doppler radar observations of horizontal shearing instability in quasi linear convective systems abstractdual doppler radar observations of two cold season wave propagating quasi linear convective systems qlcs which evolved in high shear low cape hslc environments are analyzed to deter

high thermal maturity in the lower saxony basin intrusion or deep burial abstract the lower saxony basin lsb is situated at the southern rim of the northern permian basin the most important hydrocarbon bearing province in europe in its southern part areas of high thermal maturation up to 6 rr occur which were previously explained as being caused by magmatic intrusions of turonian to santonian age that affected carboniferous to lower cretaceous rocks in this area 2d numerical basin modelling was carried out in order to reconstruct the temperature histories along two parallel n s trending seismic sections along these sections new data about maturity distribution and temperature history were obtained by vitrinite reflectance measurements and apatite fission track analysis for the areas with highest maturity values low coalification gradients were established which agree well with earlier published data on wells further towards the west this new information does not support previous hypotheses on high heat flows from magmatic intrusions even if lateral heat transport is taken into account instead comparisons with a recently published map of the subsurface structure of the lsb indicate that maturity distribution may be closely related to major tectonic structures deep burial of individual structures of the lsb which are bordered by deep e w to ese wnw trending faults is further suggested by a rapidly increasing thicknesses of preserved cretaceous strata towards the south and b structural restoration of one of the seismic sections to achieve a fit between measured and calculated palaeo temperature and vitrinite reflectance data deep burial of carboniferous source rocks during cretaceous time has to be assumed due to an inversion phase in the early and middle upper cretaceous major amounts of sediment were removed and further uplift occurred in tertiary times in contrast the northern part of the lsb experienced maximum burial and temperatures during tertiary times

a concentrated outbreak of tornadoes downbursts and microbursts and implications regarding vortex classification abstract a remarkable case of severe weather occurred near springfield illinois on 6 august 1977 aerial and ground surveys revealed that 17 cyclonic vortices an anticyclonic vortex 10 downbursts and 19 microbursts occurred in a limited 20 km 40 km area associated with a bow shaped radar echo about half of the vortices appeared to have occurred along a gust front some of the other appear to have occurred within the circulation of a mesocyclone accompanying the bow echo but these vortices seem to have developed specifically in response to localized boundary layer vorticity generation associated with horizontal and vertical wind shears on the periphery of microbursts some of these vortices and other destructive vortices in the literature do not qualify as tornadoes as defined in the glossary of meteorology a moon pragmatic definition of a tornado is suggested

mesovortices within the 8 may 2009 bow echo over the central united states analyses of the characteristics and evolution based on doppler radar observations and a high resolution model simulation abstracta derecho producing bow echo event over the central united states on 8 may 2009 is analyzed based on radar observations and a successful real data wrf simulation at 0 8 km grid spacing emphasis is placed on documenting the existence evolution and characteristics of low level mesovortices mvs that form along the leading edge of the bowing system the genesis of near surface high winds within the system is also investigated significant mvs are detected from the radar radial velocity using a linear least squares derivatives llsd method and from the model simulation based on calculated vorticity both the observed and simulated bow echo mvs predominantly form north of the bow apex mvs that develop on the southern bow tend to be weaker and shorter lived than their northern counterparts vortex mergers occur between mvs during their forward movement which causes redevelopment of some mvs in the decaying stage of the bow echo mvs located at or near the bow apex are found to persist for a not

bow echo mesovortices part i processes that influence their damaging potential abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex this bow echo produced both damaging and nondamaging mesovortices a series of sensitivity simulations were performed to assess the impact of low and midlevel shear cold pool strength and coriolis forcing on mesovortex strength by analyzing the amount of circulation maximum vertical vorticity and number of mesovortices produced at the lowest grid level it was observed that more numerous and stronger mesovortices were formed when the low level environmental shear nearly balanced the horizontal shear produced by the cold pool as the magnitude of deeper layer shear increased the number and strength of mesovortices increased larger coriolis forcing and stronger cold pools als

thermal modelling of the melut basin sudan and south sudan implications for hydrocarbon generation and migration abstract the thermal history of the melut rift basin was studied in a number of wells and along a northeast southwest cross sectionacross the basin using 1 d and 2 d basin models modelling was conducted using petromod software to test subsidence thermal history and their implications for hydrocarbon generation migration and accumulations geotherms were found ranging between 24 and 44 c km and average 32 c km and present day heat flow was found to vary between 53 and 65 averaging 59 mw m 2 a geologicaly realistic paleoheat flow model with higher heat flow peaks of 75 70 and 65 mw m 2 during the first second and third rifting phases respectively calibrated against vitrinite reflectance data was employed the model was found sensitive to cenozoic erosions and a 600 m of exhumation did support the vitrinite data in providing a reasonable fit in most locations using the easy ro vitrinite kinetic model for maturity the average present day oil window was found between 1565 and 4050 m in the wells studied and between 1705 and 4200 m along the cross section using type ii kerogen for the aptian albian source rocks the hydrocarbon generation and expulsion were modelled and revealed that the generation started as early as 95 ma in some areas but significant generation rates were during the second rifting phase and expulsion started at around 85 ma calculations of the probable expelled amounts of hydrocarbon from the northern sub basin are high and up to 2 2 10 11 bbls of oil and 2 3 10 14 ft 3 of gas migration of oils from cretaceous source rocks kitchen to the cenozoic traps was probably through faults porous carrier beds and breaching of traps cap rocks the filling of these traps might be periodic during the rifting episodes and hydrocarbons remigrated from deeper traps to shallow ones it is possible that thinner and siltier cap rocks along the hydrocarbon migration path may have allowed gas to scape but holded the oil back it is most probable that part of the hydrocarbons might have been generated from shallower source rocks areas and a 2 d hybrid darcy flow path model have demonstrated this and predicted a number of accumulations which are similar to the known large discoveries such as palogue fal and adar yale oil fields

evolution of fluid compartmentalization in a detachment fold complex oxygen carbon and strontium isotope variations in vein filling calcite and quartz cements and their host rocks are used to elucidate the origin spatial and temporal evolution and migration pathways of fluids in the detachment nuncios fold complex northeastern mexico the folded mesozoic sedimentary sequence contains two regional paleohydrostratigraphic units separated by a unit of low permeability two main generations of cements are present in both paleohydrostratigraphic units distinct differences exist between 18 o 13 c 87 sr 86 sr and fluid inclusion temperatures of early vein filling cements in the lower and the upper units these differences together with a strong correspondence between early cement and host rock 18 o and 13 c values suggest that early diagenetic fluids were compartmentalized between the two units late vein filling cements have isotopic compositions and fluid inclusion temperatures that converge to similar values indicating a change to open fluid flow between the lower and upper units we hypothesize that the fluid history of the nuncios fold complex evolved in two main stages 1 burial diagenesis and early folding during which fluids were confined within individual units and 2 late stage folding during which increased deformation associated with fold tightening caused the expulsion of fluid from the lower unit into the upper unit

petrological and geochemical investigations of potential source rocks of the central congo basin democratic republic of congo paleozoic and mesozoic outcrop and core samples remina dekese and remina samba wells covering various stratigraphic intervals from the central congo basin were analyzed for total organic carbon corg total inorganic carbon cinorg and total sulfur content rock eval analysis and vitrinite reflectance ro measurements were performed on the basis of the corg content fifteen samples were chosen for molecular organic geochemistry nonaromatic hydrocarbons hcs were analyzed by gas chromatography gc flame ionization detection and gc mass spectrometry samples of the alolo shales from the aruwimi group lindi supergroup late neoproterozoic to early paleozoic are in general very poor in corg most samples 0 5 and contain a high amount of degraded organic matter om all samples of this group revealed a type iii to iv kerogen and cannot be considered as a potential source rock permian carboniferous sediments from the lukuga group dekese well and outcrop samples contain moderate contents of organic carbon 2 the tmax values heating temperature at which the top peak of s2 occurs indicate early mature om partly also a higher level of maturity because of ro 0 6 0 7 and production index values s1 s1 s2 0 2 all samples contain hydrogen poor type iii to iv kerogen with low hc generation potential only having a very minor gas generation potential the kinds of om as well as the biological markers indicate a terrestrial dominated depositional environment organic geochemical investigations on upper jurassic stanleyville group to lower cretaceous loia group samples from the samba well and outcrops in the northeastern part of the congo basin reveal moderate to high contents of organic carbon as much as 25 the kerogen has very high hydrogen index hi values reflecting type i kerogen of excellent quality in the stanleyville group as much as 900 mg hc g corg and type i to ii kerogen in the overlying loia group as much as 900 mg hc g corg outcrop samples from the stanleyville group have variable partly high corg contents and are also characterized by very high hi values as much as 900 mg hc g corg the samples studied are too immature for petroleum generation based on biomarker analysis an aquatic anoxic depositional environment can be assumed for the stanleyville group whereas a lacustrine deposition is likely for the samples of the loia group based on the geologic knowledge of the area deposition under lacustrine conditions is most likely also for the stanleyville group both the stanleyville and loia groups can be regarded as excellent petroleum source rocks and could be part of a petroleum system if sufficient burial and maturation have occurred the presence of resedimented vitrinite particles in the lukuga group of the dekese well with a slightly higher maturation rank than the autochthonous vitrinites suggests that 3000 4000 m 9840 13 120 ft of carboniferous to devonian sediment has been eroded from the eastern margin of the congo basin finally ro data were used to create one dimensional models for the dekese and samba wells giving an overview of the burial thermal and maturity histories of the area

low level mesovortices within squall lines and bow echoes part i overview and dependence on environmental shear this two part study proposes fundamental explanations of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized simulations are used herein to study the structure and evolution of meso g scale surface vortices within qlcss and their dependence on the environmental vertical wind shear within such simulations significant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0 2 5 or 0 5 km agl layer as similarly found in observations of qlcss these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger scale bow shaped system they generally develop first near the surface but can build upward to 6 8 km agl vortex longevity can be several hours far longer than individual convective cells within the qlcs during this time vortex merger and upscale growth is common it is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme straight line wind damage as has also been observed with some qlcss surface vortices are also produced for weaker shears but remain shallow weak and short lived although similar in size and strength to mesocyclones associated with supercell storms and also sometimes producing similar hooklike structures in the rain field it is also shown that the present vortices are quite distinct structurally and dynamically most critically such vortices are not associated with long lived rotating updrafts at midlevels and the associated strong dynamically forced vertical accelerations as occur within supercell mesocyclones

