Statoil Fellowships Awarded to Baiyuan Gao and Michael Cronin

International energy company Statoil awarded fellowships to two of our GeoFluids students, Baiyuan Gao and Michael Cronin. These fellowships were awarded based on proposals submitted by the students and their advisor, Peter Flemings. This was a competitive field and we congratulate Baiyuan and Michael for their hard work at writing quality proposals. This money will go to fund their research at UT Austin.

Baiyuan Gao:
Statoil Fellowship – "Trap integrity in salt basins; sub‐salt imaging and seal vs. pore pressure challenges"

Michael Cronin:
Statoil Fellowship – "Multi-scale Pore Structure at the Core Scale in Shales: Experimental and Numerical Investigation of Mass Transport Implications"

Posted April 2013

Mark your calendar for UT GeoFluids 2014

Dear GeoFluids Members,

The 2013 UT GeoFluids Consortium Meeting, held Feb 2013, was well received as evident by the evaluation responses. If you would like to read this year’s evaluations we have compiled and posted them here

http://www.beg.utexas.edu/geofluids/g4/Meetings/Meet13/2013_Evaluation_Complete_to_members.pdf

To those of you that were able to join us this year, we appreciate your attendance and participation in the meeting. For those that were not able to join we hope you will join us in 2014. The dates of our 2014 meeting are set, please put these on your calendar. You will see that this year we have blocked off three dates. Based on feedback at the 2013 meeting we will have a session on the evening of Feb 19th to kick off the meeting.

UT GeoFluids 2014 Consortium Meeting
Feb. 19-21, 2014
University of Texas Campus at the AT&T Executive Education and Conference Center, 1900 University Ave, Austin, TX

The PowerPoint presentations, and abstracts from the 2013 UT GeoFluids Consortium meeting are available for download on the UT GeoFluids 2013 meeting website http://www.beg.utexas.edu/geofluids/Meetings/meet2013.php

Data available to Consortium members can be found on our data site http://www.beg.utexas.edu/geofluids/g4/g4database.php 
You will be prompted for a Log in and Password. Enter your company’s 2013 username and password. If you don’t know these, please contact Tessa Green (tessa.green@jsg.utexas.edu)

Finally, each year many of you are disappointed that you do not get a room in the AT&T conference center. We urge you to book early (and cancel later if you can’t join us). Tessa will send out hotel details as soon as the room block is available so keep an eye on your email.

Thank you,

Peter Flemings & Jack Germaine

Posted March 2013

UT GeoFluids Consortium Meeting 2013

The 2013 UT GeoFluids Consortium Review Meeting, held February 21 – 22, was enthusiastically attended by approximately 90 representative from 11 different companies.We had 26 presentations and many lively discussions and recommendations for future work.

Mark your calendar for the 2014 meeting Feb. 20 and 21, 2014 on the downtown U.T. Campus at the AT&T Executive Education and Conference Center.

Posted February 2013

UT GeoFluids Workshop 2013

January 13-19 the UT GeoFluids personnel gathered in Burnett TX for the annual GeoFluids workshop. Lots of progress was made in preperation for the upcoming 2013 UT GeoFluids Consortium Meeting. Students were able to practice their talks and work on current projects.

Registration is open for the 2013 UT GeoFluids Consortium Meeting:

WHEN:
Thursday, February 21 - Friday, February 22, 2013
View Agenda

WHERE:
The University of Texas
AT&T Executive Education and Conference Center, 1900 University Ave, Austin, TX 78705
Travel & Hotel Logistics

RSVP:
Please register for the 2013 meeting HERE
Regrets

Posted January 2013

Brendan Casey Winner of the 2012 Northeast Geotechnical Research Symposium Abstract Competition

The Geotechnical Engineering Group at the University of Massachusetts Amherst, in collaboration with Geosyntec Consultants, hosted the 2012 Northeast Geotechnical Engineering Graduate Research Symposium at UMass Amherst on Friday, 26 October 2012. Graduate students at all stages of research were invited to submit abstracts providing an overview of their research and the anticipated contribution to the geotechnical and geoenvironmental engineering industry. UT GeoFluids student Brendan Casey won the 2012 award with his abstract "Liquid Limit as a Predictor of Fine-Grained Soil Strength."

