scholarly journals A New Dynamic Modeling Approach to Predict Microbial Methane Generation and Consumption in Marine Sediments

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5671
Author(s):  
Mahboubeh Rahmati-Abkenar ◽  
Milad Alizadeh ◽  
Marcelo Ketzer
Keyword(s):  
Marine Sediments ◽  
Gas Hydrate ◽  
Dissolved Inorganic Carbon ◽  
Clean Energy ◽  
Reaction Model ◽  
Magnesium Concentration ◽  
Biogeochemical Processes ◽  
Pore Waters ◽  
Transport Reaction ◽  
Free Gas

Methane, as a clean energy source and a potent greenhouse gas, is produced in marine sediments by microbes via complex biogeochemical processes associated with the mineralization of organic matter. Quantitative modeling of biogeochemical processes is a crucial way to advance the understanding of the global carbon cycle and the past, present, and future of climate change. Here, we present a new approach of dynamic transport-reaction model combined with sediment deposition. Compared to other studies, since the model does not need the methane concentration in the bottom of sediments and predicts that value, it provides us with a robust carbon budget estimation tool in the sediment. We applied the model to the Blake Ridge region (Ocean Drilling Program, Leg 164, site 997). Based on seafloor data as input, our model remarkably reproduces measured values of total organic carbon, dissolved inorganic carbon, sulfate, calcium, and magnesium concentration in pore waters and the in situ methane presented in three phases: dissolved in pore water, trapped in gas hydrate, and as free gas. Kinetically, we examined the coexistence of free gas and hydrate, and demonstrated how it might affect methane gas migration in marine sediment within the gas hydrate stability zone.

scholarly journals A transfer function for the prediction of gas hydrate inventories in marine sediments

2010 ◽  
Vol 7 (1) ◽  
pp. 1057-1099
Author(s):  
M. Marquardt ◽  
C. Hensen ◽  
E. Piñero ◽  
K. Wallmann ◽  
M. Haeckel
Keyword(s):  
Transfer Function ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Numerical Models ◽  
Accumulation Rate ◽  
Parameter Analysis ◽  
General Validity ◽  
Transport Reaction ◽  
Degradation Rates ◽  
Wide Range

Abstract. A simple prognostic tool for gas hydrate (GH) quantification in marine sediments is presented based on a diagenetic transport-reaction model approach. One of the most crucial factors for the application of diagenetic models is the accurate formulation of microbial degradation rates of particulate organic carbon (POC) and the coupled biogenic CH4 formation. Wallmann et al. (2006) suggested a kinetic formulation considering the ageing effects of POC and accumulation of reaction products (CH4, CO2) in the pore water. This model is applied to data sets of several ODP sites in order to test its general validity. Based on a thorough parameter analysis considering a wide range of environmental conditions, the POC accumulation rate (POCar in g/cm2/yr) and the thickness of the gas hydrate stability zone (GHSZ in m) were identified as the most important and independent controls for biogenic GH formation. Hence, depth-integrated GH inventories in marine sediments (GHI in g of CH4 per cm2 seafloor area) can be estimated as: GHI = a · POCar · GHSZb · exp (−GHSZc/POCar/d) + e with a = 0.00214, b = 1.234, c = −3.339, d = 0.3148, e = −10.265. Several tests indicate that the transfer function gives a realistic approximation of the minimum potential GH inventory of low gas flux (LGF) systems. The overall advantage of the presented function is its simplicity compared to complex numerical models: only two easily accessible parameters are needed.

scholarly journals Estimation of the global inventory of methane hydrates in marine sediments using transfer functions

2012 ◽  
Vol 9 (1) ◽  
pp. 581-626 ◽  
Author(s):  
E. Piñero ◽  
M. Marquardt ◽  
C. Hensen ◽  
M. Haeckel ◽  
K. Wallmann
Keyword(s):  
Transfer Function ◽  
Organic Carbon ◽  
Marine Sediments ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Large Scale ◽  
Transfer Functions ◽  
Carbon Accumulation ◽  
Methane Hydrates ◽  
Transport Reaction

Abstract. The accumulation of gas hydrates in marine sediments is essentially controlled by the accumulation of particulate organic carbon (POCar) which is microbially converted into methane, the thickness of the gas hydrate stability zone (GHSZ) where methane can be trapped, and the delivery of methane from deep-seated sediments by ascending pore fluids and gas into the GHSZ. Recently, Marquardt et al. (2010) developed a transfer function to predict the gas hydrate inventory in diffusion-controlled geological systems based on POCar and GHSZ. We present a new parameterization of this function and apply it to global datasets of bathymetry, heat flow, seafloor temperature and organic carbon accumulation estimating a global mass of only 91 Gt of carbon (GtC) stored in marine methane hydrates. Seepage of methane-rich fluids is known to have a pronounced effect on gas hydrate accumulation. Therefore, we carried out a set of systematic model runs with the transport-reaction code in order to derive an extended transfer function explicitly considering upward fluid advection. Using averaged fluid velocities for active and passive margins, which were derived from mass balance considerations, this extended transfer function predicts the formation of gas hydrates along the continental margins worldwide. Different scenarios were investigated resulting in a global mass of sub-seafloor gas hydrates of 400–1100 GtC. Overall, our systematic approach allows to clearly and quantitatively distinguish between the effect of biogenic methane generation from POC and fluid advection on the accumulation of gas hydrate and hence, provides a simple prognostic tool for the estimation of large-scale and global gas hydrate inventories in marine sediments.

