Surface Heave Research Articles

Coupling analysis between wave resonance in the moonpool and heave motion of the twin hulls with mooring effect

Fluid resonance in the moonpool formed by two identical rectangular hulls in water waves is investigated by employing the Computational Fluid Dynamics (CFD) package OpenFOAMⓇ. The influence of vertical stiffness on the behavior of moonpool resonance coupling with the heave motion response is presented. Numerical simulations show that the free surface oscillation in the moonpool exhibits a two-peak variation with the incident wave frequency, defined as the first and second peak frequencies. A local Keulegan–Carpenter (KC) number is introduced for describing the influence of fluid viscosity and flow rotation on the fluid resonance and heave motion resonance. At the first peak frequency, the free surface oscillation and heave motion response show an in-phase relationship, where increase in the vertical stiffness can increase the relative motion between them. This finally leads to an increase in the KC number, indicating the increased effect of energy dissipation with increase in the vertical stiffness. At the second peak frequency with an out-of-phase relationship between the free surface oscillation and heave motion response, the variation of the KC number is not sensitive to the vertical stiffness. Correspondingly, the influence of energy dissipation is not strongly dependent on the vertical stiffness.

A New Methodology for Quantitative Risk Assessment of CO2 Leakage in CCS Projects

Summary Assessing risks during carbon dioxide (CO2) sequestration involves a systematic process to identify them (risk assessment), analyze, prioritize, score them (risk analysis), develop mitigation strategies, and plan for measurement, monitoring, and verification (MMV) activities. In this context, risk assessment and analysis are often conducted involving qualitative approaches and/or subjective evaluations based on experts judgments. In this paper, we propose to use numerical results of dynamic subsurface modeling to assess risks in a more precise, less subjective, and quantitative manner, enabling a comprehensive definition of effective MMV plans. In this context, MMV evolves into modeling, measurements, monitoring, and verification [(M)MMV]. The conceptual model used for this study integrates flow and geomechanical-coupled behavior to assess caprock integrity, faults reactivation, and ultimately the risk of CO2 leakage. Uncertainty analysis and a 4D probabilistic workflow are used to quantify the likelihood and consequences of CO2 leakage and to score risks. The proposed approach offers a general framework to enable subsurface-modeling-based quantitative risk assessment (QRA) for the definition of successful (M)MMV plans. In this study, we have focused on the QRA of leakage risks through the fault and intact caprock. Other applications are possible, such as: (1) leakage risks through the caprock resulting from caprock failure; (2) lateral CO2 migration leading to permit limits violation or inducing interferences with neighboring activities; (3) leakage risks resulting from loss of well integrity; (4) risks of faults reactivation; (5) risks of surface heave; and (6) risks of induced seismicity. All these results can be used to formulate effective (M)MMV strategies for an optimized and cost-effective risk mitigation.

Thermal-hydro-mechanical modeling of short-term ground responses due to the borehole thermal energy storage operations in a Canadian subarctic region

Seasonal borehole thermal energy storage (BTES) has been recommended as a strategic technology to make an energy transition in the off-grid communities. However, the running of BTES can create thermal disturbance to the surrounding soil formation and bring a thermal-hydro-mechanical coupled process. This coupled process is particularly significant in less permeable formations, where the clay bound water is abundant. The role of clay bound water on the ground response during thermal storage has not been investigated previously. This study aims to numerically assess the short-term ground response due to the thermal disturbance during BTES operations in a Canadian subarctic region. The numerical analysis is conducted using our in-house developed finite element code. Our numerical results demonstrate the significance of considering bound water dehydration in characterizing the ground heave process during the short-term BTES operation in an over-consolidated soil formation. The ground expansion behavior is due to the high excess pore pressure generated from thermal disturbance. The surface heave is mainly from a poroelastic impact leveraging the release of some in-situ effective stress. The neglect of bound water dehydration will underestimate the magnitude of ground heave.

