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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Environmental and Green Processes".

Deadline for manuscript submissions: closed (15 March 2024) | Viewed by 24481

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Special Issue Editors

Dr. Xiang Sun

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Guest Editor

Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071 China
Interests: numerical simulation of deep water geo-environment; geotechnical modeling in offshore geotechnical engineering; physics-informed neural network method in energy engineering
Special Issues, Collections and Topics in MDPI journals

Dr. Yizhao Wan

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Guest Editor

Qingao Institute of Marine Geology, China Geological Survey, Qingdao 266237, China
Interests: multi-physics coupling numerical simulation of petroleum reservoir; geohazard related to gas hydrate; numerical simulation methods of coupled fluid-solid problem

Dr. Lunxiang Zhang

E-Mail Website
Guest Editor

School of Energy and Power Engineering, Dalian University of Technology, Dalian, China
Interests: flow assurance; hydrate-based technology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Numerical modeling is often used to accurately predict complex deep-water geo-environmental changes and solve soil-structure interaction problems. The methods used to develop these models improve the reliability of predictions and can solve geotechnical multi-scale, multi-component, multi-phase, and multi-field problems. Recently, innovative artificial intelligence algorithms (e.g., machine learning, deep learning, and reinforcement learning) have been combined with numerical modeling, resulting in techniques that are practical for industrial applications. These processes have also accelerated deep-water modeling digitalization.

For this Special Issue, we are seeking original and novel contributions regarding research advances or well-documented applications of numerical modeling for deep-water geo-environmental changes and soil-structure interaction problems. Submissions should focus on the reliability of numerical results. Physical and numerical models should be detailed enough for readers to reproduce the results. The appendix should include verification or validation of numerical codes/models, domain size, and mesh sensitivity analysis.

Topics of interest for this Special Issue include:

Constitutive models;
Numerical simulation;
Physics-informed neural network;
Proxy modeling;
CO₂ sequestration;
Deep water energy production;
Soil-structure interaction modeling;
Artificial island and offshore slope stability analysis.

Dr. Xiang Sun
Dr. Yizhao Wan
Dr. Lunxiang Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

numerical modeling

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Published Papers (11 papers)

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Research

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12 pages, 2295 KiB

Open AccessArticle

A Modified Method for the Fredlund and Xing (FX) Model of Soil-Water Retention Curves

by Geng Niu, Liang Kong, Yusong Miao, Xue Li and Fanxiu Chen

Processes 2024, 12(1), 50; https://doi.org/10.3390/pr12010050 - 25 Dec 2023

Viewed by 1434

Abstract

The soil-water retention curve (SWRC) is fundamental in presenting the hydromechanical characteristics of soils, which are closely connected with soil deformation, permeability, and shear strength. The Fredlund and Xing (FX) model accurately fits the SWRCs of different types of soils over a wide suction range. However, experimental comparisons of the fitting showed that the obtained parameters differ from the physical meanings assigned by Fredlund and Xing. To address this issue, the traditional FX model has been improved, resulting in the proposal of a two-step FX model. Firstly, the FX model is applied without taking the correction coefficient c(ψ) into account to fit the measured SWRC. The values for α, n, and m are then determined and substituted into the FX model to refit the experimental data. Finally, the last parameter C_r can be obtained. The curves resulting from these two steps have a good agreement with the experimental results, and the obtained parameters align better with their physical meanings. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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13 pages, 1792 KiB

Open AccessArticle

A Review of CO₂ Marine Geological Sequestration

by Xiang Sun, Anran Shang, Peng Wu, Tao Liu and Yanghui Li

Processes 2023, 11(7), 2206; https://doi.org/10.3390/pr11072206 - 22 Jul 2023

Cited by 12 | Viewed by 2865

Abstract

Carbon dioxide (CO₂) sequestration plays a crucial role in reducing the levels of atmospheric CO₂ and mitigating the harmful effects of global warming. Among the various CO₂ sequestration technologies, CO₂ marine geological sequestration emerges as a safer and more efficient alternative compared with traditional terrestrial geological sequestration. This is highly attributed to its expansive potential, safe distance from aquifers, and stable temperature and pressure conditions. This paper reviews and evaluates the main CO₂ marine geological sequestration technologies, including CO₂ sequestrations in shallow marine sediments, CO₂, sub-seabed aquifers, and CO₂-CH₄ replacement. The goal of this paper is to shed light on the mechanism, potential, and challenges of each technology. Given the importance of safety in CO₂ sequestration, this review also explores the potential adverse effects of CO₂ leakage from reservoirs, particularly its impact on marine environments. Finally, we discuss potential development trends in CO₂ marine geological technology. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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13 pages, 8069 KiB