Posted November 2012

Registration is open for the 2013 UT GeoFluids Consortium Meeting

2013 UT GeoFluids Consortium Meeting
Registration is open for the 2013 UT GeoFluids Consortium meeting and workshop Feb. 21 and 22, 2013 on the downtown U.T. Campus at the AT&T Executive Education and Conference Center.

Posted October 2012

Andrew Smith Joined Successful Mission for AMGG Research School

Andrew Smith is currently working with Juergen Meinert and Stefan Buenz in the arctic marine geology and geophysics group at the University of Tromsø. He recently participated in scientific cruises to acquire high-resolution 3D seismic and multi-component data using University of Tromsø's research vessel FF Helmer Hanssen. Below is a picture of Andrew on his voyage. For more information on the cruise visit the University of Tromso site.

Posted August 2012

Peter Polito gives talk on JR field test of Downhole tools

On June 27th Peter Polito gave a talk titled "Curacao to Bermuda to the Jersey Slope to Central Park: The trials and tribulations of developing IODP technologies" to the researchers and staff of the Bureau of Economic Geology.

Summary: Over the past decade the GeoFluids group has been developing and testing a penetrometer and corresponding delivery system to be deployed on the JOIDES Resolution. Over the past year we have undergone an extensive stretch of land based bench testing in preparation for sea trials. For two weeks in May and June we were deployed on the JR in preparing for our tests while the ship transited from Curacao to Bermuda to our test site. For 48 hours straight we ran a series of tests on the New Jersey Slope with some success, a healthy dose of humility, and an education on working at sea. On June 8, at approximately 4pm I sat in Central Park, exhaled, and had a beer.

You can view Polito's powerpoint presentation here.

Visit http://www.ig.utexas.edu/research/facilities/downhole/ for more information on the Down-hole Technologies for Ocean Drilling

Posted July 2012

New Data Posted: Compression and permeability behavior of resedimented Nankai - Silt mixtures

Julia Schneider Reece performed an experimental study similar to the one on Boston Blue Clay (BBC) - Silt mixtures. However, here Julia used a marine, deepwater mudstone from offshore Japan, that was drilled during Integrated Ocean Drilling Program (IODP) Expedition 322, as the baseline mudstone instead of BBC. Then she added the same silt-sized silica to the Nankai mudstone in five varying proportions in order to analyze how grain size and also mineralogy affect compression and permeability behavior over a large range in stress (up to 21 MPa). The mineralogy of the Nankai mudstone is significantly different from BBC. The Nankai mudstone consists of almost 50% of smectite (weight %).

Julia prepared these homogeneous mudstone mixtures in the laboratory using the resedimentation technique. After pre-loading the samples to 100 kPa in the resedimentation tests, she conducted constant-rate-of-strain consolidation tests to a maximum vertical effective stress of 21 MPa, equivalent to about 2 km of burial under hydrostatic conditions. Microstructure and fabric of all samples were analyzed at two different stress states in scanning electron microscope images.

Find all UT GeoFluids data on the Member's Data Page.

Posted July 2012

Andrew Smith Awarded Master's Degree

On May 19th Andrew Smith was awarded his Master's degree. His thesis was entitled "Observations and Models of Venting at Deepwater Gulf of Mexico Vents". Andrew's work focused on the process of venting and associated hydrate formation at deepwater vents in the Gulf of Mexico. After completing his MS, he will join the marine geology and geophysics research group at the University of Tromsø in Norway as a Fulbright scholar. We wish Andrew the best of luck in his new adventure.

