inversion of multicomponent seismic time shifts for reservoir pressure and length a feasibility study pressure drops associated with reservoir production generate excess stress and strain that cause travel time shifts of reflected waves here we invert time shifts of p s and ps waves measured between baseline and monitor surveys for pressure reduction and reservoir length the inversion results can be used to estimate compaction induced stress and strain changes around the reservoir we implement a hybrid inversion algorithm that incorporates elements of gradient global genetic and nearest neighbour methods and permits exploration of the parameter space while simultaneously following local misfit gradients our synthetic examples indicate that optimal estimates of reservoir pressure from p wave data can be obtained using the reflections from the reservoir top for s waves time shifts from the top of the reservoir can be accurately inverted for pressure if the noise level is low however if noise contamination is significant it is preferable to use s wave data or combined shifts of all three modes from reflectors beneath the reservoir joint wave type inversions demonstrate improvements over any single pure mode reservoir length can be estimated using the time shifts of any mode from the reservoir top or deeper reflectors we also evaluate the differences between the actual strain field and those corresponding to the best case inversion results obtained using p and s wave data another series of tests addresses the inversion of the time shifts for the pressure drops in two compartment reservoirs as well as for the associated strain field numerical testing shows that a potentially serious source of error in the inversion is a distortion in the strain sensitivity coefficients which govern the magnitude of stiffness changes this feasibility study suggests which wave types and reflector locations may provide the most accurate estimates of reservoir parameters from compaction induced time shifts

late holocene vegetation dynamics and deforestation in rano aroi implications for easter island s ecological and cultural history abstract easter island rapa nui has been considered an example of how societies can cause their own destruction through the overexploitation of natural resources the flagship of this ecocidal paradigm is the supposed abrupt island wide deforestation that occurred about one millennium ago a few centuries after the arrival of polynesian settlers to the island other hypotheses attribute the forest demise to different causes such as fruit consumption by rats or aridity but the occurrence of an abrupt island wide deforestation during the last millennium has become paradigmatic in rapa nui we argue that such a view can be questioned as it is based on the palynological study of incomplete records owing to the existence of major sedimentary gaps here we present a multiproxy pollen charcoal and geochemistry study of the aroi core the first gap free sedimentary sequence of the last millennia obtained to date in the island our results show changing vegetation patterns under the action of either climatic or anthropogenic drivers or both depending on the time interval considered palm forests were present in aroi until the 16th century when deforestation started coinciding with fire exacerbation likely of human origin and a dry climate this is the latest deforestation event recorded so far in the island and took place roughly a century before european contact in comparison to other easter island records this record shows that deforestation was neither simultaneous nor proceeded at the same pace over the whole island these findings suggest that easter island s deforestation was a heterogeneous process in space and time and highlights the relevance of local catchment traits in the island s environmental and land management history

techniques applied to obtain very high resolution 3 d seismic imaging at an athabasca tar sands thermal pilot a high resolution 3 d seismic base survey was conducted at amoco s gregoire lake in situ steam pilot glisp located in northeastern alberta canada approximately 40 km south of fort mcmurray other partners in the project are aostra alberta oil sands technology and research authority and petro canada the prime purpose for acquiring the base survey was to use this information as a basis of comparison with future surveys of a similar type in order to locate and monitor the progress of in situ heat movement

an application of 4d seismic monitoring technique to modern coal mining to study the impact of modern coal mining on the overlying formation a full lifecycle four dimensional seismic monitoring study has been carried out four seismic data campaigns have been performed using flexi bin geometry with square bins with total duration of 171 days the four seismic datasets have been processed with the same processing workflow and parameters major problems such as statics correction signal to noise ratio resolution and consistency processing are addressed taking into account the geological features of the research area this guarantees that remaining four dimensional differences between the time lapse datasets show mostly geological factors due to the coal mining and effects such as surface subsidence our four dimensional seismic monitoring of modern coal mining shows that mined and unmined areas have significant zoning characteristics coal mining has a direct impact on the overlying formation the mining leads to obvious event subsidence which reflects that overlying formations undergo subsidence during the mining process the overlying formation appears as two zones called caving zone and fractured zone we determine the fault dip of the overlying formation at one end of the working face to be 56 or so by calculation and conversion we also see that during the coal mining process over time the overlying formation has a self recovery capability which gradually strengthens from the roof siltstone upward to the aeolian sandstone near the surface the stability of 20 m coal pillars between working faces displays a strengthening trend and remains safe during the mining process due to both coal seam supporting and formation compaction effects

