This is part two of the proceeding comment which presented an article on the deep waters of the Gulf of Mexico: Lower Tertiary play: Is it Gulf of Mexico’s final frontier?
Offshore magazine presents a companion article: Imaging challenges in deepwater US/Mexico border zone, published January 1, 2010:
http://www.offshore-mag.com/index/artic ... enges.html
So, we've seen what oil industry insiders have to say about the prospects and technical challenges of ultra-deep drilling in ultra-deepwater. Now, it's time to look at what the oil industry is mapping in order to locate this ultra- deep oil, in other words, the tectonic structures in the seabed of the Gulf of Mexico where the oil industry thinks there will be petroleum.
Exploration in the deepwater US GoM has been the main offshore focus for the US petroleum industry since the 2001 discovery of thick Paleogene submarine turbidite sand in the Baha No. 2 well (Meyer et al. 2005). The presence of the Wilcox formation sands changed the perception of the industry to deepwater exploration and identified the presence of a new deepwater play – the “Lower Tertiary Wilcox Play.”
And from the previous Offshore article:
Subsequently in the early 2000s, few geologists expected to find significant oil traps in the Lower Tertiary. The skeptics have been proven wrong with the discovery of long Lower Tertiary oil pay zones.
Of course, the reason for "changed perception" was because the "fossil" theory's "oil window" corollary of hydrocarbon's generation, which claimed there exists from roughly 7,500 feet to 15,000 feet, an "oil window" within which temperatures are appropriate for oil formation has been completely falsified by the ultra-deep oil deposits.
The challenge on both sides of the US/Mexico border is to image and to locate the Wilcox (and other) prospects adjacent to and below the salt canopy.
The Offshore article goes on:
Understanding the play-fairway opportunities in this setting requires a regional, structural, and stratigraphic context for the Wilcox including subsalt sediment distribution and a better understanding of the tectonic framework of the basement.
And, here is the money quote of the article:
Mapping the structure of the rifted basement, its impact on sedimentation, the distribution of autochthonous salt, and the location of the continental-oceanic boundary (COB) all were crucial within the workflow, which culminated in a new deep allochthonous salt isopach used to confirm existing drilled structures and to identify new prospects within the subsalt environment.
The study had a number of additional key objectives to help reach the goal of subsalt prospect identification, including:
1. Delineation of an integrated basement surface across the area
...basement density and susceptibility, location of open salt feeders, and the position of the COB.
Reference to "basement density and susceptibility", while a little vague essentially means the crustal thickness and potential for fissures and cracks where petroleum would rise up from into covering sedimentary trapping structures (or potentially oil could be located in reservoirs within the basement below fracture lines).
The Continent-ocean boundary (COB) or continent-ocean transition is the boundary between continental crust and oceanic crust. The identification of continent-ocean boundaries is important in the definition of plate boundaries and the identification and mapping of fractures, tears, and rifts in the basement in association with this boundary area.
The prior Offshore article on the Lower Tertiary play, asked this question:
Will the operators then discover another frontier beyond the Lower Tertiary in the abyssal depths of greater than 12,000 ft (3,658 m) in the Sigsbee Deep?
The answer appears to be, "Yes", because oil already has been found in the abyssal depths of the Gulf of Mexico:
http://www.agu.org/pubs/crossref/2005/2 ... 0002.shtml
Asphalt volcanoes and lava-like flows of solidified asphalt on the seafloor were first discovered and described by MacDonald et al.. The flows covered more than one square kilometer of a dissected salt dome at abyssal depths (˜3000 m) in the southern Gulf of Mexico. “Chapopote” (93°26'W, 21°54'N) was one of two asphalt volcanoes they discovered.
This area has been covered prior in this thread, but is germane to this discussion.
MacDonald et al. determined that the apparently fresh asphalt must initially have flowed in a hot state, and subsequently chilled, contracted, and solidified, much in the same way as normal lava does on the surface of the Earth.
So, it is already known that oil deposits are located in the abyssal depths of the Gulf of Mexico.
Notice what techniques are used to map the structures and find the oil:
•Construction of the final integrated basement using elements of seismic acoustic basement and magnetic basement
•2D gravity and magnetic modeling constrained with input from mapped seismic horizons, crustal thickness information, density/velocity data, and allochthonous salt distribution
Magnetic imaging has been in use by the oil industry along time and it has been previously pointed out in this discussion thread that oil deposits have a magnetic signature.
Enhanced delineation of basement structure has lead to a better understanding of the original salt depositional environment and rift morphology, which in turn has had a significant control on subsequent salt mobilization.
The work confirmed that basement structure is dominated by NW-SE and NE-SW trending lineaments/faults. Deep allochthonous salt mobilization is controlled by many of these features.
The location of the COB has been delineated across the region using evidence from all three datasets. Due to the extremely attenuated nature of the continental crust in the region (6-12 km, 3¾ - 7½ mi thickness across the study area), differentiation between what is oceanic and what is attenuated crust was a major challenge and can only be resolved by combining all three datasets.
The work confirmed that basement structure is dominated by NW-SE and NE-SW trending lineaments/faults.
What are "trending lineaments"?
Could they be larger patterns of faulting "blocks", grabens, that trap oil in their cantilever angulation?
And how much oil could these protean shapes hold in cantilevered succession across the sea floor?
The article uses the word "attenuated" to describe the continental crust. Attenuated means "thin" crust. So, the continental crust in this area is "extremely" thin. Might this be why oil has risen up through cracks and fissures in Texas to such a noticable degree?
The reason for mapping in detail the basement (also called bedrock) structure and the cracks, fissures, and rifts is clear enough, that's where the oil emanates from.