them and used to represent the characteristics of the tight sandstone reservoir. The fractal model based on mercury intrusion technique was employed to represent the pores fractal characteristics of these sandstones. The results show that fractal dimension microstructures could be separated into three groups: low fractal dimension group, two fractal dimensions group, high fractal dimension group. Thin sections show that pores in the low fractal dimension samples are mainly original unaltered, the sandstone samples with two fractal dimensions include the unaltered pores (primary intragranular pores) and dissolved ones, furthermore, stronger mechanical compression and cementation were conducted on high fractal dimension samples, so they are mainly intragranular dissolved pores. Fractal dimension is highly correlated with its physical parameters. The lower fractal dimension, the better porosity and permeability. Therefore, The fractal dimension was suitable and effective for characterizing the tight sandstone reservoir.