1,721,016 research outputs found
Datasets: Effects of temperature on the frictional behavior of material from the Alpine Fault Zone, New Zealand
No full textTriaxial friction experiments on samples from the Alpine fault, New Zealan
Effects of Heterogeneity in Lithology and Mechanical Properties on the Slip Behaviors of the Plate Boundary Fault at the Hikurangi Margin, New Zealand
Full text linkSubduction zones are known to produce large, damaging earthquakes, but they can also experience slow-slip events which cannot be felt by humans. Understanding the mechanisms which influence this variation in slip rate will allow us to better anticipate how the subduction zone will act in the future. While the seafloor sediments make up a small portion of the subducting oceanic plate, they can have a noticeable impact on its ability to produce both large earthquakes and slow-slip events. Cores containing sediments and basement rock recovered by the International Ocean Discovery Program (IODP) from the Hikurangi Subduction zone near New Zealand were scanned using X-ray fluorescence (XRF) to obtain their chemical composition. Using the XRF data with in-situ measurements of porosity, p-wave velocity, and drilling parameters, as well as lab tests to determine the strength of these rocks, we can evaluate how the composition of the sediments affects their physical properties. A strong correlation between calcium content, porosity, and p-wave velocity was seen for the volcaniclastic cores. There is also evidence to suggest that the torque on bit during drilling is an indication of rock strength as it changes sharply at certain lithologic boundaries. Triaxial compression tests in the lab were used to quantify the rock strength of the volcaniclastic materials. This investigation into the subducting sediment properties builds onto pre-existing studies into the effects of seamounts on subduction and the factors that influence the slip rate at subduction zones
Evolution of permeability across the transition from brittle failure to cataclastic flow in porous siltstone
No full textPorous sedimentary rocks fail in a variety of modes ranging from localized, brittle deformationto pervasive, cataclastic flow. To improve our understanding of this transition and its affect on fluid flowand permeability, we investigated the mechanical behavior of a siltstone unit within the Marcellus Forma-tion, PA USA, characterized by an initial porosity ranging from 41 to 45%. We explored both hydrostaticloading paths (r15r25r3) and triaxial loading paths (r1>r25r3) while maintaining constant effectivepressure (Pe5Pc–Pp). Samples were deformed with an axial displacement rate of 0.1lm/s (strain rate of 231026s21). Changes in pore water volume were monitored (drained conditions) to measure the evolutionof porosity. Permeability was measured at several stages of each experiment. Under hydrostatic loading, wefind the onset of macroscropic grain crushing (P*) at 39 MPa. Triaxial loading experiments show a transitionfrom brittle behavior with shear localization and compaction to cataclastic-flow as confining pressureincreases. When samples fail by shear localization, permeability decreases abruptly without significantchanges in porosity. Conversely, for cataclastic deformation, permeability reduction is associated with signif-icant porosity reduction. Postexperiment observation of brittle samples show localized shear zones charac-terized by grain comminution. Our data show how zones of shear localization can act as barriers to fluidflow and thus modify the hydrological and mechanical properties of the surrounding rocks. Our results haveimportant implications for deformation behavior and permeability evolution in sedimentary systems, and inparticular where the stress field is influenced by injection or pumping
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Quantitative Analysis of the Effect of Perforation Interaction on Sand Production Using the Finite Element Method
Full text linkThe study investigates perforation interaction in order to find the optimum perforation design which yields the highest productivity while maintaining mechanical stability.
The study is composed of i) evaluation of flow performance and ii) evaluation of mechanical stability. Both evaluations were performed by using the finite element method with multi-perforation mesh to distinguish the effect of perforation interaction.
The flow evaluation quantitated the productivity for various cases, allowing us to find the most prolific perforation design.
In the stability evaluation, perforation stability was quantitated under various conditions with the effect of perforation interaction. It provides us with a new insight into the effect of shot density on perforation stability
Effects of Pore Fluid Pressure on Extension and Hybrid Fractures in Berea Sandstone
No full textPore fluid pressure in the geological formation at depth varies spatially and temporarily. An increase in pore fluid pressure at depth leads to a reduction in effective normal stress, and thus affects the rock strength and deformation mode. Extremely high pore fluid pressure induces very low normal stress conditions, where extension or extension-shear hybrid fractures are formed. To better quantify the stress states and fluid pressure during fracture formation, it is important to determine mechanical strength and the transition from tensile to shear fracture at low effective stress. However, all previous experimental studies were conducted under dry conditions. This study investigates the effects of pore fluid pressure on tensile and hybrid fractures in Berea sandstone by conducting triaxial extension deformation experiments under pore-fluid-pressure controlled conditions. A series of triaxial extension tests at effective maximum principal stress (���1') ranging from 10 to 130 MPa indicate that fracture strength, inelastic strain, and strain at failure, fracture angle to ���1', and the amount of comminution increase with ���1', and that the transition of extension to shear fracture occurs at ���1' = 30 MPa. All the saturated or pore fluid pressure-controlled test specimens exhibit lower fracture strength than dry samples. It implies that the pore fluid pressure coefficient, ���, may be greater than 1 for the formation of extension and hybrid fractures, and that the use of dry tensile strength data leads to an overestimation of the pore fluid pressure or differential stress based on the attitudes of vein structures or drilling-induced tensile fractures
Effect of Scale in Proppant Transport Experiment Using PGA
Full text linkThe present experiment attempts to study the behavior of proppant mixed with fibers in slickwater fracturing using a large-scale flow equipment. Previous experiments have shown that, at small scale, PGA fibers in slickwater proved very effective in suspending proppant. The mixture was successful in creating highly conductive channels in a slot flow experimental setup. However, at such scale, the conditions for creating channels were close to ideal. The study aims at replicating the same results at a larger scale with more practical conditions.
