Effective Horizontal Stress Research Articles

A New Cleat Volume Compressibility Determination Method and Corresponding Modification to Coal Permeability Model

Coal is known as a dual-porosity media composed of cleat and matrix pore. Methane can be stored in the cleats or adsorbed on the inner surface of matrix pore. While fluid mobility is mainly controlled by the developed cleat network, methane desorption has a significant effect on cleat deformation. In the process of coalbed methane recovery, both reservoir compaction and matrix shrinkage will occur and have opposite effects on permeability evolutions. A variety of analytical permeability models have been developed to describe the transient characteristics of permeability in coals. In this study, three common permeability models are first revisited and evaluated against the experimental data under uniaxial strain condition. Shi–Durucan (S&D) model demonstrates the best performance among these models. However, constant cleat volume compressibility was used to assume for S&D model, and the generalization of S&D model is significantly limited. For ease of generalization, the relation between cleat volume compressibility and effective horizontal stress is re-derived and introduced to the derivation of permeability model. Since coal reservoirs usually demonstrate strong anisotropy and heterogeneity, the influences of elastic and adsorption properties are further tested to reveal the overall trend of permeability. The results show that S&D model and its modification with the main variable of effective horizontal stress have the best performances in matching the experimental data under uniaxial strain. The relationship between cleat volume compressibility and effective horizontal stress can be better reflected by the inverse proportional function. In addition, the strengths of reservoir compaction effect relative to matrix shrinkage effect in different models only vary with Poisson’s ratio, while their magnitudes are also affected by Young’s modulus. For a typical coal reservoir, the C&B and P&M models will observe a stronger permeability decline at the initial, while the improved P&M model will receive an earlier and more rapid rebound than the S&D and W&Z models.

Wave & current-induced progressive liquefaction in loosely deposited seabed

Quaternary newly deposited loose seabed soil widely distributes in offshore area in the world. Wave-induced residual liquefaction in loose seabed floor brings great risk to the stability of offshore structures in extreme climate. Understanding of the characteristics of wave-induced residual liquefaction in loose seabed is meaningful for engineers involved in design of offshore structures. In this study, wave & current-induced residual liquefaction in loose seabed floor is investigated deeply and comprehensively adopting a validated integrated numerical model. The time history of wave & current-induced pore pressure, effective stress, shear stress, lateral pressure coefficient K0, stress angle, displacement of seabed soil are all quantitatively demonstrated. The variation process of progressive liquefaction, stress path, as well as stress-strain relation also are illustrated in detail. The classic effective stress principle has been modified to describe the nonlinear phenomenon that the reduction rate of vertical effective stress σ′z is faster than that of horizontal effective stress σ′x and σ′y accompanying residual pore pressure build up. It is shown that the integrated numerical model FSSI-CAS 2D incorporating PZIII soil model can effectively and precisely capture a series of nonlinear dynamic response characteristics of loose seabed floor under wave & current loading. The computational results further confirm the wave & current-induced liquefaction in loose seabed soil is progressively downward, initiating at seabed surface. Besides, it is found that three physical processes, including vertical distribution of oscillatory pore pressure, time history of stress angle as well as lateral pressure coefficient K0 could be taken as indirect indicator to judge the occurrence of wave-induced residual liquefaction, and predict the residual liquefaction depth in loose seabed. It is also found that the progressive liquefaction process is significantly affected by wave height, permeability and saturation of seabed soil.

Fundamentals of the vibratory driving of piles and sheet piles

AbstractVibratory driving is a common method for installing or extracting piles and sheet piles as well as for deep vibratory compaction. The most important parameters are vibration frequency, vibration amplitude and eccentric moment. These parameters govern vibratory driving and, in particular, the soil resistance at the toe and along the shaft of a pile. Pile driving causes oscillating horizontal ground vibrations in coarse‐grained soils. It can be shown that these horizontal vibrations reduce the shaft resistance during driving. The process results in a permanent increase in the horizontal effective stress, which causes arching around the vibrated pile. The increase in horizontal effective stress is also important for deep vibratory compaction. The resonance frequency of the vibrator‐pile‐soil system significantly affects pile penetration and the emission of ground vibrations. At resonance, the vertical vibration velocity in the soil reaches a maximum and pile penetration becomes very slow, whereas beyond resonance, the vibration velocity decreases and the pile penetration speed is high. Field monitoring of the vibratory driving process can be used to optimize vibratory pile driving, as examples have shown. A new concept is proposed in which the driveability can be determined from a correlation between penetration resistance measurements (blows/depth) and penetration speed. The validity of the concept is demonstrated by a case history and project references.

Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-fluid flow models

Most of the methods currently used for pore pressure prediction in sedimentary basins assume one-dimensional compaction based on relationships between vertical effective stress and porosity. These methods may be inaccurate in complex tectonic regimes where stress tensors are variable. Modelling approaches for compaction adopted within the geotechnical field account for both the full three-dimensional stress tensor and the stress history. In this paper a coupled geomechanical-fluid flow model is used, along with an advanced version of the Cam-Clay constitutive model, to investigate stress, pore pressure and porosity in a Gulf of Mexico style mini-basin bounded by salt subjected to lateral deformation. The modelled structure consists of two depocentres separated by a salt diapir. 20% of horizontal shortening synchronous to basin sedimentation is imposed. An additional model accounting solely for the overpressure generated due to 1D disequilibrium compaction is also defined. The predicted deformation regime in the two depocentres of the mini-basin is one of tectonic lateral compression, in which the horizontal effective stress is higher than the vertical effective stress. In contrast, sediments above the central salt diapir show lateral extension and tectonic vertical compaction due to the rise of the diapir. Compared to the 1D model, the horizontal shortening in the mini-basin increases the predicted present-day overpressure by 50%, from 20 MPa to 30 MPa. The porosities predicted by the mini-basin models are used to perform 1D, porosity-based pore pressure predictions. The 1D method underestimated overpressure by up to 6 MPa at 3400 m depth (26% of the total overpressure) in the well located at the basin depocentre and up to 3 MPa at 1900 m depth (34% of the total overpressure) in the well located above the salt diapir. The results show how 2D/3D methods are required to accurately predict overpressure in regions in which tectonic stresses are important.

Laboratory measurement of stress-dependent coal permeability using pulse-decay technique and flow modeling with gas depletion

A laboratory-scale coal permeability measurement study using the pressure pulse decay method was carried out to establish the permeability variation trend impacted by the combined effects of effective stresses and coal matrix shrinkage associated with gas depletion under uniaxial strain condition for San Juan basin coal. The experimental results showed that increased effective horizontal stress negatively impacts permeability enhancement. Furthermore, effective horizontal stress dominates the permeability variation. Finally, the rate of permeability increase accelerates dramatically at low pressures as a result of decrease in effective horizontal stress due to the matrix shrinkage effect. The established pressure-dependent-permeability (PdK) was compared with modeled results using two models, Harpalani and Chen and Shi and Durucan, both based on variations in effective horizontal stress. The match with the results obtained using the Harpalani and Chen model was perfect when appropriate initial cleat porosity and matrix shrinkage strain parameters were used. However, given the analytical conditions presented, the agreement between experimental and modeled results using the Shi and Durucan model was poor. After reviewing the fundamental principles behind model development, a modification was made, based on geo-mechanical principles. The measured permeability variation matched well with the results predicted by the modified model when appropriate cleat compressibility values were used. Basically, the revised model increases the effect of matrix shrinkage on permeability changes with continued depletion. The modeled results showed a permeability trend consistent with the experimental result although the permeability of coal was overestimated at low pressures.

Field investigation of deformation characteristics and stress mobilisation of a soil slope

Stress mobilisation and deformation of a slope are important for engineers to carry out reliable design of retaining systems. However, most case histories reported mainly on the response of pore water pressure (PWP), whereas knowledge about the stress deformation characteristics of slope is limited. In this study, a saprolitic soil slope was instrumented to monitor not only the responses of PWP but also horizontal stress and horizontal displacement. To assist in the interpretation of field data, a series of laboratory tests was conducted to characterise volume change behaviour of the soil taken from the site, under the effects of both net stress and suction. During a rainstorm event when positive PWP built up, a remarkably large displacement of 20 mm was recorded between 5.5- and 6-m depths, and the top 5 m of the slope exhibited translational downslope movement. This caused an increase in Bishop’s effective horizontal stress by 350 %, which reached a peak value close to 40 % of a Bishop’s effective passive stress. During the subsequent dry season when suction was recovered, an upslope rebound of 10 mm was recorded. Comparison of field and laboratory data reveals that the rebound was attributed to suction-induced soil shrinkage. This rebound led to a decrease in the Bishop’s effective horizontal stress previously built up during the storm event.

