STRESS HETEROGENEITY IN THE NEWARK BASIN: MODELING STRESS PERTURBATION ON FAULTS

Stress in the subsurface is a critical factor in determining the mechanical properties in the shallow crust, for the safety of developing drilling and carbon storage sites, and for determining stability of faults and fractures. Stress in the subsurface impacts the behavior of rocks during deformation and earthquakes, production and storage of hydrocarbons, and the development of other energy resources. Traditionally, in situ stress has been considered to vary smoothly over large regions as determined by the tectonic setting and large-scale tectonic forces. However, many recent case studies point to variations of stress at reservoir scale, requiring detailed borehole data and analysis to detect and interpret the stress field heterogeneity. The underlying mechanisms behind this variability are still being explored. In tectonically active settings, slip on faults has been suggested; in this study, we explore this mechanism’s applicability in a ‘passive’ tectonic environment - the Newark Basin on the East Coast of the US. It has been evaluated for carbon storage and risk of induced seismicity, and preliminary work suggested significant stress variability. In this study, we use new laboratory data on formation properties to reevaluate the degree of stress heterogeneity in the basin and explore whether prior fault slip is a viable mechanism to explain it. The results show that the stress regime is more consistent with depth than previously thought and that variability in horizontal stress directions (determined from borehole indicators) can be explained by localized stress perturbations on active faults. In particular, slip on low-angle reverse faults dipping NW, with dimensions of a few hundred meters, can result in stress rotations of 20-30° that are observed in a deep stratigraphic borehole in the northern part of the basin.