Stress and pore pressure in mudrocks bounding salt systems
April 24, 2018
Speaker: Dr. Maria-Aikaterini Nikolinakou, Ph.D., Research Scientist, Bureau of Economic Geology Jackson School of Geosciences.
Abstract: We simulate the evolution of stress and pore pressure in sediments bounding salt systems. Our evolutionary geomechanical models couple deformation with sedimentation and porous fluid flow. We find that high differential stresses evolve near rising diapirs and below salt. Salt emplacement induces significant excess pressures that are comparable to the weight of the salt sheet. In addition, we show that the shear-induced component of the excess pressures is significant. We also find that low effective stresses result in low strength, which enables salt growth. We model salt as a solid viscoplastic and sediments as poro-elastoplastic materials, and calibrate the consolidation properties based on experimental testing on smectite-rich mudrocks, typical of those in Gulf of Mexico. Our approach can be applied to design stable well bores and provide insight into macroscale geological processes. Overall, we show that transient evolutionary models can provide estimates of stress and pore pressure in many geologic systems where large strains, pore fluids, and sedimentation interact. We close with a discussion of coupling field velocity measurements with geomechanical results and of better understanding material behavior at geologic stress and time scales.
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Biography: Maria-Katerina Nikolinakou is currently a Research Scientist at the Bureau of Economic Geology, Jackson School of Geosciences, at the University of Texas at Austin. Maria is a Civil/Geotechnical Engineer. She received her Science Doctorate on Theoretical Soil Mechanics from MIT in 2008. She holds a M.Sc. in Geotechnical Engineering from MIT and a Civil Engineering degree from NTUA, Greece. Before joining the Jackson School, she worked for Shell Exploration and Production on Reservoir Geomechanics. Her research focuses on understanding stress and pore pressure in complex geologic systems, including salt systems and thrust belts. She studies the behavior of geologic materials under high stress levels and complex stress paths. She develops applied workflows for pressure prediction in exploration settings.
Paleogeographic Reconstruction of the Louann Salt Basin
February 27, 2018
Speaker: Dr. John W. Snedden, Senior Research Scientist, Director, Gulf Basin Depositional Synthesis Project, Institute for Geophysics, Jackson School of Geosciences.
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Abstract:
John W. Snedden, Ian O. Norton, Michael R. Hudec, Abdulah Eljalafi, and Frank Peel, The University of Texas at Austin.
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The presence of Jurassic age salt in the Gulf of Mexico has been known for almost 60 years, originally recognized as two separate salt bodies. Reconstruction of the original saline basin as it appeared prior to sea floor spreading has been difficult to carry out due to subsequent allochthonous salt movement that obscures stratal relationships at depth. However, a new approach to seismic mapping of the Louann salt using its tectonostratigraphic character allows recognition of distinct Louann facies transitions from deep basin to onshore lapouts. Halite-dominated Louann is more ductile, often seismically dim, and readily facilitates fault detachment. Halite likely formed in the deep basin, with coeval anhydrite forming in shallow water sabhkas and evaporitic lagoons. Anhydrite-dominated sections are seismically and structurally distinct with high amplitude/continuity and a less ductile character. A zone of mixed seismic response that we infer to be interbedded halite and anhydrite separates these seismic facies.
Our new paleogeographic reconstruction of the Louann salt has been developed on the basis of this seismic facies mapping, in combination with new plate tectonic models. 87/86Sr ratios from interior salt basins indicate a proxy age of 170-ma when matched against the global strontium seawater curve. While a 170-ma age for the Louann salt is 7-8 ma earlier than previous estimates, this occurs during a phase when various plates are in closer proximity and thus conditions are more conducive to restriction and evaporation.
