molybdenum mineralization in an active geothermal system valles caldera new mexico shallow sub ore grade molybdenite mineralization has been discovered in the active high temperature geothermal system penetrated by continental scientific drilling program corehole vc 2a at sulfur springs in the western ring fracture zone of the valles caldera new mexico this mineralization is hosted by fractured quartz sericitized intracaldera ash flow tuffs younger than 1 12 ma the molybdenite is an unusual poorly crystalline variety that occurs in vuggy veinlets and breccia cements also containing quartz sericite illite pyrite and fluorite as well as local sphalerite rhodochrosite and chalcopyrite fluid inclusion data suggest that this assemblage was deposited from very dilute solutions at temperatures near 200 sup 0 c geochemical modeling indicates that under restricted ph and fo sub 2 conditions at 200 sup 0 c the molybdenite and associated phases would be in equilibrium with hydrothermal fluids now circulating in the deep subsurface the shallow molybdenite zone intersected in vc 2a may be the near surface expression of deep climax type stockwork molybdenum mineralization

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

velocity structures imaged from long offset reflection data and four component obs data at jiulong methane reef in the northern south china sea abstract in this study p and s wave velocity models were built based on two pre stack depth migration psdm profiles of long offset reflection data and 25 four component ocean bottom seismometers obs data at jiulong methane reef off sw taiwan in the passive margin of the northern south china sea scs according to the velocity models the average p wave velocity and vp vs ratio of the free gas beneath the bottom simulating reflector bsr are 1 52 1 58 km s and 4 5 5 10 respectively the depth of the bsr is found at 80 300 m below the sea floor and the sedimentary thickness of the hydrate and the free gas are about 50 100 m and 70 100 m respectively p wave velocity of about 1 75 km s in the hydrate bearing sediment is southeastward increased to about 1 85 km s above the bsr similarly vp vs ratio of about 3 06 in the hydrate bearing sediment is increased southeastward to about 3 48 above the bsr based on the pseudo 3d map of gas hydrate saturation estimated from the psdm and obs models the average saturations of hydrate and free gas at jiulong methane reef are about 7 and 0 9 2 4 respectively the highest hydrate saturation 11 is located at 5 20 m above the bsr in the se portion of the jiulong methane reef on the other hand the highest gas saturation of about 2 is observed at 10 70 m below the bsr in the nw portion of the jiulong methane reef we suggested that several normal faults dipping southeastward beneath the continental slope provided conduits for gas migrating northwestward at jiulong methane reef therefore the highest gas saturation is observed below the anticline in the nw portion of the jiulong methane reef and the highest hydrate saturation high p wave velocity and high vp vs ratio is identified above the bsr in the se portion of the jiulong methane reef

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

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

acoustic response of gas hydrate formation in sediments from south china sea abstract gas hydrate has been recognized as a potential energy resource in south china sea scs understanding the acoustic response of gas hydrate formation in the scs sediments is essential for regional gas hydrate investigation and quantification the sediments were obtained from gravity core sampling at e 115 12 52363 n 19 48 40299 gas hydrate was formed within a gas water saturated scs sediments system combination of a new bender element technique and coated time domain reflectometry tdr was carried out to study the acoustic response of hydrate occurrence in scs sediments the results show the acoustic signal becomes weak when hydrate saturation sh is lower than 14 the acoustic velocities vp vs of the sediments increase with sh during hydrate formation and vs increases relatively faster when sh is higher than 14 these results indicate that tiny hydrate particles may firstly float in the pore fluid which causes a significant acoustic attenuation but has little influence on shear modulus as time lapses and sh approaches 14 numerous particles coalesce together and contact with sediment particles as a result vs has a sharp increase when hydrate saturation exceeds 14 several velocity models were validated with the experimental data which suggests a combination of the bgtl biot gassmann theory modified by lee model and the weighted equation is suitable to estimate sh in scs

reservoir monitoring and characterization using satellite geodetic data interferometric synthetic aperture radar observations from the krechba field algeria deformation in the material overlying an active reservoir is used to monitor pressure change at depth a sequence of 11 field estimates allows us to construct a measure of diffusive traveltime throughout a reservoir the dense distribution of traveltime values means that we can construct an exactly linear inverse problem for reservoir flow properties application to interferometric synthetic aperture radar insar data gathered over a carbon dioxide c o2 injection site in algeria reveals pressure propagation along two northwest trending corridors an inversion of the traveltimes indicates the existence of two northwest trending high permeability zones the high permeability features trend in the same direction as the regional fault and fracture zones model parameter resolution estimates indicate the features are well resolved

composition diagenesis and weathering of the sediments and basement of the callabonna sub basin central australia implications for landscape evolution abstract the evolution of the callabonna sub basin central australia is described in terms of sediment provenance stratigraphy sedimentology and postdepositional mineral and chemical alteration six mineral exploration drillholes in the mundi mundi plain were studied using a combination of qualitative and quantitative xrd pimatm portable infrared mineral analyzer xrf normative analysis and sem the sedimentary cover consists of 160 210 m of diagenetically modified fluvio lacustrine tertiary clay silt and sand comprising sandy mottled and gray clay units overlain by quaternary soil the basement consists of weathered proterozoic schist gneiss siltstone and shale quartz kaolinite smectite and muscovite are the dominant minerals within the sediments whereas the weathered bedrock contains quartz feldspar kaolinite illite and muscovite characteristic wavelength absorption features from pimatm show that the youngest sandy clay unit exhibits the lowest reflectance intensities because of its lower diagenetic maturity weathering of primary minerals within the basement produced an illite kaolinite rich saprolite whose clays exhibit strong reflectance intensities and well developed crystallinity the micromorphology of all secondary products reflects their environment of crystallization low porosity and anoxic conditions within the sediments resulted in poorly developed clays of variable textures colors and compositions conversely the weathered bedrock developed over protracted periods of in situ weathering resulting in better developed secondary products this study distinguishes between preburial weathering of the basement detrital mineralogy postdepositional alteration of the sedimentary cover and subsequent weathering of previously formed mineral assemblages this has widespread implications for paleotopographic weathering reconstitution and landscape evolution thus 1 the extent of weathering of basement relative to diagenesis and maturity of sediments and gradational nature of their unconformity suggests that most of the alteration of basement occurred prior to and was sustained after deposition of sediments and 2 morphotectonic evolution of the region controlled the composition of transported materials by changing the style and patterns of fluvial systems further influencing the distribution and preservation of sediments and weathered bedrock and hence regional landscape morphology

sub sample time shift and horizontal displacement measurements using phase correlation method in time lapse seismic hydrocarbon production and fluid injection affect the level of subsurface stress and physical properties of the subsurface and can cause reservoir related issues such as compaction and subsidence monitoring of oil and gas reservoirs is therefore crucial time lapse seismic is used to monitor reservoirs and provide evidence of saturation and pressure changes within the reservoir however relative to background velocities and reflector depths the time lapse changes in velocity and geomechanical properties are typically small between consecutive surveys these changes can be measured by using apparent displacement between migrated images obtained from recorded data of multiple time lapse surveys apparent displacement measurements by using the classical cross correlation method are poorly resolved here we propose the use of a phase correlation method which has been developed in satellite imaging for sub pixel registration of the images to overcome the limitations of cross correlation phase correlation provides both vertical and horizontal displacements with a much better resolution after testing the method on synthetic data we apply it to a real dataset from the norne oil field and show that the phase correlation method can indeed provide better resolution

an interpretation of the alteration assemblages at sulphur springs valles caldera new mexico sulphur springs located near the western edge of the valles caldera north central new mexico is the only vapor dominated surface manifestation of any significance found in the valles the percolating acid sulfate waters and fumarolic gases have leached and oxidized the country rock near the hot springs to a bleached wasteland the near surface mineral assemblages at 90 c are restricted to one and two phases occurring in contact with a variety of solutions and gases the conditions of local equilibrium at 90 g are approximately halotrichite alunogen log fo2 45 log fs2 12 ph 0 3 szomolnokite pyrite log fo2 46 log fs2 16 ph 0 8 alunite log fo2 50 log fs2 10 ph 1 2 kaolinite sulphur log fo2 53 log fs2 10 ph 1 2 log ak 0 0012 m log asio2 0 0033 m and pyrite log fo2 60 log fs2 19 ph 4 3 this study has demonstrated that local equilibrium is closely approached even under the low temperature and pressure conditions found near the surface

stratigraphic relations and lithologic variations in the jemez volcanic field new mexico over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the jemez volcanic field volcanism had begun in the area by about 16 5 ma with episodic eruptions of alkaline basalts by 13 ma alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite high silica rhyolite derived from melts of lower crust also was erupting by about 13 ma basalt and high silica rhyolite continued to be erupted until about 7 and 6 ma respectively but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 ma volumetrically overshadowed all other eruptive products between 10 and 7 ma from 7 to 3 ma the dominant erupted lithology was dacite which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high silica rhyolites less than 4 3 ma volcanism was dominated by eruption of rhyolitic tuffs field relations geochemistry and dates specifically indicate the following with regards to stratigraphie relations 1 distinctions among basalt of chamisa mesa paliza canyon formation basalts and lobato basalt for other than geographic reasons are artificial basaltic volcanism was continuous in volcanic field from 13 to 7 ma 2 canovas canyon and bearhead rhyolites form a continuum of high silica rhyolite volcanism from 13 to 6 ma 3 hypabyssal and volcanic rocks of the cochiti mining district probably represent the exhumed interior of a keres group volcano s 4 temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations and 5 the tewa group formation cerro rubio quartz latite may more appropriately be considered part of the tschicoma formation of the polvadera group preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field s history

