fracture distribution on the swift reservoir anticline montana implications for structural and lithological controls on fracture intensity title of special publication folding and fracturing of rocks 50 years of research since the seminal text book of j g ramsay this research was funded by oil search ltd santos ltd and interoil through the university of aberdeen fold thrust research group electron microscopy was performed in the acemac facility at the university of aberdeen with assistance from john still joyce neilson is thanked for advice on the use of imagej software midland valley are thanked for the use of their move software for field data collection and model building we thank alfred lacazette and stefano tavani for reviewing the manuscript and providing constructive comments

transition from mildly tholeiitic to calc alkaline suite the case of chichontepec volcanic centre el salvador central america abstract the chichontepec volcano is a plio pleistocene composite volcano that erupted lavas ranging from high alumina basalts to dacites it experienced a caldera forming paroxysmal eruption during the early pleistocene pre caldera lavas are mildly tholeiitic and they evolved mainly by low pressure crystal fractionation notwithstanding the fact that most mafic lavas low mgo high alumina basalts retain traces of polybaric evolution conversely post caldera lavas which are mainly pyroxene andesites are clearly calc alkaline having evolved by open system crystal fractionation sr nd isotopic data and trace elements characteristics indicate that the same mantle source was involved in the petrogenesis of these series modelling the afc process showed that it did not play any role in the petrogenesis of these rocks a crystal fractionation model is considered to be more relevant a slight variation in the fractionating assemblage could have caused the transition from an early mildly tholeiitic trend to a late calc alkaline one mineralogical evidence mass balance calculations and elemental chemistry support this hypothesis assuming that the greater amount of pyroxene on the liquidus is at the expense of plagioclase this would have prevented the trend in iron enrichment

multiparameter two dimensional inversion of scattered teleseismic body waves 3 application to the cascadia 1993 data set this is the third paper in a three part series that examines formal inversion of the teleseismic p wave coda for discontinuous two dimensional 2 d variations in elastic properties beneath dense arrays of three component broadband seismometers in this paper the method is applied to data from the incorporated research institutions for seismology program for array seismic studies of the continental lithosphere iris passcal cascadia 1993 experiment undertaken across central oregon two major features are imaged in the resulting model the continental moho becomes evident 150 km from the coast beneath the western cascades and extends through the eastern end of the profile at 35 40 km depth in the western portion of the model oceanic crust of the subducting juan de fuca plate dips shallowly 12 at the coast and more steeply 27 below the willamette valley and is evident to depths of 100 km beneath the high cascades the abrupt increase in plate dip at 40 km depth coincides with an apparent thickening of the oceanic crust followed by a diminution in its signature building on previous work we argue that these results are consistent with the consequences of prograde metamorphic reactions occurring within the oceanic crust progressive dehydration at lower grade facies conditions culminates in the transformation to eclogite producing a pronounced increase in the seismic velocity density and dip of the subducting plate and structural complexity in the overlying wedge

structure of the mountain front flexure along the anaran anticline in the pusht e kuh arc nw zagros iran insights from sand box models this is a contribution of the group of dynamics of the lithosphere gdl financed by a collaborative project between the institute of earth sciences jaume almera csic of barcelona spain and statoilhydro tehran and statoilhydro research centre with the partial support of project team consolider ingenio 2010 no csd 2006 00041

fracture attribute and topology characteristics of a geothermal reservoir southern negros philippines the characterization of fracture networks using attribute and topology analyses has not been widely applied to geothermal resources in order to better understand and predict secondary porosity permeability and fluid flow characteristics in this study fracture length aperture intensity and topology data were acquired from remotely sensed images and surface exposures from the cuernos de negros region and compared with well cores and thin sections from the underlying active geothermal reservoir the southern negros geothermal field sngf west central philippines we show that the fracture attributes for the analogue and reservoir are best described by a power law distribution of fracture length and aperture intensity across six to eight orders of magnitude this characterization of outcrop and borehole fractures validates the use of surface exposures as analogues for the sngf reservoir rocks at depth an observed change in the scaling exponent in the 100 to 500 m length scales suggests that regional to sub regional fracture systems scale differently to those at the mesoscale and macroscale which may be a strata bound effect or a sampling issue topology analyses show a dominance of y nodes and doubly connected branches which indicates a high degree of fracture connectivity that is important for effective fluid flow thematic collection this article is part of the the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs supplementary material slopes coefficient of determination and aic values of the cumulative frequency versus length and aperture plots of all fracture transects is available https doi org 10 6084 m9 figshare c 4960559