This reconstruction also allows evaluation of two contrasting hypotheses regarding source of the original seawater that fed this saline giant in the deep Gulf of Mexico basin. Our restoration shows narrow gateways to the Atlantic Ocean, from the deep Louann basin through the Florida straits, Northern Cuba and the Bahamas. The chain of narrow basins connecting the Atlantic to the Gulf may have acted to deplete incoming seawater of all but Na and CL, evidenced by the remarkably pure Louann halite in the deep basin. The mapped configuration of narrow passages in the eastern Gulf of Mexico and dominance of basin marginal anhydrite in Mexico (versus halite elsewhere) also leads one to question the conventional model of a marine connection between the Louann basin and the Pacific Ocean. Pacific affinity macrofauna, originally a critical data point supporting the Pacific seawater entry model, are now known to be younger than the Louann salt.
Salt is a critical component of the prolific Gulf of Mexico petroleum system, setting up traps, providing top seal, and mitigating heat flow so that Mesozoic source rocks generate later in the basin burial history. Understanding the original distribution of Louann salt is also essential to basin modeling and structural restorations.
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Biography: Dr. John W. Snedden is Senior Research Scientist and Director of the Gulf Basin Depositional Synthesis Project at the Institute for Geophysics, University of Texas at Austin. He received degrees from Trinity University (San Antonio), Texas A&M University (College Station), and Louisiana State University (Baton Rouge). With multiple domestic and international assignments, he worked for Mobil and ExxonMobil for over 25 years in research, exploration, development, and production prior to joining UT. Recent research has focused on the Gulf of Basin. He has served as Vice-President of GCS-SEPM and Secretary-Treasurer of SEPM. John has won the SEPM Excellence in Oral Presentation award, GCAGS Journal Best Paper Award and AAPG’s A.I. Levorsen Best Paper Award. John was selected as one of 50 people to be presented as Heritage of the Petroleum Geologist honorees, at the upcoming American Association of Petroleum Geologists Convention in Houston, Texas, April 2-5th.
Carbonate Channel-Levee Systems Influenced by Mass Transport Complexes: Browse Basin, NW Shelf Australia.
January 23, 2018
Speaker: Dallas B. Dunlap, Research Scientist Associate IV, Bureau of Economic Geology
Abstract: Submarine channels are primary conduits for clastic sediment transport to deep-water basins, thereby controlling the location of marine depocenters and sediment bypass. The evolution and depositional character of submarine channels have broad implications to sediment dispersal, sediment quality, and hydrocarbon exploration potential. Siliciclastic channel systems have been extensively studied in modern environments, seismic and outcrop; however, carbonate channel-levee deposits have only recently been explored.
Newly released high-resolution (90 Hz) seismic-reflection data from the Australian Browse Basin was used to document the influence of mass-transport complex (MTC) deposition on the stratigraphic architecture of carbonate channel-levee systems. The 2014 vintage seismic survey is 2500 km2 and hosts numerous large Miocene-age carbonate channel-levee complexes basinward of the shelf edge. Regional horizons and individual channel forms were mapped. Channels range from ~200-300 m wide and are bounded by high-relief levee-overbank wedges (>100 ms TWTT). These channels extend across the survey area >70 km. The leveed-channels were sourced from middle and late Miocene slope gullies linked to platform carbonates. Slope-attached and locally derived MTC’s are evident throughout the Miocene section likely related to periods of basin inversion and shelf-edge gully incision. We interpret that regionally extensive (>30 km) slope-attached MTC’s can shut down a channel-levee system and trigger the initiation of a new system, whereas more locally derived (<30 km) MTC’s can promote changes in channel map-view pattern, including avulsion in some cases.
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The stratigraphic architectures of the carbonate channel-levee systems and their interactions with MTC’s are similar to siliciclastic analogs. The similarity in stratigraphic patterns between siliciclastic and carbonate depositional systems suggests similar formative processes related to submarine mass wasting and turbidity currents, which informs depositional models of carbonate slope systems and calls for re-evaluation of the controls on stratigraphic patterns in mixed siliciclastic-carbonate deep-water basins.
