HGS International Dinner - Sub-Areal Basins Below Sea Level (SABSEL Basins) Mothers to Several Super Basins
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Monday, April 16, 2017
Live Oak Room • Norris Conference Center • 816 Town and Country Blvd #210
Site Map • Floor Plan
Social Hour 5:30–6:30 pm
Dinner 6:30–7:30 pm, Presentation 7:30- 9:00 pm
Member/Emeritus/Honorary Life: $40.00
Non-Member: $45.00 WALKSUPS: $45.00
To guarantee a seat, you must pre-register on the HGS website and pay with a credit card. You may walk up and pay at the door if extra seats are available. Please cancel by phone or email within 24 hours before the event for a refund. Online & pre-registration closes Monday, April 16, at 5:00 a.m.
Speaker: Martin Cassidy
Company: University of Houston
Sub-Areal Basins Below Sea Level (SABSEL Basins) Mothers to Several Super Basins
1. Are formed at the beginning of the plate tectonic cycle during continental rifting before the basin has open access to the sea. Basaltic vulcanism, lacustrine organic-rich shales, and salts are common. These are young basins of J. Tuzo Wilson, 1968. They often underlie large basins that subside with time after the ocean returns, such as the Southern North Sea and the South Atlantic basins.
Figure1 (Formation of the sub-aerial basin below sea level)
2. And they are formed at the end of the plate tectonic cycle during the early continental collision as a basin is closed off from the sea. Salt deposits are again common along with sudden changes in sedimentation. They are the terminal basins of J. T. Wilson, 1968. Pinched off from access to the sea, they can dry up and form deep SABSEL basins before the sea again gets access such as the Mediterranean Sea.
At present, the deepest SABSEL basin is the Dead Sea of Israel and Jordan at 1371 feet below sea level.
SABSEL basins occur throughout Geologic time and can be the site of major hydrocarbon deposits. We will discuss three international examples, then the Norphlet fm. of the Gulf of Mexico basin.
Evidence of deposition in a sub-aerial sub-sea basin consists of:
- Deep-water deposits over sub-aerial deposits with no transition. Cross-bedded sand dunes under marine sediments with no loss of dune form or reworking of dune sands thick reservoirs with porosity preserved to great depth.
- Salt deposits. Good reservoir rocks are possible both above or below salt deposits.
- Canyons cut in basin margins to the level of basin bottom.
4. Fluvial or shallow water deposits over deep water sediments, with no transition. Sand reservoir facies are displaced far into Basin.
6. Deep karst in marginal carbonates. Thick reservoirs if sealed.
Examples of SABSEL basins are:
- The Southern North Sea basin wherein Permian Rotliegendes sandstones lie on Carboniferous coal-bearing clastics and limestones. A desert about 250 meters below sea level existed until suddenly flooded. The sand dunes are good reservoirs and provide natural gas to the UK.
Figure 3 (Map showing Southern North Sea Rotliegend Gas fields)
- The Mediterranean entry at the Straits of Gibraltar was sealed by the collision of Africa and Europe. The Mediterranean dried up and basins as deep as 12,000 feet deep existed during the Late Miocene Messiness Salinity crisis. Salt was deposited as well as Sapropels source of biogenic gas. The returning sea rapidly covered the area preserving the gas sources.
Figure 4 (the Mediterranean Sea showing late Miocene salt basins)
3. The South Atlantic offshore Brazil- West Africa.
Notable production exists in the passive margin basin formed above the salt and from an extensive rift terrain basin under the salt. The sub-salt early lacustrine and desert basin is rich in source rock, but it is also host to basic volcanic rock and deposits of CO2 gas. The reservoirs therein include extensive limestones deposited by bacteria and algae. The potassium salts indicate high temperatures in the subaerial deep basins. There is much to be learned about this amazing rift of several thousand kilometers long.
Figure 5 (GoM map showing key Norphlet HC discoveries)
4. Gulf of Mexico USA. Jurassic Norphlet formation desert sand dunes formed on top of the Louann salt as the entry of marine waters ceased. When the sea returned, the deep-water Brown dense portion of the Lower Smacker was deposited, which formed a good source rock and seal for the underlying Norphlet sand dunes. Even below 20,000 feet subsea, the dunes are adequate gas reservoirs. The Norphlet Desert and its Sand Dunes are in a sub-aerial basin below Sea Level.