four dimensional seismology and true direct detection of hydrocarbons the petrophysical basis figure 1 published by m king hubbert in 1962 and again in 1969 shows the exploitation of fossil fuels in a historical perspective according to this graph about half of the fossil energy on earth is being used up in a period of about 200 years half of which is by now over

case history using time lapse vertical seismic profiling data to constrain velocity saturation relations the frio brine pilot co2 injection author s al hosni m caspari e pevzner r daley tm gurevich b abstract 2016 european association of geoscientists a engineers co2 sequestration projects benefit from quantitative assessment of saturation distribution and plume extent for field development and leakage prevention in this work we carry out quantitative analysis of time lapse seismic by using rock physics and seismic modelling tools we investigate the suitability of gassmann s equation for a co2 sequestration project with 1600 tons of co2 injected into high porosity brine saturated sandstone we analyze the observed time delays and amplitude changes in a time lapse vertical seismic profile dataset both reflected and transmitted waves are analyzed qualitatively and quantitatively to interpret the changes obtained from the vertical seismic profile we perform a 2 5d elastic finite difference modelling study the results show a p wave velocity reduction of 750 m s in the proximity of the injection well evident by the first arrivals travel time delays and amplitude change and reflected wave amplitude changes these results do not match with our rock physics model using gassmann s equation predictions even when taking uncertainty in co2 saturation and grain properties into account we find that time lapse vertical seismic profile data integrated with other information e g core and well log can be used to constrain the velocity saturation relation and verify the applicability of theoretical models such as gassmann s equation with considerable certainty the study shows that possible nonelastic factors are in play after co2 injection e g co2 brine rock interaction and pressure effect as gassmann s equation underestimated the velocity reduction in comparison with field data for all three sets of time lapse vertical seismic profile attributes our work shows the importance of data integration to validate the applicability of theoretical models such as gassmann s equation for quantitative analysis of time lapse seismic data

potential of ambient seismic noise techniques to monitor the st gallen geothermal site switzerland the failures of two recent deep geothermal energy projects in switzerland basel 2006 st gallen 2013 have again highlighted that one of the key challenges for the successful development and operation of deep underground heat exchangers is to control the risk of inducing potentially hazardous seismic events in st gallen after an injection test and two acid injections that were accompanied by a small number of micro earthquakes ml 0 2 operators were surprised by an uncontrolled gas release from the formation gas kick the killing procedures that had to be initiated following standard drilling procedures led to a ml3 5 earthquake with ambient seismic noise cross correlations from nine stations we observe a significant loss of waveform coherence that we can horizontally and vertically constrain to the injection location of the fluid the loss of waveform coherence starts with the onset of the fluid injections 4 days prior to the gas kick we interpret the loss of coherence as a local perturbation of the medium we show how ambient seismic noise analysis can be used to assess the aseismic response of the subsurface to geomechanical well operations and how this method could have helped to recognize the unexpected reservoir dynamics at an earlier stage than the microseismic response alone allowed

time lapse imaging at bullwinkle field green canyon 65 offshore gulf of mexico two orthogonal preproduction seismic surveys and a regional seismic survey acquired after eight years of production from the bullwinkle field green canyon 65 gulf of mexico reveal extraordinary seismic differences attributed to production induced changes in rock and fluid properties amplitude reduction of up to 71 occurs where production and log data show that water has replaced hydrocarbons as the oil water contact moved upward separate normalizations of these surveys demonstrate that time lapse results are improved by using seismic surveys acquired in similar orientations also clearer difference images are obtained from comparing lower frequency data sets superior stratigraphic illumination in the dip oriented survey relative to the strike oriented surveys results in nongeological amplitude differences this documents the danger of using dissimilar baseline and monitor surveys for time lapse studies

