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Finding oil with the play fairway approach

Thursday, October 1, 2015

The play fairway approach to oil and gas exploration, mapping the areas of lowest exploration risk, has been successful in the North Sea. Could it also work for exploration in the Northeast Atlantic Margin?

To trap oil or gas you need a good quality source rock of sufficient maturity, a reservoir layer, the potential for the hydrocarbons to migrate to this layer, and a topseal to keep the hydrocarbons in place.

One exploration approach is to determine the probability of each of these factors being present, based on the available geoscience information, and so calculate the areas of lowest regional risk for exploration, said Joanne Cranswick, exploration team leader at LR Senergy, speaking at the Finding Petroleum London forum on May 27, 'Finding Oil in Atlantic Basins'.

LR Senergy has been conducting these regional geological studies since 2003 and published through its Ternan Reports, she said.

Ternan has studied the North Sea based on this approach and have also successfully applied the technique to the Northeast Atlantic, where much less is known about the geology.

North Sea approach

In the North Sea the approach examines the whole petroleum system, to understand how the basin has evolved.

As well as framing the geological structure, it aims to understand when sediments were deposited and their gross depositional environment.

Ternan works with all publicly available well and seismic data as well as published studies and references.

Play fairway mapping uses this data to determine areas of lowest regional risk for future exploration and identify the most likely areas for new discoveries.

There is still significant potential in the North Sea, she said.

Northeast Atlantic Margin

In the Northeast Atlantic Margin the geology is more demanding, but this exploration methodology can still be applied.

The region has over 500 exploration wells, many shallow bore holes and an extensive seismic database.

'The whole length of the Northeast Atlantic margin is also covered by gravity and magnetic data,' she said.

The study uses all this available data to define the structure of the earth's crust and map the elements of the petroleum system.

Gravity modelling highlights the sediment thickness and by inference the depositional basins.

'To properly understand the geological history of the Northeast Atlantic we have to reconstruct the plate positions during the Tertiary and Mesozoic' she said.

As Greenland separated from Norway, UK and Ireland a Mesozoic seaway was preserved along this margin and infilled with a variety of sediments and volcanic lavas.

For the North Sea stratigraphic analysis is followed by regional mapping to determine the areas of lowest exploration risk.

The Northeast Atlantic is severely disrupted by volcanism and continental breakup so plate reconstruction, seismic and potential field mapping are key parts of the work programme. Extra steps are needed to aid the understanding of reservoir distribution in areas with more complex geology and sparse well data.

The study showed that the hydrocarbon bearing reservoirs vary in age from pre-Cambrian to Eocene, a similar age to North Sea reservoirs.

'Ternan has been very successful in applying this methodology to the North Sea. We have had similar success adapting this to the Northeast Atlantic margin.'



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