Measurement and modeling of adsorptive–poromechanical properties of bituminous coal cores exposed to CO2: Adsorption, swelling strains, swelling stresses and impact on fracture permeability

The reservoir response of unmineable coal seams to primary and enhanced natural gas recovery is strongly affected by gas sorption and the swelling properties of the coal reservoir rock. In-depth understanding of the process of gas sorption/desorption in the coal matrix, induced deformation and measurement of relevant physical parameters are critical for predictive reservoir management. Models used in industry practice are based on swelling strains measured in “free” swelling coal or on empirical correlations between strain and adsorption, and predict permeability changes based on changes of porosity or stress calculated assuming an analogy with thermoelasticity. However, not only coal seams are subjected to in-situ stresses and geometrical boundary conditions but also sorption and strain are strongly coupled. Representative experiments and a truly coupled model for coal seams are needed in challenging applications. We present a set of triaxial testing measurements on 38mm diameter fractured sub-bituminous/bituminous coal cores exposed to CO2. Testing includes the measurement of fluid uptake, adsorption-induced strains and stresses, and the impact on simultaneously measured permeability. Noteworthy, we measured increases in effective stress of up to 29MPa when injecting CO2 at 5MPa and preventing the coal core to swell. The results are analyzed with a poromechanical model in which coal matrix microporosity and adsorption-induced phenomena are embedded into a fractured reservoir rock with transverse isotropic properties. The adsorptive–mechanical coupling in the coal matrix is integrated through an adsorption stress function and fractured coal permeability is estimated as a function of Terzaghi's effective stresses (parallel and perpendicular to the bedding plane). The experimental results and model predictions help identify the characteristic response of coal microporosity and cleat macroporosity on the poromechanical response of coal cores, and suggest that order of magnitude changes of reservoir permeability observed in the field are linked to sorption-induced change on Terzaghi's effective horizontal stress under laterally constrained displacement condition. Together, the modeling and experimental characterization offer unprecedented insights into the mechanics of coal.

Horizontal stress anisotropy and effective stress as regulator of coal seam gas zonation in the Sydney Basin, Australia

Coal seam gas zonation in the Sydney Basin, NSW, Australia is related to basin hydrodynamics and hydrochemical facies evolution along the flow path from the subcrop to the basin center. Biogenic methane corresponds with meteoric water under hydrostatic pressure and persists down to the top of the geopressured zone (~800 to 1000m). Thermogenic gases, including wet hydrocarbons, can reach up to relatively shallow horizons of less than 500–600m depth. In the transition zone between the top of the geopressured and base of the hydrostatic zone, a mixed water and gas regime prevails, comprising brackish waters, and gases of mixed biogenic, thermogenic and inorganic origins, including CO2. Mechanisms for and the role of stress in the development of this layered hydrogeological and gas environment are investigated in this paper.The inverse relationship between effective horizontal stress and permeability in coals through regulation of cleat volumes is well documented, and there is evidence of regionally compartmentalized stress regimes with depth within the Sydney and other eastern Australian coal basins. This regional stress regime can be overprinted by the effect of localized geological features. It is hypothesized that the in situ stress regime plays an important role in the regulation of groundwater flow regimes and extents, resulting in the development of the reported gas content and compositional zonation.Analysis of regional gas and stress data obtained from public and private databases, as well as literature, supports this hypothesis. Changes in gas concentration and composition with depth correspond with discernable variations in horizontal stress anisotropy. Gas contents generally increase with depth down to a ‘peak gas’ horizon, below which concentrations decrease. This ‘peak gas’ zone is coincident with a horizontal stress anisotropy change from moderately high to low levels, associated with reverse to strike–slip faulting conditions, respectively. The stress release zone also marks the top of the thermogenic gas zone, identified by the first appearance of ethane in the vertical profile. This zone also hosts gases of mixed origins: biogenic, thermogenic and inorganic (CO2) and represents a mixed (transitional) groundwater flow environment. The base of the mixed gas zone is the top of the ‘geopressured-only’ flow associated with thermogenic gases and is signaled by the return to high stress reverse faulting conditions below 850–900m depth in the Sydney Basin.