time lapse walkaway vertical seismic profile monitoring for co2 injection at the sacroc enhanced oil recovery field a case study abstractgeologic carbon storage involves large scale injections of carbon dioxide into underground geologic formations changes in reservoir properties resulting from co2 injection and migration can be characterized using monitoring methods with time lapse seismic data to achieve economical monitoring vertical seismic profile vsp data are often acquired to survey the local injection area we investigated the capability of walkaway vsp monitoring for co2 injection into an enhanced oil recovery field at sacroc west texas vsp data sets were acquired in 2008 and 2009 and co2 injection took place after the first data acquisition because the receivers were located above the injection zone only reflection data contain the information from the reservoir qualitative comparison between reverse time migration images at different times revealed vertical shifts of the reflectors center indicating the presence of velocity changes we examined two methods to quantify the changes in velocity standard full wa

time lapse seismic performance of a sparse permanent array experience from the aquistore co2 storage site abstracta sparse areal permanent array of buried geophones was deployed at the aquistore co2 storage site in saskatchewan canada the purpose of this array is to facilitate 4d seismic monitoring of co2 that is to be injected to the deep subsurface use of a sparse buried array is designed to improve the repeatability of time lapse data and to economize the monitoring effort prior to the start of co2 injection two 3d dynamite seismic surveys were acquired in march 2012 and may 2013 using the permanent array the objective of acquiring these data was to allow an assessment of the data repeatability and overall performance of the permanent array a comparison of the raw data from these surveys and with a conventional high resolution 3d vibroseis survey demonstrated that 1 the signal to noise ratio for the buried geophones was increased by 6 7 db relative to surface deployed geophones and by an additional 20 db for dynamite relative to a vibroseis source 2 the use of buried sensors and sources at this

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

late cretaceous india madagascar fit and timing of break up related magmatism a u pb zircon age of 91 2 0 2 myr from western india st mary islands confidently links india with the late cretaceous magmatic province in madagascar 84 92 ma and the u pb age is within analytical error of the u pb age of the analalava gabbro pluton 91 6 0 3 myr in northeastern madagascar palaeomagnetic data from india and madagascar allow us to postulate a new india madagascar fit euler latitude 14 24 longitude 38 8 and rotation angle 69 2 this fit is applicable to the late cretaceous directly prior to and during the early phase of madagascar india separation in our late cretaceous reconstruction south west india runs roughly subparallel with the first known break up related magnetic anomaly a34 it maintains a close connection between mada gascar and india but places india slightly rotated compared to the eastern margin of madagascar and more northerly compared with some reconstructions st mary magmatism is linked to the initial break up between india and madagascar and magmatism probably resulted from rift related extensional processes initially induced by the marion hotspot underlying southern madagascar during the late cretaceous

stress induced seismic azimuthal anisotropy sand shale content and depth trends offshore north west australia abstractseismic azimuthal anisotropy is apparent when p wave velocities vary with source receiver azimuth and downward propagating s waves split into two quasi s waves polarized in orthogonal directions not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations there are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand shale lithology and depth we develop a model that does so in unconsolidated sand shale sequences offshore north west australia our method naturally introduces two new concepts critical anisotropy and anisotropic depth limit critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth where the confining pressure and sediment compaction are minimal the anisotropic depth limit is the maximum depth where the stress induced azimuthal anisotropy is ex

time lapse wave equation migration velocity analysis abstracttime lapse 4d analysis of seismic data acquired at different stages of hydrocarbon production or gas fluid injection has been very successful at imaging detailed reservoir changes conventional time domain analysis of 4d data sets usually assumes a linear perturbation about a reference baseline earth model however this assumption is violated when production injection significantly alters the subsurface generating large 4d velocity changes time shifts and complicated 4d wavefield coda necessitating a more robust 4d analysis involving prestack wave equation depth migration and velocity analysis we address these situations by extending conventional 3d wave equation migration velocity analysis wemva based on one way wave equations and single scattering theory to 4d velocity estimation using a parallel inversion approach involving parallel solution of two separate inversion problems recognizing that the 4d wemva strategy requires precomputed baseline monitor image difference volumes we de

rock physics analysis and time lapse rock imaging of geochemical effects due to the injection of co2 into reservoir rocks the fundamental concept of time lapse seismic monitoring is that changes in physical parameters such as saturation pore fluid pressure temperature and stress affect rock and fluid properties which in turn alter the seismic velocity and density increasingly however time lapse seismic monitoring is called upon to quantify subsurface changes due in part to chemical reactions between injected fluids and the host rocks this study springs from a series of laboratory experiments and high resolution images assessing the changes in microstructure transport and seismic properties of fluid saturated sandstones and carbonates injected with co2 results show that injecting co2 into a brine rock system induces chemo mechanical mechanisms that permanently change the rock frame injecting co2 into brine saturated sandstones induces salt precipitation primarily at grain contacts and within small pore throats in rocks with porosity lower than 10 salt precipitation reduces permeability and increases p and s wa

