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Celebrations Began With Cognac

Deep GOM Discoveries Toasted Over 30 Years

Next July will mark the 30th anniversary of the first field discovered in the deepwater Gulf of Mexico province, defined here as water depth of greater than 600 feet (183 meters).

Since 1975, when the first commercial field (Cognac) was discovered by Shell, over 21.2 billion barrels of oil equivalent have been discovered in the province and approximately 9.2 TCFG and 2,200 MMBO have been produced between 1979 and the end of 2002.

There have been approximately 232 commercial fields discovered during the period from 1975 to the end of 2003.

The current mean size of these discoveries is 94.3 MMBOE. The two largest fields found to date are Mars (750 MMBOE) and Thunder Horse (1,000 MMBOE).

And, a statistic to remember: Initial well flow rates in the deepwater province did not exceed 10,000 BOPD until 1995 — 20 years after the discovery of Cognac field in 1975.

Only three short years later, individual well rates at Ram Powell and Troika exceeded 20,000 BOPD.

Exploration

There have been three major exploration plays in the deepwater province: the Flex Trend play, the Mini-Basin play and the Fold Belt play (see figure above).

In addition, the "subsalt play" is simply any of these plays obscured by salt.

  • The Flex Trend play began in the early 1970s with the discovery of Cognac field. It was developed just beyond the present-day shelf edge where there is a "flex" in the sea floor profile.

    Some of the larger flex trend discoveries were Lena, Zinc, Pompano and Green Canyon 18. Wells generally targeted "bright spots" on 2-D seismic. Most discoveries in the play were fields with small reserves, discontinuous sands and wells with fairly low flow rates.

Image Caption

Figure 1. Number of Fields Discovered
The number of discoveries in the deepwater Gulf of Mexico for the years 1975-2003, showing reservoir age. Note the large increase from 1995 onward, after the passing of the Royalty Relief Act. There were no discoveries in 1978, 1979 and 1992.
Data courtesy of Stephen Cossey

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Next July will mark the 30th anniversary of the first field discovered in the deepwater Gulf of Mexico province, defined here as water depth of greater than 600 feet (183 meters).

Since 1975, when the first commercial field (Cognac) was discovered by Shell, over 21.2 billion barrels of oil equivalent have been discovered in the province and approximately 9.2 TCFG and 2,200 MMBO have been produced between 1979 and the end of 2002.

There have been approximately 232 commercial fields discovered during the period from 1975 to the end of 2003.

The current mean size of these discoveries is 94.3 MMBOE. The two largest fields found to date are Mars (750 MMBOE) and Thunder Horse (1,000 MMBOE).

And, a statistic to remember: Initial well flow rates in the deepwater province did not exceed 10,000 BOPD until 1995 — 20 years after the discovery of Cognac field in 1975.

Only three short years later, individual well rates at Ram Powell and Troika exceeded 20,000 BOPD.

Exploration

There have been three major exploration plays in the deepwater province: the Flex Trend play, the Mini-Basin play and the Fold Belt play (see figure above).

In addition, the "subsalt play" is simply any of these plays obscured by salt.

  • The Flex Trend play began in the early 1970s with the discovery of Cognac field. It was developed just beyond the present-day shelf edge where there is a "flex" in the sea floor profile.

    Some of the larger flex trend discoveries were Lena, Zinc, Pompano and Green Canyon 18. Wells generally targeted "bright spots" on 2-D seismic. Most discoveries in the play were fields with small reserves, discontinuous sands and wells with fairly low flow rates.

    Needless to say, this was not a very encouraging start to exploration in the deepwater province.

  • The Mini-Basin play began in 1983 with the discovery of Bullwinkle. This play targeted the flanks of structural intraslope basins where reservoir sands pinched out and formed a combination structural/stratigraphic traps.

    Some of the larger mini-basin fields discovered are Auger, Mars, Diana, Genesis, Troika and Europa. Ram Powell was discovered in 1985 and is a very large, stratigraphic trap developed in a more unrestricted mini-basin.

    (Larger mini-basins also may have turtle structures developed in their centers.)

