Hydrate Accumulations Research Articles

Impact of Fluid Migration Conditions on Hydrate Accumulation in the Shenhu Area: Insights from Thermo-Flow-Chemical Simulation

Impact of Fluid Migration Conditions on Hydrate Accumulation in the Shenhu Area: Insights from Thermo-Flow-Chemical Simulation

Prediction of hydrate formation boundaries in pure water and salt/alcohol containing systems based on prior knowledge and artificial intelligence

As an efficient and clean energy source, natural gas plays a crucial role in optimizing the global energy consumption structure. However, the formation and accumulation of hydrates in pipelines during the exploitation and transportation of natural gas greatly jeopardize the production safety. Accurately predicting hydrate formation boundaries remains challenging due to the complex interation among various influencing factors. Although mechanistic models provide insights, they often fall short in accuracy. Conversely, machine learning models, while promising, may face limitations related to small sample sizes and a lack of physical interpretability. To overcome these limitations, this study proposed a physically guided neural network (PGNN) based on the Chen-Guo model, which integrated thermodynamic mechanisms with a neural network framework. This proposed model utilized pressure calculated from the Chen-Guo model as an input variable and incorporates physical inconsistencies into its loss function. A comparative analysis using literature data that PGNN achieved superior prediction accuracy, with an R2 value of 0.9768 for gas hydrate formation pressure prediction. The integration of thermodynamic mechanisms enhanced the prediction accuracy, as evidenced by an increase in the R2 value by 0.036, and a reduction in the MSE value by 5.56. Furthermore, the PGNN maintained a high level of prediction accuracy, ranging from 0.96 to 0.98, even with limited sample sizes, thus confirming its applicability and stability. This study validated the feasibility of PGNN for predicting gas hydrate formation conditions and offered insights into hydrate-based applications and hydrate management strategies.

РЕЗУЛЬТАТЫ НАУЧНЫХ ЭКСПЕДИЦИОННЫХ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ ПОЛЕЗНЫХ ИСКОПАЕМЫХ МОРЕЙ ДАЛЬНЕВОСТОЧНОГО РЕГИОНА РОССИЙСКОЙ ФЕДЕРАЦИИ И ТИХОГО ОКЕАНА (ПРОЕКТ «ГЕОМИР»)

The paper presents a brief overview of the results of integrated geological, geophysical and oceanographic studies for the period 2017–2023, for which interregional generalizations were made on some promising areas of study of underwater mineral resources and the environment. The data on geological underwater objects, in particular, manganese ores of the Sea of Japan and the Sea of Okhotsk and adjacent water areas; rare-earth ores of the Tomtor ore cluster, ancient and modern coastal-marine placers of the Laptev Sea coast are presented; barite ore occurrences “Barite Hills” (in the Sea of Okhotsk); ferromanganese formations of the Eastern Arctic shelf of Russia; coastal marine placers of the shelf and coast of the Far Eastern seas, including gold-bearing placers. including gold-bearing placers of the shelf zone of the south of Primorye and north of Sakhalin, titanomagnetite placers of the Kuril Islands, gold-bearing placers of the North Sakhalin Plain and others. Direct signs of hydrocarbons were obtained in areas previously considered unpromising (including the South China Sea), gas hydrate accumulations were mapped and studied in the Sea of Okhotsk and the Sea of Japan, prospecting for gas hydrates in the Bering Sea was prepared, and comparative studies of hydrate-bearing capacity of the marginal seas of the NW Pacific and the Indian Ocean were carried out. The main features of the distribution of lithologic and gas-geochemical indicators of hydrocarbon gases in bottom sediments of the southwestern sector of the East Siberian Sea, which is the least studied in terms of oil and gas content, were studied. Based on the data of gas-geochemical studies, the prospects of oil and gas content of the eastern shelf of the Arctic were assessed. The results of geomicrobiological studies in the seas of the Far East region are described. In some cases deepsea sediments themselves (peloid-like sediments, etc.) appear to be a separate huge mineral resource. At present, the “continent-ocean” transition zone and neutral waters can become the most important source of replenishing the mineral resource base of these mineral components. The presented research corresponds to the main objectives of the GEOMIR project of the national action plan within the UN Decade of Ocean Sciences for Sustainable Development (2021–2030) and was carried out mainly in accordance with the directions of the state assignment. Studies of gas hydrates were carried out within the framework of the WESTPAC working group “Gas hydrates and methane fluxes in the Indo-Pacific region” (CoSGas, 2021–2024), established on the initiative and under the leadership of Russia.

