Conduit Flow Research Articles

Simulation of horizontal injection wells in Managed Aquifer Recharge facilities using the conduit flow process (CFP) code for MODFLOW-2005

Groundwater management of coastal aquifers is a scientific and engineering challenge, as coastal aquifer systems are hydrogeologic features that are hydraulically connected with the sea while at the same time are stressed with extensive abstraction practices for irrigation. To remedy this, Managed Aquifer Recharge -MAR- is proved to be a sound and effective technology that is able to fill the gap between groundwater supply and demand. Essential part of this procedure is reliable groundwater modeling that simulates effectively all involved hydrologic processes in order to be able to predict the response of the system under different natural or artificially induced conditions. This paper describes the application of a modeling tool, for the simulation of the relative hydrologic processes between the open filter pipe of the injection well and the surrounding aquifer material with the finite difference method. More specifically, a MAR pilot setup with a horizontal direction injection well was simulated with the Conduit Flow Process (CFP) of MODFLOW-2005 code. To investigate further the applicability of CFP code, the HDDW was conceptualized with the simpler MODFLOW WEL package and the results of the two models were compared. For the two models, sensitivity analysis was conducted using UCODE_2014. Both models were calibrated successfully as the simulated values showed an acceptable fit to the observed data. The main difference between the two packages was observed in the rise of groundwater level along the horizontal well. To this end, it was indicated that CFP offered a more realistic representation of the horizontal well pipe.

Data analysis technique influences blood flow kinetics parameter estimates for moderate- and heavy-intensity exercise transitions.

What is the central question of this study? During exercise, there are fluctuations in conduit artery blood flow (BF) caused by both cardiac and muscle contraction-relaxation cycles. What is the optimal method to process Doppler ultrasound-measured BF for the purpose of characterizing the dynamic response of BF during step-transitions in exercise? What is the main finding and its importance? Continuous BF data were processed in relation to either cardiac or muscle contraction-relaxation cycles and computed based on 'binned' or 'rolling' averages over one, two or five consecutive cycles. Kinetics characterization revealed no data processing technique-specific differences in steady-state BF, but variability in the rapidity at which BF attained steady-state (i.e., mean response time) was observed. The overall rate of blood flow (BF) adjustment (i.e., kinetics) from the onset of an exercise transition can be quantified by the mean response time (MRT). However, the BF response profile can be distorted during rhythmic, dynamic exercise consequent to variations caused by the cardiac cycle (HR) and the muscle contraction-relaxation (CR) cycle. We examined the extent to which distortions imposed by HR and CR cycles affected BF kinetics. Eight healthy, young men (27 (4) years; mean (SD)) performed transitions of alternate-leg knee-extension exercise from 3W to either a moderate- (MOD) or heavy-intensity (HVY) power output. Femoral artery BF was continuously measured by Doppler ultrasound and averaged over one, two or five 'binned' (e.g., HR2b, etc.) or 'rolling' (e.g., CR5r, etc.) HR and CR cycles. Among analysis techniques, there were no differences for steady-state BF values at the 3W baseline. In MOD, MRT using contraction-relaxation cycle (CR1) was smaller than most other analysis techniques. For both MOD and HVY, the 95% confidence interval for MRT was generally larger when using HR- compared to CR-related methods, and monoexponential fits based on 'rolling' averages (HR2r, HR5r, CR2r, CR5r) had a poorer ability to estimate the true end-exercise BF in HVY than in MOD. When modelling BF kinetics, we conclude that the CR1 method is a good option because of its ability to accurately estimate the 'data-determined' end-exercise BF value from the 'model-derived' response, maintain a relatively high density of data points during the transition and yield a relatively small 95% CI.

