How do stress perturbations near salt bodies induce difficulty in salt imaging? Insights from a geomechanical model and salt imaging
Traditional methods for imaging salt bodies seldom consider near-salt stress perturbations caused by salt, and the associated velocity perturbations of seismic waves in the sediments near the salt. To demonstrate the importance of stress changes caused by the salt on accurately imaging salt bodies, in this study we develop and apply a combined method of geomechanical stress modelling and salt imaging. We simulate the stress perturbations in sediments induced by a salt sphere using a static geomechanical model, and calculate the associated velocity changes of seismic waves in the sediments by using our model stress perturbations. We use the reverse time migration and imaging method to image the salt sphere, and then analyse the imaging results of two cases including and excluding the effects of stress perturbations by the salt sphere on velocity changes of seismic waves. The results show that the near-salt velocity changes of seismic waves induced by stress perturbations near salt bodies can have a significant impact on the salt imaging.We find that when the effects of near-salt stress perturbations are ignored, the imaging of the salt sphere is clearly distorted: the salt sphere is extended vertically and becomes a salt ellipse with a vertical major axis. In contrast, when we include the effects of near-salt stress perturbations, the imaging of this salt sphere accurately matches the salt geometry and position. Thus, the near-salt stress perturbations should not be ignored in salt imaging. This study provides scientific insights for petroleum geologists and exploration geophysicists on the relationship between near-salt stress perturbations and accurate imaging of salt structures.