simulation of multi period tectonic stress fields and distribution prediction of tectonic fractures in tight gas reservoirs a case study of the tianhuan depression in western ordos basin china abstract hydraulic fracturing technology which is emerging in low or ultralow permeability oil and gas and tight gas reservoirs has become a key technology for improving the development efficiency and economic benefit of unconventional gas reservoirs the success rate of hydraulic fracturing is closely related to the development and distribution of natural fractures data obtained from outcrops cores thin sections and image logging were used to determine the developmental characteristics of tectonic fractures in the study area to obtain a quantitative forecast of the distribution of gas reservoir fractures in the tianhuan depression with the aid of burial history analysis geologic interpretation seismic inversion logging evaluation rock mechanics and acoustic emission tests 3d geomechanical models were established using the finite element method in tianhuan depression to simulate the paleotectonic stress fields during indosinian yanshanian and himalayan periods the effects of different rock mechanics parameters on the development and distribution of tectonic fractures were identified a fracture density model was established to determine the quantitative development of tectonic fractures in the upper he8 member during the production of multi period tectonic stress fields the validity of the fracture density model was verified by the fracture statistics of drill core density and gas well productivity tests favorable areas for hydraulic fracturing were also determined simulation results indicate that the maximum and minimum principal stresses and the maximum shear stress during the indosinian yanshanian and himalayan periods are controlled by the distribution of the sand body rock mechanics parameters play important roles in the development of tectonic fractures in the sedimentary basin with less faults and folds the 3d models of the multi period tectonic stress fields and density calculation modelling are not only significant for tight gas sandstone reservoirs but also for predicting of other reservoir fractures

depositional history and sequence stratigraphy of the precambrian cambrian boundary stratotype section chapel island formation southeast newfoundland abstract facies relationshps in the vendian to lower cambrian chapel island formation of southeast newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section the formation consists of five members of sandstone mudstone and minor limestone deposited in a variety of shoreline to shelf environments peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2 these make up a transgressive system tract in which small scale changes in relative sea level are superimposed on autocyclic deltaic processes the thickness 400 m of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low energy oxygen stratified basin these deposits are arranged in three large scale shoaling cycles representing three foresteping parasequences of one highstand systems tract an extensive limestone bed at the tope of member 4 contains a sequence boundary associated with or shortly postdating development of this surface is a significant epeirogenic event that resulted in basin reorganization increased subsidence and progradation of a thick clastic sequence represented by member 5 the deposits of this upper member consist of an upward coarsening storm dominated shelf to shoreface succession of sandstone and silstone deposits of nearly identical character are also found in new brunswick and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation global correlation of the paleobathymetric curve developed for the chapel island formation is considered unfeasible given the long history of epeirogenic movements during the vendian and early cambrian in this region

prediction of tensile fractures in ks2 trap kuqa depression nw china abstract tectonic fractures that generally controlled by tectonic stress field especially tensile fractures are crucial for tight reservoirs that are characterized by low porosity and low permeability prediction of fracture distribution is extremely important for further exploration and development of such reservoirs tensile fractures are developed in the upper bashijiqike formation in kuqa depression in northwest china the subject of this study was the ks2 faulted fold and the characteristics of the tensile fractures were analyzed in detail a three dimensional finite element elastic model of the faulted fold was constructed and the two factor method was applied to predict the distribution of tensile fractures in the upper bashijiqike formation in the faulted fold distributions of predicted tensile fractures reveal that positions relative to the fold axis and faults in the hinge zone both have significant influence on the distribution of tensile fractures the predicted tensile fractures are developed in the hinge zone in the faulted fold particularly in the area around fault tips which is the region with the most potential for oil and gas exploration in faulted folds

the seasat a satellite scatterometer the geophysical evaluation of remotely sensed wind vectors over the ocean on the seasat a satellite a microwave scatterometer was used to determine the vector wind over the world s oceans the technique is based on the sensitivity of microwave radar backscatter to the centimeter length ocean waves created by the action of the surface wind this paper describes the algorithm used to convert the scatterometer s measurements of ocean normalized radar cross section to the neutral stability vector wind at 19 5 m height and the comparison of these winds with high quality surface observations the wind vector algorithm used an empirical model function to describe the dependence of the ocean 0 on the 19 5 m neutral stability wind vector two model functions developed from a limited base of aircraft and satellite measurements were evaluated by using an independent set of in situ surface wind observations from the joint air sea interaction experiment jasin although these model functions were found to have some weaknesses the results of these comparisons produced better results than the seasat specifications of wind speed accuracy of 2 m s and wind direction accuracy of 20 over the 0 16 m s range of winds observed during jasin an improved model function was later developed by tuning to these jasin data so that the remaining biases between the observed surface winds and the scatterometer derived winds were minimized results are presented for this model function compared against other surface wind observations from the gulf of alaska seasat experiment and the seasat storms hurricane experiment