The Mesozoic Subduction Zone over the Dongsha Waters of the South China Sea and Its Significance in Gas Hydrate Accumulation

The Mesozoic subduction zone over the Dongsha Waters (DSWs) of the South China Sea (SCS) is a part of the westward subduction of the ancient Pacific plate. Based on the comprehensive interpretation of deep reflection seismic profile data and polar magnetic anomaly data, and the zircon dating results of igneous rocks drilled from well LF35-1-1, the Mesozoic subduction zone in the northeast SCS is accurately identified, and a Mesozoic subduction model is proposed. The accretion wedges, trenches, and igneous rock zones together form the Mesozoic subduction zone. The evolution of the Mesozoic subduction zone can be divided into two stages: continental subduction during the Late Jurassic and continental collision during the late Cretaceous. The Mesozoic subduction zone controlled the structural pattern and evolution of the Chaoshan depression (CSD) during the Mesozoic and Neogene eras. The gas source of the hydrate comes from thermogenic gas, which is accompanied by mud diapir activity and migrates along the fault. The gas accumulates to form gas hydrates at the bottom of the stable domain; BSR can be seen above the mud diapir structure; that is, hydrate deposits are formed under the influence of mud diapir structures, belonging to a typical leakage type genesis model.

Gas Hydrate Accumulation Mechanism of the Clayey Silt Reservoir in the Shenhu Area, South China Sea

Gas Hydrate Accumulation Mechanism of the Clayey Silt Reservoir in the Shenhu Area, South China Sea

The gas hydrate system of the western Black Sea Basin

The basin-scale distribution of gas hydrates and methane migration pathways in the western Black Sea remains enigmatic, owing to the region's complex geological history. Characterizing the abundant gas hydrate accumulations across temporal scales poses significant challenges. In this study, we developed and applied a 3D large-scale numerical model to study the formation, development, and fate of natural gas hydrate systems in the western Black Sea sub-basin. Our model enables us to simulate the dynamic evolution of basin geometry and facies distribution over the last 98 million years and under dynamically changing boundary conditions, e.g. due to sea-level changes. Our study estimates the total volume of gas hydrates stored within western Black Sea sediments at ∼14,607 MtC, equivalent to ∼30,073 × 1011 m3 of CH4 (at STP conditions) which is about 5 times higher than average gas hydrate density at continental margins. Our findings reveal three distinct mechanisms driving gas hydrate reservoir formation within the reconstructed sub-basin: gas hydrate recycling zones, chimney-like structure formation, and gas hydrate deposits associated with paleo-deep sea fans. We identified and simulated key controlling parameters, related to methane migration pathways and regional geomorphology, governing each type of hydrate formation. Subsequently, we conduct a detailed analysis of regional gas hydrate systems, focusing on the Dniepr paleo-fan system, the Danube paleo-fan region, multiple offshore locations near Turkey, and the central Black Sea area. Furthermore, we investigate various biogenic methane formation kinetics and their impact on basin-scale methane generation. Our sensitivity studies enable us to predict the optimal temperature range for microbial activity driving methanogenesis in the Black Sea sediments at 30 °C–40 °C. Overall, our study provides a novel understanding and quantitative correlation between methane generation, migration, and storage in the form of gas hydrates on a basin-scale in the western Black Sea.