multiparameter two dimensional inversion of scattered teleseismic body waves 2 numerical examples in this paper we investigate the formal inversion of synthetic teleseismic p coda waves for subsurface elastic properties using a ray theoretic approach which assumes single scattering bostock et al this issue we consider a model comprising an idealized lithospheric suture zone whose geometrical configuration is drawn from previous deep crustal seismic studies two dimensional pseudospectral synthetic seismograms representing plane waves propagating through this model are preprocessed to extract an estimate of the scattered wave field generated by short wavelength structure these data are employed in a series of numerical simulations which examine the dependence of multiparameter inversion results on a range of input parameters in particular we demonstrate 1 the contrasting sensitivity which forward and backscattered waves display to structural recovery 2 the diminution of the problem null space accompanied by increased source coverage 3 improvements in model reconstruction achieved through simultaneous treatment of multiple scattering modes and 4 the robustness of the method for data sets with noise levels and receiver geometries that approach those of field experiments

origin of the infracambrian salt basins of the middle east abstract during the infra and lower cambrain the arabian gulf and zagros mountains hormuz formation south oman ara formation kerman in central iran ravar formation and the salt range province in pakistan salt range formation were all sites of salt precipitation in subsiding rift basins along the middle eastern edge of gondwanaland also from 600 to 540 ma a rift system extended westwards from the sinai peninsula and north egypt across ne africa while a second rift system about 600 to perhaps 510 ma extended northwards from the sinai peninsula across the jordan valley and dead sea into se turkey the development of these rifts was contemporaneous with the left lateral najd strike slip fault system which dislocated the arabian peninsula by 300 km the najd system may be interpreted as a transform fault system which accommodated rifting between ne egypt the jordan valley north pakistan kerman and south oman the najd system is parallel to the zagros line and the latter is also the eastern depositional limit of the infracambrian hormuz formation the infracambrian zagros line may be interpreted as a right lateral strike slip fault system which caused infracambrian rifting in the arabian gulf and zagros mountains palaeontological and radiometric age constraints together with stratigraphic considerations suggest that the syn rift evaporites were first precipitated during a transgression which commenced in the latest precambrian 600 ma and again during a lower cambrian regression the regression terminated a period dominated by marine carbonates and evaporites and initiated the deposition of progradational alluvial to marginal marine sediments finally in the late lower cambrian and middle cambrian transgressive marine deposits swept across the middle east

seismic interferometry turning noise into signal turning noise into useful data every geophysicist s dream and now it seems possible the field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses complicated seismic codas the multiply scattered parts of seismic waveforms and background noise whatever is recorded when no identifiable active source is emitting and which is superimposed on all recorded data those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources the key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex looking waveforms and the answer turned out to be rather simple this article explains the operation of seismic interferometry and provides a few examples of its application

quantitative evaluation of fractures on monkshood anticline a detachment fold in the foothills of western canada monkshood anticline is a well exposed surface anticline located in the foothills in northeastern british columbia extension fractures are well developed in the prophet formation a carbonate shale chert sequence throughout this fold virtually all of these fractures are filled with some combination of calcite and quartz cements the fractures formed and the mineral cements were deposited during the fold development most fractures on monkshood anticline have formed at high angles to bedding and they commonly fall into two to three distinct orientation sets the dominant fracture trend is aligned with the fold axis through the backlimb of the fold but there is considerable variance in the dominant orientation in the forelimb an order of magnitude variation is found in fracture densities across this fold and over two orders of magnitude variation occur in mean fracture aperture these variations in density and aperture do not correlate with particular structural positions fracture trace lengths exhibit power law distribution patterns suggesting fractal character fracture aperture displays a roughly linear correlation to volumetric fracture strain but shows no consistent association with either density or trace length stochastic modeling of the fracture networks on monkshood anticline suggests density is the primary factor affecting fracture network connectivity but fracture size also can play an important supporting role the occurrence of a dominant fracture orientation set can impart a significant directional bias to connectivity measurement stations on monkshood anticline that have both high fracture densities for connectivity and substantial fracture apertures for conductance occur primarily in midlimb positions

relation of lava compositions to volcano size and structure in el salvador abstract most of the lavas at the nine volcanic centers along the volcanic front of el salvador are basalts basaltic andesites and andesites the compositional variation within and among these centers can be explained by fractionation processes within the crust cognate gabbroic inclusions found in the lavas have appropriate mineralogy plagioclase olivine magnetite and augite to be cumulates formed by fractional crystallization two main variation trends occur depending on the proportion of plagioclase removal the more common or normal trend has a high 55 proportion of plagioclase being removed a less common al rich trend has a low 40 proportion of plagioclase being removed the al rich trend is found only at volcanoes that lack large negative bouguer gravity anomalies these volcanoes are unlikely to have large shallow magma chambers and fractionation probably occurs deeper in the crust where plagioclase removal is inhibited the incompatible element na 2 o k 2 o rb ba contents of lavas vary systematically with the volume of the volcanic centers at the same level of sio 2 large volcanic centers have higher incompatible element contents than small volcanic centers this suggests that open system fractionation in a periodically refilled chamber is the controlling factor the large difference in ba contents of lavas between eastern low and western high el salvador suggests a difference in the mantle source region

