Overburden Pressure Research Articles

Review and Assessment of Material, Method, and Predictive Modeling for Fiber-Reinforced Polymer (FRP) Partially Confined Concrete Columns

The repairing and strengthening of concrete structures using external and internal partial confinements are inevitable in the construction industry due to the new standards and rapid developments. The conventional materials and methods of confinement are unable to meet modern safety and functional standards. The fiber-reinforced polymer (FRP) enhances the strength and ductility of deteriorating and new concrete columns by reducing lateral confinement pressure and resistance against seismic shocks. The precise methods of partial confinement are inevitable for effective FRP-concrete bonding, durability, and cost-effectiveness under different loading conditions and to cope with external environmental factors. Predictive modeling and simulation techniques are pivotal for the optimization of confinement materials and methods by investigating the FRP-concrete novel confinement configurations, stress–strain responses, and failure modes. The novel materials and methods for concrete columns’ partial confinement lack high compressive strength, ductility, chemical attack resistivity, and different fiber orientation impacts. This review provides an overview of recent confinement materials, novel methods, and advanced modeling and simulation techniques with a critical analysis of the research gaps for partial FRP confinement of concrete columns. The current challenges and future prospects are also presented.

Investigating the CO2 Geological Sequestration Potential of Extralow-Permeability Reservoirs: Insights from the Es1 Member of the Shahejie Formation in the Dawa Oilfield

Investigating the CO2 Geological Sequestration Potential of Extralow-Permeability Reservoirs: Insights from the Es1 Member of the Shahejie Formation in the Dawa Oilfield

Compaction localization in geomaterials: A mechanically consistent failure criterion

Compaction bands play a key role in the deformation processes of porous rocks and explain different aspects of physical processes in geological formations. The state-of-the-art description of the localized strains that lead to compaction banding has limitations from the mechanical point of view. Thus, we describe the phenomenon using a consistent axiomatic formulation. We build a viscoplastic model using minimal assumptions; we base our model on six principles to study compaction band strain localization triggered by viscous effects. We analyze different stress states to determine the conditions that trigger compaction bands. Laboratory experiments show that a material undergoes different strain localizations depending on the confinement pressure; thus, we perform a series of numerical experiments that reproduce these phenomena under varying triaxial compression conditions. These simulations use a simple viscoplastic constitutive model for creep based on Perzyna’s viscoplasticity and show how confinement changes the strain localization type for different triaxial tests.

Correlation of CPT measurements and relative density of LEAP-2017 and LEAP-2020 centrifuge models

Miniature cone penetration tests (CPTs) were conducted during the LEAP 2017 and LEAP 2020 centrifuge experiments to characterize and quantify the soil deposit properties. A total of 43 CPTs were obtained for deposits with varying relative densities. All experiments were performed using Ottawa F-65 Sand and used the same CPT tool model. A comprehensive study was undertaken to assess the quality and consistency of the CPT data. Outlier and regression analyses were used to develop an empirical relation to evaluate the relative density of Ottawa sand (centrifuge) deposits from measurements of the CPT tip resistance. This relation provides an estimate of the mean relative density profile, and associated standard deviation to quantify uncertainty. The relation accounts for the overburden pressure influence and the potential effects of container width (when the used container is narrow). The experimental results were found to have a good consistency with a regression R2 equal to 0.85.

ON THE POSSIBLE FORMATION MECHANISM OF THE OPEN FRACTURING IN SEDIMENTARY BASINS

The paper shows that the formation of orthogonal systems of open macrofractures (cleavages) of sedimentary basins can occur at the stage of diagenesis during the first hundreds of years for a small range of shelf depths (up to 100 m) during sedimentation. During this period, sediments are compacted and the excess water is slowly squeezed out, which determines the decrease in the Poisson’s ratio from values close to 0.5 to values 0.3–0.2. Because of this, in sediments, the stress state of which is almost completely determined only by the gravity of the overlying rocks, is reduced by 50 % or more of the horizontal compression stress level from the initial lithostatic pressure level. On the other hand, if the limit of pseudoplastic flow is reached in the rock, vertical compaction occurs, accompanied by an increase in horizontal compression. These two competing processes together with the factor of fluid pressure in fractures and pores determine the possibility of brittle fracture formation. It is shown that for rocks with a low level of yield strength (clay), compaction leads to an increase in the level of horizontal compression stresses, which makes brittle fracture in such rocks at the stage of diagenesis impossible. In rocks with a high level of strength (sandstone, limestone), brittle fracture due to excess water pressure in the sub­vertical microcracks starts earlier than the shear yield limit is reached.

