coupled thmc models for bentonite in an argillite repository for nuclear waste illitization and its effect on swelling stress under high temperature abstract subsurface manipulations such as those expected from the disposal of heat emanating radioactive waste in deep repositories can induce strongly coupled thermal t hydrological h mechanical m and chemical c processes adequate coupled thmc models are highly desirable or even indispensable for performance assessment of such repositories for examples for the analysis of bentonite based engineered barrier system ebs surrounding the emplaced waste in this study we present coupled thmc model simulations of a generic nuclear waste repository in an argillite with a bentonite based buffer the objective is to evaluate the chemical changes in the ebs bentonite and their effect on mechanical behavior under high temperature attempting to shed light on whether ebs bentonite can sustain temperatures higher than 100 c without significant impact on barrier s performance two scenarios were simulated for comparison a case in which the temperature near the waste canister peaks at 200 c and a case in which the temperature at the same spot culminate with about 100 c simulations for a generic case with kunigel vi bentonite as backfill and opalinus clay as host rock were conducted for 1000 years and reported in the previous study zheng et al 2015 in this paper simulations for 100 000 years have been done for two types of bentonite based buffer materials kunigel vi and febex bentonite this enables us to evaluate how different types of bentonite behave in terms of the illitization and its impact on swelling stress and whether we can generalize these results to support decision making the simulations show the occurrence of illitization in the bentonite buffer and the enhancement of illitization under high temperature however febex bentonite undergoes less illitization mainly due to the higher ion concentration in pore water and the lower content of k feldspar in the bentonite mineral composition moreover the reduction of swelling stress by chemical changes is more pronounced for kunigel vi bentonite than for febex bentonite overall the results of our model simulations suggest that an argillite repository with a bentonite based ebs that is similar to febex bentonite could sustain temperatures much higher than 100 c as far as illitization concerns model results also reveal that illitization is stabilized after about 2000 years in bentonite near the waste package but continues in bentonite near the bentonite argillite interface which manifests the strong effect of geochemical interaction between ebs bentonite and host rock on long term illitization in bentonite

tectonic quiescence punctuated by strike slip movement influences on late jurassic sedimentation in the moray firth and the north sea region

changes in physical properties of a reservoir sandstone as a function of burial depth the etive formation northern north sea abstract rock physical properties like velocity and bulk density change as a response to compaction processes in sedimentary basins in this study it is shown that the velocity and density in a well defined lithology the shallow marine etive formation from the northern north sea increase with depth as a function of mechanical compaction and quartz cementation physical properties from well logs combined with experimental compaction and petrographic analysis of core samples shows that mechanical compaction is the dominant process at shallow depth while quartz cementation dominates as temperatures are increased during burial at shallow depths

characterization of fault zones for reservoir modeling an example from the gullfaks field northern north sea a fault seal study was performed for part of the gullfaks field north sea as an aid to improve reservoir management of this complexly faulted structure the operator s statoil map data were used to build a three dimensional model of the fault network together with petrophysical logs this model was used to compute the variation of fault seal potential shale gouge ratio or fault zone percent shale on each fault surface pressure data from exploration and production wells have been projected onto the modeled fault surfaces the preproduction pressure differences at sealing faults separating different hydrocarbon columns provide information about the capillary seal at the faults across fault pressure drops at particular times during production also have been displayed these dynamic pressure drops provide a guide to the permeability of the fault zones after flow has started the calculated fault parameters displacement and shale gouge ratio can be converted to fault zone thickness and permeability and can be used to derive fault transmissibility modifiers for reservoir simulations maps have been produced showing reservoir juxtaposition areas and calculated fault permeabilities along faults throughout the study area these parameters are compatible with the recorded pressure history and tracer movement between wells and will enable key reservoir management decisions to be tested and optimized

contrasting styles of late jurassic syn rift turbidite sedimentation a comparative study of the magnus and oseberg areas northern north sea abstract contrasting types of sediment gravity flow and hemipelagite deposition are recorded by the late jurassic syn rift successions in the magnus and oseberg areas in the northern north sea in both areas the late jurassic rift interval was characterized by recurrent tectonic phases during the late oxfordian to early volgian the penguin halfgraben in the magnus area received a significant amount of coarse clastics and can be regarded as an example of a well fed deeper marine riftbasin periods with high rates of extensional faulting are characterized by isolated sediment gravity flow lobes which stack in an uneven albeit downdip shifting or backstepping manner the stratigraphic motif of these intervals is overall mud prone with coarse clastics represented by thick conglomerate sandstone mudstone aprons along the basin bounding masterfaults in contrast periods with low rates of extensional faulting are characterized by basinwide sheet like parallel layered sediment gravity flow packages which infill the riftbasin in a progradational manner from the middle volgian the penguin halfgraben became sediment starved and shows a similar development to the oseberg area in the oseberg area the late jurassic syn rift succession provides a typical example of a sediment starved deeper marine riftbasin sediment gravity flow deposition in this area is limited to periods of high rates of extensional faulting these coarser clastic depositional episodes mimic their counterparts in the penguin halfgraben being characterized by mud prone strata with localized isolated sediment gravity flow lobes and footwall derived clastic wedges along the basin bounding masterfaults in contrast to the well fed basins the intervening stages of tectonic quiescence in the sediment starved basins are characterized by basinwide blanketing of clay commonly of high source rock potential in both basins the rotational tilt packages can be subdivided into an early a climax and a late syn rotational interval based on the architecture of their contained facies tracts these depositional episodes reflect the temporal evolution of the riftbasins catchment areas and their linked depositional systems it is mainly the nature and amount of sediment supply during the following tectonic quiescence or post rift stages that determine whether the riftbasin remained sediment starved or became infilled simplified sequence stratigraphic models are of limited use in the analyses and lithology prediction of riftbasin infills as individual halfgrabens often have their own specific infill history and hence characteristic syn rift stratigraphic signature the main controls on the variability of these deeper marine syn rift sediment gravity flow hemipelagite packages are the style and rate of extensional faulting sediment supply the source area s sediment yield potential and calibre and the halfgraben configuration and location with respect to the main hinterland areas