Excess Ground Ice Profiles in Continuous Permafrost Mapped From InSAR Subsidence

AbstractExcess ground ice formation and melt drive surface heave and settlement, and are critical components of the water balance in Arctic soils. Despite the importance of excess ice for the geomorphology, hydrology and biogeochemistry of permafrost landscapes, we lack fine‐scale estimates of excess ice profiles. Here, we introduce a Bayesian inversion method based on remotely sensed subsidence. It retrieves near‐surface excess ice profiles by probing the ice content at increasing depths as the thaw front deepens over summer. Ice profiles estimated from Sentinel‐1 interferometric synthetic aperture radar (InSAR) subsidence observations at 80 m resolution were spatially associated with the surficial geology in two Alaskan regions. In most geological units, the estimated profiles were ice poor in the central and, to a lesser extent, the upper active layer. In a warm summer, units with ice‐rich permafrost had elevated inferred ice contents at the base of the active layer and the (previous years') upper permafrost. The posterior uncertainty and accuracy varied with depth. In simulations, they were best (≲0.1) in the central active layer, deteriorating (≳0.2) toward the surface and permafrost. At two sites in the Brooks Foothills, Alaska, the estimates compared favorably to coring‐derived profiles down to 35 cm, while the increase in excess ice below the long‐term active layer thickness of 40 cm was only reproduced in a warm year. Pan‐Arctic InSAR observations enable novel observational constraints on the susceptibility of permafrost landscapes to terrain instability and on the controls, drivers and consequences of ground ice formation and loss.

Integrated containment risks assessment for subsurface CO2 storage: Overburden analysis and top seal integrity study, offshore Norway

This study summarizes the OASIS (Overburden Analysis and Seal Integrity Study for CO2 Sequestration in the North Sea) project that focuses on assessing the containment risks associated with the geological carbon sequestration (CCS) of the Northern Lights project. CCS is viewed as one of the most effective solutions for reducing carbon emissions, as it captures carbon dioxide from point sources and permanently stores it in suitable geological formations. However, injecting CO2 into the subsurface may have mechanical consequences, including fault reactivation, top seal fracturing, surface heave, etc. This study proposes an interdisciplinary workflow to characterize the caprock, faults, and overburden associated with CCS projects in the Horda Platform area, to improve injection-induced containment risk assessment. Our findings show that the proposed workflows and tools effectively characterize stress-related mechanical hazards. However, due to the complex nature of rocks, it is challenging to evaluate the top seal integrity using a single method. Therefore, the proposed interdisciplinary approach is more effective for any fluid injection site's characterization, given the complex nature of the subsurface and its behavior under injection-induced stress changes. This research paper adds knowledge about the top seal integrity assessment and the reliability of injected CO2, making CCS projects more reliable and safer. Although this study focuses on the northern North Sea, the proposed methods are equally applicable globally to characterize subsurface CO2 storage sites. Apart from CCS projects, these research results can benefit other subsurface injection projects, such as water injection for reservoir management, wastewater injection for disposal, hydrogen storage, and hydraulic fracturing for unconventional hydrocarbon resources.

Geomechanical modelling of ground surface deformation induced by CO2 injection at In Salah, Algeria: Three wells, three responses

This study investigates the ground surface deformation above three injection wells throughout CO2 injection between mid-2004 to early-2011 in the In Salah CO2 storage project at Krechba, Algeria. A coupled three-dimensional finite element model of three wells (KB501, KB502, and KB503) was developed. The model accounts for the CO2 diffusion in the reservoir and structural features including permeable fractures and faults, as well as the poroelastic deformation of the reservoir and overburden layers which result in the ground surface deformations during CO2 injection. The character of the ground surface deformation above each injection well was different, suggesting a different CO2 plume shape in the subsurface. An ellipse-shaped heave above KB501 indicates that the CO2 plume shape followed the anisotropic permeability in the reservoir, KB502’s double-lobe surface heave pattern is associated with the activation and pressurization of a vertical fault and finally, the elongated surface uplift pattern above KB503 is linked to the presence of permeable fractured zone in vicinity of the well, as indicated by seismic surveys. The two distinctive structural features in the vicinity of KB502 and KB503 were included in the numerical model, accounting for a hydraulically conductive fault in the caprock and a fractured zone in the reservoir, respectively. The observed surface deformation was utilised to tune the orthotropic mechanical properties of the fault and the fractured zones. The simulation results are in good agreement with the measured InSAR data. In addition, assigning anisotropic permeability to the reservoir plays a significant role in successfully simulating surface uplift patterns.

