Mechanism of soil stratum instability induced by hydrate dissociation

Zhang, Xuhui; Lu, Xiaobing; Chen, Xuedong; Zhang, Limin; Shi, Yanxin

doi:10.1016/j.oceaneng.2016.06.015

Cited by 26 publications

(11 citation statements)

References 24 publications

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“…Oil and gas have been discovered in multiple reservoirs in different structural tectonic belts in the Qiongdongnan Basin (QDNB) (Zhang et al, 2014;Wang et al, 2015;W. Zhang et al, 2015;Zhang et al, 2016;Qin et al, 2019). The sediments deposited during the Pliocene and Quaternary possess favorable conditions for hosting biogenic gases, and these were commonly encountered in the strata shallower than 2,300 m during gas logging.…”

Section: Geological Settingmentioning

confidence: 99%

Quantitative analysis of the risk of hydrogen sulfide release from gas hydrates

et al. 2023

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The role that H2S plays in the global sulfur cycle has been studied extensively in recent years. This paper focuses on the influence of H2S released from gas hydrates on sulfur cycle and establishes a one-dimensional mathematical model to calculate the amount of H2S released from the dissociation of gas hydrates present in multiple layers in the Qiongdongnan Basin China. The results show that the sulfate and methane transition zone that covers an area of about 100 km2in the Qiongdongnan Basin contains 2.3 × 1012 g of pyrite, which requires 4.06 × 1011 mol of H2S for its formation. The H2S released from the dissociation of gas hydrates is 5.4 ×1011 mol, which is about 1.3 times that needed for the formation of pyrite. Therefore, the H2S released from the gas hydrates is an important source of H2S for the formation of pyrite in the sulfate-methane transition zone of Qiongdongnan Basin. According to the flux of H2S and the partial pressure of O2 (PO2) in the atmosphere, the critical value of the balance between the flux of H2S and PO2 turns out to be 0.13 mol kg−1∙bar−1. Furthermore, considering the effect of global sea-level changes, three risk modes are identified to categorize the amount of H2S released from the dissociation of gas hydrate into the atmosphere. We classify the periods from 5–12 Ma BP, 25–29 Ma BP, 47–52 Ma, and 57–61 Ma BP into the high-risk mode. Furthermore, the results show that a part of the H2S released from the gas hydrate dissociation is oxidized by the Fe (III) oxide metal, with much of the metal ions being released into the pore water. Another part of the H2S is re-oxidized by the O2 in the ocean, with much of SO42- released into the seawater. Therefore, the process also provides metal ions and SO42- to pore water or seawater when the H2S released from gas hydrate diffuses from the bottom. This paper provides new insights into the source of H2S in the ocean and shows that the H2S contained in gas hydrates plays an important role in the global sulfur cycle.

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Section: Geological Settingmentioning

confidence: 99%

Quantitative analysis of the risk of hydrogen sulfide release from gas hydrates

et al. 2023

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“…The hydrate layer is a poorly stable layer of sediment that has not formed into rocks . Moreover, changes in the weather and sea level may cause the hydrate to decompose and generate additional free gas, which can potentially increase the pore pressure of the hydrate sediment layer and decrease the stability of the storage layer, thereby causing geological disasters, such as landslides. − , During the hydrate dissociation, the hydrate layer softens and the pore fluid pressure exceeds the total stress of the overlying layer, leading to the formation of layered fracture between the hydrate layer and the overlying layer . To date, most international research studies have focused on large-scale submarine landslides and the stability of large-scale submarine slopes .…”

Section: Introductionmentioning

confidence: 99%

“…[23][24][25][26]31 During the hydrate dissociation, the hydrate layer softens and the pore fluid pressure exceeds the total stress of the overlying layer, leading to the formation of layered fracture between the hydrate layer and the overlying layer. 32 To date, most international research studies have focused on large-scale submarine landslides and the stability of large-scale submarine slopes. 33 The depressurization process used for gas extraction significantly changes the stress state and the mechanical properties of hydrate soils, which may lead to potential geotechnical hazards such as submarine landslide.…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis of Soil Deformation and Collapse Due to Hydrate Decomposition

et al. 2021

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Natural gas hydrates are an ideal alternative clean energy source. Many countries are currently attempting the trial production of gas hydrates. Japan became the first country to achieve offshore hydrate trial production in 2013, and China conducted 60 days of continuous trial exploitation in 2017. This study analyzes the changes in the internal stress of the hydrate zone and hydrate saturation of the soil throughout the monitoring period and calculates the failure stress of the hydrate deposit layer. The Mohr−Coulomb model is used to simulate Japan's test exploitation conditions to verify the feasibility of the method. Finally, the hydrate decomposition range, the difference in the soil dip angle in the test exploitation area, and the bearing capacity of the hydrate reservoir are numerically simulated to evaluate the stability of the soil. Through the sensitivity analysis of the hydrate decomposition range and the inclination angle of the hydrate sediment layer, it can be found that the hydrate decomposition range has the greatest impact on the deformation, and the soil around the decomposition area may be sheared and collapsed. Within 1 week of decompression and exploitation, the hydrate decomposition radius is approximately 3 m. When the inclination angle increases from 3°to 9°, the sediment deformation increases by 12 times. Therefore, it is necessary to pay attention to the critical value of the decomposition range during the exploitation process.

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“…Zhang et al performed laboratory simulations on the spray pattern produced by hydrate decomposition. , In the laboratory, the heating rod was placed in the center of the hydrate deposit. The hydrate gradually decomposed outward in a circular diffusion state, and the soil above the hydrate deposit exhibited low permeability and high intensity.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study and Numerical Simulation of Overlying Layer Soil Failure Caused by Hydrate Decomposition

2020

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During the exploration of hydrates or oil and gas exploitation through the hydrate layer, heat transfer causes hydrates to decompose. The gas and water generated by this decomposition increase the pressure of the gas in the decomposition zone, resulting in excessive pore pressure. The seepage of gas and water and the decomposition of hydrates lead to soil deformation, which may be caused by soil softening. This may lead to geological disasters, such as ocean landslides, seabed subsidence, and even gas explosions. The natural phenomena of soil eruption caused by hydrate decomposition currently include Siberian pits and Bermuda craters. From these two natural phenomena, climate change is considered to affect hydrate decomposition, causing ocean acidification and dissolved oxygen consumption, which may have more serious consequences than global warming alone. Therefore, it is extremely important to study how hydrate decomposition causes soil to erupt and release gas into the ocean and the atmosphere. This paper is primarily based on on-site data collected from the Siberian pit in the case of hydrate decomposition resulting in increased pore pressure, resulting in soil eruption. The relationship between the thickness of the upper cladding layer, the pressure causing the destruction of the upper cladding layer, and the destruction length of the upper cladding layer was obtained through numerical simulation.

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Mechanism of soil stratum instability induced by hydrate dissociation

Cited by 26 publications

References 24 publications

Quantitative analysis of the risk of hydrogen sulfide release from gas hydrates

Quantitative analysis of the risk of hydrogen sulfide release from gas hydrates

Numerical Analysis of Soil Deformation and Collapse Due to Hydrate Decomposition

Experimental Study and Numerical Simulation of Overlying Layer Soil Failure Caused by Hydrate Decomposition

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