Prices are rising,
demand is soaring, supplies are tight — and iffy, depending on
the geographic location — and many promising U.S. drilling locales
continue to be off-limits.
many are looking to the industry's Old Faithful, aka the Gulf of
Mexico, as the still-bright hope for increased domestic production.
Indeed, it's the only readily accessible region harboring some frontier-type
plays — the still-new shallow water deep gas play and the ultra-deep
water — despite its lengthy producing history.
of potential new finds in the GOM was underscored in the most recent
Central Lease Sale190 held by the MMS, which garnered the highest
number of bids of any Central Sale in the last six years. Sixty
percent of the bids were on the shelf, apparently reflecting interest
in the shallow water deep gas, according to Johnnie Burton, MMS
also indicated continuing interest in the deep water, and Burton said the large number of
tracts receiving bids in the ultra-deep water was particularly noteworthy.
As of March
2003 there had been 24 deep gas completions, with 17 discoveries,
according to Debra Winbush at the MMS, who noted 100 wells were
permitted in 2003 and 40 in 2004. The agency reported there have
been 11 industry-announced discoveries in water depths greater than
7,000 feet and noted these ultra-deep water discoveries have the
potential to open up entirely new geologic frontiers.
deep Gulf is salt country, meaning there are obstacles to overcome,
and not just in terms of iron.
challenge pretty much applies to everything," said Chad Harding,
team leader seismic imaging group at BHP Billiton. "There are two
fronts — acquisition and processing — on which we'll need to advance
to improve seismic imaging for subsalt exploration in the Gulf.
the most critical thing is in the area of acquisition," he added.
"We need to learn how to acquire data sets that better illuminate
subsalt targets. We believe — and there's a lot of evidence now
— that multi-azimuth acquisition is the way to do that."
noted that this is in contrast to what might be called single or
narrow azimuth acquisition, which is what you normally have with
conventional marine streamer equipment.
the subsurface salt-related formations in the Gulf, you have to
record reflections," said Marty Brandt, contractor acquisition and
processing team leader ChevronTexaco Energy Technology Co. "You
need those long offset, large apertures to do that.
of long offset information is a challenge," he continued, "along
with the subsequent impact it has on processing to deal with anisotropy,
tilted anisotropy and depth migration."
said the industry must continue to take advantage of declining computing
costs and improve the ability to build seismic velocity models.
a key to better sub-salt images," Harding said. "My view is that
velocity model building is a core technical competency for oil companies.
Better migration algorithms go hand in hand with velocity model
building, and the package of those two things along with better
seismic data to start with are what I think will get us where we
want to go."
begins with the data acquisition, and Harding noted there are different
approaches that afford the capability to acquire the needed wide-azimuth
data: ocean bottom sensor (OBS) nodes, ocean bottom cable (OBC)
and surface methods using streamers.
and cables both are widely-used, proven technologies in conventional
marine seismic data acquisition, depending on the environment and
the survey objective.
downside, streamers can become unwieldy around platforms and infrastructure,
and placing cables on the seafloor is a high cost undertaking. Cable
length and connector integrity are added potential issues of concern
in deeper water.
is where a lot of new discoveries will be," said Jerry Beaudoin
with the BP E&P Technology Group, "and the challenge for cable
will be overwhelming because of things like soil hardness, topography,
sedimentary features on the surface. Nodes would come into their
who has co-authored a paper discussing the results of an effort
to analyze the relative merits of cables and nodes (also known as
autonomous seafloor seismographs) to gather wide azimuth deepwater
ocean bottom seismic data, offered his analysis, which was based
on three requirements:
Wide-azimuth shot coverage is necessary to illuminate a structurally-complex
subsurface such as found with irregular salt masses.
surface shooting into sparse receivers provides adequate wavefield
within each receiver gather provide full-azimuth coverage with
to his paper, autonomous ocean bottom nodes are more efficient than
OBC technology to acquire deepwater wide-azimuth seismic data for
the purpose of properly illuminating complex subsurface structures.
The project participants observed that hundreds of nodes can cover
a much greater area in a single shooting effort than the most productive
community has a history of using autonomous seismographs for various
applications, and ocean bottom sensors have been used successfully
to acquire data in the shallow water where they send the data to
buoys at the surface.
the consensus among the E&P folks is that nodal technology is
only in its infancy from an equipment and operational perspective,
particularly in recording deepwater seismic data.
however, are scrambling to move nodal applications into the realm
of the tried and true.
Industries' Deep Z seismic data acquisition system for deep water,
for example, is being readied for use in early 2005. Depth-rated
to 9,800 feet, the system has advanced to the stage of successfully
completing a deepwater data acquisition pilot project in 7,000 feet
of water, according to Steve Mitchell, vice president operations
pod, or autonomous seismometer, is a self-contained sensor with
batteries and a highly accurate clock. Cable-free, they're laid
out in a grid in the deep water by an ROV, which later retrieves
them to download the data and re-charge the batteries prior to re-deployment.
the pods are placed about 1,300 feet apart, the shot density on
the surface is enough to yield a high-fold, wide azimuth survey.
may have an added appeal to engineers and asset managers, Mitchell
noted, because it employs ROVs, which they use routinely.
The Z pods
are placed using the Sonsub Innovator ROV, which is a large, heavy
best suited for this technology," said Wayne Abadie, sales manager
at Sonsub, "and limited only by the length of the umbilical. Right
now the maximum is 4,000 meters, but we could design for deeper;
it's just a matter of getting a larger winch and more cable."
loads one carousel with several nodes and places them in predetermined
locations," Abadie said, "and it can continuously deploy maybe several
hundred nodes during the course of the survey.
the vehicle can rapidly change locations on the seafloor if you
decide you want a different view of the reservoir," he noted.