wind direction alias removal studies of seasat scatterometer derived wind fields owing to the antenna configuration and the biharmonic nature of the anisotropic return of the probing radar the seasat scatterometer wind reports consist of as many as four wind directions at each point of observation a systematic methodology is proposed for selection of the true direction from among these in the absence of any in situ observations the techniques employed are those familiar to meteorological analysts they were subjected to rigorous testing for the jasin workshop with two teams performing independent analyses the agreement of the two analyses was striking comparison with wind directions from the jasin data set and those estimated from the analyzed pressure field show agreement largely within the seasat specifications it is concluded that the methodology employed is suitable for seasat scatterometer data users

the control of stress history and flaw distribution on the evolution of polygonal fracture networks abstract we use boundary element models of fracture propagation and linkage to investigate the factors controlling the development of two dimensional multi directional polygonal fracture networks characterised by a large number of abutting intersections between fractures the position and orientation of a number of fracture seeds are prescribed in the model which propagate when the applied stress reaches a critical value according to linear elastic fracture mechanics theory the applied boundary condition is a remote isotropic horizontal tension where the stress is increased at a steady rate throughout each model to simulate continued fracture growth realistic polygonal systems are developed with the boundary element model simulations which are comparable with those observed in natural systems such as those found within eocene and oligocene mudrocks in the north sea and on the surface of mars if conditions exist where a small number of fracture seeds propagate and develop significant structures before others then these will dominate the resulting fracture network geometry not only do such early structures represent the largest fractures in the system they also significantly modify the stress field around them preventing some other seeds from developing and influencing the propagation paths of nearby fractures fracture seeding distribution and the rate at which the stress is increased are found to be the most significant parameters affecting the development of fracture network geometry these results suggest that the geometry of evolving fracture networks should be considered not only in terms of the mechanical properties of the deforming material but also in terms of the stress rate driving deformation

microwave radiometric measurements of sea surface temperature from the seasat satellite first results initial results from the seasat scanning multichannel microwave radiometer indicate that the sea surface temperature can be measured with a root mean square sensitivity of 1 2 c or better the first microwave map of sea surface temperature for the entire pacific has been produced

latest precambrian to early cambrian basin evolution fortune bay newfoundland fault bounded basin to platform uppermost precambrian and lowest cambrian sediments of the rencontre chapel island and random formations in the fortune bay area western avalon zone consist of conglomerates sandstones and shales deposited in fluvial marginal marine and open marine settings deposition began in a small fault bounded basin alternation between nonmarine and marine deposition resulted from pulses in fault activity uplift and coarse terrestrial clastics separated by quiescent periods of basinwide thermal subsidence transgressive fine grained marine units overstepping earlier basin margins the tectonic regime may have been extensional rift or transtensional strike slip pull apart a strike slip origin is easiest to defend and is consistent with current tectonic models for the avalon zone involving prolonged extension or transtension but little spreading the fortune bay basin persisted until the beginning of the cambrian period at which time eustatic sea level rise led to widespread transgression and d

tidal deposits of the lower cambrian random formation eastern newfoundland facies and paleoenvironments the avalon tectonostratigraphic zone occupies about 25 of the area of insular newfoundland late precambrian development of the avalon terrane is distinctly different than that of other parts of the appalachian orogen and cratonic north america late precambrian volcanism and tectonic instability gave way to deposition of about 2 km of cambrian and lower ordovician dominantly epiclastic sediments on a slowly subsiding relatively stable shelf platform the lower cambrian random formation is part of the platformal sequence and is bounded by regional disconformities over much of the newfoundland avalon zone except around fortune bay where it is underlain by older terrestrial and shallow marine sediments the random formation was deposited during a time of global sea level rise and consists of up to 250 m of shoreline nearshore and open shelf deposits that record macrotidal conditions and periodic storm activity cross bedded quartzarenites occur in units to about 50 m thick one exceptional unit is 110

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

quantitative prediction of fractures using the finite element method a case study of the lower silurian longmaxi formation in northern guizhou south china abstract natural fractures have long been considered important factors in the production of gas from shale reservoirs because they can connect pore spaces and enlarge transport channels thereby influencing the migration accumulation and preservation of shale gas industrial level shale gas production has been initiated in the lower silurian longmaxi formation in northern guizhou south china however it is important to quantitatively predict the distribution of natural fractures in the lower silurian shale reservoirs to locate additional sweet spots in northern guizhou in this study data obtained from outcrops cores thin sections field emission scanning electron microscope fe sem images and x ray diffraction xrd were used to determine the developmental characteristics and controlling factors of these fractures correlation analysis indicated that the mechanical parameters of the longmaxi shale are mainly related to the total organic carbon toc quartz clay calcite and dolomite contents the spatial variations in the mechanical parameters of the longmaxi shale were determined based on the spatial variations in the toc and mineral contents then a heterogeneous geomechanical model of the study area was established based on interpretations of the fault systems derived from seismic data and acoustic emission ae experiments performed on samples of the relevant rocks the paleotectonic stress fields during the yanshanian period were obtained using the finite element method fem finally a fracture density calculation model was established to analyze the quantitative development of fractures and the effects of faults and mechanical parameters on the development of fractures were determined the results suggest that the main developmental period of tectonic fractures in the longmaxi formation was the early yanshanian period during this time the horizontal principal stress conditions were dominated by a se nw trending 135 315 compressional stress field and the longmaxi formation experienced a maximum tectonic stress of 110 120 mpa this simulated paleotectonic stress field was mainly controlled by faults and the contents of toc quartz clay calcite and dolomite at different positions along the same fault the degree of fracture development varies significantly overall the distribution of fractures in the longmaxi formation can be used to optimize well deployment and provides a basis for the future exploration of shale gas