free thermohaline convection in sediments surrounding a salt column complex groundwater convection patterns are possible near salt domes because groundwater is subject to both lateral heat and salinity gradients in order to assess the mechanisms responsible for driving convection near salt domes we use dimensional analysis and numerical simulations to investigate coupled heat and salt transport in homogeneous sediments surrounding a cylindrical salt column the dimensional analysis does not require the boussinesq assumption the coupled heat solute and groundwater transport equations are controlled by three dimensionless parameters the rayleigh number the lewis number and the buoyancy ratio the buoyancy ratio is the ratio of salinity to temperature effects on groundwater density and it directly affects the groundwater flow equation a finite difference numerical multigridding algorithm is used to iteratively solve the coupled transport equations the multigridding technique was about 3 times faster than a point wise successive overrelaxation solution boundary conditions for the numerical simulations were adjusted to represent different contrasts in the thermal gradient between the salt and the overlying sediments the contrast in thermal gradient is parameterized by the thermal conductivity ratio and is responsible for isotherms being elevated near the salt the analysis suggests that a wide range of convective flow patterns are possible with flow occurring either up or down along the salt flank the sense of convection is dependent mainly on the value of the buoyancy ratio and how sharply isotherms are pulled up near the salt these factors in turn depend on the regional salinity variation the time since diapirism and the thermal conductivity of water saturated sediments while this analysis provides useful insight into the mechanisms driving free convection near salt domes the assumptions about medium and fluid properties may limit the applicability of dimensional analysis in simulating flow in specific geologic settings

regional wave propagation in tanzania east africa 1 crust and upper mantle structure under tanzania east africa is investigated using broadband waveforms and phase travel times collected from regional events recorded by the 1994 1995 tanzania broadband seismic experiment broadband displacement waveforms from the ml 5 9 rukwa graben earthquake 18 august 1994 are modeled using a wave number integration algorithm and a new phase time inversion technique to infer a very simple crustal and upper mantle model that can be used for waveform studies of other regional earthquakes in the area displacement amplitudes for all phases in the data are predicted quite well using source parameters determined from a previous study of teleseismic waveforms the crust is parameterized by a linear gradient in velocity defined by surface and moho p velocities poisson s ratio and crustal thickness this simple parameterization is sufficient to explain arrival times and waveshapes of the three component waveforms recorded between 200 and 800 km at stations located on the craton and mozambique belt the s wave train consists of sn multiple sn and critically reflected s wave multiples in the crustal waveguide in addition to the fundamental mode rayleigh wave high phase velocity critical s wave reflections are seen to form the low group velocity lg phase prominent sp depth phases are seen in the regional waveform data which can be used to infer accurate source depths for events in the region the tanzania craton and adjacent mozambique belt crustal structure is simple and laterally homogeneous showing few effects of rift disruption high wave velocities in the uppermost mantle suggest little thermal modification from rifting processes of the east african rift

high heat flow anomalies over salt structures on the texas continental slope gulf of mexico we made 74 closely spaced 2 km apart heat flow measurements around and over two salt structures on the texas continental slope gulf of mexico the values outlined the shape of the heat flow anomalies over both structures based on a preceding high resolution seismic survey we interpreted these structures to be a cylindrical plug and a salt tongue extending from the crest of a wall shaped feeder the heat flow observations clearly reflect differences between the two features and are consistent with the prior structural interpretation the values over the salt plug are nearly all greater than 70 mw m the measurements over the salt tongue have a sharp heat flow peak of 90 mw m associated with the presumed feeder and rather uniform values around 60 mw m over the remainder the variation of heat flow over both structures is smooth and shows no apparent scatter heat flow values off these features are uniformly low around 30 mw m thermal effects from bottom water temperature fluctuation slope sedimentation diapiric movement of the salt body and pore fluid migration appear unable to provide a satisfactory explanation for the observations however thickness variations of a highly conductive salt body can easily account for the heat flow anomalies we suggest that modeling of the conductive anomaly should provide substantial constraints on the bottom geometry of the salt

the effects of salt evolution structural development and fault propagation on late mesozoic cenozoic oil migration a two dimensional fluid flow study along a megaregional profile in the northern gulf of mexico basin sequential two dimensional 2 d forward modeling of fluid flow along a north south 600 km megaregional cross section across the northern gulf of mexico basin illustrates the influence of structural stratigraphic and thermal evolution on oil generation patterns and migration paths twelve megaregional fluid flow models which span from the late cretaceous to the holocene were constructed for this study each model uses a sequential structural restoration and proprietary well data to constrain the structural and stratigraphic development of the study area and to calibrate production depths along the megaregional profile these fluid flow models specifically address the levels of influence that salt evolution sedimentation thermal history and fault development induce on temporal oil migration patterns results from the sequential 2 d fluid flow models across the northern gulf of mexico basin indicate that allochthonous salt evolution and excess pressure development from differential sedimentation strongly influenced late mesozoic cenozoic oil migration patterns along the entire megaregional profile within the lower slope part of the profile early and fairly rapid maturation of source rocks was accompanied by slow elevation of excess pressures as a result oil migration in these regions was minimal and the impact of salt evolution on the fluid flow was restricted to circulatory patterns at the base of salt stocks within the center of the profile begin page 1946 offshore louisiana shelf however the evolution of allochthonous salt and the formation of high excess pressures coeval with the development of listric and normal faults strongly impacted the oil migration patterns penetration of high excess pressure regimes by both listric and normal faults directed fluid flow vertically upward along the fault systems upon encountering salt sheets oil migration in these regions exhibited both divergent and convergent flow patterns flowing laterally along the base of the salt a similar scenario was observed in the northern part of the profile southern onshore louisiana reflected by oil migration beneath the terrebonne salt sheet upon evacuation of allochthonous salt in the central and northern regions of the profile migration patterns were primarily lateral when excess pressures in these regions exceeded 50 mpa however oil flowed vertically through the salt welds and along suprasalt faults a more localized and well constrained study of fault migration in the oligocene miocene detachment province further suggests that faults are important factors as migration pathways with episodic flow directing oil migration into observed shallow reservoirs

petroleum generation and accumulation in the berkine basin eastern algeria the berkine ghadames basin is regarded as an important hydrocarbon play in eastern algeria an evaluation of organic source facies the application of petroleum geochemistry and an extensive basin modeling study were carried out to improve the understanding of the petroleum charge of the basin geochemical data indicate that the llandoverian wenlockian and the frasnian hot shales are the most important oil prone source rocks for the known hydrocarbon accumulations in the basin maturity data reflect the late cretaceous tertiary burial and are consistent with a 60 63 mw m2 heat flow in the vicinity of the anticlines and 50 mw m2 heat flow farther away from the folded area a two dimensional basin modeling study revealed the importance of poorly constrained parameters such as the amount and rate of hercynian erosion on hydrocarbon generation and trapping efficiencies the model shows that a cretaceous tertiary petroleum generation and emplacement for both source rocks can better explain the different gas and oil fields than can an earlier hercynian event the faults related to the triassic jurassic rifting are most certainly permeable and can be considered as major migration pathways for petroleum in contrast the overpressure that developed along the el biod hassi messaoud axis in the ordovician reservoirs was probably caused by the low permeability of the faults bounding the anticlines that therefore prohibited any lateral or vertical fluid movements the model also indicates two petroleum systems that have triassic reservoirs 1 a frasnian sourced system that is confined to the central part of the basin and 2 a llandoverian wenlockian sourced system in the western part of the basin migration into paleozoic reservoirs was followed by dismigration into overlying triassic traps after the cretaceous compressive movements

oil migration in a major growth fault structural analysis of the pathfinder core south eugene island block 330 offshore louisiana the pathfinder core collected in the south eugene island block 330 field offshore louisiana provides an outstanding sample of structures associated with a major growth fault that abuts a giant oil field and that is thought to have acted as a conduit for hydrocarbon migration into the producing reservoirs where cored the growth fault zone cuts semiconsolidated pliocene pleistocene mudstone and is over 100 m wide the fault zone in the core consists of three structural domains each characterized by a distinct rock type distribution of fault dips and dip azimuths and distribution of spacing between adjacent faults and fractures although all of the domains contain oil bearing sands only faults and fractures in the deepest domain contain oil even though the oil barren fault domains contain numerous faults and fractures that are parallel to those containing oil in the deepest domain the deepest domain is also distinguished from the other two domains by a greater degree of structural complexity and by a well defined power law distribution of fault and fracture spacings sediments in this domain behaved as competent rock with respect to fault and fracture spacing whereas the departure from power law distribution of fault and fracture spacing in the other two domains may reflect deformation of unconsolidated sediment this departure from a power law spacing distribution in the upper two domains combined with stable isotope data that indicate low temperature water rock interaction within a gouge zone that separates these two fault domains indicates that the faults in those domains may have been active only early in the history of the growth fault zone when the sampled sediments were at shallow burial depths thus these faults may predate oil migration in contrast the faults in the oil bearing domain appear to have been active later in the fault zone s history when the sediments faulted as competent rock and when geologic and organic geochemical investigations indicate oil migrated into the block 330 reservoirs even though oil is present in sands throughout the core its restriction to faults and fractures in the youngest sampled portion of the fault zone implies that oil migrated only through that part of the fault that was active during the time when oil had access to it the absence of oil in fractures or faults in the other probably older fault domains indicates that the oil was never sufficiently pressured to flow up the fault zone on its own either by hydraulic fracture or by increased permeability as a result of decreased effective stress instead fluid migration along faults and fractures in the pathfinder core was enhanced by permeability created in response to relatively far field stresses related to minibasin subsidence

radar and damage analysis of severe bow echoes observed during bamex abstract this study examines damaging wind production by bow shaped convective systems commonly referred to as bow echoes recent idealized numerical simulations suggest that in addition to descending rear inflow at the bow echo apex low level mesovortices within bow echoes can induce damaging straight line surface winds in light of these findings detailed aerial and ground surveys of wind damage were conducted immediately following five bow echo events observed during the bow echo and mesoscale convective vortex mcv experiment bamex field phase these damage locations were overlaid directly onto weather surveillance radar 1988 doppler wsr 88d images to i elucidate where damaging surface winds occurred within the bow shaped convective system in proximity to the apex north of the apex etc and then ii explain the existence of these winds in the context of the possible damaging wind mechanisms the results of this study provide clear observational evidence that low level mesovortices wit

