neutron and gamma ray scattering measurements for subsurface geochemistry developed for the oil industry well logging instrumentation based on electrical acoustic and nuclear measurements has been providing information about the localization and evaluation of hydrocarbon bearing strata for petroleum geologists and engineers since 1927 this method of exploring properties of the earth9s crust without taking physical samples is attracting a growing audience of geologists and geophysicists because of recent developments that permit nondestructive measurements of subsurface geochemistry a combination of nuclear measurement techniques which use gamma ray and neutron sources can provide detailed information on rock composition of interest to both industry and academia

mantle upflow under north america and plate dynamics in the development of plate dynamics there are two fundamental questions first do the plates slide over a passive asthenosphere or are they driven by a convecting upper mantle second are all ocean ridges passive pull apart plate margins or do some lie above upcurrents in the mantle and in that sense become active margins the combination of stress orientations in the crust of north america with other geophysical and geological information favours an active mantle interpretation both for the north american plate and for the mantle upflow which lay beneath the east pacific rise in tertiary times and which now lies beneath the western united states

stress orientations from oil well fractures in alberta and texas many oil wells in alberta exhibit spalling of the walls known as breakouts which elongates the holes with the longer axis aligned northwest southeast this alignment is observed over an area in excess of 4 105 km2 in siltstones sandstones carbonate sediments and one shale formation through the stratigraphic column from devonian to cretaceous it is unrelated to dip of the beds we have elsewhere suggested that these breakouts are produced through stress concentration near the hole walls in a stress field having large unequal horizontal principal stresses and with the larger compression oriented northeast southwest it is probable that this northeast southwest principal stress is 1 this paper adds new data from oil wells in alberta and northern british columbia and shows that the breakouts and by inference the stress orientations are consistent through much of the western canadian sedimentary basin it also uses evidence from hydraulic fracturing in west central alberta and from steam injec

subsurface in situ stress magnitudes from oil well drilling records an example from the venture area offshore eastern canada this report describes a method of obtaining information on in situ stress magnitudes at depth in sedimentary basins by using information gathered while drilling oil wells if we assume that one of the principal stresses is vertical at a well site principal stress magnitudes can be estimated in the following manner sv is equated with overburden load which is obtained by integrating density log records shmin is equated with leak off test pressures measured over short open hole intervals and also from selected initial feed rate pressures shmax is derived from the equation shmax 2p1 p0 where p1 is the leak off pressure or the initial feed rate pressure and p0 is the fluid pressure over a specified depth interval this relationship is a simplified approximation of hubbert and willis well known equation pb t 3shmin shmax p0 describing hydraulic fracturing around a borehole using this approach stress magnitudes were estimated for 44 depth intervals in four wells drilled over the venture str

strength and rheology of the western u s cordillera effective elastic thickness te depends primarily on temperature composition and state of stress of the lithosphere in this paper we examine high resolution spectral estimates of te and their relationships to regional heat flow age of the lithosphere seismic properties stress orientations and earthquake focal depths of the western u s cordillera the relationship of te to heat flow indicates that ductile flow accommodates long term 106 to 108 years isostatic response at different levels of the crust and upper mantle depending principally on age and by implication bulk composition of the lithosphere isostatic response is primarily controlled by the upper mantle in archean lithosphere of the middle rocky mountains whereas te depends on lower crustal flow in early proterozoic lithosphere of the colorado plateau the yellowstone snake river plain volcanic field and significantly extended regions in the basin range and northern rocky mountains are associated with latest proterozoic aged lithosphere and indicate middle to upper crustal control of long term te we also show that azimuthal variations of te reflect deviatoric stress in the lithosphere te is found empirically to approximate the 95th percentile focal depth of background seismicity the latter relationship is inconsistent with brittle ductile control of focal depth indicating that another rheological transition e g from stick slip to stable sliding frictional behavior is responsible tectonic and structural relationships expand upon the hypothesis that the geographic distribution of tectonic features depends fundamentally on spatial variations in strength of the lithosphere moreover we find a spatial correlation of the intermountain seismic belt to a marked transition in te implying that forces responsible for this active seismic zone are derived from local buoyancy anomalies rather than from current day plate boundary interactions

