['It', 'is', 'difficult', 'in', 'directly', 'predicting', 'permeability', 'from', 'porosity', 'in', 'tight', 'sandstones', 'due', 'to', 'the', 'poor', 'relationship', 'between', 'core', 'derived', 'porosity', 'and', 'permeability', 'that', 'caused', 'by', 'the', 'extreme', 'heterogeneity', '.']