Horizontal Bed Research Articles

ЛИТОЛОГИЧЕСКАЯ ХАРАКТЕРИСТИКА БАЛТСКИХ И САРМАТСКИХ ПЕСКОВ МЕЖДУРЕЧЬЯ САВРАНКИ И КОДЫМЫ КАК ВОЗМОЖНЫХ КОЛЛЕКТОРОВ НАКОПЛЕНИЯ ТЯЖЕЛЫХ МИНЕРАЛОВ

The lithological composition of the Miocene-Pliocene sand deposits of the Middle Sarmatian and Baltian age between the rivers of the right tributaries of the Southern Bug (Savranka and Kodima rivers) was studied. Two series of sand are described in the composition of the Middle Sarmatian deposits. Under-limestone series has cross-bedding, which alternates with horizontal bedding. There are medium and coarse-grained sands with medium and good grading; there are layers of unsorted sandy-aleurite-clay material with a significant content of fine gravel. Garnet, magnetite, titanium-magnetite, ilmenite, rutile, glist predominate in the heavy fraction. Under-limestone series of the Middle Sarmatian is formed in coastal conditions with a flow hydrodynamic regime. Upper-limestone series of the Middle Sarmatian is composed of well-sorted medium-grained sands with an insignificant admixture of silt. The series is characterized by well-developed drift structure, expressed over tens of kilometers. The sands are enriched in heavy fraction, there are thin layers of black sand. Garnets, titanomagnetite, magnetite, ilmenite, rutile, glist predominate in the heavy fraction. Series is formed in the delta conditions that were established during the regression of the Sarmatian sea basin. The Baltian suite, which is the deposits of the Meotian, Pontian, Cimmerian and Akchagilian levels of the Miocene and Pliocene, was formed in continental conditions. The series is characterized by the alternation of aleurite-clay and sandy sediments, the presence of ironification, the wide distribution of clastogenic and authigenic postsedimentation carbon-bearing . The Baltian sands are predominantly fine-grained, sometimes clayey-silty, medium and well graded. Heavy minerals contain large quantities, among which ilmenite, titanium-magnetite, magnetite, garnet, zircon, and glist predominate. The Baltian suite was formed in the conditions of the alluvial plain that existed on the southern slope of the Ukrainian Shield in the Miocene-Pliocene. Compared to the Sarmatian deposits, Baltian sediments show a sharp increase in the amount of titanium-containing minerals and glists, this may be due to the erosion of new ore bodies with a decrease in the basis of erosion as a result of tectonic uplifting of the territory. The results of the study of the lithological composition and heavy fraction of Sarmatian and Baltian sandy sediments can be useful when searching for primary titanium-magnetite deposits, as well as when searching for alluvial placers on the right bank of the Southern Bug. In addition, such studies help in the reconstruction of alluvial pathways for the transfer of ore matter in the hypergenesis zone in the Northern Black Sea region.

Sedimentary diagenesis of rudist shoal and its control on reservoirs: A case study of Cretaceous Mishrif Formation, H Oilfield, Iraq

Abstract Based on the core, cast thin section, whole rock analysis, conventional physical properties and high pressure mercury intrusion test, the sedimentary diagenesis characteristics of rudist shoal in Cretaceous Mishrif Formation of H Oilfield, Iraq and its control on the reservoir were studied. The rudist shoal of the Mishrif Formation develops in the high-stand systems tract and is distributed in the high places of paleogeomorphology on the edge of platform with strong hydrodynamic force. According to the relative sea level changes, lithologic evolution and sedimentary structure characteristics of the rudist shoal, the single rudist shoal is divided into four lithologic sections: A, B, C and D, that is, low-angle cross-bedding pelletoids-rudist packstone, low-angle cross-bedding and parallel bedding arene-rudist grainstone, parallel bedding rudist gravel limestone, and horizontal bedding carbonaceous mudstone. The complete sedimentary sequence of a single rudist shoal is often disrupted. Several rudist shoals superimpose to form thick rudist shoal sediment. The single rudist shoal thickness and lithologic sections assemblage change regularly in vertical direction. The rudist shoal has the characteristics of “strong dissolution, weak cementation and strong compaction”, forming pore-type reservoir with intergranular pores, intergranular dissolved pores, mold pores, and dissolved pores. With mainly coarse pore throats larger than 5 μm, the reservoir is of medium-high porosity and high permeability. There is lithological reverse cycles inside single shoals and between single shoals, with content of mud crystals decreasing from the bottom to the top, dissolution increasing, cementation decreasing in strength, pore throats getting larger, and physical properties turning better. The rudist shoal of MB2-1 at the top of the high-stand systems tract has the largest thickness, moreover, subject to the strongest atmospheric freshwater leaching, this layer has the most significant dissolution and the largest pore throat, so it is the best reservoir of the Mishrif Formation.

