estimation of changes in water column velocities and thicknesses from time lapse seismic data sea bed diffractions are frequently observed for several of the fields in the norwegian sea and the barents sea this is a challenge in time lapse seismic analysis since diffracted multiples are difficult to remove by processing and therefore is a major source of poor time lapse data quality in this work we test if the diffractions can be used for enhanced 4d interpretation by analysing the time shift of the sea bed diffraction hyperbola between the base and monitor it is tested if changes in water velocity and tides can be estimated two models using time lapse diffraction analysis are tested the first one simply adds time shifts for the two branches of the diffraction hyperbola and this average time shift is then used to estimate the water velocity change the other method uses an inversion method based on the diffraction equation for a point diffractor to estimate the velocity change in line common midpoint shifts are estimated by subtracting the time shifts of both hyperbola branches followed by direct inversion the diffraction based time shifts are compared to time shifts estimated by standard cross correlation of the sea bed reflection the averaging method gives slightly higher uncertainties while the inversion using an exact traveltime equation gives similar uncertainties compared to the sea bed reflection method

surface rupture of the 2005 kashmir pakistan earthquake and its active tectonic implications to provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications we have conducted field mapping of the surface rupture associated with the 2005 m w 7 6 kashmir earthquake despite the difficulty arising from massive earthquake induced landslides along the surface rupture we found that typical pressure ridges and warps extend northwestward for a distance of 70 km with a northeast side up vertical separation of up to 7 m neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake but three active faults or fault segments within the sub himalaya collectively called the balakot bagh fault compose the causative fault although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures only a part of it had been mapped as active before the earthquake the location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern central segment boundary and propagated bilaterally to eventually break all three segments our obtained surface rupture traces and the along strike slip distribution are both in good agreement with results of prompt analyses of satellite images indicating that space geodesy can greatly aid in time consuming field mapping of surface ruptures assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka we tentatively estimate the earthquake recurrence interval and shortening rate on the balakot bagh fault to be 1000 3300 yr and 1 4 4 1 mm yr respectively these estimates indicate that the balakot bagh fault is not a main player of himalayan contraction accommodation graphic 1 selected field photographs and arcgis files of the mapped surface rupture traces and measured vertical separations are available in the electronic supplement to this article 1 embed inline graphic 1 gif

water velocity estimation using inversion methods it is known that the propagation velocity of sound waves in water can vary over time for a 3d seismic survey if data are acquired in adjacent lines but at different dates this implies the same reflection point will be recorded at different times to take this effect into account in seismic processing it is necessary to measure the sound velocity in water i have developed a 3d tomographic method that directly estimates it it assumes a constant sound velocity for a group of shots belonging to a single sail line using a picked water bottom reflection and an initial depth and velocity model results good for use in subsequent processing can be obtained by estimating only two parameters the variation of the propagation velocity and a constant vertical shift of the reflector depth in relation to the initial model the method was tested with both synthetic and real data the real data results were validated using two methods first i analyzed the histogram of the residuals of the final updated model second i used a specially modified kirchhoff migration algorithm to migrate the sea bottom the main advantages of this method are that it takes into account the sea bottom dips to estimate the velocities and it can be applied to each sail line separately also the inversion is not ill conditioned provided that data with large enough offsets are used as a result the method is simple to apply

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

a methodology for 7d warping and deformation monitoring using time lapse seismic data a methodology is presented for vector analysis of the image displacements warping between successive 3d seismic image volumes that provides 7d analysis including lateral and vertical displacements of in situ subsurface deformation around hydrocarbon reservoirs the key challenges are 1 assessment of just vertical shifts is insufficient and vector displacements should be determined 2 robust vertical displacements can usually be derived but lateral shifts are less well defined because of the generally smooth data character in a horizontal horizon plane 3 subvoxel resolution is necessary for correct matching and deformation analysis 4 velocity and strain effects are intrinsically combined in time lapse seismic images 5 separation of accumulated and local effects is necessary 6 apparently coherent and smooth displacement fields do not necessarily provide good strain analysis 7 warping is easily degraded by noise and good cross matching is a prerequisite to address these challenges a full 3d local warp vector derivation methodology is proposed which involves 1 constraint using prior estimates 2 local refinement with subvoxel resolution and 3 3d and vectorial conditioning using a deformable mesh with sensitivity to image match quality the warping approach is extended to separate accumulated from local effects and to analyze in situ deformation based on the displacement vector volume this is achieved by a finite element approach to determine an elemental pseudostrain tensor field and an iterative procedure to separate the pseudostrain into velocity and strain components the approach up to the strain analysis is demonstrated using a real data example which indicates the potential of the methodology accumulated overburden effects are separated to reveal a local compaction signature in the reservoir but realistic quantitative values of strain have not yet been realized

time lapse seismic monitoring some shortcomings in nonuniform processing conceptually repeat or time lapse seismic monitoring is straightforward seismic data sets acquired at different times are calibrated compared and the intersurvey differences analyzed and interpreted in terms of fluid changes or movement

integration of seismic methods with reservoir simulation pikes peak heavy oil field saskatchewan reservoir characterization is essential for providing optimal recovery from heavy oil fields the process of reservoir characterization is demonstrated for a steam injection project at pikes peak heavy oil field near lloydminster saskatchewan canada geologic geophysical and reservoir engineering data are used to improve the interpretation of reservoir conditions there is ambiguity in modeling any of these data however in modeling all data sets in cooperative inversion ambiguity is decreased thereby enhancing our knowledge of the reservoir one of the main benefits of this oil field modeling is that bypassed oil and steam fronts are effectively mapped