the petroleum geology of the unst basin north sea abstract the unst basin is situated in the northern north sea between the east shetland basin and the shetland isles the basin is essentially a three armed permo triassic fault controlled basin containing up to 3600 m of red beds this is overlain by a westerly thickening jurassic and early cretaceous sequence the stratigraphy of which is very similar to that of the east shetland basin in particular the brent group 140 m humber group 685 m and cromer knoll group 300 m are well represented as a result of laramide uplift of the area the thick upper cretaceous and palaeocene strata of the east shetland basin are absent from the unst basin this uplift resulted in substantial erosion within the unst basin providing the major source for palaeocene sands in the viking graben and the faeroes basin late palaeocene and younger tertiary strata transgress westwards across this erosion surface petroleum exploration within the basin culminated in the drilling of two exploration wells these wells encountered potential reservoir and source rocks in the jurassic section however geochemical analyses indicate these source rocks are immature for hydrocarbon generation within the unst basin it is concluded that the unst basin has a low petroleum potential

footwall uplift associated with late jurassic normal faulting in the northern north sea tilted fault blocks in the north sea show varying degrees of erosion such footwall erosion is predicted by the domino model of extension in which rigid fault blocks rotate as extension proceeds profiles of three north sea fields snorre brent and heather are analysed to estimate the amount of uplift that accompanied late jurassic normal faulting and these estimates are compared with the footwall uplift predicted by the domino model agreement between observed and predicted uplift is excellent varying from 1 km at snorre to c 100 m at heather for a given amount of extension large fault blocks tend to be bounded by large faults and to show a greater degree of erosion the brent province of the northern north sea is an area of prolific hydrocarbon discoveries almost all of the major oil fields occur in tilted fault blocks which were formed by late jurassic extension and subsequently buried by cretaceous tertiary thermal subsidence badley et al 1988 marsden et al 1990 the crests of the tilted blocks are typically eroded or degraded with varying amounts of middle lower jurassic and upper triassic section removed this footwall erosion is commonly ascribed in the literature to pre rifting doming ziegler 1982 heterogeneous stretching coward 1986 local transpression beach 1985 or even regional compression frost 1987 the purpose of this paper is to show that the uplift and degradation is a direct consequence of the late jurassic normal faulting and fault block rotation the degree of uplift is related in a simple way to the size across strike of

strain migration during multiphase extension observations from the northern north sea many rifts develop through multiphase extension it can be difficult however to determine how strain is distributed during reactivation because structural and stratigraphic evidence associated with earlier rifting is often deeply buried using 2 d and 3 d seismic reflection and borehole data from the northern north sea we examine the style magnitude and timing of reactivation of a preexisting permian triassic rift phase 1 fault array during a subsequent period of middle jurassic to early cretaceous rift phase 2 extension we show that rift phase 2 led to the formation of new n s striking faults close to the north viking graben but did not initially reactivate preexisting rift phase 1 structures on the horda platform we suggest that at the beginning of rift phase 2 strain was focused in a zone of thermally weakened lithosphere associated with the middle jurassic north sea thermal dome rather than reactivating extant faults diachronous reactivation of the permian triassic fault network eventually occurred with those faults located closer to the middle jurassic to early cretaceous rift axis reactivating earlier than those toward the eastern margin this diachroneity may have been related to flexural down bending as strain became focused within the north viking graben and or the shifting of the locus of rifting from the north sea to the proto north atlantic our study shows that the geometry and evolution of multiphase rifts is not only controlled by the orientation of the underlying fault network but also by the thermal and rheological evolution of the lithosphere and variations in the regional stress field