Semi-Analytical Prediction of Ground Surface Heave Induced by Shield Tunneling Considering Three-Dimensional Space Effect

The ground surface deformation induced by shield tunnels passing through enclosure structures of existing tunnels is a particular underground construction scenario that has been encountered in Wuhan Metro Line 12 engineering cases in China. Timely ground deformation prediction is important to keep shield tunneling safe. However, the classic ground deformation theory is difficult to accurately predict for this ground deformation. This paper develops a semi-analytical method to predict ground heave considering the space effect in this engineering condition. Based on the improved ground deformation theory, a novel deformation prediction method for the ground and enclosure structure is derived and combined with Kirchhoff plate theory. Comparing with field deformation measurements, the maximum difference between the measured and calculated deformation is 14.6%, which demonstrates that the proposed method can be used to predict the ground heave induced by shield tunnels passing through the enclosure structure of existing tunnels. The parameters of the underground diaphragm wall used in Wuhan Metro Line 12 are further studied in detail. The results show that the ground heaves have a positive correlation with the embedded ratio of the diaphragm wall, but a negative correlation with its elastic modulus and thickness. However, the thickness and embedded ratio have a limited effect on ground heaves. This study provides a technical reference for optimizing the setting of enclosure structures in order to protect existing buildings.

Integration of subsurface dynamic coupled modelling and monitoring technologies for CCS: examples from existing projects


 Introduction
 Host rock injectivity and storage complex integrity (containment) for CO2 sequestration are critical factors to ensure that capacity targets are met while preventing CO2 leakage over time and confirm permanent storage.
 
 Figure 1 sketches the typical CO2 injectivity problem. Evaluating injectivity, capacity and containment requires assessing key phenomena such as: seal and faults capillary controls, non-isothermal reactive flow, geomechanical failure induced in the seal, along faults and/or fractures and in the vicinity of the wells. Additional analyses will also be needed to evaluate the completion integrity of the wells (injectors, monitoring and existing wells) under variable load conditions in terms of pressure, temperature and chemistry. The listed phenomena, and their likely effects, are analysed by means of dynamic coupled modelling, considering co-existing (geo)mechanical and dynamic flow simulations. Therefore, coupled modelling improves the risk analysis allowing to evaluate the Thermo-Hydro-Mechanical-Chemical (THMC) processes associated to CO2 injection.
 Analyses
 In this presentation we will provide some examples of integration of subsurface dynamic coupled modelling and monitoring technologies for CCS. Some of these examples are derived from existing projects.
 
 Injectivity impairment during CO2 injection is a well-known issue often observed at well and field scale (e.g. Snøhvit, Ketzin, Decatur projects [1], [2]). Loss of injectivity is governed by the interactions between CO2-brine phase behavior, CO2-solid phase (rock) behavior, salt precipitation, multi-phase flow. Characterizing zonal injectivity and developing mitigation strategies will be therefore important for project success. Figure 2 (left and center) shows an example of time-lapse CO2 saturation evolution during injection and consecutive non-isothermal processes associated to Joule-Thompson effect (H2O vaporization, cooling and induced salt precipitation due to dry-out). Temperature and pressure changes can lead to near wellbore failure (thermal and pressure induced fracturing) impacting injection performance due to near wellbore fracturing and consecutive permeability changes (Figure 2 right).
 To close the evaluation loop, the integrated subsurface characterization workflow is completed by measurements to image the subsurface before and after CO2 injection. This provides essential insights into the storage complex quality before injection and effective monitoring during injection and permanent storage, tracking the position of the CO2 pressure and concentration plumes, assessing surface heave, and detecting any risks or potential leakage paths. There is a tight link between subsurface dynamic coupled modelling and existing monitoring technologies. This link expands the well-known MMV (Measurement, Monitoring and Verification) process into a more integrated 3MV process (Modelling, Measurement, Monitoring and Verification), opening to the definition of a subsurface digital twin supporting successful CCS operations. We will briefly introduce methods and technologies enabling the subsurface dynamic modelling and monitoring of CO2 injection and storage. Seismic and borehole petrophysical and geophysical measurements for initial subsurface characterization and consecutive monitoring will be described.