vsp beyond time to depth vsp or vertical seismic profile was originally designed and is currently primarily used to give us time to depth for seismic well ties beyond time to depth a number of possibilities exist recently there has been considerable interest in vsp imaging ray et al 2003 paulsson et al 2004 hornby et al 2004 hornby et al 2005a with extensive surveys being acquired both on land and offshore modeling studies using full waveform finite difference method fdm payne et al 1994 van gestel et al 2003 show us what we can image for a particular acquisition geometry and geology with best image results seen with 3d vsp surveys incorporating a large vsp array in the well and a 2d source pattern acquired using a surface seismic shooting vessel traditionally vsp imaging has been implemented using surface seismic processing algorithms however the vsp geometry poses its own challenges and unique opportunities in this article we explore some imaging methods to attempt to take advantage of the vsp g

imaging above an extended reach horizontal well using converted shear waves and a rig source abstractwe evaluated a method for using 3c vertical seismic profile data to image acoustic interfaces located between the surface source and a downhole receiver array the approach was based on simple concepts adapted from whole earth seismology in which observed compressional and shear wavefields are traced back to a common origin however unlike whole earth and passive seismology in which physical sources are imaged we used the observed compressional and shear wavefields to image secondary sources scatterers situated between the surface source and the downhole receiver array the algorithm consisted of the following steps first estimating the receiver compressional wavefield second using polarization to estimating the shear wavefield third deconvolving the shear wavefield using estimates of the source wavelet obtained from the direct compressional wave fourth the compressional and shear wavefields were back projected into the volume between the source and receivers where finally an imag

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

stratigraphic controls on vertical fracture patterns in silurian dolomite northeastern wisconsin vertical opening mode fractures are mapped on quarry walls to assess the stratigraphic controls on fracture patterns in the relatively undeformed silurian dolomite of northeastern wisconsin our two stage study uses maps of vertical fractures to assess the effectiveness of various types of stratigraphic horizons e g organic partings or cycle bounding mud horizons in terminating opening mode fractures first the mechanical stratigraphy of the exposures is interpreted from the observed fracture pattern both visual inspection and a newly developed quantitative method are employed to identify effective mechanical interfaces the two methods show similar results confirming the validity of qualitative visual inspection the second stage of our study stochastically predicts mechanical stratigraphy and subsequent fracture pattern from empirical relationships between the observed sedimentary stratigraphy and the interpreted mechanical stratigraphy for example 63 of cycle bounding mud horizons within the inner middle and middle shelf facies associations serve as mechanical interfaces these empirical percentages are input to a monte carlo analysis of 50 stochastic realizations of mechanical stratigraphy comparisons of the stochastically predicted and interpreted mechanical stratigraphy yield errors ranging from 13 to 33 this method yields far better results than assuming that all stratigraphic horizons act as mechanical interfaces the methodology presented in this article demonstrates an improved prediction of fracture pattern within relatively undeformed strata from both complete characterization of sedimentary stratigraphy and understanding mechanical controls on fracturing

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

fracture development and mechanical stratigraphy of austin chalk texas the mechanical stratigraphy of the upper cretaceous austin chalk is established from study of fracture intensity along its outcrop trend from dallas to san antonio and westward to langtry texas and in the subsurface from study of cores and or fracture identification logs from 30 wells three mechanical stratigraphic units are recognized 1 an upper fractured massive chalk corresponding to the big house chalk member 2 a middle ductile chalk marl corresponding to the dessau chalk and burditt marl members and 3 a lower fractured massive chalk corresponding to the atco chalk member representative samples from the three mechanical stratigraphic units were experimentally shortened dry at 10 17 34 and 70 mpa confining pressure at 24 c and at a strain rate of 2 5 10 4 sec 1 to determine if the relative mechanical behavior observed at the surface could be extrapolated into the subsurface at different simulated burial depths the experimentally determined ductilities parallel those determined from outcrop and subsurface studies multiple linear regression analysis indicates that porosity is most strongly correlated with fracture strength smectite content has the second strongest correlation for low porosity specimens 9 13 5 the strength of specimens with 4 smectite is reduced 30 42 compared to specimens with no smectite the coefficient of internal friction at 17 mpa confining pressure decreases from 1 66 to 0 61 as smectite content increases from 0 to 4 sem photomicrographs of undeformed specimens show that smectite and other clays are distributed as large 30 m discrete amorphous concentrated masses throughout the chalk they are comminuted along the induced fracture surfaces where their grain size is 0 5 m or less these observations suggest that smectite acts as a soft inclusion localizing shear failure and correspondingly weakening the material

