convection in small basins abstract convection in the world s oceans often occurs in small semienclosed basins where bottom slopes and nearby continental shelf breaks are commonplace the evolution of convectively generated heat anomalies in such settings is studied using quasigeostrophic finite difference and point vortex models the displayed behaviors divide essentially into two categories whole fluid column convection in which bottom slope effects are felt immediately and partial fluid column convection in which the topographic effects can be delayed in both cases topography significantly modifies the evolution of convective patches from that occurring over flat bottoms vertical walls induce strong self propagation mechanisms that accelerate alongslope heat transport while the continental shelf slope is repulsive and rejects lower layer anticyclones these anomalies are then stranded being too far offshore to interact with the shelf break and having lost their heton partner in the interaction weaker deep ocean topo

modern state and dynamics of the sea of azov coasts abstract results of the modern state researches of the sea of azov coasts and coastal processes influencing their evolution are presented a multidisciplinary study of coastal processes allowed us to identify main types of coast evolution abrasion accumulation and stability predominance of abrasion is the main feature of modern dynamics of the azov shores not only the parent rock shores are subjected to erosion but also accumulative forms are eroded the eastern coast of the sea retreats most rapidly the intensity of the abrasion and landslide processes is due to the weak resistance of the rocks composing the coast to the wave forcing in particular intense abrasion occurs in those parts of the coast where wave forcing is strong together with the surges caused by onshore winds while the beaches are narrow or completely absent at the same time the percentage of beach forming fractions in eroded soils is low and the major part of the abrasion material in the form of suspended matter is transported to the deep parts of the sea in general the state and dynamics of the azov coasts are influenced by abrasion accumulative processes sea level fluctuations changes in the wind wave regime parameters and fluctuations in the biogenic beach forming material volumes the biogenic factor is the most important in the balance of deposits of accumulation forms spits and bay bars anthropogenic activity also affects the current state of the shores the transport of beach forming alluvial sediments into the sea is reduced because of the regulated river discharge the natural evolution of onshore processes is disrupted during the development of the coast agricultural activities industrial and resort construction removal of sand and shell material construction of shore protection facilities

the use of vertical line sources in electrical prospecting for hydrocarbon conventional electrical prospecting can be extended to the search for deep seated hydrocarbon deposits by using the steel casings of drill holes as vertical line sources these sources produce at depth a density of current higher than the density created by point sources located at the ground surface several tests have shown that the contrast of conductivity between resistive hydrocarbon deposits and the surrounding salt water produces relevant anomalies on a resistivity map obtained with vertical line sources especially where there exists a superficial masking effect caused by a highly resistive layer in a survey carried out in the ussr combined measurements were performed both with line source and with surface point sources the detected residual resistivity anomaly roughly delineates the contours of the known hydrocarbon deposit

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

low cost reservoir tomographs of electrical resistivity the geophysics we describe here will sound different from what you have heard before because it is different it uses electric fields instead of seismic waves it is not designed for exploration it is a distant cousin of cross borehole seismic tomography although it is quite different in terms of its application and results probably the most curious aspect is that it doesn t chase the holy grail of geophysics high resolution what good could possibly come from a low resolution electrical geophysical tool the answer is found in the paradigm gradually finding favor by oil executives and reservoir engineers while finding and exploiting large new fields is important for long term growth improving recovery efficiency for existing resources also makes sense because developing a new field is increasingly expensive as a result secondary recovery methods are receiving increasing attention this shift in view requires a parallel shift in geophysics now geophysics needs to deliver useful information about field production using low cost long term monitoring techniques that have minimum impact on production operations electrical resistance tomography ert is ideally suited to these new goals ert is a method for tomographically reconstructing the electrical resistivity distribution in the subsurface using an array of electrodes typically current is driven between two of the electrodes and the resulting voltage distribution is measured on the remaining electrodes repeating this with other pairs of current electrodes in the array makes it possible to sample the subsurface electrical properties in a manner that allows calculation of the spatial distribution of those properties the electrical properties depend strongly on pore fluid content consequently ert is especially good at giving information on the movements of oil water and gas the principal fluids of interest in a petroleum reservoir an important aspect of this method is that the oil well casings themselves are used as

