Prospecting for marine gas hydrate resources

Boswell, Ray; Shipp, Craig; Reichel, Thomas; Shelander, Dianna; Saeki, Tatsuo; Frye, Matthew; Shedd, William; Collett, Timothy S.; McConnell, Daniel R.

doi:10.1190/int-2015-0036.1

Cited by 97 publications

(51 citation statements)

References 49 publications

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“…Thus, the term BGHSZ is to be interpreted as base of structure I gas hydrate, or in line with previous suggested terminology, BS I GHSZ [e.g., Boswell et al, 2016;Paganoni et al, 2016]. We further want to emphasize that our study is not concerning the detailed and local gas hydrate concentrations with depth and any localized variations therein.…”

Section: 1002/2017gc006805mentioning

confidence: 99%

Observed correlation between the depth to base and top of gas hydrate occurrence from review of global drilling data

Riedel

Collett

2017

Geochem Geophys Geosyst

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A global inventory of data from gas hydrate drilling expeditions is used to develop relationships between the base of structure I gas hydrate stability, top of gas hydrate occurrence, sulfate‐methane transition depth, pressure (water depth), and geothermal gradients. The motivation of this study is to provide first‐order estimates of the top of gas hydrate occurrence and associated thickness of the gas hydrate occurrence zone for climate‐change scenarios, global carbon budget analyses, or gas hydrate resource assessments. Results from publically available drilling campaigns (21 expeditions and 52 drill sites) off Cascadia, Blake Ridge, India, Korea, South China Sea, Japan, Chile, Peru, Costa Rica, Gulf of Mexico, and Borneo reveal a first‐order linear relationship between the depth to the top and base of gas hydrate occurrence. The reason for these nearly linear relationships is believed to be the strong pressure and temperature dependence of methane solubility in the absence of large difference in thermal gradients between the various sites assessed. In addition, a statistically robust relationship was defined between the thickness of the gas hydrate occurrence zone and the base of gas hydrate stability (in meters below seafloor). The relationship developed is able to predict the depth of the top of gas hydrate occurrence zone using observed depths of the base of gas hydrate stability within less than 50 m at most locations examined in this study. No clear correlation of the depth to the top and base of gas hydrate occurrences with geothermal gradient and sulfate‐methane transition depth was identified.

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Section: 1002/2017gc006805mentioning

confidence: 99%

Observed correlation between the depth to base and top of gas hydrate occurrence from review of global drilling data

Riedel

Collett

2017

Geochem Geophys Geosyst

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“…Core analyses at those sites determined those reflections marked the top of highly concentrated gas hydrate zones [47,67]. Similar thin, positive amplitude reflections above the BSR have also been interpreted to represent the top of a concentrated gas hydrate zones along the Chilean margin [78].…”

Section: Bottom Simulating Reflections (Bsrs)mentioning

confidence: 90%

“…Incidences of blanking below the BSR could be from either gas saturated muds, or acoustic attenuation of the seismic wave as it passes through a thick GH zone. Drilling in the GoM demonstrated that blanking above the BSR reflects minor hydrate saturations and is not considered a prospective resource zone [47]. Thus, we do not include zones of blanking in our gas-in-place estimate.…”

Section: Seismic Evidence For Gas Source and Migration Pathways Into mentioning

confidence: 99%

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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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“…To understand the spatial distribution of the reservoir quality in the upper unit, we performed an amplitude map analysis by using the reservoir top seismic horizon. Basically, NGH-bearing sediments generate an increase in impedance at the upper contact, which produces a positive or peak event (in the 0 • phase North American polarity) and a strong reflection in the seismic data (e.g., [15,17]). Therefore, seismic mapping of the amplitude is one of the generalized approaches to identify and evaluate the potential direct indication of NGH occurrence.…”

Section: Methods For the Understanding The Spatial Distribution Of Thementioning

confidence: 99%

Characterization and Prediction of the Gas Hydrate Reservoir at the Second Offshore Gas Production Test Site in the Eastern Nankai Trough, Japan

2017

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Abstract:Following the world's first offshore production test that was conducted from a gas hydrate reservoir by a depressurization technique in 2013, the second offshore production test has been planned in the eastern Nankai Trough. In 2016, the drilling survey was performed ahead of the production test, and logging data that covers the reservoir interval were newly obtained from three wells around the test site: one well for geological survey, and two wells for monitoring surveys, during the production test. The formation evaluation using the well log data suggested that our target reservoir has a more significant heterogeneity in the gas hydrate saturation distribution than we expected, although lateral continuity of sand layers is relatively good. To evaluate the spatial distribution of gas hydrate, the integration analysis using well and seismic data was performed. The seismic amplitude analysis supports the lateral reservoir heterogeneity that has a significant positive correlation with the resistivity log data at the well locations. The spatial distribution of the apparent low-resistivity interval within the reservoir observed from log data was investigated by the P-velocity volume derived from seismic inversion. The integrated results were utilized for the pre-drill prediction of the reservoir quality at the producing wells. These approaches will reduce the risk of future commercial production from the gas hydrate reservoir.

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Prospecting for marine gas hydrate resources

Cited by 97 publications

References 49 publications

Observed correlation between the depth to base and top of gas hydrate occurrence from review of global drilling data

Observed correlation between the depth to base and top of gas hydrate occurrence from review of global drilling data

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

Characterization and Prediction of the Gas Hydrate Reservoir at the Second Offshore Gas Production Test Site in the Eastern Nankai Trough, Japan

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