hydrothermal brecciation in the jemez fault zone valles caldera new mexico results from continental scientific drilling program core hole vc 1 an unusual breccia sequence penetrated in the lower 30 m of continental scientific drilling program core hole vc 1 total depth 856 m records a complex hydrothermal history culminating in hydraulic rock rupture and associated alteration at the edge of the quaternary valles caldera the breccias both tectonic and hydrothermal in origin were formed in the jemez fault zone near the intersection of this major regional structure with the caldera s ring fracture margin tectonic breccias in the sequence are contorted crushed and sheared coexisting hydrothermal breccias lack such frictional textures but display matrix flow foliation and prominent clast rounding features characteristic of fluidization these hydrothermal breccias were intensely altered during at least five major stages to quartz illite phengite pyrite aggregates traces of molybdenite occur locally this assemblage indicates interaction with hydrothermal fluid at temperatures in excess of 200 c the extrapolated present maximum temperature of 184 c in the breccia zone therefore represents considerable cooling since these phases were formed fluid inclusions in the breccias also preserve evidence of the prior passage of hotter fluids the inclusions are principally two phase liquid rich secondary in origin and concentrated in hydrothermal quartz older high salinity inclusions unrelated to brecciation homogenize in the temperature range 189 246 c younger inclusions in part of interbreccia origin are low salinity and homogenize in the temperature range 230 283 c locally coexisting liquid and vapor rich inclusions document periodic boiling of the dilute fluids these fluid inclusion data along with the probable age of the hydrothermal breccias 1 5 ma the assumed depth at which they developed about 515 m and the contemporaneous state of stress extensional can be combined to model hydrothermal brecciation at the vc 1 site the minimum fluid pressure pfr required to hydrofracture these rocks was probably about 7 5 mpa 0 0146 mpa m a boiling point versus depth curve based on these pfr values graphically defines the physical conditions prevailing when the breccias were formed when fluid pressure at the assumed depth of brecciation exceeded that curve in response to rapid release of confining pressure possibly augmented by renewed heating flashing hydrothermal fluid fractured the enclosing rock large overpressures most likely induced by sudden seismic cracking of a hydrothermally sealed portion of the jemez fault zone led to local fluidization of the resulting breccias late quartz veining hydrothermal alteration and molybdenite mineralization were probably produced by the fluids responsible for brecciation

an estimation method for effective stress changes in a reservoir from 4d seismics data advances in seismics acquisition and processing and the widespread use of 4d seismics have made available reliable production induced subsurface deformation data in the form of overburden time shifts inversion of these data is now beginning to be used as an aid to the monitoring of a reservoir s effective stress past solutions to this inversion problem have relied upon analytic calculations for an unrealistically simplified subsurface which can lead to uncertainties to enhance the accuracy of this approach a method based on transfer functions is proposed in which the function itself is calibrated using numerically generated overburden strain deformation calculated for a small select group of reference sources this technique proves to be a good compromise between the faster but more accurate history match of the overburden strain using a geomechanical simulator and the slower less accurate analytic method synthetic tests using a coupled geomechanical and fluid flow simulator for the south arne field confirm the efficacy of the method application to measured time shifts from observed 4d seismics indicates compartmentalization in the tor reservoir more heterogeneity than is currently considered in the simulation model and moderate connectivity with the overlying ekofisk formation

compressional wave velocity measurements through sandy sediments containing methane hydrate an experimental apparatus was built to measure p wave velocity vp of sandy sediment during hydrate formation from brine and free methane gas the influences of hydrate saturation initial brine saturation conversion ratio of water to hydrate and grain size of sand upon vp were investigated the experimental results demonstrate that vp strongly depends on both hydrate saturation and initial brine saturation whereas the influence of the grain size of sand is unremarkable during the formation of hydrate for different experimental runs at identical initial brine saturation vp increases with the increase of hydrate saturation while it decreases dramatically with the increase of initial brine saturation for a given hydrate saturation the correlation between vp and conversion ratio of water into hydrate was studied and it was found that the relation between vp and the conversion ratio of water to hydrate is approximately the same for different experimental runs regardless of how big the differences in initial saturation of brine and the size of sand grain are vp was calculated for four different hydrate distribution models the results suggest that low conversion ratio of water to hydrate hydrate mainly acts as a load component of a dry frame matrix whereas at higher conversion ratio of water to hydrate it partly acts as a cement that coats grains at grain contacts and thereby leads to a dramatic increase in vp compared with the hydrate saturation the conversion ratio of water to hydrate has a large role in distributing hydrate in the pores of sediments

high temperature hydrothermal origin for fractured carbonate reservoirs in the blackburn oil field nevada geologic note 1 preliminary petrographic and fluid inclusion studies of drill cuttings and core from the blackburn oil field reveal that many of the oil saturated fractures veinlets and breccias in the dolomite reservoir rock may be of high temperature hydrothermal origin textures of the earliest formed fracture veinlet networks and breccias suggest development by explosive hydrothermal fracturing the veinlets themselves preserve evidence that high temperature fluids favorable for such natural hydrothermal rock rupture once circulated in these rocks primary fluid inclusion homogenization temperatures indicate that early vein dolomite precipitated from hydrothermal brines at temperatures exceeding 350 degrees c 662 degrees f younger quartz sphalerite galena veinlets developed from dilute aqueous solutions at temperature of more than 225 degrees c 437 degrees f the high paleotemperatures recorded by early vein dolomite in the now much cooler about 120 degrees c or 248 degrees f blackburn reservoir rock imply an ancient magmatic heat source in this case almost certainly a small granodiorite stock tertiary adjoining and possibly underlying the field other carbonate hosted petroleum reservoirs in eastern nevada are also intimately associated with felsic intrusives we propose that igneous related high temperature hydrothermal fracturing could have created reservoir porosity and permeability at some or all of these fields and that future petroleum exploration in the basin and range might profitably incorporate the search for concealed plutons

experimental evidence for fluidization processes in breccia pipe formation results of small scale fiuidization spouting and channeling experiments suggest that similar processes may have been involved in the formation of many breccia pipe features various cylindrical parallel plate and boxlike model containers were filled with mixtures of particulate materials ranging from clay sized powdered kaolinitc to 1 cm gravel and each container was attached at its base to a large volume compressed air source features generated during the course of the various experimental runs are analogous to the majority of features observed in breccia pipes complex branching fracture systems developed in models containing abundant cohesive material appear to be similar to incipient crackle breccias steep walled funnel to cone shaped conduits formed readily and in some models inward dipping fractures ring fractures marginal shear folds and or downwarps and or high angle normal faults developed in adjacent material thorough mixing of heterogeneous particulate materials from throughout the stratigraphic column commonly was achieved and blocks of more cohesive materials were readily rounded and comminuted convective particle motion spouting was most effective in the mixing process and was accompanied by downwarping and fragmentation of adjacent strata downward migration of wall rock blocks along conduit margins and generation of annular zonation of conduit filling material in some systems annular size classification resulted in fine layering parallel to conduit walls crude centroclinally nested saucer bedding developed in some experiments where air fall ejecta were generated and these beds commonly were transported essentially intact downward within the pipe during a bubbling fiuidization event a gas streaming or channeling process in which finer material was elutriated or cleared out of coarser material led to the formation of channelways or chimneys which in natural systems would provide excellent avenues for introduction of later magma or hydrothermal solutions in model systems enriched in strongly cohesive clay sized particles accretionary pelletal spherules commonly were generated fluidization and related processes have been defined to describe highly controlled industrial systems problems of scale and strength of materials are significant when comparing experimental with geologic systems but the striking similarity of many features observed in both experimental and natural breccia pipe systems suggests that a similar genetic process is reasonable although many pipes clearly are not formed by fiuidization and related processes these processes may be important in the development of or some developmental stage of some breccia pipes

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

multi stage fluid circulation in a hydraulic fracture breccia of the larderello geothermal field italy abstract the deep well mv5a drilled in the western part of the larderello geothermal field crossed a 20 cm thick hydraulic fracture breccia unit at a depth of 1090 m below ground level b g l this breccia occurs in a fine grained triassic metasandstone and consists of angular to subangular clasts of up to some centimeters in size pervasive alteration has affected the breccia clasts and wall rock around the breccia with the formation of mg fe chlorite after such alteration hydrothermal circulation caused the precipitation of two generations of calcite cement then ankerite partially replaced these two calcite generations ankerite also precipitated in late veinlets with chlorite late hydrothermal activity led to the crystallization of albite quartz and finally anhydrite the calcite contains vapor rich inclusions and two populations of liquid rich l1 and l2 inclusions l1 inclusions are characterized by homogenization temperatures between 304 and 361 c and salinities from 7 4 to 11 6 wt nacl equivalent l2 inclusions revealed homogenization temperatures in the range of 189 245 c and salinities from 2 6 to 6 3 wt nacl equivalent the fluids contained in l2 inclusions were probably trapped coevally with some vapor rich inclusions under boiling conditions after the l1 inclusions formed some of the abundant vapor rich inclusions in calcite may also represent early low temperature inclusions affected by decrepitation and or stretching and or leaking during l1 trapping the liquid rich l inclusions trapped at later stages in ankerite albite and anhydrite display respectively homogenization temperature ranges of 189 198 c 132 145 c and 139 171 c and salinities ranging from 1 6 to 1 7 wt nacl equivalent 1 4 to 2 1 wt nacl equivalent and 3 7 to 6 2 wt nacl equivalent the inclusions studied record the evolution over time of the fluids flowing in the breccia level l1 inclusions capture high temperature fluid about 300 to 350 c of high salinity around 10 wt nacl equivalent at above hydrostatic pressures up to about 150 bar the l2 inclusions in calcite and liquid rich inclusions in ankerite and albite represent subsequent hydrothermal fluid evolution toward lower temperatures about 250 to 130 c pressures 45 to a few bar and salinities 6 3 to 1 4 wt nacl equivalent during this stage boiling processes and infiltration of meteoric waters probably occurred finally moderately saline fluids around 5 wt nacl equivalent at a temperature about 160 c close to that of present day in hole measurements was trapped in the anhydrite inclusions the liquids trapped in liquid rich inclusions circulated at 41 000 years maximum age of calcite or later this age represents an upper limit for the development of vapor dominated condition in this part of the geothermal system the fluids circulating at the breccia level were probably meteoric and or connate waters these fluids may have interacted with the anhydrite and carbonate bearing formations present in the larderello area the occurrence of the hot and saline fluids trapped in l1 inclusions at above hydrostatic pressure suggests that similar fluids but with higher pressure 167 bar and temperature 360 c may have been responsible for rock fracturing