sand waves along the dutch coast sand waves defined as longshore wave like movements of the shoreline measured in a horizontal plane are described along several stretches of the shoreline of the netherlands they have a celerity in the order of 50 200 m yr a period of 50 150 years and an amplitude of 30 500 m they are found along the whole dutch shoreline analysis of sand waves shows that the assumed effect of groins might be very small along this shoreline there are indications that groins did not have any long term effect on coastal regression

effect of well casings on surface electrical surveys surface electrical surveys are being used as alternative oil exploration tools in both developed and frontier areas we have examined the resistivity ip response of steel oil well casings which are common in developed oil fields two numerical models were constructed a solution of laplace s equation in the spatial wavenumber domain and an integral equation approach using the galerkin weighted residual technique which simulate hollow infinite length cylinders and finite length cylindrical shells respectively embedded in a uniform half space induced polarization effects can be simulated in these models by including a complex frequency dependent surface impedance on the outer surface of the cylinder significant anomalies are generated by pipes having physically realistic dimensions and conductivities important parameters governing the response are the longitudinal conductance length and radius of the pipe and the number of pipes and their distances from the survey line comparison of field data

persistent shoreline shape induced from offshore geologic framework effects of shoreface connected ridges mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations oceanographic deployments and numerical modeling analysis of shoreline positions from the past 50 years along fire island new york a 50 km long barrier island demonstrates a persistent undulating shape along the western half of the island the shelf offshore of these persistent undulations is characterized with shoreface connected sand ridges sfcr of a similar alongshore length scale leading to a hypothesis that the ridges control the shoreline shape through the modification of flow to evaluate this a hydrodynamic model was configured to start with the us east coast and scale down to resolve the fire island nearshore the model was validated using observations along western fire island and buoy data and used to compute waves currents and sediment fluxes to isolate the influence of the sfcr on the generation of the persistent shoreline shape simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape the model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations in one location however the ridge crest connects to the nearshore and leads to an offshore directed transport that produces a difference in the shoreline shape this qualitatively supports the hypothesized effect of cross shore fluxes on coastal evolution alongshore flows in the nearshore during a representative storm are driven by wave breaking vortex force advection and pressure gradient all of which are affected by the sfcr

coastline sand waves on a low energy beach at el puntal spit spain abstract coastline sand waves have been observed at el puntal spit located on the north coast of spain the spit has been monitored by an argus video system since 2003 and the formation and destruction of sand waves has been observed coastline data from the video images are analyzed by means of principal components analysis obtaining a mean sand wave length of 125 150 m and a maximum amplitude of 15 m it is also observed that sand waves reach their maximum amplitude at about 15 days no propagation of these sand waves is noticed during the approximately two month long events analyzed sand wave formation and evolution are examined in relation with the prevailing local wave conditions during that period incident waves at the west end of the spit approach from the east northeast with a very high angle with respect to the shoreline field observations suggest that sand waves may result from an instability in alongshore sediment transport caused by moderate energy waves with a high angle incidence

finite element analysis of top casing electric source method for imaging hydraulically active fracture zones author s um es kim j wilt mj commer m kim ss abstract 2019 society of exploration geophysicists imaging hydraulically active fracture zones hafz is of paramount importance to subsurface resource extraction geologic storage and hazardous waste disposal we have developed advanced 3d finite element fe electrical imaging algorithms for hafz in the presence of a steel cased well the algorithms use tetrahedral fe meshes in the simulation domain and coarse rectangular finite difference meshes in the imaging domain this heterogeneous dual mesh approach is well suited to modeling the multiscale earth model due to steel cased wells we find that the algorithms accurately and efficiently simulate surface electric field measurements over a 3d hafz at depth when one end point of a surface electric source is connected to a wellhead for brevity this configuration is called the top casing electric source method by replacing a hollow cased well with a solid prism we improve our computational efficiency without affecting the solution accuracy the sensitivity of the top casing source method to hafz highly depends on the continuity of a steel cased well because it makes currents preferentially flow to hafz the sensitivity also depends on conductivity structures around the well because they control current leaking from the steel cased well we find that the method can image a localized hafz and detect changes in its width and height the imaging results are improved when a volume of the imaging domain is constrained from geomechanical perspectives a primary advantage of the method is the fact that the sources and receivers are placed on the surface thus not interrupting the well operation