evolution of a quasi linear convective system sampled by phased array radar abstracton 2 april 2010 a quasi linear convective system qlcs moved eastward through oklahoma during the early morning hours wind damage in rush springs oklahoma approached enhanced fujita ef1 scale intensity and was likely associated with a mesovortex along the leading edge of the qlcs the evolution of the qlcs as it produced its first bow echo was captured by the national weather radar testbed phased array radar nwrt par in norman oklahoma the nwrt par is an s band radar with an electronically steered beam allowing for rapid volumetric updates 1 min and user defined scanning strategies the rapid temporal updates and dense vertical sampling of the par created a detailed depiction of the damaging wind mechanisms associated with the qlcs key features sampled by the par include microbursts an intensifying midlevel jet and rotation associated with the mesovortex in this work par data are analyzed and compared to data from nearby operational radars highlighting the advantages of using

how sandstone porosity and permeability vary with diagenetic minerals in the scotian basin offshore eastern canada implications for reservoir quality abstract the scotian basin is an under explored offshore basin that has produced gas and minor oil from jurassic cretaceous deltaic sandstones reservoir quality is an important exploration risk in the basin this study evaluates whether there are systematic stratigraphic or geographic variations in diagenetic mineral assemblage control of reservoir porosity and permeability three data sets are used a compilation of all available core plug porosity and permeability measurements 3271 in total a subset of 577 corresponding to thin sections with lithofacies assignments and a subset of 35 thin sections principally from reservoir sandstones in which modal abundance of diagenetic minerals has been determined by image analysis of scanning electron microscope backscattered electron images abundances above a 4 threshold of diagenetic kaolinite calcite and ankerite correlate inversely with permeability but chlorite and possibly siderite correlate positively diagenetic assemblages show no systematic variation with stratigraphy or geography both of which may involve variable detrital supply permeability shows the well known variation with grain size and depth of burial but after correcting for these effects it is greatest in estuarine channel and river mouth turbidite sandstones this is because these facies preferentially develop chlorite rims on detrital quartz grains and are also the sites of enhanced flow of late basinal fluids resulting in secondary porosity local effects such as facies distribution architecture of channel sandstones fluid pathways related to complex salt tectonics and the effects of overpressure are more important than predictable basin wide effects in controlling sandstone reservoir quality

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment yet few studies have investigated spatially distributed groundwater fluxes in deep ocean environments such as continental slopes heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity these assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow ocean temperature changes and seabed thermal conductivity variations on deep ocean sediment temperature profiles temperature observations from the sediment and bottom ocean water on the scotian slope off eastern canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid the spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper middle slope and discharge on the lower slope we speculate that the downward groundwater flow inferred on the scotian slope is due to density driven processes arising from underlying salt domes in contrast with upward slope systems driven by geothermal convection improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length

fluid rock interactions in the salt dome environment an introduction and review abstract the salt dome environment in the gulf of mexico coast u s a provides one of the most diverse and long lived records of fluid rock interactions in an active sedimentary basin dominated by saline formation waters the geochemical record most of which is isotopic appears to span a temperature range between earth surface temperatures and lower greenschist facies most mineral forming processes in the salt dome cap rocks appear to involve mixtures of warm saline formation fluids from deep basin sources and cool dilute meteoric waters papers in this issue of chemical geology document some of the current research on fluid rock interactions in the salt dome environment these papers highlight the diversity of opinion about salt dome processes offering clues for further research the present paper reviews some of the key and more current literature on salt dome geochemistry fluid convection around salt domes and fluid rock interactions within salt and within the salt dome environment

quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

bow echo mesovortices part ii their genesis abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex in part ii of this study mesovortex genesis was investigated for vortices formed at different stages of convective system evolution during the early cellular stage cyclonic mesovortices were observed the cyclonic mesovortices formed from the tilting of baroclinic horizontal vorticity acquired by downdraft parcels entering the mesovortex as the convective system evolved into a bow echo cyclonic anticyclonic mesovortex pairs were also observed the vortex couplet was produced by a local updraft maximum that tilted baroclinically generated vortex lines upward into arches the local updraft maximum was created by a convective scale downdraft that produced an outward bulge in th

thermal history of the periphery of the junggar basin northwestern china geochemical analyses of rock core samples show that the basin periphery has experienced low thermal stress present day heat flows are in the range of 25 35 mw m 2 and have not been significantly higher than the worldwide mean of approx 63 mw m 2 since the mid permian present day heat flows were determined from corrected borehole temperatures and rock thermal conductivities paleo heat flows were determined by first order reaction kinetic modeling of several geochemical paleothermometers vitrinite reflectance clay mineral diagenesis and relative proportions of sterane and hopane biological marker diastereomers

an overview of the petroleum systems of the northern deep water gulf of mexico the northern deep watergulf ofmexico is one of themost active deep water petroleum provinces in the world this paper introduces the regional geologic setting for the northern deep water gulf of mexico and briefly discusses the importance of technology in developing the area s resources exploration has focused on four major geologic provinces basins subsalt fold belt and abyssal plain these provinces formed from the complex interactions between mesozoic cenozoic sedimentation and tectonics improved understanding of the geology of these provinces has largely been accomplished by improvements in seismic acquisition and processing in addition advances in drilling technology have permitted drilling and field development in increasingly greater water depths the 226 oil and gas fields and discoveries in the northern deep water gulf of mexico are summarized in terms of their exploration and development history producing facility ages of reservoirs upper jurassic upper paleocene lower eocene oligocene lower miocene upper pleistocene and trap type structural combined structural stratigraphic and stratigraphic in addition the interpreted regional distribution of upper jurassic and possible lower cretaceous source source rocks is shown in part based on the 26wells that have penetrated these source rocks the eight papers in this special issue review the geology of the mississippi canyon and northern atwater valley protraction areas the first five papers review the subregional structural setting and the evolution of its tectonics and petroleumsystems the final three papers summarize the geologic evolution of two economically important intraslope basins thunderhorse andmensa in terms of their stratigraphy structural evolution and petroleumsystems these two basins contain two of the larger oil and gas fields respectively in the northern deep water gulf of mexico copyright 2017 the american association of petroleum geologists all rights reserved

heat flow measurement in lacustrine or oceanic sediments without recording bottom temperature variations water bottom temperature variations btv introduce many uncertainties into heat flow density hfd values determined from the temperature depth t z plot from a one time probe insertion into the top few meters of sediments the btv have to be carefully monitored for a number of years up to the date of the probe measurements this makes the method time consuming and economically unattractive in this paper we present the theory for a promising new technique the method does not require monitoring of the btv but does require at least two t z profiles separated in time by only a few months a generalized inversion of the btv history using the separated t z data and any other a priori information that is available is then performed in the frequency domain to give the most probable bayesian estimates of various parameters and their error bounds numerical examples show that the inversion can resolve not only the hfd but also the mean sediment surface temperature and gives information on the longer term trend as well as details of the btv over the previous year these together with thermal properties structure are the factors that contribute most to the shape of the time dependent t z profiles used in a typical situation where a uniform half space with a background hfd 60 mw m 2 has been perturbed by complex btv with a maximum variation of 1 8 k using a misguessed hfd of 90 100 mw m 2 in the inversion of two t z profiles taken 3 months apart over a 2 to 5 m section results in a posteriori hfd of 58 11 m w m 2 although the technique gives an optimally determined mean hfd its principal value lies in the ability to place reliable error bounds on the mean

hydrocarbon provinces in the swiss southern alps a gas geochemistry and basin modelling study abstract in order to evaluate the petroleum potential of southern switzerland south alpine fold and thrust belt gas geochemical investigations including free and adsorbed gases were combined with a basin modelling analysis the palaeotectonic setting and alpine orogenic movements were recognized as main controls in the evolution of the petroleum generation potential three main hydrocarbon provinces are distinguished 1 the arbostora anticline which developed from an early jurassic high has excellent but immature source rocks which probably at no time generated hydrocarbons because of their swallow level in the nappe edifice 2 the stabio anticline south of the arbostora anticline in southernmost switzerland where wet gases are observed at the surface that are likely to have been generated from late cretaceous to present day from triassic source rocks occurring deeper in the nappe pile and 3 the m generoso basin with prevailing petroleum generation in the early jurassic and possible minor generation in marginal areas during cretaceous and tertiary times

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

petroleum source rocks of the tarfaya basin and adjacent areas morocco abstract this work characterizes the source rock potential of the tarfaya basin and enabled us to reconstruct its geochemical history outcrop samples covering different stratigraphic intervals plus the northwestern part of the zag tindouf basin bas draa area were analyzed for total organic carbon corg and total inorganic carbon contents and total sulfur content rock eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis corg content a set of 45 samples were extracted and non aromatic hydrocarbons were analyzed by way of gas chromatography flame ionization detection gc fid and gc mass spectrometry gc ms non isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks high quality petroleum source rocks with high corg content and hydrogen index hi values were found for samples of eocene coniacian turonian and cenomanian age most samples were carbonate rich and organic sulfur values were high to moderate various maturity parameters indicated immature or possibly early mature organic matter based on organic geochemical and petrological data the organic matter is of marine aquatic origin cenomanian or a mixture of aquatic and terrigenous material eocene the early cretaceous interval did not contain high quality source rocks but indications of petroleum impregnation were found

the effect of allochthonous salt on the petroleum systems of northern green canyon and ewing bank offshore louisiana northern gulf of mexico the northern green canyon ewing bank region northern gulf of mexico basin contains the oxfordian neogene tithonian neogene albian neogene turonian neogene and eocene neogene petroleum systems the systems encompass 42 fields or discoveries in the study area and include four subsalt discoveries essential elements of the systems include source shales of oxfordian tithonian albian turonian and eocene age neogene siliciclastic turbidite reservoirs allochthonous salt and overburden strata ranging in age from jurassic to quaternary the petroleum systems of the area are significantly affected by the evolution of allochthonous salt the high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation and migration from them most traps were formed during the pliocene pleistocene and the generation migration accumulation of petroleum ranges from early miocene to the holocene the critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying sediments and allochthonous salt evolution the impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt where salt welds form petroleum migration is unimpeded and continues vertically by integrating predictions of potential source rocks structural restorations thermal maturation modeling regional salt maps and petroleum systems logic we can determine petroleum migration pathways and zones of concentration all 42 fields or discoveries within the study area are associated with predicted zones of paleosubsalt petroleum concentration present day salt geometries do not delineate many of these zones because of salt weld formation during the pleistocene this generation migration and accumulation technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success