Integration of conventional well logs and core samples to predict porosity of tight reservoir: a case study from Ordos Basin

To the reservoirs of the oil wells with no cored data, predicting porosity from wireline logs and core samples is an effective approach. Integration of conventional well logs and core samples to predict porosity with large accuracy is a particularly challenging work due to complex logging responses of tight sandstone. Therefore, a novel predicting workflow based on linear interpolation algorithm (LIA) is described to estimate porosity from well logs in the present study. Based on core reposition, porosity correction under overburden pressure, core-log data matching, and calculation of shale content, two multi regression formulas to estimate porosity values are obtained by nearest neighbor algorithm and linear interpolation algorithm respectively. The formulas are applied to the tight sandstone in Chang 9 member of Yanchang Formation in northeast Wuqi Oilfield, Ordos Basin. The comparison results indicate that the porosity predicted from the formula obtained by LIA is in better agreement with the measured porosity, showing a better prediction effect. The application example demonstrates that the LIA formula is of good applicability for the core porosity prediction in the study region. This methodology can further be applied for porosity prediction in other oil regions that have similarities in geological background.

Reservoir characterization of the Abu Roash D Member through petrography and seismic interpretations in Southern Abu Gharadig Basin, Northern Western Desert, Egypt

This research combines petrography and seismic analysis to assess the Upper Cretaceous Abu Roash (AR)/D’s carbonate member composition in the Southwest Abu-Sennan oil field in the Southern Abu Gharadig Basin within the Northern Western Desert of Egypt. Various datasets were used, including petrographic thin sections, and electrical well logs for four stratigraphic wells (01, -02, -03, and, -04), along with a time domain seismic dataset covering the study area. Petrographic analysis across multiple depths and intervals has provided valuable insights. Well-01 demonstrates mud-wackstone with diverse mineral components at 1671–74 m MD, indicating favorable reservoir quality. Well-02 exhibits diverse compositions at intervals 1740–43 m MD and 1746–49 m MD, also showcasing good reservoir quality. Well-03 reveals a packstone rock type at 1662–65 m MD with favorable reservoir characteristics. Well-04 displays peloids Wack-Packstone and Oolitic Packstone at intervals 1764–67 m MD and 1770–73 m MD, respectively, both indicating good reservoir quality. Integrating the petrography and seismic attributes results concerning the structural level of AR/D concerning the used wells, it's evident that Well-03 stands out due to its relatively high structural level, drilled near a major fault, revealing distinct fracture sets that contribute to a notably high reservoir quality as depicted in the RMS amplitude and Ant track attributes maps. AR/D reservoir levels in wells 02, and, 04, are relatively positioned at structurally lower levels, and face challenges with overburden pressure and mechanical compaction, resulting in diminished facies quality for the reservoir. Seismic attributes like the Ant track and RMS amplitude indicated that the presence of fractures within the AR/D Member's carbonate is linked to the prevalence of interpreted normal faults. The implemented procedure in this research can be applied to enhance comprehension of AR/D carbonate reservoirs in adjacent regions, thereby increasing the hydrocarbon exploration possibilities.

Prediction of the Permeability Tensor of Marine Clayey Sediment during Cyclic Loading and Unloading of Confinement Pressure Using Physical Tests and Machine Learning Techniques

In this study, a method was introduced to validate the presence of a Representative Elementary Volume (REV) within marine clayey sediment containing cracks during cyclic loading and unloading of confinement pressure. Physical testing provided the basis for this verification. Once the existence of the REV for such sediment was confirmed, we established a machine-learning predictive model. This model utilizes a hybrid algorithm combining Particle Swarm Optimization (PSO) with a Support Vector Machine (SVM). The model was trained using a database generated from the aforementioned physical tests. The machine-learning model demonstrates favorable predictive performance based on several statistical metrics, including the coefficient of determination (R2), mean residual error (MSE), mean relative residual error (MRSE), and the correlation coefficient R during the verification process. Utilizing the established machine-learning predictive model, one can effortlessly obtain the permeability tensor of marine clayey sediment containing cracks during cyclic loading and unloading of confinement pressure by inputting the relevant stress condition parameters. The original research cannot estimate the permeability tensor under similar loading and unloading conditions through REV. In this study, the physical model test was used to determine the REV of marine cohesive sediments with cracks by cyclic-constrained pressure loading and unloading. Referring to the results of physical tests, we developed a machine-learning prediction model that can easily estimate the permeability tensor of marine cohesive sediments with cracks under cyclic loading and constrained pressure unloading conditions. This method greatly saves time and computation and provides a direct method for engineering and technical personnel to predict the permeability tensor in this case.