thickness and spatial distributions of clastic dykes northwest sacramento valley california abstract the geometry and distribution of the clastic dykes of the ono district north sacramento valley are examined within stream sections five traverses along dry stream beds provide good exposure allowing the spacing thickness and geometry of the dykes to be recorded the spatial and thickness distribution of the dykes are considered using cumulative frequency plots allowing a visual estimation of a best fit distribution dyke thickness conforms best to a log normal distribution there is also a characteristic minimum dyke thickness in a traverse and this is attributed to the minimum aperture that a fluid with sand clasts is able to exploit dyke spacing however shows a good correlation with a power law distribution for four traverses suggesting that there is a mechanistic control on the spatial distribution plotting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation unlike veins and igneous dykes clastic dykes continue to provide preferential pathways for fluid flow subsequent to their intrusion thus inhibiting intrusion in the area surrounding a pre existing dyke a combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the ono district california

strangelove ocean before the cambrian explosion the palaeozoic and mesozoic eras were terminated by faunal changes involving mass extinction of the old and explosive evolution of the new fauna but the fossil record shows only a cambrian explosion at the end of the precambrian stanley speculated that the explosion was only possible after the ubiquitous algae community had been largely eliminated1 ecological niches were thus liberated for explosive evolution if the cambrian explosion were preceded by a mass mortality or by a mass extinction such an event should leave a record in the form of geochemical anomalies we have undertaken a search for geochemical anomalies at the precambrian cambrian contact we report here the discovery of a sharp negative carbon isotope shift in the carbonate of a clay immediately above a marker in the precambrian cambrian boundary the china c marker and interpret this signal as evidence of sudden decrease in fertility before the cambrian explosion of invertebrate evolution the discovery suggests that the precambrian cambrian boundary might be defined by an event marker at a palaeontologically correlative horizon

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

the evolution of pore scale fluid saturation in low permeability sandstone reservoirs in many tight gas basins of the western united states distinguishing between productive and non productive low permeability sandstones and predicting relative amounts of gas and water production is difficult comparison of gas shows calculated water saturations and saturation height profiles between gas productive and non productive sandstones of equal reservoir quality all appear similar capillary pressure derived height functions are difficult to apply and classic rock typing procedures lack the predictive capability that is common to more traditional reservoirs basin reconstructions suggest the timing of petroleum charge and migration preceded maximum burial and uplift this initial charge was likely a primary drainage displacement with reservoir porosity greater by a factor of 2 3 relative to values found today and permeability greater by 1 3 orders of magnitude these reservoir systems became low permeability following initial charge reflecting continued diagenesis throughout burial subsequent uplift and erosion with burial decreasing pore volume caused water saturations and gas columns to increase during uplift and erosion gas columns adjusted to changing structural configuration in some cases this led to gas accumulations being leaked and spilled in other cases structural readjustment resulted in capillary imbibition and in some cases secondary or higher order drainage and imbibition within trapped accumulations gas expansion upon uplift further increased gas columns in cases where gas columns were spilled or within migration pathways imbibition led to residual or near residual water saturations conventional formation evaluation is fundamentally rooted in concepts associated with primary drainage displacement tight gas reservoirs that have experienced late uplift following an earlier phase of charge are unlikely to be characterized by primary drainage and are much more likely to be characterized by imbibition or secondary or higher order drainage and possibly imbibition the hysteresis between primary drainage and imbibition or secondary or higher order drainage and imbibition in tight gas reservoirs is significant and unlike many more traditional reservoirs does not tend to converge on a narrow range of values estimates of water saturation are scalar values and do not contain information that allows the saturation history and displacement direction to be deciphered recognition that reservoirs are unlikely to be in primary drainage equilibrium is a fundamental paradigm shift that impacts petroleum evaluation at all scales ranging from basin potential to completion decisions within a given well although this paper is written from the perspective of tight gas petroleum systems the principles are equally applicable to low permeability oil reservoirs