understanding lotem data from mountainous terrain long offset transient electromagnetic lotem data from the vesuvius volcano in italy show that the em response of the topography is a potential cause of data distortions a modeling study was carried out to simulate the effect of mountainous terrain on vertical magnetic field time derivatives using a 3 d finite difference code the objectives were to assess the importance of topographic effects and to help identify them in existing field data the total effect of topography on the lotem response can be considered as a combination of four distortions of the corresponding responses for a flat terrain first the receiver is at some height above the flat surface second the mountain acts as a conductive body displacing air third large loop receivers are nonhorizontal and sense a combination of horizontal and vertical magnetic fields finally the electromagnetic coupling between the mountain and deeper lying structure modifies the structure response each of the effects can be identified in field data

numerical modeling analysis of short offset electric field measurements with a vertical electric dipole source in complex offshore environments abstractwe simulated and analyzed short offset transient electric field measurements excited by a vertical electric dipole ved source over complex 3d offshore models a finite element time domain modeling algorithm was used to efficiently model complex offshore structures using a series of cross sectional snapshots of transient electric fields in the complex offshore models we examined the characteristics of the short offset seafloor electric field measurements the numerical modeling analysis indicated that the short offset horizontal electric field ex measurements are very sensitive to subtle multidimensional seafloor topography near a ved source and can show a sign reversal at late times the sign reversal occurs because the ved source is no longer normal to the seafloor the occurrence of the sign reversal limits the application of the 1d inversion to the ex measurements even at a short source receiver offset in contrast the short offset vertical electric field ez measurements are robust to

decoupling processes and scales of shoreline morphodynamics abstract behavior of coastal systems on time scales ranging from single storm events to years and decades is controlled by both small scale sediment transport processes and large scale geologic oceanographic and morphologic processes improved understanding of coastal behavior at multiple time scales is required for refining models that predict potential erosion hazards and for coastal management planning and decision making here we investigate the primary controls on shoreline response along a geologically variable barrier island on time scales resolving extreme storms and decadal variations over a period of nearly one century an empirical orthogonal function analysis is applied to a time series of shoreline positions at fire island ny to identify patterns of shoreline variance along the length of the island we establish that there are separable patterns of shoreline behavior that represent response to oceanographic forcing as well as patterns that are not explained by this forcing the dominant shoreline behavior occurs over large length scales in the form of alternating episodes of shoreline retreat and advance presumably in response to storms cycles two secondary responses include long term response that is correlated to known geologic variations of the island and the other reflects geomorphic patterns with medium length scale our study also includes the response to hurricane sandy and a period of post storm recovery it was expected that the impacts from hurricane sandy would disrupt long term trends and spatial patterns we found that the response to sandy at fire island is not notable or distinguishable from several other large storms of the prior decade

sea stack formation and the role of abrasion on beach mantled headlands sea stacks are common and striking coastal landforms but few details are known about how how quickly and under what conditions they form we present numerical and analytical models of sea stack formation due to preferential erosion along a pre existing headland to address these basic questions on sediment rich rocky coasts as sea cliffs erode and retreat they produce beach sediment that is distributed by alongshore sediment transport and controls future sea cliff retreat rates depending on their width beaches can encourage or discourage sea cliff erosion by acting either as an abrasive tool or a protective cover that dissipates wave energy seaward of the cliff along the flanks of rocky headlands where pocket beaches are often curved and narrow due to wave field variability abrasion can accelerate alongshore directed sea cliff erosion eventually abrasion induced preferential erosion can cut a channel through a headland separating it from the mainland to become a sea stack under a symmetrical wave climate i e equal influence of waves approaching the coastline from the right and from the left numerical and analytical model results suggest that sea stack formation time and plan view size are proportional to preferential erosion intensity caused by for example abrasion and or local rock weakness from joints faults or fractures and initial headland aspect ratio and that sea stack formation is discouraged when the sediment input from sea cliff retreat is too high i e sea cliffs retreat quickly or are sand rich when initial headland aspect ratio is too small and the headland is rounded much wider in the alongshore direction at its base than at its seaward apex the headland is less conducive to sea stack formation on top of these geomorphic and morphologic controls a highly asymmetrical wave climate decreases sea stack size and discourages stack formation through rock sediment interactions copyright 2014 john wiley sons ltd