Open AccessArticle

Dynamic Evolution and Quantitative Characterization of Fractures in Coal at the Eastern Edge of Ordos Basin under Axial Loading

by Yinghao Zhu, Yineng Tan, Songhang Zhang, Mengdie Wang and Bingyi Wang

Processes 2023, 11(6), 1631; https://doi.org/10.3390/pr11061631 - 26 May 2023

Cited by 2 | Viewed by 1359

Abstract

Understanding the evolution of pore-fracture networks in coal during loading is of paramount importance for coalbed methane exploration. To shed light on these dynamic changes, this study undertook uniaxial compression experiments on coal samples collected from the eastern edge of the Ordos Basin, complemented by μ-CT scanning to obtain a 3D visualization of the crack network model. The compression process was divided into three stages, namely, micro-crack compaction, linear elasticity, and peak failure. An increase in stress resulted in greater concentration and unevenness in fractal dimensions, illustrating the propagation of initial cleats and micro-cracks in the dominant crack direction and the ensuing process of crack merging. These results provide valuable insights into the internal structure and behavior of coal under stress, informing more efficient strategies for coalbed methane extraction. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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20 pages, 45846 KiB

Open AccessArticle

Experimental Study on Cyclic Hydraulic Fracturing of Tight Sandstone under In-Situ Stress

by Xiaolong Wu, Yintong Guo, Xin Chang, Zhenhui Bi, Guokai Zhao, Hanzhi Yang and Wuhao Guo

Processes 2023, 11(3), 875; https://doi.org/10.3390/pr11030875 - 15 Mar 2023

Cited by 5 | Viewed by 1753

Abstract

Sandstone oil–gas reservoirs in the Junggar Basin, China have great development potential. However, their ultra-deep formation depth leads to high crustal stress and high breakdown pressure. Therefore, in this research, we studied the cyclic hydraulic fracturing of tight sandstone with different combinations of “high-pressure duration + low-pressure duration” under high-stress conditions. Through laboratory experiments, the pump pressure curves, hydraulic fracture morphology, acoustic emission counts, and peak frequency of the samples were obtained. The results showed that: (1) Compared with conventional hydraulic fracturing, the breakdown pressure of cyclic hydraulic fracturing was reduced by more than 30%, the minimum threshold of cyclic pump pressure required for sample breakdown was between 60%P_b and 70%P_b, and cyclic hydraulic fracturing more easily formed complex and diverse hydraulic fractures. (2) In cyclic hydraulic fracturing, under the same upper limit of cyclic pump pressure, the shorter the high-pressure duration, the fewer the cycles required for sample breakdown. (3) Under the same “high-pressure duration + low-pressure duration” condition, the lower the upper limit of the cyclic pump pressure, and the greater the number of cycles required for sample breakdown. (4) The AE cumulative counts curves fluctuated greatly during cyclic hydraulic fracturing, rising in an obvious step-wise manner and the AE peak frequency was banded and mainly divided into three parts: low frequency, medium frequency, and high frequency. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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16 pages, 102776 KiB

Open AccessFeature PaperArticle

Study on the Hydraulic Fracturing of the Inter-Salt Shale Oil Reservoir with Multi-Interfaces

by Daihong Li, Xiaoyu Zhang and Zhixiang Chen

Processes 2023, 11(1), 280; https://doi.org/10.3390/pr11010280 - 15 Jan 2023

Cited by 1 | Viewed by 1920

Abstract

Hydraulic fracture morphology and propagation mode are difficult to predict in layers of the various lithological strata, which seriously affects exploitation efficiency. This paper studies the fundamental mechanical and microscopic properties of the two main interfaces in inter-salt shale reservoirs. On this basis, cement-salt combination samples with composite interfaces are prepared, and hydraulic fracturing tests are carried out under different fluid velocities, viscosity, and stress conditions. The result shows that the shale bedding and salt-shale interface are the main geological interfaces of the inter-salt shale reservoir. The former is filled with salt, and the average tensile strength is 0.42 MPa, c = 1.473 MPa, and φ = 19.00°. The latter is well cemented, and the interface strength is greater than that of shale bedding, with c = 2.373MPa and φ = 26.15°. There are three basic fracture modes for the samples with compound interfaces. Low-viscosity fracturing fluid and high-viscosity fracturing fluid tend to open the internal bedding interface and produce a single longitudinal crack, respectively, so properly selecting the viscosity and displacement is necessary. Excessive geostress differences will aggravate the strain incompatibility of the interface between different rock properties, which makes the interfaces open easily. The pump pressure curves’ morphological characters are different with different failure modes. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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12 pages, 5005 KiB