Modelling laboratory horizontal stress and coal permeability data using S&D permeability model

A modelling study was carried out on a set of recently published horizontal (radial) stress and permeability data, obtained under uniaxial strain conditions, using Shi and Durucan permeability model. During the permeability experiment, the no-displacement lateral boundary condition was maintained through adjusting the applied confining pressure as the pore pressure was reduced to simulate coalbed methane production. The reported variations in the effective horizontal stress for a San Juan Basin core sample were first matched by tuning the elastic properties (Young's Modulus and Poisson's ratio) for the coal sample, which were unknown. The Young's Modulus was found to fall in a rather narrow range of 2.35 to 2.55GPa, with the corresponding Poisson's ratio in the range between 0.25 and 0.35. The availability of both permeability and horizontal stress data allows for the determination of the cleat volume compressibility. It was found that the semi-log plot of permeability increase vs. reduction in the effective horizontal stress displayed a bi-linear trend. The results of this study have demonstrated that the published laboratory horizontal stress and permeability data can be adequately described by S&D permeability model.

Discussion of “Shielding Piles from Downdrag in Consolidating Ground” by S. Y. Lam, C. W. W. Ng, and H. G. Poulos

Discussion of “Shielding Piles from Downdrag in Consolidating Ground” by S. Y. Lam, C. W. W. Ng, and H. G. Poulos

Field Investigation of Pile Setup in Mixed Soil

An instrumented test pile was installed at the Bayou Zourie bridge reconstruction site as part of a Louisiana Department of Transportation and Development (LADOTD) research initiative to study the setup phenomenon of piles driven in Louisiana soils. Pile instrumentation included pressure cells to measure the total pressure at the pile face, piezometers to monitor the excess pore water pressure at the pile face, and “sister bar” strain gauges to measure the strain distribution along the pile. Additional instrumentation consisted of multilevel piezometers installed within soils at different locations/depths from the pile and accelerometers attached to the piles during dynamic load testing. A total of two static load tests and four dynamic load tests were conducted on the test pile. During the static load tests, the strains within the pile were measured by the strain gauges, which were used to calculate the distribution of load transfer along the pile. Both static and dynamic load tests demonstrated the increase in pile resistance with time (setup). Results of dynamic load tests confirmed that pile setup occurs at a logarithmic rate after the end of driving (EOD) and is mainly attributed to the increase in side resistance. Good correlation was observed in this study between the pile setup and the percentage of dissipated excess pore water pressure with time. The measured excess pore water pressure suggested that the surrounding soil, along the pile (within distance 2B), is significantly influenced during pile driving. Results indicated that the changes in side resistance are directly related to the changes in the horizontal effective stress acting on the pile face.

Numerical analysis of the installation effect of diaphragm walls in saturated soft clay

The construction of diaphragm wall panels can cause the stress change and soil movements in adjacent ground. In this paper, the construction sequence of a typical diaphragm wall panel in saturated soft clay is simulated with a 3D finite element program. The soil is assumed to behave as an isotropic linear elastic/Mohr–Coulomb plastic material with a soil–water coupled consolidation response. Influence of the pore water pressure is concerned to consider the consolidation behavior of the saturated soft clay. The analysis shows that the changes in effective horizontal stress and pore water pressure during diaphragm wall installation depend on arching mechanism and permeability. The variation in stresses and movements of ground computed by the coupled consolidation analysis and the total stress analysis are compared. Influences of the permeability coefficient on the installation effects are discussed by parametric studies. Finally, a case study of a diaphragm wall construction in Shanghai, in which the ground settlements were monitored, is presented to illustrate the prediction procedure of coupled consolidation analysis.

The effect of kerogen on the elastic anisotropy of organic-rich shales

The elastic properties of reservoir rocks are important for geomechanics applications; the most important of which are: analysis of stress changes due to production, analysis of rock deformation and failure, wellbore trajectory optimization, and the design of hydraulic fractures. Organic-rich shales are often observed to be strongly anisotropic due to the partial alignment of anisotropic clay minerals and the bedding-parallel lamination of organic material within the shale. Neglecting shale anisotropy may lead to incorrect estimates of the in situ stress or stress changes resulting from production. As a result, isotropic models may fail to describe geomechanical behavior correctly. The distribution of the organic phase plays an important role in determining the elastic properties of organic-rich shales, and this has a significant effect on production-induced stress changes. The presence of kerogen leads to a decrease in all of the elastic moduli, and has a significant effect on the geomechanical behavior of shales. The change in horizontal effective stress for a given change in pore pressure resulting from production is greater for kerogen-rich shales, and the neglect of anisotropy in predicting such stress changes may lead to significant errors.