A new thermodynamic model for predicting the 3-D phase equilibrium surface of gas hydrates considering the effect of salt concentration

An accurate understanding of the thermodynamic stability of gas hydrates in salt-bearing systems is of great significance for predicting the extent of hydrate accumulation and determining the hydrate decomposition domain. Therefore, this study proposes a thermodynamic model for predicting the temperature–pressure-salt concentration three-dimensional phase-equilibrium surface. The model considered the interaction of the electrolyte in a mixed salt solution system and non-spherical shaped hydrate crystal cavity. The modified van der Waals-Platteeuw (vdW-P) model and Benedict-Webb-Rubin-Starling (BWRS) equation of state were used to describe the hydrate phase. The Pitzer-Debye-Hückel equation and nonelectrolyte non random two liquid non random factor (N-NRTL-NRF) activity coefficient model were used to describe the fluid phase. The prediction results of the model agreed with the experimental data, and the absolute average relative deviation in temperature (AARD-T) under pure water conditions was only 0.08, and the AARD-T under electrolyte conditions did not exceed 0.15, which proved the accuracy and reliability of the model. The calculation results showed that when the mole fraction of chloride salt was greater than 0.02 and the pressure was higher than 20 MPa, chemical factors caused the p-T curves to translate. When the pressure was low, the temperature gradient along the direction of the salt concentration changed drastically, and the p-T curves no longer had translation characteristics. In comparison, under the same mole fraction, AlCl3 had a stronger inhibitory effect on the CH4 hydrate than the other chloride salts. The lnp-X-1/T three-dimensional surface of the CH4 hydrate exhibited good Clausius-Clapeyron linear behavior locally, and the surface had certain nonlinear characteristics. The degree of nonlinearity of the lnp-X-1/T three-dimensional surfaces of different types of chloride salts was different. A better inhibitory effect of the chloride salt electrolyte on the CH4 hydrate was associated with stronger nonlinearity between 1/T and lnp.

Evaluating The Thickness Of A Cyclopentane Hydrate Film Over A Sessile Water Drop Using PLIF And PIV

The accumulation of hydrates presents an important flow-assurance challenge. Herein, we performed an experimental study to quantify the thickness of a hydrate layer growing laterally along the interface of a water drop submerged in the bulk phase of cyclopentane at sub-zero temperatures. Spatially-resolved velocity and temperature measurements in both liquid phases were taken independently using particle image velocimetry, one- or two-color planar laser-induced fluorescence. We found that the appearance of hydrates leads to a displacement of the temperature maximum away from the phase boundary, which is typically observed very close to the interface due to the recirculating motion of water inside the drop. Making an assumption that, when hydrates are absent, this recirculating motion is retained in time and the maximum position is, thus, unchanged, we conclude that this shift should indicate the hydrate layer should mostly protrude into the drop, and its thickness was evaluated to be around 0.38 mm.

Numerical Simulations in Support of a Long-Term Test of Gas Production From Hydrate Accumulations on the Alaska North Slope: Water Production and Associated Design and Management Issues

Numerical Simulations in Support of a Long-Term Test of Gas Production From Hydrate Accumulations on the Alaska North Slope: Water Production and Associated Design and Management Issues

Dynamic accumulation of a high-grade gas hydrate system: insights from the trial production gas hydrate reservoir in the Shenhu area, northern South China Sea