4 d constrained depth conversion for reservoir compaction estimation application to ekofisk field ekofisk field in the norweigian sector of the north sea is a remarkable example of a strongly compacted chalk reservoir since the start of production in 1971 the water bottom has subsided by over 8 m as a result of reservoir compaction hermansen et al the field wide waterflood begun in 1989 was expected to halt pressure depletion and reservoir compaction after a few years of waterflooding ekofisk reservoir pressure began increasing but compaction and subsidence continued laboratory studies on chalk cores indicated that high porosity oil filled chalk compacts strongly when flushed with seawater these studies along with reservoir flow simulation and geomechanic modeling led to a model of a water weakening compaction sylte et al ongoing efforts deployed to monitor the reservoir compaction and seabed subsidence include twice a year compaction logging in a monitoring well daily gps measurements at the platforms and periodic bathymetry surveys nine surveys from 1970 to 1999

long term seismic behavior of a fault involved in a multiple fault rupture insights from tectonic geomorphology along the neodani fault central japan abstract multiple faults with different paleoseismic histories sometimes rupture simultaneously resulting in a larger earthquake than expected to test behavioral models for a fault involved in a multiple fault rupture we performed detailed tectonic geomorphological mapping along the neodani fault central japan one of several faults that ruptured simultaneously during the devastating 1891 m w 7 5 nobi earthquake our mapping showed that the along strike distributions of the long term rates of left lateral and vertical slips generally mimic in shape those of the 1891 slip implying that the slip patch behavior in which smaller more frequent earthquake ruptures fill in low slip portions of the 1891 rupture does not apply to the neodani fault if the earthquake recurrence interval estimated from a previous paleoseismic trench is correct however the neodani fault should not be characterized by repetition of same slip function earthquake ruptures or the characteristic slip function behavior the observations can instead be explained by the semicharacteristic slip function behavior in which a similarly shaped slip distribution is repeated independently of the rupture of adjacent faults but the amount of slip varies nonetheless characteristic slip function behavior may still be a valid interpretation if some of the paleoseismic events identified in the trench are minor sympathetic slip events although we found that the shape of the slip distribution has been quite stable through successive earthquakes including a multiple fault rupture earthquake further paleoseismic efforts are warranted to examine the stability in the amount of slip

application of time lapse ert imaging to watershed characterization time lapse electrical resistivity tomography ert has many practical applications to the study of subsurface properties and processes when inverting time lapse ert data it is useful to proceed beyond straightforward inversion of data differences andtakeadvantageofthetime lapsenatureofthedata weassess various approaches for inverting and interpreting time lapse ertdataanddeterminethattwoapproachesworkwell thefirst approachismodelsubtractionafterseparateinversionofthedata from two time periods and the second approach is to use the inverted model from a base data set as the reference model or prior information for subsequent time periods we prefer this second approach data inversion methodology should be considered when designing data acquisition i e to utilize the second approach it is important to collect one or more data sets for which the bulk of the subsurface is in a background or relatively unperturbed state athird and commonly used approach to time lapse inversion invertingthedifferencebetweentwodatasets localizes the regions of the model in which change has occurred however varying noise levels between the two data sets can be problematic to further assess the various time lapse inversion approaches weacquiredfielddatafromacatchmentwithinthedry creek experimental watershed near boise idaho u s a we combined the complimentary information from individual static ertinversions time lapseertimages andavailablehydrologicdatainarobustinterpretationschemetoaidinquantifyingseasonalvariationsinsubsurfacemoisturecontent

illumination based normalization for wave equation depth migration illumination problems caused by finite recording aperture and lateral velocity lensing can bias amplitudes in migration results in this paper i develop a normalization scheme appropriate for wave equation migration algorithms that compensates for irregular illumination i generate synthetic seismic data over a reference reflectivity model using the adjoint of wave equation shot profile migration as the forward modeling operator i then migrate the synthetic data with the same shot profile algorithm the ratio between the synthetic migration result and the initial reference model is a measure of seismic illumination dividing the true data migration result by this illumination function mitigates the illumination problems the methodology can take into account reflector dip as well as both shot and receiver geometries and because it is based on wave equation migration it naturally models the finite frequency effects of wave propagation the reference model should be as close to the true model as possi

mapping the fluid front and pressure buildup using 4d data on norne field norne field in the southern part of the nordland ii area in the norwegian sea approximately 100 km north of aasgard field is producing from an fpso the main field is a horst block approximately 9 3 km figure 1 the reservoir rocks are sandstones of lower and middle jurassic age the hydrocarbon reserves consist of a gas cap 75 m mainly situated in garn formation and an oil leg 110 m mainly situated in ile and tofte formations the sandstones are very good quality with porosities and permeabilities of 25 32 and 200 2000 md respectively net to gross is close to 1 for most reservoir zones oil production started in 1997 the first 4d seismic survey was acquired in 2001 and 4d information has been actively used in subsequent reservoir management