the khaviz anticline an outcrop analogue to giant fractured asmari formation reservoirs in sw iran the carbonate reservoirs in the late oligocene early miocene asmari formation in the dezful embayment of sw iran are characterized by low matrix permeability and effective drainage is dependent on the occurrence of open fractures limited information on fracture orien tation and fracture density is available from core and borehole image data and high quality high resolution three dimensional seismic is often lacking in this area well and core data do not contain information on important fracture parameters like length distribution crosscutting relationships fracture density v lithology and bed thickness the understanding of fracture distri bution and formation in the region and their effects on fluid flow has been greatly improved by the use of outcrop analogue data exposures of the asmari formation in the khaviz anticline are in close vicinity to the giant hydrocarbon fields the khaviz anticline has a similar geometry and structural history to the major hydrocarbon fields in the area and represents an excellent analogue for these two types of fracture features were observed diffuse fracturing and fracture swarms the diffuse fractures form networks and comprise structures grouped into four fractures sets which are the typical for this type of anticline two orthogonal fracture sets are oriented parallel and perpendicular to the fold axis and two conjugate fracture sets are oblique to the fold axis with their obtuse angle intersecting the trend of the fold axis the fractures are typically stratabound sub perpendicular to bedding and commonly about the bounding stratigraphic surfaces to a large extent the density and height of fractures in the asmari formation are controlled by the mechan ical stratigraphy which is controlled by the depositional environment and cycles these outcrop data have been essential in the generation of discrete fracture network dfn models and the population of the fracture properties in the reservoir models

2 d density and directional analysis of fault systems in the zagros region iran on a regional scale in this paper 2 d spatial variation of the frequency and length density and frequency length relation of large scale faults in the zagros region iran as a typical fold and thrust belt were examined moreover the directional analysis of these faults as well as the scale dependence of the orientations was studied for this purpose a number of about 8000 faults with l 1 0 km were extracted from the geological maps covering the region and then the data sets were analyzed the overall pattern of the frequency length distribution of the total faults of the region acceptably fits with a power law relation with exponent 1 40 with an obvious change in the gradient in l 12 0 km in addition maps showing the spatial variation of fault densities over the region indicate that the maximum values of the frequency and length density of the faults are attributed to the northeastern part of the region and parallel to the suture zone respectively and the fault density increases towards the central parts of the belt moreover the directional analysis of the fault trends gives a dominant preferred orientation trend of 300 330 and the assessment of the scale dependence of the fault directions demonstrates that larger faults show higher degrees of preferred orientations as a result it is concluded that the evolutionary path of the faulting process in this region can be explained by increasing the number of faults rather than the growth in the fault lengths and also it seems that the regional scale faults in this region are generated by a nearly steady state tectonic stress regime

new evidence and model on the evolution of the southeast anatolian orogen this paper describes the orogenic evolution of the southeast anatolian orogenic belt based mostly on new geologic data collected from its constituent tectonic units in the course of new mapping programs of the past decade the southeast anatolian orogenic segment of the alpides may be divided into three approximately east west trending zones from south to north they are the arabian platform followed by a zone of imbrication and then a zone of nappes the arabian platform includes a mostly marine sedimentary succession deposited from early cambrian to middle miocene time the zone of imbrication is a narrow belt sandwiched between the arabian platform and the zone of nappes it consists of imbricated thrust slices emplaced onto a late cretaceous to early miocene sequence the zone of nappes is the highest tectonic unit consisting of two stacks of nappes simply designated the lower and upper nappes the lower nappe is represented by the slices of a polyphase metamorpbic ophiolitic assemblage and the maden group the upper nappe rests on the lower nappe and is represented by the bitlis and poturge metamorphic massifs southeastern anatolia underwent two major episodes of alpide deformation the first occurred during the late cretaceous period when ophiolite was emplaced on the arabian platform this event was not the consequence of a continental collision the ophiolite obduction onto the arabian platform was followed by a regionwide extension and a new marine transgression over the platform immediately after the ophiolite obduction the second episode of deformation occurred during middle eocene miocene time in two distinct stages as a result of the progressive elimination and complete closure of the ocean s which led to the collision between the zone of nappes located to the north being a part of eurasia and the arabian plate the maden marginal basin formed north of the subduction zone that eliminated the ocean between eurasia and arabia along the southern margin of the taurus belt and abutted the arabian plate much later during the final collision the second episode of deformation formed the present orogenic segment leading to the amalgamation of different tectonic units these amalgamated nappes collided with the arabian plate and welded onto it at the latest stage of the orogenic evolution during the miocene epoch

conceptual modeling of onshore hydrocarbon seep occurrence in the dezful embayment sw iran petroleum and gas seeps on the ground surface are direct indicators of accumulations of hydrocarbons in the subsurface and could reflect the migration of hydrocarbons in a sedimentary basin quantitative analyses of the spatial pattern of hydrocarbon seeps and their spatial associations with geological features could aid in deducing geological controls on their occurrence in this study the fry analysis was applied to study the spatial pattern of mapped hydrocarbon seeps whereas spatial association analyses were implemented to quantify the spatial association of mapped seeps and their alteration products with geological features the spatial pattern analysis of hydrocarbon seeps showed that oil seeps followed prominent nw se and ne sw trends while gas seeps followed nw se and n s trends suggesting that nne ssw and nw se fractures are possible migration pathways for hydrocarbons to reach the surface the results of the spatial association analysis illustrated strong positive spatial associations of oil and gas seeps with the gachsaran and the mishan formations implying upward migration of hydrocarbons through permeable micro fractures and micro pores in their strata a conceptual model has proposed for the occurrence of onshore hydrocarbon seeps in the dezful embayment