The ultimate enrichment level and quantity of gas hydrate resources are influenced by the dynamic process of accumulation and preservation. High-resolution 3-D seismic data, logging while drilling (LWD), pressured coring, and in situ testing were used to characterize the dynamic accumulation and preservation of the trial production high-grade gas hydrate reservoir (HGGHR) in the Shenhu area. Through seismic variance analysis and ant-tracking, we found that newly identified mud diapir-associated faults with three development stages controlled the migration and accumulation of gas hydrate and shifted the base of the gas hydrate stability zone (BGHSZ), resulting in dynamic accumulation and dissociation of gas hydrates. The recognized double bottom simulating reflectors (BSRs) were concluded to have been formed due to the shift of the BGHSZ caused by the variational equilibrium conditions. The interval between the double BSRs was inferred to be a disequilibrium zone where gas recycling occurred, contributing to the coexistence of gas hydrates and free gas and the dynamic formation of the HGGHR. Multiple gliding faults formed within the GHSZ in the late period have altered the HGGHR and control the present thickness and distribution of the gas hydrates and free gas in the hanging wall and footwall. Under the influence of geothermal fluids and the fault system associated with the mud diapir, the HGGHR experienced dynamic accumulation with three stages, including early accumulation, medium-term adjustment, and late alteration and preservation. We conclude that four factors affected the formation, distribution, and occurrence of the HGGHR: the geothermal fluids accompanying the deep mud diapir below the reservoir, the dual supply of thermogenic gas and biogenic gas, the recycling of hydrate gas beneath the BGHSZ, and the post-gas hydrate faults developed within the GHSZ. A geological model illustrating the dynamic formation of the trial production HGGHR was proposed, providing a reference for future exploration of HGGHRs with a great production potential in deepwater settings.

Identification of Mass Transport Deposits and Insights into Gas Hydrate Accumulation in the Qiongdongnan Sea Area, Northern South China Sea

Identification of Mass Transport Deposits and Insights into Gas Hydrate Accumulation in the Qiongdongnan Sea Area, Northern South China Sea

Origin and microbial degradation of thermogenic hydrocarbons within the sandy gas hydrate reservoirs in the Qiongdongnan Basin, northern South China Sea

Large-scale natural gas hydrate accumulations (generally over one billion cubic meters of natural gas) in coarse-grained marine sediments are the most valuable types for commercial exploration and exploitation. The formation of such a gas hydrate deposit generally requires a sufficient natural gas supply such as deeply buried thermogenic gas source. However, the worldwide discovered thermogenic gas hydrate deposits are rare, leaving relatively a poor understanding of their formation and evolution. Based on the geochemical and microbial analyses of eleven hydrate-related gas and five sediment samples from the thermogenic gas hydrate deposits in the Qiongdongnan Basin in northern South China Sea, we systematically investigated the origin and evolution of thermogenic hydrocarbons within sandy gas hydrate reservoirs. Results show that natural gas within high saturated gas hydrate-filled sandy sediments is predominately of thermogenic (the proportion is 57.1–70.5%), characterized by “dry gas” (99.38–99.7% C1, 0.26–0.47% C2 and <0.5% C3+), relatively lower C1/(C2+C3) ratio (187–376), and heavier δ13C–C1 values (−55.0 to −31.3‰). In addition, typical biomarkers (including the alkanes, tricyclic terpanes, hopanes and steranes) generated from mature source rocks were detected in the hydrate-filled fine sand reservoir, as well as the biomarker indicators (including the unresolved complex mixtures (UCMs) hump and the 25-norhopane homologous series) for severe hydrocarbon biodegradation. Furthermore, large amounts of hydrocarbon degrading bacteria (50.5% of bacteria) and methanogenic archaea (34.3% of archaea) were detected within hydrate-filled sandy sediment. Our results indicated that the deeply buried thermogenic source can indeed provide sufficient gas supply for the formation of a large-scale gas hydrate deposit, but thermogenic liquid hydrocarbons within gas hydrate reservoirs are very susceptible to be degraded and consumed by hydrocarbon degrading bacteria. In addition, we also found that the clay components of argillaceous gas hydrate reservoirs can adsorb and store large amounts of in situ immature organic matter, which can significantly obscure or cover up the original geochemical signatures of thermogenic hydrocarbons therein. These findings suggest that the relative contribution of deeply buried thermogenic source for gas hydrate accumulation worldwide may be underestimated, because we have previously ignored the fact that thermogenic hydrocarbons within gas hydrate reservoirs would be significantly consumed by hydrocarbon degrading microbes or diluted by in situ immature sedimentary organic matter. Our findings are highly significant for the evaluation and exploration of thermogenic gas hydrate accumulations worldwide.