seismic monitoring of water floods a petrophysical study seismic velocities were measured in the laboratory on 67 samples as a function of pressure and temperature when saturated with gas and a 35 api 141 5 density at 1 atmosphere and 60 f 131 5 mineral oil and flooded with pentane and fresh water respectively using an ultrasonic pulse transmission method the rock samples consisted of 39 carbonate cores from eight reservoirs 22 sandstone cores from six formations and six unconsolidated samples from three origins the results show that water flooding increases the compressional velocity vp by more than 5 percent in most of the gas saturated cores at effective pressures overburden pressure minus pore pressure less than 20 mpa such vp increase is less than 5 percent in about half of the carbonate cores and some of the sandstone cores with normal pentane and in all the consolidated cores both carbonates and sandstones saturated with the 35 api oil however in unconsolidated samples saturated with gas pentane or oil water flooding increases th

time lapse seismic analysis of fulmar field this report discusses the analysis of time lapse seismic data from fulmar field in the central north sea this case study evaluates the potential of time lapse seismic technology for monitoring fluid movement and pressure changes in a reservoir using legacy preexisting data

effects of filling fluid type and composition and joint orientation on acoustic wave propagation across individual fluid filled rock joints abstract wave propagation and attenuation in subsurface rock masses could be highly affected by rock joints filled with fluids however the understanding of acoustic behaviours across fluid filled rock joints is still at its infancy to determine the effects of the type and composition of filling fluids as well as joint orientation on compressional wave propagation and attenuation across individual fluid filled rock joints extensive laboratory acoustic tests were conducted in this paper results showed that the existence of water in fluid filled rock joints results in higher wave velocity more wave transmission and less wave attenuation compared to light oils in most circumstances increasing liquid content in a single liquid filled joint enhances wave velocity and wave transmission for dual liquid filled joints both wave velocity and wave transmission increase with increasing water content joint orientation significantly affects wave characteristics of rock joints partially filled with liquids while it has slight influences on wave attributes of rock joints fully filled with liquids in addition wave velocity and attenuation across fluid filled rock joints increases with increasing central frequency of incident compressional waves

seismic monitoring of steam based recovery of bitumen since 1985 imperial oil has been using a recovery process cyclic steam stimulation css to commercially produce bitumen from the clearwater formation near cold lake alberta canada figure 1 the clearwater reservoir an unconsolidated sand with a porosity of 32 percent and a permeability of 1 darcy is saturated with an extremely viscous bitumen viscosity about 150 000 cp the css oil recovery process involves injection of steam at high temperatures and pressures 310 c and 10 mpa followed by the production of bitumen from the same well twenty wells are directionally drilled from a single surface location or pad more than 2000 wells are spaced on a regular 1 6 hectares grid producing 100 000 b d

prediction of residual oil saturation by using the ratio of amplitude attributes of time lapse seismic data abstractsubtraction of baseline and monitoring seismic data is a common step in highlighting reservoir changes in time lapse seismic interpretation however ambiguity exists in the interpretation of the amplitude difference which is controlled by fluid change and reservoir thickness to estimate the residual oil saturation quantitatively we have developed a time lapse seismic interpretation method that uses the ratio of amplitude attributes extracted from the baseline and monitoring seismic data the relationship between impedance change and the ratio of the baseline and monitoring amplitude attributes is determined to avoid the influence of reservoir thickness subsequently the fluid saturation is calculated from the impedance change by using a proper petrophysical relationship we have tested our new method on a real time lapse seismic data set from a water flooded reservoir in the deepwater area of west africa the water flooded area determined from the amplitude difference does not completely matc