framework of hydrocarbon generation and destruction in eastern smackover trend laminated lime mudstones of the lower member of the jurassic smackover formation are significant source rocks for crude oil across mississippi alabama and florida the source facies was deposited in an anoxic and perhaps hypersaline environment that preserved algal derived kerogen the distribution of kerogen along laminations of depositional origin and along stylolites of diagenetic origin resulted in efficient expulsion of crude oil with increasing thermal maturity crude oil initially emplaced in reservoirs was cracked to yield gas condensate and then methane rich in nonhydrocarbon gases such as hydrogen sulfide carbon dioxide and nitrogen early destruction of methane was driven by thermochemical sulfate reduction the thermal maturity framework of the smackover rend explains the distribution of hydrocarbon discoveries and suggests areas previously overlooked by exploration

the garden city kansas storm during vortex 95 part ii the wall cloud and tornado abstract on 16 may 1995 a supercell storm produced an f1 tornado near garden city kansas during vortex verification of the origins of rotation in tornadoes experiment this event provided the first opportunity to synthesize data collected by a new airborne radar platform called eldora electra doppler radar developed by the national center for atmospheric research the evolution of the low and midlevel mesocyclone was presented in a companion paper in this paper the sequence of events that triggered tornadogenesis within the mesocyclone circulation is shown the occlusion downdraft documented in part i appears to promote vortex breakdown resulting in the generation of multiple vorticity centers it is one of these centers that intensifies into the garden city tornado the structural relationship between the observed wall cloud and the radar reflectivity associated with the developing hook echo and the kinematic wind field is also presented although the wall cloud appears to be uniform there

chemical kinetic model of hydrocarbon generation expulsion and destruction applied to the maracaibo basin venezuela this paper describes the development and application of a compositional chemical model of hydrocarbon generation expulsion and destruction for the cretaceous la luna formation source rock of the maracaibo basin venezuela applications include both laboratory and geological settings laboratory pyrolysis experiments were used to study bulk oil generation expulsion and associated changes in composition of the kerogen extractable organic matter and expelled and unexpelled hydrocarbons the laboratory experiments were also used to determine kinetic parameters to quantitatively describe organic reactions via a computer model that also includes simulation of pressure driven primary expulsion over widely varying conditions we show that the chemical model accurately sim lates the experimental results thermal history models for wells in the maracaibo basin were used to simulate hydrocarbon generation and pore pressure development in the la luna formation and expulsion into nearby cretaceous reservoirs results of the modeling indicate that both compaction disequilibrium and organic maturation play important roles in the development of excess pore pressure in the la luna formation the model simulation of the variation of indicators such as rock eval parameters and extract and oil compositions shows generally good agreement with measurements from remaining kerogen oils and extracts recovered from the la luna formation and from nearby cretaceous reservoirs

gas saturation and co2 enhancement potential of coalbed methane reservoirs as a function of depth the influence of moisture temperature coal rank and differential enthalpy on the methane ch4 and carbon dioxide co2 sorption capacity of coals of different rank has been investigated by using high pressure sorption isotherms at 303 318 and 333 k ch4 and 318 333 and 348 k co2 respectively the variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding langmuir parameters in combination with a geothermal gradient of 0 03 k m and a normal hydrostatic pressure gradient taking the gas content corresponding to 100 gas saturation at maximum burial depth as a reference value the theoretical ch4 saturation after the uplift of the coal seam was computed as a function of depth according to these calculations the change in sorption capacity caused by changing pressure temperature conditions during uplift will lead consistently to high saturation values therefore the commonly observed undersaturation of coal seams is most likely related to dismigration losses into adjacent formations and atmosphere finally we attempt to identify sweet spots for co2 enhanced coalbed methane co2 ecbm production the co2 ecbm is expected to become less effective with increasing depth because the co2 to ch4 sorption capacity ratio decreases with increasing temperature and pressure furthermore co2 ecbm efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between co2 and ch4 for low mature coals

sub bottom temperature perturbations due to temperature variations at the boundary of inhomogeneous lake or oceanic sediments abstract for many years continental heat flow data were obtained from temperature gradients measured in boreholes and conductivity measurements made on representative cores because of the difficulty of obtaining deep holes in suitable regions increasing use is being made of measurements made in the top few meters of the sediments at the bottom of continental lakes for reliable heat flow results two conditions must be met first an accurate record of the temperature history at the top of the sediment should be available preferably over a time span of 4 or 5 years second if the thermal properties are not constant with depth then the depth dependence should be known errors that may arise if either or both of these conditions cannot be met can be serious using various surface thermal histories we compare results from models assuming constant diffusivity a diffusivity changing exponentially with depth and a layered medium all being structures based upon observed variations near the sediment water interface where conductivity may change by a factor of two over 2 or 3 m in some situations errors as large as several hundred percents may occur but in such cases it should be possible to deduce from the data that something has occurred to make the data unreliable more realistically there are occasions where a temperature depth plot which is linear within normally acceptable limits of accuracy and with a gradient that is within the range of expectations may be as much as 100 in error

the evolution of allochthonous salt along a megaregional profile across the northern gulf of mexico basin sequential restorations of a north south megaregional cross section across the north central gulf of mexico basin from east central louisiana to the abyssal plain define a dynamic complex history of sedimentation salt flowage and salt evacuation proprietary composite seismic profiles 590 km 33 wells and published depth to basement maps were used to constrain the section in depth thirteen sequential structural restorations incorporating both decompaction and isostatic subsidence thermal and tectonic were then constructed from the late cretaceous to the holocene the restorations highlight and constrain a protracted history of deformation that is primarily controlled by gravity and the progradation of cenozoic sediments over salt early stages of the tectonic history of the northern gulf of mexico basin were related to differential thermal subsidence resulting from early middle jurassic rifting during the cenozoic the evolution of the basin was dominated by the influx of large clastic depocenters which caused the basinward evacuation of autochthonous jurassic salt salt extrusion from the autochthonous layer was accomplished by inclined salt bodies which flowed into salt glaciers or sheets near the sea floor evacuation of allochthonous salt layers provided significant sediment accommodation and unusually thick sedimentary sections were deposited such as the terrebonne trough of southern louisiana 3 7 km of miocene strata salt sheet formation and evacuation occurred progressively basinward through time in response to basinward shifts of major cenozoic sedimentary depocenters as a salt sheet neared complete evacuation the underlying autochthonous salt layer would begin to evacuate providing additional sediment accommodation that caused autochthonous salt flowage basinward and the formation of the next allochthonous salt sheet basinward of the depocenter the area of autochthonous salt progressively decreased through time and currently represents at most 45 of its maximum along this transect the total area of salt through time was more stable with variations of only 30 from its maximum this relationship is a function of lateral salt flow into and out of the plane of section and possible salt dissolution the restorations indicate that very little translation or extension 1 46 occurred at the autochthonous salt level during the evolution of the basin the majority of translation or extension occurred above allochthonous salt sheets 25 and was compensated laterally by salt flow displacements above allochthonous salt sheets were driven by gravitational instabilities caused by the slope gradient

the genesis of mesovortices within a real data simulation of a bow echo system abstractthe genesis of two mesovortices mvs within a real data convection resolving simulation of the 8 may 2009 central u s bow echo system is studied both mvs form near the bow apex but differ distinctively in intensity lifetime and damage potential the stronger and longer lived mesovortex mva stays near the bow apex where the system scale rear inflow jet rij is present the descending rij produces strong downdrafts and surface convergence which in turn induce strong vertical stretching and intensification of mva into an intense mesovortex in contrast the weaker and shorter lived mesovortex mvb gradually moves away from the bow apex accompanied by localized convective scale downdrafts lagrangian circulation and vorticity budget analyses reveal that the vertical vorticity of mvs in general originate from the tilting of near surface horizontal vorticity which is mainly created via surface friction the circulation of the material circuit that ends up to be a horizontal circuit at the fo

high winds generated by bow echoes part ii the relationship between the mesovortices and damaging straight line winds airborne radar analysis of a mesovortex that developed near the apex of a bow echo is presented the mesovortex was shown to play a critical role in determining the location of intense straight line wind damage at the surface the perturbation pressure gradient force in natural coordinates along the parcel path accelerated the horizontal winds however intense mesovortices modified the low level outflow and largely determined the locations where the strongest winds occurred regions of maximum winds are accounted for as a superposition of the vortex and the flow in which it is embedded the strongest winds occur on the side of the vortex where translation and rotation effects are in the same direction this model explains the observed tongue of high wind speeds that were confined to the periphery of the mesovortex the origin of the mesovortex is also examined similarities and differences of this bow echo event with recent modeling studies are presented

the art of maturity modeling part 2 alternative models and sensitivity analysis the sensitivity of exploration decisions to variations in several input parameters for maturity modeling was examined for the miti rumoi well hokkaido japan decisions were almost completely insensitive to uncertainties about formation age and erosional removal across some unconformities but were more sensitive to changes in removal during unconformities which occurred near maximum paleotemperatures exploration decisions were not very sensitive to the choice of a particular kinetic model for hydrocarbon generation uncertainties in kerogen type and the kinetics of different kerogen types are more serious than differences among the various kinetic models results of modeling using the tti method were unsatisfactory thermal history and timing and amount of hydrocarbon generation estimated or calculated using the tti method were greatly different from those obtained using a purely kinetic model we strongly recommend use of the kinetic r o method instead of the tti method if we had lacked measured r o data subsurface temperature data or both our confidence in the modeling results would have been sharply reduced conceptual models for predicting heat flow and thermal conductivity are simply too weak at present to allow us to carry out highly meaningful modeling unless our input is constrained by measured data maturity modeling therefore requires the use of more not fewer measured temperature and maturity data the use of sensitivity analysis in maturity modeling is very important for understanding the geologic system for knowing what level of confidence to place on the results and for determining what new types of data would be most necessary to improve our confidence sensitivity analysis can be carried out easily using a rapid interactive maturity modeling program