Stylolites and stylolite networks as primary controls on the geometry and distribution of carbonate diagenetic alterations

There is ongoing debate on whether stylolites act as barriers, conduits, or play no role in fluid transport. This problem can be tackled by examining the spatial and temporal relationships between stylolites and other diagenetic products at multiple scales. Using the well-known Lower Cretaceous Benicàssim case study area (Maestrat Basin, E. Spain), we provide new field and petrographic observations of how bedding-parallel stylolites can influence different diagenetic processes during basin evolution. The results reveal that stylolites can serve as baffles or inhibitors for different carbonate diagenetic reactions, and act as fronts for dolomitization, dolomite recrystallization and dolomite calcitization processes. Anastomosing stylolites that pre-date burial dolomitization probably acted as a collective baffle for dolomitization fluids in the study area, resulting in stratabound replacement geometries at the metre-to-kilometre scale. The dolomitization front coincides with stylolites, and can be traced along consecutive anastomosing ones. Such anastomosing stylolites are typical of mud-dominated facies that characterize limestone-dolostone transition zones. Conversely, dolostone bodies tend to correspond to more grain-dominated facies characterized by parallel (non-anastomosing) stylolites. Stylolites subsequently acted as fluid flow conduits and barriers when the burial and stress conditions changed. Stylolitic porosity enhanced by dissolution within dolostones close to faults appears filled with saddle dolomite riming the stylolite pore, and high-temperature blocky calcite cements filling the remaining porosity. The fluids responsible for these reactions were likely released from below at high pressure, causing hydraulic brecciation, and were channelised through stylolites, which acted as fluid conduits. Stylolites are also found acting as baffles for subsequent dolomite calcitization reactions during meteoric diagenesis and occasionally appear filled with iron oxides likely released by calcitization. This example demonstrates how the same type of stylolites (bedding-parallel) can act as barriers/inhibitors and/or conduits for different types of diagenetic reactions through time, and how important it is to consider their collective role when they form networks.

Geologic structures associated with gold mineralization in the Kirk Range area in Southern Malawi

Abstract In this contribution, we use a newly acquired high-resolution airborne geophysical data set and field geological investigations in the Kirk Range area in southern Malawi to understand structures that control gold mineralization. Gold in this area is alluvial, mined by artisanal miners and detailed information regarding the structures controlling primary mineralization remains sparse. Structural interpretations are afforded by in-depth investigation of airborne magnetic and radiometric data, which are then supported by ground geological mapping and by microscopic observations using X-ray computed tomography (XCT) and optical microscopy. The results show that the Kirk Range displays extensive faulting and shearing with a NE–SW trend as the prevalent structural grain of the region. Gold mineralization is hosted in NE–SW trending structures. The wall rock alteration associated with gold mineralization results in a pronounced K/Th anomaly, which is suggested as an important radiometric guide for future exploration efforts. Exploration in the Kirk Range region should focus on the NE–SW structures, which represent potential conduits for fluid flow.

Extracardiac conduit adequacy along the respiratory cycle in adolescent Fontan patients.

OBJECTIVESAdequacy of 16–20mm extracardiac conduits for adolescent Fontan patients remains unknown. This study aims to evaluate conduit adequacy using the inferior vena cava (IVC)–conduit velocity mismatch factor along the respiratory cycle.METHODSReal-time 2D flow MRI was prospectively acquired in 50 extracardiac (16–20mm conduits) Fontan patients (mean age 16.9 ± 4.5 years) at the subhepatic IVC, conduit and superior vena cava. Hepatic venous flow was determined by subtracting IVC flow from conduit flow. The cross-sectional area (CSA) was reported for each vessel. Mean flow and velocity was calculated during the average respiratory cycle, inspiration and expiration. The IVC–conduit velocity mismatch factor was determined as follows: Vconduit/VIVC, where V is the mean velocity.RESULTSMedian conduit CSA and IVC CSA were 221 mm2 (Q1–Q3 201–255) and 244 mm2 (Q1–Q3 203–265), respectively. From the IVC towards the conduit, flow rates increased significantly due to the entry of hepatic venous flow (IVC 1.9, Q1–Q3 1.5–2.2) versus conduit (3.3, Q1–Q3 2.5–4.0 l/min, P < 0.001). Consequently, mean velocity significantly increased (IVC 12 (Q1–Q3 11–14 cm/s) versus conduit 25 (Q1–Q3 17–31 cm/s), P < 0.001), resulting in a median IVC–conduit velocity mismatch of 1.8 (Q1–Q3 1.5–2.4), further augmenting during inspiration (median 2.3, Q1–Q3 1.8–3.0). IVC–conduit mismatch was inversely related to measured conduit size and positively correlated with conduit flow. The normalized IVC–conduit velocity mismatch factor during expiration and the entire respiratory cycle correlated with peak VO2 (r = –0.37, P = 0.014 and r = –0.31, P = 0.04, respectively).CONCLUSIONSImportant blood flow accelerations are observed from the IVC towards the conduit in adolescent Fontan patients, which is related to peak VO2. This study, therefore, raises concerns that implanted 16–20mm conduits have become undersized for older Fontan patients and future studies should clarify its effect on long-term outcome.