An experimental investigation into soil–structure interactions of integral bridge abutments due to cyclic translations

Integral bridges are built without expansion joints to avoid many of the persistent issues with joint degradation and maintenance problems regularly experienced by traditional bridges. In the absence of expansion joints, the cyclic thermal displacements of the integral bridge would be transferred unmitigated by the joints to the abutment resulting in accentuated soil–structure interactions. Previous studies have mainly focussed on the rotational mode of integral abutment movement while the translational mode of movement and backfill deformations have received much less attention. This paper presents the results of laboratory tests conducted on a semiscale (1:2) physical model, which was designed using dimensional analysis to achieve field stress and strain similarity with a full-scale 1.92 m high-prototype integral abutment. The comparative effects from five tests covering low to high cyclic translation amplitude on backfill surface settlement and heave, and lateral earth pressures behind the abutment were investigated over assumed 120 seasonal cycles. Asymptotic settlement depth of the backfill was obtained in each test. Full passive failure surface was observed when the cyclic translation amplitude of the test exceeded the threshold amplitude. The findings also suggest that the settlement depth seemed to be linked to the development of passive failure surface in the following sense—the asymptotic settlement depth in those tests which developed full passive failure surface would attain the same (ultimate) asymptotic depth; conversely, when the passive failure surface had not or only partially developed in that test, the asymptotic settlement depth was dependent on the cyclic translation amplitude, but it was less than the ultimate observed for full passive failure surface. Lateral earth pressure only stabilized to an asymptotic state for the test with the lowest cyclic translation amplitude during the 120 cycles. Shakedown limit state was observed for this case. At larger cyclic translation amplitudes, the lateral earth pressure did not stabilize but continued to evolve with the elapsed cycles, and shakedown limit state was not observed for these cases.

Time-dependent study of load transfer mechanism in geocell reinforced soil bed

Geocell-reinforced embankments are commonly subject to rail or road traffic which comprises repetitive loads. However, the existing equations for the analysis and design of geocell-reinforced systems are based on performance under static loads. Hence, it is imperative to study the performance of geocell-reinforced embankments under repetitive loads. The study addresses the shortage of time-dependent studies on geocell-reinforced systems by analyzing the performance of geocell-reinforced embankments under repetitive loads over time. The actual curvature of honeycomb-shaped pockets is carefully modeled for accurate analysis of the load transfer mechanism of geocell-reinforced soil. The study analyses two different geocell configurations that are conventionally adopted in practice. In the first case, the geocell platform is placed at the embankment base and restrained within the toe of the embankment. In the second case, the platform is extended on both sides to serve as a working platform. The study aims to assess the effect of the configuration of geocell reinforcement under different types of loading. The time-dependent response of the embankment over the geocell platform is then analyzed for static and repetitive loads to assess the performance of geocell-supported embankments under different loading applications. The lateral deformation at the toe, stress on the subgrade, and heave characteristics are analyzed for time. It is observed that the presence of geocell at the embankment base not only reduces the stress transferred to the subgrade but also mitigates differential settlement over time. The difference in reinforcing effect under static and repetitive loads is notable in the case of surface heave reduction. Both configurations reduce stress on the subgrade. However, for a significant reduction in surface heave, it is recommended to place the geocell mat as a working platform extending beyond the embankment toe on both sides.

Ground surface movement of Shallow-Buried Large-Sectional tunnel under Full-Ring Pipe-Jacking roof and ground freezing

The Gongbei Tunnel is an important part of the Hong Kong–Zhuhai–Macao Bridge, with a super-large section of 336.9 m2 and an extremely shallow cover section 5 m from the tunnel crown. The Gongbei Tunnel mainly passes through a weak muddy soil layer with a high water level. In addition, Gongbei Port (connecting Zhuhai city and Macao) is immediately above the tunnel. Thus, the environmental concerns and political sensitivity regarding this area necessitate very strict control of ground surface movements. Therefore, a full ring of a pipe-jacking roof (with 36 pipes) was used to control the ground movements caused by tunnel excavation. In addition, a ground-freezing method was adopted to prevent water inflow during the tunnel excavation. The tunnel excavation was divided into 14 sections and was conducted step-by-step to control the excavation-induced ground surface settlement. Generally, the ground surface movement appeared as an uplift, owing to the ground freezing. The most significant ground surface heave was greater than 500 mm, and the settlement at the tunnel crown was less than 20 mm, indicating that the new construction method protected the tunnel effectively during the excavation but had a significant effect on the surrounding environment. To better understand the coupled effects of ground freezing and tunnel excavation on the ground response, the ground surface movement induced by ground freezing was predicted using the stochastic medium theory. Consequently, the ground surface settlement induced by tunnel excavation was obtained by subtracting the calculated ground surface heave caused by the ground freezing from the observed ground surface movement. The calculated freezing-induced ground surface movement was consistent with the measurements. The calculated results show that the distribution shape of the ground surface movement changes from a concave type to a spandrel type when the frozen wall exceeds the tunnel cover depth. Finally, three key parameters influencing the ground surface movement were discussed: the development velocity of the frozen wall, the frost heave ratio, and the primary influence angle. A parametric study shows that the frost heave ratio has the most significant effect on the ground surface movement and should be addressed more carefully via freezing temperature control in the ground freezing process.

