Three-dimensional seismic and structural investigation of a suspected hydrothermal dolomite reservior in the Trenton-Black River, Saybrook, Ohio

Trenton-Black River reservoirs in the Appalachian Basin are typically associated with fault-related hydrothermal dolomites that are sealed by unaltered host rocks. However the details of fault geometry and where porosity develops around faults remains poorly documented. Integration of 3-D seismic, wireline and production data from Saybrook Field in northeastern Ohio has shown that the productive trend is controlled by a 3.4mi (5.5 km) long, NW-SE oriented basement fault that was probably reactivated during the Taconic Orogeny in the Mid- to Late Ordovician. The far-field stresses of this compressional activity caused strike-slip movement of the pre-existing fault to create echelon synthetic shear faults that branch 1350ft (411.5m) upward into the Trenton-Black River interval. Circular collapse structures between overlapping shear faults are the primary drilling targets. Faults were mapped using amplitude and coherency versions of the seismic data. Curvature analysis of horizons mapped in the seismic data allowed us to further constrain the location and orientation of subtle structures. Fault morphology provides insights into the path of the dolomitizing fluids. The distribution of porosity, and thus the location of the reservoir, has been mapped in 3-D using a seismic attribute study that integrated wireline log-based measurements of porosity with seismic attributes. Our results show that the best porosity is developed in areas between overlapping synthetic shear faults. These locations likely represent areas where antithetic shear faults formed, and when combined with minor dip-slip movement created conduits for subsequent porosity generating fluids. The results of this study and the methodology presented here have application in analog settings elsewhere.