The 15 January 2022 Hunga (Tonga) eruption: A gas-driven climactic explosion

An extraordinarily powerful, explosive eruption occurred from Hunga volcano in the Tonga island arc on 15 January 2022 and generated an eruption column 58 km high. The explosive eruption also generated atmospheric gravity waves, extreme runup tsunamis and quite unusual and destructive meteotsunamis. Together these place this VEI 6 eruption as, globally, one of the largest of the past 300 yearsBased on the oceanic context of Hunga volcano, it has previously been assumed that the eruption was phreatomagmatic through a fuel-coolant Surtseyan-type interaction, but this is not supported by satellite imagery. Similarly, it has been suggested that a caldera-collapse was the eruption trigger, but this is not supported by bathymetric data or the seismicity recorded during the eruption. Here we develop a new model based on the observed energetics and time sequence of the eruption integrated with understanding of the internal structure of active volcanoes and their characteristic high flux discharges of volcanic gas.It has been shown elsewhere that magma-derived reactive gases (H2O, CO2, SO2, HCl, etc) aggressively alter the volcanic rocks in the core of a volcano leading to selfsealing of gas flow to the surface and consequent changes to deviatoric stress in the structure. Common minerals developed by these reactions include anhydrite (CaSO4), sulphides and silica (quartz). all of which have been recorded in volcanic ejecta including at Hunga.We here develop a first order numerical model that quantifies how the free discharge of such gas to the surface may progressively become choked by these sealing reactions leading to increased internal gas pressure. Hydraulic fracture of the seal occurs when the transmitted pressure of the compressed magmatic gas beneath the seal increases to a value greater than the lithostatic pressure plus the tensile strength of the sealed rock. This initiates the explosive release of compressed gas whose high-power discharge progressively develops and enlarges a crater. At the same time the explosion feeds upon itself by generating larger pressure gradients in the pressurized gas within the fractured porous rock mass of the core of the volcano. Excavation of the crater may intersect high level intrusions and produce the pumice rafts that were observed after the eruption. The eruption itself diminished in intensity as the gas pressure in the reservoir declined.At Hunga the eruption excavated an 850 m deep, 2-3 km diameter steep-walled crater. This volume may be assumed to approximate the volume of fractured porous rock (the control volume of the eruption) whose trapped gas was mined by the eruption until surrounding gas pressure was depleted. Our numerical model shows that the calculated potential energy of the trapped compressed gas matches the independent observations of the scale of the eruption. Sensor data have since shown that gas bubble flares continued for at least 6 months after the eruption indicating continued depletion of the gas reservoir of rocks surrounding the new crater. The systems-based, gas-driven model for the Hunga climactic eruption developed here also applies to Plinean-type eruptions on subaerial arc volcanoes such as at Pinatubo (Philippines) 1991.

Fractal study on the nonlinear seepage mechanism during low-permeability coal water injection

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient.

Influences of Cyclic Confining Pressure on Deformation Behaviors of Soft Clay under Intermittent Cyclic Loading

Influences of Cyclic Confining Pressure on Deformation Behaviors of Soft Clay under Intermittent Cyclic Loading

A constitutive model of solid propellants considering aging and confinement pressure

AbstractAging during storage and confinement pressure during launch are the two major loading conditions that affect the integrity of solid rocket motors. In comparison to other component materials, solid propellants, as highly filled composites, have a low modulus and fracture toughness and are therefore common sources of failure. The key to improving the integrity of the solid rocket motor is in assessing the health of the solid propellants during storage or launch. To address this issue, we revised the previous model for the progressive damage viscoelasticity of solid propellants to include the effect of chemical aging during storage and the influence of confinement pressure during launch. Specifically, the increase in relaxation time due to aging and the nonequilibrium volume dilatation characteristics under triaxial tension and compression of solid propellants have been considered. To validate the developed model, standard relaxation tests and uniaxial tensile tests on solid propellants without aging were used to calibrate the model parameters. Furthermore, the model was validated by comparison with uniaxial tensile tests under confined pressure after aging and well predicts the aging temperature/time‐dependent mechanical responses of solid propellants. After validation, the developed model was used to study the influence of confinement pressure on microscopic damage evolution and macroscopic volume expansion. Overall, the developed model can be used for the analysis of the integrity of the solid rocket motor after the aging process.