slide block of jurassic sandstone and submarine channels in the basal upper cretaceous of the viking graben norwegian north sea abstract seismic facies analysis of a seismically anomalous sequence of mid cretaceous cenomanian turonian basin fill in lease block 34 8 viking graben norwegian north sea reveals a possible slide block composed of jurassic age brent group strata that apparently detached from the adjacent structural high 34 8 structure and slid downslope onto lower cretaceous sediments in the viking graben floor in addition this mid cretaceous sequence contains two broad submarine channels that trend southward into the graben from the southern tip of the slide block and the adjacent structural high the channels appear to be erosional features formed by turbidity currents and mass wasting processes the brent slide block may represent an additional hydrocarbon prospect within the lease block 34 8

palaeoecology of syn rift topography a late jurassic footwall island on the josephine ridge central graben north sea abstract understanding rift topography is essential for determining source areas sediment pathways and the type of sediment delivered to a rift basin factors essential for interpreting petroleum systems in ancient rifts here we investigate upper jurassic sediments from the josephine ridge region of the central graben north sea by integrating geophysical palynological petrophysical and sedimentological datasets to analyse the palaeoenvironments of the jade and judy horsts the tops of which are not preserved interpretation of geophysical and petrophysical data together with core descriptions shows study wells to step progressively away from the josephine ridge into adjacent grabens one hundred and five palynological samples from six wells range from the oxfordian to the lower tithonian spanning the syn rift period of the central graben samples from the adjacent grabens and the jade horst are rich in dinoflagellate cysts and possess

the middle jurassic oseberg delta northern north sea a sedimentological and sequence stratigraphic interpretation the aalenian oseberg formation 0 80 m thick is an important reservoir unit in the middle jurassic brent group in the northern north sea consisting of multiple sets of sandy gilbert type deltas small scale 1 5 10 m fining upward units seen in the gamma ray log correspond with individual delta sets as independently confirmed by steepening upward trends seen in the dip log within each set the steep foreset slopes typically show thinly bedded sandstone facies avalanche grain flows whereas the lower foreset slopes toesets and bottomsets are formed largely by massive sandstone facies sandy debris flows on an intermediate scale up to 40 m the gamma ray logs show both fining upward and coarsening upward trends through stacked delta sets and these trends traceable between wells are interpreted in terms of decelerating and accelerating rates of relative sea level rise respectively the relative abundance of the sandy debris flow deposits reflects a periodic and significant instability of the delta s upper foreset slope probably during times of increased water depth in front of the delta the normal progradation of individual gilbert type sets however is likely to have been along a subhorizontal topography during periods of little or no change in water depth the long term change to produce the observed vertical stacking of deltaic sets was one of a generally rising relative sea level modeling of the sea level rise in a steplike manner can account for the rarity of topsets the progressive eastward truncation of the underlying drake formation on the horda platform by the oseberg formation suggests tectonic uplift and a lowstand of sea level immediately prior to the development of the oseberg deltas the oseberg formation is thus seen as a lowstand prograding wedge that developed during an interval of relatively high sediment supply and a variably rising sea level culminating in the latest aalenian flooding seen in the base of the overlying rannoch formation the dip log data integrated with cores and other logs are critical to correctly interpreting the reservoir s internal architecture the slope readjustment model predicts that the development of stacked massive reservoir sandstones of oseberg type will occur preferentially in local areas of high subsidence or syndepositional faulting or where there is deeper water in the lee of already existing fault scarps

influence of fault reactivation during multiphase rifting the oseberg area northern north sea rift abstract multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults the resulting fault patterns tend to be complex and difficult to decipher in this work we use seismic reflection data to examine the evolution of a normal fault network in the oseberg fault block in the northern north sea rift system a rift system that experienced permian early triassic and middle jurassic early cretaceous rifting and exhibits n s nw se and ne sw oriented faults both n s and nw se striking faults were established during the permian early triassic rifting as indicated by triassic growth packages in their hanging walls in contrast the ne sw striking faults are younger as they show no evidence of permian early triassic growth and offset several n s and nw se striking faults structural analysis show that a new population of nw se striking faults formed in the lower middle jurassic inter rift period together with reactivation of n s striking permian early triassic faults indicating a ne sw inter rift extension direction during the middle jurassic early cretaceous rifting faults of all orientations n s nw se and ne sw were active however faults initiated during the middle jurassic early cretaceous rifting show mainly n s orientation indicating e w extension during this phase these observations suggest a reorientation of the stress field from e w during the permian early triassic rift phase to ne sw during inter rift fault growth and back to e w during the middle jurassic early cretaceous rift phase in the oseberg area hence the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population

development of rift basins illustrated by the structural evolution of the oseberg feature block 30 6 offshore norway the mesozoic tilted fault block in norwegian north sea block 30 6 containing the giant oseberg oil and gas field is used to illustrate basin development during the jurassic and cretaceous there is seismic evidence for an early rifting phase in the northern viking graben on which the jurassic cretaceous rifting phase early bathonian to berriasian is overprinted the oseberg structure is representative of other fault blocks bordering the northern viking graben axis planar normal faults and listric faults which were restricted to the rifting phase dominate both fault types exhibit syn fault sedimentation listric faulting is recognized on seismic sections by the differential tilting reverse drag antithetic faulting and a wedge shaped syn rift reflector package the initiation of rifting is dated by baselap onto pre rift reflectors and cessation is dated by an unconformity beneath the generally onlapping post rift sediments steeply dipping planar normal faults often active along previously established fault zones played a significant part in the post rift development of the basin the last movement on planar normal faults in the oseberg fault scarp becomes younger away from the rift axis and this produced the complex fault scarp visible on many seismic lines the topography defined by the post rift unconformity is a composite surface which formed in response to subsidence processes it is not the result of orogenic events such as the kimmerian 9orogeny9 footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests

modelling of bed contours and cross sections adjacent to planar normal faults the geometry of beds in the volume surrounding a single blind planar fault depends on i the axial ratio of the fault surface ellipse ii the ratio between the maximum displacement and the maximum dimension of the fault surface iii the displacement distribution on the fault surface from the point of maximum displacement to zero displacement at the tip line loop fault surface displacement profile and iv the rate at which the displacement decreases to zero along a normal to the fault surface reverse drag displacement profile these relationships which are either known or can be estimated are incorporated in a computer model which generates structural contours on horizons intersected by a planar fault structural contour patterns also vary with the pre faulting dip and strike of beds the dip and strike of the fault and the level at which a bed intersects the fault surface when the boundary conditions are relaxed to include synsedimentary faults the ratio of hangingwall to footwall displacement varies systematically with fault dip a synthetic structural contour map is matched with that of an actual fault model isopachs based on simple depositional models are generated for synsedimentary units cross sections are generated for synsedimentary faults by sequential fault growth and sedimentary deposition and show features similar to actual cross sections the soft domino model is applicable primarily to dip slip tectonic faults with maximum displacements of up to about 5 km listric faults are not considered

conditions and timing of quartz cementation in brent reservoirs hild field north sea constraints from fluid inclusions and sims oxygen isotope microanalysis abstract the conditions and timing of quartz cementation in the brent sandstones in the hild field norwegian north sea were constrained on the basis of oxygen isotope microanalysis and fluid inclusion microthermometry combined with optical and cathodoluminescence cl microscopy studies samples of the tarbert and the ness formations were investigated in three different wells presently lying at 3 8 4 3 km subsea and at 140 155 c quartz cement is present in all wells abundance varies from 3 to 26 and tends to increase with depth of burial two distinct separate episodes of quartz cementation referred to as q1 and q2 are readily distinguished by cl microscopy the two episodes are also recognized in the bimodal distribution of fluid inclusion temperatures and oxygen isotope microanalyses the data indicate that q1 quartz formed in the early tertiary 65 35 ma at 95 110 c and 2 3 3 0 km burial depth and that q2 mainly precipitated in the oligocene miocene 40 10 ma at 125 135 c and 3 1 3 7 km q1 quartz precipitation follows the onset of overpressuring in the reservoir while precipitation of q2 seems to slightly precede and accompany the main phase of oil filling 35 10 ma secondary ion mass spectrometry sims oxygen isotope microanalyses yield 18o values ranging from 17 to 25 averaging 23 2 for q1 and 19 5 1 5 for q2 calculated 18o values of quartz forming waters are similar for q1 and q2 ranging from 1 to 3 and are similar to the 18o value 2 of present day formation water in the reservoir quartz cementation in the brent reservoir of the hild field occurred during deep burial at high temperature from evolved 18o rich basinal water most likely derived from the viking graben two episodes of enhanced quartz precipitation are recorded around 100 c and 130 c no evidence was found for any significant contribution of 18o depleted jurassic meteoric water and or low temperature precipitation of quartz cement

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

growth and linkage of a segmented normal fault zone the late jurassic murchison statfjord north fault northern north sea abstract the structure of the 25 km long northeastern portion of the murchison statfjord north fault zone and adjacent syn rift stratigraphy are integrated to reconstruct the temporal and spatial evolution during c 30 5 myr of late jurassic north sea rifting based on a structural analysis d d data alone approximately 14 precursor fault strands are identified incorporation of stratigraphic data shows that only six of these strands were important in controlling stratal architecture and distribution three main stages in the evolution of the fault zone are recorded in the syn rift stratigraphy and are biostratigraphically constrained these are 1 following initiation of rifting six isolated fault strands developed each 9 km long fault segments separated by a 2 km wide relay ramp that controlled the stratigraphy for at least the following c 10 5 myr and 3 the two fault segments hard linked forming a single continuous fault trace during the final c 7 myr of rifting the results of this study reveal the necessity to adopt an integrated structural and stratigraphic approach when reconstructing the evolution of normal fault zones the results may also help to further constrain models of fault evolution