ongoing tectonic reactivation of the outer carpathians and its impact on the foreland results of borehole breakout measurements in poland abstract the direction of present day maximum horizontal compression shmax tectonic stress was interpreted for 62 wells in poland using the method of borehole breakout analysis of 4 arm and 6 arm dipmeter logs the study area covers complex tectonic junction of the carpathian orogen and its foreland which comprises the east european craton eec divided by the teisseyre tornquist zone ttz from the palaeozoic platform of western poland for this area frequent deviation of the shmax direction from nw se characteristic for the atlantic ridge push has been interpreted in terms of the alcapa tectonic push in the upper silesian segment of the polish outer carpathians poc nne ssw oriented shmax in the accretionary wedge differs significantly from nnw sse shmax in the autochthonous basement the above discrepancy points to uncoupled type of the suture in this segment of the poc in this scenario the alcapa push involves the nappes and is compensated in the top of the basement which is expressed by systematic shmax rotations in the accretionary wedge of the eastern malopolska segment shmax follows the trend perpendicular to the strike of nappes it is in general agreement with nne ssw oriented shmax in the autochthonous basement that also parallels the alcapa push direction similarity in stress orientation between these structural levels implies coupled suture zone in this segment of the poc further to the north alcapa push is transmitted into the foreland plate where it causes n s orientation of shmax as determined for sedimentary cover of the eec within the baltic portion of the eec further shmax rotation towards the intermediate nnw sse position suggests balance between the alcapa push and the ridge push components within the ttz common shmax rotations from n s to nw se indicate structurally controlled accommodation of the alcapa push in the palaeozoic platform of western poland mesozoic complex of the fore sudetic monocline reveals nne ssw directed shmax that differs from nw se oriented shmax in the variscan accretionary wedge here mechanical decoupling along zechstein evaporates is likely presented set of breakout data from poland shows that recent compressive reactivation of the carpathians exerts strong impact on the stress field of the foreland plate at a distance of 700 km from the suture due to this effect the fore carpathian stress domain within the north european stress province can be discriminated

orientation of in situ stresses in the oceanic crust two in situ measurements of principal stress directions have been made in dsdp holes 504b south of the costa rica rift on the nazca plate and 597c west of the east pacific rise on the pacific plate in both cases the orientations of in situ principal stresses determined from borehole breakouts are consistent with the stress directions inferred from intraplate earthquakes located near the sites

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

tectonic stress field in the indian subcontinent a map of maximum horizontal compressive stress orientation in the indian subcontinent has been prepared using orientations derived from three different stress indicators borehole elongation breakouts in situ hydraulic fracturing measurements and earthquake focal mechanisms most part of the subcontinent appears to be characterized by a compressional stress regime thrust and strikeslip faulting imposed by plate boundary forces although shmax orientations do not in general show clear correlation with the direction of motion of the indian plate four provinces are recognized on the basis of regionally consistent orientations these are the midcontinent stress province the southern shield the bengal basin and the assam wedge their boundaries have been determined taking into consideration regional tectonics and seismicity central and northern india including the shillong plateau stretching up to the great himalaya pakistan and nepal are included in a broad midcontinent stress province characterized by nne ene oriented shmax the mean orientation of shmax in this province is n23 e subparallel to the direction of compression expected to arise from the net resistive forces at the himalayan collision zone suggesting that it is largely determined by the tectonic collision processes much of southern india mysore plateau and the high grade metamorphic terrain south of the plateau appears to be part of a second stress province characterized by nw oriented shmax these appear close to those of the intraplate stress field prevailing in the central indian ocean a third stress province was recognized in the bengal basin including parts of west bengal tripura manipur and mizoram in northeastern india and most of bangladesh this province extends eastward from the marginal fault in the western margin of the bengal basin to the indo burma subduction zone and is bounded on the north by the e w striking dauki fault shmax within the sedimentary pile of the bengal basin is oriented in e w direction while p axes of earthquakes within the basement and the crust beneath the basin and within the subducted slab of the indian plate beneath the indo burman ranges generally trend north n30 e shmax orientations within the sedimentary pile of the basin are parallel to the local approximately e w direction of the convergence of indian and burmese plates suggesting a casual relation to the resistive forces at the subduction zone in the indo burma region interestingly the stress field in the basement and the crust beneath the bengal basin and in the subducted slab is similar to the one prevailing in the midcontinent stress province assam wedge stress region occupies the northeastern corner of the indian plate including upper assam arunachal pradesh and much of nagaland this region subducts beneath a sharply bent continental collision boundary consisting of the northeastern limb of the himalayan and northern limb of the indo burman fold belts as a result the stress field in this province is depth differentiated and most likely responsible for the absence of consistent shmax directions