An analysis of the structural characteristics of karst conduit by the time-concentration curve of a tracer test

The structural characteristics of karst conduit have an important influence on the rational use and protection of karst groundwater resources and the safe construction of underground engineering. At present, when using the tracer test curve to analyze the structural characteristics of karst conduit, there are some problems, including the curve superposition shape, blunt front shape, irregular rise and fall of curve, connection relationship between multiple karst conduit, location of underground lake and groundwater state. In this paper, the time concentration curve of the tracer test is used to explain the structural characteristics of karst conduit through the numerical simulation of the karst conduit flow tracer test and the change of water flow state. The results show that (1) the number of curve peaks corresponds to the number of karst conduit, and there are three models for the parallel curve of double pipelines due to the difference of the length and velocity of karst conduit runoff. (2) The number of the single karst conduit curve decline gradients corresponds to the number of blue hole, and the relationship between the decline gradients and the number of blue hole should be analyzed for multiple karst conduit in combination with the number of karst conduit and the location of blue hole. There are four types of parallel karst conduits. (3) The rapid change of curve shape indicates the mutual transformation of surface flow and pressure flow.

Novel observations of capelin (Mallotus villosus) spawning directly on a brown algae species (Desmarestia viridis) in coastal Newfoundland, Canada

Capelin (&lt;em&gt;Mallotus villosus&lt;/em&gt;) is a key forage fish species within its circumpolar range. This species’ importance lies in its role in the typical marine ‘wasp-waist’ food web, where capelin acts as a conduit for energy flow from lower to higher trophic levels. Herein we describe a novel observation of capelin spawning subtidally on an annual brown algae species, &lt;em&gt;Desmarestia viridis&lt;/em&gt;, during July–August 2019 in Placentia Bay, Newfoundland, Canada. Based on extensive video surveys of the seabed along with shoreline surveys and sediment sampling, we did not find other nearby sites with typical capelin subtidal and intertidal spawning habitat (i.e. medium sand to pebble gravel). Findings suggest that capelin spawned directly on this brown algae species, &lt;em&gt;D. viridis&lt;/em&gt;. Eggs adhered to &lt;em&gt;D. viridis&lt;/em&gt; developed normally and hatched successfully. As temperatures of intertidal areas are predicted to increase above temperatures suitable for capelin egg rearing (2–12°C) with climate change, &lt;em&gt;D. viridis&lt;/em&gt; may become a high-quality subtidal spawning habitat for capelin and other fish species. In support, this algal species is adapted to colonize high disturbance areas, allowing protection from egg predators in a high flow environment while also being resistant to urchin grazing.

Left atrial conduit flow rate at baseline and during exercise: an index of impaired relaxation in patients with heart failure and preserved ejection fraction

Abstract Introduction In healthy subjects, adrenergic stimulation augments left ventricular (LV) long-axis shortening/lengthening, and increases left atrial (LA) to LV intracavitary pressure gradients in early diastole. Lower increments are observed in patients with heart failure with preserved ejection fraction (HFpEF). Purpose We hypothesized that exercise in HFpEF would similarly impair passive LV filling in early-mid diastole, during conduit flow from pulmonary veins. Methods Twenty HFpEF patients (67.8±9.8 years; 11 women), diagnosed according to 2007 ESC recommendations, underwent ramped semi-supine bicycle exercise to submaximal target heart rate (∼100) or symptoms. Seventeen asymptomatic subjects (64.3±8.9 years; 7 women) served as controls. Simultaneous LA and LV volumes were measured from pyramidal 3D echocardiographic full-volume datasets acquired from apical window at baseline and during stress, together with brachial arterial pressure. LA conduit function was computed, from minimum LV volume to ECG P wave, as [LV volume (time) – LV minimum volume] – [LA maximum volume – LA volume (time)] and expressed as average flow rate. The slope of the single-beat preload recruitable stroke work (PRSW) quantified LV inotropic state. Results There were divergent responses in conduit flow rate, which increased by 40% during exercise in control subjects (+17.8±37.3 ml/s) but decreased by 18% in patients with HFpEF (−9.6±42.3 ml/s) (p=0.046); increments during stress correlated with PRSW slope changes (p=0.003). Conclusion In HFpEF conduit flow rate decreases when diastolic dysfunction develops during exercise, in parallel with LV inotropic state changes, thereby contributing to impaired stroke volume reserve. Conduit flow can be measured as a marker of LV relaxation. Funding Acknowledgement Type of funding sources: None.