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

fracture patterns in the zagros fold and thrust belt kurdistan region of iraq abstract fracture data have been collected in the kurdistan region of iraq which is a poorly accessible and unexplored area of the zagros pre to early folding ne sw striking extensional fractures and nw se striking contractive elements represent the older set affecting the exposed multilayer of the area these latter structures are early syn folding and followed by folding related mesostructural assemblages which include elements striking parallel to the axial trend of major folds longitudinal fractures bedding perpendicular joints and veins and extensional faults belonging to this second fracture set are located in the outer arc of exposed anticlines whilst longitudinal reverse faults locate in the inner arcs consistently these elements are associated with syn folding tangential longitudinal strain the younger two sets are related to e w extension and nne ssw to n s shortening frequently displaying reactivation of the older sets the last shortening event which is described along the entire zagros belt probably relates with the onset of n s compression induced by the northward movement of the arabian plate relative to the eurasian plate in comparison between the inferred palaeostrain directions and the kinematics of recent gps measurements we conclude that the n s compression and the partitioning into nw se trending folds and nw to n trending strike slip faults likely remained unchanged throughout the neogene tectonic history of the investigated area

superposed folding and associated fracturing influence hypogene karst development in neoproterozoic carbonates sao francisco craton brazil abstract porosity and permeability along fractured zones in carbonates could be significantly enhanced by ascending fluid flow resulting in hypogene karst development this work presents a detailed structural analysis of the longest cave system in south america to investigate the relationship between patterns of karst conduits and regional deformation our study area encompasses the toca da boa vista tbv and toca da barriguda tbr caves which are ca 107 km and 34 km long respectively this cave system occurs in neoproterozoic carbonates of the salitre formation in the northern part of the sao francisco craton brazil the fold belts that are around and at the craton edges were deformed in a compressive setting during the brasiliano orogeny between 750 and 540 ma based on the integrated analysis of the folds and brittle deformation in the caves and in outcrops of the surrounding region we show the following 1 the caves occur in a tectonic transpressive corridor along a regional thrust belt 2 major cave passages at the middle storey of the system considering both length and frequency developed laterally along mainly a ne sw to e w and b n to s oriented anticline hinges 3 conduits were formed by dissolutional enlargement of subvertical joints which present a high concentration along anticline hinges due to folding of competent grainstone layers 4 the first folding event f1 was previously documented in the region and corresponds with nw se to n s trending compression whereas the second event f2 documented for the first time in the present study is related to e w compression and 5 both folding events occurred during the brasiliano orogeny we conclude that fluid flow and related dissolution pathways have a close relationship with regional deformation events thus enhancing our ability to predict karst patterns in layered carbonates

sedimentological controls on the fracture distribution and network development in mesaverde group sandstone lithofacies uinta basin utah usa the mesaverde group uinta basin utah is the source of current significant natural gas production and contains several trillion cubic feet of undiscovered natural gas resources to evaluate and model the potential connectivity of hydraulically induced fractures to natural fractures in the subsurface the natural fracture network was examined using scanline sampling image and well logs core and microstructural analyses regional fracture sets include subvertical fractures with dominant orientations of north south 006 0158 ne 045 0598 nnw 326 3428 and a wnw 271 2868 sedimentologic and diagenetic characteristics of seven sandstone lithofacies control the fracture development and distribution in the group key sedimentologic and diagenetic influences on fracture distribution include bed thickness stratigraphic architecture the degree of cementation and the type of cement from these sedimentologic controls on the character of natural fractures lithofacies can potentially predict fracture distribution within the mesaverde group based on environments of deposition the presence of nw trending discontinuous sandstone reservoirs deposited in meandering fluvial environments that are highly fractured by a pervasive wnw striking fracture set helps to explain fairways of prolific natural gas production within

true amplitude recovery in reverse time extrapolation of plane and spherical waves one of the challenging outstanding problems in reverse time extrapolation is recovering accurate amplitudes at reflectors from the receiver wavefield various migrations have been developed to produce accurate image locations rather than correct amplitude information because of inadequate compensation of attenuation dispersion and transmission losses we first evaluated the requirements and demonstrated the theoretical feasibility of true amplitude recovery of 2d acoustic and elastic seismic data by using the analytic zoeppritz equations for plane wave reflection and transmission coefficients then we used synthetic acoustic and elastic wavefield data generated by elastodynamic finite differences to verify the recovery in the reverse time propagation of spherical waves and illustrated the salient differences between the incident wavefields reconstructed from reflection data only and from the combination of reflection and transmission data these examples quantitatively verified that recovering an