a review on the applications of image logs in structural analysis and sedimentary characterization abstract image logs provide important information on lithology sedimentary textures paleoflow directions fractures and in situ stress analysis lacking of criteria used for establishing the image log facies limits the applications of image logs in sedimentary reservoir interpretation this paper provides a thoroughgoing review focusing on the recent applications of borehole image logs for sedimentological and structural description and interpretation and aims to establish image log facies which can provide guidelines in sedimentary reservoir interpretation this paper firstly summarizes the principles and basic characteristics of various imaging logging tools and then briefly introduces the pre processing workflow of the image log data then the generated images are used for depth and orientation shifts of cores by calibrating individual sedimentary and structural features descriptive and concise image log facies are established based on combinations of image textures including dip type dip pattern and color scheme and the characteristics as well as physical criteria for each individual image facies are summarized the established image log facies are then interpreted in terms of structural and sedimentological features such as lithology sedimentary structures vugs fractures and faults the image log facies and its stacking patterns are then used to interpret the lithofacies associations by calibrating with cores and conventional logs natural fractures and induced fractures are recognized by image logs and the principles of breakouts and drilling induced fractures for in situ stress analysis are reviewed then the applications of image logs in investigation of fracture attitudes and states as well as in computation of fracture parameters are summarized the procedures to evaluate fracture effectiveness through image logs are discussed at last the application of image logs for structural dip analysis is reviewed and image logs are used for recognizing faults fracture sets and attitudes of stratum through the dip patterns the basic procedures for paleocurrent reconstruction which includes dip picking of cross beddings structural dip determination and structural dip removal are reviewed then the paleocurrent directions of the lower cretaceous bashijiqike formation in the kuqa depression were reconstructed which could help further understanding of the depositional systems this review will help extend the utility of image logs in interpreting small to large scale sedimentary and structural features and bridges the gaps between well log analysis and sedimentary and structural interpretation

in situ stress from breakouts in the danish sector of the north sea abstract borehole breakouts from 26 wells situated in the danish central graben and one well situated in the northwestern section of the ringkobing fyn high have been studied the data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4 7 km statistics were used to obtain a mean azimuth of breakouts for each well and each individual breakout was weighted by its length data quality of breakouts is assigned according to the world stress map quality ranking scheme the breakout data reveal that s h orientations in the danish central graben are extremely scattered no regional trend in mean s h orientation can be identified as a result of the large standard deviation 77 similar scatterings of s h orientations have been reported from adjacent regions of the north sea the results indicate that the state of stress in the sedimentary cover of the danish central graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the post chalk group chalk group and pre chalk group

magnetic fabric strain and paleostress in the canadian rocky mountains abstract the paper reports a detailed study of the anisotropy of magnetic susceptibility at two localities 100 km apart in the canadian rocky mountains both in the miette group of precambrian sediments which was folded during the laramide orogeny from the orientations of the susceptibility ellipsoids we infer principal strain axes and assuming irrotational deformation possible laramide paleostress orientations at wynd siding near jasper in the main ranges oriented samples were taken from both limbs and the nose of a plunging syncline near tete jaune cache at the western boundary of the main ranges a small syncline and steeply dipping beds of one limb of a large anticline were sampled minimum principal susceptibilities transverse to the strike of the rockies dominate the magnetic fabric at both localities and it is clear that regional shortening of the whole rock mass has obliterated any original depositional fabric and any small scale fold related fabric at both sites writing k1 k2 k3 for the principal susceptibilities the k3 axis and by inference the axis of principal shortening is horizontal with azimuth n52 e at wynd and plunges 10 20 along azimuth n26 e at tete jaune cache k1 is vertical at wynd but horizontal and along the fold axis n61 w at tete the uniformity of axes of susceptibility and inferred strain through each locality suggests irrotational deformation and encourages the further inference of possible paleostress orientations with 1 aligned with k3 2 with k2 and 3 with k1 the magnetic fabrics then indicate a thrust type paleostress field at wynd consistent with the laramide thrusts in the eastern rockies but a strike slip type paleostress field at tete jaune cache the change of stress orientation may reflect deeper burial in laramide times of the rocks sampled at tete jaune cache consistent with the much higher grade of metamorphism there