time lapse seismic imaging using regularized full waveform inversion with a prior model which strategy full waveform inversion is an appealing technique for time lapse imaging especially when prior model information is included into the inversion workflow once the baseline reconstruction is achieved several strategies can be used to assess the physical parameter changes such as parallel difference two separate inversions of baseline and monitor data sets sequential difference inversion of the monitor data set starting from the recovered baseline model and double difference inversion of the difference data starting from the recovered baseline model strategies using syntheticmarmousi data sets we investigate which strategy should be adopted to obtain more robust and more accurate time lapse velocity changes in noise free and noisy environments this synthetic application demonstrates that the double difference strategy provides the more robust time lapse result in addition we propose a target oriented time lapse imaging using regularized full waveform inversion including a prior model and model weighting if the prior information exists on the location of expected variations this scheme applies strong prior model constraints outside of the expected areas of timelapse changes and relatively less prior constraints in the time lapse target zones in application of this process to the marmousi model data set the local resolution analysis performed with spike tests shows that the target oriented inversion prevents the occurrence of artefacts outside the target areas which could contaminate and compromise the reconstruction of the effective time lapse changes especially when using the sequential difference strategy in a strongly noisy case the target oriented prior model weighting ensures the same behaviour for both time lapse strategies the double difference and the sequential difference strategies and leads to a more robust reconstruction of the weak time lapse changes the double difference strategy can deliver more accurate time lapse variation since it can focus to invert the difference data however the double difference strategy requires a preprocessing step on data sets such as time lapse binning to have a similar source receiver location between two surveys while the sequential difference needs less this requirement if we have prior information about the area of changes the target oriented sequential difference strategy can be an alternative and can provide the same robust result as the doubledifference strategy

recent advances in time lapse laboratory rock physics for the characterization and monitoring of fluid rock interactions abstractmonitoring thermo chemo mechanical processes geophysically e g fluid disposal or storage thermal and chemical stimulation of reservoirs or natural fluids simply entering a new system raises numerous concerns because of the likelihood of fluid rock chemical interactions and our limited ability to decipher the geophysical signature of coupled processes one of the missing links is understanding the evolution of seismic properties together with reactive transport because rock properties evolve as a result of chemical reactions and vice versa capturing this coupling experimentally is one of the missing elements in the existing literature this paper describes recent advances in rock physics experiments to understand the effects of dissolution induced compaction on acoustic velocity porosity and permeability this paper has a dual aim understanding the mechanisms underlying permanent modifications to the rock microstructure and providing a richer set of experimental information to inform th

time dependent reservoir characterization of the lf sand in the south eugene island 330 field gulf of mexico one of the most important features of time dependent reservoir characterization is the added additional constraints that can be incorporated to update the initial reservoir model uncertainty of the model may be gradually reduced as the iteration of time dependent reservoir characterization continues

time lapse seismic reservoir monitoring time lapse seismic reservoir monitoring has advanced rapidly over the past decade there are currently about 75 active projects worldwide and more than 100 cumulative projects in the past decade or so the present total annual expenditures on 4 d seismic projects are on the order of 50 100 million us this currently represents a much smaller market than 3 d seismic but the use of 4 d seismic has grown exponentially over the past decade and is expected to continue to do so

time lapse monitoring of the duri steamflood a pilot and case study this article describes a successful 4 d seismic pilot project in duri field indonesia the site of the world s largest steamflood two baseline and six monitor 3 d seismic surveys were recorded over the same steam injection pattern between 1992 and 1995 seismic analysis thermal simulation and acoustic modeling show the engineering relevance of these data and provide new insights into the seismic response of reservoirs during active steamflooding analyses of the data demonstrate that for the duri steamflood the horizontal and vertical distribution of steam can be tracked over time

feasibility of borehole ambient noise interferometry for permanent reservoir monitoring the analysis of seismic ambient noise acquired during temporary or permanent microseismic monitoring campaigns e g improved enhanced oil recovery monitoring surveillance of induced seismicity is potentially well suited for time lapse studies based on seismic interferometry no additional data acquisition required ambient noise processing can be automatized to a high degree and seismic interferometry is very sensitive to small medium changes thus there is an opportunity for detection and monitoring of velocity variations in a reservoir at negligible additional cost and effort data and results are presented from an ambient noise interferometry study applied to two wells in a producing oil field in romania borehole microseismic monitoring on three component geophones was performed for four weeks concurrent with a water flooding phase for improved oil recovery from a reservoir in ca 1 km depth both low frequency 2 hz 50 hz p and s waves propagating through the vertical borehole arrays were reconstructed from ambient noise by the virtual source method the obtained interferograms clearly indicate an origin of the ambient seismic energy from above the arrays thus suggesting surface activities as sources it is shown that ambient noise from time periods as short as 30 seconds is sufficient to obtain robust interferograms sonic log data confirm that the vertical and horizontal components comprise first arrivals of p wave and s waves respectively the consistency and high quality of the interferograms throughout the entire observation period further indicate that the high frequency part up to 100 hz represents the scattered wave field the temporal variation of apparent velocities based on first arrival times partly correlates with the water injection rate and occurrence of microseismic events it is concluded that borehole ambient noise interferometry in production settings is a potentially useful method for permanent reservoir monitoring due to its high sensitivity and robustness

