Deepwater Gulf of Mexico 2004: America's Expanding ... - OCS BBS

Reduction of royalty payments is also available through an application process for some deepwater fields
that were leased prior to the DWRRA but had not yet gone on production. The fixed suspension volume
provision of the DWRRA (for new leases issued 1996-2000) expired on November 28, 2000. Leases
acquired between November 28, 1995, and November 28, 2000, will retain the incentives until their
expiration. Exploration and production incentives have continued since 2000 for leases in water depths
greater than 400 m (1,312 ft). Royalty relief volumes range from 5 MMBOE in water depths of
400-799 m (1,312-2,621 ft) to 12 MMBOE of relief in depths greater than 1,600 m (5,249 ft). Royalty
relief is granted to individual leases, not fields 1 as in the DWRRA. Post-DWRRA provisions are subject
to change for each lease sale.
SEISMIC ACTIVITY
A combination of factors including the DWRRA, several key deepwater discoveries, the recognition of
high deepwater production rates, and the evolution of deepwater development technologies, spurred a
variety of deepwater activities. One of the first impacts was a dramatic increase in the acquisition of 3-D
seismic data (figure 2). (Note that figures 2 and 3 illustrate areas permitted for seismic acquisition. The
actual coverage available may be slightly different than that permitted.) Three-dimensional seismic data
are huge volumes of digital energy recordings resulting from the transmission and reflection of sound
waves through the earth. These large “data cubes” can be interpreted to reveal likely oil and gas
accumulations. The dense volume of recent, high-quality data may reduce the inherent risks of traditional
hydrocarbon exploration and allow imaging of previously hidden prospects. Figure 2 illustrates the surge
of seismic activity in the deepwater GOM during the last 12 years. Seismic acquisition has stepped into
progressively deeper waters since 1992. Figure 3 shows the abundance of 3-D data now available. These
data blanket most of the deepwater GOM, even beyond the Sigsbee Escarpment (a geologic and
bathymetric feature in ultra-deep water). Note that many active deepwater leases were purchased before
these 3-D surveys were completed (only the more sparsely populated 2-D datasets were available).
The seismic permitting coverage shown in figure 3 does not tell the whole story of geophysical activity in
the deepwater GOM. Pre-stack depth migration (PrSDM) of seismic data has greatly enhanced the
interpretation capabilities in the deepwater GOM, particularly for areas hidden below salt canopies.
While PrSDM was once used sparingly, the availability of large speculative PrSDM surveys allows the
widespread use of this technology in the early phases of exploration. Subsalt discoveries like Mad Dog,
Thunder Horse, North Thunder Horse, Atlantis, and Tahiti demonstrate the importance of subsalt
exploration. Figure 4 provides a partial inventory of speculative PrSDM coverage. This figure was
assembled from publicly available sources and provides a good indication of the current widespread
coverage of PrSDM processing.
Time-lapse seismic surveys (also known as 4-D) will likely be the next significant seismic technology to
be applied routinely in the deepwater GOM. The technique can be applied to characterize reservoir
properties, monitor production efficiency, and estimate volumetrics from inception through the life of the
field (Shirley, 2001). The high cost of drilling deepwater wells and challenges associated with reentry of
deepwater wells may promote the use of 4-D technology in the deepwater GOM.
EXPLORATION ACTIVITY
Modern seismic data often generate new ideas leading to surges in leasing and drilling activities.
Exploration drilling in the deepwater GOM in 2002 and 2003 has found over 2 billion BOE. Traditional
deepwater mini-basin plays are still providing many exploration opportunities (consider the Thunder
Horse and North Thunder Horse discoveries in southern Mississippi Canyon), but recent discoveries in
new deepwater plays continue to expand the exploration potential of the deepwater GOM. Figure 5
illustrates the fact that 99 percent of total GOM production is from Neogene-age reservoirs (Pleistocene,
Pliocene, and Miocene); however, several recently announced deepwater discoveries encountered large
potential reservoirs in sands of Paleogene age (Oligocene, Eocene, and Paleocene). This older portion of
the geologic section has been very lightly tested in the GOM and the discovery of reservoirs of this
geologic age may open wide areas of the GOM to further drilling. Figure 6 illustrates two frontier
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