CBTH Researchers at AAPG 2015

• TITLE: La Vela Bay, Offshore Falcon Basin, Western Venezuela: Eastern Extension to the La Perla Carbonate Reservoir Trend
  AUTHORS: Joan M. Blanco, Paul Mann
  ABSTRACT: Discovery of the 16 TCF La Perla gas giant in 2009 was the first major carbonate hosted giant reservoir discovered in northern South America. Moreover, the La Perla discovery was found in the northern part of the Gulf of Venezuela on the exotic Caribbean plate and did not involve the more familiar hydrocarbon habitat in Venezuela of foreland basin clastic reservoirs sourced by the Cretaceous passive margin. We describe the La Vela carbonate reservoir, offshore Falcon basin, western Venezuela, located 170 km southwest of La Perla and consisting of an Early Miocene reefal reservoir directly overlying igneous-metamorphic basement with associated Miocene age source rocks. The reservoir produces both light-medium oil and gas and more than half of the reservoir presents effective porosities between 8 and 15%, and permeabilities less than 15 mD. We used 960 km2 of 3D seismic data tied to 40 wells to map the reef reservoir facies over an area of 11000 km2. The thickness of the limestone varies from several meters to 150 m. Well data show that the facies is a shallow carbonate ramp with localized reef buildups. We use the curvature and other attributes for the seismic volume to show that variations in porosity are controlled by diagenetic effects rather than by fracturing. The level of deformation is much less than in the neighboring areas of the onland, inverted Falcon basin to the south. We have identified good seals at local and regional scales that correspond to maximum flooding shale units. We use paleogeographic maps to show a possible Miocene reefal carbonate trend running along the southern edge of the exotic Caribbean plate and linking the La Vela area to the La Perla area of the Gulf of Venezuela.



• TITLE: Controls of Asymmetrical Rifting on Giant Oil Habitats within Conjugate, Pre-Salt Carbonate Sag Basins of Brazil and West Africa
  AUTHORS: Patrick Loureiro, Paul Mann, Mike Saunders
  ABSTRACT: The largest deepwater oil discoveries of the past 10 years were found in carbonate-filled, sag basins of the Equatorial and South Atlantic Ocean. We explain the asymmetrical distribution and thickness variations in the areas of pre-salt carbonate sag basins in Brazil and West Africa by, first, isostatically correcting the top of oceanic crust in the area of the Santos to Espirto basins of Brazil and their conjugates in the Namibe and Kwanza basins of Namibia and Angola to improve the location of the continent-ocean boundaries in these areas; and, second, using bathymetric, gravity, magnetic and 1,700 km of regional seismic transects to define the footwall versus hanging wall of the asymmetrical rift margins for both conjugates. For the Santos-Namibe conjugate, we propose Santos to be the hanging wall of an asymmetrical rift system with a 200-km-wide rifted margin and overlying sag basin with carbonate reservoir facies and sloping bathymetric profile; and the Namibe to be the footwall with a 125-km-wide rift and sag basin and steeper bathymetric profile. For the Campos-Kwanza conjugate 400 km to the north, we propose Campos to be the footwall with a 150-km-wide rift zone and overlying sag basin and sloping bathymetric profile. Well data shows that thicker the carbonate sag (135- 325 m) and its overlying salt basin (up to 2 km) are associated with the hanging wall blocks of Kwanza and Santos and the thinner carbonate sag (15-75 m) and its overlying salt basins (up to 1.5 km) are associated with the footwall blocks in accord with predictions based on recent analog modeling. Reservoirs within the sag phase of these conjugate margins include high porosity and permeability lacustrine carbonates deposited in high-energy ooid and oncoid beds along with highly porous travertine hot-spring deposits that include very porous tufa mounds sealed by 1 km or more of overlying salt. These reservoirs are sourced by brackish-lacustrine shales deposited during the sag phase, interbedded with the carbonates. Based on these correlations we predict more potential for larger discoveries in thicker sags/carbonate reservoirs associated with hanging walls underlying Santos and Kwanza.