dynamic reservoir characterization of vacuum field this article briefly describes the 4 d 3 c technique and a research application of it at vacuum field new mexico by the reservoir characterization project rcp at the colorado school of mines rcp a consortium of 32 oil companies has been involved in 4 d 3 c research since 1995 because this technique has the potential to provide the most complete information needed for efficient reservoir characterization for example when three components of source are used nine times the data of a conventional 3 d p wave survey are recorded

time lapse velocity analysis application to onshore continuous reservoir monitoring in 4d seismic the velocity model used for imaging and reservoir characterization can change as production from the reservoir progresses this is particularly true for heavy oil reservoirs stimulated by steam injection in the context of sparse and low fold seismic acquisitions conventional migration velocity analyses can be inadequate because of a poorly and irregularly sampled offset dimension we propose to update the velocity model in the context of daily acquisitions with buried sources and receivers the main objective is to demonstrate that subtle time lapse effects can be detected over the calendar time on onshore sparse acquisitions we introduce a modified version of the conventional prestack time migration to detect velocity changes obtained after cross correlation of the base and monitor surveys this technique is applied on a heavy oil real data set from the netherlands and reveals how the steam diffuses over time within the reservoir

seismic reservoir monitoring on gullfaks until recently time lapse seismic monitoring was considered unproven for tracking the movement of an oil water contact owc however statoil petrophysicists working on sonic logs from the gullfaks field in the norwegian north sea uncovered changes in log response that were favorable for seismic monitoring open hole logs from three wells drilled through the original owc compared to logs from wells drilled into water flushed areas showed consistently higher velocities in the water filled zones than in those filled with oil

reciprocity based passive monitoring with individual sources time lapse changes in the subsurface can be analyzed by comparing seismic reflection data from two different states one serving as the base survey and the second as the monitor survey conventionally reflection data are acquired by placing active seismic sources at the acquisition surface alternatively these data can be acquired from passive sources in the subsurface using seismic interferometry si unfortunately the reflection responses as retrieved by si inherit an imprint of the passive source distribution therefore monitoring with si requires high passive source repeatability which is very often not achievable in practice we have developed an alternative by using active seismic data for the base survey and a single passive source e g a seismic tremor produced by induced seismicity for the monitor survey by constraining the source radiation pattern of the active base survey according to the characteristics of the passive monitor survey we succeed in extracting the time lapse response in the image domain we tested our method with numerically modeled data

cere la ronde a laboratory for time lapse seismic monitoring in the paris basin the cere la ronde gas storage reservoir is in the loire valley in central france an area famous for its many castles it is used as a test site by gaz de france the french national gas company to study reservoir monitoring methods it is a water bearing sandstone reservoir in a faulted anticline structure at a depth of 900 m with an average thickness of 20 m modeling this reservoir resulted in a 1 5 ms transit time and a 12 db expected amplitude variation after gas injection

stress and mass changes at a wet volcano example during the 2011 2012 volcanic unrest at kawah ijen volcano indonesia since 2010 kawah ijen volcano has been equipped with seismometers and its extremely acid volcanic lake has been monitored using temperature and leveling sensors providing unprecedented time resolution of multiparametric data for an acidic volcanic lake the nature of stress and mass changes of the volcano is studied by combining seismic analyses and volcanic lake measurements that were made during the strongest unrest ever recorded by the seismic network at kawah ijen the distal vt earthquake swarm that occurred in may 2011 was the precursor of volcanic unrest in october 2011 that caused an increase in shallow earthquakes the proximal vt earthquakes opened pathways for fluids to ascend by increasing the permeability of the rock matrix the following months were characterized by two periods of strong heat and mass discharge into the lake and by the initiation of monochromatic tremor mt activity when steam gases interacted with shallow portions of the aquifer significant seismic velocity variations concurrent with water level rises in which water contained a large amount of steam gas were associated with the crises that caused an although the unrest did not affect the shallow hydrothermal system at a large scale whereas shallow vt earthquakes likely reflect a magmatic intrusion mt and relative seismic velocity changes are clearly associated with shallow hydrothermal processes these results will facilitate the forecast of future crises