scholarly journals Estimation of the global inventory of methane hydrates in marine sediments using transfer functions

2013 ◽  
Vol 10 (2) ◽  
pp. 959-975 ◽  
Author(s):  
E. Piñero ◽  
M. Marquardt ◽  
C. Hensen ◽  
M. Haeckel ◽  
K. Wallmann
Keyword(s):  
Transfer Function ◽  
Marine Sediments ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Large Scale ◽  
Transfer Functions ◽  
Methane Hydrates ◽  
Continental Margins ◽  
Transport Reaction ◽  
Methane Generation

Abstract. The accumulation of gas hydrates in marine sediments is essentially controlled by the accumulation of particulate organic carbon (POC) which is microbially converted into methane, the thickness of the gas hydrate stability zone (GHSZ) where methane can be trapped, the sedimentation rate (SR) that controls the time that POC and the generated methane stays within the GHSZ, and the delivery of methane from deep-seated sediments by ascending pore fluids and gas into the GHSZ. Recently, Wallmann et al. (2012) presented transfer functions to predict the gas hydrate inventory in diffusion-controlled geological systems based on SR, POC and GHSZ thickness for two different scenarios: normal and full compacting sediments. We apply these functions to global data sets of bathymetry, heat flow, seafloor temperature, POC input and SR, estimating a global mass of carbon stored in marine methane hydrates from 3 to 455 Gt of carbon (GtC) depending on the sedimentation and compaction conditions. The global sediment volume of the GHSZ in continental margins is estimated to be 60–67 × 1015 m3, with a total of 7 × 1015 m3 of pore volume (available for GH accumulation). However, seepage of methane-rich fluids is known to have a pronounced effect on gas hydrate accumulation. Therefore, we carried out a set of systematic model runs with the transport-reaction code in order to derive an extended transfer function explicitly considering upward fluid advection. Using averaged fluid velocities for active margins, which were derived from mass balance considerations, this extended transfer function predicts the enhanced gas hydrate accumulation along the continental margins worldwide. Different scenarios were investigated resulting in a global mass of sub-seafloor gas hydrates of ~ 550 GtC. Overall, our systematic approach allows to clearly and quantitatively distinguish between the effect of biogenic methane generation from POC and fluid advection on the accumulation of gas hydrate, and hence, provides a simple prognostic tool for the estimation of large-scale and global gas hydrate inventories in marine sediments.

High-resolution seismic velocity analysis as a tool for exploring gas hydrate systems: An example from New Zealand’s southern Hikurangi margin

2016 ◽  
Vol 4 (1) ◽  
pp. SA1-SA12 ◽  
Author(s):  
Gareth J. Crutchley ◽  
Guy Maslen ◽  
Ingo A. Pecher ◽  
Joshu J. Mountjoy
Keyword(s):  
High Resolution ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Seismic Velocity ◽  
Coarse Grained ◽  
Velocity Analysis ◽  
Low Velocity ◽  
Free Gas ◽  
Velocity Models

The existence of free gas and gas hydrate in the pore spaces of marine sediments causes changes in acoustic velocities that overprint the background lithological velocities of the sediments themselves. Much previous work has determined that such velocity overprinting, if sufficiently pronounced, can be resolved with conventional velocity analysis from long-offset, multichannel seismic data. We used 2D seismic data from a gas hydrate province at the southern end of New Zealand’s Hikurangi subduction margin to describe a workflow for high-resolution velocity analysis that delivered detailed velocity models of shallow marine sediments and their coincident gas hydrate systems. The results showed examples of pronounced low-velocity zones caused by free gas ponding beneath the hydrate layer, as well as high-velocity zones related to gas hydrate deposits. For the seismic interpreter of a gas hydrate system, the velocity results represent an extra “layer” for interpretation that provides important information about the distribution of free gas and gas hydrate. By combining the velocity information from the seismic transect with geologic samples of the seafloor and an understanding of sedimentary processes, we have determined that high gas hydrate concentrations preferentially form within coarse-grained sediments at the proximal end of the Hikurangi Channel. Finer grained sediments expected elsewhere along the seismic transect might preclude the deposition of similarly high gas hydrate concentrations away from the channel.