holocene depositional history of a microtidal cuspate foreland cape cape lookout north carolina abstract the holocene stratigraphy of cape lookout north carolina and the connecting barrier limb core banks displays sharply contrasting depositional histories beneath the core banks barrier chain a transgressive sequence of overwash storm deposits rests on back barrier silty sands and salt marsh peats evidence of the island s erosive landward migration however core holes drilled at cape lookout reveal a regressive vertical stacking of sediments that marks a major holocene facies change here fine grained burrowed shoreface deposits are overlain by coarse grained horizontally bedded barrier washover sands cape lookout has evolved during the late holocene as a prograding cuspate spit type of headland this accretion is a result of the combined effects of oceanic washover deposition with sand accumulated from a dominant southerly longshore transport during the past 4000 years the rate of sea level rise slowed markedly in the area resulting in a decreased rate of landward migration for core banks as the island became relatively stable with respect to sea level rise large volumes of sand were being transported along shore to cape lookout and offshore to its subaqueous shoals the slower landward retreat of the island probably allowed for a rapid southerly extension of core banks along with a buildup of the cape lookout shoals the sedimentation and growth of cape lookout over the past 4000 years probably reflects a similar history of development for other capes and shoals along the southeastern coast of the united states the large scale cuspate morphology present today may therefore be a relatively recent phenomenon

cross front mixing and frontal upwelling in a controlled quasi permanent density front in the gulf of st lawrence abstract ctd data obtained from three transects across a controlled quasi permanent density front in the gulf of st lawrence were analyzed for the purpose of investigating cross front mixing mechanisms for frontal convergence secondary circulation induced by the front and relationship between surface mixed layer properties and frontal structure water mass analysis indicates that mixing takes place mainly in the ambient water from the lower boundary of the frontal layer down to 100 m on the side of heavier water there is a region of low surface temperature the water masses have a distribution suggestive of upwelling in the low surface temperature region the thickness of the surface mixed layer varies across he front outside the frontal zone there is a well developed mixed layer of a thickness of about 25 m it disappears completely in the low surface temperature zone and is re established in the frontal layer with a reduced thickness horizontal intrusions below the frontal layer and interleavin

structure and seasonal characteristics of the gaspe current ctd and current meter data from the northwestern gulf of st lawrence were analyzed to study the structure and variability of the gaspe current since the current is buoyancy driven its properties are strongly influenced by the seasonal variation of the freshwater discharge from the st lawrence estuary from june to november maximum speed decreases from 110 cm s 1 to 60 cm s 1 high vertical shears exist in the upper 40 m of the water column during the same period the width of the current decreases and the position of the current maximum shifts from near the shore to about 14 km from the shore these changes in the structure can be understood in terms of geostrophy and baroclinic deformation radius in the temperature salinity field the most prominent change from june to november is the continuing increase of surface salinity temperature change occurs mainly in the september november period when atmospheric cooling accelerates the effect of atmospheric cooling is also reflected in the density distribution with the result that in november currents in the upper 30 m are seaward in the entire section from sept iles to marthe de gaspe while in the summer months the currents are seaward in the southern part and westward in the northern part of the section momentum balance of the current system is also investigated it was found that east of pointe des monts geostrophic balance is maintained while west of pointe des monts the observations do not seem to be consistent with the assumption of geostrophy

formation and circulation of the cold intermediate layer in the gulf of saint lawrence 1 the local heat content and formation rate of the cold intermediate layer cil in the gulf of saint lawrence are examined using a combination of new in situ wintertime observations and a three dimensional numerical model the field observations consist of five moorings located throughout the gulf over the period of november 2002 to june 2003 the observations demonstrate a substantially deeper surface mixed layer in the central and northeast gulf than in regions downstream of the buoyant surface outflow from the saint lawrence estuary the mixed layer depth in the estuary remains shallow 60 m throughout winter with the arrival of a layer of near freezing waters between 40 and 100 m depth in april an eddy permitting ice ocean model with realistic forcing is used to hindcast the period of observation the model simulates well the seasonal evolution of mixed layer depth and cil heat content although the greatest heat losses occur in the northeast the most significant change in cil heat content over winter occurs in the anticosti trough the observed renewal of cil in the estuary in spring is captured by the model the simulation highlights the role of the northwest gulf and in particular the separation of the gaspe current in controlling the exchange of cil between the estuary and the gulf in order to isolate the effects of inflow through the strait of belle isle on the cil heat content we examine a sensitivity experiment in which the strait is closed this simulation shows that the inflow has a less important effect on the cil than was suggested by previous studies