time lapse ert monitoring of an injection withdrawal experiment in a shallow unconfined aquifer toquantifyperformanceof3dtime lapseelectricalresistivity tomography ert a sequential injection withdrawal experiment was designed for monitoring the pump and capture remediation of a conductive solute in an unconfined alluvial aquifer prior information is incorporated into the inversion procedure via regularization with respect to a reference model according to threeprotocols 1independentregularizationinvolvingasingle reference model 2 background regularization involving a referencemodelobtainedviainversionofpreinjectiondata and3 time lapseregularizationinvolvinganevolvingreferencemodel obtained via inversion of data from previous experimental stages emplacementandsequentialwithdrawalofthesoluteisclearly imaged for all protocols time lapse regularization results in greater amounts of model structure while providing significantcomputationalsavings ert estimatedelectricalconductivity is used to predict solute concentration and solute mass in the aquifer at any experimental stage we are able to estimate total solute mass in the aquifer with a maximum accuracy of 60 85 depending on regularization protocol and survey geometry wealsoestimatethewithdrawnsolutemassforeveryexperimentalstagethechangeinmassbetweenexperimentalstages withdrawn mass estimates are more reliable than total mass estimates and do not exhibit systematic underprediction or dependence on regularization protocol withdrawn mass estimates areaccurateforchangesinmassbelow2 4 kgofpotassiumbromide kbr for horizontal and vertical dipole dipole surveys respectively estimating the withdrawn solute mass does not require background subtraction and thus does not require backgrounddata

cross equalization data processing for time lapse seismic reservoir monitoring a case study from the gulf of mexico nonrepeatable noise caused by differences in vintages of seismic acquisition and processing can often make comparison and interpretation of time lapse 3 d seismic data sets for reservoir monitoring misleading or futile in this gulf of mexico case study the major causes of nonrepeatable noise in the data sets are the result of differences in survey acquisition geometry and binning temporal and spatial amplitude gain wavelet bandwidth and phase differential static time shifts and relative mispositioning of imaged reflection events we attenuate these acquisition and processing differences by developing and applying a cross equalization data processing flow for time lapse seismic data the cross equalization flow consists of regridding the two data sets to a common grid applying a space and time variant amplitude envelope balance applying a first pass of matched filter corrections for global amplitude bandwidth phase and static shift corrections followed by a dynamic warp to align mispositioned events and finally running a second pass of constrained space variant matched filter operators difference sections obtained by subtracting the two data sets after each step of the cross equalization processing flow show a progressive reduction of nonrepeatable noise and a simultaneous improvement in time lapse reservoir signal

repeatability issues of 3 d vsp data increased repeatability is recognized as one major issue for improving the time lapse seismic technology as a reservoir management tool a 3 d vertical seismic profiling vsp data set acquired over a period of two days is used to analyze how repeatable a permanent installed geophone array can be and how repeatability changes with inaccuracies in source positioning it is found that for a frequency range between 3 5 and 50 hz the difference root mean square rms level between two recorded traces belonging to two different shots is about 8 this fact shows that there is a potential for acquiring very accurate time lapse seismic data by using a permanently installed downhole geophone array repeatability variation with increasing shot separation distances is analyzed showing a rapid decrease in repeatability as the accuracy of the positioning of the repeat survey decreases horizontal geophone components show approximately the same degree of repeatability compared to the vertical component but horizontal geophone data is slightly more sensitive to positioning errors the results show that repeated 3 d vsp surveys preferably using permanently installed geophone arrays might be an efficient tool for detailed and precise monitoring of fluid and pressure changes within a hydrocarbon reservoir

fault slip and earthquake recurrence along strike slip faults contributions of high resolution geomorphic data article i nfo understanding earthquake eq recurrence relies on information about the timing and size of past eq ruptures along a given fault knowledge of a fault s rupture history provides valuable information on its potential future behavior enabling seismic hazard estimates and loss mitigation stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing eqs analysis of the latter data sets culminated during the mid 1980s in the formulation of now classical eq recurrence models now routinely used to assess seismic hazard within the last decade light detection and ranging lidar surveying technology and other high resolution data sets became increasingly available to tectono geomorphic studies promising to contribute to better informed models of eq recurrence and slip accumulation patterns after reviewing motivation and background we outline requirements to successfully reconstruct a fault s offset accumulation pattern from geomorphic evidence we address sources of uncertainty affecting offset measure ment and advocate approaches to minimize them a number of recent studies focus on single eq slip distribu tions and along fault slip accumulation patterns we put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation cv for eq inter event time and slip per event and find that a single event offsets vary over a wide range of length scales and the sources for offset variability differ with length scale b at fault segment length scales single event offsets are essentially constant c along fault offset accumulation as resolved in the geomorphic record is dominated by essentially same size large offset in crements and d there is generally no one to one correlation between the offset accumulation pattern constrained in the geomorphic record and eq occurrence as identified in the stratigraphic record revealing the higher resolution and preservation potential of the latter while slip accumulation along a fault segment may be dominated by repetition of large nearly constant offset increments timing of surface rupture is less regular