The origin and morphology of Al-Tar caves, West Karbala, Iraq

This study aims to interpret the origin and morphology of Al-Tar caves based on comprehensive analysis of fractures. The current research highlights the significant impacts of the geological system (especially jointing and lithology) in forming and developing caves in the study area. Around 50 caves and 100 joints planes have been recognised. Field measurements were transformed into three dimensions in geometric form. A location map, stratigraphic column, and survey data map of caves have been produced in order to resolve the bond of Al-Tar caves with joints in the study area. Caves and joints systems are linked with the nearly horizontal beds in the stable shelf of Iraq. Caves created by two sets of joints. Joints form two main systems; each system comprises two orthogonal sets of vertical or nearly vertical joints. A three-dimension model was used dependent on field measurements, and the model predicted where caves occurred and how they formed. Presuming autonomy, the way of alignment of caves was acquired, which was related to the direction of joints. Joints and passages orientations are consistent with regionally expected directions. After examining the anatomy and organisational position of these caves, it was demonstrated that they have large spaces or corridors, which have circular or steep entrances, most importantly where the dip angles of rock layers are sub-horizontal.

Weathering Controlled Landslide in Deccan Traps: Insight from Mahabaleshwar, Maharashtra

Landslide is one of the devastating natural phenomenon that threatens human life and property. Every year a number of persons lost their lives due to the landslides. Therefore, a better understanding and characterization of landslide is very essential for adopting mitigation strategies to contain the adversities of this natural hazard. Information on landslides from different climatic setup are very essential for better understanding of the influence of weathering, rainfall, or topography on landslide generation. Weathering is one of the important causative factor for landslide generation in the moderate topography or inactive mountainous terrain. The Western Ghats including the Deccan Traps, an inactive mountain range, receives torrential rainfall. Intense rainfall in these areas enhances the weathering processes and fabricates thick soil covers. Mahabaleshwar area, Maharashtra was chosen as a case study, where high elevated part is covered by lateritic layer and each lava flow unit is separated by a thin weathered bed of red bole. The area experiences series of landslides during the summer monsoon months. Mainly two types of landslides have been identified in the area confined with the red bole bed and powdery lateritic soil. The first type of landslides occur at higher elevations (≥1200m) where horizontal beds of permeable laterites underlined by impermeable thick basalt beds. The rain water infiltrates down and spread laterally within the permeable lateritic beds. It finally spouts at lower plateau elevations and triggers mainly debris flows. The other category of landslides occurs where the weathered red bole bed separates two successive lava flows. The percolating water from the secondary porosities (joints and inter connected vugs) comes out from the contact zones of basalt and red bole bed in the form of seepages. It erodes the red bole bed and as a result the overlying masses hang and consequently lead to rock fall. The Chemical Index of Alteration (CIA) of the representative samples from landslide locations indicates significant weathering. The CIA values for the fine lateritic soil are up to 98% whereas for the red bole bed it varies from 77 to 85%. This suggests a high chemical weathering and higher erodibility. The association of active landslide locations with the red bole bed and fine lateritic soil suggests a close relation between weathering and landslide occurrences in the area.