Posted June 2012

Athma Bhandari Joins UT GeoFluids Group

We are excited to welcome Athma Bhandari to the UT GeoFluids group as a postdoctoral fellow. Athma earned his Ph.D. from University of Southampton, and M. Eng degree in Civil Engineering from the University of Tokyo. Athma's main research interests lie in experimental geomechanics, more specifically, laboratory study of deformation and flow in geomaterials (soils and rocks). During his PhD, he developed a novel digital image-based deformation measurement system for triaxial tests and used it to study the initiation and evolution of failures in a naturally locked sand. He examines the underlying mechanics of observed macro-scale behavior of geomaterials. In his work with UT GeoFluids Athma will will focus on measuring and interpreting mass transport in low permeability shales.

Posted May 2012

Andrew Smith Awarded Best Student Presentation at the Gordon Research Conference on Natural Gas Hydrate Systems 2012

The 2nd Annual Gordon Research Conference on Natural Gas Hydrates was held March 18-23 in Ventura, CA. Andrew Smith presented his poster titled "Multiphase heat and salt transport at a deepwater gulf of Mexico vent." Andrew was honored with the Best Student Presentation Award.

Abstract:
Deepwater vents in the Northern Gulf of Mexico are actively releasing water and hydrocarbons. They are ubiquitous across the continental slope, and we focus on one in the Ursa Basin at lease blocks MC852/853. The vent is elevated ~75 meters relative to the surrounding seafloor, and its core is ~1.6 km in diameter. It is bounded by a strong negative polarity seismic reflection. We interpret that this reflection records a negative impedance contrast marking the boundary between hydrate above and gas below: it is the Bottom Simulating Reflector (BSR). This BSR rises sharply at the boundaries of the vent and is horizontal within a few meters of the seafloor beneath the vent edifice. High temperature gradients and elevated salinities are present within the vent (Ruppel et al., 2005; Paull et al., 2005). We model the coexistence of elevated temperature gradients, saline fluids, and an uplifted BSR by assuming that warm, salty fluids are sourced from depth and expelled vertically through the vent conduit. We show that both the observed temperature gradients and salinities cannot be reconciled with a single-phase flow model. They can, however, be reconciled if gas and water are flowing upwards together, and if the flux of gas is large relative to the flux of water. A better understanding of the hydrogeological processes at vents is important for estimating the fluxes of water and gas from vents and for understanding the conditions under which deep-sea biological communities exist at vent locations.

Related References:
Smith, A. J., Flemings, P.B., Fulton, P.M. , in review, Hydrocarbon flux from natural deepwater Gulf of Mexico vents, Science

Posted April 2012

UT GeoFluids Consortium Meeting

The 2012 UT GeoFluids Consortium Meeting, held February 16 – 17, was enthusiastically reviewed by approximately 70 attendees representing 10 different companies. Some of the meeting highlights included preliminary observational and modeling results from the new field study at Mad Dog, the first demonstration of experimental capability in resistivity measurements, and a synthesis talk on our work on resedimented mudstones around the world.

The newly developed experimental database for consortium members was launched at this years' meeting. This database gives members immediate access to laboratory test results, analysis and scanning electron microscope (SEM) images of the various substrates tested within the GeoMechanics Laboratory.  

Presentation are available to consortium members on the 2012 meeting site.

Mark your calendar for the 2013 meeting Feb. 21 and 22, 2013 on the downtown U.T. Campus at the AT&T Executive Education and Conference Center.

Peter B. Flemings presentation to 2012 Consortium Members

Posted March 2012

UT GeoFluids Workshop

January 10 - 14 the UT GeoFluids personnel gathered in Burnett TX for the annual GeoFluids workshop.

Posted January 2012

Julia Schneider Awarded Doctoral Degree

On December 3rd Julia Schneider was awarded her doctoral degree. Her dissertation was entitled "Compression and permeability behavior of natural mudstones". Julia will continue her research with the UT GeoFluids Consortium as a Postdoctoral Fellow. We are excited to have her stay on and look forward to her talks at the upcoming UT GeoFluids Consortium Meeting.