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

geomorphic origin of merritt island cape canaveral florida usa a paleodelta of the reversed st johns river abstract the merritt island cape canaveral miccsc sedimentary complex consists of a series of adjacent non conformable beach ridge sets that suggest a multi phase constructional history but the feature s geomorphic and sedimentary origins are not well understood in spite of its notable sedimentary volume surface area 1200 km2 the miccsc lacks a clear sediment source or supply mechanism to explain its presence today previously published u th radiocarbon and osl dates indicate that beach ridge deposition was active during mis 5 130 80 ka on merritt island but has occurred over a shorter younger time interval on cape canaveral proper 6 ka to present in this paper it is proposed that the miccsc is an abandoned paleodelta whose fluvial source provided a sediment supply sufficient for coastal progradation although the miccsc today does not receive an appreciable sediment supply the nearly 23 000 km2 drainage basin of the st johns river may well have provided such a sediment supply during mis 5 times this low gradient fluvial system currently empties to the atlantic ocean some 200 km north of the miccsc near jacksonville florida but may have flowed southward during the time of miccsc sedimentary construction then experienced flow reversal since mis 5 times three possible uplift mechanisms are proposed to explain the northward down tilting that may have reversed the flow direction of the st johns abandoning deltaic construction of the miccsc 1 karst driven flexural isostatic uplift in response to carbonate rock dissolution in central florida 2 glacio hydro isostatic tilting back tilting cycles during loading and unloading of the laurentide ice sheet during the pleistocene and 3 mantle convection driven dynamic topography operating within southeastern north america since the pliocene this example testifies to the sensitivity of low gradient low relief landscapes to various sources of uplift be they isostatic or otherwise

morphology formation and migration of longshore sandwaves long point lake erie canada this paper describes the morphology and dynamics of features termed here longshore sandwaves which are developed on a large barrier spit in the great lakes the sandwaves are local beach protuberances with alongshore lengths of 500 2500 m and maximum widths at the downdrift end of 50 90 m which migrate alongshore in the direction of net drift at 150 300 m yr 1 they have a lifespan of 10 yrs or more and their spatial and temporal scales are an order of magnitude greater than the rhythmic topography associated with the nearshore bars and rip cells which are also characteristic of the littoral zone the sandwaves are initiated by the onshore movement and welding of inner nearshore bars during nonstorm periods in areas of local sediment abundance the alongshore movement of the sandwaves occurs through downdrift extension which is initiated by attachment of a landward migrating nearshore bar to the downdrift end of the sandwave and subsequent infilling of the trough landward of the bar the presence and movement of the sandwaves results in a complex spatial temporal pattern of beach and dune erosion and accretion with accretion occurring opposite the sandwave and erosion focused in the embayments between sandwaves

longshore sand waves at southampton beach new york observation and numerical simulation of their movement abstract this paper describes measurements and numerical simulations of the movement of longshore sand waves observed at southampton beach long island new york these large morphologic features are created by periodic opening of a small inlet and subsequent welding of its ebb shoal to the beach longshore sand waves are wave like forms that maintain identity while moving along the shore and represent a simple type of collective sediment movement or largescale coastal behavior despite being described as early as 1939 few measurements of longshore sand waves have been made and their dynamic behavior is not well understood eleven longshore sand waves were identified along southampton beach and have an average length of 0 75 km and an amplitude of 40 m migration speed was greatest under winter wave action and reached an average 1 09 km year 1 and yearly average speed including summer calms was a much lower 0 35 km year 1 during a 16 month observation period the longshore sand waves did not disperse during their steady migration westward in the direction of predominant wave incidence and longer waves moved faster than those with smaller wavelengths a numerical model of shoreline change including both standard particulate longshore sand transport and a component describing migration of a longshore sand wave is developed in which the velocity of the wave is related to the calculated longshore discharge of water the model shows wave refraction to be an important mechanism contributing to the longevity of longshore sand waves acting to retard the otherwise expected diffusion model calculations of the migration of a single longshore sand wave agree quantitatively with the observations