discovery controls and hazards of widespread deep seated gravitational slope deformation in the etsumi mountains central japan deep seated gravitational slope deformation dsgsd is a largely unnoticed but important long term mass wasting process that may result in catastrophic failure of mountain slopes manifested by small topographic irregularities such as ridge parallel scarps and linear depressions it has been predominantly reported in alpine landscapes above timber lines on the basis of area wide high resolution topographic data acquired by light detection and ranging lidar surveys we here show that 96 of existing gravitational scarps have been hidden under forest canopies in the etsumi mountains central japan the scarps are surprisingly widespread over the mountains with a mean line density of as large as 0 87 km km2 our analyses of the scarp distribution suggest that uphill facing scarps are primary geomorphic signals of dsgsd with a destabilized rock mass larger than 105 m2 whereas downhill facing scarps principally occur in response to more localized slope deformation in terms of controls topography is by far the most influential factor in triggering and promoting dsgsd despite the m 7 5 earthquake in 1891 impact of large local earthquakes proves to be not very strong comparison with preexisting landslide maps further suggests that dsgsd and large scale landslide are not different slope processes but represent different stages of the same process our results highlight limitation of aerial photograph interpretation in forest covered mountains and the need for lidar assisted mapping for deeper understanding of this long term process and interactions between surface and tectonic processes

developing sub 5 m lidar dems for forested sections of the alpine and hope faults south island new zealand implications for structural interpretations abstract kilometre wide airborne light detection and ranging lidar surveys were collected along portions of the alpine and hope faults in new zealand to assess the potential for generating sub 5 m bare earth digital elevation models dems from ground return data in areas of dense rainforest bush cover as an aid to mapping these faults the 34 km long franz whataroa lidar survey was flown along the densely vegetated central most portion of the transpressive alpine fault six closely spaced flight lines 200 m apart yielded survey coverage with double overlap of swath collection which was considered necessary due to the low density of ground returns 0 16 m 2 or a point every 6 m2 under mature west coast podocarp broadleaf rainforest this average point spacing 2 5 m allowed for the generation of a robust high quality 3 m bare earth dem the dem confirmed the zigzagged form of the surface trace of the alpine fault in this area originally recognised by norris and cooper 1995 norris and cooper 1997 and highlights that the surface strike variations are more variant than previously mapped the 29 km long hurunui hope lidar survey was flown east of the main divide of the southern alps along the dextral slip hope fault where the terrain is characterised by lower rainfall and more open beech forest flight line spacings of 275 m were used to generate a dem from the ground return data the average ground return values under beech forest were 0 27 m 2 and yielded an estimated cell size suitable for a 2 m dem in both cases the lidar revealed unprecedented views of the surface geomorphology of these active faults lessons learned from our survey methodologies can be employed to plan cost effective high gain airborne surveys to yield bare earth dems underneath vegetated terrain and multi storeyed canopies from densely forested environments across new zealand and worldwide

satellite imaging of the 2015 m7 2 earthquake in the central pamir tajikistan elucidates a sequence of shallow strike slip ruptures of the sarez karakul fault

hydraulic fracturing in a sedimentary geothermal reservoir results and implications field experiments in a geothermal research well were conducted to enhance the inflow performance of a clastic sedimentary reservoir section due to depths exceeding 4050 m bottom hole temperatures exceeding 140 c and open hole section dual zone technically demanding and somewhat unprecedented conditions had to be managed the fracturing operations were successful fractures were created in two isolated borehole intervals and the inflow behaviour of the reservoir was decisively enhanced the effective pressures applied for fracture initiation and propagation were only slightly above in situ pore pressures nevertheless the stimulation ratio predicted by fracture performance modelling could not be achieved multiple reasons could be identified that account for the mismatch an insufficient fracture tie back as well as chemical and mechanical processes during closure led to reduced fracture conductivities and therefore diminished productivity the insights gained are the basis for further fracture design concepts at the given and geologic comparable sites

rough seas and time lapse seismic time lapse seismic surveying has become an accepted tool for reservoir monitoring applications thus placing a high premium on data repeatability one factor affecting data repeatability is the influence of the rough sea surface on the ghost reflection and the resulting seismic wavelets of the sources and receivers during data analysis the sea surface is normally assumed to be stationary and indeed to be flat the non flatness of the sea surface introduces amplitude and phase perturbations to the source and receiver responses and these can affect the time lapse image we simulated the influence of rough sea surfaces on seismic data acquisition for a typical seismic line with a 48 fold stack a 2 m significant wave height sea introduces rms errors of about 5 10 into the stacked data this level of error is probably not important for structural imaging but could be significant for time lapse surveying when the expected difference anomaly is small the errors are distributed differently for sources and receivers because of the different ways they are towed furthermore the source wavelet is determined by the sea shape at the moment the shot is fired whereas the receiver wavelet is time varying because the sea moves significantly during the seismic record

a decade of tomography over the past 10 years ray based postmigration grid tomography has become the standard model building tool for seismic depth imaging while the basics of the method have remained unchanged since the late 1990s the problems it solves have changed dramatically this evolution has been driven by exploration demands and enabled by computer power there are three main areas of change first standard model resolution has increased from a few thousand meters to a few hundred meters this order of magnitude improvement may be attributed to both high quality complex residual moveout data picked as densely as 25 m to 50 m vertically and horizontally and to a strategy of working down from long wavelength to short wavelength solutions second more and more seismic data sets are being acquired along multiple azimuths for improved illumination and multiple suppression high resolution velocity tomography must solve for all azimuths simultaneously to prevent short wavelength velocity heterogeneity from being mistaken for azimuthal anisotropy third there has been a shift from predominantly isotropic to predominantly anisotropic models both vti and tti with four component data anisotropic grid tomography can be used to build models that tie pz and ps images in depth