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

fracture development in paleozoic shale of chongqing area south china part one fracture characteristics and comparative analysis of main controlling factors abstract natural macro and micro fractures in the longmaxi shale lower silurian from yuye 1 well and the niutitang shale lower cambrian from yuke 1 well are characterized regional geological structural evolution and shale geochemistry including toc and mineral composition etc are analyzed the controlling factors of natural fractures in palaeozoic shale in the southeast of chongqing have been confirmed which have been analyzed qualitatively or semi quantitatively the results show that fractures are abundant in both the longmaxi shale and niutitang shale due to the multiphase strong tectonic movement in the southeast of chongqing therefore tectonic factors are the principal factors that control fracture development in the paleozoic shale of this region followed by the mineral composition of the shale vertically the mineral composition of shale in yuke 1 well has a high dispersion degree and a strong heterogeneity the dispersion coefficients of quartz and dolomite were 0 48 and 1 respectively therefore the development and distribution of fractures are controlled by quartz and dolomite content in the niutitang shale moreover the quartz content shows positive correlation with the fractures quantity and fractures are most abundant where dolomite content up to 64 7 while the mineral composition of shale in yuye 1 well has a low dispersion degree and a strong homogeneity in a vertical position the dispersion coefficients of quartz and plagioclase were 0 15 and 0 26 respectively which shows unconspicuous control effect for fractures therefore the development and distribution of fractures are mainly controlled by the toc content moreover the toc content shows positive correlation with the fractures quantity fractures are sealed by calcite quartz and pyrite although sealed fractures do not contribute to the permeability of the reservoir they are important planes of weakness that tend to be reactivated by hydraulically induced fractures sem images show that intergranular pore is connected by microfractures thereby the validity of porosity has been improved the mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

wave formed coarse grained ripples and their relationship to hummocky cross stratification abstract wave formed coarse grained ripples cgr form in water depths ranging from 3 to 160 m on transgressive surfaces in upper and lower shoreface sediments and in finer grained offshore transition deposits cgr have crest spacings of 0 25 3 0 m with amplitudes of 5 35 cm internal stratification is rarely preserved but where present crossbeds dip en echelon away from the ripple crest and individual laminae feather out away from the crest waves that form cgr commonly have wavelengths on the order of 2 5 m with periods of 8 to 14 sec these are not large storm events especially on a geological scale cgr commonly occur in close association laterally and vertically with hummocky cross stratification it is postulated that if sediment is medium to very coarse grained sand or pebbly sand then two dimensional cgr will be formed from oscillatory or oscillatory dominant flow if however sediment is very fine to fine grained sand then three dimensional hummocky cross stratification will be formed the wave conditions under which cgr form are similar to those which would form hummocky cross stratification it is only the grain size that is different reported and calculated wave conditions for hummocky cross stratification are almost identical to those for cgr modern cgr crests trend parallel to the local shoreline and bathymetry as such ancient ripple crests are a useful tool for basin reconstruction

modelling approaches to understanding fold development implications for hydrocarbon reservoirs a mechanics based approach to the evolution of buckle folds is proposed existing analytic and simple numerical models are used to demonstrate that dramatic changes in layer parallel stress occur in developing folds and that the bulk effective rheology of folding rocks is strongly reduced in relation to neighbouring rocks with no folds a methodology for estimating regions of folds more or less likely to suffer fracture is set out in this methodology a simple abstraction of the natural fold is identified and the stress history during its development is calculated using linear viscosity as a proxy for competence this simple and computationally cheap approach allows all salient features of natural multilayer folds to be recreated in numerical experiments the final step in the method is to use the stress conditions for three types of fracture failure tensile failure dilatant shear failure and grain crushing to define potential functions that indicate increased or decreased probability of failure results give predictions that agree well with observation in the simple cases studied a novel method for approximating three dimensional deformations is used to model the propagation of folds in the axial direction and it is found that this occurs rapidly and allows constructive and destructive interference of propagating folds below a certain amplitude this provides a means by which perturbations may interact over a certain distance such a mechanism was an implicit requisite of classic fold theories but its identity has been obscure for three decades it is shown that many small perturbations are needed to give patches of coherent folds and that few large perturbations give single arc folds

simulation of paleotectonic stress fields and quantitative prediction of multi period fractures in shale reservoirs a case study of the niutitang formation in the lower cambrian in the cen gong block south china abstract reservoirs where tectonic fractures significantly impact fluid flow are widespread industrial level shale gas production has been established from the lower cambrian niutitang formation in the cen gong block south china the practice of exploration and development of shale gas in the cen gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures in this study the data obtained from outcrop cores and logs were used to determine the developmental characteristics of such tectonic fractures by doing an analysis of structural evolution acoustic emission burial history logging evaluation seismic inversion and rock mechanics tests 3 d heterogeneous geomechanical models were established by using a finite element method fem stress analysis approach to simulate paleotectonic stress fields during the late hercynian early indo chinese and middle late yanshanian periods the effects of faulting folding and variations of mechanical parameters on the development of fractures could then be identified a fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells the simulation results indicate the magnitude of minimum principal stress during the late hercynian early indo chinese period within the cen gong block is 100 110 mpa with a direction of se nw 140 320 and the magnitude of the maximum principal stress during the middle late yanshanian period within the cen gong block is 150 170 mpa with a direction of nnw sse 345 165 during the late hercynian early indo chinese period the mechanical parameters and faults play an important role in the development of fractures and fractures at the downthrown side of the fault are more developed than those at the uplifted side folding plays an important role in the development of fractures in the middle late yanshanian period and faulting is a secondary control this 3 d heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas but also have a practical significance for the prediction of other reservoir fractures