regressive and transgressive cycles in a rift basin depositional model and sedimentary partitioning of the middle jurassic hugin formation southern viking graben north sea abstract the jurassic hugin formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the sleipner area in the norwegian north sea the formation encompasses coarsening upward units of mouth bar and shoreface facies interpreted to record delta outbuilding during regression and fining upward units with tidal channel dune and tidal flat facies interpreted as part of an estuary environment during transgression the correlations reveal that the studied part of the hugin formation consists of 8 sequences each with a transgressive and a regressive unit representing the transgressive systems tract and the highstand systems tract respectively the sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the viking graben rifting led to the development of an elongate graben where tidal currents were amplified wave action damped and longshore drift as sediments supply reduced or absent lowstand and forced regressive systems tracts are not identified and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level through facies interpretation and sequence stratigraphic correlations between wells these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a landward to basinward orientation these thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass balance during regression the focus of sedimentation was pushed basinward and during transgression it was pushed landward as sediments were trapped there the mapping of these sequence stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets

thermohydromechanics of partially saturated geological media governing equations and formulation of four finite element models this paper presents the general governing equations for coupled thermohydromechanical thm processes in saturated and unsaturated geologic formations and reviews four finite element codes for modeling of such system three of the codes are developed for the special purpose of analyzing coupled thm processes in unsaturated porous and fractured geological media and the fourth is a commercial code that has been used in its standard version with a few adaptations for this specialized problem the basic assumptions and fundamental equations for coupled thm processes in unsaturated porous fractured rock are presented and formulations of the four finite element models are compared

crustal thinning and nature of extension in the northern north sea from deep seismic reflection profiling a regional network of deep seismic reflection profiles recorded in the northern north sea has been used to map mesozoic and cenozoic basin thickness and crustal thickness in the viking graben and adjacent platform areas depth to the reflection moho varies from about 20 km in parts of the viking graben to about 32 km beneath the shetlands and the norwegian margin the shallowing of the reflection moho beneath the viking graben implies crustal stretching factors for mesozoic extension greater than 2 in the center of the north sea basin the axis of crustal thinning is located directly beneath the viking graben the axis of the sedimentary basin steeply dipping basin bounding faults are imaged in the upper crust and several dipping reflectors are observed in the upper mantle but no continuous reflective feature extending from the sedimentary basin to beneath the moho is observed on any of the deep profiles thus these data do not support the existence of lithosphere penetrating low angle detachments zones of simple shear as the cause of extension in the northern north sea some of the mantle reflectors dip to the west and some to the east suggesting that simple shear if it occurs in the upper mantle is not of uniform sense rather these data suggest a complex depth dependent pattern of brittle extensional deformation in the upper crust pervasive ductile extension bulk pure shear in the lower crust which is decoupled from deformation in the mantle and extension accommodated by discrete dipping shear zones in the lithospheric mantle

zinc solubility speciation and deposition a role for liquid hydrocarbons as ore fluids for mississippi valley type zn pb deposits abstract although the ore fluid for mississippi valley type mvt deposits is universally considered to be a basinal brine the common occurrence of liquid hydrocarbons as inclusions in one of the ore minerals sphalerite raises the question of whether liquid hydrocarbons could play a role in metal transport here we explore the potential of liquid hydrocarbons to act as an ore fluid by determining the steady state concentration of zinc in crude oil and evaluating the factors that promote its dissolution to this end zinc wires were reacted with a series of oils labelled oils a b and c at 150 200 and 250 c and the steady state concentration of zn was determined zinc concentrations were observed to increase with temperature and with the total acid number tan of the oils the latter of which is strongly correlated to the carboxylic acid content of crude oil crude oil b the highest tan oil dissolved 1700 0 8 ppm at 250 c which is comparable to the highest zn concentration inferred to have been dissolved in brines interpreted to represent mvt ore fluids x ray photoelectron spectroscopic xps analyses performed on the residual oil coating the zinc wires after the reaction supported the conclusion that zn has a strong chemical affinity for carboxylic acids in crude oil finally an experiment designed to precipitate sphalerite crystals from a zn rich synthetic oil at room temperature showed that sphalerite precipitation from liquid hydrocarbons proceeds efficiently in a carbonate buffered h2s rich environment

the structural evolution of the northern viking graben and its bearing upon extensional modes of basin formation recent advances in the understanding of rift basin formation coupled with the increasing public availability of seismic and well data across the northern viking graben 60 61 n have enabled a detailed analysis of its development two rifting episodes can be recognized late permian early triassic and bathonian ryazanian major regional unconformities thought to be primarily tectonic rather than eustatic in origin separate and subdivide the rifting episodes the earlier episode involved extension about a n s axis ensuing triassic mid jurassic thermal subsidence was accommodated on steep faults during the later episode a new ne sw fault trend was superimposed on pre existing patterns major block rotation marking active rifting ceased at the end of the ryazanian during the second post rift episode there was a progressive migration of active faulting towards the basin margins and as a result a widening with time of the area undergoing subsidence asymmetric subsidence of the central part of the basin was hinged at the western margin of the horda platform and accommodated to the nw on major faults within the tampen spur factors for the second rifting episode were calculated both by relating subsidence to extension and by measuring observed extension values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases but are greater for the latter phase subsidence patterns are similar for both rifting and thermal subsidence episodes so that there is vertical stacking of relatively thick sequences in the axis of the northern viking graben these factors preclude the application of models involving uniform and non uniform stretching and also preclude oblique extension depth dependent stretching is preferred