stereopaired morphometric protection index red relief image maps stereo mpi rrims effective visualization of high resolution digital elevation models for interpreting and mapping small tectonic geomorphic features

target oriented joint least squares migration inversion of time lapse seismic data sets two related formulations are proposed for target oriented joint least squares migration inversion of time lapse seismic data sets time lapse seismic images can be degraded when reservoir overburden is complex or when acquisition geometries significantly differ because the migration operator does not compensate for the resulting amplitude and phase distortions under these circumstances time lapse amplitudes are poor indicators of production related changes in reservoir properties to correct for such image degradation time lapse imaging is posed as joint inverse problems that utilize concatenations of target oriented approximations to the linear least squares imaging hessian in both formulations spatial and temporal constraints ensure inversion stability and geologically consistent time lapse images using two numerical time lapse data sets we confirmed that these formulations can attenuate illumination artifacts caused by complex overburden or geometry differences and that they yield better quality images than obtainable with migration

slip in the 1857 and earlier large earthquakes along the carrizo plain san andreas fault the moment magnitude mw 7 9 fort tejon earthquake of 1857 with a 350 kilometer long surface rupture was the most recent major earthquake along the south central san andreas fault california based on previous measurements of its surface slip distribution rupture along the 60 kilometer long carrizo segment was thought to control the recurrence of 1857 like earthquakes new high resolution topographic data show that the average slip along the carrizo segment during the 1857 event was 5 3 1 4 meters eliminating the core assumption for a linkage between carrizo segment rupture and recurrence of major earthquakes along the south central san andreas fault earthquake slip along the carrizo segment may recur in earthquake clusters with cumulative slip of 5 meters

overburden complexity and repeatability of seismic data impacts of positioning errors at the oseberg field north sea repeatability of seismic data plays a crucial role in time lapse seismic analysis there are several factors that can decrease the repeatability such as positioning errors varying tide source variations velocity changes in the water layer marine data and undesired effects of various processing steps in this work the complexity of overburden structure as an inherent parameter that can affect the repeatability is studied a multi azimuth three dimensional vertical seismic profiling data set with 10 000 shots is used to study the relationship between overburden structure and repeatability of seismic data in most repeatability studies two data sets are compared but here a single data set has been used because a significant proportion of the 10 000 shots are so close to each other that a repeatability versus positioning error is possible we find that the repeatability decreases by a factor of approximately 2 under an overburden lens furthermore we find that the x and y components have approximately the same sensitivity to positioning errors as the z component for the same events in this three dimensional vertical seismic profiling experiment this indicates that in an area with complex overburden positioning errors between monitor and base seismic surveys are significantly more critical than outside such an area this study is based on a three dimensional three component vertical seismic profiling data set from a north sea reservoir and care should be taken when extrapolating these observations into a general four dimensional framework

numerical simulation of the environmental impact of hydraulic fracturing of tight shale gas reservoirs on near surface groundwater background base cases shallow reservoirs short term gas and water transport hydrocarbon production from unconventional resources and the use of reservoir stimulation techniques such as hydraulic fracturing has grown explosively over the last decade however concerns have arisen that reservoir stimulation creates significant environmental threats through the creation of permeable pathways connecting the stimulated reservoir with shallower freshwater aquifers thus resulting in the contamination of potable groundwater by escaping hydrocarbons or other reservoir fluids this study investigates by numerical simulation gas and water transport between a shallow tight gas reservoir and a shallower overlying freshwater aquifer following hydraulic fracturing operations if such a connecting pathway has been created we focus on two general failure scenarios 1 communication between the reservoir and aquifer via a connecting fracture or fault and 2 communication via a deteriorated preexisting nearby well we conclude that the key factors driving short term transport of gas include high permeability for the connecting pathway and the overall volume of the connecting feature production from the reservoir is likely to mitigate release through reduction of available free gas and lowering of reservoir pressure and not producing may increase the potential for release we also find that hydrostatic tight gas reservoirs are unlikely to act as a continuing source of migrating gas as gas contained within the newly formed hydraulic fracture is the primary source for potential contamination such incidents of gas escape are likely to be limited in duration and scope for hydrostatic reservoirs reliable field and laboratory data must be acquired to constrain the factors and determine the likelihood of these outcomes

pitfalls in three dimensional seismic interpretation footprints of an irregular source receiver layout abstract this paper shows how nonuniform source receiver spacing in a three dimensional 3 d land acquisition creates footprints that could easily be mistaken for geology in a 3 d time migrated seismic volume from the midcontinent united states amplitude extraction along the top of the mississippian limestone formation shows a sinkhole like feature which is justified from a depositional perspective however an inspection of the acquisition layout shows that the sinkhole is a replica of the fold distribution in land surveys where source and receivers seldom have a regular distribution and for unconventional plays that are not developed through patterned drilling a thorough review of processing and acquisition parameters is necessary before interpreting amplitude maps