Spark erosion in a metal spheres bed: Experimental study of the discharge stability and energy efficiency

Pulsed spark discharge in metallic granular beds in aqueous media was studied for the granular bed geometry affecting the discharge parameters, stability and powder production. Experiments were carried out in horizontal bed and columnar reactors filled with 4-mm steel spheres. The pulse energy and the powder production depend on the bed height, showing its maximum within 9–14 mm growing with the pulse repetition frequency from 200 to 800 pulses per second and degrading in spark erosion time due to the bed vibrational compaction and accumulation of the erosion products short-circuiting intergranular gaps.

Study of reinforcement support mechanisms for wide-span horse-shoe-shaped openings in horizontally layered jointed rock using the distinct element method

Wide-span openings in horizontally layered jointed rock were analysed using the distinct element method (DEM) to provide additional insight into rock bolt support mechanisms and forces. The rock bolt forces in the DEM calculations exhibited distinct mechanisms, identified here as reinforced rock unit, beam building or suspension mechanisms. Each of these mechanisms was found to be associated with certain characteristics in the jointed rock structure. In jointed rock with thick horizontal beddings, the rock bolt forces at the roof tapered off with distance leading to a reinforced rock unit where each layer exhibited a self-support mechanism akin to a voussoir beam. In jointed rock with thinner horizontal beddings not capable of self-supporting, a beam building mechanism took place. When the rock bolts were extended into a rigid layer above the thinner layers, a suspension mechanism took place. Potential inaccuracies of thrust line predictions and the benefits of rock bolt tensioning were investigated, and their effects were found to be sensitive to the bedding thickness. A case history of the cavern roof of the underground car park for the Sydney Opera House was modelled. The calculated deflections of the cavern roof compared well with field measurements reported in the literature. The findings in this paper highlight the importance to ensure that the reinforcement support for wide-span underground excavations in horizontally layered jointed rock are tailored to the geological conditions being encountered.

Structural traits dictate abiotic stress amelioration by intertidal oysters

Abstract Autogenic ecosystem engineers often provide cool microhabitats which are used by associated organisms to reduce thermal extremes. The value of such habitats is, however, dependent on key structural traits of the ecosystem engineer, and the intensity and duration of thermal exposure. Using an experimental mesocosm that mimicked the rocky intertidal environment, we assessed how the spatial configuration of the habitat formed by an autogenic ecosystem engineer, the oyster, influences its capacity to mitigate heat stress experienced by invertebrates during simulated emersion periods on tropical, Hong Kong rocky shores. At the average temperature experienced during summer low tides, oyster habitat ameliorated environmental and organismal temperatures, irrespective of the structural configuration of the oyster bed. As temperatures increased, however, vertically orientated oysters provided microclimates that facilitated cooler invertebrate body temperatures than horizontal beds, which no longer conferred any associational benefit as compared to bare rock surfaces. In the absence of oysters, physiological indicators of stress to associated organisms (i.e., heart rate and osmolality) increased with the intensity and duration of exposure to high temperatures. Such effects were, however, mitigated by association with vertical but not horizontal oyster configurations. In contrast, the osmolality of the oysters was not related to temperature, suggesting they remained in a state of metabolic quiescence throughout emersion. Structural traits such as the spatial configuration of ecosystem engineers are therefore critical to their effectiveness in environmental amelioration. As such, variations in the morphological traits of ecosystem engineers, which have important implications for their ecological role, need to be incorporated into conservation and restoration projects aimed at climate change adaptation. A plain language summary is available for this article.

Influence of process conditions on the product properties in a continuous fluidized bed spray granulation process