Left atrial conduit function: A short review.

Three‐dimensional echocardiography can elucidate the phasic functions of the left atrium if a simultaneous acquisition of a pyramidal full‐volume dataset, as gathered from the apical window and containing the entire left atrial and left ventricular cardiac sections, is obtained. Hence, conduit can be quantified as the integral of net, diastolic, instantaneous difference between synchronized atrial and ventricular volume curves, beginning at minimum ventricular cavity volume and ending just before atrial contraction. Increased conduit can reflect increased downstream suction, as conduit would track the apex‐to‐base intracavitary pressure gradient existing, in early diastole, within the single chamber formed by the atrium and the ventricle, when the mitral valve is open. Such a gradient increases in response to adrenergic stimulation or during exercise and mediates an increment in passive flow during early diastole, with the ventricle being filled from the atrial reservoir and, simultaneously, from blood drawn from the pulmonary veins. In this context conduit, and even more conduit flow rate, expressed in ml/sec, can be viewed as an indirect marker of left ventricular relaxation.It is well known, however, that a large amount of conduit (in relative terms) is also supposed to contribute to LV stroke volume in conditions of increased resistance to LV filling, when diastolic function significantly worsens. Stiffening of the atrio‐ventricular complex implies increments in LA pressure more pronounced in late systole, causing markedly elevated “v” waves, independently of the presence of mitral insufficiency. The combination of increased atrio‐ventricular stiffness and conduit flow is associated with an elevation of the right ventricular pulsatile relative to resistive load that negatively impacts on exercise capacity and survival in these patients.Atrial conduit is an “intriguing” parameter that conveys a noninvasive picture of the complex atrioventricular coupling condition in diastole and its backward effects on the right side of the heart and the pulmonary circulation. Given the easiness associated with its correctly performed quantification in the imaging laboratory, I am sure that conduit will survive the competitive access to the list of valuable parameters capable of deciphering, although not necessarily simplifying, the complex diastolic scenario in health and disease.

DRAG REDUCTION FOR SINGLE-PHASE WATER FLOW IN AND AROUND 180O BENDS

The economic and engineering importance of additive drag reduction (DR) has provided motivation and wealth of data on the phenomena in straight conduit flows. Study into the effect of drag-reducing additives (DRAs) on complex and under-developed flows in and after bends is very limited. Novel results of DR in and around U-bends is presented in this work. Three polymer types were tested and the radii of curvature ( R ) of the U-bends were 100 and 200 mm with pipe diameter of 19 mm . DR increased with polymer concentration and flow rate up to certain thresholds. DR differed among the different sections considered with the highest value recorded for developed flows upstream of the bend and the least values recorded in the bend. DR increased with flow development after the bend and increased with polymer molecular weight before and after the bend. The effect of bend curvature ratio on DR was predominant after the U-bend. For R = 100 m m , the highest DR recorded upstream of bend, in the bend, immediately after and further downstream of the bend were 57, 31, 36 and 33% respectively.