fracture and in situ stress patterns and impact on performance in the khuff structural prospects eastern offshore saudi arabia abstract we characterized natural fractures and in situ stresses for exploration and prospect evaluation in nine periclinal structural traps in the eastern province of saudi arabia where several major gas discoveries were made in the deeply buried permian triassic khuff formation borehole image logs oriented cores seismic gravity magnetic data and dynamic observations were used in the study two fracture systems were identified a younger major system which enhances reservoir permeability and an older minor fully mineralized system the older system consists of subordinate northerly striking extensional mesofractures including joints and faults which are fully mineralized by anhydrite and calcite this mineralization occurred during an early diagenetic phase this system acted as paleo fluid conduits facilitating the occlusion of matrix porosity and deteriorating the reservoir quality in the immediate vicinity of the fractures the younger system is regionally dominant and includes mesofractures with persistent strike ranging from ne sw to ese wnw irrespective of local structure these younger fractures are nearly parallel to the present day maximum horizontal in situ stress and perpendicular to the minimum horizontal in situ stress which are dominated by the zagros plate tectonics the development of this system commenced during the convergence of the arabian and eurasian plates late cretaceous to cenozoic and culminated during the continental collision the fractures are predominantly extension joints and hybrid extensional shear fractures and were facilitated by increases in pore pressure due to the oil placement and the subsequent cracking of this oil into gas hydrocarbon migration into the khuff reservoirs was crucial in slowing down diagenesis and preserving both fracture apertures and matrix porosity therefore most of the fractures in this system tend to be partly mineralized mainly by carbonates and or coated with hydrocarbons these fractures show channel type apertures that enhance permeability and productivity of the khuff by up to two fold the channel apertures can endure operational changes in reservoir pressure with little or no reduction of their permeability critically stressed open fractures have no major role geomechanical analyses show that they are estimated to occur under the upper limits of differential stresses within the margin of error of stress estimates the static and dynamic observations show the permeability and productivity enhancement follows mechanical layering patterns production and pressure profiles in individual wells indicate lack of vertical communication seal breach across the different reservoir units similar pre production pressure and hydrocarbons across the khuff reservoir units is the result of normalization over geological time hydrocarbon migration across the anhydrite seals happened via episodic paleoseismic pumping along faults with no sufficient vertical offset to permanently breach the reservoir seals

fracture detection in oil based drilling mud using a combination of borehole image and sonic logs abstract the deeply buried 5 5 7 1 km lower cretaceous bashijiqike sandstones are important fractured reservoirs in the kuqa depression in these high temperature high pressure drilling environments oil based muds are used to limit drilling risks and improve efficiency making facture detection using resistivity based image logs difficult the maximum horizontal stress sh max trends close to north south 0 10 based on orientations of the drilling induced fractures and borehole breakouts core descriptions thin sections and image logs used to describe the fractures in the bashijiqike sandstone reservoirs show that opening mode natural fractures are common and the fractures range from fully open to sealed by calcite and clay minerals the open fractures are dominantly steeply dipping or vertical and primarily strike north south locally horizontal fractures or fractures with low angle dip are detected we compare fracture visibility on image logs acquired in the same ks 2 2 12 key well in oil based mud and water based mud fmi hd logs successfully detect large 0 1 mm aperture vertical fractures in oil based mud better than obmi image logs and the two imaging tools have a similar ability in detecting the high dip angle fractures since the ubi tool is not affected by oil based muds most of the fractures can be picked out on ubi images minor negative deviations of bulk density could be observed in fractured zones and the presence of fractures obviously causes an increase in sonic transit time full waveforms from dsi tools combined with electrical image logs detect fractured zones both the velocity and amplitude of the sonic waves are sensitive to fractures and the fractured zones could be identified according to the attenuation of stoneley waves the combination of cores image logs and full wave sonic logs offers comprehensive detection of fractures in oil based mud environments