feasibility of time lapse seismic reservoir monitoring the physical basis as reservoir fluids are produced or fluids are injected during enhanced oil recovery the reservoir s seismic properties may change if these changes are large enough repetitive surveys can map fluid distributions pressure fluid fronts and temperature changes which means at least in theory that we can perform time lapse seismic reservoir monitoring herein called tlsrm instead of the popular but inaccurate term 4 d seismology

from velocity and attenuation tomography to rock physical modeling inferences on fluid driven earthquake processes at the irpinia fault system in southern italy we retrieve 3 d attenuation images of the crustal volume embedding the fault system associated with the destructive ms 6 9 1980 irpinia earthquake by tomographic inversion of t measurements a high qp anomaly is found to be correlated with the 1980 fault geometry while the qs model shows regional scale variations related to the ne edge of the uplifted pre tertiary limestone an upscaling strategy is used to infer rock properties such as porosity consolidation type of fluid mixing and relative saturation percentage at 8 10 km fault depth we constrain the porosity and consolidation in the ranges 4 5 and 5 9 respectively with the possible fluid mixes being both brine co2 and ch4 co2 the consolidation parameter range indicates high pore pressures at the same depths these results support the evidence for a fracture system highly saturated in gases and a seismicity triggering mechanism at the fault zone which is strongly controlled by fluid induced pore pressure changes

preseismic fault creep and elastic wave amplitude precursors scale with lab earthquake magnitude for the continuum of tectonic failure modes tectonic faults fail in a continuum of modes from slow earthquakes to elastodynamic rupture precursory variations in elastic wavespeed and amplitude interpreted as indicators of imminent failure

assessment of 4d seismic repeatability and co2 detection limits using a sparse permanent land array at the aquistore co2 storage site abstracttwo 3d time lapse seismic surveys were acquired in 2012 and 2013 at the aquistore co2 storage site prior to the start of co2 injection using these surveys we determined the background time lapse noise at the site and assessed the feasibility of using a sparse areal permanent receiver array as a monitoring tool applying a standard processing sequence to these data we adequately imaged the reservoir at 3150 3350 m depth evaluation of the impact of each processing step on the repeatability revealed a general monotonic increase in similarity between the data sets as a function of processing the prestack processing sequence reduced the normalized root mean squared difference nrms from 1 13 between the raw stacks to 0 13 after poststack time migration the postmigration cross equalization sequence further reduced the global nrms to 0 07 a simulation of the changes in seismic response due to a range of co2 injection scenarios suggested that co2 was detectable within the reservoir at the aquistor

seismic monitoring of the duri steamflood application to reservoir management the duri steamflood operated by caltex pacific indonesia has employed time lapse seismic monitoring technology as an important component of its reservoir management process since the completion of a successful pilot study in 1995 see seismic monitoring of the duri steamflood a pilot and feasibility case study in this issue of tle time lapse seismic surveys have been shot in six areas of varying steamflood maturity and new surveys will be acquired as undeveloped areas are placed on steam injection

strengthening the virtual source method for time lapse monitoring time lapse monitoring is a powerful tool for tracking subsurface changes resulting from fluid migration conventional time lapse monitoring can be done by observing differences between two seismic surveys over the surveillance period along with the changes in the subsurface differences in the two seismic surveys are also caused by variations in the near surface overburden and acquisition discrepancies the virtual source method monitors below the time varying near surface by redatuming the data down to the subsurface receiver locations it crosscorrelates the signal that results from surface shooting recorded by subsurface receivers placed below the near surface for the mars field data redatuming the recorded response down to the permanently placed ocean bottom cable obc receivers using the virtual source method allows one to reconstruct a survey as if virtualsources were buried at the obc receiver locations and the medium above them were a homogeneous half space separating the recorded wavefields