a theoretical study of surface to borehole electromagnetic logging in cased holes a new electromagnetic logging method in which the source is a horizontal loop coaxial with a cased drill hole and the secondary axial fields are measured at depth within the casing has been analyzed the analysis which is for an idealized model of an infinite pipe in a conductive whole space has shown that the casing and formation are uncoupled at the low frequencies that would be used in field studies the field inside the casing may be found by first finding the field in the formation and then using this field as an incident field for the pipe alone this result permits the formation response to be recovered from the measured field in the borehole by applying a correction for the known properties of the casing if the casing response cannot be accurately predicted a separate logging tool employing a higher frequency transmitter could be used to determine the required casing parameters in the vicinity of the receiver this logging technique shows excellent sensitivity to changes in formation conduct

finite element analysis for model parameters distributed on a hierarchy of geometric simplices abstracta resurgence of interest in the problem of electrical or electromagnetic scattering from thin conductors either on a line or in a plane has been motivated in recent years by time lapse fracture monitoring in the near surface enhanced geothermal reservoirs and unconventional hydrocarbon plays however finite element modeling of small electrical features in large computational domains results in a disproportionately large number of elements concentrated in a volumetrically insignificant fraction of the mesh and it focuses computational resources away from areas of interest elsewhere such as receiver locations we have developed a novel hierarchical electrical model is proposed for unstructured tetrahedral finite element meshes in which the usual volume based conductivity on tetrahedra is augmented by facet and edge based conductivity on the infinitesimally thin regions between elements doing so allows a slender borehole casing of arbitrary shape to be coarsely approximated by set of connec

a land based controlled source electromagnetic method for oil field exploration an example from the schoonebeek oil field controlled source electromagnetic csem data are sensitive to the subsurface resistivity distribution but 3d inversion results are ambiguous and in depth interpretation is challenging resolution and sensitivity analysis as well as the influence of noise on resolution have been used to quantify 3d inversion performance based on these numerical studies a land based csem survey was designed and carried out at the schoonebeek oil field the netherlands the acquired data were processed and subsequently inverted for the resistivity distribution the 1d and 3d inversion of horizontal electric field data show the reservoir at the right depth matching well log data without using a priori knowledge about the actual reservoir depth we used a 1d model with fine layering as a starting model for 3d inversion synthetic data inversions and sensitivity tests demonstrate that resistive or conductive bodies inside the reservoir zone may be well detectable with our limited acquisition geometry spatial variations in the reservoir resistivity are visible in the measured data and after inversion by assuming good knowledge of the background resistivity distribution the reservoir resistivity and size however have to be interpreted with care considering the intrinsically low resolution of electromagnetic em which is further reduced by manmade em noise

a method of moments approach to modeling the electromagnetic response of multiple steel casings in a layered earth in oil and gas production environments controlled source electromagnetics can be used to aid brownfield exploration development and reservoir monitoring efforts however such environments typically have many highly conductive steel cased wells in the area of interest we present a modeling algorithm using a method of moments approach to calculate the electromagnetic response of multiple 3d steel cased wells of arbitrary geometry in a layered earth conductivity model this approach involves dividing each casing into a collection of segments each carrying a uniform current density a matrix is computed that describes how the casing segments interact with each other electromagnetically then we solve a linear system for the current within each casing segment given a transmitter of arbitrary frequency and location from these currents we are able to solve for the secondary electromagnetic fields produced solely by the casings at any point in our layered model and add these to the primary fields produce

modeling large scale shoreline sand waves under oblique wave incidence waves develop with wavelengths between 2 and 5 km they migrate downdrift at about 0 5 km yr and they reach amplitudes up to 120 m within 13 years larger wave obliquity higher waves and shorter wave periods strengthen the shoreline instability cross shore transport is essential for the instability and faster cross shore dynamics leads to a faster growth of the sand waves simulations with variable wave incidence angles alternating between 60 and 30 show that a large proportion of high angle waves is required for spontaneous sand wave formation at least 80 insight is provided into the physical mechanism behind high angle wave instability and the occurrence of a optimal length scale for sand wave growth the generic model results are consistent with existing observations of shoreline sand waves in particular with those along the southwest coast of africa

