Dealing with shallow-water flow in the deepwater Gulf of Mexico

Ostermeier, R.M.; Pelletier, J.H.; Winker, Charles D.; Nicholson, J. W. G.; Rambow, Frederick H.K.; Cowan, K.M.

doi:10.1190/1.1497320

Cited by 66 publications

(35 citation statements)

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“…In fact, at Ursa, pressure measurements record signifi cant present-day overpressure throughout this section (Flemings et al, 2008;Ostermeier et al, 2002).…”

Section: Discussionmentioning

confidence: 95%

Continuous deep-seated slope failure recycles sediments and limits levee height in submarine channels

Sawyer

Flemings

Nikolinakou

2014

Geology

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Channel-levee systems are responsible for constructing deep sea fans, among the largest sedimentary deposits on Earth. Levee height plays a key role in defi ning the volume and texture of the material that is deposited in the bounding levees, and thus the morphology of submarine fans. Models of channel formation and evolution generally assume that the levees aggrade in response to the cumulative overspill of turbidity fl ows, and that their height is controlled by these fl ows. In contrast, we show that levee growth in the Ursa Basin (Gulf of Mexico) is limited by the mechanical strength of the levee, not the fl ow behavior. While many studies document sidewall failures in levee systems, our poro-mechanical model is the fi rst to demonstrate that collapse of levees is a large-scale, deep-seated process driven by the interaction of levee formation and high fl uid pressure. Rapid deposition of a regional sand unit induced large fl uid overpressure in the underlying mud, which preconditioned the system for levee failure, which then fed a large volume of sediment back into the channel-levee system. Long-lived levee failures continually reintroduced previously deposited levee material back into the channel system. This implies that a large volume of sediment is continuously recycled, which has not been previously understood. Turbidite fl ow models generally assume that fl ows progressively lose their fi ne-grained component due to levee overspill as they traverse the channel. In contrast, we show a mechanism by which fi ne-grained material can re-enter the system in large quantities, and this has signifi cant and broad importance for models of channel and fan evolution. We also show that that levee failure introduces signifi cant unconformities, in contrast with the common assumption that levees offer complete and high-resolution records of climate, tectonics, and sea level.

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“…In fact, at Ursa, pressure measurements record signifi cant present-day overpressure throughout this section (Flemings et al, 2008;Ostermeier et al, 2002).…”

Section: Discussionmentioning

confidence: 95%

Continuous deep-seated slope failure recycles sediments and limits levee height in submarine channels

Sawyer

Flemings

Nikolinakou

2014

Geology

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“…The low permeability of the sediments and the short time between cutting the hole and imaging indicate approximately undrained conditions associated with borehole failure. (Moore et al, 2007;Ostermeier et al, 2000Ostermeier et al, , 2002 Ratio of observed excess pore pressure to difference between lithostatic and hydrostatic pressure (λ*) 0.6 0 .6 Sediment probe measurements Pore pressure ( 1 -ν))σ v for a setting with no lateral expansion]; Twiss and Moores, 1992, p. 189 Note: The stress regime is extensional with submarine sliding; therefore, to a first order, σ v = σ 1. Also, because the slope at Site U1322 is very low (~3°), and the principal stress has to be perpendicular to the free surface (water bottom) of no shear stress, σ v is essentially equivalent to σ 1 .…”

Section: State Of Stress In the Boreholementioning

confidence: 99%

“…The vertical stress is derived from the integration of borehole sample wet bulk density measurements and is very reliable. The estimate of minimum principal stress (σ 3 ) is from hydrofracture and leakoff tests (Ostermeier et al, 2000(Ostermeier et al, , 2002Moore et al, 2007) conducted near MARS oil production platform (see Fig. 1).…”

Section: State Of Stress In the Boreholementioning

confidence: 99%

Untitled

Moore

2011

Geosphere

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“…Once penetrated these sands flow into the wells, washout, erode around the exterior of casing strings, and locally flow to the surface [1]. Once penetrated these sands flow into the wells, washout, erode around the exterior of casing strings, and locally flow to the surface [1].…”

Section: Introductionmentioning

confidence: 99%

“…Once penetrated these sands flow into the wells, washout, erode around the exterior of casing strings, and locally flow to the surface [1]. In the Ursa drilling area (Figure 1) the shallow-water sands are overpressured which initiates the flow into the boreholes [1,3]. In areas where this behavior has occurred, the seafloor appears to be undergoing subsidence associated with sediment loss at depth.…”

Section: Introductionmentioning

confidence: 99%

Fluid Migration and State of Stress Above the Blue Unit, Ursa Basin: Relationship to the Geometry of Injectites

Moore¹,

Iturrino

Flemings

et al. 2007

All Days

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSands penetrated at shallow depths (< 1 km) in the Gulf of Mexico can flow to the surface and undermine seafloor installations. Here we explore aspects of natural fluid expulsion structures from these "shallow-water sands". Highresolution seismic data shows no obvious sand injection structures from the Blue Unit, a shallow-water sand, in the Ursa area, but perhaps nascent dike formation. Also, channel sands stratigraphically above the Blue Unit are overpressured, with a possible pressure source in the latter. In the Ursa area the maximum principal stress is vertical and constrained by the integrated unit weight of the sediments at IODP Site U1324. The stress necessary to form hydrofractures (the minimum principal stress plus negligible tensional strength of the sediment) is about 85% of the maximum principal stress indicating an approximately isotropic state of stress. High Poisson's ratios (0.46-0.49), determined from wireline compressional and shear wave velocities at Site U1324, are also consistent with a nearly isotropic state of stress at shallow depths. Estimated maximum fluid pressures are about 80% of the total overburden stress, less than necessary to hydrofracture the sediment. Therefore, the fluid pressure is insufficient to form sand injectites. The formation of sand injectites, as observed in the geologic record, may require very high fluid pressures, approaching lithostatic values. Diverse orientations of ancient injectites support the necessity of very high fluid pressures and a nearly isotropic state of stress.

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Dealing with shallow-water flow in the deepwater Gulf of Mexico

Cited by 66 publications

References 0 publications

Continuous deep-seated slope failure recycles sediments and limits levee height in submarine channels

Continuous deep-seated slope failure recycles sediments and limits levee height in submarine channels

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Fluid Migration and State of Stress Above the Blue Unit, Ursa Basin: Relationship to the Geometry of Injectites

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