lithostratigraphy of the cambrian lower ordovician saint john group southern new brunswick the cambrian lower ordovician saint john group of the saint john area southern new brunswick has historically been subdivided into 11 formations the existing scheme is inappropriate however as many of the supposed formations particularly those of middle cambrian early ordovician age were distinguished on a biostratigraphic rather than lithostratigraphic basis we suggest the sequence can be more appropriately subdivided into seven formations each of which can be clearly and easily identified by the field geologist lower cambrian formations comprise from base to top the ratcliffe brook glen falls and hanford brook formations all of which are retained from the previous nomenclature middle cambrian strata comprise the forest hills formation to replace the fossil brook and porter road formations and upper cambrian strata the king square formation to replace the hastings cove and agnostus cove formations and silver falls formation to replace the black shale brook and narrows formations

cloud cover from high resolution scanner data detecting and allowing for partially filled fields of view we present a new technique for obtaining cloud cover and determining clear sky radiances using high resolution infrared scanner data the technique which can be automated uses the spatial structure of the ir radiance field to identify radiances associated with fields of view that are either free of clouds or completely covered by clouds drawn from one or more distinct layers as the method uses only infrared radiances it should provide equally good results for both daytime and nighttime observations the approach is particularly suited for determining clear sky radiances over oceans from which sea surface temperature might be derived in addition for single layered systems the cloud cover fraction for a given region may be obtained from the clear sky radiance the completely cloud covered radiance and the mean radiance for the region for such systems the separation of completely covered from partially covered fields of view allows an estimate of the errors associated with commonly used threshold techniques for determining cloud cover these errors are in general shown to be highly sensitive to the applied threshold and to depend on the cloud areal size distribution in addition unlike the spatial coherence method described here histograms and correlations of visible and ir radiances as proposed for archiving information on cloud cover may fail to reveal the layered structure of cloud systems furthermore the high local structure observed for the visible radiances of regions that appear to be completely cloud covered makes it impossible to obtain reliable estimates of the cover from visible radiances alone

bathymetry estimates in the southern oceans from seasat altimetry a mean sea surface height based on seasat altimeter data has been high pass filtered to reveal a pattern of geoid anomalies which are highly correlated with sea floor topography the technique is used to locate new bathymetric features in the poorly surveyed southern oceans

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

fracture initiation growth and effect on stress field a numerical investigation a numerical investigation was made of the relationships between fracture initiation growth stress field and boundary conditions two dimensional plane strain continuum models were used in which fractures appeared as zones of strain localization developed through application of a strain softening mohr coulomb constitutive model r and r fractures developed first followed by y fractures at larger strains the models showed that equal development of conjugate r and r fractures is easily changed to favor one or the other set by minor variations in model initial conditions strength loss in fractures caused stress field rotations in regions bounded by fractures altering the orientation of subsequent fractures the amount and sense of stress field rotation is dependent on the strength loss during displacement on the fractures the orientation of fractures and on the boundary conditions y oriented fractures could be explained on the basis of a mohr coulomb failure criterion provided that stress field rotation is accounted for monitoring of fracture slip activity showed that under conditions of constant boundary velocity slip was discontinuous in time alternating on fractures throughout the model

role of shale thickness on vertical connectivity of fractures application of crack bridging theory to the austin chalk texas abstract contrasting material properties of alternating chalk and shale layers control vertical connectivity of fractures our field observations within the austin chalk texas indicate that 1 the majority of vertical fractures occur in chalk layers and abut against contacts with shale layers 2 thicker shale layers have greater resistance to fracture propagation than thinner shale layers from these observations we hypothesize both the resistance of shale to fracturing and the thickness of shale layers may inhibit fracture propagation across the shale and into the next chalk layer we model crack propagation within a three layered system brittle chalk fracture resistant shale brittle chalk the modeled crack extends across the shale but closing tractions applied to the crack segment within the shale layer simulate resistance of shale to fracturing the crack tip lies a short distance within the unfractured chalk layer simulating a coplanar flaw with potential to propagate if the stress intensity factor at the flaw exceeds the chalk fracture toughness the crack propagates thereby bridging and eventually rupturing the shale layer for any chalk thickness there is a critical shale thickness above which fractures cross the shale layer and below which fractures arrest at shale finite element method fem analysis evaluates the influence of shale ductility within the chalk shale chalk system although remote and fluid pressure driven fractures produce identical stress intensity factors in elastic chalk shale systems lower driving stresses are required to propagate fluid pressure driven fractures through a system ductile shale layers than fractures under remote tension

