seismic noise based time lapse monitoring of the valhall overburden we used two vintages of ambient seismic noise recorded at the valhall life of the field seismic network in 2004 and 2005 to perform a passive time lapse imaging of the subsurface first the cross correlations between each pair of stations were computed for both vintages to extract scholte waves second the relative velocity variations between the 2004 and 2005 cross correlations were measured on the ballistic waves using the moving window cross spectral technique finally the best quality relative velocity variation measurements were regionalized using a modified eikonal tomography technique the results albeit noisy because of the short duration of the available records show a large patch of increased seismic velocity in the southern part of the network and a weaker anomaly in the northern part the southern increase of velocity can be attributed to the exploitation of the southern flank of the valhall reservoir with new wells and is in good agreement with a previous time lapse study using scholte waves

continuous seismic surveillance of valhall field since the permanent seismic system was installed over valhall field five years ago 11 surveys have been collected each designed acquired and recorded with a high repeatability and efficiency the time lapse 4d data have been processed using a consistent and fast workflow that generates results within weeks the fast turnaround ensures that information is relevant and has maximum impact on short and long term management decisions

a cross anisotropic elastoplastic model applied to sedimentary rocks abstract strength and deformability properties of sedimentary rocks are difficult to characterize as these geomaterials show anisotropic mechanical behavior which cannot be adequately evaluated by an isotropic constitutive model this essay proposes a cross anisotropic elastoplastic model to evaluate stress strain relationships of sedimentary rocks the approach couples the twelve parameter lade kim isotropic model with a non uniform scaling of the stress tensor and includes two scaling parameters that link the orientation of the bedding planes with the loading direction the anisotropic model parameters can be conveniently determined using bayesian analysis we illustrate our method using triaxial tests on a variety of confining stresses and bedding plane orientations for a travertine and a tournemire shale our results demonstrate that the predicted maximum deviatoric stresses and the simulated stress strain curves are shown to be in good agreement with the measured data

determination of strength parameters and quality assessment of denizli travertines sw turkey abstract travertine carbonate rich sedimentary rocks which are deposited by hot and cold waters as with all natural stones strength properties of travertines have great importance depending on the using conditions and places naturally porous structure of travertines is the most important parameter affecting the overall strength denizli basin is one of the world s major travertine regions in this study strength properties and relations between obtained parameters of denizli travertines were studied uniaxial compressive strength ucs values of travertines are widely ranging between 9 58 and 132 32 mpa noche type travertines are identified to have 59 100 higher strength than other type of travertines flexural strength under concentrated load 3 point flexural strength fls 3 and flexural strength under constant moment 4 point flexural strength fls 4 tests which are required for ce certification were also carried out on travertine samples between these tests linear relationship expressed as fls 4 0 98 fls 3 0 094 was found variations of strength parameters depending on the stone cutting type have been presented for the first time in this study it is found that the strength values under parallel loading to lamination are 1 44 times higher than the perpendicular loading

water absorption and p wave velocity changes during freeze thaw weathering process of crosscut travertine rocks the turkish travertine is widely used in the domestic and foreign construction industry as slabs and tiles in this study the travertine samples were obtained from four different quarries located in the part of southwestern turkey mineralogical and petrographic properties of the travertine rocks were studied using a polarizing optical microscope and sem the laboratory tests mechanical and physical properties capillary water absorption freeze thaw f t process p wave velocity were performed according to technical specification european standard ts en standards the pore size distribution was determined by means of high pressure mercury porosimetry mip the most of the pores 80 of tested travertine have a pore access diameter of 0 1 m some engineering properties of the rock are severely affected by f t cycles such as ultrasonic p wave velocities water absorption weight and strength the porosity of the travertine presents significantly higher values after the cycles of freeze thaw which also leads to the increase in the absorption by immersion the water absorption method showed that water absorption weight of the specimens varied from 0 32 to 0 88 after the 25 period the freeze and thaw effects of the samples which were tested after exposing to water were measured at a certain time the obtained dry saturated and frozen p wave velocities were examined by the changes of four travertine samples p wave velocity increase is in the range of 4 99 5 97 for tested travertine rocks these studies explain that the p wave velocity changes in freezing travertine exclusively due to changing velocities of pore infill i e water air and ice