    The first mini-basin fields brought on-line (Bullwinkle in 1989, Auger in 1994) produced at much higher than expected rates, had better than expected aquifer support and needed fewer wells to develop them. Many of the early production ended up being facilities constrained.

  • There are at least three fold belt trends: the Mississippi Fan, the Perdido and the Port Isabel fold belt.

    The Fold Belt play began in 1995 with the discovery of Neptune in Atwater Valley 575 in the Mississippi Fan fold belt.

    BAHA was the first discovery in the Perdido fold belt in 1996. To date, there has not been a discovery in the Port Isabel fold belt.

    The largest field discovered to date (Thunder Horse) was not discovered until 1999, a full 24 years after the first discovery in the flex trend play (Cognac).

There have been consistently more than 10 discoveries per year in the period after 1995 when the Royalty Relief Act was established, which allowed producers to postpone paying royalties until most of the exploration and development costs are recovered.

Exploration success rates in the deepwater Gulf have been estimated to be about 1 in 4.

During the first nine years of exploration in the deepwater Gulf of Mexico, 15 fields were discovered, all with reservoirs of either Pliocene and/or Pleistocene age. More Pleistocene reservoirs were discovered in 1984 than in any other year, and the most Pliocene reservoirs were discovered in 1995. The first Miocene reservoirs were not discovered until 1984 at Tahoe, although these were gas-bearing, thin-bedded (laminated) reservoirs.

Other Miocene reservoirs were later discovered at Ram Powell in 1985, Mensa, Kepler and Coulomb in 1987, Mars in 1989, Mickey and Pompano in 1990, and Crosby in 1991.

More recently, Paleogene age reservoirs have been discovered in the Fold Belt play.

Fewer than 10 companies were operating discoveries in the deepwater in the first 13 years of exploration; in 2003, there were approximately 44 companies operating discoveries in the deep water. Shell has been by far the most successful operator, with approximately 52 discoveries through early 2004.

ExxonMobil is the second most successful operator with approximately 17 discoveries.

Reserves and Production

Approximately 21.2 billion barrels of oil equivalent have been discovered in the deepwater Gulf of Mexico. The most reserves were added in 2001, when 32 fields were discovered.

Large additions of reserves greater than 1,000 MMBOE per year were added in 1989, and during the period 1998-2002. During the period of exploration from 1975-2003, reserves in excess of 500 MMBOE have been added in 13 of the 29 years.

No discoveries were made, and no reserves were added, during the years of 1978, 1979 and 1992.

Mars (750 MMBOE), discovered in 1989, was often thought to be the largest field in the province until Thunder Horse (1,000 MMBOE) was discovered in 1999. The sizes of these fields suggest that there is still a possibility that several fields in the range of 750 MMBOE to 1,000 MMBOE still wait to be discovered.

The first oil field to start production in the province was Cognac, in 1979. This was followed in 1980 by the first gas field (GB 236).

It was not until 1984 that the third field (Lena) started production, almost 10 years after the first commercial discovery.

The first 24 fields to start production in the deep water either produced from Pleistocene or Pliocene reservoirs.

Initial per well production rates were disappointing during the first few years of production from the early producing fields. Peak well rates at Lena, which started production in 1984, were only 500 to 2,200 BOPD. It was clear from these early producing fields that higher per well flow rates had to be achieved if the deepwater province was to be economically viable.

Fields that started production in the late 1980s achieved slightly higher per well rates. The Green Canyon 18 A-8 well flowed at 7,400 BOPD during January 1989, but that rate was short-lived. Rates of 3,000-6,000 BOPD were achieved at Bullwinkle, but these rates were reached years after the startup of the field.

The first Miocene reservoirs started producing in 1994, almost 20 years after the first discovery in the province. It was not until 1994 that the first Miocene and early Pliocene reservoirs were brought into production at Tahoe and Auger.

Higher per well rates were first achieved at Auger field — four came on-line in 1994 — but it was not until 1995 that the first well at Auger achieved a rate in excess of 10,000 BOPD. It was then realized that high per well rates from the Deepwater Province were possible.

Just three years later, well rates at Troika and Ram Powell exceeded rates of 20,000 BOPD.

At the end of 2003 there were 136 fields producing in the Deepwater Province. Sixteen fields started production in 2003.

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