Posted December 2011

Recent Publications

Gang Luo and Maria Nikolinakou have two upcoming publications in the AAPG Bulletin on geomechanical modeling and pore pressure response in salt-sediment systems. You may access their publications at the following links with your company log in.

Luo, G., Nikolinakou, M.A., Flemings, P.B., Hudec, M.R., Geomechanical modeling of s tresses adjacent to salt bodies: 1. Uncoupled models, AAPG Bulletin, (in press)

Nikolinakou, M.A., Luo, G., Hudec, M.R., Flemings, P.B., 2011, Geomechanical modeling of stresses adjacent to salt bodies: 2. Poro-Elasto-Plasticity and Coupled Overpressures, AAPG Bulletin (in press).

Posted November 2011

Andrew Smith Attends ICGH

In July 2011, Andrew Smith traveled to Edinburgh, Scotland to present ongoing research on a gas vent in the Gulf of Mexico at the 7th International Conference on Gas Hydrates. His oral presentation focused on identifying the hydrogeological process of gas venting and the associated hydrate formation. He discussed his research with experts in the field of natural gas hydrates and received invaluable feedback that will help him as he completes his Master's thesis this year.

Posted July 2011

Congratulations to Julia Schneider

Julia received an ‘Outstanding Student Paper Award’ from the Mineral and Rock Physics Section of AGU. Her poster was presented at the Fall 2010 AGU meeting in San Francisco and was entitled “Experimentally derived model to predict permeability behavior of mudstones.”

Posted April 2011

Yao You Receives 'Best Poster' Award

Congratulations to Yao You (Doctoral Candidate) for receiving a 'Best Poster' award for his presentation "Coupling of the evolution of pore pressure and the retrogressive slope failure during breaching " at the recent SIAM Conference on Mathematics & Computational Issues in the Geosciences held in Long Beach California.

Posted March 2011

New Consortium Member

Statoil has joined the UT GeoFluids consortium and will attend the 2011 consortium meeting. We are excited to welcome Statoil to the UT GeoFluids Consortium.

Posted February 2011

UT GeoFluids Workshop

On Jan 12 - 16, the GeoFluids Team had a research workshop at Canyon of the Eagles on Lake Buchanan. They practiced presentations, worked on research, and spent quality time as a group.

Posted January 2011

Derek Sawyer Awarded Doctoral Degree

Derek Sawyer was awarded his doctoral degree from The University of Texas December 4, 2010. His dissertation was entitled "Failure mechanics, transport behavior, and morphology of submarine landslides".

Derek studied sedimentation, deformation, and fluid flow on continental margins. His study area was the Mars-Ursa region outboard of the Mississippi River on the upper Mississippi Fan, Gulf of Mexico. Rapid Pleistocene sedimentation of a sand-rich basin-floor fan, two channel-levee systems, and numerous submarine landslides created a fascinating hydrodynamic system. He participated on Integrated Ocean Drilling Program Expedition 308 as a shipboard sedimentologist and has had summer internships at BP and Shell as a graduate student.

Derek has joined ExxonMobil in Houston, Texas in the Operations Geology group.

Posted December 2010

Message from the Director
UT GeoFluids Update: GEOFLUIDS MEETING Feb. 17-18, 2011 in Austin Texas

This is an update on the UT GeoFluids Consortium. We have been hard at work here in Austin Texas!

1. Our annual meeting will be held on February 17-18, 2011 in Austin, Texas. Please hold the date. Details will be forthcoming
2. As always, our website can be found here: http://www.beg.utexas.edu/geofluids/. There is a 'members only' button that you can access with your companies username and password. If you don't know the username and password, please contact me (pflemings@jsg.utexas.edu) and I will forward it to you.
3. I am very pleased to announce that Tessa Green has accepted a position as Program Coordinator for UT GeoFluids. Many of you will meet her in person or by email.
4. Recent publications:
   Matt Reilly's paper entitled, Deep Pore Pressures and Seafloor Venting in the Auger Basin, Gulf of Mexico, has been published.
   Two papers on modeling of stress and pressure in salt systems have been submitted for publication:

   1. Luo, G et al., Geomechanical modeling of stresses adjacent to salt bodies: 1. Uncoupled models, AAPG Bulletin.
   2. Nikolinakou et al, Geomechanical modeling of stresses adjacent to salt bodies: 2. Poro-Elasto-Plasticity and Coupled Overpressures, AAPG Bulletin.
   Hui Long's publication on mudstone compaction has been accepted for publication: Long et al, Consolidation and Pore Fluid Pressure of Ursa Sediments, Deepwater Gulf of Mexico, Earth and Planetary Science Letters
5. Our online software (Frac, McFrac, and Pstar) have been modified to work on the web and may be accessed here: http://www.beg.utexas.edu/geofluids/g4/software.php
   These software packages provide some simple approaches to predict trap integrity in overpressure (Frac, McFrac) and to simulate flow focusing (pstar).
6. Student news:
   We have taken on 4 new graduate students and I have them working hard (http://www.beg.utexas.edu/geofluids/personnel.php)
   Derek Sawyer is scheduled to defend his dissertation next week and will be joining ExxonMobil late in the year.
   Julia Schneider won a very prestigious Ocean Drilling Fellowship for her work on compaction of sediment mixtures.

Please drop me a note if you have any questions.

I look forward to seeing many of you in February.

Peter B. Flemings
Jackson Professor of GeoSystems
Jackson School of Geosciences
http://www.ig.utexas.edu/research/projects/basin/
pflemings@jsg.utexas.edu
tel: 512-475-9520

Posted November 2010

Flemings Presents Talk at BEG Seminar

Dr. Peter Flemings presented a talk entitled Deep pore pressures and seafloor venting in the Auger Basin, Gulf of Mexico as part of the Bureau of Economic Geology seminar series. You can view the streaming video of the presentation online at: http://www.beg.utexas.edu/abs/Flemings_040910.php

Abstract: Pore fluid overpressures in four reservoir sandstones in the Auger Basin, deepwater Gulf of Mexico, are similar across the basin, suggesting that these sandstones are hydraulically connected over distances >20 km. Small overpressure gradients within them suggest upward flow rates between 1 and 20 mm/yr. At the crest of these sandstones, pore pressure equals or exceeds the least principal stress, and we interpret that high fluid pressure is fracturing the caprock and driving flow vertically. A well drilled into the crest of the Auger sandstones confirmed the presence of extreme overpressures that converge on both the least principal stress and the overburden stress. Above these zones, spectacular mud volcanoes are venting fluids today. Overpressured aquifers with significant structural relief may drive fluid vents and mud volcanoes around the world.

Posted May 2010

2010 Consortium Meeting

The UT GeoFluids Annual Meeting 1.0 was held on February 11-12, 2010 at the University of Texas at the Pickle Research Campus. More than 40 industry attendees represented the 10 members of the consortium. The UT team presented more than 20 talks on their cutting-edge research. A special thank you to Neil Braunsdorf and Brent Couzens of Shell for also giving presentations. For more information on the meeting, including the presentations and attendees, please see the meeting website at the link above.

Posted March 2010

October 16, 2009 - Following are the abstracts for the papers that have been accepted from UT GeoFluids researchers for the upcoming 4th International Symposium of Submarine Mass Movements and Their Consequences in Austin, Texas, November 7 – 12, 2009.

For more information on this conference, visit http://www.beg.utexas.edu/indassoc/dm2/Conference2009/home.htm

Subaqueous Landslides in Clay-Rich Systems
Derek E. Sawyer, Peter B. Flemings, David Mohrig

We simulated subaqueous landsliding within sedimented beds of clay-rich material. We deposited beds inside a flume and gradually increased the bed angle until failures developed. In a preliminary experiment, localized debris flows developed at bed angles of ~25° in a thin (2 cm thick) bed of kaolinite clay (60% by weight) and silica silt (40% by weight). Failure surfaces were confined to the upper 0.5cm. In one flow we observed outrunner blocks that accelerated away from the main flow and created linear grooves along the upper bed surface. In future experiments we aim to understand: 1) how landslide rates and styles vary as a function of material properties (clay mineralogy, grain size, and presence of thin interbeds of sand); and 2) the process of retrogression by measuring pore pressure in several locations behind retrograding headscarps. This work will illuminate the processes that drive subaqueous landsliding on continental slopes.