characterization and quality assessment of granitic building stone deposits a case study of two different portuguese granites abstract several factors determine building stone exploration in order to maximize the extraction processing and application of these natural materials some factors are intrinsic to stones such as their physical mechanical properties while others are related to their exploitability such as quarry reserves or fracturing density during an exploration campaign these factors are not always considered or properly weighed in terms of the negative consequences on quarry activities or rock behaviour under particular conditions in this study two well known portuguese granites are assessed to highlight the main factors these granites have different characteristics weathered and sound and are exploited in quarries with different joint densities the most relevant physical mechanical properties were evaluated and related to the specific petrophysical features of each granite the fracture patterns were identified in the quarries and then modelled in order to compute the quarry yield the weathered granite shows an important microcrack network and a general alteration of the rock forming minerals which has an important impact on its physical mechanical properties and on the resistance to environmental factors moreover the extreme differences in the degree of weathering require careful choices for the possible applications in both quarries the joint sets are similar to the regional faulting but some random joints can be found and consequently diminish the quarry yield the development of horizontal sheet joints during the exploitation process could have a great influence on the quarry productivity if they are not used do delimitate the extracted blocks the modelling of the natural fracture pattern allows us to determine the potential volume of blocks that could be exploited however the quality of the information gathered could lead to an over estimation of the quarry production this example shows the importance of the exhaustive researches during a building stone assessment campaign

sedimentology three dimensional geobody reconstruction and carbon dioxide origin of pleistocene travertine deposits in the ballik area south west turkey the denizli basin in the west anatolian extensional province in western turkey is well known for its numerous travertine occurrences a combined sedimentological diagenetic and geochemical investigation is executed on the ece and faber travertines of the ballk area the largest travertine site in the denizli basin the first aim of this study is the reconstruction of a three dimensional geo model in combination with a detailed sedimentological description from fabric to lithotype lithofacies and geobody scale with a focus on integrating pore typing the second aim involves the delineation of the co2 origin of ancient travertine precipitating waters peloidal phyto and dendritic lithotypes dominate the studied travertines and honeycomb and bacteriform shapes and encrusted bacterial or fungal filaments related to their fabrics suggest a microbial influence the environment of travertine precipitation evolved from dominantly sub aqueous as represented by the sub horizontal and biostromal reed travertine facies to dominantly sub aerial in a thin water film resulting in the cascade waterfall and biohermal reed travertine facies a general progradation of the travertine mound is indicated by the occurrence of stacked waterfall travertines this results in sigmoidal clinoforms inside a general mound boundary configuration strontium and oxygen carbon isotope signatures of the travertines point to a mixing mechanism of palaeofluids with deeply originated heavy carbon co2 with lighter carbon co2 of shallow origin these deposits can thus be considered as endogenic travertines carbonates of the lycian nappes acted as main parent carbon source rocks the relative contribution of the lighter carbon isotopes is most likely to have originated from organic matter or soil co2 this study provides a unique three dimensional insight into the ballk travertine architecture that potentially can be used as an analogue for subsurface travertine reservoirs worldwide and illustrates the importance of the combined use of c 13 and sr 87 sr 86 signatures in the delineation of the co2 origin of travertine precipitating waters

reply to comments by s yagiz on determination of strength parameters and quality assessment of denizli travertines sw turkey by ibrahim cobanoglu and sefer beran celik engineering geology 129 130 2012 38 47

fracture networks and strike slip deformation along reactivated normal faults in quaternary travertine deposits denizli basin western turkey abstract the denizli basin in the west anatolian extensional province in western turkey is known for its numerous quaternary travertine occurrences travertine morphology is often dependant on the relative position of the deposition with respect to basin bounding faults the travertine occurrences examined in this study are situated at the intersection of the locally e w oriented denizli basin and the adjacent ne sw oriented baklan graben in the ne based on an extensive field campaign including lidar scanning several high resolution fault fracture maps of five large quarries 300 m in length and 60 m in height are constructed in which this world class travertine deposit is currently excavated a structural analysis is performed in order to determine the tectonic overprinting of the travertine body and to derive the stress states of the basin after travertine deposition the mostly open non stratabound joints are several tens of metres long and often bifurcate creating a dense fracture network minor infill of the joints resulted in the presence of a few colour banded calcite veins based on the e w ne sw and nw se orientation of three dominant joint sets it is concluded that the joint network is caused by local n s extension alternated by nw se and ne sw extension exemplifying the presence of stress permutations in the quaternary high angle e w to wnw ese faults cross cut the quarries faults are filled with travertine debris and clastic infill of above lying sedimentary units indicative of the open nature of the faults the specific e w fault orientation in the locally e w trending denizli basin indicates that they initiated as normal faults a paleostress inversion analysis performed on kinematic indicators such as striations on the clayey fault infill and the sinistral displacement of paleosols shows that some of the normal faults were reactivated causing left lateral deformation in a transient strike slip stress field with a ne sw oriented 1