spatio temporal evolution of strain accumulation derived from multi scale observations of late jurassic rifting in the northern north sea a critical test of models for lithospheric extension abstract we integrate observations of lithospheric extension over a wide range of spatial and temporal scales within the northern north sea basin and critically review the extent to which existing theories of lithospheric deformation can account for these observations data obtained through a prolonged period of hydrocarbon exploration and production has yielded a dense and diverse data set over the entire viking graben and its flanking platform areas these data show how syn rift accommodation within the basin varied in space and time with sub kilometer scale spatial resolution and a temporal resolution of 2 3 myr regional interpretations of 2d seismic reflection refraction and gravity data for this area have also been published and provide an image of total basin wide stretching for the entire crust these image data are combined with published strain rate inversion results obtained from tectonic subsidence patterns to constrain the spatio temporal evolution of strain accumulation throughout the lithosphere during the 40 myr 170 130 ma period of late jurassic extension across this basin for the first 25 30 myr strain localisation dominated basin development with strain rates at the eventual rift axis increasing while strain rates over the flanking areas declined as strain rates across the whole basin were consistently very low 16 s l thermally induced strength loss cannot explain this phenomenon the strain localisation is manifest in the near surface by a systematic migration of fault activity the pattern and timing of this migration are inconsistent with flexural bending stresses exerting an underlying control especially when estimates of flexural rigidity for this area are considered the best explanation for what is observed in this time period is a coupling between near surface strain localisation driven by brittle or plastic failure and the evolving thermal structure of the lithosphere we demonstrate this process using a continuum mechanics model for normal fault growth that incorporates the strain rate dependence of frictional strength observed in laboratory studies during the final 10 myr of basin formation strain accumulation was focused within the axis and strain rates declined rapidly replacement of weak crust by stronger mantle material plus crustal buoyancy forces can adequately explain this decline

relations between normal fault geometry tilting and vertical motions in extensional terrains an example from the southern gulf of suez abstract earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern gulf of suez are approximately planar with dips of 30 40 from the surface to around 10 km depth these faults and the blocks they bound appear to rotate about a horizontal axis as they move causing tilting this tilting is seen both in young vertical movements of the coastline such as raised beaches and marshlands and in the distribution of middle miocene marine rocks which are uplifted to elevations of 400 500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens the absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw tooth topography on a regional subsidence caused by crustal and lithospheric thinning the observations required for this simple model are the present day fault dip the amount of tilting and the width of the rotating blocks the virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents

on the impact of temperatures up to 200 c in clay repositories with bentonite engineer barrier systems a study with coupled thermal hydrological chemical and mechanical modeling abstract one of the most important design variables for a geological nuclear waste repository is the temperature limit up to which the engineered barrier system ebs and the natural geologic environment can be exposed up to now almost all design concepts that involve bentonite backfilled emplacement tunnels have chosen a maximum allowable temperature of about 100 c such a choice is largely based on the consideration that in clay based materials illitization and the associated mechanical changes in the bentonite and perhaps the clay host rock could affect the barrier attributes of the ebs however existing experimental and modeling studies on the occurrence of illitization and related performance impacts are not conclusive in part because the relevant couplings between the thermal hydrological chemical and mechanical thmc processes have not been fully represented in the models this paper presents a fully coupled thmc simulation of a nuclear waste repository in a clay formation with a bentonite backfilled ebs for 1000 years two scenarios were simulated for comparison a case in which the temperature in the bentonite near the waste canister can reach about 200 c and a case in which the temperature in the bentonite near the waste canister peaks at about 100 c the model simulations demonstrate some degree of illitization in both the bentonite buffer and the surrounding clay formation other chemical alterations include the dissolution of k feldspar and calcite and precipitation of quartz chlorite and kaolinite in general illitization in the bentonite and the clay formation is enhanced at higher temperature however the quantity of illitization is affected by many chemical factors and therefore varies a great deal the most important chemical factors are the concentration of k in the pore water as well as the abundance and dissolution rate of k feldspar less important ones are the concentration of sodium and the quartz precipitation rate in our modeling scenarios the calculated decrease in smectite volume fraction in bentonite ranges from 1 to 8 of the initial volume fraction of smectite in the 100 c scenario and 1 27 in the 200 c scenario chemical changes in the 200 c scenario could also lead to a reduction in swelling stress up to 15 18 whereas those in the 100 c scenario result in about 14 15 reduction in swelling stress for the base case scenario model results also show that the 200 c scenario results in a much higher total stress than the 100 c scenario mostly due to thermal pressurization while cautions should be taken regarding the model results due to some limitations in the models the modeling work is illustrative in light of the relative importance of different processes occurring in ebs bentonite and clay formation at higher than 100 c conditions and could be of greater use when site specific data are available

