Pré-Sal
– The Next Frontier
26
November 2009 London
Evening Meeting
Chairman Dr Bob Allwood,
Cranfield University
Sponsored by Western Geco
Report
Flyer
Overview
One of the stories
dominating the offshore oil and gas industry at present is the
discovery of giant pré-sal deposits (or presalt or subsalt,
depending on where you are in the world). In 2007, Petrobras
announced that it had made the biggest oil discovery in the Americas
since the 1970s in the subsalt layer of the Brazilian coast. The
field could extend from the coast of Bahia down to the southern
state of Santa Catarina. The Brazilian government isn't quite sure
how much oil is buried beneath the thick layer of salt, but
estimates indicate reserces of between 25 and 100 billion barrels
(announced on 25 September 2009).
Subsalt deposits are not
just present off the Brazilian coast, oil and gas reserves below
salt have now been identified in the deepwater GoM, West Africa, the
Middle East, the North Sea and, to a lesser extent, offshore Eastern
Canada. Scientists from Sonangol have said that geological
similarities between Angola and Brazil's subsalt areas suggest that
future exploration drilling on Angola's continental shelf may find
reserves similar to Brazil's large discoveries. The deep subsalt
discoveries in the outer fringes of the GoM rank among the largest
finds in the world. The BP Atlantis, Mad Dog and Thunder Horse
developments, the Chevron Jack II well drilled to 8600m TD in 2100m
of water on Walker Ridge and, more recently, Shell's record-setting
well in its Perdido development have helped renew optimism in the
potential of the deep and ultra deepwater GoM.
However, with these
world-class discoveries come a hose of world-class challenges. This
evening meeting's presentations explained what is meant by subsalt
and explored two of the key technical challenges (seismic imaging
and drilling through salt) to be overcome in developing these
deposits.
Presentations
Are We Finally Learning How to
Image through and around Salt?
Paul Taylor, Marketing Manager,
Geophysical Solutions, Western Geco
It has been said that in the
battle to generate seismic images around and below salt bodies in the
Gulf of Mexico (GoM), the salt is still winning. "The mysterious salt is
keeping her charm and form well hidden." This statement was made several
years ago, and the author's identity is unknown (at least to the
speaker), but it could have been said by just about any of the
subsurface teams working in slat prone areas of the GoM at that time.
This presentation provided an overview of why seismic imaging around
salt is technically challenging and focus on the new techniques that are
finally stating to allow us to see through salt bodies to the structures
lying below.
Salt Drilling Challenges
and Mitigation – The Zechstein Experience
Oladele Owoeye, Lead Drilling
Engineer, BP
Though Carnallite and
Bischofite salt minerals are considered to be the only true
squeezing salts, other salts can be mobile given the required
temperature, time and differential stress. In the Southern North
Sea, drilling the Zechstein Group 'the regional seal to the main
reservoirs of the Rotliegendes sandstones' is a major challenge and
has been the major cause of schedule and cost overrun. Typical
problems encountered while drilling the section include mobile or
'squeezing' salts, brine flows, carbonate rafts causing high
pressure kicks, and basal carbonates resulting in kicks and/or
losses, stuck pipe, casing collapse or even loss of well. This
presentation tried to highlight various design and operational
strategies use successfully to either eliminate the risk or minimise
the effect if encountered.
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