Open AccessArticle

One−Dimensional Seepage of Unsaturated Soil Based on Soil−Water Characteristic Curve

by Longtan Shao, Shixiong Wu, Xiaoxia Guo and Tiande Wen

Processes 2022, 10(12), 2564; https://doi.org/10.3390/pr10122564 - 2 Dec 2022

Cited by 3 | Viewed by 1824

Abstract

The uneven pore water distribution in unsaturated soil will cause water movement, change the hydraulic and mechanical characteristics of soil, and then cause soil damage. Therefore, it is important to study the hydraulic characteristics of unsaturated soil. In this paper, the law of conservation of mass and Darcy’s law were used to analyze the unit soil after seepage to obtain a continuous equation. Combined with the soil-water characteristic curve (SWCC), the effect of matric suction and permeability coefficient of unsaturated soil on infiltration rate is substituted into the equation. Through the analysis of pore water stress of the unit soil, the function of the unsaturated permeability coefficient with the effective saturation degree is obtained, and the theoretical formula of the one-dimensional infiltration rate of unsaturated soil is derived. Compared with other models, this formula has fewer parameters and is easy to use. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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19 pages, 4649 KiB

Open AccessArticle

Numerical Study on Pile Group Effect and Carrying Capacity of Four-Barreled Suction Pile Foundation under V-H-M Combined Loading Conditions

by Zhen Qi, Tongzhong Wei, Changtao Wang, Fengyun Wang, Yin Wang, Jianghong Wang and Juan Li

Processes 2022, 10(11), 2459; https://doi.org/10.3390/pr10112459 - 20 Nov 2022

Cited by 2 | Viewed by 2055

Abstract

Multi-barreled composite foundations are generally used in offshore oil platform structure. However, there is still a lack of theoretical analyses and experimental research. This paper presents the results of a three-dimensional finite element analysis of a four-barreled suction pile foundation in heterogeneous clay foundation. The pile group effect and carrying capacity are numerically simulated. The effects of different pile embedment depths, pile spacings and non-uniformity coefficients of clay on the pile group effect are studied. Considering the changes in the foundation carrying capacity under vertical, horizontal and bending moment coupling loads, the foundation carrying capacity envelopes under horizontal and moment (H-M) and vertical, horizontal and moment (V-H-M) loading modes are drawn. The results show that pile spacing and embedment depth have great influence on the pile group effect. The bearing capacity envelope of foundations under V-H-M loading mode is greatly affected by vertical load V. This can provide a reference for the selection of pile spacing and embedded depth in practical engineering design. Furthermore, the stability of foundations can be evaluated according to the relative relationship between design load and failure envelope. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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20 pages, 6222 KiB

Open AccessArticle

Deformation Coupled Effective Permeability Change in Hydrate-Bearing Sediment during Depressurization

by Xiang Sun, Hao Luo and Kenichi Soga

Processes 2022, 10(11), 2210; https://doi.org/10.3390/pr10112210 - 27 Oct 2022

Cited by 1 | Viewed by 1952

Abstract

Methane hydrates found in the sediments of deep sea and permafrost regions draw global interest. The rate of gas production from a depressurized well is governed by the effective permeability of the hydrate-bearing sediments around the wellbore. During depressurization, a decrease in pore pressure leading to soil compaction and hydrate dissociation results in a dynamic change in the effective permeability. To describe the change in the effective permeability in detail, in this study, a simple coupled compressibility–permeability analysis method is proposed to identify the conditions under which the effective permeability increases or decreases after depressurization. An analytical solution is derived for the effective permeability change with pore pressure and temperature, considering hydrate dissociation and soil compaction. We found that when there is a sufficient heat supply, hydrate dissociation dominates the effective permeability during hydrate dissociation, but after hydrate dissociation, soil compaction is the governing factor for permeability change. When there is an insufficient heat supply, however, compaction mainly determines the permeability, and the effect of hydrate dissociation is limited. This work will be helpful for rapid reservoir assessment. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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14 pages, 2023 KiB