determining the dilation factor in 4d monitoring of compacting reservoirs by rock physics models hydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers 4d prestack seismic data can be used to detect these changes because compaction stretching causes changes in traveltimes and seismic velocities we show that by using two different petro elastic models at varying effective pressures a good approximation is to assume that the fractional changes in layer

a method for estimating apparent displacement vectors from time lapse seismic images reliable estimates of vertical inline and crossline components of apparent displacements in time lapse seismic images are difficult to obtain for two reasons first features in 3d seismic images tend to be locally planar and components of displacement within the planes of such features are poorly resolved second searching directly for peaks in 3d crosscorrelations is less robust more complicated and computationally more costly than searching for peaks of 1d crosscorrelations i estimate all three components of displacement with a process designed to mitigate these two problems i address the first problem by computing for each image sample a local phase correlation instead of a local crosscorrelation i address the second problem with a cyclic sequence of searches for peaks of correlations computed for lags constrained to one of the three image axes

hydrothermal alteration in the valles caldera ring fracture zone and core hole vc 1 evidence for multiple hydrothermal systems two types of hydrothermal mineral assemblages kaolinite alunite and sericite chlorite were recognized in outcrop and core samples from the jemez volcanic field new mexico active and fossil acid sulfate hydrothermal activity producing kaolinite alunite alteration occurs along the caldera ring fracture and within the resurgent dome whereas alterations of the chlorite sericite type are mostly confined to subsurface rocks k ar dates on illitic clays 2 m 2 0 25 m and 0 25 m separated from hydrothermally altered samples are used to document hydrothermal episodes in pre caldera rocks of the jemez volcanic field the clay separates are illitic 75 95 illite layers with k2o contents of 8 24 8 95 in the core samples and 4 22 6 67 in the outcrops three episodes of hydrothermal alteration are now recognized in the jemez mountains region based on k ar age dates of illites the earliest event 17 11 ma n 4 occurred within altered and illite rich 90 illite layers lowermost paleozoic rocks in core hole vc 1 and may correlate with the inception of volcanism in the jemez region 16 5 ma illitic clays from altered andesite and rhyolite from the topographic rim of the valles caldera were dated at 8 2 and 6 96 ma suggesting that a hydrothermal event related to the waning stages of the keres group volcanism 13 5 8 ma was responsible for the alteration these dates overlap minimum ages obtained on slightly altered basalt 8 05 ma and andesite lava 7 07 ma from the southern and northwestern topographic rim of the valles caldera respectively ages of 1 21 and 1 34 ma from illite rich 90 illite layers hydrothermally altered paleozoic sandstone at a depth of 479 m in vc 1 suggest hydrothermal activity contemporaneous with the formation of the toledo 1 45 ma and valles 1 12 ma calderas ore minerals of sphalerite chalcopyrite galena barite and molybdenite mineralization occur in the lower half of vc 1 and are related to the toledo and valles caldera forming eruptions

inferred role of natural fractures veins and breccias in development of the artificial geothermal reservoir at the ogachi hot dry rock site japan 1 at the ogachi hot dry rock hdr test site located in a neogene caldera northeast japan two artificial reservoirs the upper one at 700 m depth and the lower one at 1000 m depth were created in granitic basement by hydraulic stimulation the new fracture sets forming the reservoirs propagated in different directions the upper one to the east and the lower one to the nne water recovery rate from a production well penetrating the two reservoirs was at best 25 which is very low compared to other hdr test sites such as fenton hill united states and soultz france in order to understand these phenomena natural fractures were investigated using mainly core samples from the production well it was found that natural fractures in the upper and lower reservoirs are remarkably different the upper reservoir at depths less than 900 m is more densely fractured and contains far fewer thick hydrothermal veins than in the lower reservoir it is believed that these features are due to hydrothermal brecciation associated with neogene caldera formation and that they could greatly affect the hdr reservoir system thick hydrothermal veins and andesite dykes are expected to loci for reservoir fracture propagation and major flow paths because the veins and dykes occupy a prominent fracture system whose orientation coincides well with that of the reservoir propagation on the other hand the intensely brecciated zone is not associated with any major flow paths

stress induced temporal variations in seismic anisotropy observed in microseismic data summary in situ stress monitoring of crustal rocks is desirable as it yields insights into earthquake mechanisms volcanic eruptions and changes in hydrocarbon reservoirs shear wave splitting induced by stress controlled cracks in the shallow crust provides a way to infer this stress temporal variations in these observations can be difficult to quantify due to scatter in the data and discontinuous observations here we present evidence of temporal variations in shear wave splitting from a continuous time series with a high occurrence of microseismic events recorded in a borehole we interpret these observations in terms of stress controlled cracks and are able to infer changes in stress and via modelling suggest the cause of the anisotropy possible origins of the temporal variation in per cent anisotropy are tidal or oil field production processes our results suggest that shear wave splitting is a viable probe for inferring changes in crustal stress in cracked rock

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

k ar dates of hydrothermal clays from core hole vc 2b valles caldera new mexico and their relation to alteration in a large hydrothermal system abstract seventeen k ar dates were obtained on illitic clays within valles caldera 1 13 ma to investigate the impact of hydrothermal alteration on quaternary to precambrian intracaldera and pre caldera rocks in a large long lived hydrothermal system 1 0 ma to present clay samples came from scientific core hole vc 2b 295 c at 1762 m which was spudded in the sulphur springs thermal area and drilled into the boundary between the central resurgent dome and the western ring fracture zone six illitic clays within quaternary caldera fill debris flow tuffaceous sediment and ash flow tuff 48 to 587 m depth yield ages from 0 35 to 1 09 ma illite from miocene pre caldera sandstone 765 m gives an age of 6 74 ma two dates on illite from sandstones in permian red beds 1008 and 1187 m are 4 33 and 4 07 ma respectively surprisingly three dates on illites from altered andesite pebbles within the red beds 1010 1014 m are 0 95 to 1 06 ma four illite dates on variably altered precambrian quartz monzonite 1615 1762 m range from 2 90 to 276 ma post valles age illite is not correlated with alteration style argillic to propylitic rather post valles ages are uniformly obtained from illites in highly fractured intensely altered caldera fill rocks and the permian volcanic clasts generally finer clay fractions from identical samples yield younger ages plots of 40 ar 36 ar versus 40 k 36 ar and 40 ar versus 40 k for the illites in caldera fill rocks lie close to a 1 ma isochron most illite dates older than valles caldera are difficult to interpret because they correspond to the ages of pre valles volcanic and hydrothermal episodes in the jemez volcanic field 13 ma in addition older dates may be caused by co mingling of different illites during sample preparation or by inherited argon or lost argon in illites from rocks with potentially complex hydrothermal histories however the range of ages obtained from illites in permian sands and pebbles and from precambrian crystalline rocks indicates that valles hydrothermal activity is overwhelming illite produced by earlier geologic events

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

light lithophile element boron lithium abundances in the valles caldera new mexico vc 1 core hole boron and lithium abundance distributions are very different in the sedimentary and volcanic sections of the vc 1 core hole valles caldera new mexico in the sedimentary section the wide variations in boron and lithium abundances probably reflect both diagenesis and introduction of these elements in early hydrothermal fluids late higher temperature fluids appear to have leached boron and lithium from some rocks adjacent to fault zones and aquifers the correlation of boron with lithium suggests that these elements behave in similar ways during diagenesis and hydrothermal alteration the small variation of boron and lithium abundances in most of the vitreous volcanic rocks from the upper part of the core implies that their source was relatively homogeneous following primary devitrification boron appears to have been stable but lithium was mobile boron may have been stabilized by the development of boron bearing submicroscopic phenocrysts in the lavas or boron may be less soluble than lithium in relatively cool groundwater

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

cross matching with interpreted warping of 3d streamer and 3d ocean bottom cable data at valhall for time lapse assessment legacy streamer data and newer 3d ocean bottom cable data are cross matched and analysed for time lapse analysis of geomechanical changes due to production in the valhall field the issues relating to time lapse analysis using two such distinctly different data sets are addressed to provide an optimal cross matching workflow that includes 3d warping additionally an assessment of the differences between the imaging using single azimuth streamer and multi azimuth ocean bottom cable data is provided the 3d warping utilized in the cross matching procedure is sensitive to acquisition and processing differences but is also found to provide valuable insight into the geometrical changes that occur in the subsurface due to production as such this work also provides a demonstration of the use of high resolution 3d interpreted warping to resolve the 3d heterogeneity of the compaction and subsidence this is an important tool for valhall and possibly other fields where compaction and subsidence and monitoring thereof are key factors in the reservoir management since the predominant observed production induced changes are compaction of the soft high porosity chalk reservoir due to pore pressure reduction and the resultant overburden subsidence such reservoir compaction could have significant implications for production by changing permeabilities and production rates furthermore the subsidence effects could impact upon subsea installations and well bore stability geomechanical studies that have previously been used to model such subsidence and compaction are only constrained by observed surface displacements and measured reservoir pressure changes with the geological overburden being largely neglected the approaches suggested herein provide the potential for monitoring and assessment in three dimensions including the probable heterogeneity and shearing that is needed for full understanding of reservoir compaction and the resultant effects on the overburden to for example mitigate well bore failures