This work focuses on continuously operated spray granulation processes in horizontal fluidized beds highlighting the influence of process conditions on the particle properties of the resulting product granules. The drying process has a decisive influence on the kinetics of the growth rate and thus also on the properties of the particles, such as the morphological structure, particle moisture content and porosity as well as density, compression strength and the wetting behavior. This influence has been considered in this study in more detail on the basis of the model material sodium benzoate. In order to compare the produced granules at different drying conditions and spray rates of the suspension an external product classification was used to achieve a certain product granule size. The obtained experimental results show a deep influence of the thermal conditions onto granule morphology and structural properties, which is in qualitative agreement with recent experimental observations (Rieck et al., 2015; Hoffmann et al., 2015a; Schmidt et al., 2017b). The overall trend of the results reveal smoother product granules with decreasing spray rates of the suspension and increasing drying temperatures. These smoother surface morphologies lead to a more homogeneous layering which has as a consequence that the internal particle porosity is decreasing while the solids density and the compression strength of the particles are increasing at the same time. In this study the purely qualitative classification of the surface texture from previous experimental studies was extended by the topographic analysis of the product granules, giving the possibility to quantify the morphological structure by means of roughness measurements. This makes the morphological design accessible as product property and permits the utilization of models that describe the morphology according to the process conditions.

Experimental and Numerical Study of the Effects of Layer Orientation on the Mechanical Behavior of Shale

Bedding planes are common in shale and significantly affect its mechanical behavior. In this paper, the main focus is investigating the effects of layer orientation on the mechanical behavior of shale under different confining pressures through physical experiments and numerical simulations. First, confining pressure tests were performed to investigate the parameter differences of specimens with vertical bedding planes (SVBPs) and specimens with horizontal bedding planes (SHBPs). Second, the statistical results of the length and spacing of bedding planes were employed to construct the simulation model. Third, the microparameters of the proposed model were confirmed with the results obtained from physical experiments, in which four key factors including deviatoric stress versus axial strain curve, peak strength, Young’s modulus and failure mode were all used to calibrate the feasibility and reliability of the numerical simulation. Finally, a systematic simulation was conducted to investigate the effects of layer orientation on the mechanical behavior of shale. The results show that the mechanical parameters (deviatoric stress vs. axial strain curve, peak strength, Young’s modulus, cohesion and internal friction angle) are greatly affected by layer orientation. Tensile cracking of the rock matrix is dominant in specimens with both vertical and horizontal bedding planes. The crack initiation threshold (CIT) of SVBPs is smaller than that of SHBPs, but the crack damage threshold (CDT) is similar. The percentages of CIT and CDT are nearly unchanged under different confining pressures in both types of specimens. The conformity between the simulation results and physical experiment results suggests that the research method proposed in this study can advance the understanding of rock mass mechanical behavior.

Assessment of the combined in‐plane and out‐of‐plane behavior of brick infill walls within reinforced concrete frames under seismic loading

SummaryUnderstanding the out‐of‐plane response of masonry infill walls and preventing their progressive collapse mechanisms is very important for earthquake‐prone countries to prevent loss of life and economic loss. In fact, having a realistic collapse mechanism assessment allows suitable prevention measures to be adopted. With this purpose in mind, two full‐scale one‐bay one‐story substructures of reinforced concrete frames (RCF) with infill walls were tested on a shake table. These 2 specimens were designed to represent the response of a typical RC Frame at the fifth floor of an 8‐story building, namely the out‐of‐plane failure of its infill wall under combined bidirectional seismic load. Both specimens were composed of a single‐leaf clay brick infill wall surrounded by the RC Frame. However, while the first specimen corresponds to an unreinforced masonry configuration, the second specimen includes horizontal bed joint reinforcement as a strengthening/retrofitting technique. The main novelty of this study is the application of a bidirectional and simultaneous dynamic loading to the specimen, such that in‐plane and out‐of‐plane effects are evaluated together. This work presents several interesting experimental results, with particular emphasis on the bearing capacity of the specimens against out‐of‐plane failure. As expected, the in‐plane capacity of the reinforced infill specimen is larger than that of the unreinforced infill specimen. Nevertheless, the out‐of‐plane bearing capacities of the two specimens are very similar, in contrast to their ductility capacity, which is significantly increased in the reinforced masonry specimen. The capacities of the two specimens for both in‐plane and out‐of‐plane directions, as predicted by formulations in the literature, are given. The differences found between these calculations and the results of the tests are discussed, and may possibly be explained by the parameters considered in the different formulations.

