Benefits of PSTM and PSDM Reprocessing in the Exploration of the Deep Malay Basin

Abstract

In May 2008 TOTAL E&P Malaysia (TEPMY) was awarded, together with his partner Petronas Carigali, two blocks with ultra HP/HT deep exploration targets. Work commitments on these blocks included seismic acquisition, reprocessing and drilling of two deep exploration wells below the conventional mature plays. Imaging problems in the Malay basin are related to coal-bed multiples and absorption, pull-down effects and seismic resolution in a fluvio-deltaic to coastal plain depositional environments during Lower Miocene and lacustrine environment during the Oligocene. To perform our "deep frontier exploration in a mature basin" TEPMY first analyzed available vintage dataset on the area. Most 3D seismic data have been acquired or processed in the last 10 years with long enough streamers (5 to 6 km) for our exploration targeting reservoirs from 2.5 to 5km deep. But vintage processing sequence was dedicated to conventional targets from 1 to 2 km deep, where imaging issues are limited. TEPMY and his partner decided to reprocess all data covering identified prospects and leads on one block. New PSTM processing sequence was focused on multiple attenuation in target window with careful velocity picking and application of 3D-SRME despite shallow water depth. It results in a significant seismic improvement of lower Miocene sedimentary fairways imaging leading to exploration risk reduction. More reliable velocity analysis was also a key outcome in the evaluation of overpressure zone in the Malay Basin. In parallel with time reprocessing, we have also launched depth reprocessing on the two main prospects of the southern block, prospect A and prospect B affected by strong structural uncertainties related to low velocity anomalies in several areas. Multi-approach accurate velocity model building strategy, including in-house Full-Waveform Inversion in shallower part, together with strong iterative interpretation input, leads to significantly improve structural image of the prospect B which now become a candidate for drilling. We consider this time and depth reprocessing approach is a key parameter to properly evaluate deep exploration potential of Malay Basin as well as mature drillable prospects.