Permeability Data Treatment from Analogous Outcrop for Use in Three-Dimensional Reservoir Model

Over the past forty years, the study of analogous outcrops has become a common practice in the petroleum industry to access more comprehensive geological datasets and better parameterize various geological features. As most reservoirs do not outcrop and all the data obtained are restricted to those collected from wells located in areas of major interest or from indirect measurements, the study of analogous outcrops has brought important contributions to improve the production routines and still represents a helpful information resource. The use of data from analogous outcrops permits, for example, to estimate the sedimentary facies distribution in true reservoirs, and thus to improve on the reliability of fluid flow modeling during the oil field exploration. However, such data must be processed to become equivalent to the data collected under the reservoir conditions and the results obtained to be more realistic. This work presents the statistical method used to make permeability data obtained from an outcrop compatible with the subsurface conditions of poorly consolidated and tectonically deformed sandstone reservoirs. The studied outcrop is predominantly composed of Eocene fluvial sandstones (Resende Formation) of the Volta Redonda Basin, located in the Central Segment of the Continental Rift of Southeastern Brazil. These deposits are affected by deformation bands and faults. From statistical analysis, it was intended that the permeability data become more suitable to be used, in the next phase of the studies, to build a 3D flow model, in which it will be possible to test the potential of different tectonic structures acting as hydraulic barriers in poorly consolidated and deformed reservoirs. The methodological approach applied in this study made it possible to turn compatible the permeability data obtained in conditions of no confining pressures from the outcrop with reservoir conditions under confinement pressures of 2,000 psi. Such pressure conditions are frequently observed in important Maastrichtian reservoirs found in the Brazilian Southeastern Margin.

Diagenesis and pressure evolution in Ediacaran carbonate rocks in the North Slope (Penglai area) of the central Sichuan Basin (SW China)

The Penglai area is an emerging giant gas field in the Sichuan Basin supporting the carbon neutrality goal. To accelerate the exploration, this study combines petrographic observations using optical and cold cathodoluminescence microscopy, fluid inclusion microthermometry, Raman spectroscopy, 1D basin modeling and fluid inclusion PVTX modeling techniques to reveal the paleo-fluid P-T evolution in the second member of the Dengying Formation (Ediacaran age). The results firstly showed a diagenetic sequence which includes three phases of dolomite (1–3), bitumen, quartz (core and overgrowth) and fluorite. Then, ten paleo-fluid episodes were identified based on microthermometric histograms of different mineral phases. Finally, by integrating the Raman results, the hydrostatic and lithostatic gradients calculated by the constructed 1D basin model, and the existing equation of states, the homogenization pressure of fluid inclusions from each fluid episode was determined. By assuming the system was saturated by CH4 as suggested by Raman results, the homogenization pressure equals to the trapping pressure. The P-T trajectory indicates that the second member of the Dengying Formation experienced two sever pressure accumulation stages. One is between fluid episode #3 and #4 recorded by dolomite 3, due to oil generation, and the other is from fluid episode #5 in dolomite 3 to episode #7 in quartz overgrowth to episode #8 in fluorite due to oil cracking to gas. Also, two pressure releasing periods were recorded by fluid episode #5 in dolomite 3 and #9 and #10 in fluorite, caused by both basin uplifting and fluid pressure reaching the lithostatic pressure. This study provides insights into fluid pressure evolution in deeply buried carbonate reservoirs. The understandings can support further geoenergy utilization and reduce exploration risks.

Analytical method for laterally loaded offshore slender piles near sandy slopes considering slope deformation

This paper presents an analytical method to study the lateral response of offshore slender piles near sandy slopes. A slope deformation model is constructed to evaluate the slope displacement induced by the load transfer of a pile at the slope crest. A modified strain wedge (SW) model is developed by considering the slope deformation and the impact of the slope on the effective overburden pressure. A geometric transformation is employed to facilitate the analysis of the edge distance. The efficiency and accuracy of the method are demonstrated through comparisons of its results with those of six centrifuge piles and four model piles. Finally, the effects of the slope angle and edge distance on the pile response are discussed. This method introduces the slope deformation into the analysis of soil-pile interaction, allowing for comprehensive consideration of the combined effects of slope angle and edge distance.