in situ stresses in the southern bonaparte basin australia implications for first and second order controls on stress orientation four arm dipmeter logs from six wells and a formation microscanner fms image log from one well in the southern bonaparte basin were interpreted for in situ stress indicators results of the analysis reveal a consistent ne sw in situ maximum horizontal stress hmax orientation 055 n this orientation is parallel to the average hmax determined in the northern bonaparte basin the onshore canning basin and in new guinea the data support the interpretation that the ne sw hmax orientation in the area reflects a first order stress pattern controlled by plate boundary forces along the northeastern margin of the indo australian plate iap and contradict the suggestion that ne sw hmax in the northern bonaparte basin is a second order effect associated with boundary induced flexural stresses numerical modeling suggests that the divergence of hmax from an orientation parallel to plate motion can be explained by the heterogeneous nature of the northeastern boundary of the iap

energy balance of ice streams analysis of the cross flow transmission of force from the central parts of a well lubricated ice stream to its margins shows that there is a corresponding shift in the lateral location of motion induced heat generation the rate of basal heat generation in the center can be substantially smaller than the local rate of potential energy loss given by driving stress times the speed of downslope motion the basal heating is a maximum for an intermediate level of lubrication for which speed is about 40 of the speed over a frictionless bed and base stress is about 25 of the driving stress stable and unstable balances between meltwater production and drainage on the bed are identified a stable steady state with a speed less more than that giving maximum heat generation is termed drainage production limited since an increase in speed would lead to increased decreased basal melting and must need not be balanced by increased drainage it is shown that gradual evolution of the basal water drainage system and the factors affecting basal melting can cause discontinuous jumps between fast and slow moving states a simplified analysis applied to six cross sections of west antarctic ice streams b d e and rutford ice stream shows them to be diverse in the level of support from the sides and corresponding shift of mechanical heating sideward from their central parts the cross sections of ice stream b near upstream b may be production limited because of especially high lubrication and related support from the sides cross sections in the upper part of ice stream d ice stream e and rutford ice stream are in a drainage limited condition substantial reduction of basal heat generation by side drag in most cases and expected high heat flow into the basal ice associated with low thickness in some cases tends to favor basal freezing nevertheless all of the examined cross sections except one are expected to experience basal melting with a modest geothermal heat flux density of 60 mw m or less in some cases the lower part of ice stream b is an exception where the analysis indicates that geothermal flux density must exceed 80 100 mw m to maintain melting if this high geothermal flux is not present then the base of the lower part of ice stream b may be freezing which would suggest continued deceleration of this part of ice stream b

well bore bottom stress concentration and induced core fractures the orientation spacing and shape of drilling induced disking petal and petal centerline fractures in core commonly are remarkably uniform these fractures result from concentrations of in situ stress by the well bore bottom hole cavity and in oriented core their strikes commonly have been used as indicators of the horizontal principal stress directions however an understanding of how these varied fractures are produced has been limited by the lack of detailed knowledge of the distribution of stresses near the bottom hole in this paper we present our result of studying these stress concentrations using full three dimensional finite element modeling for a variety of applied far field in situ stress conditions and as a function of core stub length in nearly all cases purely tensional concentrated stresses are generated within the core by the compressive in situ stresses the directions and magnitudes of these tensions vary with the applied stress indicating the morphology of many of the observed drilling induced core fractures cupped shape disking fractures result from a state of uniform horizontal biaxial stress these fractures also initiate within the rock at the root of the core stub as the horizontal stresses become more anisotropic the point of fracture initiation shifts to the surface of the core and saddle shaped core disks are possible such fractures strike in the direction of the most compressive in situ horizontal principal stress increasing the magnitude of the overburden stress eventually results in petal and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 1 1996 revised manuscript received december 2 1996 final acceptance june 19 1997 2institute of geophysics meteorology and space physics department of physics university of alberta edmonton alberta canada e mail yongyi phys ualberta ca doug phys ualberta ca this work is supported in part by nserc lithoprobe supporting science grant nserc and the alberta oil sand technology and research authority d schmitt acknowledges the assistance of the a v humboldt foundation during revisions of this paper constructive reviews and comments of b r kulander j c lorenz and s l dean were greatly appreciated this paper is lithoprobe submission number 882