3d geomechanical modeling and numerical simulation of in situ stress fields in shale reservoirs a case study of the lower cambrian niutitang formation in the cen gong block south china abstract an analysis of the in situ state of stress in a shale reservoir was performed based on comprehensive information about the subsurface properties from wellbores established during the development of an oil and gas field industrial level shale gas production has occurred in the niutitang formation of the lower cambrian cen gong block south china in this study data obtained from hydraulic fracturing drilling induced fractures borehole breakout global positioning system gps and well deviation statistics have been used to determine the orientation of the maximum horizontal principal stress additionally hydraulic fracturing and multi pole array acoustic logging xmac were used to determine the vertical variations in the in situ stress magnitude based on logging interpretation and mechanical experiments the spatial distributions of mechanical parameters were obtained by seismic inversion and a 3d heterogeneous geomechanical model was established using a finite element stress analysis approach to simulate the in situ stress fields the effects of depth faults rock mechanics and layer variations on the principal stresses horizontal stress difference horizontal stress difference coefficient k h and stress type coefficient s p were determined the results show that the direction of the maximum principal stress is ese 120 additionally the development zones of natural fractures appear to correlate with regions with high principal stress differences at depths shallower than 375 m the stress type is mainly a thrust faulting stress regime at depths ranging from 375 to 950 m the stress type is mainly a strike slip faulting stress regime when the depth is 950 m the stress type is mainly a normal faulting stress regime depth fault orientation and rock mechanics all affect the type of stress the knowledge regarding the cen gong block is reliable and can improve borehole stability casing set point determination well deployment optimization and fracturing area selection

predicting the regional distribution of fracture networks using the distinct element numerical method previous research has shown the importance of understanding the relationship between fault geometry and current applied tectonic stresses in the prediction of critically stressed faults and their propensity for fluid flow via generated fracture networks along and or around the fault plane this article summarizes research aimed at increasing this understanding by applying the distinct element method dem to predict stress within a rock mass generated by far field stress on seismically resolvable faults within a modeled area we showed that increases in differential over regional stress can be correlated with the presence of fractured rock as detected by petrophysical logs and core and drilling data a case study example is used to illustrate the methodology from the penola trough otway basin south australia modeled using two dimensional dem assuming a reasonable understanding of 1 rock properties 2 structure and 3 far field or regional stress then the technique described in this article provides a valid workflow to increase confidence in the prediction of the generation of fractures and their spatial distribution

an approach to the present day three dimensional 3d stress field and its application in hydrocarbon migration and accumulation in the zhangqiang depression liaohe field china abstract from the measurements of bore hole breakout hydrofracturing and rock acoustic emission in the zhangqiamg depression liaohe field china we have determined that the orientation of the maximum principal compressive stress is nearly east west with a small angle of pitch no more than 10 and the regression equations of stress gradient with depth are 1 8 359 0 0142h r 0 96 and 3 5 801 0 00437h r 0 94 the present day three dimensional 3d stress field of the zhangqiang depression is approached using measured data and by 3d modeling the approach shows that a full 3d crustal stress field analysis of an oil basin is consistent with the actual measurements and then we use fluid potential or gradient to discuss the quantitative correlation between crustal stress and hydrocarbon migration and accumulation the results show that low fluid potential areas surrounded by high regions are eligible for hydrocarbon accumulation and have been tested at the keerkang oil field the results also show that the distribution of favorable areas for hydrocarbon accumulation varies in different layers in space and is used in hydrocarbon exploration in the zhangqiang depression therefore the understanding of the 3d crustal stress field of a basin is essential for evaluating hydrocarbon migration and accumulation and the technology and methodology developed here can be applied to other petroliferous basins

shallow water gravity flow deposits chapel island formation southeast newfoundland canada a remarkable suite of shallow water gravity flow deposits are found within very thinly bedded siltstones and storm generated sandstones of member 2 of the chapel island formation in southeast newfoundland medium to thick siltstone beds termed unifites range from non graded and structureless type 1 to slightly graded with poorly developed lamination type 2 to well graded with lamination similar to that described for fine grained turbidites type 3 unifite beds record deposition from a continuum of flow types from liquefied flows type 1 to turbidity currents type 3 calculations of time for pore fluid pressure dissipation support the feasibility of such transitions raft bearing beds consist of siltstone with large blocks or rafts of thinly bedded strata derived from the underlying and adjacent substrate characteristics suggest deposition from debris flows of variable strength estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters an assumed density of 2 0 g cm 1 and a compaction estimate of 50 gives a strength estimate of 79 7 dyn cm 2 and a depositional slope estimate of 0 77 the lithologies and sedimentary structures in member 2 indicate an overall grain size distribution susceptible to liquefaction inferred high sediment accumulation rates created underconsolidated sediments metastable packing types of sediment failure included in situ liquefaction disturbed bedding sliding and slumping raft bearing debrites resulted from sliding and incorporation of water locally hummocky cross stratified sandstone directly overlies slide deposits and raft bearing beds linking sediment failure to the cyclical wave loading associated with large storms the gravity flows of the chapel island formation closely resemble those described from the surfaces of modern mud rich marine deltas details of deltaic gravity flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side scan sonar