Analysis of the Deformation Law of Deep and Large Foundation Pits in Soft Soil Areas

Taking a deep excavation in Suzhou soft soils adopting three support schemes as the background, the excavation performance metrics, including the heave and lateral deformation of diaphragm walls, surface vertical deformation, vertical deformation of surrounding buildings, and earth pressure, are thoroughly investigated based on 15 excavation cases collected in the soft soil area of Suzhou. Based on the analysis of monitoring data, some findings were achieved: the foundation pit deformation is greatly affected by the spatial effect. The existing station can constrain the foundation pit deformation. Benefiting from the combination of various support solutions, the average maximum deflection of the diaphragm wall is 0.10% He. The maximum lateral movement depth of the diaphragm wall (δhm) is mainly located at (He-7, He+12.5). The vertical deformation of the wall top is greatly affected by the excavation exposure time and soil conditions. The heave range of the wall top is (−0.08∼0.26%) He. Under the action of the displacement of the diaphragm wall to outside the pit and the upward displacement of the wall top, the ground surface is uplifted, and the maximum uplift is (0.02∼0.14%) He, ranging from 0.12δhm to 1.13δhm. The maximum surface settlement is (−0.01% ∼ −0.15%) He, ranging from −0.22δhm to −3.11δhm. The form of building heave is mainly affected by the surface heave and the distance from the diaphragm wall (d). When d is within a certain range, there is a heave settlement difference between the adjacent side and the opposite side of the excavation, and the adjacent side undergoes mostly subsidence, while the opposite side undergoes mostly uplift. The peak value of the apparent earth pressure (AEP) envelope is 0.59γHe, which falls within (0.47∼0.78) He. The calculation scheme proposed by Kim can be used to predict the AEP for multiple soil types.

Deformation analysis of pipe-jacking process for a large-section shallow-covered project crossing highway

This paper introduces an engineering example of a large cross-section shallow soil covered rectangular pipe jacking of East-West double track crossing expressway. The cross-section size of pipe jacking is 9.90m × 8.15m, the length of single section is 1.5m, the through length of east line and west line is 80m, and the thickness of soil covering is 2.48 ∼3.13M. In order to reduce the impact of pipe jacking construction on the expressway, measures such as setting of the frontal jacking pressure, the control of the friction resistance of the slurry sleeve, the control of the slurry pressure and the settings of φ 824 ×12@1100 steel pipe concrete curtain. The vertical displacement of the steel pipe curtain and the displacement of the highway pavement was monitored. The results show that the road surface heave is controlled within 3cm: the maximum heave of the north shoulder near the pipe curtain launching shaft is 27.8mm, the heave of the central road arch is 16.2mm ∼ 19.1mm, the maximum heave of the south shoulder near the receiving shaft is 12.7mm, and the maximum heave of each section is less than 1.5mm The position is the axis of pipe jacking machine. From the cross-sections of pipe jacking crossing, the range of transverse influence area of 5mm road uplift is about 2.0 ∼ 3.0 times the width of pipe jacking machine, and the range of transverse influence area of 10mm road uplift is 1.0 ∼ 2.0 times the width of pipe jacking machine. The monitoring results show that the construction parameters of pipe jacking are reasonable

Effect of Aperture Size on the Performance of Bamboo Mat Reinforced Soil Bed

ABSTRACT Soil reinforcement using natural materials has become popular due to the concern over the environmental issues associated with geosynthetics. Bamboo is one of the fine materials used as soil reinforcement in different forms. This paper investigates the efficacy of bamboo mats with different aperture sizes for soil reinforcement. In India, handwoven mats are utilized from ancient times onwards for various households and other applications. Bamboo mats with rectangular weaving patterns with and without aperture were used for the study. The aperture sizes are expressed in terms of the width of each strip in the bamboo mat (w). The bamboo mat with a square aperture of 0.5 w × 0.5 w, 1 w × 1 w, 2 w × 2 w, 3 w × 3 w and 4 w × 4 w were used for the study. Series of laboratory model tests were performed to assess the performance of bamboo mat reinforced soil bed. The test results show that the inclusion of bamboo mat improves the bearing capacity and reduces footing settlement. The effect of aperture size on the performance of bamboo mat reinforced soil is studied in detail and the results are presented in the paper. The formation of surface heave is considerably reduced and heave reduction factors for different mat types are also reported.