the marine controlled source electromagnetic response of a steel borehole casing applications for the neptune canada gas hydrate observatory gas hydrates are a potential energy resource a possible factor in climate change and an exploration geohazard the university of toronto has deployed a permanent seafloor time domain controlled source electromagnetic csem system offshore vancouver island within the framework of the neptune canada underwater cabled observatory hydrates are known to be present in the area and due to their electrically resistive nature can be monitored by 5 permanent electric field receivers however two cased boreholes may be drilled near the csem site in the near future to understand any potential distortions of the electric fields due to the metal we model the marine electromagnetic response of a conductive steel borehole casing first we consider the commonly used canonical model consisting of a 100 m 100 m thick resistive hydrocarbon layer embedded at a depth of 1000 m in a 1 m conductive host medium with the addition of a typical steel production casing extending from the seafloor to the resistive zone results show that in both the frequency and time domains the distortion produced by the casing occurs at smaller transmitter receiver offsets than the offsets required to detect the resistive layer second we consider the experimentally determined model of the offshore vancouver island hydrate zone consisting of a 5 5 m 36 m thick hydrate layer overlying a 0 7 m sedimentary half space with the addition of two borehole casings extending 300 m into the seafloor in this case results show that the distortion produced by casings located within a 100 m safety zone of the csem system will be measured at 4 of the 5 receivers we conclude that the boreholes must be positioned at least 200 m away from the csem array so as to minimize the effects of the casings

effects of well casing on potential field measurements using downhole current sources1 a mathematical formulation for the electric potential from point current sources coaxial with a metal casing has been obtained the excitation caused by the axial point sources will produce currents in the pipe by assuming that the pipe can be divided into many cylindrical ring segments with constant axially directed current the solution of the fields inside and outside the pipe can be formulated in an integral form the integral equation applied to the segmented pipe yields a set of simultaneous linear equations which are solved for the currents in the pipe these are then used to calculate the potentials anywhere outside the pipe in the medium this solution has been used to study the distribution of the potentials in a half space for a single current source at and beyond the bottom of a finite length of casing for a casing 0 1 m in radius and 0 006 m in wall thickness with a conductivity of 106 s m in a half space of 10 2 s m it was found that only in a region very near the pipe does the pipe exert substantial influence on the fields of a point source 100 casing diameters beyond the end of the pipe it appears that cross hole resistivity surveys can be implemented without corrections for the casing if the source is located at least 50 100 casing diameters beyond the end of the casing hole to surface surveys are much more affected by the pipe for a pipe source separation of 100 casing diameters the surface measurements must not be closer than a half pipe length for a 5 or less field distortion

analysis of electromagnetic induction for hydraulic fracture diagnostics in open and cased boreholes in this paper the sensitivity and detectability of an electromagnetic induction tool for hydraulic fracture detection are analyzed by calculating the electromagnetic response from an orthogonal transverse fracture otf in an open or cased borehole using the improved numerical mode matching method the otf is modeled as a slim circular disk which is axially symmetric with respect to the borehole axis and filled with a conductive or magnetic proppant the feasibility of the induction tool for fracture diagnostics was validated via scaled down experimental measurements we then quantitatively analyze the induction response sensitivity to different proppant parameters such as conductivity and permeability to evaluate the effectiveness of the induction logging tool for fracture detection the analysis reveals that the short spaced receiver can accurately locate the fracture position and distinguish small sized fractures while the long spaced receiver can differentiate fractures with large dimension casings with different thicknesses conductivities and permeabilities are modeled together with the fracture to investigate their effects in fracture detection finally the application of the induction tool to a fracture network is evaluated

sand spit dynamics in a large tidal range environment insight from multiple lidar uav and hydrodynamic measurements on multiple spit hook development breaching reconstruction and shoreline changes

