Re-determining source faults of the Upper Cretaceous Putaohua oil layer in Sanzhao sag of Songliao Basin, NE China

Abstract

From the deformation characteristics of two walls of a fault caused by fault activities, the activation of faults in the critical moment of oil and gas accumulation (structural inversion period) was analyzed to determine the source faults in the Upper Cretaceous Putaohua oil layer of the Sanzhao sag in Songliao Basin. Based on the previous classification and research results of activity patterns of the faults in the Sanzhao sag, the analysis of the structural deformation characteristics during the deposition of the 2nd and 3rd members of the Upper Cretaceous Nenjiang Formation and the inversion reveals that the feature of cutting to T06 reflection layer (bottom interface of the third member of the Nenjiang Formation) can not be taken as the basis to judge whether the faults were activated during the inversion or not. But during the structural inversion period, the structural deformation caused by faults would lead to fault-propagation inverted folds and fault-bend inverted folds, which would further lead to obvious deformation differences between hanging walls and foot walls of faults, this can be taken as the basis to determine if the faults were activated or not in the inversion period, and then the source faults of the Putaohua oil layer can be determined. Furthermore the source faults can be divided into two kinds, concealed faults and penetrating faults, according to if the source faults cut through layers of inversion period or not. These two kinds of source faults show more obvious control over the planar oil distribution in the Putaohua layer than the previous study results. Key words: Songliao Basin, Sanzhao sag, Putaohua oil layer, source fault, structural inversion