pleistocene holocene tectonic reconstruction of the ballik travertine denizli graben sw turkey de formation of large travertine geobodies at intersecting grabens abstract travertine geobodies have been identified as potential reservoir analogues to carbonate build ups in pre salt hydrocarbon systems to investigate travertine geobody deformation faults were mapped in 35 travertine quarries that excavate the ballik travertine i e a c 12 5 km2 large travertine geobody that precipitated at the intersection of the ne margin of the denizli basin and neighbouring baklan graben sw turkey this travertine precipitated from cooling carbonate saturated thermal spring waters that resurfaced along the margin fracture fault network and through neogene unconsolidated underlying sediments from the denizli basin floor to the uplifted graben shoulders fault orientation is dominantly wnw ese oriented with major basin faults showing a left stepping trend along the upper denizli margin travertine is only deformed by extensional normal faults along the lower margin travertine starts with a subhorizontal facies but evolves to a travertine facies formed by a sloping topography with a domal architecture paleostress inversion of fault slip data reveals that an early pleistocene nne ssw extensional transtensional phase initiated the wnw ese oriented graben facing normal fault network in the middle pleistocene the ballik fault network was left lateral strike slip reactivated because it acted as a transfer zone between the nw se extending neighbouring baklan basin and nw se extension along ne sw oriented margin faults of the dghs in this stress configuration travertine precipitated along the sw margin fault of the baklan graben after strike slip reactivation a late pleistocene to current nne ssw extensional stress regime reinstalled during which margin faults widened and active travertine precipitation moved to more central parts of the dghs as different tectonic regimes affect graben intersections reservoir analogues can have a complex deformation history driven by fault reactivation and recurrent stress permutations this study concludes that large travertine geobodies can form at graben intersections because of their susceptibility to enhanced fluid flow through the complex fault fracture network

calendar time interpolation of amplitude maps from 4d seismic data a calendar time interpolation method for 2d seismic amplitude maps done in two steps is presented the contour interpolation part is formulated as a quadratic programming problem whereas the amplitude value interpolation is based on a conditional probability formulation the method is applied on field data from the sleipner co2 storage project the output is a continuous image movie of the co2 plume besides visualization the output can be used to better couple 4d seismic to other types of data acquired the interpolation uncertainty increases with the time gap between consecutive seismic surveys and is estimated by leaving a survey out blind test errors from such tests can be used to identify problems in understanding the flow and possibly improve the interpolation scheme for a given case field life cost of various acquisition systems and repeat frequencies are linked to the time lapse interpolation errors the error in interpolated amplitudes increased by 3 4 per year of interpolation gap for the sleipner case interpolation can never fully replace measurements

changes in phosphorus biogeochemistry along an estuarine salinity gradient the iron conveyer belt we used sequential extractions to quantify different forms of particulate phosphorus pp in sediments along the salinity gradient of the patuxent river estuary about 50 90 of the pp was phosphate bound to iron oxides fe p and 8 30 was organic p org p loosely sorbed phosphate sorb p detrital apatite and authigenic plus biogenic apatite each made up 10 of the pp suspended sediments from the watershed and deposited sediments in tidal freshwater had the highest concentrations of fe p ranging about 30 55 mmol g21 sediment as pore water salinity increased to 7 along the estuarine gradient fe p declined to 15 25 mmol g21 org p increased from 4 to 10 mmol g21 sorb p increased from 0 5 to 2 5 mmol g21 and total sediment pp declined from 60 to 40 mmol g21 concentrations of pore water solutes also changed with salinity as salinity increased dissolved fe and ammonium decreased while dissolved phosphate increased near the freshwater end of the gradient the molar ratio of pore water ammonium phosphate was generally 16 the redfield ratio and ranged up to 700 while at the saline end of the gradient the ratio was generally 16 and ranged down to 1 5 our observations are consistent with the hypothesis that phosphate is released from terrigenous sediments when they are deposited in saline portions of the estuary where sulfide may enhance dissolution of fe p and form fe sulfide precipitates such phosphate release may contribute to the generally observed switch from phosphorus limitation in freshwater to nitrogen limitation in coastal marine water

investigation of induced microseismicity at valhall using the life of field seismic array here we use data from the life of field seismic lofs surface array in conjunction with a migration style approach to locate microseismic events in valhall field during 6 5 hours of hydraulic fracturing we identify an event distribution that extends roughly 300 m vertically and 200 m horizontally with sources both within the chalk layer containing the reservoir and the overburden however the temporal distribution of the events is not consistent with the induced fracturing extending into the overburden instead the synchronous increase in event activity with downhole pressure could be interpreted as evidence that elastic wavefronts originating from well activity trigger movement on faults where the in situ stress is very close to that required for failure

