A new study by geoscientists at the University of Texas at Austin gives explorers fresh insight into the depositional history of the Gulf of Mexico -- and it also confirms that the Gulf remains one of the world's great exploration provinces.
The industry-sponsored study targeted 18 major Cenozoic depositional episodes, made up of 10 Neogene and eight Paleogene genetic sequences.
Researchers acquired and combined a wealth of public data and university owned data for the project, known as the UT-Gulf of Mexico Basin Depositional Synthesis Project (UT-GBDS). That approach made the effort seem like piecing together a puzzle, according to William E. Galloway, UT professor of geological sciences.
"You realize that all the bits and pieces of the picture were always there," he said, "but because they had never been put together side-by-side, no one had appreciated the relationships."
Of the 18 depositional episodes, or depisodes, at least 13 or 14 are characterized by extensive relocation of sand onto the Gulf Basin floor, Galloway noted.
"You understand very quickly that there is an immense amount of sand that has been transported, not only over the shelf edges and onto the Paleo-Continental slopes, but also out onto the ((deeper) deep basin) floor," he said.
Galloway called this finding "a very positive perspective for Gulf exploration, since it implies an abundance of largely untested sedimentary reservoirs:
"That's not saying that if you go out and drill anywhere in the Gulf Basin you're going to find reservoirs," he commented.
"But in any of at least 14 or so of these major stratigraphic units, somewhere in the Gulf there's a family of reservoirs to be prospected."
A Sea of Data
Galloway serves as one of two principal investigators for the Gulf depositional synthesis. The other is Richard T. Buffler, senior research scientist at UT's Institute for Geophysics.
Buffler said the project includes two phases.
The first phase, completed last September, combined seismic data from the UT Institute of Geophysics with well data and other public information. Researchers drew on a trove of data from Gulf exploration, including old Gulf Oil seismic, he said.
Results from Phase 1 already have been made available to the study's industry sponsors, according to Buffler. Those include Agip Petroleum, Amoco Production, Anadarko Petroleum, BHP Petroleum, Burlington Resources, Conoco, Elf Exploration, Exxon Exploration, Marathon Oil, Oryx Energy, Mobil Exploration and Producing US, Norsk Hydro, PEMEX, Phillips Petroleum Texaco USA, Total Exploration Production USA and Vastar Resources.
Phase 2, projected for completion after two years, will add additional seismic and well data to update maps and will include analysis and interpretation of the data, Buffler said.
"Probably, the overriding goal of Phase 1 was to synthesize the immense amount of data, much of it interpretive information, that have been generated over a very long period of Gulf exploration -- publications, maps, cross-sections, datasets that could be local or regional," Galloway noted.
Resources included basin-wide 2-D seismic lines that date back as far as the 1970s, plus several published well-log cross-section sets, supplemented by data from more than 100 additional wells, most of them on the Continental Slope.
"Most of the other data actually came from public, though not necessarily published sources he added. "The primary additional material was the well logs from the slope, which we got from our supporting companies or acquired from the U.S. Minerals Management Service."
Far from having too little information, the researchers found themselves buried in data.
Galloway called the main difficulty of Phase 1 "the sheer volume of data and the fact that most of it was not in standardized form." A geographic information system (GIS) utilizing ARC/INFO software was used to sort and store the material.
"The obvious technology to use was GIS, because it is designed to handle and merge graphical information. Essentially, what we created was a database with three major components," he said.
The resulting basin study provides the most thorough, generally available picture of the Gulf's Cenozoic depositional history.
In addition to seismic and well data, the study combined information from about 300 published and unpublished references, Galloway said -- including numerous maps.
Mapped features included depo centers, shelf edges, major deltas, canyon complexes, fluvial systems, submarine fans and, as Galloway noted, "whatever anyone has mapped, from Yucatan right on around to Florida."
A 'Valuable Tool'
Industry sponsors received the data in digital files, in what Galloway characterized as a CD-based "physical atlas." A primary product of Phase 1 was a suite of maps for the 18 sequences, encompassing all of the major sand-bearing units of the Cenozoic, he noted.
Roger Gassett, principal geophysicist for Vastar Resources, said the UT Phase 1 results provided a valuable tool for the company's team looking at Gulf of Mexico deep-water prospects. The data combined a fast-track introduction to the basin with the convenience of a comprehensive overview.
"It was the latest research that was going on at an academic institution, and it was Gulf-wide," Gassett said. "My main motivations were the fast-track learning and the scope (of the basin study).
"Although I had worked the Gulf of Mexico, I had not worked the deep water," he continued. "And I had worked a fairly small area. I felt like this gave me a quick look at the Gulf, and in that sense it was a convenient product."
Gassett found the interpretive elements of the study especially helpful -- for instance, maps and analysis connecting the Gulf margin with the deeper basin.
"You've got all this salt in between," he said, "so that's very hard to see."
In terms of information content, "the one other thing we probably would have liked to have received was the well-logs in digital form, the cross-sections in digital format," Gassett said. But he acknowledged that would have been outside the reach of the study and also prohibitively expensive, given the project budget.
"We certainly got what we bargained for," he said. "From that point of view, we're very favorable about it. We like what we got."
Completed at a cost of $1.1 million, Phase 1 required substantial outlays for data acquisition and compilation. Phase 2, budgeted at $250,000, will add additional data to sharpen the study's focus.
"The practical side is that we are now going to concentrate on the Miocene and younger sections, which are primarily the exploration targets for the Outer Continental Shelf slope deep basin." Galloway said.
"The outer shelf to deep water slope is a fast-moving area in terms of data acquisition. There are places where our maps have little data. Part of Phase 2 is to try to improve the picture."
Galloway also wants to publish some details of the study, and plans to submit a paper for the AAPG BULLETIN. He'll create a summary of the Phase 1 findings, but said any journal article will have to be "a summary of the summary," since even the basic overview will include about 60 figures, most of them maps.
Buffler and Galloway credited several other individuals with key contributions before and during the synthesis project. They include:
- Patty Gainey-Curry, who serves as both project data manager and coordinator for the industry associates
- Xiang Li, a geologist who came to UT as a visiting scholar from the People's Republic of China and became a "GIS expert," Galloway said.
- Thomas McKenna, a student finishing his PhD at the university who created customized tools inside ARC/INFO for the study
- Jian Hua Feng, who defined and mapped the Gulf Cenozoic as a thesis project.
Galloway said the basin depositional synthesis should reinforce the industry's interest in the Gulf of Mexico, in addition to providing a new, comprehensive look at its Cenozoic history.
"People have been appreciating more and more that sand transfer to the deep Gulf has been a routine aspect of this basin," he said. "There is an immense volume of potential reservoir targets that you might wish to explore.
"It's a very positive perspective for hydrocarbon exploration, right on out to the deepest parts of the basin."