The Effect of Infill Steel Plate Thickness on the Cycle Behavior of Steel Plate Shear Walls

The effect of changing in the bed slope of stilling basins produces changing in characteristics of the hydraulic jump such as sequent depth ratio, length of jump ratio, length of the roller and energy dissipation ratio, consequently the dimensions of stilling basin changed. In this study hydraulic jump investigated on smooth bed (without any appurtenances) for three adverse slopes (- 0.03, - 0.045, - 0.06) in addition to horizontal bed slope, the experiments were applied for the range of Froude number (Fr1) between 3.99 and 7.48. The results showed a reduction about10 % in sequent depth ratio, 22.1 % in length of jump ratio, 20.51 % in length of roller ratio and 13.87% in the energy dissipation ratio when the adverse slope (- 0.06) used instead of horizontal bed for the same Froude numbers. Empirical equations for the sequent depth ratio, length of roller ratio and the energy dissipation ratio were obtained from the experimental data

Application of horizontal flow constructed wetland and solar driven disinfection technologies for wastewater treatment in India

Abstract The present study was conducted to treat primary and secondary treated sewage for its reuse in irrigation, soil enrichment and aquaculture activities. The study involves treatment of this sewage through a subsurface horizontal gravity-fed gravel filter bed with an area of 35 m2. The effluent was then subjected to filtration by zeolite medium and disinfection by inline electrolytic production of chlorine. In order to provide pathogen-free water, an anodic oxidation (AO) disinfection system was implemented, treating a flow of up to 10 m3/d. The gravity-driven constructed wetland and solar-driven disinfection systems were evaluated for their treatment capacity for various physico-chemical and biological parameters. The wetland removed almost 84% of the nitrate (NO3−) and 77% of the phosphate (PO43−). Five-day biological oxygen demand was reduced from 48 mg/l to 10 mg/l from the secondary treated wastewater. The wetland was able to remove 65–70% of bacteria in the wastewater, whereas the AO disinfection system removed the bacterial content to below the detection limit. The implementation of the systems will provide a suitable option for the treatment of wastewater in a very economical and sustainable way.

A 2DH hybrid Boussinesq-NSWE solver for near-shore hydrodynamics

This paper presents a numerical model that simulates the nearshore circulation and the propagation of waves in two horizontal dimensions (2DH) across the coastal zone, from intermediate depth to zero depth. Pre-breaking, wave propagation is calculated using a Boussinesq equation set with enhanced dispersion characteristics, discretised using second-order central differences and solved using the conjugate gradient method with fourth order Runge-Kutta time integration. In the breaker zone, the Boussinesq dispersive terms are gradually switched off, and the resulting non-linear shallow water equations solved using a finite volume MUSCL-Hancock scheme with an HLLC approximate Riemann solver. Broken waves are treated as hydraulic bores. A wetting and drying algorithm models the moving wet/dry front at the shore. Waves are generated by a line of independently moving piston paddles which are represented through a linear mapping, stretching and compressing the grid in the region of the paddles. Model verification tests include wave sloshing in a frictionless basin, seiching in a parabolic basin with bed friction, solitary wave propagation over a horizontal bed, and the interaction of a solitary wave with a conical island. After calibration, the model simulates the generation of wave-induced currents by regular waves as they interact with sinusoidal and tricuspate beaches, and the propagation of a uni-directional focused wave group over a plane beach. Results are compared against previously published laboratory data. The validation tests confirm that the 2DH model reproduces several important coastal hydrodynamic phenomena including wave-induced currents and multi-component wave packets. The model can thus be used to replicate wave basin experiments, and could be extended to multi-directional waves, leading to a better understanding of hydrodynamic processes in shallow coastal waters.