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

integration of the life of field seismic data with the reservoir model at the valhall field the frequent time lapse observations from the life of field seismic system across the valhall field provide a wealth of information the responses from the production and injection wells can be observed through time shift and amplitude changes these observations can be compared to modelled synthetic seismic responses from a reservoir simulation model of the valhall field the observed differences between the observations and the modelling are used to update and improve the history match of the reservoir model the uncertainty of the resulting model is reduced and a more confident prediction of future reservoir performance is provided a workflow is presented to convert the reservoir model to a synthetic seismic response and compare the results to the observed time lapse responses for any time range and area of interest correlation based match quality factors are calculated to quantify the visual differences this match quality factor allows us to quantitatively compare alternative reservoir models to help identify the parameters that best match the seismic observations three different case studies are shown where this workflow has helped to reduce the uncertainty range associated with specific reservoir parameters by updating various reservoir model parameters we have been able to improve the match to the observations and thereby improve the overall reservoir model predictability the examples show positive results in a range of different reservoir modelling issues which indicates the flexibility of this workflow and the ability to have an impact in most reservoir modelling challenges

burying receivers for improved time lapse seismic repeatability co2crc otway field experiment 4d seismic is widely used to remotely monitor fluid movement in subsurface reservoirs this technique is especially effective offshore where high survey repeatability can be achieved it comes as no surprise that the first 4d seismic that successfully monitored the co2 sequestration process was recorded offshore in the sleipner field north sea in the case of land projects poor repeatability of the land seismic data due to low s n ratio often obscures the time lapse seismic signal hence for a successful on shore monitoring program improving seismic repeatability is essential stage 2 of the co2crc otway project involves an injection of a small amount around 15 000 tonnes of co2 ch4 gas mixture into a saline aquifer at a depth of approximately 1 5 km previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions near surface geology and farming activities in order to improve time lapse seismic monitoring capabilities a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability a small scale trial of such an array was conducted at the otway site in june 2012 a set of 25 geophones was installed in 3mdeep boreholes in parallel to the same number of surface geophones in addition four geophones were placed into boreholes of 1 12m depth in order to assess the gain in the signal to noise ratio and repeatability both active and passive seismic surveys were carried out the surveys were conducted in relatively poor weather conditions with rain strong wind and thunderstorms with such an amplified background noise level we found that the noise level for buried geophones is on average 20 db lower compared to the surface geophones the levels of repeatability for borehole geophones estimated around direct wave reflected wave and ground roll are twice as high as for the surface geophones both borehole and surface geophones produce the best repeatability in the 30 90 hz

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

predicting the unconfined compressive strength of the breathitt shale using slake durability shore hardness and rock structural properties abstract compressive strength is the most widely used design parameter in the construction industry and in rock engineering for example bieniawski bieniawski z t estimating the strength of rock materials is j s afr inst min metall 1974 74 312 320 reported that mining engineers request the uniaxial compressive strength ucs more often than any other rock property however standards set for specimen preparation are very demanding therefore it is quite difficult and sometimes impossible to fulfill these requirements using weak rocks and especially shales this paper evaluates the use of the slake durability and shore hardness tests to estimate ucs based on laboratory correlations performed for this study and others and based on analysis of structural and physical material properties affecting both strength and durability

generating value from 4d through efficient integration abstract the use of time lapse 4d seismic at bp now has a track record stretching back more than 20 years in the north sea reservoir types such as tertiary turbidites and cretaceous chalks produced clear 4d signals and uptake increased rapidly in the late 1990s in the gulf of mexico 4d was generally more challenging due to greater subsurface complexity but the industry made breakthroughs with modern acquisition systems such as ocean bottom nodes obn the challenge now is to maximize the value of existing and new surveys by better integration of 4d into reservoir management as part of this effort the authors implemented fit for purpose workflows for 4d assisted history matching 4dahm and 4d geomechanical modeling in an example from west of the shetland isles uk running the 4dahm match quality tool on multiple monitors from the clair field allows the field team to quickly see how changes in the reservoir simulation model affect the match to the 4d and identify areas of concern the 4d geome

modeling the effect of freezing and thawing for sedimentary rocks engineering parameters of rocks mostly depend on internal properties such as mineralogical composition and texture physical and chemical processes can cause changes in these engineering parameters freeze thaw is one of the most detrimental phenomena affecting rock properties this study focuses on the effect of freeze thaw cycles on the engineering properties of sedimentary rocks the degree of alteration in the rock type of cement and the presence of fossils were decisive on rock disintegration during freeze thaw cycles models from two different studies that investigated the weathering behavior under freeze thaw cycles were applied to the test results of this study simple and multiple regression analyses were performed on the test results to predict the ucs values of rocks after 25 cycles using the results of simply applicable tests at the initial conditions without having to conduct tedious and destructive freeze thaw tests

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