a case history of time lapse 3d seismic surveys at cold lake alberta canada time lapse 3d seismic surveys were acquired across a bitumen field at cold lake alberta canada during a production cycle 1990 and a steam injection cycle 1992 of a thermal enhanced oil recovery eor program we observed changes in interval traveltime and amplitude distributions between the processed surveys we interpret the increased traveltimes observed over most of the injection survey to be a result of lowered interval velocities in the reservoir caused primarily by higher temperature and lower effective pressure reflection strength variations within the reservoir are present in each data set and change spatially between the surveys in general we interpret the amplitude anomalies seen only on the production survey to be caused by local free gas and the amplitude anomalies seen only on the injection survey which are close to the perforation depths to be caused by thin vertically restricted steamed zones

quantitative estimation of compaction and velocity changes using 4d impedance and traveltime changes in some hydrocarbon reservoirs severe compaction of the reservoir rocks is observed this compaction is caused by production and it is often associated with changes in the overburden time lapse or 4d seismic data are used to monitor this compaction process since the compaction causes changes in both layer thickness and seismic velocities it is crucial to distinguish between the two effects two new seismic methods for monitoring compacting reservoirs are introduced one based on measured seismic prestack traveltime changes and the other based on poststack traveltime and amplitude changes in contrast to earlier methods these methods do not require additional empirical relationships such as for instance a velocity porosity relationship the uncertainties in estimates for compaction and velocity change are expressed in terms of errors in the traveltime and amplitude measurements these errors are directly related to the quality and repeatability of time lapse seismic data for a reservoir at 3000 m depth wit h9mo fcompaction and assuming a 4d timeshift error of 0 5 ms at near offset and 2 ms at far offset we find relative uncertainty in the compaction estimate of approximately 50 60 using traveltime information only

sea bed diffractions and their impact on 4d seismic data a sea bed reflection is used to estimate changes in water layer velocities between timelapse seismic surveys such corrections are crucial in order to obtain high quality 4d seismic data this might be a challenge in areas where rough sea bed topography creates sea bed diffractions that interfere with the sea bed reflection as in several of the northern fields in the norwegian sea these diffractions and diffracted multiples are difficult to attenuate during data processing and become a source of noise in time lapse data in this work we study how cross correlation analysis of time lapse seismic data at a sea bed reflection may be perturbed by the presence of diffractions the seabed topography from the norne field is used in 2d finite difference modelling to explain some of the observed variation in a water layer time shift in field data we find that a rough sea bed and the diffracted energy it induces cause residual noise on the 4d data the variation to the water layer time shift increases with sea bed complexity and is amplified by interaction with other sources of non repeatability like water column variations mis positioning and strength of the ice scours creating the diffracted energy time shift variations with mis positioning and velocity changes between the surveys seem to best explain the observed variation in the time shift for time lapse seismic field data from norne

seismic time lapse imaging using interferometric least squares migration case study seismic time lapse surveys are susceptible to repeatability errors due to varying environmental conditions to mitigate this problem we propose the use of interferometric least squares migration to estimate the migration images for the baseline and monitor surveys here a known reflector is used as the reference reflector for interferometric least squares migration and the data are approximately redatumed to this reference reflector before imaging this virtual redatuming mitigates the repeatability errors in the time lapse migration image results with synthetic and field data show that interferometric least squares migration can sometimes reduce or eliminate artifacts caused by non repeatability in time lapse surveys and provide a high resolution estimate of the time lapse change in the reservoir

a proven method for acquiring highly repeatable towed streamer seismic data seismic reservoir monitoring has become an important tool in the management of many fields monitoring subtle changes in the seismic properties of a reservoir caused by production places strong demands on seismic repeatability a lack of repeatability limits how frequently reservoir changes can be monitored or the applicability of seismic monitoring at all in this paper we show that towing many streamers with narrow separation combined with cross line interpolation of data onto predefined sail lines can give highly repeatable marine seismic data results from two controlled zero time lag monitoring experiments in the north sea demonstrate high sensitivity to changing water level and variations in lateral positions after corrections by deterministic tidal time shifts and spatial interpolation of the irregularly sampled streamer data relative rms difference amplitude levels are as low as 12 for a deep structurally complex field and as low as 6 for a shallow structurally simple field reducing the deg

airborne lidar analysis and geochronology of faulted glacial moraines in the tahoe sierra frontal fault zone reveal substantial seismic hazards in the lake tahoe region california nevada usa we integrated high resolution bare earth airborne light detection and ranging lidar imagery with field observations and modern geochronology to characterize the tahoe sierra frontal fault zone which forms the neotectonic boundary between the sierra nevada and the basin and range province west of lake tahoe the lidar imagery clearly delineates active normal faults that have displaced late pleistocene glacial moraines and holocene alluvium along 30 km of linear right stepping range front of the tahoe sierra frontal fault zone herein we illustrate and describe the tectonic geomorphology of faulted lateral moraines we have developed new three dimensional modeling techniques that utilize the high resolution lidar data to determine tectonic displacements of moraine crests and alluvium the statistically robust displacement models combined with new ages of the displaced tioga 20 8 1 4 ka and tahoe 69 2 4 8 ka 73 2 8 7 ka moraines are used to estimate the minimum vertical separation rate at 17 sites along the tahoe sierra frontal fault zone near the northern end of the study area the minimum vertical separation rate is 1 5 0 4 mm yr which represents a two to threefold increase in estimates of seismic moment for the lake tahoe basin from this study we conclude that potential earthquake moment magnitudes m w range from 6 3 0 25 to 6 9 0 25 a close spatial association of landslides and active faults suggests that landslides have been seismically triggered our study underscores that the tahoe sierra frontal fault zone poses substantial seismic and landslide hazards