Upward‐Doming Zones of Gas Hydrate and Free Gas at the Bases of Gas Chimneys, New Zealand's Hikurangi Margin

AbstractFocused gas migration through the gas hydrate stability zone in vertical gas conduits is a global phenomenon. The process can lead to concentrated gas hydrate formation and seafloor gas seepage, which influences seafloor biodiversity and ocean biogeochemistry. However, much is unknown about how gas and gas hydrate co‐exist within and around gas conduits. We present seismic imaging of the gas hydrate system beneath a four‐way closure anticlinal ridge at New Zealand's southern Hikurangi subduction margin. Gas has accumulated beneath the base of gas hydrate stability to a thickness of up to ∼240 m, which has ultimately led to hydraulic fracturing and propagation of a vertical gas conduit to the seafloor. Despite the existence of an array of normal faults beneath the ridge, these structures are not exploited as long‐range gas flow conduits. Directly beneath the conduit, and extending upward from the regional base of gas hydrate stability, is a broad zone characterized by both negative‐ and positive‐polarity reflections. We interpret this zone as a volume of sediment hosting both gas hydrate and free gas, that developed due to partial gas trapping beneath a mass transport deposit. Similar highly reflective zones have been identified at the bases of other gas conduits, but they are not intrinsic to all gas conduits through gas hydrate systems. We suggest that pronounced intervening sealing units within the gas hydrate stability zone determine whether or not they form.

Hydrochemical and Isotopic Difference of Spring Water Depending on Flow Type in a Stratigraphically Complex Karst Area of South Korea

Characterizing the subsurface flow in karstic areas is challenging due to distinct flow paths coexisting, and lithologic heterogeneity makes it more difficult. A combined use of hydrochemical, environmental isotopic, and hydrograph separation study was performed to understand the subsurface flow in a karst terrain where Ordovician carbonate rocks overlie Jurassic sandstone and shale along thrusts. Spring water collected was divided into Type Ⅰ (n= 11) and Ⅱ (n= 30) based on flow patterns (i.e., low and high discharge, respectively). In addition, groundwater (n= 20) was examined for comparison. Three Type Ⅱ springs were additionally collected during a storm event to construct hydrographs using δ18O and δD. As a result, Type Ⅱ had higher electrical conductivity, Mg2+, HCO3−, and Ca2+/(Na++ K+) than Type Ⅰ and was mostly saturated with calcite, similar to deep groundwater. The hydrochemical difference between Types Ⅰ and Ⅱ was opposite to the expectation that Type Ⅱ would be undersaturated given fast flow and small storage, which could be explained by the distinct geology and water sources. Most Type Ⅱ springs and deep groundwater occurred in carbonate rocks, whereas Type Ⅰ and shallow groundwater occurred in various geological settings. The carbonate rocks seemed to provide conduit flow paths for Type Ⅱ given high solubility and faults, resulting in 1) relatively high tritium and NO3−and Cl−viashort-circuiting flow paths and 2) the similar hydrochemistry and δ18O and δD to deep groundwaterviaupwelling from deep flow paths. The deep groundwater contributed to 83–87% of the discharge at three Type Ⅱ springs in the dry season. In contrast, Type Ⅰ showed low Ca2++ Mg2+and Ca2+/(Na++ K+) discharging diffuse sources passing through shallow depths in a matrix in mountain areas. Delayed responses to rainfall and the increased concentrations of contaminants (e.g., NO3−) during a typhoon at Type Ⅱ implied storage in the vadose zone. This study shows that hydrochemical and isotopic investigations are effective to characterize flow paths, when combined with hydrograph separation because the heterogenous geology affects both flow paths and the hydrochemistry of spring water passing through each pathway.

Different types of gravity-driven flow deposits and associated bedforms in the Upper Bengal Fan, offshore Myanmar

This study uses 3D reflection seismic data to investigate how sediment gravity flows contribute to the evolution of the lower continental slope of the Myanmar margin that is part of the Bengal Fan, the largest deep-water fan system in the world. Seafloor and subseafloor data show large sediment wave fields that developed on both flanks of an extensive submarine canyon. The sediment waves exhibit asymmetric stoss and lee sides, wave lengths and heights of 850–3000 m and 25–70 m, respectively, and an upslope direction of migration. Seismic data reveals the presence of multiple fields of vertically stacked sediment waves, interbedded with units characterised by a chaotic seismic facies that accumulate mainly in the troughs of the sediment waves and can be tracked laterally to the adjacent canyons. According to their seismic facies, geometry, and internal architecture these chaotic units are interpreted as debrites. Seismic attributes extracted from different horizons indicate that the sediment waves are dominated by fine-grained sediment, while the debrites are probably associated with coarser-grained deposits. The debrites fill the troughs of the sediment waves, as well as the downstream portions of canyon thalweg, thus flattening the paleo-seafloor. The sediment waves are interpreted as cyclic steps formed by low-density turbidity currents flowing across the slope down to the basin floor, where the change in gradient favours the formation of hydraulic jumps and the transition from supercritical to subcritical flow conditions. A conceptual model for the sediment wave evolution was proposed for the study area, in the transitional environment on the lower slope, with low-density gravity flow deposits and high-density debris flow deposits alternatively accumulating on the major gravity flow conduits.