the impact of inter bed cohesion on fold related fracture development stillwell anticline west texas usa abstract the interpretation of fracture networks in contractional folds is challenging due to the range of factors that control fracture formation we use outcrop based analysis of fractures in plan view pavements and in a 9 bed cross sectional exposure to evaluate the fracture system within cretaceous limestone layers of a laramide fold in west texas the stillwell anticline opening mode extension fractures veins at high angles to bedding dominate the fracture population although shear fractures and faults cut bedding at low angles within the forelimb analysis of extension fractures reveals nw striking axial parallel and ne striking axial perpendicular fracture sets interpreted to have formed during contractional folding a third n striking fracture set formed during subsequent basin and range extension and a fourth ese striking fracture formed due to unloading during exhumation fracture fill textures suggest that many fracture apertures increased during exhumation the relative abundances of the four fracture sets and the intensity of each set vary from bed to bed in cross section because beds display no significant differences in mechanical strength and there is no correlation between bed thickness and fracture intensity we attribute this bed to bed variability to differences in cohesion between beds bed decoupling when combined with low extensional

locating microseismic sources using migration based deconvolution abstractwe have developed a method for finding microseismic hypocenters from data recorded by arrays of triaxial motion sensors the method reconstructs the elastic time series signatures for possible microseismic sources at any point in 3d space using full waveform migration of the recorded vector wavefield the imaging condition for the migration is based on a semblance weighted deconvolution between two or more reconstructed source signatures requiring similarity and simultaneity of the reconstructed signatures this imaging condition eliminates the need for an absolute timing of the data gives optimum resolution for the location of the microseismic sources better than correlation based approaches and ensures numerical stability by adapting to the signal and noise conditions of the data because the method eliminates time consuming phase picking and traditional event association it should be well suited for fully or semiautomated data processing the method was tested by an application to field dat

regional stratigraphic architecture and reservoir types of the oligo miocene deposits in the dezful embayment asmari and pabdeh formations sw iran

salt flank delineation by interferometric imaging of transmitted p to s waves we describe how vertical seismic profile vsp interferometric imaging of transmitted p to s ps waves can be used to delineate the flanks of salt bodies unlike traditional migration methods interferometric ps imaging does not require the migration velocity model of the salt and or upper sediments in order to image the salt flank synthetic elastic examples show that ps interferometric imaging can clearly delineate the upper and lower boundaries of a realistic salt body model results also show that ps interferometric imaging is noticeably more accurate than conventional migration methods in the presence of static shifts and or migration velocity errors however the illumination area of the ps transmitted waves is limited by the width of the shot and geophone aperture which means wide shot offsets and deeper receiver wells are needed for comprehensive salt flank imaging interferometric imaging results for vsp data from the gulf of mexico demonstrate its superiority over the traditional migration method we also discuss other arrivals that can be used for interferometric imaging of salt flanks for comparison reduced time migration results are presented which are similar in quality to those obtained for interferometric imaging we conclude that ps interferometric imaging of vsp data provides the geophysicist with a new tool by which salt flanks can be viewed from both above and below vsp geophone locations

distribution of joints in the hinge line culmination of foreland verging overturned anticlines an example from the montagna dei fiori structure in the central apennines of italym francioni et al distribution of joints in overturned anticlines the distribution of joints veins and shear fractures in the montagna dei fiori overturned anticline is here reported two joint sets longitudinal and transverse to the nnw sse anticline axial trend and a conjugate system of shear fractures are recognized the transverse and longitudinal joint sets have a pre folding development likely related to the foreland foredeep flexure the transverse joints were reopened during layer parallel shortening along with the development of the shear fractures then during syn folding outer arc extension and hinge line culmination fold axial parallel extension both the longitudinal and transverse joints were enhanced and reactivated respectively

sedimentary and diagenetic controls on the multiscale fracturing pattern of a carbonate reservoir the madison formation sheep mountain wyoming usa a multidisciplinary approach has been applied to characterize the madison formation in the sheep mountain anticline at different scales in order to illustrate the relationship between sedimentology diagenesis and fracturing pattern sedimentary facies are organized into three types of elementary facies sequences showing different vertical evolutions of their petrophysical properties this is controlled by the double influence of the initial sedimentary facies and the diagenetic evolution three main sets of fractures related to the sevier and laramide compressive phases and to the folding of sheep mountain have been described at three orders of scale at small scale the sevier related set i and folding related set iii are the most abundant set ii dated from the early stage of the laramide compression exhibits the highest fracture intensity there is also a clear faciologic control on the fracture intensity small scale mechanical units correspond to entire facies sequences when no or little petrophysical property contrasts between beds are observed conversely small scale mechanical units correspond to each bed of a facies sequence in the case of high contrasts of petrophysical properties between beds at intermediate scale set ii is not present and sets i and iii show the highest fracture intensities the latter are partly controlled by the mechanical unit thickness intermediate and large scale mechanical unit distribution is mainly controlled by the overall faciologic vertical stacking pattern and by the position across the sheep mountain anticline forelimb or backlimb sheep mountain outcrops provide a good spatial representation of the carbonate reservoir heterogeneities from the micro to the field scale illustrating the complexity of fractured carbonate reservoirs