Distribution of gyrotactic micro-organisms in complex three-dimensional flows. Part 1. Horizontal shear flow past a vertical circular cylinder

As a first step towards understanding the distribution of swimming micro-organisms in flowing shallow water containing vegetation, we formulate a continuum model for dilute suspensions in horizontal shear flow, with a maximum Reynolds number of 100, past a single, rigid, vertical, circular cylinder that extends from a flat horizontal bed and penetrates the free water surface. A numerical platform was developed to solve this problem, in four stages: first, a scheme for computation of the flow field; second, a solver for the Fokker–Planck equation governing the probability distribution of the swimming direction of gyrotactic cells under the combined action of gravity, ambient vorticity and rotational diffusion; third, the construction of a database for the mean swimming velocity and the translational diffusivity tensor as functions of the three vorticity components, using parameters appropriate for the swimming alga, Chlamydomonas nivalis; fourth, a solver for the three-dimensional concentration distribution of the gyrotactic micro-organisms. Upstream of the cylinder, the cells are confined to a vertical strip of width equal to the cylinder diameter, which enables us to visualise mixing in the wake. The flow downstream of the cylinder is divided into three zones: parallel vortex shedding in the top zone near the water surface, oblique vortex shedding in the middle zone and quasi-steady flow in the bottom zone. Secondary (vertical) flow occurs just upstream and downstream of the cylinder. Frequency spectra of the velocity components in the wake of the cylinder show two dominant frequencies of vortex shedding, in the parallel- and oblique-shedding zones respectively, together with a low frequency, equal to the difference between those two frequencies, that corresponds to a beating modulation. The concentration distribution is calculated for both active particles and passive, non-swimming, particles for comparison. The concentration distribution is very similar for both active and passive particles, except near the top surface, where upswimming causes the concentration of active particles to reach values greater than in the upstream strip, and in a thin boundary layer on the downstream surface of the cylinder, where a high concentration of active particles occurs as a result of radial swimming.

Productivity and chemical properties of Salix viminalis in a horizontal subsurface flow constructed wetland during long-term operation

The paper presents the results of a study of selected parameters of common osier (Salix viminalis) biomass sampled annually, over a 12-year period, from a constructed wetland wastewater treatment plant. The focus of the study was on parameters that were relevant to biomass energy management. The study was conducted in a constructed wetland wastewater treatment plant consisting of one horizontal flow bed with a total area of 186 m2, planted with osier willows. The following biomass parameters were analysed: biomass yield, volume, humidity, ash content, higher and lower heating values, and contents of N, P, K in different parts of plant stems. The study showed that osier biomass harvested from the investigated constructed wetland system could be used as an energy source in thermochemical processes. The higher and lower heating values were similar to those obtained by other authors (18.13 and 17.38 MJ·kg−1, respectively). The energy yield (17.49 MJ·m−2) and energy density (3486–5411 MJ·m−3) were also calculated. Young shoot parts had higher ash and micronutrient contents and lower energy parameters than old parts.

Experimental investigation on sea ripple evolution over sloping beaches

This paper reports on a wave flume experimental campaign carried out to investigate the appearance, the growth and the migration of small scale bedforms on a sloping sandy bed due to both regular and random waves. A Vectrino Profiler along with a structured light approach were used for velocity and morphodynamic measurements at two positions, one located above the horizontal bed, and the other one above the sloping beach. The velocity was computed by phase averaging the velocity measurements. Several velocity profiles were analyzed, identifying an offshore-directed steady current that extends from few centimeters above the bottom for all the analyzed water column. Ripple geometry was measured by a structured light approach and compared with that predicted by several models to shed light on the effects induced by the sloping beach on the shape and asymmetry. Along the sloping beach, the ripples appeared strongly asymmetric with the onshore half wavelengths smaller than the offshore ones. Finally, ripple geometry and migration triggered by regular waves were compared with those generated by random waves with comparable flow orbital amplitude showing a good agreement.

A study on mud particle velocities and mass transport in wave-current-mud interaction

The upper fluid mud layer in muddy environments absorbs wave energy and, in turn, moves due to the wave action. In addition to these two major phenomena of wave-mud interaction, introduction of current in the wave field also changes the wave characteristics as well as the rates of mud mass transport. The present study offers an experimental investigation of wave-current-mud interaction to address the wave transformation and mud mass transport on a horizontal bed. A number of laboratory tests were conducted to measure the mud particle velocities as well as wave attenuation rates under following, opposing, and no current conditions. Both the wave energy dissipation and mud mass transport increase with the presence of opposing currents and decrease when following currents are introduced. A semi-analytical model was also presented and the numerical results are compared with the laboratory experiments, showing acceptable agreements.