• TITLE: Trends and Predictions for Giant Oil and Gas Field Discoveries, 2000-2019
  AUTHORS: Paul Mann, Naila Dowla, Myron K. Horn
  ABSTRACT: We have updated our compilation of giant oil and gas fields of the world for the period of 2000 to 2014 using over 1400 articles and reports. During this decade and half of observation, 185 new giants bring the total number of the world’s giants discovered from 1868 to 2014 to 1063. Of these 187 newly discovered giants, 90 are oil giants and 85 are gas giants and 12 combination oil and gas giants. 137 were discovered offshore while 48 were discovered onshore. Of the 137 offshore giants, 67 are gas, 60 are oil and 10 are a combination of both oil and gas. Of the 48 onland giants, 22 are gas, 24 are oil and 2 are combinations. The tectonic settings of the newly discovered giants closely follow a pattern we described in 2003 for pre-2000 giant discoveries. The majority of the 2000-2014 discoveries are found along continental passive margins fronting major ocean basins (18 in West Africa, 13 in the Gulf of Mexico, 13 in East Africa, 8 in the Persian Gulf, 7 in the Mediterranean Sea, 20 in Brazil, and 9 in Sunda). Far fewer giants were found on continental and arc collision margins (14 in the Persian Gulf, 6 in the Caspian Sea and 4 in China), and rift and inverted rift settings (11 in the Caspian Sea, 9 in Siberia, 8 in the Barents Sea and 6 in North Africa). We predict that the decade 2010-2019 is on track to be the fourth highest giant discovery decade since 1868 with 117 new giants added. Emerging giant clusters - defined as areas with new giant discoveries in areas that previously lacked giants - include the passive margins of East Africa and the eastern Mediterranean Sea.



• TITLE: Recent Progress in Understanding a Two-Stage Opening Model for the Gulf of Mexico and Its Implications for Deepwater Exploration in the U.S. and Mexican Maritime Zones
  AUTHORS: Paul Mann, Murad Hasan
  ABSTRACT: We review opening models for the Gulf of Mexico (GOM) in light of our own studies of deep-penetration seismic reflection data in the eastern GOM. Most groups agree that the first phase of syn-rift GOM opening is late Triassic-early Jurassic (235-174 Ma) in age, NW-to-SE in extension direction, and responsible for creating a broad zone of thinned, continental crust along the northern margin of the GOM and underlying the northern salt basins of Texas, Louisiana and Mississippi. This Late Triassic-early Jurassic rift zone is an along-strike continuation of Triassic rifts present along the eastern margin of North America - but in the northern GOM case failed to culminate in production of a parallel and contiguous zone of oceanic crust across the broad northern GOM. Progress has been slow in understanding the early history and crustal structure of this area in the GOM due to the obscuring presence of an overlying sag basin of post-early Jurassic age filled by 3-4 km of depositional salt (now remobilized). The second and much better understood phase of GOM opening is late Jurassic (156-145 Ma) and post-salt in age and formed a large expanse of salt-free, Jurassic oceanic crust underlying the deepwater GOM shared by the US, Mexico and Cuba. This second late Jurassic opening phase occurred along a highly arcuate slow spreading ridge now well imaged on basin-wide, satellite gravity maps. We have georeferenced our grid of deep-penetration seismic and well data in the EGOM along with recent refraction studies to both ground-truth these satellite images and provide details of the early breakup and separation. Our eastern and NE GOM continent-ocean boundary defined by deep seismic profiles is within 20 km of that inferred from satellite gravity. We have used the shape of the satellite-imaged fracture zones in the Mexican GOM to improve the pole position for this second phase of GOM opening which is located in the Straits of Florida. This pole restores trends of crustal fabric in Florida and the Yucatan Peninsula seen on gravity and magnetic maps to pre-rotation parallelism. We use this pole to create a kinematic plate model for the second phase of GOM opening that respects all available seismic reflection, refraction, well, and satellite imagery.