Controls on Deep and Shallow Gas Hydrate Reservoirs in the Dongsha Area, South China Sea: Evidence from Sediment Properties

The Dongsha area, a key region in the northern South China Sea (SCS), features both diffusive deep and seepage shallow gas hydrate reservoirs. Utilizing sediment samples from gas hydrate reservoirs and adjacent layers at sites W08 and W16 in the Dongsha area, this study aims to uncover the sediment property differences between deep and shallow gas hydrate reservoirs and their impact on gas hydrate accumulation through grain size, X-ray diffraction, and specific surface area (SSA) analyses. The findings classify the study intervals into four distinct layers: shallow non-gas hydrate layer (shallow-NGHL), shallow gas hydrate reservoir (shallow-GHR), deep non-gas hydrate layer (deep-NGHL), and deep gas hydrate reservoir (deep-GHR). In the clayey silt sediment reservoirs, grain size has a minor influence on gas hydrate reservoirs. Both shallow and deep NGHLs, characterized by high smectite content and SSA, possess a complex structure that impedes gas and fluid migration and offers limited potential reservoir space. Consequently, both shallow and deep NGHLs function as sealing beds. The deep GHR, having low smectite content and SSA, exhibits a strong capacity for gas and fluid migration and greater potential reservoir space. As a result, sediment properties significantly influence the deep GHR. Seepage primarily controls the shallow GHR.

Study on the Mechanism of Natural Gas Hydrate Decomposition and Seabed Seepage Triggered by Mass Transport Deposits

Previous studies indicate that mass transport deposits are related to the dynamic accumulation of natural gas hydrates and gas leakage. This research aims to elucidate the causal mechanism of seabed seepage in the western region of the southeastern Qiongdongnan Basin through the application of seismic interpretation and attribute fusion techniques. The mass transport deposits, bottom simulating reflector, submarine mounds, and other phenomena were identified through seismic interpretation techniques. Faults and fractures were identified by utilizing variance attribute analysis. Gas chimneys were identified using instantaneous frequency attribute analysis. Free gas and paleo-seepage points were identified using sweetness attributes, enabling the analysis of fluid seepage pathways and the establishment of a seepage evolution model. Research has shown that in areas where the mass transport deposits develop thicker layers, there is a greater uplift of the bottom boundary of the gas hydrate stability zone, which can significantly alter the seafloor topography. Conversely, the opposite is true. The research indicates that the upward migration of the gas hydrate stability zone, induced by the mass transport deposits in the study area, can result in the rapid decomposition of gas hydrates. The gas generated from the decomposition of gas hydrates is identified as the principal factor responsible for inducing seabed seepage. Moderate- and low-speed natural gas seepage can create spiny seamounts and domed seamounts, respectively.

Pore Water Conversion Characteristics during Methane Hydrate Formation: Insights from Low-Field Nuclear Magnetic Resonance (NMR) Measurements

Understanding the conversion characteristics of pore water is crucial for investigating the mechanism of hydrate accumulation; however, research in this area remains limited. This study conducted methane hydrate formation experiments in unconsolidated sands using an in-house low-field nuclear magnetic resonance (NMR) system. It focused on pore water conversion characteristics and influencing factors such as initial water saturation and sand particle sizes. Results show that methane hydrate formation enhances the homogeneity of the effective pore structure within sand samples. The conversion rate of pore water is significantly influenced by differences in heat and mass transfer capacity, decreasing as initial water saturation and sand size increase. Pore water cannot be fully converted into hydrates in unconsolidated sands. The final conversion ratio of pore water in water-poor sand samples nears 97%, while in water-rich sand samples, it is only 65.80%. Sand particle size variation has a negligible impact on the final conversion ratio of pore water, with ratios exceeding 94% across different particle sizes, differing by less than 3%.