Permeability increase in Bowen Basin coal as a result of matrix shrinkage during primary depletion

Matrix shrinkage in coal-seam gas reservoirs as a result of production, and the resultant impact on absolute permeability, is a current area of intense interest. A number of publications have documented the existence of this phenomenon. The exponential growth behaviour of coal seam permeability with reservoir pressure depletion has been observed previously at the Fairway wells in the San Juan basin. More recently, an exponential trend has also been confirmed for a group of 10 wells in a region northeast of Fairway. An increase in the absolute permeability of coal seam is a result of matrix shrinkage caused by gas desorption, which becomes a dominant factor on cleat permeability over the effective horizontal stress change during production. Bottom hole pressure recovery during shut-in periods can provide valuable data concerning the impact of coal seam gas production on reservoir permeability. Arrow Energy's historical production data, from the MGP field in the Bowen Basin, contains over 60 instances of data on pressure recovery during shut-in. These time lapse build-up periods have been analysed using the pseudo-pressure method (Kamal and Six, 1991) in an effort to gain an understanding of the extent and effect of this phenomenon within the company's existing assets. The method is based on a pseudo pressure function that uses the adsorption isotherm and the relative permeability relations of the reservoir. The infinite acting radial flow regime was identified and the gradient was recorded on a semi log plot of the pseudo pressure versus dimensionless time. Results from these tests show multi fold increase in absolute permeability as a function of the estimated reservoir pressure.

Mechanical characterization of slope sediments: Constraints on in situ stress and pore pressure near the tip of the megasplay fault in the Nankai accretionary complex

We performed mechanical tests on mudstone samples cored in the hanging wall of a major out of sequence thrust fault in the Nankai accretionary complex prism, SW Japan, (1) to understand the consolidation and shear behaviors of slope sediments that form the fault zone and wall rock of this important structural feature in the upper several kilometers, and (2) to constrain in situ stresses and pore pressure, two fundamental parameters governing deformation processes in subduction zones, which are notoriously difficult to measure. We conducted deformation experiments on a suite of samples taken from depths of 20–150 mbsf, including six uniaxial consolidation tests and one isotropic consolidation test. For three of these tests, we conducted undrained triaxial compression testing following consolidation. Our results suggest that in situ pore pressure is hydrostatic and that during sedimentation and burial, the effective horizontal stress is ∼41% of the effective vertical stress. In combination with analysis of wellbore failures documented during drilling of the borehole, our experimental data allow us to define the complete stress tensor, including the magnitude of in situ minimum and maximum horizontal stresses, in the hanging wall of this major fault zone. The maximum horizontal stress magnitude is comparable to that expected for sedimentation and uniaxial burial, whereas the minimum horizontal stress lies below this value. This suggests (1) that the shallow sedimentary section was subjected to extension subparallel to the trench during or following burial and (2) that stresses associated with plate convergence are not effectively transmitted within these shallow sediments.

Effect of Directional Stress History on Anisotropy of Initial Stiffness of Cohesive Soils Measured by Bender Element Tests

ABSTRACT This paper describes the initial stiffness of reconstituted kaolinite clay in both vertical and horizontal planes under three different stress histories. The initial shear stiffness was obtained from bi-directional bender element tests during isotropic and K0 stress loading and unloading. An empirical correlation was established based on the initial stiffness of normally consolidated soils. Unlike the unique relationship of the initial vertical stiffness of normally consolidated clays, the initial stiffness in the horizontal plane is dependent on the stress ratio and previous stress history; thus, three different relationships of the initial horizontal stiffness were obtained for the three loading programs. The effect of the stress history on the initial horizontal stiffness can be considered properly by defining the degree of overconsolidation in terms of the horizontal effective stress. The change in the initial stiffness has a directional dependency on the stress history in the direction of the particle motion and wave propagation in the bender element tests.