discrimination between phase and amplitude attributes in time lapse seismic streamer data time lapse seismic experiments aim to obtain information about production related effects in hydrocarbon reservoirs to increase the recovery percentage however nonrepeatability problems such as acquisition differences overburden effects and noise are often significantly stronger than the imprint of production changes in time lapse seismic data sets consequently it is very difficult to appraise the changes in petrophysical reservoir parameters over time we introduce a 4d monitoring approach based on the spectral ratio method this method produces two time lapse attributes the relative change in reflection coefficient and the traveltime shift at reflecting interfaces these attributes can be used for appraising production related changes in the subsurface the approach corrects for time invariant nonrepeatability effects in the overburden and source receiver coupling problems in time lapse surveys the validity of the method is limited to structurally simple overburden and reservoirs with weak lateral variations first we validate the methodology using a synthetic time lapse seismic experiment next we apply the method to a real time lapse data set from the troll west gas province in the north sea in the real example we could not detect movement in the fluid contact of 5 15 m the expected change in amplitude is less than 10 which is probably below the background noise level for this data set

lidar and field observations of slip distribution for the most recent surface ruptures along the central san jacinto fault we measured offsets on tectonically displaced geomorphic features along 80 km of the clark strand of the san jacinto fault sjf to estimate slip per event for the past several surface ruptures we identify 168 offset features from which we make over 490 measurements using b4 light detection and ranging lidar imagery and field observations our results suggest that lidar technology is an exemplary supplement to traditional field methods in slip per event studies displacement estimates indicate that the most recent surface rupturing event mre produced an average of 2 5 2 9 m of right lateral slip with maximum slip of nearly 4 m at anza a m w 7 2 7 5 earthquake average multiple event offsets for the same 80 kms are 5 5 m with maximum values of 3 m at anza for the penultimate event cumulative displacements of 9 10 m through anza suggest the third event was also similar in size paleoseismic work at hog lake dates the most recent surface rupture event at ca 1790 a poorly located large earthquake occurred in southern california on 22 november 1800 we relocate this event to the clark fault based on the mre at hog lake we also recognize the occurrence of a younger rupture along 15 20 km of the fault in blackburn canyon with 1 25 m of average displacement we attribute these offsets to the 21 april 1918 m w 6 9 event these data argue that much or all of the clark fault and possibly also the casa loma fault fail together in large earthquakes but that shorter sections may fail in smaller events online material topographic contour maps and hillshades generated from b4 lidar data corresponding field photographs and data tables comparing lidar based and field based slip measurements for individual geomorphic features along the clark fault

the impact of water velocity variations on deepwater seismic data during marine seismic acquisition obtaining complete subsurface coverage may require combining data from different acquisition dates the time gaps between the overlapping coverage may vary from hours separating subsequent boat passes to months when large surveys are acquired in sections time lapse data are an extreme example of overlapping data sets acquired at widely varying acquisition dates unfortunately between the different times of acquisition changes in physical ocean properties such as temperature or salinity can cause variations in water velocity the result is a dynamic change in recorded traveltimes that makes accurate combination of the data difficult in shallow water the distortions are small and do not affect data quality however in deepwater the cumulative distortions can pose a serious impediment to accurate imaging the existence of water velocity variations has been documented previously barley 1999 water temperature changes are the primary cause of velocity variations figure 1 shows an area just south of nova scotia coastline in red the outlined seismic survey area is approximately 3600 km2 the satellite images show surface temperature variations with each color contour representing 1 c in the approximately two week period shown surface temperatures varied as much as 10 figure 1 surface temperature variations offshore nova scotia each color contour is 1 c the survey area is outlined in the approximately two week period shown up to 10 of temperature variation can be seen the temperature structures evident in figure 1 are caused by eddies in the gulf stream and are indicative of deepwater temperature variations significantly each degree of change causes over 3 m s of water velocity variation the effect of such changes on seismic data collected in deepwater can be significant figure 2 shows two midpoint gathers after moveout correction the gathers are from the nova scotia survey outlined in figure 1 the shallowest event is the

synchronized gravitational slope deformation and active faulting a case study on and around the neodani fault central japan abstract earthquakes are considered to be important triggers of deep seated gravitational slope deformation dgsd in seismically active regions and if that is the case dgsd features could be candidates for off fault paleoseismology investigations on the basis of pit excavations and sediment cores at an off fault dgsd site and a trench excavation across the active neodani fault at a nearby site we examined the records of dgsd and surface rupturing paleoearthquakes of the neodani fault the four most recent dgsd events were dated at after 240 cal bp 1710 340 cal bp 4730 3970 cal bp and 5570 5340 cal bp the four most recent surface rupturing earthquakes were dated at 1891 ce the nobi earthquake 2010 1220 cal bp 7180 2110 cal bp and before 9540 cal bp we conclude that the ages of the four dgsd events are consistent with surface rupturing earthquakes on the adjacent neodani fault we infer that static crustal strain from repeated seismogenic faulting plays an important role in the occurrence of dgsd events at least in the immediate vicinity of active faults although coseismic severe shaking would have at least some effect on them our case study suggests that off fault dgsds can be used to reconstruct or refine the paleoseismic history of a nearby active fault we propose that an ideal dgsd for that purpose would be located in an area of concentrated strain near a termination bend or stepover of the target fault