molecular nitrogen in natural gas accumulations generation from sedimentary organic matter at high temperatures the occurrence of natural gas accumulations with high percentages up to 100 of molecular nitrogen in various hydrocarbon provinces represents a largely unresolved problem and a serious exploration risk in this context a geochemical and basin modeling study was performed to evaluate the potential of sedimentary organic matter to generate molecular nitrogen the masses of nitrogen present in coals if converted into molecular nitrogen are sufficient to fill commercial gas reservoirs a calculation for gas accumulations in northern germany where percentages of molecular nitrogen range from less than 5 to greater than 90 reveals that the molecular nitrogen generated in underlying coal bearing strata is sufficient to account for the nitrogen gas even in the largest fi lds in addition much of the total nitrogen in clay rich rock types such as shales and mudstones is fixed in sedimentary organic matter and may add to the nitrogen generation capacity of the coals a kinetic interpretation of the nitrogen and methane generation characteristics of humic coals during laboratory pyrolysis indicates that nitrogen is generated from organic matter in sedimentary basins at higher temperatures than methane minimum temperatures for preferential nitrogen generation are in excess of 300 c for extremely low heating rates or isothermal conditions lasting over 300 m y thus nitrogen rich gases are mainly formed in the final stage of gas generation when sedimentary rocks grade into metamorphic rocks applications of the kinetic parameters for the generation of nitrogen and methane from coaly organic matter in carboniferous sedimentary rocks are presented for part of the northwest german basin in this area immense volumes of the methane rich gas gener ted during the late paleozoic and mesozoic were lost to the atmosphere the present gas composition mainly reflects the latest cenozoic gas generation this cenozoic gas is nitrogen rich where the carboniferous source rock sequences are highly mature and deeply buried

petroleum generation and migration in the styrian basin pannonian basin system austria an integrated geochemical and numerical modelling study abstract source rock analysis and numerical modelling techniques have been applied to evaluate the hydrocarbon potential of the styrian basin oil and gas prone sediments occur in the lower miocene section ottnangian and karpatian levels kinetic parameters indicate that hydrocarbons are generated at higher temperatures and within a narrower temperature interval from ottnangian sediments than from karpatian sediments the thermal history of the basin is governed by miocene magmatic activity due to subduction along the carpathian front heat flow during magmatic activity in close vicinity to the volcanic centres was about 300 mw m2 decreasing to about 120 mw m2 at a distance of a few kilometres after the magmatic activity the heat flow decreased and has remained at 60 85 mw m2 since the end of the middle miocene the increased heat flow resulted in an early miocene karpatian to early badenian petroleum generation phase near the volcanoes because no traps were formed at that time the generated hydrocarbons may have been lost thus the early magmatic episode had a negative impact on the hydrocarbon potential from a timing aspect at some distance from the volcanoes generation continued up to the end of the middle miocene early sarmatian hydrocarbons generated during and since the middle badenian have had a good chance of becoming trapped and forming accumulations only small amounts of oil formed after the middle miocene the numerical modelling of petroleum migration provides important information on its timing and pathways and predicts correctly the only drilled hydrocarbon occurrence in the styrian basin the calculated gas to oil ratio is 0 5 the integration of all these data helps to define areas with high petroleum potential

a method for determining terrestrial heat flow in oil basinal areas abstract a method for determining the terrestrial heat flow has been studied in the oil gas basinal areas in japan to estimate the heat flow an available zone was selected from a geologic section observed in a well the selected zone is covered by many bottom hole temperatures sufficient to determine a reliable geothermal gradient the bottom hole temperature was converted into an equilibrium formation temperature mainly by using the simple equation obtained from the relations between bottom hole and reservoir temperatures the thermal conductivity of the zone was primarily determined by both the measurements of well core samples and the experimental relations of thermal conductivity to porosity of some specific rocks then the conductivity was adjusted to subsurface temperature by using the empirical equation deduced from the relations of thermal conductivities of materials to temperatures

high winds generated by bow echoes part i overview of the omaha bow echo 5 july 2003 storm during bamex abstract an analysis of a bow echo that produced damaging winds exceeding f1 in intensity on the fujita scale near omaha nebraska is shown part i of this study presents a combination of airborne doppler derived wind syntheses with a comprehensive damage survey in order to document the generation of strong winds at the surface a detailed kinematic analysis of the evolution of a quasi linear convective system into a bow shaped and subsequently a spearhead echo is shown for the first time it is hypothesized that a large cyclonic bookend vortex 70 80 km in diameter north of the bow apex enhanced the rear inflow jet and initiated the bowing process a hook shaped echo and mesovortex formed at the apex of a bowed segment of the convective line and was located to the north of the swath of strong damage rated greater than f1 in damage intensity the peak single doppler radial velocity recorded by the tail radar was 43 m s 1 in the low level outflow near the apex of the bow echo the regions of the str

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

diagenetic barite and sphalerite in middle mesozoic sandstones scotian basin as tracers for basin hydrology cementation of sandstone by minor late barite and sphalerite is widespread in the scotian basin at burial depths 2 km 1 mi providing information on fluid flow in the basin the texture and geochemistry of these minerals were analyzed by scanning electron microscopy and electron microprobe on samples from conventional core barite and sphalerite postdate silica and carbonate cementation occurring in veins or occupying secondary porosity they occur with diagenetic chlorite kaolinite pyrite titania minerals kutnohorite and mn siderite this study relates barite and sphalerite to the salt tectonic evolution of the basin based on seismic interpretation and the thermal history of the basin based on fluid inclusion studies barite is readily transported in basinal fluids 100 c 212 f yet is consistently a very late diagenetic mineral this implies that the source of ba is because of the late diagenetic breakdown of k feldspars at 2 3 km 1 2 mi depth which is confirmed by covariation of ba and rb in sandstones sulfur isotope data suggest that the was derived from argo formation evaporites that include 1 7 anhydrite sphalerite is mobile only in saline formation water 140 c 284 f and requires long distance transport through sandstones with zn rich fe ti oxides active detachment faults on salt welds provide potential pathways and a source of salt for migrating formation water the particularities of source and transport of both barite and sphalerite allow the pathways of basinal fluids and their relationship to active salt tectonics to be inferred providing indirect dating of the later stages of diagenetic paragenesis corresponding to times of hydrocarbon charge

ephemeral thermal and solute plumes formed by upwelling groundwaters near salt domes geochemical observations made by previous workers indicate that rapid upward advection of hot water has occurred along the flanks of some salt domes in the northern gulf of mexico basin and in the danish central trough the observations are based on pore fluid chemistry and on high temperatures of formation of metal sulfides and other diagenetic minerals near the crests of salt domes some of the diagenetic minerals formed at 40 c to 80 c above the ambient temperature of the host rocks numerical simulations of coupled heat and dissolved salt transport show that thermal perturbations in excess of 60 c can be repeatedly produced near the crest of a salt dome by focused dewatering of a thick strongly overpressured sedimentary interval around the dome in our simulations dewatering was triggered and stopped by cyclically changing the permeability at the salt sediment interface the thermal plumes dissipated within 100 kyr after dewatering ceased stratigraphically shallow brine plumes were also formed by dewatering and these gravitationally unstable plumes dissipated more slowly by sinking within 1 m y simulations showed that free thermohaline convection can also generate thermal perturbations near the crest of a dome in this mode of upwelling thermal perturbations reached 30 c when the vertical permeability of the hydrostatically pressured interval was 10 14 m2 10 mdarcy because such permeabilities seem large for the hydrostatically pressured interval as a whole in the northern gulf of mexico basin the formation of high temperature metal sulfide deposits near the crests of salt domes seems more likely to be due to dewatering of the overpressured interval with very strong focusing of expelled waters along the flanks of salt domes

density driven groundwater flow near salt domes active halite dissolution occurs around numerous salt domes in louisiana forming brines with as much as 300 g l 1 tds tds total dissolved solids most of which is na and cl we numerically modeled the possible dynamics of 1 brine density flow induced by solute concentration gradients and 2 thermal convection induced by temperature gradients around hypothetical salt domes calculated maximum flow velocities due to brine density flow range from 0 01 to 1 m yr 1 even in low permeability sediments much greater than velocities due to thermal convection immense quantities of halite can be dissolved by brine density flow up to 3 km3 myr 1 and formation of brine plumes can occur very rapidly in some cases requiring 1 myr maximum flow velocities increase with bulk permeability and decrease with increasing anisotropy geopressured waters bleeding upward into the hydropressured zone may affect brine formation in the hydropressured zone provided permeability of the geopressured zone is sufficiently high

pn wave velocities beneath the tanzania craton and adjacent rifted mobile belts east africa p wave travel times from regional earthquakes recorded by the tanzania broadband seismic experiment have been inverted for long wavelength 100 km pn velocity variations beneath tanzania using a generalized inverse algorithm pn velocities on average are 8 40 to 8 45 km s beneath the center of the tanzania craton 8 30 8 35 km s beneath the terminus of the eastern branch of the rift system and 8 35 8 40 km s beneath the western branch these velocities indicate that there are no broad 100 km wide thermal anomalies in the uppermost mantle beneath areas of rifting in tanzania and suggest that thermal anomalies present deeper in the mantle have not yet reached the base of the crust

the relationship between bitumens and mineralization in the south pennine orefield central england like many examples of mississippi valley type mineralization the south pennine orefield is well known for the occurrence of hydrocarbons within hydrothermal mineral veins bitumens from this area along with oils from the east midlands have been characterized using standard organic geochemical techniques and compared with potential source rocks lower namurian mudstones from the widmerpool gulf and the gainsborough and goyt troughs were rejected as possible sources for the bitumens and oils on the grounds of lack of sufficient thermal maturity and or essential biomarker correlation lower namurian mudstones with type ii kerogen from the edale gulf are proposed to offer a likely hydrocarbon source for the area with a minor more localized contribution from organic rich type ii mudstone partings within the dinantian limestones simple geochemical models consistent with recent sequence stratigraphic interpretation suggest a late carboniferous age for hydrocarbon generation where geothermal gradients were slightly higher c 50 c km 1 than the present day microthermometric analysis of fluid inclusions from fluorite and calcite allowed three fluid types to be distinguished one na ca cl bearing fluid was discerned to be dominant throughout the orefield being of low temperature uncorrected t h 70 110 c and high salinity c 20equiv wt nacl a second high salinity na ca cl fluid uncorrected t h 70 120 c c 24equiv wt nacl distinguished from the first by varying na ca contents was observed in the westernmost extremities of the orefield a third nacl bearing fluid of higher temperature t h 100 145 c and lower salinity 4 wt nacl was detected in the northernmost part of the orefield hydrocarbon bearing inclusions were not observed in any of the three fluids in this study sulphur isotopic analyses performed on a selection of sulphides sulphates and bitumens to gauge the role of organic matter in sulphate reduction reactions proved inconclusive the mineralization is thought to have occurred as several events that in the north is thought to be derived from the dewatering of the edale gulf towards the end of the carboniferous whilst other mineralization events occurred from the early permian onwards with the ore fluids having more distal sources predominantly from the east with a minor input from the west the main phases of hydrocarbon generation and mineralization appear to be unrelated

