It is recommended that the stress shadow should be taken into consideration for optimization of hydraulicfracture spacing. This is particularly important for Marcellus shale because of its low Young's modules.Conclusions1. Properties of Marcellus shale including fracture closure stress, instantaneous shut-in pressure (ISIP),process zone stress (PZS), formation leak-off coefficient and type were estimated from DFIT analysis.2. Pressure-dependent leak-off was observed from DFIT analysis. This indicates the presence of thenatural fractures (fissure) intersected by the hydraulic fracture.3. The stress profile was determined using vertical well log measurements (MIP-3H) and was calibratedusing DFIT analysis.4. The predicted fracture grows more upward in Marcellus Shale, if the stress shadowing effects areignored.5. The higher is the fracture height, the greater is the impact stress shadowing in Marcellus Shale.6. Stress shadowing negatively impacts the gas production.7. The stress shadowing effect decreases with increasing fracture spacing.8. Ignoring stress shadowing leads to higher estimated gas recovery.Ref