numerical assessment of potential impacts of hydraulically fractured bowland shale on overlying aquifers natural gas extracted from hydraulically fractured shale formations potentially has a big impact on the global energy landscape however there are concerns of potential environmental impacts of hydraulic fracturing of the shale formations particularly those related to water quality to evaluate the potential impact of hydraulically fractured shale on overlying aquifers we conduct realizations of numerical modeling simulations to assess fluid flow and chloride transport from a synthetic bowland shale over a period of 11 000 years the synthetic fractured shale was represented by a three dimensional discrete fracture model that was developed by using the data from a bowland shale gas exploration in lancashire uk chloride mass exchange between fractures and the rock matrix was fully accounted for in the model the assessment was carried out to investigate fluid and chloride mass fluxes before during and after hydraulic fracturing of the bowland shale impacts of the upward fracture height and aperture as well as hydraulic conductivity of the multilayered bedrock system are also included this assessment this modeling revealed that the hydraulically fractured bowland shale is unlikely to pose a risk to its overlying groundwater quality when the induced fracture aperture is 200 m with the fracture aperture 1000 m the upward chloride flux becomes very sensitive to the upward fracture height growth and hydraulic conductivity of the multilayered bedrock system in the extremely unlikely event of the upward fracture growth directly connecting the shale formation to the overlying sherwood sandstone aquifer with the fracture aperture 1000 m the upward chloride mass flux could potentially pose risks to the overlying aquifer in 100 years the model study also revealed that the upward mass flux is significantly intercepted by the horizontal mass flux within a high permeable layer between the bowland shale and its overlying aquifers reducing further upward flux toward the overlying aquifers

sensitivity analysis and application of time lapse full waveform inversion synthetic testing and field data example from the north sea norway time lapse refraction can provide complementary seismic solutions for monitoring subtle subsurface changes that are challenging for conventional p wave reflection methods the utilization of refraction time lapse has lagged behind in the past partly due to the lack of robust techniques that allow extracting easy to interpret reservoir information however with the recent emergence of the full waveform inversion technique as a more standard tool we find it to be a promising platform for incorporating head waves and diving waves into the time lapse framework here we investigate the sensitivity of 2d acoustic time domain full waveform inversion for monitoring a shallow weak velocity change 30 m s or 1 6 the sensitivity tests are designed to address questions related to the feasibility and accuracy of full waveform inversion results for monitoring the field case of an underground gas blowout that occurred in the north sea the blowout caused the gas to migrate both vertically and horizontally into several shallow sand layers some of the shallow gas anomalies were not clearly detected by conventional 4d reflection methods i e time shifts and amplitude difference due to low 4d signal to noise ratio and weak velocity change on the other hand full waveform inversion sensitivity analysis showed that it is possible to detect the weak velocity change with the non optimal seismic input detectability was qualitative with variable degrees of accuracy depending on different inversion parameters we inverted the real 2d seismic data from the north sea with a greater emphasis on refracted and diving waves energy i e most of the reflected energy was removed for the shallow zone of interest after removing traces with offset less than 300 m the full waveform inversion results provided more superior detectability compared with the conventional 4d stacked reflection difference method for a weak shallow gas anomaly 320 m deep

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration

detection of subtle tectonic geomorphic features in densely forested mountains by very high resolution airborne lidar survey abstract despite successes elsewhere in the world 2 m resolution dems from a standard airborne lidar survey failed to detect small tectonic geomorphic features in densely forested high relief mountains of central japan our new 0 5 m dems from an unprecedentedly high resolution lidar survey along the neodani fault now reveal a number of previously unknown fault scarps as well as other hidden geomorphic features the survey achieves a ground return density of 6 2 m 2 out of a total shot density of as much as 12 7 m 2 the main factor to gain sufficient ground returns in unfavorable conditions is a large side lap of 70 between flight swaths which means that any specific area in the target zone is scanned three or more times from different angles evaluation of dems with resolution from 0 25 to 10 m assures that a 0 5m resolution lidar dem is necessary for the detection of subtle tectonic breaks another key factor for complete detection of small tectonic geomorphic features is the application of a recently developed dem visualization red relief image map rrim which allows mapping of all the small features with various sizes orientations and morphology overcoming major drawbacks of classic dem visualizations a very high resolution lidar survey aided with rrim visualization as used in this study provides a more reliable approach for the detailed mapping of slight active fault traces hidden under dense vegetation

field test of a permanent in well fiber optic seismic system a deviated borehole was drilled and completed to test systems for deployment of permanent in well three component fiber optic seismic sensors two systems were developed and tested for deployment of these sensors the first system involved using a passive mandrel device to enable coupling of the sensors simply using the weight of the tubing the second system involved use of an active mandrel that incorporates a spring loaded pad device to isolate the sensor from the tubing vibration in addition reference wireline vertical seismic profile data were acquired both in the empty cased borehole and through the tubing at the same location as the fiber optic sensor analysis of the data showed that best results were obtained using the active design tubing related resonances were noted on data acquired using the passive design whereas the active design did a good job of discriminating among these undesirable signals