influence of structural position on fracture networks in the torridon group achnashellach fold and thrust belt nw scotland abstract in fold and thrust belts rocks undergo deformation as fold geometries evolve deformation may be accommodated by brittle fracturing which can vary depending on structural position we use 2d forward modelling and 3d restorations to determine strain distributions throughout folds of the achnashellach culmination moine thrust belt nw scotland fracture data is taken from the torridon group a thick coarse grained fluviatile sandstone deposited during the proterozoic modelling infers a correlation between strain and simple curvature we use simple curvature to infer how structural position and strain control fracture attribute variations in a fold and thrust belt in high curvature regions such as forelimbs fracture intensities are high and fractures are short and oriented parallel to fold hinges in low curvature regions fractures have variable intensities and are longer fracture orientations in these regions are scattered and vary over short distances these variations do not relate to strain data suggests lithology may influence fracturing the strain history of fold structures also influences fracturing structures with longer deformation histories exhibit consistent fracture attributes due to moderate high strain during folding despite present day low curvature this is in contrast to younger folds with similar curvatures but shorter deformation histories we suggest in high strain regions fracturing is influenced by structural controls whereas in low strain regions lithology becomes more important in influencing fracturing

uplift induced residual strain release and late thrusting extension in the anaran mountain front anticline zagros iran abstract in this work we present and discuss the pattern of extensional faults of the anaran anticline lurestan province of the zagros iran one of the most aesthetically appealing mountain front anticlines of the zaros this 100 km long structure is affected by extensional faults occurring in different along strike sectors of the anticline running parallel and oblique to the local trend of the fold hinge line and having displacements of hundreds of metres relationships between fold growth and extensional deformation are investigated by quantitatively analysing the attributes i e curvature elevation and throw across faults of a 3d surface representing the top of the ilam formation results indicate that the main stage of extensional deformation occurred during folding in particular we deduce that extensional faulting was associated with the erosional uplift of the crestal sector of the anticline where exhumation of previously shortened strata implied release of residual compressive strain with consequent annihilation of the horizontal stress component paralleling the tectonic transport direction this determined the onset of a large scale extensional regime at the shallower structural levels of the growing anticline

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

joint development and tectonic stress field evolution in the southeastern mesozoic ordos basin west part of north china abstract major joint sets trending e w j1 ene wsw j2 ne sw j3 n s j4 nnw sse j5 nne ssw j6 nw se j7 and wnw ese j8 respectively are recognized in mesozoic strata within the southeast of ordos basin among them the j1 j2 and j3 joint sets are systematic joints while the other five joint sets j4 j5 j6 j7 j8 are nonsystematic joints there are three groups of orthogonal joint systems i e j1 and j4 sets j2 and j5 sets and j6 and j8 sets and two groups of conjugate shear fractures ene wsw and nne ssw ene wsw and ese wnw in the study area joint spacing analysis indicates that 1 layer thickness has an effect on the joint spacing but the correlation of joint spacing and layer thickness is low 2 joint density of systematic joints is greater than nonsystematic joints and the joint density of a thin layer is also greater than that of a thick layer and 3 the joints of mesozoic strata in the basin are the result of tectonic events affected by multiple stress fields all these joints in the mesozoic strata are formed in the two main tectonic events since late mesozoic times one is the westward subduction of the pacific plate beneath the eurasia plate which formed the approximately e w trending compressive stress field in the china continent the trends of the j1 joint set e w and the bisector of conjugate shear fractures composed of ene wsw and ese wnw fractures are all parallel to the trend of maximum compressive stress e w the other stress field is related to the collision of the indian and eurasian plates which formed the ne sw trending compressive stress field in the china continent the trends of the j3 joint set and bisector of conjugate shear fractures composed of ene wsw and nne ssw fractures are all parallel to the trend of maximum compressive stress ne sw finally we conclude that the j1 and j4 sets are formed in the e w trending compressive stress field and the j2 j3 j5 j6 j7 and j8 sets are formed in the ne sw trending stress field