Coupled hydro-mechanical analysis of underground gas storage at Sarajeh field, Qom formation, Iran

Production or injection of fluids from/in an underground storage site causes variations of pore pressure and stress states. These fluctuations significantly affect implications for hydraulic fracturing, wellbore integrity, top surface subsidence and heave, fault-reactivation, and stability of reservoir and caprock. Therefore, in order to keep optimal conditions during the process of gas injection and production, it is of paramount importance to have accurate estimates of the pore pressure. In this investigation, coupled fluid flow and geomechanical simulations, as well as rock mechanical tests, are performed on the Sarajeh field, Iran to investigate the geomechanical behavior of the Sarajeh reservoir during gas injection and production as well as estimate the caprock and reservoir integrity and evaluate the risk of fault reactivation. The results show up to −16 cm subsidence due to the production and 6 cm heave due to the injection. The critical pressures for the reservoir rock's failure and activation of the faults are 11,283 psi and 9986 psi, respectively, which make the operator able to store gas up to 2.2 and 1.9 times higher than the maximum reservoir pressure. Hydro-mechanical evaluation of the Sarajeh field determines essential information about the effect of gas injection and production for safe and successful seasonal gas storage.

Analytical Solution of Three-Dimensional Heaving Displacement of Ground Surface during Tunnel Freezing Construction Based on Stochastic Medium Theory

Many studies indicate that the heaving displacement during tunnel freezing construction can be regarded as a plane strain problem. However, due to the fact that many of the frozen pipes are placed obliquely in practical engineering, it should be a three-dimensional problem. Therefore, considering stochastic medium theory, the analytical solution of three-dimensional heaving displacement of ground surface during tunnel freezing construction is established, and the analytical solution is applied to the project case in Beijing. The calculation results show that, considering the inclination angle between the freezing pipe and the center axis of the tunnel, the maximum heaving displacement of the ground surface occurs at the tunnel center. When the inclination angle is equal to 0°, the analytical solution of three-dimensional ground surface heaving displacement is in good agreement with that of the two-dimensional prediction model, which further verified the reliability of the established analytical solution of the three-dimensional frost heave prediction model.

Use of digital correlation techniques for investigating behaviour of geothermal driven piles

Geothermal energy has established its huge potential as renewable source of energy for general building establishments. A key feature here is the use of energy piles which serve as major energy exchange system which is sustainable and low-cost. Energy piles are basically driven precast piles employed to provide structural support to structures and act as heat exchange units to provide heating / cooling to buildings. The behaviour of energy piles is influenced by temperature, physical and engineering properties of soil. However, uncertainty still exists at pile soil interface irrespective of its heating or cooling conditions. The present study examines the suitability of using digital correlation technique (DIC) namely GeoPIV-RG software to study the soil deformation at pile soil interface in sandy soil. A rectangular test tank made of steel with a size of 60 × 20 × 45 cm is used for experimental studies. Hollow half section aluminum piles closed at the ends with two different pile length to outer pile diameter ratios viz., 10 and 15 of same flexural rigidity are used for the experimental studies. The piles are subjected to sustained loading simulated through Universal testing machine and movements of soil around the pile are captured using a digital camera. The image analysis software named GeoPIV-RG is used to determine the shear strains and soil displacements. Analysis of results indicated that this technique could capture deformation characteristics and surface heave formation in the surrounding infill medium.

Structural Behavior of Pipelines Buried in Expansive Soils under Rainfall Infiltration (Part I: Transverse Behavior)

Landslides, fault movements as well as shrink/swell soil displacements can exert important additional loadings on soil buried structures such as pipelines. These loadings may damage the buried structures whenever they reach the strength limits of the structure material. This paper presents a two-dimensional plane-strain finite element analysis of an 800 mm diameter water supply pipeline buried within the expansive clay of the Ain-Tine area (Mila, Algeria), considering the unsaturated behavior of the soil under a rainfall infiltration of 4 mm/day intensity and which lasts for different time durations (8, 15 and 30 days). The simulations were carried out using the commercial software module SIGMA/W and considering different initial soil suction conditions P1, P2, P3 and P4. The soil surface heave and the radial induced forces on the pipeline ring (i.e., Axial , Shear forces and bending moments ) results indicated that following the changes of suction the rainfall infiltration can cause considerable additional loads on the buried pipeline. Moreover, these loads are proportionally related to the initial soil suction conditions as well as to the rainfall infiltration time duration. The study highlighted that the unsaturated behavior of expansive soils because of their volume instability are very sensitive to climatic conditions and can exert adverse effects on pipelines buried within such soils. As a result, consistent pipeline design should seriously consider the study of the effect of the climatic conditions on the overall stability of the pipeline structure.

