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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association


25th Annual Convention Proceedings (Volume 1), 1996
Pages 367-375

Understanding Multiples to Upgrade Low-Relief Prospects

Sunu H. Praptono, Witan O. Ardjakusumah


In an area with thick horizontal shale sequences such as the Malacca Strait PSC, it is often hard to discriminate whether a seismic horizon beneath the shale sequence is a primary event or a multiple of an overlying event due to insufficient structural dip and/or a stacking velocity contrast. This gives rise to difficulties especially in identifying low-relief structures (i.e. structures which have less than 15 ms of closure which is one of the main successful play types tested in the PSC), particularly when the reservoir reflection is masked by multiples of overlying shales.

Pegleg multiples should be expected to occur under such geophysical conditions. This type of multiple is very simple conceptually. However, they are always difficult to predict during data acquisition, and often misinterpreted as primary events in processing and interpretation.

A comparison of two parallel seismic lines, one with short cable and the other long, shows that extra information from the near offset traces (short cable data) are effective in attenuating pegleg multiples which occur more frequently in long cable seismic data. This data provides another way of attenuating seismic multiples during the acquisition stage. Being aware of this condition could lead to additional prospects being identified or upgraded for drilling.

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