Novel production method of tracer particles for residence time measurements in gas-solid processes

In order to measure the residence time distribution (RTD) in continuous gas-solid processes tracer particles are used. In this contribution, a novel production concept for magnetizable particles has been developed and optimized. The process includes coating of a fraction of the investigated bed material with a magnetizable paint in a laboratory spouted bed. The coated particles fulfill the requirements of tracer material, are resistant, harmless to health and reusable. After passing a continuously operated process, the tracer material can be separated by a magnetic rod from the sample, which allows the fast and easy calculation of the exit age distribution as demonstrated in this contribution with a horizontal fluidized bed.

Analysis of wellbore stability considering the effects of bedding planes and anisotropic seepage during drilling horizontal wells in the laminated formation

With the exploration and development of gas shale in recent years, layer structures (bedding planes) of laminated rock and its effects on mechanical properties of rock and wellbore stability have arisen great attention. In this paper, we mainly concerns the wellbore stability during drilling horizontal wells in the laminated formation with horizontal bedding planes, meanwhile, the effects of anisotropy of permeability paralleled to bedding planes and that perpendicular to bedding planes are taken into consideration as well. Models of pore pressure distribution and seepage stresses under anisotropic seepage are established. Combining the effects of anisotropic seepage and bedding planes, we have investigated the equivalent collapse density (ECD) around horizontal wellbores. The results based on the input data in this paper reveal that the ECD considering the weakness of bedding planes is far higher than that without considering bedding planes, and the shape of zones where surrounding rock is relatively easier to collapse is similar as two couples of cat ears. The point where ECD reaches its maximum value tends to move from wellbore wall to internal rock if drilling close to the direction of minimum in-situ stress, and the higher anisotropic permeability ratio is, the more obvious the phenomenon is. The effect of anisotropic seepage can be ignored if the weakness of bedding planes is omitted, it otherwise can not be left out and the maximum ECD around wellbore instead of the maximum value at wellbore wall should be used to design for drilling operation. This study simultaneously investigates the effects of anisotropic seepage and weak bedding planes on wellbore stability during drilling horizontal wells, it is promising to provide a theoretical basis and practical guidance for the further researches on wellbore stability in future.

Crustal Radial Anisotropy and Linkage to Geodynamic Processes: A Study Based on Seismic Ambient Noise in Southern Madagascar

AbstractWe determined radial anisotropy in the crust of southern Madagascar from the differences between the speeds of vertically and horizontally polarized shear waves (VSV and VSH), which we derived from Rayleigh and Love wave dispersion determined from seismic ambient noise correlations. The amalgamated Precambrian units in the east and the Phanerozoic Morondava basin in the west of southern Madagascar were shaped by different geodynamic processes. The crystalline basement was strongly deformed and metamorphosed to varying degrees during the assembly of Gondwana in the Pan‐African Orogeny, whereas the Morondava basin was completed with the separation of Africa and Madagascar. The different developments are reflected in first‐order differences in the radial anisotropy patterns. In the Precambrian domains, positive anisotropy (VSV<VSH) is found in the upper and lower crust, with a layer of negative anisotropy (VSV>VSH) sandwiched in between. The upper crustal anisotropy may reflect shallowly dipping layering within the Archean and adjacent imbricated nappe stacks, whereas the lower crustal anisotropy likely represents fossilized crustal flow during the postorogenic or synorogenic collapse of the Pan‐African Orogen. The negative anisotropy layer may have preserved vertically oriented large shear zones of late Pan‐African age. Within the Morondava basin, negative anisotropy in the uppermost ∼5 km could have been generated by steep normal faults, jointing, and magmatic dike intrusions. The deeper sediments and underlying crustal basement are characterized by positive anisotropy. This is consistent with horizontal bedding in the sediments and with fabric alignment in the basement created by extension during the basin formation.