Impact of Formation Dilation–Recompaction on Cyclic Steam Stimulation

SummaryAn integrated modeling of the cyclic steam stimulation (CSS) at the Peace River heavy-oil/oil-sand deposits in Alberta, Canada, is challenging because of the presence of compositional gradient, faulting, and bottomwater pockets, and the variations in the oil viscosity, rock dilation, fracturing, and the pay-zone-thickness variation. Both gravity and viscosity are marked by declining quality with depth, biodegradation, and compartmentalization.The high oil viscosity and low water mobility at Peace River cause low initial injectivity. High injectivity during the CSS is achieved by high-pressure injection to fail the formation mechanically and trigger fracturing and pore deformation. Moreover, the pore dilation/recompaction triggers relative permeability hysteresis.History matching of high steam injectivities is challenging when reasonable fracture lengths and rock compressibilities are used. To match injectivities, most reservoir simulations have used either a larger compressibility (“spongy-rock” approach) or long fractures. The spongy-rock approach predicts a steady increase in injection pressure, whereas during the early time of the injection cycles, injection pressures increase and then level off for most of the cycle.We describe the enhancements made in an iteratively coupled geomechanical–flow model to incorporate the modeling of both pore deformation and relative permeability hysteresis to match the injection pressures, steam injectivity, and oil/water productions from CSS at Peace River that are otherwise difficult to reproduce. The geomechanical model explains surface heave and high injectivity caused by dilation attributable to shear failure, increase in pore pressure/formation compressibility, and decrease in effective stress. A dilation pressure is specified, below which the behavior is elastic and above which a higher compressibility is used. Above a maximum porosity, further dilation is not permitted. Also, the hysteresis model calculates gridblock relative permeabilities that lie on or between the imbibition/drainage curves, making it possible to use the laboratory-derived two-phase oil–water relative permeabilities and still match the field-measured water- and oil-production volumes.By combining an iteratively coupled reservoir–geomechanical model for the CSS with stochastic workflows, including the Latin-hypercube design (LHD) and response-surface methodology (RSM), the impacts of dilation/recompaction factors (fracturing pressure, maximum injection pressure, dilation pressure, recompaction pressure, and formation compressibility) are quantified through history matching the field results and automated stochastic sensitivity analysis and uncertainty assessment.

Modelling groundwater rebound in recently abandoned coalfields using DInSAR

Advances in differential interferometric synthetic aperture radar (DInSAR) processing algorithms, such as the Intermittent Small Baseline Subset (ISBAS), and increased data availability from SAR systems, such as Sentinel-1, provide the opportunity to increase the spatial and temporal density of ground deformation measurements. Such measurements, when combined with modelling, have the potential to make a significant cost-effective contribution to the progressive abandonment strategy of recently closed coalfields. Applications of DInSAR over coalfields have observed heave in coal measures rocks and temporal correlations between the rise of mine water and deformation time-series. The cessation of systematic dewatering can have a variety of detrimental impacts and knowledge of the time-scales (i.e. the rate of rebound) and structure of the mine system are crucial to the remediation strategy. Although mine plans and borehole measurements provide vital information in this regard, mine plans are often incomplete or inaccurate, whereas monitoring boreholes are spatially sparse. Consequently, groundwater can flow in unanticipated directions via goaf, mine shafts and roadways, making it difficult to determine where the impacts of rebound are likely to occur. In this study, ground deformation data obtained using ISBAS DInSAR on ENVISAT (2002–2009) and Sentinel-1 (2015–2019) data are used to develop a simple method to model groundwater rebound in abandoned coalfields. A forward analytical model based upon the principle of effective stress and mine water ponds is first implemented to estimate surface heave in response to changes in groundwater levels measured in monitoring boreholes. The forward model is then calibrated and validated using the ground deformation data. The DInSAR data were subsequently inverted to map the change in groundwater levels in greater detail across the coalfield and forecast surface discharges in order to support mitigation strategies.