Figure 6 (Map of Albian South Atlantic Basin showing paleogeography, sub-aerial shelves & Aptian salt basins)
During the late Triassic, the extension of Pang area future Gulf of Mexico rifting began with a horst and graben terrain that was filled with clastic non-marine sediments. As extension and subsidence continued, the ocean entered depositing evaporates ending with the Louann Salt formation. At that time, the portal from the Pacific Ocean was closed, but the area of the present Gulf of Mexico continued to subside well below sea level, the arid environment continued, and desert sand dunes were deposited in the Norphlet desert on top of the Louanne salt.
Sands on the shores of the basin were swept into cross-bedded red sand dunes that were distributed throughout the basin by regional and adiabatic winds. When the barrier to the ocean finally broke, the sea flooded in, and water rose like it was filling a bathtub. The dunes were not eroded but submerged by hundreds of feet of water. Deepwater black, finely laminated pyritic limestones (the lower Smackover limestone) directly overly the dunes with no transitions. The dunes maintained their shapes and were not been eroded by a transgressing sea.
Norphlet sandstones are good reservoirs even at 20,000 feet below sea level as seen in Mobil well 76-1 in Mobile Bay, Alabama. The 412 feet of fine to medium grained sandstones of the gas column had an average porosity of 11.1%, 7.7 md permeability. At 11,240 psi formation pressure and BHT of 414 degrees Fahrenheit, the well had an AOF of 37.3 MMCF/D. Chlorite coatings of grains prevent quartz overgrowths, preserving porosity and permeability to great depth. Norphlet reservoirs should exist in local areas throughout the Gulf of Mexico and be prospective of gas production where ever within drilling depth. Good seismic will help predict the location of thick deposits. The distinctive shape of the large dunes can be seen even on 2D seismic lines. The Norphlet Sandstone is the prospective reservoir immediately above the original Louann salt, where the salt used to be or carried upon first generation salt domes. The laminated fine-bedded dark limestone/ dolomite of Smacker Brown dense formation is a marker of deep-flooded basins and may mark areas prospective for underlying sand dunes of the Norphlet. The updip edge of the black organic-rich mudstone should mark the edge of the first filling of the SABSEL basin like the bathtub ring left by dirty bathwater. The black mudstones overly the Norphlet in deep-water fields and the deep fields of Mobil Bay.
The Norphlet desert sand dunes are probably prospective in all the basins wherein the Louanne salt was deposited. Cross-bedded Jurassic desert sandstones equivalent to the Norphlet are even found offshore Mexico west of the Yucatan and are reported to be productive there from the E.K. Balam Field.
Considering the model of the South Atlantic, is there a terrain under the original Louanne Salt wherein tilted fault block are bounded by organic-rich lacustrine shales? Are early sandstones and microbial limestones present? Only the drill bit can tell us!
Thanks are due to all the many oil companies that have published about the deep reservoirs of the Gulf of Mexico and especially to Exxon Mobile for their detailed presentations about Mobile Bay fields.
MARTIN CASSIDY worked for Amoco for 32 years around the world in assignments in production geology, new ventures, and operations. After his retirement from Amoco, he earned a PhD in geology from the University of Houston. (His undergraduate degree in geology was from Harvard University, and he also has an MS in geology from the University of Oklahoma.)
Since receiving his PhD, Mr. Cassidy has continued as a research scientist at the University of Houston, and he also continued to write and consult about petroleum exploration, basin analysis, and subsurface gases (both hydrocarbon and non-hydrocarbon). He gives special emphasis to CO2, particularly its relevance to exploration for oil and gas.
During 2012-2013, Martin also served as President of the Houston Geological Society.
His publications include:
Cassidy, M. M. (2005), Occurrence and origin of free carbon dioxide gas deposits in the earth’s continental crust. Houston, Texas, University of Houston, Dept. of Geosciences. Ph. D. Dissertation, 242 pages.
Gilfillan, S.M.V., C. J. Ballentine, G. Holland, D. Blagburn, B. Sherwood Lollar, S. Stevens, M. Schoell, M. Cassidy (2008), The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA. Geochimica et Cosmochimica Acta
v. 72, p. 1174-1198.
Dr. Martin M. Cassidy, research scientist. Department of Earth and Atmospheric Sciences, University of Houston. Houston, Texas
(713) 503 8331
University of Houston
Instructions to Norris Conf. Center:
The Norris Conference Center is on the Second (2nd) Floor, and cannot be seen from the street. From Town and Country Blvd, turn west at Plaza Way and go past "Kendra Scott" store to STOP sign. Turn right = North and go to Level 3 of the parking structure.The parking structure can also be reached from the northbound Beltway 8 frontage road. Turn into the driveway that is 0.33 mi. north of Kimberley Ln., just before the Amegy Bank sign.
816 Town & Country Blvd, Suite 210
Houston, TX 77024
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