Seismic data and its role in Hydrocarbon Exploration
Jim Martin
Jim Martin first explained how his career had been within companies developing seismic techniques to identify potential hydrocarbon deposits that would be suitable for exploiting in the oil and gas industries.
He introduced us to some basic concepts like reflectivity which measures the changes that occur as energy passes across the interfaces of different materials, using the simple analogy of the impact of double glazing on reflections. In the real world there are identifiable changes at different rock or liquid boundaries.
Data on land is gathered when signals from, for example, a vibrating truck, are reflected back by different strata to receivers or geo-phones. In marine situations specialist ships tow various arrays of equipment, from which the air gun chamber[s] releases bubbles at a pressure of 2000psi. A towed array of hydrophones then pick up the return of the reflected signals. Martin further introduced us to 3D seismic data, ie cube like, and finally 4D data where results over time are compiled.
Processing the huge quantity of data obtained varies from a few days for 2D to up to a year or more for 3D.
Martin then moved us on to the interpretation side of detecting hydrocarbons
locations. These originate as organic material in a source rock, which then migrates upwards via porous or permeable material to so called reservoir rocks. The latter rocks in turn need to be capped or sealed, eg by salt deposits, to allow exploitable oil or gas to accumulate.
For practical examples Jim now focused on the North Sea and quoted the recent 33rd Round where geographical blocks were offered for exploration in 4 broad areas. He illustrated what seismic data shows in each of these areas.
He concluded by interpreting various graphs showing how, whilst UK North Sea production is currently about 800,000 barrels a day, usage in the UK is about 1.32 million barrels. By 2050 the decline curve still shows a production of about 200,000 barrels daily with demand still up at 650,000 barrels. Or as Martin succinctly put it – ‘not easy to stop’!
Jim Handley