A transparent acrylic panel, 4’ x 16’ x 4.5", with several inlets was fabricated to simulate an open fracture plane.
The results of the study are as follows:
• o Large-scale slot-flow experimental setup was designed and constructed.
• o The setup could successfully perform experiments to observe proppant distribution.
• o Two experiments showed a proppant bank, a phenomenon often observed in previous studies. Experiment 3 showed channels as a result of mixing fibers and proppant.
• o The large-scale setup could perform experiments at more rigorous conditions than the small scale and offer more objective results.
• o It has 4 times more viewing area.
• o The fracture width can be varied from 0.1” – 0.5”.
• o The number of inlets is 5.
• o It could handle up to 2 psig pressure buildup.
• o It could perform experiments with flow rate of up to 24 gpm for 4 vertical foot.
• o Mixing mechanism still requires improvement
Investigation of Propagating Fractures with Shear and Normal Stresses Using Low-Frequency Distributed Acoustic Sensing
Full text linkLow-frequency distributed acoustic sensing (LF-DAS) can be used as a monitoring tool for hydraulic fracture propagation using measured values of strain. To understand subsurface conditions with shear and normal stresses, a laboratory-scale hydraulic fracture experiment was performed to simulate the LF-DAS response to fracture propagation with embedded distributed optical fiber strain sensors. The objectives of this research were to generate hydraulic fractures of known geometry with shear and normal stresses, measure the strain response along distributed fiber sensors embedded in the sample, and use the results to reveal insights of fracture propagation.
The experiment was performed on a uniaxially-compressed, transparent 8-inch cube of epoxy with a radial initial flaw angled to the applied load. Water was injected into the epoxy block to generate a fracture with shear and normal stresses along the plane of the fracture. These experiments used distributed high-definition fiber optic strain sensors with tight spatial resolutions. The measured strains were compared to experiments with a purely normal stress component to understand how the zero-strain method for fracture geometry apply to the studied case when a shear stress on the fracture plane is introduced.
The experimentally acquired strain and strain-rate waterfall plots with shear and normal stresses on the fracture plane exhibit comparable results to the strain responses of purely normal stresses with a narrowing region of extension surrounded by compression as a fracture approached and intersected a fiber optic cable. However, unlike the experiments with purely normal stresses on the fracture plane, the introduction of a shear stress created an asymmetrical strain signature over the fracture plane. This dominant strain response on one side of the fracture plane suggests the existence of a shear stress on the plane of the fracture
Evaluation of Strength and Consolidation State of Input and Prism Sediments at the Hikurangi Margin
No full textSlow slip events (SSEs) recur periodically and release energy slowly in contrast to regular earthquakes that radiate destructive ground motions and high-frequency seismic waves. Understanding the mechanics of SSEs and earthquakes and their interrelations are crucial for earthquake hazard mitigation. At the northern Hikurangi margin offshore New Zealand, SSEs occur periodically at relatively shallow depths. The International Ocean Discovery Program (IODP) Expeditions 372 and 375 drilled, cored, and installed observatories to investigate the mechanics of SSEs along the Hikurangi Margin. Drilling performance analysis and laboratory consolidation and deformation experiments were conducted to document in-situ strength, mechanical properties, and deformation behaviors of sediments of the accretionary prism near the trench at Site U1518 that may host SSEs as well as sediments on the incoming plates at Site U1520 that are to be incorporated to the system. Mechanical specific energy determined in the drilling performance analysis indicates the formation strength of the prism sediments at Site 1518 is generally greater than the incoming sediments at Site U1520, and the hanging wall of the P��paku fault is stronger than the footwall at Site U1518, implying that the prism sediments particularly in the hanging wall of the P��paku fault, are further consolidated than the incoming sediments. A consolidation experiment on the incoming sediment indicates nearly normal consolidation, whereas a consolidation experiment on the footwall sample at Site U1518 infers underconsolidation. Conventional triaxial deformation experiments at an effective pressure of 0.5 MPa on one sample from Site U1520 and two samples from the same core recovered in the footwall of P��paku fault at Site U1518 indicate mixed results; the input sample from Site U1520 is stronger than one U1518 specimen but weaker than the other specimen. Because the unclear elastic-plastic transition and variations in the strength determined for the footwall of the P��paku fault observed in the laboratory experiments might be attributed to sample disturbance and/or local deformation and loading conditions, more experiments on the core samples from different depths in the footwall are necessary
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