pitfalls of using entrenched fracture relationships fractures in bedded carbonates of the hidden valley fault zone canyon lake gorge comal county texas characterizing natural fracture systems involves understanding fracture types faults joints and veins patterns orientations sets and spacing within sets size distributions penetration across layering aperture and trace length and timing relationships traditionally observation based relationships to lithology mechanical stratigraphy bed thickness structural position failure mode and stress history have been proposed for predicting fracture spacing along with the relative abundance of opening mode fracture versus faults in fractured rocks developing a conceptual fracture model from these relationships can be a useful process to help predict deformation in a fractured reservoir or other fractured rock systems a major pitfall when developing these models is using assumptions based on general relationships that are often site specific rather than universal in this paper we examine a mixed carbonate shale sequence that is cut by a seismic scale normal fault where fracture attributes do not follow commonly reported fracture relationships specifically we find 1 no clear relationship between frequency or spacing of opening mode fractures joints and veins and proximity to the main fault trace and 2 no detectable relationship between fracture spacing and bed thickness however we did find that 1 the frequency of small displacement faults is strongly and positively correlated with proximity to the main fault trace 2 fracture networks change pattern and failure mode extension versus shear fracture from pavement to pavement through the mechanically layered stratigraphic section and 3 faults are more abundant than opening mode fractures in many areas within the fracture network we interpret that the major fracturing initiated near maximum burial under relatively high differential stress conditions where shear failure dominated and that mode 1 extension fracturing occurred later under lower differential stress conditions filling in between earlier formed shear fractures we conclude that whenever possible site specific observations need to be carefully analyzed prior to developing fracture models and perhaps a different set of fracture network rules apply in rocks where shear failure dominates and mechanical stratigraphy influences deformation

depositional sequences diagenesis and structural control of the albian to turonian carbonate platform systems in coastal fars sw iran abstract this study covers a 300 km long ne sw oriented transect including five outcrop sections and provides new biostratigraphic data and a sequence stratigraphic interpretation of the albian cenomanian and turonian sediments kazhdumi and sarvak formations present in coastal fars sw iran two different carbonate depositional systems are distinguished one for the albian and one for the cenomanian turonian during the albian eustatic control was the dominant factor influencing sedimentation while during the cenomanian and turonian large and small scale tectonics were dominant this resulted in significant thickness variations and local diagenetic overprint of the sequence boundaries regional correlations were established constrained by ammonite data as well as sedimentological and sequence stratigraphic considerations in the albian interval including the kazhdumi formation and re dated mauddud member three 3rd order sequences have been distinguished the depositional system consists of muddy carbonate ramps rich in orbitolinid benthic foraminifers which laterally interfinger with green marls albian deposits are present throughout the area and vary in thickness from 100 to 160 m subaerial exposure has only been observed on top of the albian 3 sequence top mauddud member in the upper part of the succession which is of cenomanian turonian age the depositional system changed to rudist rimmed carbonate platforms surrounding local organic rich intra shelf basins the thickness in this interval varies greatly from 0 to 300 m which was controlled by both large scale qatar fars high and local scale salt domes tectonic processes in this tectonically active setting three cenomanian and one turonian 3rd order sequences have been distinguished several sequence boundaries show evidences for long lasted subaerial exposures up to 13 ma with the local preservation of soil sequences and continental deposits the expression of these exposures varies laterally considerably and macroscopic evidences are sometimes lacking petrographic and c o stable isotope investigations supplement classic sedimentology to reveal the record of these exposures

implications of heterogeneous fracture distribution on reservoir quality an analogue from the torridon group sandstone moine thrust belt nw scotland abstract understanding fracture network variation is fundamental in characterising fractured reservoirs simple relationships between fractures stress and strain are commonly assumed in fold thrust structures inferring relatively homogeneous fracture patterns in reality fractures are more complex commonly appearing as heterogeneous networks at outcrop we use the achnashellach culmination nw scotland as an outcrop analogue to a folded tight sandstone reservoir in a thrust belt we present fracture data is collected from four fold thrust structures to determine how fracture connectivity orientation permeability anisotropy and fill vary at different structural positions we use a 3d model of the field area constructed using field observations and bedding data and geomechanically restored using move software to determine how factors such as fold curvature and strain influence fracture variation fracture patterns in the torridon group are consistent and predictable in high strain forelimbs however in low strain backlimbs fracture patterns are inconsistent heterogeneities in fracture connectivity and orientation in low strain regions do not correspond to fluctuations in strain or fold curvature we infer that where strain is low other factors such as lithology have a greater control on fracture formation despite unpredictable fracture attributes in low strain regions fractured reservoir quality would be highest here because fractures in high strain forelimbs are infilled with quartz heterogeneities in fracture attribute data on fold backlimbs mean that fractured reservoir quality and reservoir potential is difficult to predict

appraisal of fracture sampling methods and a new workflow to characterise heterogeneous fracture networks at outcrop abstract characterising fractures at outcrop for use as analogues to fractured reservoirs can use several methods four important fracture data collection methods are linear scanline sampling areal sampling window sampling and circular scanline sampling in regions of homogeneous fracture networks these methods are adequate to characterise fracture patterns for use as outcrop analogues however where fractures are heterogeneous it is more difficult to characterise fracture networks and a different approach is needed we develop a workflow for fracture data collection in a region of heterogeneous fractures in a fold and thrust belt which we believe has applicability to a wide variety of fracture networks in different tectonic settings we use an augmented circular scanline method along with areal sampling to collect a range of fracture attribute data including orientation length aperture spatial distribution and intensity this augmented circular scanline method more than halves the time taken for data collection provides accurate unbiased data that is representative of local fracture network attributes and involves data collection of a wider range of fracture attributes than other sampling techniques alone