Fracture pattern of the Lower Paleozoic sedimentary cover in the Lublin Basin of southeastern Poland derived from seismic attribute analysis and structural restoration

Abstract

We have characterized Late Devonian fracture systems in the northeastern part of the Lublin Basin in Poland using two independent approaches: (1) seismic data conditioning and volumetric attribute analysis and (2) structural restoration, geomechanical modeling, and fracture modeling. The study area was subjected to reverse faulting in the basement and fault-related folding at the end of Devonian. These late Devonian structures were not overprinted by later deformation events. We have applied a set of structurally oriented filters and seismic attributes aimed at highlighting discontinuities to reduce the seismic noise and improved the fracture visibility on structural steering volume. The main faults cutting intra-Neoproterozoic and intra-Ordovician horizons are principal east–west-striking reverse faults and minor northwest–southeast-oriented normal faults. Based on analysis of the seismic-scale faults, we have carried out fracture modeling for strike-slip and compressional stress fields, with a northwest–southeast-oriented axis of maximum compression. We have correlated tentative strikes for tensile, shear, and closing-mode fractures for both stress regimes, with fault-likelihood attribute maps. The observed fracture system can have developed in the strike-slip stress regime, although cracks generated due to gas overpressure, or of pre-Devonian age, are not excluded. The final fracture model may be extrapolated into Silurian strata, but the results should be perceived as a general approximation of structural trends due to significant differences in mechanical properties of Silurian shales and underlying Ordovician carbonates. Improved model calibration could be achieved after inspection of scanner image logs. We believe that understanding the fracture distribution within the gas-bearing Silurian strata may contribute to effective planning and performing of hydraulic fracturing because part of these fracture planes may be reopened and provide new conduits for fluid flow.