Gas hydrates in coarse-grained reservoirs interpreted from velocity pull up: Mississippi Fan, Gulf of Mexico

Madof, Andrew S.

doi:10.1130/g40031.1

Cited by 15 publications

(25 citation statements)

References 11 publications

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“…Therefore, we tentatively reject carbonate mechanisms as viable drivers of VPU for the P3 accumulation and hypothesize that gas hydrates are more plausible. If present, gas hydrates may have been charged by both short‐range diffusion of dissolved gas (see Madof, ) and faulting at depth (Figure c); the former is generally associated with a biogenic origin and the latter with a thermogenic source (see Weimer et al, for discussion of hydrocarbon systems in Mississippi Canyon and Atwater Valley). Future work is needed to better evaluate source rock areas, migration mechanisms and pathways, and gas hydrate formation time scales.…”

Section: Discussionmentioning

confidence: 99%

“…Velocities from well logs were partitioned into values associated with either sand‐gravel (coarse) or mud‐silt (fine) as determined from cuttings and core, and were fitted to compaction‐driven exponential trends of the following form (Japsen et al, ):

v = v_{m} - ((), v_{m} - v_{c}) e^{- z / b}

where v is V p , v m is the upper limit of matrix V p , v c is V p at critical porosity (constrained as 1,500 m/s), z is depth, and b is a positive constant. Curves from equation were used to calculate lithologically driven travel time deficits using the following equation (modified from Madof, ):

\begin{matrix} true \\ {italicVPU}_{lith} (t) = 2 \sum_{i = 0}^{n} [(\frac{v_{{coarse}_{normali}}}{v_{{fine}_{i}}} - 1) \frac{{∆ z}_{i}}{v_{{fine}_{i}}}] \end{matrix}

where VPU lith (t) is the VPU caused by lithologic contrasts, v coarse is the V p associated with the coarse fraction, v fine is the V p associated with the fine fraction, and Δ z i is the vertical sampling rate of the data set. To place VPU lith into the same domain as seismic data (TWTT), one‐dimensional depth‐to‐time corrections of the following form were used:

{TWTT}_{msbsf} = 2 \sum_{i = 0}^{n} ((), \frac{{∆ z}_{i}}{v_{{fine}_{i}}})

where TWTT msbsf is TWTT (ms) below the seafloor.…”

Section: Methodsmentioning

confidence: 99%

“…where v is V p , v m is the upper limit of matrix V p , v c is V p at critical porosity (constrained as 1,500 m/s), z is depth, and b is a positive constant. Curves from equation (1) were used to calculate lithologically driven travel time deficits using the following equation (modified from Madof, 2018):…”

Section: Borehole Methodsmentioning

confidence: 99%

“…Bathymetric map and seismic section of the Mississippi Fan, Gulf of Mexico. (a) Location map (from geomapapp.org) displaying orientation of P0–P3 deep‐water channelized turbidite deposits (modified from Madof, ), location of solid, liquid, and gas hydrocarbon discoveries (from Milkov and Sassen, ), and protraction areas (Atwater Valley = AT, DeSoto Canyon = DC, Green Canyon = GC, Henderson = HE, Lloyd Ridge = LL, Lund = LU, Mississippi Canyon = MC). (b) Uninterpreted (top) and interpreted (bottom) seismic section showing stratigraphic architecture of P0 (deeper) and P1–P3 (shallower) accumulations.…”

Section: Introductionmentioning

confidence: 99%

“…Although the study of Madof () concluded that a large and formerly unknown gas hydrate province may be located in Mississippi Fan sediments, it noted that lithologically driven differences in V p could also create VPUs. This concept was further elaborated in Cook and Portnov (), which concluded that water‐saturated sands contained within the P3 reservoir may be responsible for a portion, and potentially all, of observed VPUs (see also Madof, ).…”

Section: Introductionmentioning

confidence: 99%

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Interpretation of Gas Hydrate Province Supported by Petrophysical Analyses: Mississippi Fan, Gulf of Mexico

Madof

Baumgardner

Laugier

et al. 2019

Geophysical Research Letters

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A vast accumulation of high‐saturation gas hydrates has been hypothesized to be present in the central Gulf of Mexico; the interpretation was based on seismic travel time deficits underlying high velocity Pleistocene coarse‐grained turbidites. While these deposits could represent one of the largest‐known gas hydrate reservoirs, some workers have concluded that lithologic contrasts are instead the primary cause of observed velocity pull‐ups. Here, using cuttings and core, well logs, and seismic data from the Mississippi Fan, we demonstrate that lithologic differences can account for a maximum of ~6–33% of the total observed travel time deficits. This conclusion supports the previous interpretation of a gas hydrate province, provides a basis for distinguishing the cause of velocity pull‐ups, and suggests that the future of gas hydrate exploration should continue to include the coarsest‐grained component of the Earth's largest near‐seafloor submarine fans.

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Section: Discussionmentioning

confidence: 99%