Exploring the Origin and Characteristics of Mass Transport Deposits
Ursa Basin, Gulf of Mexico
Hilary E Strong, Peter B Flemings, Ruarri J. Day-Stirrat, Derek E. Sawyer, Julia Schneider

Seismic, core, and logging data from Integrated Ocean Drilling Program (IODP) Expedition 308 record multiple Mass Transport Deposits (MTDs) within the upper 600 meters below seafloor (mbsf) of the Ursa Basin, northern Gulf of Mexico. The most prominent, MTD-2, is 35 to 100m thick, spans all three drill sites – U1324, U1323 and U1322 – and is located approximately 100 mbsf. MTD-2 is seismically imaged with a positive, low-amplitude top reflection, and negative, high-amplitude basal reflection. MTD-2 is identified in core and logging data as a low porosity, high bulk density, zone. At U1324, the basal sediments of MTD-2 are 7 porosity units less than those immediately below, while at U1322, the basal sediments are 10 porosity units less. This decline in porosity corresponds to a 5% increase in bulk density from overlying bounding sediments to MTD-2. We hypothesize that MTD densification is a result of sediment remolding during debris flow. Remolding is defined as shearing sediment at unaltered water content, thus removing the original fabric and resulting in weaker, more compressible material. We also suggest that the arrested flow is buried and consolidated under uniaxial strain. Initial high resolution X-ray texture goniometry (HRXTG) fabric analysis shows greater basal plane alignment of smectite and chlorite in a MTD specimen, compared to a non-MTD specimen. Mercury Injection Capillary Pressure (MICP) tests confirm a reduction in pore throat size within the MTD-2; however this is a function of decline in porosity, not position within the MTD. Consolidation curves from initial uniaxial experiments show that at a given porosity, a synthetically remolded specimen has on average a 2MPa lower vertical effective stress than the original intact specimen. Pre-consolidation effective stresses measured for Constant Rate of Strain (CRS) consolidation tests on 11 MTD and 13 non-MTD Ursa specimens suggest that the pre-consolidation stresses are approximately the same whether within or outside of an MTD. We further explored these hypotheses through CRS tests on 3 intact Ursa core specimens above MTD-2 (75mbsf), below MTD-2 (125mbsf) and within MTD-2 (115mbsf). Our results show (1) Weaker consolidation curves for MTD vs. non-MTD specimens; (2) Decreased sediment compressibility correlating with decline in porosity, irrespective of location within MTD vs non MTD; (3) Slightly higher permeability within the MTD, but still within the range of Ursa mudstones; and (4) No distinction in linear pre-consolidation stress trend between MTD and non-MTD specimens. Ultimately, MTDs pose a hazard because it takes longer for suction anchor piles and jetted conductors – installed for production platforms – to penetrate MTDs relative to bounding sediment.

History of pore pressure build up and slope instability in mud-dominated
sediments of Ursa Basin, Gulf of Mexico continental slope
Roger Urgeles, Jacques Locat, Derek E. Sawyer, Peter B. Flemings, Brandon Dugan4 and Nguyen Thi Thanh Binh

The Ursa Basin, at ~1000 m depth on the Gulf of Mexico continental slope, contains numerous Mass Transport Deposits (MTDs) of Pleistocene to Holocene age. IODP Expedition 308 drilled three sites through several of these MTDs and encompassing sediments. Logs, sedimentological and geotechnical data were collected at these sites and are used in this study for input to basin numerical models. The objective of this investigation was to understand how sedimentation history, margin architecture and sediment properties couple to control pore pressure build-up and slope instability at Ursa. Measurements of porosity and stress state indicate that fluid overpressure is similar at the different sites (in the range of 0.5 to 0.7) despite elevated differences in sedimentation rates. Modeling results indicate that this results from pore pressure being transferred from regions of higher to lower overburden along an underlying more permeable unit: the Blue Unit. Overpressure started to develop at ~53 ka, which induced a significant decrease in FoS from 45ka, especially where overburden is lower.

