Subsurface gas hydrates in the northern Gulf of Mexico

Boswell, Ray; Collett, Timothy S.; Frye, Matthew; Shedd, William; McConnell, Daniel R.; Shelander, Dianna

doi:10.1016/j.marpetgeo.2011.10.003

Cited by 299 publications

(284 citation statements)

References 71 publications

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“…Zones of high amplitude reflections occurring above the BSR akin to the Upper BSRs we observe in our seismic data were also found in the Nankai prism [75], in the GoM [6,76], and in the eastern Nankai Trough [67,77]. Core analyses at those sites determined those reflections marked the top of highly concentrated gas hydrate zones [47,67].…”

Section: Bottom Simulating Reflections (Bsrs)supporting

confidence: 66%

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

2017

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Methane hydrate concentrated zones (MHCZs) have become targets for energy exploration along continental margins worldwide. In 2013, exploratory drilling in the eastern Nankai Trough at Daini Atsumi Knoll confirmed that MHCZs tens of meters thick occur directly above bottom simulating reflections imaged in seismic data. This study uses 3-dimensional (3D) seismic and borehole data collected from the Kumano Basin offshore Japan to identify analogous MHCZs. Our survey region is located~100 km southwest of the Daini Atsumi Knoll, site of the first offshore gas hydrate production trial. Here we provide a detailed analysis of the gas hydrate system within our survey area of the Kumano forearc including: (1) the 3D spatial distribution of bottom simulating reflections; (2) a thickness map of potential MHCZs; and (3) a volumetric gas-in-place estimate for these MHCZs using constraints from our seismic interpretations as well as previously collected borehole data. There is evidence for two distinct zones of concentrated gas hydrate 10-90 m thick, and we estimate that the amount of gas-in-place potentially locked up in these MHCZs is 1.9-46.3 trillion cubic feet with a preferred estimate of 15.8 trillion cubic feet. Keywords: gas hydrates; Kumano Basin; bottom simulating reflections; methane hydrate exploration; 3D seismic interpretation; Nankai Trough IntroductionNatural gas hydrates (GH) are crystalline inclusion compounds that form within the pore space of marine sediments along continental margins worldwide. These hydrate deposits are stable at specific pressure-temperature relationships, host highly compressed gas molecules (most commonly methane), and are proposed to be the largest dynamic reservoir of organic carbon on this planet [1][2][3]. GHs have enticed global interest for several reasons including climate change and potential slope stability hazards, but primarily because these deposits could prove to be an unconventional energy resource [3,4]. At the exploration stage, it is important to develop systematic GH exploration methods that consider gas source, migration mechanisms into the hydrate stability field, zones of free gas, indicators of gas hydrate accumulation, and at least a first order volumetric gas-in-place estimate for apparent zones of concentrated hydrates [5,6].Seismic imaging is an important tool for identifying GH because both GH and free gas alter the physical properties of marine sediments, which will in turn affect the travel path and attenuation of the seismic wavelet [7][8][9]. Concentrated hydrate deposits tend to form at and just above the base of gas hydrate stability (BGHS). This results in a sharp contrast in mechanical properties at the phase boundary between GH saturated layers overlying a zone where free gas, water, and potentially non-cementing hydrate occupy the pore space [10]. This contrast in physical properties is expressed in seismic data as bottom simulating reflections (BSRs), and BSRs remain our strongest remotely sensed indicator to infer the presence of GH [11...

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Section: Bottom Simulating Reflections (Bsrs)supporting

confidence: 66%

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

2017

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“…If the overall transport rates remain relatively low under these circumstances, free gas may reform gas hydrate near the base of the GHSZ. In longrange migration, fluid flow can transport methane over very large distances and has often been proposed as the primary migration process for gas hydrate formation in permeable sand layers (e.g., Uchida et al, 2009;Boswell et al, 2012). Methane transported over long distances by fluid flow and advection could be microbial, as in short-range migration, or thermogenic, being generated at high temperatures well below the base of the GHSZ.…”

Section: Methane Transport Mechanisms In Gas Hydrate Systemsmentioning

confidence: 99%

“…For gas hydrate deposits formed by long-range migration, methane (microbial or thermogenic) comes from below and is transported upward into the GHSZ. If long-range migration is the primary active methane transport mechanism, gas hydrate deposits can be predicted using a petroleum systems approach that considers the presence of deep methane sources, migration pathways, and reservoir layers (e.g., Boswell et al, 2012). With the long-range migration mechanism, the amount of methane generated in situ within the GHSZ is not a critical requirement for gas hydrate formation.…”

Section: Methane Transport Mechanisms In Gas Hydrate Systemsmentioning

confidence: 99%

Testing short-range migration of microbial methane as a hydrate formation mechanism: Results from Andaman Sea and Kumano Basin drill sites and global implications

