AbstractFor many decades, Enhanced Oil Recovery (EOR) scheme has been initiated to improve recovery factor for various oil and gas fields worldwide and Malaysian basins also are no exception. Monitoring reservoir during EOR schemes has become a priority for oil and gas companies operating in Malaysian basins. Monitoring reservoir has an incontrovertible part in reservoir management and field development planning. As a monitoring technique, 4D seismic method has proven its ability to surveil primary production of the oil and gas reservoirs. This technique has also been used to monitor the reservoirs under various phases of enhanced oil recovery schemes.4D seismic reservoir surveillance provides a sizable coverage over reservoirs which makes it possible to depict reservoir fluids movement. This advantage and also its ability to capture acoustic contrasts between various reservoir fluids have made the 4D seismic as a widespread technique for monitoring purposes. 4D seismic reservoir surveillance has been implemented for a field located in Malaysian basins. The first seismic survey has been shot in 1995 prior to production and injection activities. In 2000, production started from reservoir I-X in the field and water injection scheme also commenced exactly in the same year. Field asset team including geoscientists and engineers faced with early water production for a producer well; therefore, they decided to run another seismic survey in 2006.Time-lapse seismic data analysis has been performed based on the qualitative interpretation of 4D seismic data. The analysis has been done separately for both seismic surveys and also on seismic differences of monitor minus the baseline. This analysis has been done on amplitude for both seismic surveys and also on 4D amplitude values. In addition, 4D seismic attributes have been used to monitor the reservoir and depict the movement of injected water. 4D Phase shift (−90°), and 4D acoustic inversion complement the injected water monitoring.The results for various time-lapse seismic attributes are similar which indicate the expansion of injected water from injector wells after six years of aggressive water injection scheme. This expansion seems almost uniform for the five downdip injector wells; however, uneven pattern in water distribution for updip injector well proves the inefficient oil sweep for that region. Remaining oil area has been determined based on the analysis of 4D seismic attributes. The early water breakthrough for a producer well has been contributed to a channel between the well pairs (Injector and producer).