Failure caused by breaching in subaqueous sand
Yao You, Peter B. Flemings, David Mohrig

Submarine failures can be divided into two categories: liquefaction failure and breaching failure. During liquefaction failure the sediment matrix contracts while during breaching failure the sediment matrix dilates. Dilation causes the pore pressure in the sediment deposit to decrease, thereby temporarily increasing its shear strength. The tangent of failure angle increases in proportion with the ratio of effective stress to total stress: . Degree of dilation is greatest near the failure front and decays quadratically with distance away from failure. Finer sand or poorly sorted sand creates a higher failure angle and slower erosion rate during breaching because of stronger dilative response and lower diffusivity. In preliminary experiments we have documented pressure drawdown and identified the fraction due to dilation and the part due to change in stresses. We will present recent results from laboratory experiments and a numerical model that characterize how the behaviors of the dilative failures vary with different sand compositions.

Posted October 2009

June 10, 2009 - Hilary Strong, an M.S. student with the UT GeoFluids Consortium, received third place in the AAPG student poster competition for her Poster entitled, Consolidation Characteristics of Mass Transport Deposits in Ursa Basin, Northern Gulf of Mexico

ABSTRACT: Seismic, core, and logging data from Integrated Ocean Drilling Program (IODP) Expedition 308 record multiple Mass Transport Deposits (MTDs) within the upper 600 meters below seafloor (mbsf) of the Ursa Basin, northern Gulf of Mexico. The most prominent, MTD-2, is 35 to 100m thick, spans all three drill sites – U1324 U1323 and U1322 – and is located approximately 100mbsf. MTD-2 is seismically imaged with a positive, low-amplitude top reflection, and negative, high-amplitude basal reflection. MTD-2 is identified in core and logging data as a low porosity, high bulk density, zone. At U1324, the basal sediments of MTD-2 are 7 porosity units less than those immediately below, while at U1322, the basal sediments are 10 porosity units less. This decline in porosity corresponds to a 5% increase in bulk density from overlying bounding sediments to MTD-2. We hypothesize that MTD densification is a result of sediment remolding during debris flow. Remolding destroys the original chaotic fabric, resulting in shear-aligned grains that have lower porosity. We also suggest that the arrested flow is buried and consolidated under uniaxial strain. Initial high resolution x-ray texture goniometry (HRXTG) fabric analysis shows greater basal plane alignment of smectite and chlorite in a MTD specimen, compared to a non-MTD specimen. Consolidation curves from initial uniaxial experiments show that at a given porosity, a synthetically remolded specimen has on average a 2MPa lower vertical effective stress than the original intact specimen. Pre-consolidation effective stresses measured for Constant Rate of Strain (CRS) consolidation tests on 11 MTD and 13 non-MTD Ursa specimens suggest that the pre-consolidation stresses are approximately the same whether within or outside of an MTD. We will further explore these hypotheses through HRXTG fabric analysis and CRS tests on natural and synthetically remolded Ursa core specimens. If our hypotheses are correct, we expect (1) weaker consolidation curves for MTD vs. non-MTD specimens; (2) Similar consolidation curves for MTD and remolded specimens; (3) No distinction in linear pre-consolidation stress trend between MTD and non-MTD specimens; and (4) Chaotic fabric in non-MTDs, and shear-aligned fabric in remolded and MTD specimens. Ultimately, MTDs pose a hazard because it takes longer for suction anchor piles and jetted conductors – installed for production platforms – to penetrate MTDs relative to bounding sediment.

Posted June 2009