If seismic acquisition and leasing activity are accurate indicators, the Gulf of Mexico's East Breaks region is on its way to becoming one of the busiest spots in the deep water frontier play.
Several discoveries there over the last couple of years have sparked intense interest.
East Breaks is offshore Texas in the Western Gulf of Mexico, and oil companies are keenly interested in unraveling the geology in hopes of big finds.
Partners Exxon Exploration and BP Exploration, as well as Reading & Bates Development and Shell Offshore, have the nearest significant discoveries. Exxon and BP are continuing to explore its acreage on the border of Alaminos Canyon and East Breaks, and Reading & Bates and Shell are delineating a find in East Breaks.
The most important discovery in the region to date is Exxon and BP's Hoover Field, where the firms have estimated reserves at over 100 million barrels of oil equivalent.
Based on those successes and the industry's interest, seismic companies are busy acquiring 3-D seismic data over the region.
Geco-Prakla is currently shooting a 6,500-square-kilometer, non-exclusive survey that is one of the largest the company has ever put together.
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"Several oil companies showed strong interest in this area," said Robert Hubbard, manager of exploration services with Geco-Prakla's marine division, "and based on our research we felt this was an area of high potential that needed 3-D coverage."
Water depths in the survey region range from 5,000 feet at the deepest point on the south up to about 1,000 feet at the northern limits, where it comes up on the shelf edge.
Leasing activity in last August's Western Gulf lease sale certainly bears out that strategy. The Minerals Management Service received 402 bids over the entire Western Gulf, and over 51 of those bids was in Geco-Prakla's survey area -- including one of the most hotly contested blocks in the sale, according to Hubbard.
The second highest bid in the sale was for East Breaks 981. Spirit Energy won the block with a bid of over $31 million.
East Breaks Geology
Geology, of course, is the primary driver for any exploration play and that's certainly true in this region.
"The Lower and Middle Miocene series consists of an expanded section deposited in deep water on the north flank of a regional salt ridge," said George Jamieson, interpretation services supervisor with Geco-Prakla. "The ridge was formed as the result of Eocene to Late Oligocene sediments prograding into the deep waters of the western Gulf of Mexico. The weight of the sediment mobilized the salt and pushed it into a thick ridge. The ridge formed a barrier behind which sediments, including potential reservoirs, were trapped in mini-basins.
"This subsequently resulted in a tremendous expansion of the geologic section, and salt was remobilized by the overburden of the Lower and Middle Miocene sediments deposited on the Early Miocene slope," Jamieson said. "The loading of the basin caused the thick salt to spread across the slope to form the large amalgamated salt canopies out to the Sigsbee Escarpment.
"Significantly, the stratigraphic history of the Early and Middle Miocene Epoch in this area shows similarities to the geology around the giant Mars Field in the Mississippi Canyon area," he continued. "The Exxon-BP Hoover and Diana fields are just southeast of our survey area and are stratigraphically in younger sections of Plio-Pleistocene age sediments.
"Three-D seismic data will help resolve these complex structures in the salt controlled mini-basins."
The hydrocarbons in this deep water Gulf region are sourced from a continuous Cretaceous basin that extends from Florida to the Yucatan in Mexico, added Andy Hannan, a geologist with Geco-Prakla.
"The key is to find the right plumbing to tap that source," Hannan said.
"Exxon's discoveries are in one of these mini-basins, and there are other analogous basins out there," he said. "Each one of these mini-basins is unique, but if you look at the regional picture you see there is a whole trend of these mini-basins that is truly a new frontier play the industry is now beginning to explore."
The Hoover Project
The Hoover Field, 160 miles south of Galveston in 4,800 feet of water, is the largest of a string of recent successes by Exxon and BP in the sand-rich, Plio-Pleistocene Diana field intraslope basin of the western Gulf, according to a paper by James W. Higgins, a geologist and geophysical interpreter with Exxon, and Dean Chergotis and Jay C. Nania with BP.
Higgins presented the paper at a Houston Geological Society meeting last year.
The discovery is an amplitude-supported, oil and gas find located in Alaminos Canyon blocks 25 and 26. The field is on an anticlinal closure in the central portion of the Diana basin and produces from two zones -- a shallow Pleistocene gas and the more prolific, high quality Pliocene oil zone.
The Exxon/BP AC 25 No. 1 discovery well was drilled in early 1997 and found 47 feet of gross pay in the Pleistocene and 97 feet of gross oil pay in the lower portion of the Upper Pliocene.
Although the companies expected high quality reservoirs, the Pliocene exceeded their expectations, according to Higgins. The reservoir has average porosity in excess of 30 percent and average permeability of over 1,000 millidarcies.
"The Hoover discovery is in stark contrast to the largely unsuccessful Rockefeller prospect, five miles west," the authors said.
Although an anticlinal closure like Hoover, Rockefeller had no thermogenic hydrocarbons, they wrote. In late 1995 Exxon drilled the Exxon EB 992 No. 1 and No. 1 ST, which found full saturation biogenic gas in only one of four objectives.
Following that unsuccessful venture, Exxon and BP conducted a detailed vertical and lateral migration analysis of the entire Diana intraslope basin to ensure that Hoover and the surrounding prospects had adequate migration to warrant drilling.
The study found Rockefeller to be heavily dependent on a single fault for vertical migration from the early Tertiary source. Hoover, however, had several prospective vertical migration conduits within its lateral migration drainage basin.
"This analysis provided the critical technical justification to proceed with exploration at Hoover," the study concluded. "With these latest discovery volumes, the Exxon/BP partnership should be able to fully exploit Hoover, the sizable Diana reserves discovered in 1990, and surrounding satellite discoveries and prospects."
Reading & Bates Development and Shell Offshore logged a discovery in the East Breaks region just to the north of the Exxon/BP fields. The East Boomvang is in East Breaks blocks 688 and 732 and the 2 OCS-G 9191 was drilled in 1997 to below 10,000 feet and encountered about 220 net feet of hydrocarbon pay in the target sands, according to Petroleum Information/Dwights LLC.