exploring the geological features and processes that control the shape and internal fabrics of late diagenetic dolomite bodies lower khuff equivalent central oman mountains abstract the lower permian carbonate rock succession of the oman mountains represents a stratigraphical surface analogue for middle eastern lower khuff hydrocarbon reservoirs the characteristics of the carbonate rocks are highly variable both laterally and vertically due to the superposition of several episodes of dolomitization a stratabound early dolomitization event affected the well bedded limestones during triassic times subsequently a later burial dolomitization led to the emplacement of several hundreds of meter wide and tens of meter thick dolomite bodies the goal of our study is to understand the distribution and genetic controls on the formation of late diagenetic dolomite bodies field mapping in wordian to capitanian beds was conducted in the jebal akhdar tectonic window in the central oman mountains to determine the shape internal fabrics and associated structures of late diagenetic dolomite bodies the longest extension of late diagenetic dolomite bodies was found to follow predominantly the strike direction of fracture planes bed to bed contacts the precambrian permian unconformity and the bottom rim of early diagenetic dolomite two groups of diagenetic fabrics were observed in association to fractures and bedding planes first vug related fabrics comprise vuggy pores and zebra dolomite second breccia related fabrics consist of either small scale crackle mosaic breccia fabrics and centimeter sized vugs followed by bedding parallel vugs lined up petrographic analysis revealed three types of diagenetic phases referred to as d1 d2 and d3 the matrix replacive phase d1 represents the main diagenetic phase formed during burial coarse crystalline dolomite rhombs phase d2 and saddle dolomite phase d3 were found along stylolites in vugs and in fractures based on the presence of saddle dolomite and zebra dolomite textures late diagenetic dolomite bodies are interpreted to have formed by the circulation of warm dolomitizing fluids of at least 60 c

the hydrothermal outflow plume of valles caldera new mexico and a comparison with other outflow plumes stratigraphic temperature gradient hydrogeochemical and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the valles caldera hydrothermal ouflow plume hydrologic data suggest that 25 50 of the discharge of the valles outflow is confined to the jemez fault zone which predates caldera formation thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the jemez fault zone up to 190 c km shallow heat flow above the hydrothermal plume is as high as 500 mw m 2 near core hole vc 1 jemez fault zone to 200 mw m 2 at fenton hill jemez plateau chemical and isotopic data indicate that two source reservoirs within the caldera redondo creek and sulphur springs reservoirs are parents to mixed fluids flowing in the hydrothermal plume however isotopic data borehole data basic geology and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing the valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits jemez fault zone that strike away from the source reservoir stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks the valles configuration is contrasted with the configuration of the hydrothermal plume at roosevelt hot springs which is dominated by lateral flow through a near surface widespread permeable aquifer data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings have varying reservoir compositions and have different flow characteristics although temperature reversals are commonly observed in wells penetrating outflow plumes reversals are not observed in all plumes less information is available on the absolute age of hydrothermal outflow plumes although the data show that they can be as old as 106 years and display episodic behavior

warping prestack imaged data to improve stack quality and resolution accurate seismic imaging requires that a geologic feature be located at the same lateral and vertical position in images obtained by 3d prestack migration from different data bins such as common offset or common angle subvolumes misalignment of those images degrades the quality of the stack for dipping reflectors and lateral discontinuities imperfect imaging causes both lateral and vertical misalignment in current practice the vertical component of the misalignment is used to estimate updates in velocity and other imaging parameters the lateral component is largely ignored we show that recent developments in seismic attribute analysis allow us to examine the lateral misalignment of prestack volumes with similar resolution to that achieved in examining vertical moveout to measure lateral moveout we pick maxima from local 2d crosscorrelations computed between slices from 3d attribute volumes we then use these measurements to correct for the lateral misalignment by applying a warping procedure to the corresponding slices in the prestack migrated seismic data we apply our technique to a 3d land survey acquired over the fort worth basin in texas and obtain subtle but potentially important improvements in the quality and resolution of the stack as well as in the attribute images computed from the corrected data

insights on the thermal history of the valles caldera new mexico evidence from zircon fission track analysis abstract the zircon fission track dating method was applied to the vc 2b core obtained from the active hydrothermal system at sulphur springs valles caldera new mexico four samples were analyzed to obtain both zircon ages and track length data from permian strata to precambrian quartz monzonite the present temperatures of which are from 222 to 294 c zircon ages obtained from the deeper three samples indicate partially annealed ages of about 450 600 ma thus zircons from permian strata probably originated from precambrian rocks contrary to the normal relationship between ft ages and temperatures of the sampling points non correlation between them is probably due to hot fluid flow and or hot vein emplacement associated with recent volcanic activity zircon ages of the shallowest sample were much younger than the permian the reason for which is unknown the closure temperature of the zircon fission track dating method seems to be higher than that previously determined from geological data

comparison of hydrothermal alteration of carboniferous carbonate and siliclastic rocks in the valles caldera with outcrops from the socorro caldera new mexico abstract continental scientific drilling program csdp drill hole vc 2b total depth 1761 7 m 5780 ft maximum temperature 295 c was continuously cored through the sulphur springs hydrothermal system in the western ring fracture zone of the 1 14 ma valles caldera among other units the hole penetrated 760 2 m 2494 1 ft of paleozoic carbonate and siliciclastic strata underlying caldera fill and precaldera volcanic and epiclastic rocks comparison of the vc 2b paleozoic rocks with corresponding lithologies within and around the 32 1 ma socorro caldera 192 km 119 miles to the south southwest provides insight into the variability of alteration responses to similar caldera related hydrothermal regimes the pennsylvanian madera limestone and sandia formation from vc 2b preserve many of the sedimentological and diagenetic features observed in these units on a regional basis and where unaffected by high temperatures or hydrothermal activity micrites in these formations in vc 2b are generally altered and mineralized only where fractured or brecciated that is where hydrothermal solutions could invade carbonate rocks which were otherwise essentially impermeable alteration intensity and correspondingly inferred paleopermeability is only slightly higher in carbonate packstones and grainstones low to intermediate in siltstones and claystones and high in poorly cemented sandstones hydrothermal fracture filling phases in these rocks comprise sericite and phengite chlorite allanite apatite an unidentified zeolite and sphene in various combinations locally with sphalerite galena pyrite and chalcopyrite terrigenous feldspars and clays are commonly altered to chlorite and seriate and euhedral anhydrite porphyroblasts with minor chlorite occur in sandia formation siltstone fossils are typically unaltered but the walls of some colonial bryozoans in the madera limestone are altered to the assemblage chlorite sericite epidote allanite la ce and nd are present in an unidentified hydrothermal mineral occurring throughout much of the vc 2b pennsylvanian sequence carboniferous carbonate and siliciclastic formations within and around the socorro caldera show a similar style of alteration and mineralization to their valles caldera counterparts but by contrast locally host commercial caldera related base metal sulfide deposits as in the valles rocks mineralization and alteration in those of the socorro caldera were strongly controlled by porosity unless disrupted by fractures breccias or karst cavities not identified in valles caldera drill holes the rocks remained relatively unaltered where these features allowed ingress of mineralizing hydrothermal solutions base metal sulfides and rare earth element bearing minerals were precipitated

loading rate impact on fracturing pattern lessons from hydrocarbon recovery lacq gas field france using scaling parameters of induced seismicity in size and space domains seismic b value and spatial correlation dimension d respectively we analyze the fracturing pattern of the gas reservoir of lacq in correlation with the production rate on the basis of previous observations and a previous model segall et al 1994 we assume that the cause of induced seismicity is a poroelastic stressing such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir during the 20 year study period the production rate has decreased dramatically leading to a change of poroelastic stress rate from 4 5 10 3 to 1 5 10 3 mpa yr accordingly we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing both arguing for a stress rate impact on the fracturing pattern in the gas field we interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased this hypothesis is supported by independent evidence from a number of experimental numerical and field studies the loading rate thus appears as a possible candidate to drive changes of b and d in time and space the apparent sensitivity of the earth s crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the earth s crust deformation mode itself be frequency dependent also our observations may have strong implications in contexts where the loading rate is induced by human intervention e g hydrocarbon recovery mines suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs

tectonic and litho stratigraphic controls on kaolin deposits within volcanic successions insights from the kaoliniferous district of north western sardinia italy abstract in northwestern sardinia a tertiary calc alkaline volcanic succession linked to the subduction of insubric oceanic crust and subsequent post collisional slab break off crops out and hosts several kaolin deposits we have undertaken field and laboratory studies to establish how the tertiary geodynamic setting of the western mediterranean and the composition and texture especially porosity of the volcanic rocks control the geometry and quality of the deposits massive andesites dacites and mildly welded rhyodacitic ignimbrites are the precursors of the kaolin kaolin deposits from the andesites contain pyrite and jarosite and the deposits which formed from the dacites contain up to 5 alunite the amounts of pyrite and alunite are negligible in deposits which formed from ignimbrite fracture controlled fluid dominated systems izawa 1986 responsible for the formation of the deposits are linked to nnw sse trending normal faults which formed during burdigalian to serravallian extension following on from collision between adria and europe corsica sardinia crust four types of deposit morphology bedform mushroom fault parallel and funnel are recognised based on the attitude fracturing and porosity of the precursor rock the remarkable funnel morphology was generated by repeated hydrothermal eruptions

reservoir processes and fluid origins in the baca geothermal system valles caldera new mexico at the baca geothermal field in the valles caldera new mexico 19 deep wells were drilled in an attempt to develop a 50 mwe megawatts electric power plant the chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes two distinct reservoir fluids exist at baca these fluids originate from the same deep high temperature 335 c saline 2500 mg kg cl parent water but have had different histories during upflow one fluid from wells 4 and 13 is isotopically light high in radiogenic noble gases co2 and hco3 and low in ca it has a temperature of 290 295 c and a reservoir chloride near 1900 mg kg this fluid resulted from rapid upward flow through 1 1 to 1 4 m y old bandelier tuff reservoir rocks after long residence in pre bandelier 7 m y sediments and precambrian basement rocks and 25 dilution with high altitude cold groundwater from redondo peak the other water from wells 15 19 and 24 moved slowly through the bandelier tuff and cooled conductively with minor steam loss for well 19 from 335 c to 280 260 c apparently short residence in old basement rocks has left this water with low radiogenic gases conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water the recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the valles caldera area gases are in equilibrium in all liquid reservoir fluids at near reservoir temperatures and the concentrations of atmospheric gases are similar to those of air saturated water indicating little boiling and steam loss all water solutes and gases in the reservoir fluids originate from air saturated meteoric recharge water watermineral reactions and rock leaching with the possible exception of excess 3he that must have an ultimate mantle source this gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the bandelier

