Overpressure and consolidation near the seafloor of Brazos‐Trinity Basin IV, northwest deepwater Gulf of Mexico

Schneider, J.; Flemings, Peter B.; Dugan, Brandon; Long, Hui; Germaine, John T.

doi:10.1029/2008jb005922

Cited by 31 publications

(18 citation statements)

References 51 publications

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“…Currently, the timing, scale, and dynamics of slope failures along the Lesser Antilles Arc are only moderately constrained [e.g., Boudon et al, 2007;Watt et al, 2012;Le Friant et al, 2015]. Rapid sedimentation can elevate subsurface fluid pressure, promoting slope failure [e.g., Dugan and Flemings, 2000;Schneider et al, 2009], and recent studies suggest that the largest submarine landslide deposits offshore of Montserrat are complex multistage events in which the rapid deposition of debris avalanche deposits generated excess pore pressure in weaker undrained marine sediments downslope, resulting in progressive failure with relatively little downslope transport [Watt et al, 2012[Watt et al, , 2014. Le Friant et al [2015] make similar arguments, and note that the relatively intact, small-offset nature of marine deposits found in submarine slides offshore Montserrat indicates possible slow-slip deformation.…”

Section: Introductionmentioning

confidence: 99%

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure

et al. 2015

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Recent studies hypothesize that some submarine slides fail via pressure‐driven slow‐slip deformation. To test this hypothesis, this study derives pore pressures in failed and adjacent unfailed deep marine sediments by integrating rock physics models, physical property measurements on recovered sediment core, and wireline logs. Two drill sites (U1394 and U1399) drilled through interpreted slide debris; a third (U1395) drilled into normal marine sediment. Near‐hydrostatic fluid pressure exists in sediments at site U1395. In contrast, results at both sites U1394 and U1399 indicate elevated pore fluid pressures in some sediment. We suggest that high pore pressure at the base of a submarine slide deposit at site U1394 results from slide shearing. High pore pressure exists throughout much of site U1399, and Mohr circle analysis suggests that only slight changes in the stress regime will trigger motion. Consolidation tests and permeability measurements indicate moderately low (~10−16–10−17 m2) permeability and overconsolidation in fine‐grained slide debris, implying that these sediments act as seals. Three mechanisms, in isolation or in combination, may produce the observed elevated pore fluid pressures at site U1399: (1) rapid sedimentation, (2) lateral fluid flow, and (3) shearing that causes sediments to contract, increasing pore pressure. Our preferred hypothesis is this third mechanism because it explains both elevated fluid pressure and sediment overconsolidation without requiring high sedimentation rates. Our combined analysis of subsurface pore pressures, drilling data, and regional seismic images indicates that slope failure offshore Martinique is perhaps an ongoing, creep‐like process where small stress changes trigger motion.

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Section: Introductionmentioning

confidence: 99%

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure

et al. 2015

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“…The slope, λ , of the critical state line when projected onto the

v - \ln p^{'} [normalkPa]

space (with v as the specific volume and

p^{'}

as effective pressure) determines the compressibility. Values for λ are highly variable, with an average upper limit 0.25 for hemipelagic sediments [ Valent et al , ; Demars , ; Bayer and Wetzel , ; Leynaud et al , ; Dugan , ; Schneider et al , ]. The elastic logarithmic bulk modulus, κ , is commonly estimated as 1/10 of λ [ Powrie , ] and is 0.025 in all models.…”

Section: Methodsmentioning

confidence: 99%

What causes large submarine landslides on low gradient (<2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation?

et al. 2015

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Submarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine megaslides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/kyr), such as off northwest Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties, and stratigraphic layer configurations. The simulations show that, in general, it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes.

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“…This abnormally high pore pressure gradient has caused many drilling incidents (eg, kicks and blowouts). However, not many cases were reported on pore pressure prediction and overpressure mechanism studies in shale plays (eg, []).…”

Section: Introductionmentioning

confidence: 99%

Geological characteristics and abnormal pore pressure prediction in shale oil formations of the Dongying depression, China

Zhang

Yong

et al. 2020

Energy Science & Engineering

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Pore pressures in shale oil formations in the Dongying depression of the Bohai BayBasin are highly overpressured. Understanding overpressure principles not only can reveal the mechanism of shale oil generation to provide prospects for shale oil exploration and production, but also can reduce potential drilling risks and provide insights for sweet spot identification. Overpressure generation mechanisms are analyzed based on petrophysical data, core analysis, sedimentation rate, oil saturation, and smectite and illite data. We find that undercompaction, oil generation, and smectite and illite transformation are primary causes of overpressures. Undercompaction is the major cause of overpressures in the Es3 formations because of their rapid deposition rate of 300-700 m/m.y. For the overpressures primarily generated by undercompaction, sonic transit time can be used to predict shale pore pressure with correctly selected depth-dependent normal compaction trend. In the Es3 and Es4 formations, overpressure data are consistent with the increase of vitrinite reflectance and oil saturation, indicators of oil generation. Additionally, in shallow formations, starting at about 2000 m, the smectite to illite transformation occurs, which makes rock property changes with depth. A composite normal compaction trendline is proposed to account for the smectite to illite transformation. Using well log data, the shale oil formations can be identified and there are two shale oil formations in the studied area, and a shale oil geo-marker is found. At this geo-marker, the pore pressure gradient reaches the highest value. This high pore pressure behavior is beneficial for shale oil production because of a higher pore pressure corresponds to a higher production. K E Y W O R D Soil generation, petroleum geology, pore pressure prediction, shale oil, sonic transit time, undercompaction

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Overpressure and consolidation near the seafloor of Brazos‐Trinity Basin IV, northwest deepwater Gulf of Mexico

Cited by 31 publications

References 51 publications

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure

What causes large submarine landslides on low gradient (<2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation?

Geological characteristics and abnormal pore pressure prediction in shale oil formations of the Dongying depression, China

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