Effects of differential tectonic activities on overpressure evolution in the deep-water area of the Qiongdongnan Basin: implications for gas hydrate accumulation

The lack of data on the complex tectonics of the Qiongdongnan Basin has thus far restricted our understanding of the overpressure, deep hydrocarbon and shallow gas hydrate distribution. We therefore combined integrated seismic, well and borehole test data with basin models to clarify the relationship between tectonic activity and overpressure evolution, as well as the potential effects of the subsurface pressure on gas hydrate accumulation. The results show differences in tectonic activity and pressure characteristics between the eastern and western basins. Large numbers of faults and magmatic intrusions have developed in the post-rift layer of the eastern basin (the Baodao to Changchang sub-basins) since the Late Miocene ( c. 10.5 Ma), although they seldom formed in the western basin (the Lengdong to Lingshui sub-basins). Correspondingly, the eastern basin was characterized by lower overpressures (up to 40 MPa) and the western basin displayed higher overpressures (up to 110 MPa). The results indicate that tectonic activity since c. 10.5 Ma caused the relief of overpressure in the eastern basin. In stark contrast, the overpressure in the western basin increased significantly due to the lack of structural conduits and rapid sedimentation of the thick Pliocene and Quaternary deposits. Numerical models reveal that the faults and gas chimneys associated with the intrusions constituted shallow plumbing systems through which deep natural gas was able to migrate upwards. The formation of gas hydrates relied on the migration of deep gas to the hydrate stability zone below the seafloor. The relatively lower overpressured zones due to pressure relief in the eastern basin are therefore considered the next areas potentially favourable for the formation of gas hydrates. Thematic collection: This article is part of the Emerging knowledge on the tectonics of the South China Sea collection available at: https://www.lyellcollection.org/topic/collections/south-china-sea

Field-scale numerical investigation of a hybrid gas production method from the oceanic hydrate accumulation at site NGHP-02-09 in the Krishna-Godavari Basin, and the associated geomechanical responses

The objectives of this study are to investigate (a) the technical feasibility of gas production from a gas hydrate accumulation at Site NGHP-02-09 in the Krishna-Godavari Basin, India Ocean using a hybrid production method involving a combination of depressurization and thermal stimulation, as well as (b) the associated geomechanical system response when considering both a simplified and a full geomechanical model. This is an extension of the earlier numerical study of Moridis et al. (2019a) of the site using cylindrical (single-well) 2D systems, which indicated (a) the main source of the produced gas to be CH4 dissolved in the water rather than CH4 from hydrate dissociation because of the presence of a high-permeability water-bearing zone that short-circuits the depressurization process and (b) the possibility of adverse geomechanical issues caused by significant displacements that could not be adequately investigated and resolved by the one-way coupling scheme invoked in that study. The proposed hybrid production plan involves two vertical wells in a 3D Cartesian domain: an injection well of warm ocean (saline) water and a production well at an appropriate distance, with the expectation that the hydrate dissociation caused by the depressurization at the production well can be augmented by the thermal effect of the injected warm water (as well as by its salinity), thus mitigating the effects of the high-permeability water zone. The results of this study that uses high-resolution 3D grids indicate that (a) the hybrid production scheme does not appear to offer any advantage over the simple single-well depressurization method of the earlier study, (b) the majority of the produced gas originates from CH4 exsolution from the water rather from hydrate dissociation, and (c) consideration of full geomechanics leads to generally slightly higher dissociation and fluid production because of the evolution of lower porosities and permeabilities, but also to the disappearance of the gas phase after 62 days of production, after which time CH4 from hydrate dissociation is fully dissolved in the water before production. Thus, the hybrid scheme investigated here appears ineffectual in enhancing hydrate dissociation and gas production, and the hydrate deposits at the Site NGHP-02-09 do not appear to be a promising production target under the conditions in this study, in agreement with the earlier conclusion of Moridis et al. (2019a).