virgin rock temperatures from well logs accuracy analysis for some advanced inversion models abstract temperature data from 18 measurement series obtained during logging of the oseberg field in the northern north sea are presented because the measurement series are taken at approximately the same depth they should give identical temperatures after depth correction and are suitable for assessing the performance of different models used to determine virgin rock temperatures from well log information we have used this data set to test the properties of the different models given by shen and beck 1986 although these models were built to simulate closely the thermal recovery of a well and are unbiased the uncertainties in the temperature estimates when applied to real data are found to be no less than those from simpler biased models this fact confirms the conclusion of hermanrud 1989a who showed that physical factors other than those presently accounted for significantly influence the thermal recovery of a borehole

shallow geothermal anomalies overlying deeper oil and gas deposits in rocky mountain region eight of nine rocky mountain area oil and gas fields surveyed by shallow geothermic methods show hot spots or positive shallow temperature anomalies at depths ranging from 500 ft 150 m to as shallow as 10 ft 3 m the magnitudes of these anomalies generally range from 1 to 3f 0 5 to 1 5c but in one case reached 16f 8 9c at 500 ft 150 m similar shallow thermal anomalies associated with oil or gas fields are reported in russian and other literature the methodology of drilling shallow holes and recording accurate temperatures therein is fairly simple inexpensive and rapid the primary cause of the observed temperature anomalies at and above oil and gas fields is unknown but the writers believe that lateral and upward fluid movements through subsurface rocks are an important contributing factor because four of the fields that show both shallow and deep positive temperature anomalies are stratigraphically controlled and are not on or near crests of structural features the commonly held belief that positive temperature anomalies over oil and gas fields simply reflect structural highs is not supported by our data the addition of shallow geothermal surveys to the suite of conventional exploratory methods should improve exploratory efforts to find new oil and gas fields

measured radiogenic heat production in sediments from continental margin of eastern north america implications for petroleum generation measurements of radiogenic heat production are presented for most of the major sedimentary formations beneath the rifted continental margin off nova scotia canada the measurements were made on 32 samples from 14 deep exploratory wells drilled in the area the results show that heat production ranges from about 1 8 to 0 3 w m 3 and varies with lithology the effect of this radiogenic heat production is to increase the heat flow and the temperatures within the sediments by up to 15 and 30 6 f 17 c respectively these temperature changes will increase the rate of organic maturation so that for example oil generation should occur 10 to 30 ma earlier in jurassic sediments than if those sediments exhibited no heat production it is noted ho ever that other thermal properties of the sediments must be studied before predictions of organic maturation and the timing of oil generation can be considered reliable the results presented here show that radiogenic heat production in sediments is an important parameter in making reliable predictions of their thermal maturity and thus should be included in future studies of thermal models for sedimentary basins

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

adiabatic decompression of aqueous solutions applications to hydrothermal fluid migration in the crust adiabatic decompression may result in the heating of geologic aqueous fluids on the order of tens of degrees celsius adiabatic expansion may be either reversible in which case geologically important fluids cool on decompression or irreversible if the irreversible adiabatic expansion involves a significant pressure loss due to internal work generation and kinetic and gravitational effects can be ignored and the joule thompson coefficient is large and negative fluids heat up upon decompression the joule thompson coefficient becomes increasingly negative i e the heating effect dominates at high pressures low temperatures high m nacl and high x co 2 we predict that high concentrations of divalent and trivalent ions in solution will also increase the magnitude of the heating effect

oil fields a source of heat flow data abstract a method of calculating terrestrial heat flow from oil fields is evaluated by reviewing its application to twelve petroliferous basins three of them in brazil and nine in indonesia in each well terrestrial heat flow was calculated by multiplying the temperature gradient obtained by commonly used procedures by the effective thermal conductivity the latter was calculated from quick thermal conductivity measurements on core samples by a transient hot wire method and from the lithologic log typically in each basin the conductivity of about 300 core specimens was measured and logs of 50 150 wells were examined in each formation penetrated by a well the total thickness of each rock type such as shale sandstone etc was determined from the composite lithologic log the harmonic mean of the thermal conductivity of a formation in the well was computed from these thicknesses and the average values of the conductivities of the rock types measured on cores collected from that formation the conductivity of the well is the harmonic mean of the conductivities of the formations the average precision of the determination of formation conductivity can be expressed as the 95 limits divided by the average value for twelve basins this measure of precision for formation conductivities averages 3 6 and the average precision of the conductivity of a basin is 2 0 on the same basis the precision of the determination of the temperature gradient in a basin averages 4 7 and that of the heat flow 5 8 expressing the variability of the geothermal quantities in a basin determined at discrete locations as the standard deviation divided by the average value we get for the mean variability in the twelve basins 6 7 for conductivity 15 0 for the gradient and 16 4 for the heat flow the variability must come in part from natural causes in general at the present level of accuracy no correlation between anomalous heat flow and the occurrence of oil in a basin was found values of thermal conductivity of sedimentary rocks and their variation with depth are useful in calculating paleotemperatures the magnitude of the mean heat flows of the basins is normal 63 mw m2 for the jurassic basins of the stable continental margin of brazil and somewhat elevated in the tertiary basins of indonesia north of the sunda trench subduction zone the values decreasing from 130 mw m2 in central sumatra to 70 mw m2 in eastern kalimantan future improvements in the procedures for determining conductivity might possibly bring out local anomalies in heat flow that might be caused by vertical seepage of water this would support the hydraulic theory of accumulation of oil and gas

source and thermal history of oils from lockhart crossing livingston parish louisiana abstract in 1982 lower tuscaloosa production at the lockhart crossing field was supplemented with a major discovery of significant petroleum reserves in the wilcox whole oil and biomarker source parameters definitively prove that the oils found in wilcox reservoir rocks constitute one single oil family oils produced from the tuscaloosa formation comprise a separate oil family unrelated to the oils in the wiilcox formation within each formation the oils become progressively more mature with depth this is believed to be due to thermal cracking which as taken place after the oil charged with the reservoirs the chemistry of the oils produced from wilcox reservoirs shows that these oils were generated from clay rich shales with a significant input of bacterial organic matter eukaryotic algae and higher plants also contributed organic matter to the source rocks comparisons with cuttings from nearby wells prove that wilcox shales are the source facies for these oils biomarker and other maturity parameters indicate that the wilcox oils were generated from source rocks that were within the thermal regime associated with early oil generation tuscaloosa reservoir fluids are significantly more thermally mature than the petroleum in the wilcox the tuscaloosa oils are presently in the thermal conditions associated with late stage oil gas condensate generation because of this advanced degree of thermal stress correlation of the tuscaloosa oils to their source sediments is difficult cuttings from wells updip from lockhart crossing indicate that the lower marine tuscaloosa shales are viable source rocks equivalent downdip shales are the likely source for the lockhart crossing tuscaloosa gas condensates the study proves that future wilcox discoveries in the area need not be associated with deeper tuscaloosa production

the numerical simulation of non supercell tornadogenesis part i initiation and evolution of pretornadic misocyclone circulations along a dry outflow boundary abstract high resolution three dimensional simulations are used to study misocyclone initiation and development along the leading edge of an outflow boundary model conditions were designed such that this development could be simulated independent of moist processes the outflow boundary is allowed to propagate into a region of southerly low level flow which results in a vertical vortex sheet along the outflow s leading edge lobe and cleft instabilities follow and provide perturbations for the subsequent development of horizontal shearing instabilities these growing instabilities are the inaugural circulations of leading edge misocyclones with wavelengths ranging from 1 6 to 3 2 km the structure of these modeled misocyclones compares favorably to observed pretornadic misocyclones along outflow boundaries in northeast colorado vortex sheet dynamics are observed to exert substantial control over the structure of the evolving outflow leading edge the vertical vortex sheet passes through discrete evoluti

two dimensional velocity model of the crust beneath the south cambay basin india from refraction and wide angle reflection data summary a deep seismic sounding study was carried out in western india in the southern part of the cambay basin along a 230 km long profile between the cities of mehmadabad 22 50 n 72 46 e and billimora 20 46 n 72 58 e during the year 1976 1977 seismic refraction as well as near and wide angle reflection data were obtained from various boundaries from the sedimentary section to the moho kaila et al published models based on analogue versions of these data in this study we digitized reprocessed modelled and reinterpreted the data from the mehmadabad billimora seismic survey using modelling techniques that were not available at the time that kaila et al published their results our extensive modelling and interpretation of a large number of seismic record sections in south cambay basin reveal three tertiary sedimentary subbasins the mehmadabad jambusar basin the jambusar kosamba basin and the kosamba billimora basin these basins are vertically offset relative to the each other along high angle faults and the maximum depth 9 5 km to the granitic proterozoic basement 5 8 6 0 km s 1 in the region occurs in the jambusar broach region near surface sedimentary rocks within the subbasins are underlain by deccan trap volcanics 4 75 5 2 km s 1 which have also been vertically offset throughout the study area although a prominent traveltime delay in first arrivals which is often indicative of low velocity layers is not observed on many of the seismograms our modelling of secondary reflected arrivals indicate the presence of lower velocity mesozoic sediments below the deccan trap volcanics within the subbasins the upper crust 6 0 6 3 km s 1 which is about 15 km thick also appears to be stratified in places with a low velocity zone 5 5 km s 1 in the depth range of 12 5 14 5 km between the cities of nadiad and kathana however this low velocity zone tapers and merges with the top of lower crust 6 5 6 8 km s 1 south of the city of jambusar the lower crust consists of two layers an upper layer 6 5 6 8 km s 1 and a lowermost layer 7 2 7 5 km s 1 with the discontinuity between the two lower crustal layers occurring at 23 25 km depth we interpret the higher velocity 7 2 7 5 km s 1 lowermost crustal layer as rocks that were magmatically underplated to the crust during rifting associated with the large scale extrusion of the deccan volcanics the moho discontinuity 8 0 km s 1 is about 31 33 km deep between the cities of mehmadabad and jambusar and increases to 37 km from south of the city of ankleshwar the large thickness of tertiary sediments in the cambay basin and a relatively thin crust as compared to the surrounding regions suggests that rifting in the region occurred from the cretaceous until the tertiary