alteration in the madera limestone and sandia formation from core hole vc 1 valles caldera new mexico core hole vc 1 penetrated the southwestern ring fracture zone of the 1 1 ma valles caldera and at a depth of 333 m intersected the top of the paleozoic section including the abo formation madera limestone and sandia formation reaching a total depth of 856 m the paleozoic rocks which consist of thin bedded limestone siltstone mudstone sandstone and local conglomerate are overlain by volcanic rocks of the caldera moat that are less than 0 6 ma diagenetic and at least three hydrothermal alteration stages were identified in the madera limestone and sandia formation diagenetic clay alteration was pervasive throughout the sedimentary rocks volcanic activity at 16 5 ma and continuing through the formation of the valles caldera resulted in high thermal gradients which caused recrystallization of diagenetic clay minerals interstratified smectite illite is the most diagnostic clay mineral throughout the section structurally the illite component in the ordered interstratified illite smectite changes gradationally from 70 at the top of the madera limestone to 95 at the base of the section in the sandia formation pyrite that occurs as small clots and lenses as well as finely disseminated is interpreted as being of diagenetic origin especially in organic rich beds low permeability of much of the paleozoic section precluded the deposition of hydrothermal minerals except in fractures and intergranular space in some of the more permeable sandstone and brecciated horizons three stages of hydrothermal mineral deposition are defined stage i is widespread and includes mainly chlorite calcite pyrite and interstratified smectite illite that was formed prior to caldera development at temperatures approximating 200 c stage ii is characterized by quartz sericite and scarce sulfides deposited locally by fluids at approximately 275 c shortly before or at the time of early caldera related volcanism the stage iii hydrothermal event associated with formation of the valles caldera caused complex brecciation accompanied by deposition of phengite and molybdenite at temperatures locally approaching 300 c mostly in rocks underlying the madera limestone during the present drilling program thermal aquifers were encountered at 483 m 113 c 533 m 125 c and 845 m 184 c very close to the stage ii and iii mineralized zones however measured temperatures of the present hydrothermal system are much lower than during the main hydrothermal events good permeability has been maintained in these three levels for a long time while the rest of the madera limestone and sandia formation was sealed by hydrothermal mineral precipitation

hydrothermal alteration in the baca geothermal system redondo dome valles caldera new mexico thermal fluids circulating in the active hydrothermal system of the resurgent redondo dome of the valles caldera have interacted with their diverse host rocks to produce well zoned alteration assemblages which not only help locate permeable fluid channels but also provide insight into the system s thermal history the alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers permeability along many of these channels has been reduced or locally eliminated by hydrothermal self sealing alteration from the surface through the base of the miocene paliza canyon formation is of three distinctive types argillic propylitic and phyllic argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs beneath the argillic zone pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed high temperature alteration phases at baca are presently found at much lower temperatures we suggest either that isotherms have collapsed due to gradual cooling of the system that they have retreated without overall heat loss due to uplift of the redondo dome that the system has shifted laterally or that it has contracted due to a drop in the water table the deepest well b 12 3423 m in the dome may have penetrated through the base of the active hydrothermal system below a depth of 2440 m in this well hydrothermal veining largely disappears and the rocks resemble those developed by isochemical thermal metamorphism the transition is reflected by temperature logs which show a conductive thermal gradient below 2440 m this depth may mark the dome s neutral plane which separates an upper permeable zone of extensional fracturing from a lower less permeable compressional regime the baca hydrothermal system is similar to those which have formed ore deposits in other calderas particularly creede colorado type epithermal silver base metal veins and stockworks recent scientific drilling has also intersected a deep zone of strong phyllic alteration and molybdenum mineralization in the valles caldera s ring fracture system a setting which localized a large stockwork molybdenite orebody in the nearby questa caldera

explosive rhyolitic volcanism in the jemez mountains vent locations caldera development and relation to regional structure the jemez volcanic field straddles the western margin of the rio grande rift where the rift is intersected by the jemez lineament in north central new mexico the field has a record of volcanism extending back to before 13 ma initial basaltic activity was related to active rifting with minor rhyolitic eruptions occurring along n s rift bounding faults between 10 and 7 ma voluminous andesitic volcanism took place in the central jemez mountains area overwhelming contemporaneous basaltic and rhyolitic magmatism an apparent tectonic lull took place from 7 to 4 ma accompanied by lower eruption rates during this interval dacitic magmas were erupted to form the tschicoma volcanic center but mafic and rhyolitic volcanism virtually ceased since 4 ma accompanying resumption of rifting a growing silicic magma system has been present under the central part of the jemez mountains ultimately evolving to the magma body that produced the voluminous rhyolitic bandelier tuffs explosive rhyolitic eruptions from this large magma body have occurred many times since 3 to 4 ma early eruptions 3 6 2 8 ma produced high silica rhyolite ignimbrites restricted to the southwest part of the jemez mountains formation of these units may have been accompanied by caldera collapse these events were followed by the two caldera forming bandelier tuff ignimbrite eruptions 1 45 and 1 12 ma post caldera explosive and effusive rhyolite eruptions have also tapped the magma body from vents generally located along ring fractures after both bandelier events vent and caldera locations for the rhyolitic eruptions during 3 4 ma have been inferred from grain size characteristics dispersal patterns and facies variations in the plinian deposits and ignimbrites lithic breccia zones of the pre bandelier ignimbrites indicate possible caldera sources in the southwest part of the present valles caldera during the eruption of both bandelier tuffs initial plinian falls and early pyroclastic flows emanated from vents centrally located in the jemez mountains in the lower bandelier tuff eruption a transition to ring fracture vents occurred before the emission of later pyroclastic flows but there is no strong evidence to suggest such a transition occurred during the upper bandelier eruption calderas associated with the lower and upper bandelier tuffs toledo and valles respectively are almost identical in location as are the plinian vent sites for these two large eruptions the toledo embayment northeast of the valles caldera contains lava domes from up to 3 6 ma and may be a caldera or crater associated with early explosive dacitic volcanism in the tschicoma volcanic center post 1 4 ma lava domes also fill this depression the main volcanic features of the jemez mountains field including the valles caldera complex eruption vents and the apical graben of the post valles redondo resurgent block appear to be aligned along the ne sw trending jemez fault zone this zone the local expression of a precambrian basement feature the jemez lineament has exerted strong control on the location and style of eruptions from the bandelier rhyolitic magma system

microthermometry of fluid inclusions from the vc 1 core hole in valles caldera new mexico fluid inclusions in vein quartz and calcite from core samples of the vc 1 hole were studied with microscope heating freezing and crushing stages all samples originate from hydrothermally altered paleozoic rocks predating formation of the jemez mountains volcanic field and valles caldera most homogenization temperatures th of the liquid rich inclusions are above the present well temperature but some th of primary inclusions from 515 m and those of secondary inclusions from 723 m fit the present well temperature curve measured 10 months after completion of the well the maximum temperature recorded by the primary inclusions is 275 c from hydrothermal quartz in the sandia formation at 811 m depth the total range of th for samples from several depths 90 c indicates cooling from the maximum temperature the salinity of fluid inclusions in hydrothermal quartz and calcite is generally low 1 wt nacl eq high salinity fluid up to 5 wt nacl eq has been found in several calcite veins from the lower part of the madera limestone the salinity decreases with decrease of th of the secondary inclusions and that with lowest th at the lower part of the madera limestone is similar to those from the other depths these data show that early hot water circulation system involved several types of fluid whereas the later one was a homogeneous fluid the salinity of fluid inclusions in detrital quartz presumably inherited inclusions is higher than that in hydrothermal minerals some of these inclusions show extraordinary low temperatures of final melting point of ice about 40 c suggesting that a cacl2 component is present co2 contents in fluid inclusions were estimated by the bubble behavior on crushing crushing results indicate that co2 content of the early fluid is 0 35 wt and that of the later fluid is 0 2 0 3 wt geothermal fluid trapped in the fluid inclusions representing the present temperature regime is comparable in composition to those from the baca geothermal field inside the caldera and to those from hot springs in san diego canyon

utilizing the onset of time lapse changes a robust basis for reservoir monitoring and characterization time lapse monitoring is useful for imaging changes in geophysical attributes due to fluid flow in trying to use time lapse data for reservoir characterization difficulties often arise when relating changes in geophysical observations to changes in fluid saturation and pressure as an alternative approach for reservoir monitoring and characterization we introduce the idea of an onset time the time at which a measured quantity such as a seismic traveltime or a reflection amplitude begins to deviate from its background value we illustrate the idea and demonstrate its utility through the consideration of traveltimes recorded by the continuous active source seismic monitoring system at the frio pilot site near houston texas the system which transmits an elastic wave every 15 min is used to monitor the movement of carbon dioxide injected into a permeable sand formation from these data we can estimate the onset of changes in seismic traveltimes to six receivers in an adjacent borehole numerical simulation and synthetic tests indicate that the onset times are not very sensitive to the method used to compute the effective fluid bulk modulus and correspondingly the seismic compressional velocity rather the onset times are strongly influenced by saturation changes within the formation specifically by the break through time of the injected fluid phase by means of an iterative inversion algorithm we use the onset times to estimate permeability variations between the boreholes at the frio pilot site the authors 2014 published by oxford university press on behalf of the royal astronomical society

application of a linear finite frequency theory to time lapse crosswell tomography in ultrasonic and numerical experiments time lapse seismic monitoring is the geophysical discipline whereby multiple data sets recorded at the same location but at different times are used to locate and quantify temporal changes in the elastic parameters of the subsurface we validate a time lapse monitoring method by crosswell tomography using two types of wavefield modeling experiments 1 a 3d real ultrasonic waveform experiment and 2 2d synthetic finite difference wavefield simulations for both wavefield experiments a time lapse structure simulating a fluid sweep in a reservoir layer is applied the time lapse tomographic monitoring approach is based on the standard ray theory and a finite frequency wavefield theory where the latter takes into account the finite frequency properties of recorded wavefields the inverted time lapse models compiled with either the ray theory or the finite frequency wavefield theory locate and correctly quantify the flooding zone in the simulated fluid sweep model both wavefield theories provide an adequate result because the flooding zone is comparable in size to the fresnel volume