A Multi-scale Model of Overburden Pressure and Water Content in Montmorillonite-Bearing Clayey Soils

A Multi-scale Model of Overburden Pressure and Water Content in Montmorillonite-Bearing Clayey Soils

A Fractal-Based Quantitative Method for the Study of Fracture Evolution of Coal under Different Confining Pressures

To study the dynamic crack evolution process of loaded coal from the perspective of fractals, we carried out in situ industrial CT scanning tests of loaded coal under different confining pressures, visualizing loaded coal fracturing. Combined with fractal theory, the temporal and spatial evolution law of coal cracks is described quantitatively. The results provide two findings: (1) from the perspective of two-dimensional images and three-dimensional space, the evolution characteristics of cracks in coal under different confining pressures were basically the same in each loading stage. During the loading stages, the cracks exhibited a change rule of a slow reduction, initiation/development, rapid increase, expansion, and penetration. (2) The fractal dimension of coal was calculated by introducing fractal theory, and its change law was in good agreement with the dynamic changes of the cracks, which can explain the influence of the confining pressure on the loaded coal. The fractal dimension showed three stages: a slight decrease, a stable increase, and then a significant increase. The larger the confining pressure, the more obvious the limiting effect. Thus, our approach provides a more accurate method for evaluating the spatial and temporal evolution of cracks in loaded coal. This study can be used to predict the instability failure of loaded coal samples.

Deformation characteristics and creep behaviour of rigid particulates-EPS beads composites

The compression behaviour of the mixture of glass beads (representing rigid particles) and EPS beads (representing deformable particles) during the loading-unloading process is systematically examined through performing two sets of large-size oedometer experiments, including incremental step-by-step and one-step loading scenarios. At each step during the loading-unloading cycle, the void ratio (e) and the at-rest coefficient of lateral earth pressure (K0) are measured for pure rigid samples and rigid-soft particle mixtures. To consider the creep effect, the overburden pressure at the final loading step is maintained on the sample for 24 hours prior to unloading. The results show that at a given overburden pressure, with the addition of soft particles to the pure rigid aggregates, the values of e and K0 decrease. Additionally, for both pure rigid samples and rigid-soft particle mixtures, with increasing the overburden pressure, e decreases whereas K0 augments. Moreover, due to the creep behaviour during the constant loading step, K0 decreases over time for both samples; the phenomenon which is observed to be more pronounced for pure rigid aggregates compared to rigid-soft particle mixtures. Finally, a well-established creep model is used to simulate the creep behaviour of pure rigid samples and rigid-soft particle composites.

Axial compressive behavior of predamaged RC columns retrofitted with precast steel-reinforced grout jackets

Steel jacketing and concrete jacketing are popular retrofitting techniques to strengthen the axial compressive behavior of reinforced concrete (RC) columns. However, these retrofitting methods lack efficiency in practical application due to intensive labor and time-consuming installation. In order to improve the retrofit efficiency of damaged RC columns, this study proposed a novel precast steel-reinforced grout jacket (PSRGJ) consisting of early-strength cementitious grout and a steel frame. Ten columns were tested to investigate the axial compressive behavior of predamaged RC columns retrofitted with PSRGJ. The tested parameters were the stirrup reinforcement ratio, the transverse reinforcement ratio of PSRGJ, and the predamage level. The results indicated that the columns’ peak load and ductility index I10 were significantly improved by PSRGJ retrofitting and increased with the increase of transverse reinforcement ratio of PSRGJ. Besides, the peak load and the initial stiffness of PSRGJ-retrofitted RC columns decreased with the predamage level, while the ductility index I10 increased. In addition to the confinement effect, PSRGJ carried 11%−17% of the peak load through the interfacial bonding effect. Based on the test results, the actual confinement pressure model and interfacial bonding strength model were proposed. Further, peak load models considering the size effect were developed for PSRGJ-retrofitted intact and predamaged RC columns. The predictions of the proposed models agreed well with the test results from this study and the literature.

Study the Behaviour of the Natural Clay Soil Shallow Foundation System Subjected to Impact Loads

In civil engineering, there are many problems related to the transmission of pressure waves through the soil due to dynamic loads. In industrial applications, these vibrations remain often caused by the impact of weights on the foundation machine. Typically, these basics transmit effective vertical stresses to the surface layers. Accordingly, the dynamic performance of natural clay soils under the influence of individual active loads was careful in this work. Energy A deflection scale system dropped different loads from several elevations. The application of this research was to study the surface soil responses only. These responses include the vertical displacements, velocities, and accelerations implied by impacts on the soil surface. Some of the results showed a decrease in the displacement value of the natural clay soil by a rate ranging from 25% to 35%, a result of an increase in the overburden pressure based on an increase in the embedment depth, which led to a rise in the stiffness of the clayey soil.