Malinverno

Goldberg

2015

Earth and Planetary Science Letters

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Methane gas hydrates in marine sediments often concentrate in coarse-grained layers surrounded by finegrained marine muds that are hydrate-free. Methane in these hydrate deposits is typically microbial, and must have migrated from its source as the coarse-grained sediments contain little or no organic matter. In "long-range" migration, fluid flow through permeable layers transports methane from deeper sources into the gas hydrate stability zone (GHSZ). In "short-range" migration, microbial methane is generated within the GHSZ in fine-grained sediments, where small pore sizes inhibit hydrate formation. Dissolved methane can then diffuse into adjacent sand layers, where pore size does not restrict hydrate formation and hydrates can accumulate. Short-range migration has been used to explain hydrate accumulations in sand layers observed in drill sites on the northern Cascadia margin and in the Gulf of Mexico. Here we test the feasibility of short-range migration in two additional locations, where gas hydrates have been found in coarse-grained volcanic ash layers (Site NGHP-01-17, Andaman Sea, Indian Ocean) and turbidite sand beds (Site IODP-C0002, Kumano forearc basin, Nankai Trough, western Pacific). We apply reactiontransport modeling to calculate dissolved methane concentration and gas hydrate amounts resulting from microbial methane generated within the GHSZ. Model results show that short-range migration of microbial methane can explain the overall amounts of methane hydrate observed at the two sites. Short-range migration has been shown to be feasible in diverse margin environments and is likely to be a widespread methane transport mechanism in gas hydrate systems. It only requires a small amount of organic carbon and sediment sequences consisting of thin coarse-grained layers that can concentrate microbial methane generated within thick fine-grained sediment beds; these conditions are common along continental margins around the globe.

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“…Numerous studies have examined these and other GOM phenomena, including seeps (MacDonald et al, 2002), complex stratigraphy (Cooper and Hart, 2003), and various interactions between gas hydrates, free gas, porewater chemistry, heat flow, and fluid flow (Boswell et al, 2012;Ruppel et al, 2005).…”

Section: Gulf Of Mexico (Md02) (Jip Leg 1)mentioning

confidence: 99%

“…Inter-bedded finer-grained sediment, however, may also contain some gas hydrate. Sandy GH reservoirs are not only present in permafrost-related Arctic locations, but are also offshore, e.g., Nankai Trough (Uchida and Takashi, 2004)) and the Gulf of Mexico (Hutchinson et al, 2008a;Robertson et al, 2013;Boswell et al, 2012).…”

Section: Grain Sizementioning

confidence: 99%

Comparison of the physical and geotechnical properties of gas-hydrate-bearing sediments from offshore India and other gas-hydrate-reservoir systems

Winters

Wilcox-Cline

Long

et al. 2014

Marine and Petroleum Geology

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a b s t r a c tThe sediment characteristics of hydrate-bearing reservoirs profoundly affect the formation, distribution, and morphology of gas hydrate. The presence and type of gas, porewater chemistry, fluid migration, and subbottom temperature may govern the hydrate formation process, but it is the host sediment that commonly dictates final hydrate habit, and whether hydrate may be economically developed.In this paper, the physical properties of hydrate-bearing regions offshore eastern India (KrishnaGodavari and Mahanadi Basins) and the Andaman Islands, determined from Expedition NGHP-01 cores, are compared to each other, well logs, and published results of other hydrate reservoirs. Properties from the hydrate-free Kerala-Konkan basin off the west coast of India are also presented. Coarser-grained reservoirs (permafrost-related and marine) may contain high gas-hydrate-pore saturations, while finer-grained reservoirs may contain low-saturation disseminated or more complex gas-hydrates, including nodules, layers, and high-angle planar and rotational veins. However, even in these finegrained sediments, gas hydrate preferentially forms in coarser sediment or fractures, when present. The presence of hydrate in conjunction with other geologic processes may be responsible for sediment porosity being nearly uniform for almost 500 m off the Andaman Islands.Properties of individual NGHP-01 wells and regional trends are discussed in detail. However, comparison of marine and permafrost-related Arctic reservoirs provides insight into the inter-relationships and common traits between physical properties and the morphology of gas-hydrate reservoirs regardless of location. Extrapolation of properties from one location to another also enhances our understanding of gas-hydrate reservoir systems. Grain size and porosity effects on permeability are critical, both locally to trap gas and regionally to provide fluid flow to hydrate reservoirs. Index properties corroborate more advanced consolidation and triaxial strength test results and can be used for predicting behavior in other NGHP-01 regions. Pseudo-overconsolidation is present near the seafloor and is underlain by underconsolidation at depth at some NGHP-01 locations.Published by Elsevier Ltd.

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Subsurface gas hydrates in the northern Gulf of Mexico

Cited by 299 publications

References 71 publications

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

Testing short-range migration of microbial methane as a hydrate formation mechanism: Results from Andaman Sea and Kumano Basin drill sites and global implications

Comparison of the physical and geotechnical properties of gas-hydrate-bearing sediments from offshore India and other gas-hydrate-reservoir systems

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