OVERPRESSURE IDENTIFICATION USING SEISMIC AND WELL LOGS, PATTANI BASIN, GULF OF THAILAND

Abstract

The prevention of drilling kicks, the drilling risk in connection with expected formation pressure and the casing design are typical industry problems associated with pore pressure prediction before and during exploration well drilling. Currently, seismic velocities still remain a major input for pre-drill prediction. This is especially true for frontier depth intervals within the explored areas. The main topic in this thesis is overpressure. The overpressure zone is the zone that the pressure exceeds normal hydrostatic pressure at a given depth. This thesis focuses on two fields in Southern Pattani Basin which are Funan and South Gomin fields. Funan field has high pressure whereas South Gomin has lower pressure compared to Funan field. Seismic velocity contains information about lithology changes including velocity in each rock layer. An extraction of the target overpressure signal from seismic velocity input is based on theoretical prediction which is then compared to the observed relevant seismic velocity information to detect changes related an overpressure anomaly. The seismic velocity data from pre-stack time migration (PSTM) velocity cube can be converted to interval velocity by Dix’s equation and used for investigating possible overpressure anomalies. The overpressure zone shows slower interval velocity compared to hydrostatic pressure zone. The slower interval velocity can be visualized in some areas by velocity isochronal mapping and volume changes. Also, Eaton’s method was tested to predicted pore pressure from seismic volume. The result of pressure prediction using seismic velocities is restricted by the resolution of seismic velocity picking and cause of overpressure.