correlation of sandstones using heavy minerals an example from the statfjord formation of the snorre field northern north sea correlation of sandstones using heavy minerals is dependent on the recognition and quantification of provenance sensitive parameters suitable criteria include ratios of minerals that have similar hydraulic and diagenetic behaviour and properties of populations of individual mineral species sandstones of the statfjord formation in the snorre field display marked variations in their heavy mineral assemblages although hydraulic and diagenetic processes have played some part in generating these variations major changes in the nature of the source material can be detected on the basis of heavy mineral ratio and varietal data these changes in sand provenance can be used to produce a detailed stratigraphic breakdown of the sequence and to correlate from well to well eleven heavy mineral zones have been recognised on the basis of variations in monazite zircon garnet zircon and rutile zircon ratios on the incoming of chloritoid and on the composition of garnet populations the marked changes in provenance result from the proximity of the depositional location to the hinterland and it is considered unlikely that the detailed correlation made in the snorre field area applies to statfjord sandstones in other parts of the northern north sea however there is evidence for some degree of allogenic control on the heavy mineral variations and therefore some events may have regional significance

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

structural styles and depositional architecture in the triassic of the ninian and alwyn north fields implications for basin development and prospectivity in the northern north sea abstract interpretation of well calibrated three dimensional seismic volumes sedimentological analysis and electrical well log correlations from the ninian and alwyn north fields challenge the long held view that mid late jurassic extensional faults in the east shetland basin represent a simple reactivation of older triassic fault systems restoration for the effects of the younger predominantly eastward dipping mid late jurassic structures clearly demonstrates that triassic precursors had a steep westerly dip in contrast to the eastern flank of the viking graben e g troll and oseberg areas where the west dipping triassic structures are reutilised in the mid late jurassic those of the east shetland basin have largely been dissected and rotated during the later event those west dipping faults that did see later movement appear to have simply acted as minor antithetic structures to the throughgoing east dipping ones the triassic normal fault patterns actively controlled sediment thicknesses and facies distribution within the lunde and teist formations in the basin use of seismic stratigraphic surfaces calibrated by biostratigraphy and chemostratigraphic markers provides strong evidence that the triassic depocentres are spatially offset from their mid late jurassic counterparts the combination of structural stratigraphic and sedimentary effects reveal the existence of an emergent deeper triassic play opportunity in footwall locations to the mid late jurassic normal faults which has the potential to extend the life of what is otherwise mature acreage

application of high resolution sequence stratigraphy to northwest hutton field northern north sea implications for management of a mature brent group field the middle jurassic brent group reservoirs in northwest hutton comprise shallow marine marginal marine and coastal plain reservoir sandstones of both channelized and sheet geometries the connectivity and production characteristics of these sandstones can be predicted through the application of high resolution sequence stratigraphic correlation techniques the broom formation overlies a basal brent sequence boundary and is a lowstand to transgressive systems tract tidal estuarine complex the overlying rannoch formation comprises shoreface sands that represent a highstand systems tract the overlying etive formation is a multilayer fluvial to estuarine channelized system of near fieldwide development interpreted as incised valley fills the superjacent ness formation is genetically related to the etive and is the main oil bearing interval over much of the field the lower ness comprises mouth bar parasequences and is interpreted to be a transgressive systems tract to the etive lowstand the upper ness is a nonmarine delta plain succession interpreted as a highstand systems tract upper ness channel sands typically correlate between several wells and are oriented west east an interval of widespread stacked channels indicates a change in drainage orientation and is related to a high frequency relative sea level fall the uppermost reservoir unit is the tarbert formation related to a further major sequence boundary original repeat formation tester data support a stratigraphically well connected reservoir model compartmentalization exists and is due to stratigraphic layering laterally persistent mudstones creating low vertical permeability and variable dimensions of channels and valley fills

mesozoic regional tectonics and south viking graben formation evidence for localized thin skinned detachments during rift development and inversion abstract a regional thin skinned model of south viking graben development is presented in which zechstein marginal evaporites and interpreted salt have acted as a key de collement horizon along which mechanical decoupling of post salt triassic and younger strata from pre salt basement has occurred the western margin of the south viking graben defines an asymmetrical late jurassic half graben controlled by episodic extension along a nne ssw trending eastward dipping fault system an initial minor phase of rifting in the triassic is suggested by the slight westward thickening and associated divergence of interpreted triassic sequences at depth the scarcity absence of upper triassic and lower jurassic sequences is believed to result from a subsequent phase of uplift which affected the region in the mid cimmerian attributed to the development of a thermal dome at the future site of a jurassic rift triple junction to the southwest the onset of large scale extension from the late callovian onwards marked the major phase of half graben formation and created a regional hanging wall tilt which locally caused gravity gliding of post salt section to the wnw with resultant low angle extensional faulting upslope and salt cored buckling downslope the late jurassic half graben was subsequently tightened by a phase of thin skinned inversion in the latest jurassic early cretaceous associated with back steepening of the western margin fault system with resulting reactivation of the extensional detachment system the effects of this inversion have been noted in many parts of the northern north sea within the south viking graben shortening estimates vary between 14 and 18 and are expressed on seismic data by localized hanging wall folds and the back steepening of faults along the western margin fault complex of the graben together with out of graben thrusting up the hanging wall dip slope variation in both the extension and inversion mechanisms appears to be controlled by interpreted nw se transfer systems which compartmentalize the graben into three subgraben within which differential zechstein basin development occurred

