Some NELP offshore blocks are from past rounds

Vol 8, PW 24 (09 Mar 05) Exploration & Production

Interest in the eight offshore NELP-V blocks could be muted due to the presence of discarded areas offered in earlier rounds.

Take offshore Saurashtra block GS-OSN-2003/1. This block is the western half of BB-OS-5, earlier held by Essar and Petrom but relinquished two years ago.

ONGC and Essar each drilled a well on this block. Geologists question the decision to offer only the western half of the original block.

The western half lies west of the Diu Arch but the main generation of hydrocarbons is from the Dahanu Depression on the eastern side. No migration of hydrocarbons is possible beyond the Diu Arch, we are told.

It is surprising that the eastern half of the block has been excluded. The eastern half lies in the vicinity of ONGCs SN series of gas fields and some distance from Tapti.

GS-OSN-2003/1 has very poor prospectivity. Data indicates small stratigraphic accumulations in the south western portion.

Similar is deepwater block KG-DWN-2003/1. This block is made up of areas in earlier blocks rejected by Cairn Energy and ONGC.

The western portion of the block is covered with Cairn seismic and the eastern portion by ONGC seismic. Both found nothing promising and relinquished these portions from their blocks.

No different is block CB-OSN-2003/1 in the Gulf of Cambay. ONGCs (non-producing) discovery structures A and D are not part of this block, which is made up of portions of the relinquished areas of (pre-NELP) block CB-OS/1.

Data indicates four small closures in the north east. The reservoir depth could be around 2500 metres and water depth is less than 50 metres.

Prospectivity is marginal. Only Mahanadi Basin block MN-DWN-2003/1 is attractive because of two or three structural mounds-cum-channel sands indicated by data.

Bidders can expect gas here at depths of up to 9500 metres. This block lies in water depths of around 2500 metres.

This is a good block for Reliance or ONGC, we learn. Both have blocks in the vicinity.