fracture permeability created by perturbed stress fields around active faults in a fractured basement reservoir several researchers have suggested that perturbed stress fields associated with active faults significantly affect flow properties in the subsurface to examine this insight quantitatively we combine an elastic dislocation model of active faults and a stress compliant function for fracture apertures to evaluate flow properties in a fractured basement reservoir in the yufutsu field japan the most productive well in the reservoir shows about 90 of rotation of the axes of horizontal stresses along the well trajectory whereas the directions of horizontal stresses at nonproductive wells are commonly oriented consistently with those of the regional stresses additionally results of step rate hydraulic injection tests at the nonproductive well indicate that fracture apertures fluctuate significantly in response to the magnitude of stresses normal to the fracture surfaces these observations support the important effect of perturbed stress fields on flow properties the observed stress orientation profiles are correlated to those from a geomechanical model nonproductive wells were drilled in the area where the regional stress state prevails and the most productive well penetrates the area near the tips of active faults where the stress concentration leads to enhancements in fracture permeability by opening or shearing the modeled perturbed stress fields combined with a stress compliant function for opening of fracture apertures can explain the observed difference of well performances to the first order the model demonstrates that areas near the tips of active faults have high potentials for hydrocarbon production in fractured basement reservoirs

methodology for predicting reservoir breakdown pressure and fracture opening pressure in low permeability reservoirs based on an in situ stress simulation abstract using numerical simulations of the paleostress field during the time of fracture formation we predict the occurrence of fractures in the reservoirs of the second member of the funing formation in the tongcheng fault zone subei basin east china we use sonic velocity measurements from rock cores and microseismic monitoring to determine the in situ stress which is combined with fracture data to calculate the magnitude of the in situ stress at the well site by determining the mechanical parameters of the rock we use the finite element method fem to develop a geomechanical model and conduct numerical simulations of the in situ stress field based on the occurrence of fractures and the numerical simulation results of the in situ stress field we predict the opening pressure and opening sequence of natural fractures in the reservoirs the results indicate that the maximum horizontal principal stress in the second member of the funing formation in the tongcheng fault zone is oriented ene during the injection process the ene trending fractures open first and the ese trending fractures open later the opening pressure of the fractures increases as the angle between the fracture strike and the maximum horizontal principal stress increases and the burial depth of the fractures also has a relatively positive correlation with the opening pressure at the structurally high site 1850 m 2350 m the opening pressure of the fractures is in the range of 25 mpa 50 mpa and at the structurally low site 3300 m 4000 m the opening pressure of the fractures is in the range of 45 mpa 75 mpa by calculating the actual fracture pressure of the reservoirs we propose using different injection pressures in different blocks to ensure the high and stable production of oil from wells

oceanography from space active and passive spaceborne instruments that can observe the sea are discussed attention is given to satellite observations of ocean surface temperature and heating wind speed and direction ocean currents wave height ocean color and sea ice specific measurements now being made from space are described the accuracy of various instruments is considered and problems associated with the analysis of satellite data are examined it is concluded that the satellites and techniques used by different nations should be sufficiently standard that data from one satellite can be directly compared with data from another and that accurate calibration and overlap of satellite data are necessary to confirm the continuity and homogeneity of the data

dissolution pores in shale and their influence on reservoir quality in damintun depression bohai bay basin east china insights from sem images n2 adsorption and fluid rock interaction experiments abstract shale pore characterization is crucial for understanding the mechanism of shale hydrocarbon accumulation and its effective exploitation x ray diffraction xrd optical microscopy scanning electron microscopy sem pore extraction nitrogen n2 adsorption and fluid rock interaction experiments were used to study the shale pore structure of the fourth member of the paleogene shahejie formation in the damintun depression east china the damintun shale included three types of pores organic matter pores mineral matrix pores and microfractures the dissolution pores were mainly developed between and inside the matrix minerals such as calcite dolomite and feldspar the average shale visible dissolution porosity determined using sem was 1 12 n2 adsorption analysis revealed that the less than 20 nm pores were the main reservoir space in the damintun shale fluid rock interaction experiments indicated that the degrees of dissolution of the calcite and dolomite were similar and stronger than those of the k feldspar and plagioclase the shale with a high content of carbonate minerals calcite and dolomite exhibited more intense dissolution the degree of dissolution pores development was positively correlated with total organic carbon toc and carbonate mineral calcite and dolomite contents the average contribution of the dissolution porosity to the total porosity of the shale was 18 20 however the contribution of the dissolution pores increased with increasing pore size only when the average pore diameter was larger than 12 nm this may be due to the fact that small pores diameter