Open AccessArticle

Evolution Prediction of Hysteresis Behavior of Sand under Cyclic Loading

by Pingxin Xia, Longtan Shao, Wen Deng and Chao Zeng

Processes 2022, 10(5), 879; https://doi.org/10.3390/pr10050879 - 29 Apr 2022

Cited by 3 | Viewed by 2620

Abstract

Soil cyclic degradation is a serious issue that should be considered in engineering design and maintenance. The hysteretic response causes strength degradation and excessive settlement of soil structure in engineered and natural geosystems. Hysteresis is essentially the coupling deformation of elastic and plastic components during reloading and unloading processes. Conventional hysteretic models for sand in the elastoplastic framework rely highly on yield surface or potential surface evolution and fall short on complexity and inaccuracy. This study proposes a decoupling method to describe the hysteretic response of sand. In contrast to the conventional elastoplastic approach, this decoupling method can directly decouple the elastic and plastic components by determining the boundary between the elastic strain extension domain and the plastic strain extension domain for each stress cycle. In this way, the elastic and plastic stress–strain branches during cyclic loading can be separately obtained, and the corresponding elastic and plastic parameters are employed to characterize mechanical behavior. With the respective evolution of elastic and plastic strains, the hysteretic behavior of sand is reproduced by combining all the branches. Finally, this decoupling method is validated by three conventional cyclic loading tests. The predictions are consistent with the experiments, indicating that the decoupling method is generally effective in describing the hysteretic behavior under cyclic loading. This decoupling method provides new insight to obtain elastic and plastic deformation behaviors separately, without recourse to complicated plastic surface and hardening law. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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Review

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15 pages, 2683 KiB

Open AccessReview

Fast Formation of Hydrate Induced by Micro-Nano Bubbles: A Review of Current Status

by Zhiyong Jing, Yaxin Lin, Chuanxiao Cheng, Xiaonan Li, Jianxiu Liu, Tingxiang Jin, Wenfeng Hu, Yaoli Ma, Jiayi Zhao and Shijie Wang

Processes 2023, 11(4), 1019; https://doi.org/10.3390/pr11041019 - 28 Mar 2023

Cited by 4 | Viewed by 2252

Abstract

Hydrate-based technologies have excellent application potential in gas separation, gas storage, transportation, and seawater desalination, etc. However, the long induction time and the slow formation rate are critical factors affecting the application of hydrate-based technologies. Micro-nano bubbles (MNBs) can dramatically increase the formation rate of hydrates owing to their advantages of providing more nucleation sites, enhancing mass transfer, and increasing the gas–liquid interface and gas solubility. Initially, the review examines key performance MNBs on hydrate formation and dissociation processes. Specifically, a qualitative and quantitative assembly of the formation and residence characteristics of MNBs during hydrate dissociation is conducted. A review of the MNB characterization techniques to identify bubble size, rising velocity, and bubble stability is also included. Moreover, the advantages of MNBs in reinforcing hydrate formation and their internal relationship with the memory effect are summarized. Finally, combining with the current MNBs to reinforce hydrate formation technology, a new technology of gas hydrate formation by MNBs combined with ultrasound is proposed. It is anticipated that the use of MNBs could be a promising sustainable and low-cost hydrate-based technology. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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26 pages, 6267 KiB

Open AccessReview

A Review of the Hydraulic Fracturing in Ductile Reservoirs: Theory, Simulation, and Experiment

by Dawei Zhu, Guofeng Han, Honglan Zou, Mingyue Cui, Chong Liang and Fei Yao

Processes 2022, 10(10), 2022; https://doi.org/10.3390/pr10102022 - 7 Oct 2022

Cited by 6 | Viewed by 2998

Abstract

The bottom-hole pressure of hydraulic fracturing in ductile reservoirs is much higher than that of the hydraulic fracturing simulation, and the fracture toughness inferred from the field data is 1–3 orders of magnitude higher than that measured in the laboratory. The rock apparent fracture toughness increases with the increase in the confining pressure. Excluding the influence of the fluid viscosity and the fluid lag on the apparent fracture toughness, the fracture process zone (FPZ) at the fracture tip can explain the orders of magnitude of difference in the apparent fracture toughness between the laboratory and the field. The fracture tip is passivated by plastic deformation, forming a wide and short hydraulic fracture. However, the size of the FPZ obtained in the laboratory is in the order of centimeters to decimeters, while an FPZ of 10 m magnitude is speculated in the field. The FPZ size is affected by the rock property, grain size, pore fluid, temperature, loading rate, and loading configuration. It is found that the FPZ has a size effect that tends to disappear when the rock specimen size reaches the scale of meters. However, this cannot fully explain the experience of hydraulic fracturing practice. The hydraulic fracturing behavior is also affected by the relation between the fracture toughness and the fracture length. The fracture behavior of type II and mixed type for the ductile rock is poorly understood. At present, the apparent fracture toughness model and the cohesive zone model (CZM) are the most suitable criteria for the fracture propagation in ductile reservoirs, but they cannot fully characterize the influence of the rock plastic deformation on the hydraulic fracturing. The elastic-plastic constitutive model needs to be used to characterize the stress–strain behavior in the hydraulic fracturing simulation, and the fracture propagation criteria suitable for ductile reservoirs also need to be developed. Full article

(This article belongs to the Special Issue Advances in Numerical Modeling for Deep Water Geo-Environment)

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