Identification of a zone of fluid pressure-induced fractures from log and seismic data - a case history

Undercompaction anomalies are known to be related to abnormal pressure conditions and can be detected from seismic velocities. The case history presented here deals with another type of anomalous zone that has been encountered below an undercompacted section and which is believed to be due to an open fracture system under high fluid pressure conditions. After a short presentation of some geomechanical concepts and the geological context, this paper focuses on three aspects: the identification of the anomalous zone using drilling, log and seisrnic velocity data; the understanding of the mechanisms involved in the initiation and development of the anomalous zone; and the main consequences for petroleum exploration.