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

the wind stress patterns over the indian ocean during the summer monsoon of 1979 abstract a detailed analysis of the wind stress patterns over the indian ocean was made from 1 may to 31 july 1979 a combination of cloud motion and ship data obtained once per day was used to diagnose the surface wind patterns to a degree of detail not possible in the past for an individual season these data show the monsoon development and the fluctuations of the somali jet and the southern hemispheric tradewinds wind stress patterns produced by two traveling tropical storms are discussed these combined to exert an unusually high westerly wind stress on the equator before the monsoon developed

bypass zone tempestite facies model and proximality trends for an ancient muddy shoreline and shelf member 2 of the late precambrian to lower cambrian chapel island formation of southeast newfoundland was primarily deposited in storm influenced nearshore and shelf environments along a fine grained coastline deposition took place within or adjacent to a deltaic system that supplied abundant silts and clays thin bedded graded sandstone beds hummocky cross stratified beds and a variety of very thin conglomerate units contain evidence for deposition by storm currents sedimentological and stratigraphic evidence is used to reconstruct the relative paleobathymetric position of the three major facies in member 2 the gutter cast facies is a shallow subtidal deposit characterized by very thin sandstone laminae and abundant pot and gutter casts the siltstone dominated facies contains more laterally extensive thin bedded sandstones and fewer erosional features and was deposited in the inner shelf the sandstone dominated facies consists of thin to medium graded and hummocky cross stratified sandstone beds deposited in a more distal shelf setting but above storm wave base the facies model and set of proximality trends developed for member 2 deposits may be applicable to other storm influenced fine grained shorelines in this model the shallow subtidal is a zone of throughput with high velocity sediment laden flows eroding deep narrow scours gutter casts and depositing very little sand outside of these scours as the storm generated flows move into deeper water they decelerate resulting in less erosion of the sea floor and depositing thicker and more continuous sand beds siltstone dominated facies further from shore bed thickness reaches a maximum sandstone dominated facies and hummocky crossstratification is abundant even more distally bed thickness decreases again represented by thinly laminated siltstones of the overlying member 3 analysis of sedimentary structures and paleocurrent data suggests deposition by storm currents that transported sediment nearly perpendicular to shore

quantitative prediction of lower order faults based on the finite element method a case study of the m35 fault block in the western hanliu fault zone in the gaoyou sag east china

simulation of three dimensional tectonic stress fields and quantitative prediction of tectonic fracture within the damintun depression liaohe basin northeast china abstract tectonic fractures are important factors that influence oil and natural gas migration and accumulation within buried hill reservoirs to obtain a quantitative forecast of the development and distribution of reservoir fractures in the damintun depression we analyzed the characteristics of regional structural evolution and paleotectonic stress field setting a reasonable geological model of the research area was built based on an interpretation of the geological structure a test for rock mechanics and experiment on acoustic emission thereafter a three dimensional paleotectonic stress field during the yanshan movement was simulated by the finite element method rock failure criterion and comprehensive evaluation coefficient of fractures were used to determine the quantitative development of fractures and predict zones that are prone to fracture development under an intense yanshan movement high stress strength is distributed in the south and northeast parts of the study area where stress is extremely high the fracture development zones are mainly controlled by the tectonic stress field and typically located in the same areas as those of high maximum principal and shear stresses the predicted areas with developed fractures are consistent with the wells with high fracture linear density and in locations with high producing oil and gas wells

numerical study of multi period palaeotectonic stress fields in lower cambrian shale reservoirs and the prediction of fractures distribution a case study of the niutitang formation in feng gang no 3 block south china abstract fractures not only control the distribution of oil and gas reservoirs but also are key points in the research of oil and gas reservoir development programmes the tectonic fractures in the lower cambrian shale reservoirs in the feng gang no 3 block are effective reservoir spaces for hydrocarbon accumulation and these fractures are controlled by palaeotectonic stress fields therefore quantitatively predicting the development and distribution of tectonic fractures in the lower cambrian shale reservoir is important for the exploration and exploitation of shale gas in the feng gang no 3 block in the present study a reasonable geological mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data fracture characteristics from drilling data uniaxial and triaxial compression tests and experiments on the acoustic emissions ae of rocks then a three dimensional 3 d finite element method is applied to simulate the palaeotectonic stress field with the superposition of the yanshan and himalayan movements and used to predict the fracture distribution the simulation results indicate that the maximum principal stress value within the study area ranged from 269 97 mpa to 281 18 mpa the minimum principal stress ranged from 58 29 mpa to 79 64 mpa and the shear stress value ranged from 91 05 mpa to 106 21 mpa the palaeotectonic stress field is controlled by the fault zone locations the fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults at the end of the fault zones at the inflection point and at the intersection of the fault zones