Osmium isotope evidence for rapid melt migration towards the Moho in the Oman ophiolite

The oceanic crust, covering two-thirds of the Earth's surface, is formed along mid-oceanic ridges by crystallization at shallow levels of melts formed at depth by partial melting of mantle peridotite. Yet, the process of melt transport to the ridge axis remains poorly understood. Ophiolites, which provide a window into the uppermost mantle, contain dunite bodies often interpreted as relics of melt flow conduits, formed by pyroxene dissolution during melt-peridotite interaction. Here, we present structural and geochemical data on peridotites from the southeastern Oman ophiolite where three types of dunite, corresponding to the Moho transition zone (MTZ), the main and basal mantle sections, are identified. We focus on osmium isotopes, which are particularly well-adapted to tracing melt flow through peridotites. Osmium isotope signatures from host harzburgites accord with abyssal peridotite values and do not vary systematically with setting. In contrast, dunite Os compositions depend on structural context. Basal dunites display compositions similar to harzburgite values, while MTZ dunites have highly radiogenic compositions similar to those of the overlying crust, requiring extensive interaction with melts more radiogenic than MORB. Modeling shows that melts percolating through and equilibrating with dunite channels would acquire unradiogenic compositions, inconsistent with the observed Os signatures of MTZ dunites and lower crust. Thus, our findings require melt transport without equilibration with dunite or harzburgite, arguing for rapid or at least chemically isolated melt migration from the mantle source to the Moho.

Left atrial conduit flow rate at baseline and during exercise: an index of impaired relaxation in HFpEF patients.

AimsIn healthy subjects, adrenergic stimulation augments left ventricular (LV) long‐axis shortening and lengthening, and increases left atrial (LA) to LV intracavitary pressure gradients in early diastole. Lower increments are observed in patients with heart failure with preserved ejection fraction (HFpEF). We hypothesized that exercise in HFpEF would further impair passive LV filling in early‐mid diastole, during conduit flow from pulmonary veins.Methods and resultsTwenty HFpEF patients (67.8 ± 9.8 years; 11 women), diagnosed using 2007 ESC recommendations, underwent ramped semi‐supine bicycle exercise to submaximal target heart rate (∼100 bpm) or symptoms. Seventeen asymptomatic subjects (64.3 ± 8.9 years; 7 women) were controls. Simultaneous LA and LV volumes were measured from pyramidal 3D‐echocardiographic full‐volume datasets acquired from an apical window at baseline and during stress, together with brachial arterial pressure. LA conduit flow was computed from the increase in LV volume from its minimum at end‐systole to the last frame before atrial contraction (onset of the P wave), minus the reduction in LA volume during the same time interval; the difference was integrated and expressed as average flow rate, according to a published formula. The slope of single‐beat preload recruitable stroke work (PRSW) quantified LV inotropic state. 3D LV torsion (rotation of the apex minus rotation of the base divided by LV length) was also measurable, both at rest and during stress, in 10 HFpEF patients and 4 controls. There were divergent responses in conduit flow rate, which increased by 40% during exercise in controls (+17.8 ± 37.3 mL/s) but decreased by 18% in patients with HFpEF (−9.6 ± 42.3 mL/s) (P = 0.046), along with congruent changes (+1.77 ± 1.13°/cm vs. −1.94 ± 2.73°/cm) in apical torsion (P = 0.032). Increments of conduit flow rate and apical torsion during stress correlated with changes in PRSW slope (P = 0.003 and P = 0.006, respectively).ConclusionsIn HFpEF, conduit flow rate decreases when diastolic dysfunction develops during exercise, in parallel with changes in LV inotropic state and torsion, contributing to impaired stroke volume reserve. Conduit flow is measurable using 3D‐echocardiographic full‐volume atrio‐ventricular datasets, and as a marker of LV relaxation can contribute to the diagnosis of HFpEF.