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

overburden 4d time shifts indicating undrained areas and fault transmissibility in the reservoir abstract production induced geomechanical stress changes cause velocity changes in the overburden that might be detected as 4d seismic time shifts the strength of the velocity changes depends on the degree of pressure changes and the elastic properties of the reservoir and overburden layers even small velocity changes less than 1 might accumulate into detectable seismic time shifts at the top reservoir since the overburden thickness typically ranges from one to several kilometers reservoir pressure changes inducing seismic time shifts are observed in the overburden of the snorre heidrun and statfjord fields all located on the norwegian continental shelf the strong correlation between overburden time shifts geomechanics and reservoir pressure changes is used to indicate undrained areas and transmissibility across faults which is useful information for increased oil recovery well planning and reservoir model updating 4d geomechanical models are built with input from simulated reservoir pres

investigating the behaviour of mg isotopes during the formation of clay minerals abstract we present elemental and isotopic data detailing how the mg isotope system behaves in natural and experimentally synthesized clay minerals we show that the bulk mg isotopic composition 26 mg of a set of natural illite montmorillonite and kaolinite spans a 2 range and that their isotopic composition depends strongly on a balance between the relative proportions of structural and exchangeable mg after acid leaching these natural clays become relatively enriched in isotopically heavy mg by between 0 2 and 1 6 results of exchange experiments indicate that the mg that has adsorbed to interlayer spaces and surface charged sites is relatively enriched in isotopically light mg compared to the residual clay the isotopic composition of this exchangeable mg 1 49 to 2 03 is characteristic of the isotopic composition of mg found in many natural waters further experiments with an isotopically characterized mgcl 2 solution shows that the clay minerals adsorb this exchangeable mg with little or no isotopic fractionation although we cannot discount the possibility that the uptake of exchangeable mg does so with a slight preference for 24 mg to characterize the behaviour of mg isotopes during clay mineral formation we synthesized brucite mg oh 2 which we consider to be a good analogue for the incorporation of mg into the octahedral sheet of mg rich clay minerals or into the brucitic layer of clays such as chlorite in our experiment the brucite mineral becomes enriched in the heavy isotopes of mg while the corresponding solution is always relatively enriched in isotopically light mg the system reaches a steady state after 10 days with a final fractionation factor solid solution of 1 0005 at near neutral ph this result is consistent with the general consensus that secondary clay minerals preferentially take up isotopically heavy mg during their formation however our results also show that exchangeable mg is an important component within bulk clay minerals and can have an important influence over the bulk clay 26 mg value modeling shows that in certain soils or sediments where the percentage of exchangeable mg is 30 and the isotopic composition of the exchangeable mg is around 2 the generation of bulk 26 mg values of 26 mg values that are closer in composition to the ucc despite this results of modeling together with experimental observation suggests that the uptake of exchangeable mg into these clay rich sediments could cause a decrease in the bulk 26 mg value by up to 0 3 0 4 this should be accounted for when assessing the 26 mg value of sediments on a crustal scale

time lapse tomographic inversion using a gaussian parameterization of the velocity changes most seismic studies of changes in traveltimes are of a qualitative nature and a major challenge in four dimensions is to use the information contained in time shifts to quantify the nature of velocity changes in the subsurface layers we propose a 4d tomographic inversion method that uses time shifts from prestack seismic data to estimate parameters describing the 2d velocity field after changes have occurred prestack data allow for the usage of many offsets thus increasing the information input for the inversion the velocity changes are parameterized by a chosen number of gaussian functions in two dimensions and weighted least squares inversion is used to estimate the parameters describing these functions we have found that the parameters describing the position and shape of the gaussian velocity anomalies can be estimated with this method for simple synthetic cases for more complex cases with overlapping gaussian functions resolution of the parameters can be difficult and in these cases our recom

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

a multimethod global sensitivity analysis to aid the calibration of geomechanical models via time lapse seismic data time lapse seismic attributes are used extensively in the history matching of production simulator models however although proven to contain information regarding production induced stress change it is typically only loosely i e qualitatively used to calibrate geomechanical models in this study we conduct a multimethod global sensitivity analysis gsa to assess the feasibility and aid the quantitative calibration of geomechanical models via near offset time lapse seismic data specifically the calibration of mechanical properties of the overburden via the gsa we analyse the near offset overburden seismic traveltimes from over 4000 perturbations of a finite element fe geomechanical model of a typical high pressure high temperature hpht reservoir in the north sea we find that out of an initially large set of material properties the near offset overburden traveltimes are primarily affected by young s modulus and the effective stress i e biot coefficient the unexpected significance of the biot coefficient highlights the importance of modelling fluid flow and pore pressure outside of the reservoir the fe model is complex and highly nonlinear multiple combinations of model parameters can yield equally possible model realizations consequently numerical calibration via a large number of random model perturbations is unfeasible however the significant differences in traveltime results suggest that more sophisticated calibration methods could potentially be feasible for finding numerous suitable solutions the results of the time varying gsa demonstrate how acquiring multiple vintages of time lapse seismic data can be advantageous however they also suggest that significant overburden near offset seismic time shifts useful for model calibration may take up to 3 yrs after the start of production to manifest due to the nonlinearity of the model behaviour similar uncertainty in the reservoir mechanical properties appears to influence overburden traveltime to a much greater extent therefore reservoir properties must be known to a suitable degree of accuracy before the calibration of the overburden can be considered

intracaldera volcanic activity toledo caldera and embayment jemez mountains new mexico the toledo caldera was formed at 1 47 0 06 ma during the catastrophic eruption of the lower member bandelier tuff the caldera was obscured at 1 12 0 03 ma during eruption of the equally voluminous upper member of the bandelier tuff that led to formation of the valles caldera earlier workers interpreted a 9 km diameter embayment located ne of the valles caldera toledo embayment to be a remnant of the toledo caldera drill hole data and new k ar dates of toledo intracaldera domes redefine the position of toledo caldera nearly coincident with and of the same dimensions as the younger valles caldera the toledo embayment may be of tectonic origin or a small tschicoma volcanic center caldera this interpretation is consistent with distribution of the lower member of the bandelier tuff and with several other field and drilling related observations explosive activity associated with cerro toledo rhyolite domes is recorded in tuff deposits located between the lower and upper members of the bandelier tuff on the northeast flank of the jemez mountains recorded in the tuff deposits are seven cycles of explosive activity most cycles consist of phreatomagmatic tuffs that grade upward into plinian pumice beds a separate deposit of the same age and consisting of pyroclastic surges and flows is associated with rabbit mountain located on the southeast rim of the valles toledo caldera complex these are the surface expression of what may be a thicker more voluminous intracaldera tuff sequence the combined deposits of the lower and upper members of the bandelier tuff toledo and valles intracaldera sediments tuffs and dome lavas form what we interpret to be a wedge shaped caldera fill this sequence is confirmed by deep drill holes and gravity surveys this fill accumulated in depressions formed during precaldera rifting and episodes of caldera collapse we interpret the toledo valles caldera complex to be a pair of nearly coincident trapdoor calderas with the hinge on the west side and thick caldera fill in the east

internal geology and evolution of the redondo dome valles caldera new mexico deep geothermal drilling in the resurgent redondo dome of the valles caldera has allowed us to define a consistent intracaldera stratigraphic sequence that differs in a number of respects from the temporally equivalent sequence outside the caldera above the deeply eroded pliocene paliza canyon formation felsic ash flows and sediments in the dome area form a complex sequence of undetermined age that we call the lower tuffs an erosional interval separates these rocks from the overlying otowi member 1 4 m y of the bandelier tuff another period of erosion during which a tuffaceous sandstone was deposited separates the otowi from the overlying tshirege member 1 1 m y of the bandelier both the otowi and tshirege members with maximum thicknesses of 833 and 1155 m respectively are substantially thicker within the caldera than outside indicating simultaneous deposition and cauldron subsidence both are predominantly densely welded with distinctive interior zones of granophyric crystallization resurgent doming was initiated after emplacement of the tshirege member as evidenced by erosion of the upper portions of the cooling unit prior to deposition of overlying units an isopach map of the sandstone deposited during this erosional period shows that streams draining the uplifting dome were localized along the present redondo creek trend subsequent volcanic activity resulted in the formation of at least three additional ash flow tuff cooling units prior to deposition of caldera fill and eruption of the redondo creek member of the valles rhyolite a numerical model applied to formation of the redondo dome suggests that the top of the causative magma body is located at a depth of about 4700 m 1458 m beneath the bottom of the deepest geothermal well in the dome no wells have penetrated intrusives that could be related to this magma we suggest that the locations of faults bounding the apical graben of the dome were influenced by older faults associated with the northeast trending jemez lineament these faults were active early in the uplift history of the dome and account for many of the structural differences between hypothetical dome development and reality

