Dulang oil field, an anticline classtic reservoirs with areal extended about 330sq.km in offshore Peninsular Malaysia Basin was discovered in 1981 with water depth of 76m and total STOIIP around 1BSTB (Figure 1). The field was on production since 1991 with cumulative production (as at Jan 2010) around 21% of STOIIP. Immiscible Water-Alternating Gas (IWAG) EOR injection has been identified to be implemented which can enhance the oil recovery further. A Pilot injection project was carried out in sub-block area of the main reservoirs for a period of four (4) years. Full field injection plan has been formulated and has moved-up to execution phase. Monitoring the flood front movement by IWAG injection becomes a major challenge in this project especially with wide well spacing and high reservoir heterogeneity where "fingering" effect is prone to occur. This paper will describe the application of time-lapse (4D) seismic in the full field IWAG to monitor the flood front movement through times. A feasibility study was carried out to investigate the detectability and repeatability between two seismic vintages in order to understand the uncertainty. Factors contribute to the chances of success (COS) of the project also being identified. The result shows that through simulation prediction, a cumulative acoustic impedance of 6% to 8% can be observed after two years IWAG injection cycles. Also being described in this paper are the planning of the full field project right from technology identification, screening study, feasibility study and finally the full field implementation. This information’s are valuable to the industry especially to enhance oil recovery projects where full scope of formulizing the 4D seismic application being evaluated in order to enhance the surveillance and monitoring programme hence ensure the success of the EOR projects.

Summary Seabed acquisition is expected to deliver broadband seismic data by using a combination of pressure and particle motion or acceleration measurements to eliminate the free surface ghost. In this paper, we have investigated the frequency bandwidth delivered by different seabed acquisition systems, i.e. two component ocean bottom cable (2C-OBC), four component ocean bottom cable (4C-OBC) and four component ocean bottom node (4C-OBN) systems on the low frequency side, under different geological settings and acquisition environments. The study was carried out by analysing the effect of total system (source, receiver and recording instrument) response and frequency bandwidth for different types of seabed acquisition systems and sensors. The analysis shows that after optimal compensation for total system response, different seabed systems and sensors deliver comparable low freaquency signal in the band of 2–5 Hz given the variations in the local seabed conditions. Introduction The recent emergence of towed streamer based broadband seismic technologies poses an interesting question, "how broad really is the broadband data delivered by various seabed acquisition systems, especially at the low frequency end?" During the last few years, PETRONAS has acquired more than 1,200 sq. km. of 3D and 540 LKM of 2D seabed seismic data using 2C and 4C acquisition technologies. Majority of the data were acquired using OBC technology and different acquisition systems with a limited amount of data acquired using OBN technology. The main objectives of the study were to analyse:The effect of total system (source, receiver and recording instrument) response on the signal bandwidth and the effect of source-receiver notchesThe frequency bandwidth delivered by different seabed acquisition systems and the conventional towed streamer system. The effect of source volume on the bandwidth, if any, was not analyzed in this study. One of the main benefits of seabed acquisition is that it delivers broadband and wide azimuth seismic data. The high frequencies are important for improving the resolution, while the low frequencies provide the opportunity for better seismic inversion and well ties. The seabed acquisition improves the signal bandwidth by enhancing both high and low frequency ends of the spectrum. It uses co-located measurements of two vertical components (P and Z) which help to remove the free surface ghost (Fig 1) and improve the overall signal bandwidth.

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