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Total to run new seismic sweep over Laggan and Tormore

Total to run new seismic sweep over Laggan and Tormore
A new seismic acquisition campaign is planned in 2009 over Laggan and Tormore, according to a paper presented at the 7th Petroleum Geology Conference in London.

A new seismic acquisition campaign is planned in 2009 over Laggan and Tormore, according to a paper presented at the 7th Petroleum Geology Conference in London.

Delegates at this event, which takes place every four years and is organised jointly by the Geological Society, Energy Institute (EI) and Petroleum Exploration Society of Great Britain (ESGB), were told that the primary objective is to help optimise the location and often complex trajectories of the planned Laggan and Tormore development wells.

The hope at operator Total is that this will lead to improved understanding of the geological lay-out of Laggan and Tormore, with an expected improvement in seismic imaging.

Laggan, located west of Shetland, was discovered in 1986, but the economics of the discovery were finely balanced until the finding of Tormore in 2007, so tipping the balance in favour of a combined development project, for which planning is now at an advanced stage.

Laggan and Tormore are Paleocene gas condensate discoveries in about 600m (1,960ft) water depth. The traps are both stratigraphic with updip closure against bounding faults.

The reservoir comprises sand-rich turbidite channelised lobes and permeability is good.

There are four exploration and appraisal wells on Laggan, which was identified by the 206/1-2 well, which encountered lean gas condensate.

In 1996, the second well, 206/1-3, targeted an amplitude shut-off downdip.

The well encountered the gas-water contact and confirmed that there was no oil rim. 206/1a-4a was drilled in 2004 to appraise the crest of the structure and then side-tracked downdip (as well 206/1a-4z).

The conference was told that the potential of Tormore was recognised by applying the geoscience understanding of Laggan to help de-risk the prospect.

In particular, it was recognised that Laggan could be used as an analogue for the Tormore trapping configuration and reservoir potential and that AVO could be used to help define the gas-water contact. (AVO means amplitude variation with offset and is a variation in seismic reflection amplitude with change in distance between shotpoint and receiver).

The exploration well, drilled in 2007, was successful in finding a similar reservoir as was encountered in Laggan. However, the fluid encountered was a gas condensate about three times richer than Laggan – a big plus for Total.

This same paper also discussed a seismic anomaly which has been identified at the Upper Palaeocene T38 level in the northern Judd Basin – which will be tested by the drillbit in 2009.

In the past, exploration in the Judd Basin focused predominantly on the deepwater “aggradational” reservoirs of the Middle Palaeocene, with oil production from the Foinaven and Schiehallion fields – primarily from the T28-T35 reservoirs.

Delegates learned that prospectivity at shallower levels has been largely ignored due to the fact that the main regional seal in the area was recognised to be the T35/T36 shales below the Kettla Tuff.

However, seismo-stratigraphic analysis of the T38 sequence directly above the tuff has identified the potential for a new play type, especially adjacent to fault zones where these shales are potentially breached, allowing hydrocarbons to migrate from the Upper Jurassic source kitchen into any traps identified at the T38 and T45/T50 level.

It therefore appears that this year’s well could open up a new play in a province which, despite several decades of exploration, is still only lightly prospected.

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