sensitivity of compaction induced multicomponent seismic time shifts to variations in reservoir properties abstractpore pressure variations inside producing reservoirs result in excess stress and strain that influence the arrival times of reflected waves inversion of seismic data for pressure changes requires better understanding of the dependence of compaction induced time shifts on reservoir pressure reduction using geomechanical and full waveform seismic modeling we investigate pressure dependent behavior of p s and ps wave time shifts from reflectors located above and below a rectangular reservoir embedded in a homogeneous half space our geomechanical modeling algorithm generates the excess stress strain field and the stress induced stiffness tensor as linear functions of reservoir pressure analysis of time shifts obtained from full waveform synthetic data shows that they vary almost linearly with pressure for reflectors above the reservoir but become nonlinear for reflections from the reservoir or deeper interfaces time shift misfit curves computed with respect to noise contaminated data from a

three dimensional seismic monitoring of an enhanced oil recovery process seismic reflection data were used to monitor the progress of an in situ combustion enhanced oil recovery process three sets of three dimensional 3 d data were collected during a one year period in order to map the extent and directions of propagation in time acquisition and processing parameters were identical for each survey so that direct one to one comparison of traces could be made seismic attributes were calculated for each common depth point data set and in a unique application of seismic reflection data the preburn attributes were subtracted from the midburn and postburn attributes the resulting difference volumes of 3 d seismic data showed anomalies which were the basis for the interpretation shown in this case study profiles and horizon slices from the data sets clearly show the initiation and development of a bright spot in the reflection from the top of the reservoir and a dim spot in the reflection from a limestone below it interpretation of these anomalies is supported by informa

effects of changes in rock microstructures on permeability 3 d printing investigation rocks are naturally heterogeneous two rock samples with identical bulk properties can vary widely in microstructure understanding how the microstructure and bulk properties of rocks then evolve during experiments and computations simulating diagenesis is inherently a multiscale problem the advent of modern 3 d printing has provided an unprecedented opportunity to link those scales by combining the strengths of digital and experimental rock physics in this study we take a computerized tomography scanned model of a natural carbonate pore space then iteratively digitally manipulate 3 d print and measure the flow properties in the laboratory this approach allows us to access multiple scales digitally and experimentally and test hypotheses about how changes in rock microstructure due to compaction and dissolution affect bulk transport properties in a repeatable manner

repeatability of 3 d ocean bottom cable seismic surveys recent advances allow time lapse 3 d sometimes called 4 d seismic surveys to map gas oil and oil water contacts some have used legacy 3 d data i e data not originally acquired for a 4 d study and found that the varying quality of the different vintages of the data limited the resolution that could be attained how then do we best carry out acquisition and processing for a 4 d seismic program so that the data are repeatable to the extent that differences are attributable to movement of the reservoir fluids and not to the acquisition processing or other factors

time lapse full waveform inversion with ocean bottom cable data application on valhall field abstractknowledge of changes in reservoir properties resulting from extracting hydrocarbons or injecting fluid is critical to future production planning full waveform inversion fwi of time lapse seismic data provides a quantitative approach to characterize the changes by taking the difference of the inverted baseline and monitor models the baseline and monitor data sets can be inverted either independently or jointly time lapse seismic data collected by ocean bottom cables obcs in the valhall field in the north sea are suitable for such time lapse fwi practice because the acquisitions are of a long offset and the surveys are well repeated we have applied independent and joint fwi schemes to two time lapse valhall obc data sets which were acquired 28 months apart the joint fwi scheme is double difference waveform inversion ddwi which inverts differenced data the monitor survey subtracted by the baseline survey for model changes we have found that ddwi gave a cleaner and more easily interpr

wave velocities in hydrocarbon saturated rocks experimental results this paper contains laboratory measurements of the temperature dependence of velocities determined by ultrasonic pulse transmission methods in hydrocarbon liquids and rock samples saturated by the liquids the samples discussed include 26 hydrocarbons of varying molecular weight nine mixtures of these hydrocarbons four heavy oils tar three saturated sandstones and a saturated sand the data provide encouragement that high frequency high resolution seismic techniques may infer formation temperature changes thereby detecting the progress of thermal enhanced oil recovery processes