petroleum generation and accumulation in the golfo san jorge basin argentina a basin modeling study abstract the golfo san jorge basin located in patagonia is very important for the oil and gas production of argentina in spite of the long history of exploration and production few geochemical studies were performed until now for this study a set of possible source rocks was analyzed by organic geochemical and petrographical methods the samples of the pozo d 129 fm range from mature to overmature and contain from less than 0 5 to 2 45 toc there is some evidence indicating an algal origin of the more hydrogen rich kerogen present in part of the basin almost all the samples of pozo anticlinal aguada bandera and pozo cerro guadal fm are overmature toc values range from less than 0 5 to 2 5 the maturation of source rocks and generation expulsion and migration of hydrocarbons was evaluated by means of 1d and 2d basin models the 1d models constructed for the western part of the basin and 2d models applied for the eastern part both indicate maximum burial in miocene times the thickness of the tertiary at times of maximum burial ranged from 1000 to 1500 m and the generally small tertiary thickness now present in the fold belt region is assumed to be the result of erosion the main tectonic inversion took place in the late neogene the models strongly suggest that a magmatic event between 20 and 30 ma combined with the maximum burial at miocene times produced a very important pulse in hydrocarbon generation within the major part of the basin dated intrusive and extrusive magmatic rocks extended all over the basin account for this period of elevated heat flow migration pathways are extensively discussed for the 2d model probably major faults acted as important conduits for petroleum

numerical simulation of the thermal maturation oil generation and migration in the songliao basin northeastern china abstract the discovery of the giant daqing oil field in the songliao basin led to the realisation of the significant petroleum potential of non marine basins in order to reconstruct the basin evolution and oil formation an integrated organic geochemical basin modelling study along a regional transect across the songliao basin was conducted it provided a regional heat flow evolution model and revealed post orogenic or late syn orogenic maturation in the central depression and pre orogenic maturation in the southeast uplift zone kinetic parameters of petroleum generation for the lacustrine source formations are the basis for the simulation of oil generation and migration in the songliao basin using the principle activation energy peaking at 54 kcal mol and a pre exponential factor of about 4 2 1027 ma 1 the simulation obtained a relatively good match with the measured transformation ratios the qingshankou formation in the west and east central depressions constituted the major source in the basin major oil generation migration and accumulation occurred during the early tertiary in the west central depression the generated oils migrated upwards into the yaojia formation followed by the updip migration into the daqing anticline and towards the local structural high along the west slope in contrast the oil migration in the east central depression was dominated by the downward movement from the lower member of the qingshankou formation followed by the updip migration towards the caoyang anticline the simulated oil accumulations are in good agreement with discovered oil fields implying a potential application of the model for prediction and evaluation of new exploration targets in the basin

large scale hot water migration systems around salt diapirs in the danish central trough and their impact on diagenesis of chalk reservoirs abstract fracture filling calcite from the piercement fields of east rosa skjold rolf north arne nils and vagn directly underlain by salt diapirs and the dome field dan overlying a deep seated salt structure have been studied by fluorescence and cathodoluminiscence microscopy fluid inclusion microthermometry and carbon and oxygen isotopes the carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured the temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs the flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments the thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water by combining fluid inclusion thermometry with o isotope data for the fracture filling calcites ranges of o isotopic values of the flushing water are deduced in skjold rolf north arne nils and vagn 18o 1 to 7 smow values typical of sedimentary porewater of sea water origin in east rosa 18o 4 and 4 smow which combined with data on fluid inclusion salinities suggest that the flushing waters were responsible for substantial salt dissolution lower 18o values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields in the case of north arne nils vagn and dan 13c values of the fracture filling calcites are similar to those of normal chalk 0 5 to 3 5 however calcites from rolf skjold and east rosa are depleted by 1 8 6 2 and 16 7 respectively only in east rosa is the matrix chalk itself depleted in 13c range 2 0 to 0 7 the low 13c values are interpreted as the result of biodegration sulphate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons this process produced 13c depleted bicarbonate which was incorporated into the fracture filling calcites

development of a new system for shallow sea heat flow measurement and its test application in the gulf of thailand abstract a new technique has been developed for the heat flow measurement in shallow seas the temperature in the sediment is measured at every 10 cm to the depth of 5 m by only one thermistor which moves up and down in the probe from the temperature data thus obtained the geothermal gradient is calculated in the least square sense by solving the thermal diffusion equation that is assuming an annual sinusoidal temperature variation at the sea bottom of which amplitude and initial phase are parameterized this system was used in the gulf of thailand and detailed temperature distributions were obtained in the future however to obtain more accurate heat flow values it is considered necessary to measure the temperature to at least the depth of 7 10 m

hydrothermics in the wyoming overthrust belt a thermal study was made across a 25 km 15 5 mi traverse of the overthrust belt in southwestern wyoming estimates of relative heat flow from temperature measurements made in shallow 30 m or 98 ft boreholes reveal a systematic variation of at least 400 mw m2 10 cal cm2 sec magnitude across the study area the cause of this variation is believed to be forced convection of heat by moving ground water two relative heat flow highs coincide with zones where structurally related faults possibly providing avenues for vertical water flow project to the surface between those two zones in a topographically elevated area low and predominately negative temperature gradients were observed in opposite seasons these shallow negative gradients are believed to exist seasonally in quasisteady state and could be indicative of a broad zone of ground water recharge the association of two relative heat flow highs with the two major deep geologic structures implies either a direct vertical communication of deep and shallow ground water or a coupling of deeper and shallower ground water systems the two structures studied are hydrocarbon bearing and associated with whitney canyon and ryckman creek fields the thermal measurements support the possibility that ascending waters have influenced the hydrocarbon migration and accumulation in these structures such measurements may be useful in delineating and understanding similar features in other areas

tornadogenesis in a simulated mesovortex within a mesoscale convective system abstractthe advanced regional prediction system arps is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes the mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system mcs that traversed southwestern and central oklahoma on 8 9 may 2007 the simulation used 100 m horizontal grid spacing and is nested within two outer grids with 400 m and 2 km grid spacing respectively both outer grids assimilate radar upper air and surface observations via 5 min three dimensional variational data assimilation 3dvar cycles the 100 m grid is initialized from a 40 min forecast on the 400 m grid results from the 100 m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex scale tornado like vortex tlv closer examination of the genesis of the tlv suggests that a strong low level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex

the origin of severe winds in a tornadic bow echo storm over northern switzerland abstract a severe bow echo storm over northern switzerland is investigated wind damage occurred along a track 15 km long and some 100 m wide damage data meteorological data from a ground micronet and doppler radar data are analyzed volume scan radar data in the direction of the approaching storm are available every 2 5 min the storm reached a weak evolution mode when the damage occurred updraft impulses followed each other in time steps of typically 5 min the damage track can be attributed to a strong radar observed vortex of 2 7 km diameter the vortex developed at a shear line that was formed by the downdraft outflow of an earlier thunderstorm cell most of the damage was collocated with the strongest doppler winds but some of the damage occurred beneath the strongest signature of azimuthal shear a weak tornado was observed in that shear region the two extremes in doppler velocity associated with the vortex and referred to as inflow and outflow velocities are analyzed separately early stren

the framework of hydrocarbon generation and migration gulf of mexico continental slope abstract the occurrence of large volumes of crude oil and thermogenic gas in plio pleistocene reservoirs and holocene seeps of the gulf of mexico slope argues that the process of hydrocarbon generation and migration continues at the present time calculated thermal maturity models based on deep seismic stratigraphy indicate that cretaceous and possibly early tertiary sediments are presently within the thermal maturity range for generation and expulsion of crude oil the cretaceous and early tertiary sediments are suggested as possible source rocks because younger sediments are thermally immature for crude oil generation and older sediments are thermally overmature for crude oil preservation the calculated thermal maturity profile for the slope indicates that some generation of crude oil could occur as shallow as 6 km and that liquid hydrocarbons could be preserved as deep as 9 km thermogenic gas is stable at even greater depths migration with a strong vertical component must be invoked to explain thermogenic hydrocarbons in shallow reservoirs and seeps of the slope the great depth at which liquid hydrocarbons and dry gas can be preserved in reservoirs of the gulf of mexico salt basin indicates that huge volumes of prospective section remain essentially unexplored

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

a temperature probe survey on the louisiana shelf effects of bottom water temperature variations a survey of temperature gradients in the uppermost sediments of the louisiana continental shelf was done in 1983 by gulf oil corporation using a 5 m long temperature probe the survey covered 450 sq mi with an average grid spacing of less than 1 mi the purpose was to detect heat flow anomalies due to subsurface fluid flow however thermal perturbations due to seasonal variation of bottom water temperature mask the temperature gradients due to geological heat flow bottom water temperature variations similar to those recorded near the survey area in 1963 1965 explain most of the observed spatial and temporal changes in shallow temperature depth profiles the data set from this detailed survey has been donated to a publicly accessible scientific database to spur resear h into heat flow measurement on continental shelves

petroleum geochemistry of the midyan and jaizan basins of the red sea saudi arabia abstract during the 1960s petroleum exploration activities in the offshore red sea areas of saudi arabia tested gas and condensate reservoired in the miocene sands immediately below the mansiyah evaporites in the offshore midyan basin recent onshore exploration activity in the red sea has resulted in the discovery of accumulations of oil gas and condensate in the lower miocene maqna group in the midyan and jaizan basins as a result of this exploration success an effort to understand the origin of these hydrocarbons was initiated the two basins were assessed geochemically by addressing 1 the potential source rocks 2 the extent of the hydrocarbon kitchens and 3 characterization of the hydrocarbons the potential source rocks for the reservoired hydrocarbons are 1 the organic rich oil prone shales of the predominantly evaporitic mansiyah formation 2 the variable quality shales and carbonates of the magna group and 3 the moderately organic rich shales of the burqan and tayran groups the reservoired hydrocarbons were characterized by carbon isotopes gas chromatography mass spectrometry and gas chromatography and compared with the potential source rocks the results showed an acceptable match to the maqna and burqan organic rich units detailed burial history thermal modelling projects were undertaken to assess the hydrocarbon kitchens of both basins results for the midyan basin indicated that over large areas tayran and burqan sediments are oil to gas mature and may be sources for the gas and or condensate accumulations whereas the limited area of mature maqna sediments may be responsible for sourcing the black oil accumulations in the jaizan basin the maqna and burqan sediments range from high oil maturity to thermally spent due to high geothermal conditions and excessive burial the burial of the source rocks increases fairly rapidly from east to west in the jaizan basin