a strontium isotope study of the vc 1 core hole and associated hydrothermal fluids and rocks from valles caldera jemez mountains new mexico chemical and strontium isotopic analyses have been performed on 10 geothermal waters from the valles caldera jemez mountain region as well as 10 rock samples collected in the vc 1 scientific core hole the 87sr 86sr values of other rocks sampled in the jemez mountains have also been used in this study to understand relations between the fluids and rocks of the volcanically driven geothermal system and the lateral outflow plume discharging down the jemez fault zone the strontium content of groundwater is linked to the host rock composition the aquifer temperature and therefore the solubility of sr containing minerals low sr concentrations in the fluid are found with a high temperature and or volcanic host rocks whereas high sr concentrations are characteristic of a low temperature and or a paleozoic sedimentary aquifer important variations of the 87sr 86sr value in hydrothermal waters 0 70842 0 72193 are related to chemical composition sr content and host rocks for vc 1 core samples the sr isotopic ratios are also markedly variable 0 70459 0 75686 low for the quaternary volcanics and high for the paleozoic sedimentary rocks the same observation is made for other jemez mountains rocks 0 70465 0 8163 with in addition high 87sr 86sr values for precambrian crystalline rocks a good correspondence is generally found between the waters and the reservoir rocks studied here which indicates that isotopic equilibrium is rapidly attained the following suite of hydraulically related fluids displays a progressive enrichment in radiogenic strontium baca wells 87sr 86sr 0 7084 0 7094 vc 1 core hole at 483 m 0 7152 0 7154 main jemez spring 0 7217 and soda dam 0 7219 this trend is associated with flow through paleozoic rocks and with the length of the flow path from the center of valles caldera primary geothermal fluids toward san diego canyon along the jemez fault zone derivative waters

quantitative 3d strain analysis in analogue experiments simulating tectonic deformation integration of x ray computed tomography and digital volume correlation techniques abstract the combination of scaled analogue experiments material mechanics x ray computed tomography xrct and digital volume correlation techniques dvc is a powerful new tool not only to examine the 3 dimensional structure and kinematic evolution of complex deformation structures in scaled analogue experiments but also to fully quantify their spatial strain distribution and complete strain history digital image correlation dic is an important advance in quantitative physical modelling and helps to understand non linear deformation processes optical non intrusive dic techniques enable the quantification of localised and distributed deformation in analogue experiments based either on images taken through transparent sidewalls 2d dic or on surface views 3d dic x ray computed tomography xrct analysis permits the non destructive visualisation of the internal structure and kinematic evolution of scaled analogue experiments simulating tectonic evolution of complex geological structures the combination of xrct sectional image data of analogue experiments with 2d dic only allows quantification of 2d displacement and strain components in section direction this completely omits the potential of ct experiments for full 3d strain analysis of complex non cylindrical deformation structures in this study we apply digital volume correlation dvc techniques on xrct scan data of solid analogue experiments to fully quantify the internal displacement and strain in 3 dimensions over time our first results indicate that the application of dvc techniques on xrct volume data can successfully be used to quantify the 3d spatial and temporal strain patterns inside analogue experiments we demonstrate the potential of combining dvc techniques and xrct volume imaging for 3d strain analysis of a contractional experiment simulating the development of a non cylindrical pop up structure furthermore we discuss various options for optimisation of granular materials pattern generation and data acquisition for increased resolution and accuracy of the strain results three dimensional strain analysis of analogue models is of particular interest for geological and seismic interpretations of complex non cylindrical geological structures the volume strain data enable the analysis of the large scale and small scale strain history of geological structures

time lapse pre stack seismic data registration and inversion for co2 sequestration study at cranfield pre stack seismic data are indicative of subsurface elastic properties within the amplitude versus offset characteristic and can be used to detect elastic rock property changes caused by co2 injection we perform time lapse pre stack 3 d seismic data analysis for monitoring co2 sequestration at cranfield the time lapse amplitude differences of cranfield datasets are found entangled with time shifts to disentangle these two characters we apply a local correlation based warping method to register the time lapse pre stack datasets which can effectively separate the time shift from the time lapse seismic amplitude difference without changing the original amplitudes we demonstrate the effectiveness of our registration method by evaluating the inverted elastic properties these inverted time lapse elastic properties can be reliably used for monitoring co2 plumes

origin of the duvertepe kaolin alunite deposits in simav graben turkey timing and styles of hydrothermal mineralization abstract the duvertepe district located on the western end of the simav graben is the largest known fossil hydrothermal kaolin deposit in turkey active hot springs occur to the north of simav city eynal citgol nasa and geothermal fields occur to the west of the graben hisaralan kaolin in the duvertepe district formed at the expense of miocene rhyolites rhyodacites and tuffs emplaced in a tectonically active system undergoing n s extension upward fan shaped deposits of silicification and kaolin are found along fault zones and define areas of enhanced kaolinization silica sinters located above the kaolin zones suggest that hydrothermal fluids followed the fracture systems and mark outflow of geothermal waters fractured volcanic rocks rich in glass shards bear sufficient porosity and permeability for hydrothermal circulation two mineral facies kaolinite and alunite dominate the deposits which respectively include 1 kaolinite alunite quartz and 2 alunite opal ct quartz halloysite kaolinite crystals are well formed hexagonal vermiform habits and alunite crystals are idiomorphic rhombohedral forms needle and tubular shaped halloysites are common in the alunite facies the 34 s values for alunite range from 1 55 to 6 18 kaolinites have d ranging from 49 0 to 94 3 and the 18 o values range from 5 8 to 14 8 calculated formation temperatures of kaolin mineralization using 18 o values suggest that hydrothermal alteration occurred in the range of 38 to 129 c independent k ar and 40 ar 39 ar ages of alunite are concordant and indicate that alteration occurred from 20 1 to 20 6 ma in the southern part of the graben and 17 3 to 19 2 ma in the northern part these results suggest that metasomatism by steam heated hydrothermal fluids sourced by rhyolitic magma is responsible for the duvertepe kaolin and alunite deposit origins

kaolin a most diverse rock in genesis texture physical properties and uses the rock kaolin exhibits wider diversity in genesis texture physical properties and uses than probably any other common rock its diverse textures shown in scanning electron micrographs are correlative with and indicative of genesis and industrial use of kaolin kaolin originates by weathering by hydrothermal alteration or by crystallization from colloid size sediment whose chemical composition is congruent with that of kaolinite some kaolins freely slake into clay sized particles when wetted with water and likewise develop natural plasticity their texture is characterized by loosely expanded and packed crystals industrial uses of this type of kaolin exploit its free slaking property other kaolins of diametrically opposite properties do not slake and do not become plastic when immersed in water their texture is one of compact tightly interlocking crystals they are appropriately used in industry where selected size shape and original bulk density in crushed clay particles must be maintained despite wetting

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

paleomagnetism and rock magnetism of quaternary volcanic rocks and late paleozoic strata vc 1 core hole valles caldera new mexico with emphasis on remagnetization of late paleozoic strata paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples collected at approximately 1 to 3 m intervals of continental scientific drilling program core hole vc 1 have prompted reinterpretations of the quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late paleozoic strata attending fluid circulation and mineral deposition during and after development of the toledo and valles calderas the results from quaternary units banco bonito obsidian i 35 4 a95 2 8 inclination only determinations n 33 battleship rock tuff d 359 6 i 42 4 a95 2 8 n 5 site means surface sites vc 1 rhyolite i 39 2 a95 12 8 n 7 upper vc 1 tuff i 37 2 a95 10 7 n 13 middle vc 1 tuff i 42 1 a95 2 1 n 39 south mountain rhyolite d 350 9 i 49 9 a95 3 4 n 10 one surface site are consistent with isotopic age data indicating that the entire moat volcanic sequence intersected is less than 650 kyr monitoring of natural remanent magnetization nrm intensity nrm directions directions of magnetizations isolated during progressive demagnetization median destructive forces and rock magnetization parameters has identified systematic variations within the thick banco bonito obsidian and vc 1 tuff units the permian abo formation pennsylvanian to earliest permian madera limestone and pennsylvanian sandia formation typically contain a moderate positive inclination magnetization component abo formation i 52 2 a95 7 4 n 16 madera limestone i 58 4 a95 2 8 n 105 sandia formation i 53 9 a95 4 8 n 21 when residing in magnetite it is usually unblocked in the laboratory by 350 c when carried by hematite it is unblocked by 550 c a moderate negative inclination e g madera and abo strata d 173 1 i 46 6 a95 5 5 n 47 samples assuming a north seeking positive inclination rm providing a useful means of core orientation oppositely directed magnetization is occasionally isolated and removed at higher laboratory unblocking temperatures up to 550 c in magnetite dominated and 600 c in hematite dominated lithologies where present magnetizations of shallower inclination e g madera and abo strata d 160 1 i 10 9 a95 4 4 n 28 are removed over higher ranges of unblocking temperatures and these are probably of late paleozoic age the moderate negative and positive inclination magnetizations are in all likelihood viscous partial thermoremanent magnetizations trms vptrms these were activated at moderate 300 c temperatures between 1 45 and 0 97 ma attending and following the main stages of toledo valles caldera development during the matuyama and at near present downhole temperatures 100 180 c during the brunhes and possibly within the last 10 kyr respectively importantly the preservation of negative inclination rm components in magnetite dominated lithologies of the madera limestone dictates that temperatures during the brunhes chron past 730 kyr did not exceed approximately 300 350 c the inferred temperatures for thermal activation of the vptrms based upon the middleton and schmidt thermal activation curves for both magnetite and hematite derived following walton agree with independent estimates of thermal activity using fluid inclusion and k ar isotopic age determination data during the quaternary the results further illustrate the potential usefulness of thermal activation theories for inferring temperatures of past geologic events especially when they can be applied to magnetizations of similar age residing in both magnetite and hematite and of paleomagnetic and rock magnetic studies in general in continuous coreholes in complex geologic environments