hydro frac monitoring using ground time domain electromagnetics as motivation for considering new electromagnetic techniques for hydraulic fracture monitoring we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations this model shows that even a 5 improvement in stimulated reservoir volume for a 1 billion barrel bbl field results in over 1 billion u s dollars us in net present value over 24 years for us 100 bbl oil and us 0 5 billion for us 50 bbl oil the application of conductivity upscaling often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes is shown to be inaccurate for the high electrical contrasts needed to represent steel cased wells in the earth finescale finite difference modeling with 12 22 mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing we consider conductively enhanced proppant such as coke breeze coated sand and a highly saline brine solution to produce electrically conductive fractures for a relatively small frac job at a depth of 3 km involving 5 000 bbl of slurry and a source midpoint to receiver separation of 50m the models show that the conductively enhanced proppant produces a 15 increase in the electric field strength in line with the transmitter in a 10 m background in a 100 m background the response due to the proppant increases to 213 replacing the conductive proppant by brine with a concentration of 100 000 ppm nacl the field strength is increased by 23 in the 100 m background and by 2 3 in the 10 m background all but the 100 000 ppm nacl brine in a 10 m background produce calculated fracture induced electric field increases that are significantly above 2 a value that has been demonstrated to be observable in field measurements

electrical resistivity characterization of an industrial site using long electrodes an electrical resistivity survey was completed at the t tank farm at the hanford nuclear site in washington state u s a the purpose of the survey was to define the lateral extent of waste plumes in the vadose zone in and around the tank farm the t tank farm consists of single shell tanks that historically have leaked and many liquid waste disposal facilities that provide a good target for resistivity mapping given that the site is highly industrialized with near surface metallic infrastructure that potentially could mask any interpretable waste plume it was necessary to use the many wells around the site as long electrodes to accommodate the long electrodes and to simulate the effects of a linear conductor the resistivity inversion code was modified to assign low resistivity values to the well s location the forward model within the resistivity code was benchmarked for accuracy against an analytic solution and the inverse model was tested for its ability to recreate images of a hypothetical targe

dynamics of a buoyancy driven coastal jet the gaspe current a primitive equation ocean model is applied to the process study of the gaspecurrent and cyclonic circulation over the northwestern gulf of st lawrence nwg the model is driven by river discharge and barotropic boundary flows two types of model domains are used an idealized basin with a flat bottom and piecewise coastline and a realistic basin with model resolved nwg bathymetry the model domains are initially filled with horizontally uniform but vertically stratified waters the river discharge is expressed in terms of lower salinity and a weak barotropic inflow in the upper waters at the estuary head the early developments of the estuarine plume and coastal current system driven by the river discharge are qualitatively similar in both basins after a short period adjustment a buoyant plume is developed near the estuary mouth with a surface intensified coastal current advecting the estuarine water seaward in the direction of kelvin wave propagation the coastal current initially follows the coastline closely but later becomes unstable with backward breaking waves developed along the outer edge of the current the kinetic energy analysis reveals that the plume current system is baroclinically unstable with the transient motions resulting primarily from the mean available potential energy with the river discharge at the head as the only driving force the offshore front of the estuarine plume expands continuously seaward leading to a large scale anticyclonic circulation over the nwg the addition of a barotropic westward jet along the quebec shore however is able to restrain the seaward expansion of the offshore front of the plume and therefore form a large scale cyclonic motion over this region

holderness coast erosion and the significance of ords a sample ord a low section of beach characteristic of the holderness coast is examined as it moved southwards between 1977 and 1983 and its significant role in coast erosion is demonstrated the reduction in beach level at the cliff foot by up to 3 9 m enabled most hwn tides to reach it as compared with only some hws tides along the inter ord beach and the volume of till eroded from the cliffs increased by eight times to an annual mean of 72m3m 1 the holderness tills are shown to be composed of 31 per cent sand and coarser sediment which is the sediment range of the beaches where an ord is sited the massive injection of beach sediment goes to form the ord s most prominent constructional feature the lower beach ridge which extends southwards from the centre of the ord analysis of 12 months observer wave data collected at withernsea in 1969 70 indicates that a net southward sand movement of 144 000 m3 occurred comparison of this rate with beach sediment input rates along the whole coast backed by till cliffs suggests a sediment deficit at the northern end and a surplus towards the southern end this conclusion is supported by an overall increase in beach sediment volume southwards from barmston within this longshore sediment transport system the ords migrate southwards from their point of origin in the barmston skipsea area without losing their identity until reaching the tip of spurn head