the role of fault interaction and linkage in controlling synrift stratigraphic sequences late jurassic statfjord east area northern north sea examination of well constrained three dimensional seismic data demonstrates the role of fault interaction and linkage in controlling the nature of synrift sequences on the hanging wall of the statfjord east fault a typical late jurassic structure in the northern north sea brent province al though now a single fault the statfjord east fault originally consisted of several en echelon segments each of which defined individual subbasins structural and stratigraphic evidence both along and across fault strike indicates that the fault resulted from segment propagation interaction and linkage facies architecture thickness variations and the internal character of synrift formations are temporally and spatially related to the subbasin geometry variations in displacement along the fault segments exhibit characteristics of interacting en echelon faults including anomalous displacement gradients in regions of segment overlap we attribute the observed shifts in depocenters to local enhancement of displacement rates resulting from the interaction of neighboring fault segments the results have far reaching consequences for synrift plays in the northern north sea because they imply that only from the perspective of fault growth and linkage can the late jurassic structure and stratigraphy be fully understood

processus d alteration thermique physico chimique et biologique de constituants organiques et genese d une mineralisation sulfuree le gite zn pb de la florida cantabria espagne the la florida lead zinc deposit cantabria spain which is hosted by urgonian carbonates is located on the border of the basco cantabric lower cretaceous basin the stratiform orebody which is composed of sphalerite galena and barite in iron dolostones occurs in an envelope of dolostone organic matter studies have been carried out on samples from this deposit to understand its genesis and later evolution the results of this work reveal the immatury of the autochthonous organic matter despite a slight paleothermal anomaly centred on the deposit various alteration processes have affected the hydrocarbons associated with autochthonous organic matter and or allochthonous bitumens namely geochromatographic fractionation water washing and biodegradation together with previous geological work the results of this study are consistent with epigenetic and or diagenetic emplacement of the mineralization the proposed genetic scheme involves hydrothermal fluids that would have acquired at least so

evolution of the oseberg fault block in context of the northern north sea structural framework abstract the central segment 60 20 61 n of the northern north sea 170 km in width demonstrates contrasting basin geometries related to permo triassic and jurassic rift episodes in the oseberg area representing a part of this segment major faults of two generations dip in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin ca 20 km in width is underlain by a wider ca 35 km w tilted permo triassic half graben the early jurassic thickness distribution was governed by a westerly palaeotilt mild extensional tectonics influenced early jurassic rhaetian aalenian deposition whereas the middle late jurassic main rift episode is expressed by an accelerated fault related subsidence from the late bajocian during the middle late jurassic the oseberg area evolved through a series of high frequency rift phases characterized by rotational tilt events separated by periods during which extension was less severe this allows the subdivision of the jurassic stretching episode into distinct rift phases 4 6 myrs which involved smaller scale units corresponding to rotational tilt events 1 2 myrs the large scale pattern of middle late jurassic syn rift infill is overall one of upwards fining reflecting a deepening trend as the rift evolved syn rotational sediment architecture related to a single rift phase shows systematic variations from a threefold shallow marine sandstone mudstone sandstone motif tarbert fm through a twofold shallow marine sandstone mudstone motif heather fm to a twofold deep marine conglomerate sandstone mudstone motif draupne fm the vertical stacking of these syn rotational packages reflects an inability of sediment supply to keep pace with the rift related subsidence and the temporal evolution from a sediment balanced through a sediment underfilled to a sediment starved rift basin

the organic geochemistry of two mississippi valley type lead zinc deposits the organic matter associated with two mississippi valley type deposits gays river nova scotia and shullsburg southwestern wisconsin has been characterized by petrographic isotopic spectrophotometric gas chromatographic and mass spectral methods comparisons were made of distributions of organic species identified from unmineralized and mineralized samples the primary variations in the distributions of organic species isolated from the two deposits reflect variations in host rock paleoecology facies and geologic age secondary effects were microbial degradation thermal maturation and mineralization mineralization in both deposits caused an increase in the concentrations of low molecular weight hydrocarbons the genetic model tested in this study presumed that mineralizing brines evolved from sedimentary basins and migrated to the ore host rocks this model implies that an epigenetic generation of organic matter should occur in the deposits in the gays river deposit the probable aquifer for the mineralizing solutions contained an organic distribution markedly different from the indigenous organic matter in the host reef and can be interpreted as a second epigenetic organic fraction added to the deposit evidence was not observed for an epigenetic organic generation in the shullsburg deposit the thermal maturity of the organic matter in the wisconsin district supports a previous estimate of 0 25 m y to form a major orebody in the district