relationship between karstification and burial dolomitization in permian platform carbonates lower khuff oman large breccia fabrics associated with karst constitute an important structure in massive limestone successions the dimensions and shapes of breccia structures are controlled by the initial fracture pattern of the limestone and preferential pathways of the karstifying fluids but subsequently breccia fabrics can also govern the migration of later fluids therefore breccias are highly relevant features to capture for reservoir characterisation outcrop analogues for lower khuff units in the middle east present in the central oman mountains reveal brecciated fabrics up to 10 s of meters in diameter these brecciated units are closely associated with dolomite bodies of late diagenetic origin based on an integrated set of data the breccias are interpreted as collapsed karst cavities either formed by meteoric or hypogenic fluids the exact origin of the fluids could not be constrained due to an overprint by later dolomitizing fluids based on the composition of the clasts and matrix in the breccias two dolomitization events are interpreted to have affected the succession one prior to early diagenetic ed dolomite and one after brecciation late diagenetic dt2 dolomite dolomite of shallow burial origin ed dolomite was only observed as clasts within breccia and is much more frequent than late diagenetic medium to deep burial dolomite clasts thus the timing of the brecciation and collapse is assumed to postdate shallow burial early diagenetic dolomitization late diagenetic replacive dolomite dt2 dolomite forms 90 of the matrix in the breccia fabrics with the exception of a small area that was not affected by dolomitization but is rarely present as clasts stable isotope measurements 18o 2 5 to 6 vpdb and 13c 2 9 to 4 8 vpdb suggest a burial origin for the late diagenetic dolomite potentially with the participation of hydrothermal fluids the dolomitized matrix indicates a migration of late dolomitizing fluids subsequent to or postdating the collapse of the karstic cavities thus early karstification processes seem to have played a big role in controlling subsequent loci of late dolomitization in the oman mountains and potentially in other similar settings elsewhere

time lapse seismic data registration and inversion for co2 sequestration study at cranfield abstractthe time lapse seismic survey for co2 sequestration study at cranfield can be problematic because of misalignments between time lapse data sets such misalignments can be caused by the seismic data processing workflow and may result in the wrong interpretation of time lapse seismic amplitude differences we propose an efficient local correlation based warping method of registering the time lapse poststack data sets which can align these data sets without changing original amplitudes application of our registration method to cranfield time lapse data demonstrates its effectiveness in separating time shift character from seismic amplitude signature after registration time lapse differences show an improved consistency in vertical cross sections and a more localized distribution of difference amplitudes along the horizon allowing us to apply a high resolution basis pursuit inversion bpi for acoustic impedances inversion results show that decreases in acoustic impedances occur mostly at the to

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

long lived crustal scale fluid flow the hydrothermal mega breccia of hidden valley mt painter inlier south australia the palaeozoic hidden valley breccia in the northern flinders ranges of south australia is exceptional for 1 its size of about 10 km2 2 the large continuous range in clast sizes from tens of microns to hundreds of metres and 3 thorough mixing of lithologies of different provenance some originally kilometres apart stratigraphically the size distribution follows a single fractal dimension of about unity over at least 6 orders of magnitude implying that a single process was responsible for diminution from the 100 m scale down to 12 km exhumation which lasted about 200 myrs starting during the 500 ma delamerian orogeny and continuing during the alice springs orogeny fluids released during exhumation were structurally focussed towards hidden valley where an estimated 20 5 30 km3 total fluid volume caused the extensive brecciation brecciation initiated in neoproterozoic cover metasedimentary rocks at a level that is now fully exhumed as hydrothermal fluid ascent continued with ongoing exhumation the level of brecciation shifted down into the underlying mesoproterozoic basement rocks taking with it clasts of cover rocks in this model rocks pass through the zone of brecciation which can thus incorporate a variety of lithologies that were originally kilometres apart

rapid subsidence over oil fields measured by sar interferometry the lost hills and belridge oilfields are in the san joaquin valley california the major oil reservoir is high porosity and low permeability diatomite extraction of large volumes from shallow depths causes reduction in pore pressure and subsequent compaction forming a surface subsidence bowl we measure this subsidence from space using interferometric analysis of sar synthetic aperture radar data collected by the european space agency remote sensing satellites ers 1 and ers 2 maximum subsidence rates are as high as 40 mm in 35 days or 400 mm yr measured from interferograms with time separations ranging from one day to 26 months the 8 and 26 month interferograms contain areas where the subsidence gradient exceeds the measurement possible with ers sar but shows increased detail in areas of less rapid subsidence synoptic mapping of subsidence distribution from satellite data powerfully complements ground based techniques permits measurements where access is difficult and aids identification of underlying causes

mobility and depositional controls of radioelements in hydrothermal systems at the long valley and valles calderas abstract the loci and abundance of u and th were examined in tuffaceous rocks encompassing hydrothermal systems at the long valley caldera california and the valles caldera new mexico aspects of these systems may be analogous to conditions expected in a potential site for a high level waste repository in welded tuff examination of radioelements in core from scientific drill holes at these sites was accomplished by gamma ray spectrometry and fission track radiography in the lateral flowing hydrothermal system at the long valley caldera where temperatures range from 140 to 200 c u is concentrated to 20 ppm in fe rich zones of varved tuff and to 50 ppm with fe rich mineral phases in tuff fragments of a calcite cemented breccia u series disequilibrium in some of these samples suggests mobilization deposition of parent u and or its daughters in the vapor zone of the valles caldera s hydrothermal system temperature 100 c the concordance of high u low th u and decreasing whole rock o isotope ratios suggests that u was concentrated in response to hydrothermal circulation when the system was formerly liquid dominated in the underlying present day liquid dominated zone temperature to 210 c u up to several tens of parts per million occurs with pyrite and fe oxide minerals and in concentrations to several percents with a ti nb y rare earth mineral in the valles system s outflow zone u is also concentrated in fe rich zones as well as in carbonaceous rich zones in the paleozoic sedimentary rocks that underlie the quaternary tuff th associated with accessory minerals predominates in breccia zones and in a mineralized fault zone near the base of the paleozoic sedimentary sequence relatively high concentrations of u occur in springs representative of water recharging the valles caldera s hydrothermal system in contrast considerably lower u concentrations occur in hot waters 220 c and in the system s outflow plume suggesting that u is concentrating in the hotter part of the system the long valley and valles observations indicate that u and ra are locally mobile under hydrothermal conditions and that reducing conditions associated with fe rich minerals and carbonaceous material are important factors in the adsorption of u and thus can retard its transport in water at elevated temperature

geological mineralogical and chemical characterization of devonian kaolinite bearing sediments for further applications in the ceramic tiles industry in la paz bolivia clay minerals are widely distributed in bolivia among them illitic clays are most common in the altiplano where they are mined for use in the ceramic industry that has been growing in the last few years in addition to illitic sediments kaolinitic sediments have been recently discovered in sedimentary units in the bolivian altiplano residual ball clay occurrences in devonian sedimentary units were studied as part of this work geological mapping and geophysical studies ert and gpr were done for better understanding the origin of the deposits and were part of a preliminary study of the mineral potential to define the relationship with the host rock chemical and mineralogical techniques such as x ray diffraction scanning electron microscopy and inductively coupled plasma analyses were performed in samples from the studied area to verify the presence of kaolinite atterberg limits and behaviour of the raw material in ceramic specimens supported by chemical analyses show that this material is suitable for manufacturing tile ceramics this study provides fundamental knowledge for deposit exploitation and future generation of an alternative source of employment for the inhabitants of micaya

temporal patterns of tephra alterations in various geologic settings the jemez volcanic field and the adjacent morrison formation in new mexico and colorado abstract authigenic mineral assemblages and temporal constraints of tephra layers altered by hydrothermal activities subaerial weathering and burial diagenesis are described clay size assemblages in the jenez volcanic field the hydrothermal illite smectites in core hole vc 2a range between 0 66 and 0 83 ma for subsurface plio pleistocene tephra deposits 1 14 1 78 ma and interbedded volcaniclastic units whereas similar clays from altered miocene rocks yield ages between 5 6 and 8 1 ma these clays formed during hydrothermal alterations related to the waning phases of the various volcanic episodes of the area clinoptilotites from the zeolitized tephra units from the late jurassic morrison formation gave discordant dates ranging from 154 to 83 ma whereas the illite smectites from the bentonite beds of the same formation yielded two age groups 29 69 38 2 and 53 7 56 ma all the k ar results were interpreted using the k ar isochron method and in most cases the isochron ages are similar to the conventional k ar results the altered tephra layers provide diagnostic regional marker horizons in addition to recording concisely the time of diagenetic processes in various geologic settings

time lapse seismic analysis of pressure depletion in the southern gas basin in the southern gas basin sgb of the north sea there are many mature gas fields where time lapse monitoring could be very beneficial in extending production life however the conditions are not immediately attractive for time lapse seismic assessment this is primarily because the main production effect to be assessed is a pore pressure reduction and frame stiffening because of gas production in tight sandstone reservoirs that also have no real seismic direct hydrocarbon indicators modelling based on laboratory measurements has shown that such an effect would be small and difficult to detect in seismic data this paper makes two main contributions firstly this is to our knowledge the first time lapse study in the sgb and involves a real data assessment of the viability for detecting production in such an environment secondly the feasibility of using markedly different legacies of data in such a study is addressed including an assessment of the factors influencing the crossmatching from the latter it is found that significant spatially varying time shifts need to be and are successfully resolved through 3 d warping after the warping the primary factors limiting the crossmatching appear to be residual local phase variations possibly induced by the differing migration strategies structure reverberations and different coherencies of the volumes caused by differences in acquisition structure azimuth and acquisition fold despite these differences a time lapse amplitude signature is observed that is attributable to production the character of the 4 d amplitude anomalies may also indicate variations in stress sensitivity e g because of zones of fracturing additionally warping derived time attributes have been highlighted as a potential additional avenue for detection of pressure depletion in such reservoirs although the effects are subtle they may indicate changes in stress pressure in and around the reservoir because of production however to fully resolve the subtle time lapse effects in such a reservoir the data differences need to be better addressed which may be possible by full re processing and pre stack analysis but more likely dedicated 4 d acquisition would be required