Stress‐Driven Failure of Cylindrical Volcanic Conduits

AbstractMany explosive volcanic eruption sequences are characterized by exceedingly unsteady behavior, often punctuated by multiple explosive phases, separated by hours to days. What causes this unsteady behavior is not fully understood. Here, we explore one possible mechanism: stress‐driven failure of the volcanic conduit wall rock. We present a multiphase conduit flow model that predicts the shear and normal tractions exerted on the conduit wall, and couple (one way) these tractions with a numerical model of host rock failure. While analytical estimations of host rock stress serve as useful guides, analytical approximations which ignore shear tractions are insufficient to adequately predict conduit instability. Failure generally initiates near the fragmentation depth, where shear tractions are highest and magma pressure is low relative to the lithostatic stress. Shear tractions on the conduit wall, caused by viscous drag, promote strain localization and failure. The in situ stress state not only determines the range of conduit pressures which promotes failure, but also influences the style of failure. The mechanism that is most likely to lead to the disruption of flow, where wall rock moves radially into the conduit along normal faults, occurs in extensional stress regimes when large shear tractions at the fragmentation depth enhance normal fault formation. The results of this study indicate that conduit stability strongly depends on the ambient stress field and the nature of conduit flow at the fragmentation depth.

Machine Learning-Based Propped Fracture Conductivity Correlations of Several Shale Formations.

In hydraulic fracturing operations, small rounded particles called proppants are mixed and injected with fracture fluids into the targeted formation. The proppant particles hold the fracture open against formation closure stresses, providing a conduit for the reservoir fluid flow. The fracture’s capacity to transport fluids is called fracture conductivity and is the product of proppant permeability and fracture width. Prediction of the propped fracture conductivity is essential for fracture design optimization. Several theoretical and few empirical models have been developed in the literature to estimate fracture conductivity, but these models either suffer from complexity, making them impractical, or accuracy due to data limitations. In this research, and for the first time, a machine learning approach was used to generate simple and accurate propped fracture conductivity correlations in unconventional gas shale formations. Around 350 consistent data points were collected from experiments on several important shale formations, namely, Marcellus, Barnett, Fayetteville, and Eagle Ford. Several machine learning models were utilized in this research, such as artificial neural network (ANN), fuzzy logic, and functional network. The ANN model provided the highest accuracy in fracture conductivity estimation with R2 of 0.89 and 0.93 for training and testing data sets, respectively. We observed that a higher accuracy could be achieved by creating a correlation specific for each shale formation individually. Easily obtained input parameters were used to predict the fracture conductivity, namely, fracture orientation, closure stress, proppant mesh size, proppant load, static Young’s modulus, static Poisson’s ratio, and brittleness index. Exploratory data analysis showed that the features above are important where the closure stress is the most significant.

Conduit system, degassing, and flow dynamics of a rhyolite lava: A case study of the Shiroyama lava on Himeshima Island, Japan

This study presents a description of a rhyolite lava-forming eruption, including the conduit system, degassing history during the lava flow dynamics. We examined the Pleistocene Shiroyama rhyolite lava on Himeshima Island, Japan. The lava is mainly characterized by locally developed obsidian. Based on the structural variation, the obsidian lithofacies correspond to the shallow conduit. The geological investigation and FTIR analyses showed that gas removal from the conduit magma proceeded via vesiculation, fracturing, and brecciation, allowing formation of the dense obsidian. Since the lava originally maintained some extent of water, the lava effervesced just after the effusion. This vesiculation resulted in pervasive bubble coalescence and the formation of abundant permeable pathways. The volcanic gasses escaped via those pathways, allowing collapse of the bubbles and deflation of the lava. AMS (anisotropy of magnetic susceptibility) results indicate that the lava spread concentrically.

