Incidence of Tectonic Stress on Overpressure Development in Ukrainian Basins

The data from oil-bearing Ukrainian basins outline the tectonic control of overpressure development in areas characterized by recent episodes of folding and active compression (dominantly horizontal stress regime). Based on the data presented, vertical compaction alone is not sufficient to account for the observed overpressure development. Tentatively, tectonic deformation is proposed as the dominant factor for overpressure development in sedimentary layers in recently folded regions. During folding, the opening of fractures results in local density decrease and helps in driving the migrating fluids, i.e., both hydrocarbon and formation waters, in the carrier beds toward the top of the structures. Ductile flow of shaly interbeds toward anticlinal closures can also enhance the sealing capacity of these layers. In the Ukrainian Carpathians and salt domes of the Dniepr-Donetz Basin, direct relationships have been evidenced to link and predict the amount of overpressure as a function of the amplitude of the folds. The use of measurements and of the monitoring of overpressures for evaluating the horizontal stress intensity and for the forecasting of earthquakes is also suggested.