Gas hydrate in the North Carnarvon Basin, offshore Western Australia

Analysis of hydrate systems across basins is not common, as most studies are focused on smaller sites. Using petroleum industry well and seismic data, we identify natural gas hydrate accumulations across the entire North Carnarvon Basin, offshore Western Australia. Out of 120 wells, 52 wells have evidence for gas hydrate, though hydrate is distributed throughout the hydrate stability zone in low concentrations. In addition, we do not observe a connection between the presence of hydrate in wells and deeper thermogenic gas reservoirs. From 3D seismic data, we observe bottom simulating reflections (BSRs) are very rare. In addition, while faults are common across the basin, shallow bright spots, which indicate shallow free gas, are uncommon. Based on all these observations from well and seismic data, we argue that hydrate across the North Carnarvon Basin formed predominantly from in-situ gas that is microbial in nature.

Characterization of the Structural–Stratigraphic and Reservoir Controls on the Occurrence of Gas Hydrates in the Eileen Gas Hydrate Trend, Alaska North Slope

One of the most studied permafrost-associated gas hydrate accumulations in Arctic Alaska is the Eileen Gas Hydrate Trend. This study provides a detailed re-examination of the Eileen Gas Hydrate Trend with a focus on the gas hydrate accumulation in the western part of the Prudhoe Bay Unit. This integrated analysis of downhole well log data and published geophysical data has provided new insight on structural, stratigraphic, and reservoir controls on the occurrence of gas hydrates in the Eileen Gas Hydrate Trend. This study revealed the relatively complex nature of the gas hydrate occurrences in the Eileen Gas Hydrate Trend, with gas hydrates present in a series of coarsening upward, laterally pervasive, mostly fine-grained sand beds exhibiting high gas hydrate saturations. Most of the gas hydrate-bearing reservoirs in the Eileen Gas Hydrate Trend are laterally segmented into distinct northwest- to southeast-trending fault blocks, occur in a combination of structural–stratigraphic traps, and are only partially hydrate filled with distinct down-dip water contacts. These findings suggest that the traditional parts of a petroleum system (i.e., reservoir, gas source, gas migration, and geologic timing of the system formation) also control the occurrence of gas hydrates in the Eileen Gas Hydrate Trend.

Geomorphologic and infilling characteristics of the shelf-incising submarine canyon in the eastern Makran accretionary prism, offshore Pakistan

Seven shelf-incising submarine canyon systems are developed in the Makran accretionary prism, offshore Pakistan. This paper uses multibeam bathymetric data and multichannel seismic profiles to study the geomorphologic and infilling characteristics of E Canyon in the east of accretionary prism. The E Canyon extends nearly north–south from the upper slope to lower slope, the bottom of the canyon is located in 1000 to 3000 m water depth, the main axis extends about 55 km, and the width varies from 5 to 9 km. The E Canyon shows U-shaped concave features in the northern cross-section view and V-shaped concave features in the southern cross-section view. Two continuous erosion pools are developed at the fifth and third ridges of the southern segment, respectively. The steepest sidewall (with slopes of 25.75° and 40.47°) of E Canyon was found near the third ridge. The filling sequence of coarse channel lags, slump debris flows, stacked channel sands and mass transported deposits and turbidite deposits from bottom to top is developed in the northern segment of the canyon. Strong erosion is developed in the southern part of the canyon and there is no sedimentation inside. On the abyssal plain, the continuation of the E Canyon is clearly erosive. Our preliminary analysis shows that the factors controlling the evolution of E Canyon may include sediment gravity flow, tectonic activity, sea-level change, climate and onshore rivers activity. The correlation between evolution of E Canyon and gas hydrates was explored, and it is believed that the erosion of E Canyon plays a destructive role in hydrate accumulation. At the same time, the destruction of hydrate-bearing layer induces the escape and leakage of hydrocarbon-bearing fluid, leading to the development of pockmark on the sidewalls of E Canyon. And the evolution model of gas hydrate accumulation in the development area of E Canyon was established.