Numerical predictions of the behaviour of soft clay with two anisotropic elastoplastic models

The numerical predictions obtained with the Melanie and MIT-E3 models are compared. Firstly, the performance of the constitutive models is checked against undrained triaxial tests. The models are then used to replicate the behaviour of an embankment built on soft clay. The numerical results are compared with the field data in terms of settlements, lateral displacements and excess pore pressures. Additionally, the numerical predictions are also analysed in terms of yield area, contours of vertical effective stresses, horizontal effective stresses and shear stresses and in terms of effective stress paths.

Evaluation of K0 of Granular Soils using DMT Indices

A series of CPTs and DMTs are performed in the calibration chamber in order to develop methods that estimate the coefficient of at-rest earth pressure (K0), which is an indirect measure evaluating the stress history of granular soil. Among DMT indices and the qc value, KD is observed to be the most sensitive to the stress history while qc and ED show the similar trend of change as the vertical stress and stress history. The relation of Baldi et al. (1986) appears to be applicable for only NC sands as it does not include the term representing the effect of horizontal effective stress. The relations suggested in this study, KD/K0 = χ(ED/)δ and KD/K0 = a0(ED/pa)a1(/pa)a2, are observed to provide comparable accuracy in K0 values with those of Jamiolkowski and Robertson (1988) and Mayne (1995, 2001), regardless of the stress history. Suggested relations use only DMT indices while Jamiolkowski and Robertson (1988) require both CPT and DMT results, and Mayne (1995, 2001) needs both the CPT result and the OCR value. Although the adoption of OCR in Mayne (1995, 2001) offers a considerable improvement in the accuracy of the K0 value, it is not considered practical since the inclusion of both soil property (OCR) and index parameters in an empirical correlation provides excessive redundancy.

Linking microseismic event observations with geomechanical models to minimise the risks of storing CO 2 in geological formations

For carbon capture and storage (CCS) in geological formations to be scientifically viable, we must be able to model and monitor the effects of geomechanical deformation on the integrity of the caprock. Excess deformation may open fractures, providing pathways for CO 2 leakage from the reservoir. An acceptable geomechanical model must provide a good match with field observations. Microseismic activity is a direct manifestation of mechanical deformation, so it can be used to constrain geomechanical models. The aim of this paper is to develop the concept of using observations of microseismic activity to help ground truth geomechanical models. Microseismic monitoring has been ongoing at the Weyburn CO 2 Storage and Monitoring Project since 2003. We begin this paper by presenting these microseismic observations. Less than 100 events have been recorded, documenting a low rate of seismicity. Most of the events are located close to nearby producing wells rather than the injection well, a pattern that is difficult to interpret within the conventional framework for injection-induced seismicity. Many events are located in the overburden. Without geomechanical simulation it is difficult to assess what these observations mean for the integrity of the storage formation. To address these uncertainties we generate numerical geomechanical models to simulate the changes in stress induced by CO 2 injection, and use these models to predict the generation of microseismic events and seismic anisotropy. The initial geomechanical model that we generate, using material properties based on laboratory core measurements, does not provide a good match with either event locations or S-wave splitting measurements made on the microseismic events. We find that an alternative model whose reservoir is an order of magnitude softer than lab core-sample measurements provides a much better match with observation, as it leads shear stresses to increase above the production wells, promoting microseismicity in these areas, and generates changes in effective horizontal stresses that match well with S-wave splitting observations. This agreement between geophysical observations and a softer-than-lab-measurements reservoir model highlights the difficulties encountered in upscaling lab scale results. There is a strong need to link geomechanical models with observable manifestations of deformation in the field, such as induced seismicity, for calibration. Only then can we accurately assess the risks of leakage generated by mechanical deformation.

A seepage-stress coupled analysis of seabed deformation induced by the decomposition of gas hydrate

The deformation of seabed considering seepage-stress coupling is analysed using finite element method in this study, the effect of the varying pore pressure on stress field is accounted in the analysis, and the impact of reservoir permeability and the well pressure on the decomposition radius is studied. The changes of mechanical parameters due to hydrate decomposition are achieved by using user defined field subroutine. The results show that vertical and horizontal effective stress of soil in the dissociated area increase significantly while gas hydrates are decomposed by depressurisation. The reservoir permeability and well pressure have significant impact on the decomposition radius. The seabed deformation increases non-linearly with the increasing of the gas hydrate decomposition radius. The maximum vertical displacement reaches 18 m and the maximum horizontal displacement reaches 7.5 m.