Gas hydrate and free gas volumes in marine sediments: Example from the Niger Delta front

1997 ◽  
Vol 14 (3) ◽  
pp. 245-255 ◽  
Author(s):  
M. Hovland ◽  
J.W. Gallagher ◽  
M.B. Clennell ◽  
K. Lekvam
Keyword(s):  
Marine Sediments ◽  
Gas Hydrate ◽  
Niger Delta ◽  
Delta Front ◽  
Free Gas

scholarly journals A transfer function for the prediction of gas hydrate inventories in marine sediments

2010 ◽  
Vol 7 (9) ◽  
pp. 2925-2941 ◽  
Author(s):  
M. Marquardt ◽  
C. Hensen ◽  
E. Piñero ◽  
K. Wallmann ◽  
M. Haeckel
Keyword(s):  
Transfer Function ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Numerical Models ◽  
Order Approximation ◽  
Parameter Analysis ◽  
General Validity ◽  
Transport Reaction ◽  
Degradation Rates ◽  
Wide Range

Abstract. A simple prognostic tool for gas hydrate (GH) quantification in marine sediments is presented based on a diagenetic transport-reaction model approach. One of the most crucial factors for the application of diagenetic models is the accurate formulation of microbial degradation rates of particulate organic carbon (POC) and the coupled formation of biogenic methane. Wallmann et al. (2006) suggested a kinetic formulation considering the ageing effects of POC and accumulation of reaction products (CH4, CO2) in the pore water. This model is applied to data sets of several ODP sites in order to test its general validity. Based on a thorough parameter analysis considering a wide range of environmental conditions, the POC accumulation rate (POCar in g/m2/yr) and the thickness of the gas hydrate stability zone (GHSZ in m) were identified as the most important and independent controls for biogenic GH formation. Hence, depth-integrated GH inventories in marine sediments (GHI in g of CH4 per cm2 seafloor area) can be estimated as: GHI = a · POCar · GHSZb · exp (– GHSZc/POCar/d) + e with a = 0.00214, b = 1.234, c = –3.339,         d = 0.3148, e = –10.265. The transfer function gives a realistic first order approximation of the minimum GH inventory in low gas flux (LGF) systems. The overall advantage of the presented function is its simplicity compared to the application of complex numerical models, because only two easily accessible parameters need to be determined.

scholarly journals Gas Hydrate Estimate in an Area of Deformation and High Heat Flow at the Chile Triple Junction

2018 ◽  
Author(s):  
Lucía Villar-Muñoz ◽  
Iván Vargas-Cordero ◽  
Joaquim P. Bento ◽  
Umberta Tinivella ◽  
Francisco Fernandoy ◽  
...  
Keyword(s):  
Heat Flow ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Triple Junction ◽  
High Heat ◽  
Spreading Ridge ◽  
High Heat Flow ◽  
Geothermal Gradients ◽  
Free Gas ◽  
Chile Triple Junction

Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a zone of very high heat flow and intense rock deformation above the downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables vigorous fluid migration. Here we present an analysis of the spatial distribution, concentration, estimate of gas phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism and forearc sediments offshore Taitao (45.5° - 47° S). Velocity analysis of Seismic Profile RC2901-751 indicates gas hydrate concentration values <10% of the total rock volume, and extremely high geothermal gradients (<190 °Ckm-1). Gas hydrates are located in shallow sediments (90-280 meters below the seafloor). The large amount of hydrate and free gas estimated (7.21x1011 m3 and 4.1x1010 m3, respectively), the high seismicity, the mechanically unstable nature of the sediments, and the anomalous geothermal conditions, set the stage for potential massive releases of methane to the ocean mainly through hydrate dissociation and/or migration directly to the seabed through faults. We conclude that the Chile Triple Junction is an important methane seepage area and should be the focus of novel geological and ecological research.

scholarly journals Gas Hydrate Estimate in an Area of Deformation and High Heat Flow at the Chile Triple Junction

Geosciences ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 28 ◽  
Author(s):  
Lucía Villar-Muñoz ◽  
Iván Vargas-Cordero ◽  
Joaquim Bento ◽  
Umberta Tinivella ◽  
Francisco Fernandoy ◽  
...  
Keyword(s):  
Heat Flow ◽  
Marine Sediments ◽  
Gas Hydrate ◽  
Triple Junction ◽  
High Heat ◽  
Spreading Ridge ◽  
High Heat Flow ◽  
Geothermal Gradients ◽  
Free Gas ◽  
Chile Triple Junction

Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a regime of very high heat flow and intense rock deformation above the downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables vigorous fluid migration. Here, we present an analysis of the spatial distribution, concentration, estimate of gas-phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism, and forearc sediments offshore Taitao (45.5°–47° S). Velocity analysis of Seismic Profile RC2901-751 indicates gas hydrate concentration values <10% of the total rock volume and extremely high geothermal gradients (<190 °C·km−1). Gas hydrates are located in shallow sediments (90–280 m below the seafloor). The large amount of hydrate and free gas estimated (7.21 × 1011 m3 and 4.1 × 1010 m3; respectively), the high seismicity, the mechanically unstable nature of the sediments, and the anomalous conditions of the geothermal gradient set the stage for potentially massive releases of methane to the ocean, mainly through hydrate dissociation and/or migration directly to the seabed through faults. We conclude that the Chile Triple Junction is an important methane seepage area and should be the focus of novel geological, oceanographic, and ecological research.

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