Soil structure and soil moisture dynamics inferred from time-lapse electrical resistivity tomography

The semi-arid sagebrush steppe in the western United States faces pressures from the agriculture industry, recreation use, invasive grasses, and a changing climate. A key to facilitating the healthy management of this ecosystem is understanding the distribution and behavior of soil moisture in the vadose zone in both natural and agricultural settings. Within unsaturated environments, soil moisture is spatially and temporally heterogeneous, and changes in porosity and permeability within arid soils complicate characterization of soil hydrologic properties. Importantly, accumulations of ‘caliche’ or pedogenic calcium carbonate in arid soils can greatly limit permeability; however, observing the role that caliche plays in the hydrologic process is difficult because the installation of in situ instruments disturbs the soils and only provides information at a single point. To investigate vadose zone processes on a broad temporal and spatial scale, we installed a 7x8m2 electrical resistivity tomography (ERT) array at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. Existing soil moisture observations show that infiltration is limited to depths less than 60 cm at this site, as compared to at least 90 cm at other sites in the watershed. To capture the seasonal wetting and drying of the soils, as well as the soils’ response to rainfall events, we monitored the site bi-weekly during the spring, summer, and fall of 2015 and 2016. A time-lapse ERT array was placed adjacent to coaxial impedance dielectric reflectometry (CIDR) probes so that the time-lapse ERT data could be referenced to precise measurements of volumetric water content. In addition to the measurements provided by the ERT array and CIDR probes, soil texture analysis and soil profile descriptions from a near-by soil pit show typical arid soil morphology, with accumulations of clays and calcium carbonate in the B horizon. The resulting ERT inversions show the following soil structure: (1) a high-resistivity top layer corresponding with minor amounts of pedogenic calcium carbonate; (2) a low-resistivity intermediate layer at depths corresponding with substantial accumulations (stage IV) of carbonate; and (3) a high-resistivity deep saprolite. The resistivity of the top layer varies seasonally with changes in precipitation, while the intermediate carbonate soil layer does not. This agrees well with the changes in soil moisture with depth measured by the CIDR probes and suggests that the top of the carbonate soil layer limits infiltration. However vertical structure and cracks within the carbonate soil layer create vertical preferential flow paths; resistivity within these flow paths responds to large precipitation events and seasonal changes in soil moisture. This implies that the preferential flow paths are a conduit for soil moisture flow that is not captured by the CIDR probes. From the combined interpretation of the ERT and CIDR we conclude that soil structure and the presence of calcic soil horizons inhibits soil moisture infiltration during both the summer dry months and the winter wet flux period; however, preferential flow paths provide an important vertical connection between the deep and shallow portions of the critical zone.

Breakthrough curves of dye tracing tests in karst aquifers: Review of effective parameters based on synthetic modeling and field data

Breakthrough curves (BTCs) are known as adequate evidence to characterize karst aquifers which mainly specified by dual flow systems (matrix and conduit) as well as some degree of connection between dual media. Conduit Flow Process version 2 (CFPv2) is a discrete conduit continuum model applying which it is possible to simulate such characteristics. In this research, first CFPv2 was employed to evaluate the effect of several factors including hydraulic conductivity, exchange flow, tracing distance, hydraulic gradient, and conduit diameter and roughness on BTCs in a synthetic karst aquifer. Then, 253 BTCs from 24 dye tracing tests, conducted in karstic aquifers of Iran, were analyzed to evaluate the effect of hydraulic gradient and tracing distance on the BTCs with taking into account the effect of medium type (matrix or conduit) and karst development. These tests were conducted under either natural or elevated man-made hydraulic gradient conditions. The results revealed that peak concentration decreased with enlarging conduit diameter because of considerable flow rate. Likewise, it decreases over longer distances specifically in the elevated man-made hydraulic conditions. However, with increasing hydraulic gradient, peak concentration and its timing have upward and downward trends, respectively. When BTCs start to demonstrate tailing and become flattened, it could be an indication of low matrix hydraulic conductivity or lower hydraulic gradient in conduit as a result of less exchange flow from the matrix into conduits. Based on this study a new intermixture of flow and solute transport parameters was engineered to classify karst development. High peak concentration, short peak time, high velocity particularly over long distances and under the natural hydraulic gradient conditions and feasible conduit flow regime whether laminar or turbulent suggested as indication of well-developed karstic system.