burial history and thermal maturity assessment of upper cretaceous lower tertiary formations in the cankiri basin turkey abstract a burial history and thermal maturity investigation has been carried out on upper cretaceous lower tertiary deposits from the cankiri basin this basin which contains post deformational deposits of campanian maastrichtian to pliocene ages forms part of a rich hydrocarbon province defined by the presence of potential hydrocarbon source rocks the stratigraphic sequence was recorded at the cankiri bayat areas and topuzsaray 1 and sagpazar 1 wells at each area the succession was found to be incomplete and important unconformities were present indicating periods of non deposition and or erosion these unconformities are of variable extent a potential source rock interval of upper ypresian and lutetian the yoncali formation which has only the organic rich strata among the other formations in the cankiri basin has been identified it is composed of laminated dark gray shales dominated by type iii kerogen with turbiditic sandstones which were deposited in relatively deep water conditions total organic carbon content values range from 0 5 to 1 0 assessments of time temperature index tti values indicate that the top of the main zone of oil generation is at a depth of 3000 3250 m and the onset of oil generation window for the bayat area took place in the miocene 10 5 my ago and continued into the present coal samples collected from the karabalcik formation of lutetian age are high in ash and sulfur petrographic identifications on the polished blocks in reflected light indicate that the coal samples include abundant huminite vitrinite group macerals mean random huminite vitrinite reflectance values of the coal samples are between 0 51 and 0 53 rrandom oil av 0 52 rr oil indicating low rank coals subbituminous a high volatile c bituminous according to the astm classification

heat flow and gravity responses over salt bodies a comparative model analysis two dimensional numerical modeling of sea floor heat flow and water bottom gravity responses to systematic variations in simple subsurface salt body geometries provides insight on the relative usefulness of these two data types for extracting salt geometry information for a given salt body geometry diffusion of heat through overlying sediments results in a dramatic decrease in the amplitude of heat flow anomalies as the depth to the top of the salt body increases for top of salt depths greater than about 1 km the heat flow response is insensitive to the length of salt feeder stocks and to the thickness of salt tongues sheets this shallow depth to top of salt sensitivity range in addition to a number of environmental factors that can adversely affect interpretation of heat flow anomalies in terms of heat refraction towards and through salt bodies severely limits the usefulness of sea floor heat flow data for constraining aspects of salt body geometry for gravity data the critical factor for addressing salt body geometry is the distribution of salt relative to the sediment salt density crossover depth above and below which salt is more and less dense respectively than the surrounding sediment except when the relevant geometry information being sought presence and or length of feeder stock thickness of salt tongue or sheet is near the density crossover depth the geometry related information content of the gravity field is greater than that of the heat flow field based on these model results measurement uncertainty considerations and data limitations we conclude that gravity data generally offer an order of magnitude greater resolution capability than sea floor heat flow data for addressing salt body geometry issues of exploration interest

damaging surface wind mechanisms within the 10 june 2003 saint louis bow echo during bamex abstract detailed radar and damage survey analyses of a severe bow echo event that occurred on 10 june 2003 during the bow echo and mesoscale convective vortex mcv experiment are presented a bow echo formed just east of saint louis missouri and produced a continuous straight line wind damage swath approximately 8 km in width and 50 km in length along with five f0 f1 tornadoes careful superposition of the damage survey analysis and weather surveillance radar 1988 doppler wsr 88d data from saint charles missouri klsx showed that the primary straight line wind damage swath was not collocated with the bow echo apex as has been suggested in previous studies rather the primary damage swath was found north of the bow apex collocated with a low level vortex that formed on the leading edge of the bow echo much of the primary damage swath appeared to have been created by the low level vortex moreover most of the surface straight line wind damage was generated during the early stages of bow echo mo

thermal maturity of jurassic shales from the newark basin u s a influence of hydrothermal fluids and implications to basin modeling abstract organic geochemical investigations were conducted on a series of cores that systematically sampled the uppermost jurassic strata from the northern newark basin each sedimentary unit consists of fluvial red sandstones and siltstones with cyclic deposits of interbedded black lacustrine shales and gray deltaic siltstones in a suite of organic rich shales from the boonton towaco and feltville formations organic maturation parameters were used to determine aspects of the thermal history of the newark basin comparisons of model calculations and measured maturities support 39 ar 40 ar geochronometer studies that indicate a hydrothermal event occurred 175 ma ago an increase in the regional geothermal gradient to 7 5 c 100 m for 5 ma best conforms to the organic geochemical observations biomarker compounds in boonton and towaco strata should have been relatively unaltered by this regional event but anomalous molecular distributions in the organic rich rocks may have resulted from localized heating by hydrothermal fluids the effects of this interaction would be very subtle and may be indistinguishable from variations caused by differences in organic facies within this uncertainty sterane and hopane isomerization and steroid aromatization reactions advanced in the boonton and towaco formation strata primarily because of burial and normal geothermal heating that followed the hydrothermal event biomarker kinetic models indicate that 2400 m of boonton and post boonton strata were eroded after basinal uplift commenced 50 ma ago

vortex structure and evolution within bow echoes part i single doppler and damage analysis of the 29 june 1998 derecho abstract single doppler radar along with damage observations are examined to investigate the structural evolution of vortices observed within the 29 june 1998 derecho event that propagated through southeastern iowa into central and eastern illinois a total of 13 meso scale vortices observed primarily at low levels 0 3 km agl along the leading edge of the convective system were detected by the weather surveillance radar 1988 doppler wsr 88d radars at davenport iowa and lincoln illinois all but one of the vortices formed after the system evolved into a bow echo ten of the vortices formed north of the apex while three formed south of the apex seven of the vortices produced tornadoes that created f0 f1 surface damage none of the vortices exhibited appreciable upscale growth careful analysis of the radar data suggests that it may be possible to discern between the tornadic and nontornadic vortices the tornadic vortices tended to be stronger longer lived and deeper than their nontornadic count

the art of maturity modeling part 1 finding a satisfactory geologic model an example of one dimensional maturity modeling of the miti rumoi well a stratigraphic test drilled in a frontier area of japan is worked out in detail to illustrate how maturity modeling should be carried out prior to and during modeling an effort was made to integrate all available geological geochemical and geophysical concepts and data to create a single geologic model called here the good model that was as plausible and internally consistent as possible where data sets were internally inconsistent or in conflict with other data decisions had to be made about data reliability some vitrinite reflectance data subsurface temperatures and thermal conductivity measurements were rejected for a variety of reasons the justifications for these decisions which influenced the results of the modeling are discussed in detail using the good model we evaluated the timing and amount of oil and gas generation from coals in the haboro formation the only proposed source rocks in northwest hokkaido japan generation has occurred continually since the middle miocene but the fractional conversion of kerogen to hydrocarbons to date has been small as a result the total volume of hydrocarbons available for expulsion and migration from the haboro source rock probably is small unless very large volumes of coal are present the good model does not represent a unique solution however it thus should be regarded as one of a number of viable models rather than as the only correct one alternative models are considered in a companion paper the modeling process itself by which and during which we learn much about the geologic system is at least as important as the final numerical answer highly interactive modeling programs greatly aid in proper modeling

origin of crude oil in the wilcox trend of louisiana and mississippi evidence of long range migration abstract geochemical characterization of crude oils from wilcox reservoirs in central louisiana and southwest mississippi suggests that they represent a single crude oil family that is distinct when compared to crude oils in deeper tuscaloosa and smackover reservoirs this observation is consistent with geologic constraints that suggest an origin of crude oil from within the wilcox group itself although shales of the shallow wilcox group in central louisiana and southwest mississippi contain gas prone kerogen and are thermally immature a more oil prone source facies is present in marine shales of the deep wilcox group in southcentral louisiana thermal maturity measurements based on pyrolysis suggest a broad area of effective wilcox source rock in southcentral louisiana migration distances from source to reservoir rocks of the downdip wilcox trend of southcentral louisiana appear to be relatively short however long range updip migration sometimes greater than 100 km from deeply buried wilcox source facies provides the best explanation for emplacement of crude oil in the shallow wilcox trend of central louisiana and southwest mississippi

analysis of hydrodynamic factors in petroleum migration and entrapment the basic equations developed by m king hubbert to describe the water and buoyancy forces driving hydrocarbons through an aquifer can be expanded and combined with j a f plateau s equations on capillary pressure phenomena to allow study of oil migration and entrapment patterns the new equations are used to evaluate the sensitivity of entrapment processes to variations in temperature fluid densities and geologic parameters water drive is not important except when the tops of the petroleum transporting strata have very low dips in all other cases oil movement is governed by buoyancy drive increases in capillary pressure sufficient to cause petroleum entrapment seem important only when porosities drop below 5 the equations are also used in a computer analysis to combine the effects of all the variables and examine two hypothetical field cases specifically the computer model examines the impact of changes in transport strata transmissivity upon oil entrapment the resulting changes in potentiometric surface gradients in a structure of low dip can cause significant changes in both entrapment potential and location of the trap on the structure

low level mesovortices within squall lines and bow echoes part ii their genesis and implications this two part study proposes a fundamental explanation of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized experiments with a numerical cloud model show that significant low level mesovortices develop in simulated qlcss especially when the environmental vertical wind shear is above a minimum threshold and when the coriolis forcing is nonzero as illustrated by a qlcs simulated in an environment of moderate vertical wind shear mesovortexgenesis is initiated at low levels by the tilting in downdrafts of initially crosswise horizontal baroclinic vorticity over a 30 min period the resultant vortex couplet gives way to a dominant cyclonic vortex as the relative and more notably planetary vorticity is stretched vertically hence the coriolis force plays a direct role in the low level mesovortexgenesis a downward directed vertical pressure gradient force is subsequently induced within the mesovortices effectively segmenting the previously nearly continuous convective line in moderate to strong environmental shear the simulated qlcss evolve into bow echoes with straight line surface winds found at the bow echo apex and additionally in association with and in fact induced by the lowlevel mesovortices indeed the mesovortex winds tend to be stronger more damaging and expand in area with time owing to a mesovortex amalgamation or upscale vortex growth in weaker environmental shear in which significant low level mesovortices tend not to form damaging surface winds are driven by a rear inflow jet that descends and spreads laterally at the ground well behind the gust front