Deflected Polygonal Faults as Paleo-Stress Indicator and Tool to Analyze Hydraulic Conductivity in Senonian Reservoirs of Western Siberia (Russian Federation)

Polygonal Fault Systems (PFS) were identified in seismic in 1994 and afterwards recognized in more than 100 basins in the world. They appear related to radial shrinkage suggested by the hexagonal prone shapes and dewatering evidenced by fluid escape features. Several driving mechanisms have been proposed, however, dewatering and contraction of smectite rich sediments could be of significance for the Senonian deposits analyzed here. The random orientation observed in PFS indicates that the horizontal stress was isotropic over large areas at the time of formation. When the isotropic horizontal stress associated to PFS is modified by anisotropic lateral stress, the randomly oriented polygonal geometry of PFS is re-oriented to parallelize to the principal horizontal stress directions, arrangement called here Deflected Polygonal Fault System (DPFS). It has been observed in 3D seismic related to a large N–S trending E dipping normal growth fault coeval with the deposition of unit NB1 and associated to a corridor of “en- echelon” normal growth faults coeval with the deposition of unit NB2. The analysis of paleo stress trajectories evidenced by DPFS combined with the study of critically stressed conductive faults provides a criterion to define optimum horizontal well trajectories for each specific area.