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Biography: Dr. Dunlap is a received B.S. and M.S. degrees in Geology from the University of Texas at Austin and is pursuing a Ph.D. in Geology. He is Research Scientist Associate IV, Quantitative Clastics Laboratory, Bureau of Economic Geology, The University of Texas at Austin (2006 - Present). Research within the Quantitative Clastic Laboratory pertains to the use of seismic geomorphic data and processes to understand depositional architectures from shallow tidal systems to the deepest of abyssal plains and how sediment is transported downslope. My study area in 2017-2018 consists of seismic geomorphology of deepwater systems in the central and western Gulf of Mexico, U.S and basin scale variability of shelf systems of the Northwest Shelf, Australia.
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Acting Database Coordinator - Research Scientist Associate II-IV, Bureau of Economic Geology, The University of Texas at Austin (1998 - Present). Successfully balancing geophysical duties on several concurrently running projects that include seismic interpretation, time-to-depth conversions, and mapping, while assisting with geotechnical software support and geologic data administration. Other duties include software and hardware maintenance, testing and evaluation of proposed software, training of new employees on multiple geologic applications.
Permafrost Thaw In the Kobuk Valley National Park, Alaska - from Polygon to Lanscape Scale.
November 28, 2017
Dr. Dinwiddie discussed three effects of climate warming on arctic systems from the polygon to the landscape scale: (i) ice wedge degradation, which causes morphological changes to polygonal terrain, (ii) changes to thaw lake surface area in arctic lowlands, including lake drainage, and (iii) thermal erosion on slopes that result in active layer detachments, thaw slumps, hillslope soil erosion, debris flows, and landslides. She will describe her group’s remote sensing image and data analyses as well as local-to-landscape-scale freeze/thaw and slope stability modeling performed to inventory the recent situation, quantify past change, and forecast future states for permafrost in Kobuk Valley National Park, Alaska. Dr. Dinwiddie will also update the Society on freeze/thaw modeling she performed for the Great Kobuk Sand Dunes subsequent to her last presentation on her team’s geophysical characterization of the area.
TexNet Texas Seismological Network
October 24, 2017
Texas Seismological Network. In an effort to better understand the causes of recent seismicity events and to monitor earthquake activity in general, the 84th Texas Legislature included funding to create a statewide, seismic monitoring program, known as TexNet. The goal of TexNet is to provide authenticated data needed to evaluate the location, frequency and likely causes of natural and induced earthquakes, the latter potentially associated with the development of hydrocarbons and associated disposal of wastewater. TexNet will consist of at least 22 new permanent seismic monitoring stations across Texas, augmenting the 17 existing stations. In addition, 36 portable seismometers will be deployed to further examine seismic events, particularly in areas with denser population or critical infrastructure. The first insights of the seismicity of the State is available and will be presented through this talk.
Where is all the water coming from at the Barton Springs pool: Integrated geophysical case study, Austin, Texas
September 26, 2017
Speaker: Dr. Mustafa Saribudak, Ph.D., P.G., Principal Environmental Geophysics Associates
Abstract: Barton Springs is a major discharge site for the Barton Springs Segment of the Edwards Aquifer and is located in Zilker Park, Austin, Texas. Barton Springs actually consists of at least four springs. The main Spring discharges into the Barton Springs pool from the Barton Springs fault and several outlets along a fault, a cave and several fissures, as well as gravel-filled solution cavities on the floor of the pool west of the fault.
Surface geophysical surveys [resistivity imaging, induced polarization (IP), self-potential (SP), seismic refraction, and ground penetrating radar (GPR)] were performed across the Barton Springs fault and at the vicinity of Main Barton Springs in south Zilker Park. The purpose of the surveys was two-fold: 1) to locate the precise location of submerged conduits (caves, voids) carrying flow to Main Barton Springs; and 2) to characterize the geophysical signatures of the fault crossing the Barton Springs pool.
The geophysical survey results indicate significant anomalies to the south of the Barton Springs pool. A majority of these anomalies indicate a fault-like pattern, in front of the south entrance to the swimming pool. In addition, resistivity and SP results, in particular, suggest presence of a large conduit in in the southern part of the Barton Springs pool. The groundwater flow-path to the Main Barton Springs could follow the locations of those resistivity and SP anomalies along the newly discovered fault, instead of along the Barton Springs fault, as previously thought.
