the analysis of oil trapped during secondary migration abstract during secondary migration there is an opportunity for oil to be trapped as fluid inclusions fis within framework grains such as quartz and within diagenetic cements that have a crystalline structure oil saturation on migration pathways remains relatively low so typically fewer oil inclusions get trapped compared with samples from an oil column geochemical analysis of the much smaller amounts of inclusion oil present in samples from interpreted oil migration pathways has been attempted for two samples from the champagny 1 and delamere 1 wells in the vulcan sub basin northern offshore australia a combination of petrographic analysis bulk geochemical inclusion analysis and log evaluation confirmed that both samples were from oil migration pathways despite the small number of oil inclusions reliable geochemical data were acquired from both samples that were significantly above the levels detected for the system and outside rinse blanks the fi oil trapped on the interpreted oil migration pathway in champagny 1 was generated from clay rich marine source rock with little terrigenous organic matter input it was generated at peak oil window maturity and correlates best with oils derived from the late jurassic lower vulcan formation in contrast the delamere 1 fi oil contains evidence of greater input of terrigenous organic matter and was generated at early oil window maturity this fi oil also contains a signature of a biodegraded component which could have been generated either from the middle jurassic plover formation or from an older source rock these data indicate that it is feasible to geochemically map migration pathways across prospects or basins and to analyse palaeo oil compositions in oil zones where the few inclusions get trapped this also suggests that the few oil inclusions that sometimes occur in proterozoic or archaean rocks may be analysable in the future which would provide relatively pristine and robust data on the composition and diversity of earth s early biosphere

quantitative characterization of connectivity and conductivity of sandstone carriers during secondary petroleum migration applied to the third member of eocene shahejie formation dongying depression eastern china abstract studies on migration pathways remain qualitative albeit extensive quantification of migration forcing in this study hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the third member of eocene shahejie formation in the dongying depression bohai bay basin eastern china on the basis of their lithofacies and physical properties spatial relationships and data availability secondary migration conduits are then quantified a carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals the carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration a method of quantifying sandstone carrier units using common physical properties is developed first a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes second physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory third the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit last the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters the results for sandstone carrier units in the third member of the shahejie formation are used in numerical models addressing pleistocene secondary migration the model results explain the discovered accumulation and hydrocarbon shows well and the model predictions on exploration targets have been confirmed by drilling

controls and predictability of carbonate facies architecture in a lower jurassic three dimensional barrier shoal complex djebel bou dahar high atlas morocco spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics external controls and degree of predictability of the facies architecture of shallow water carbonate platform tops to quantify the spatial distribution and vertical stacking of lithofacies within an outer platform shoal barrier complex integrated facies analysis and digital field technologies have been applied to a high relief carbonate platform exposed in the djebel bou dahar lower jurassic high atlas morocco the outer platform is characterized by subtidal cross bedded coarse grainstone to rudstone grading into supratidal pisoidal packstone rudstone with tepees that together formed a 350 to 420 m wide shoal barrier belt parallel to the margin this belt acted as a topographic high separating a restricted lagoon from the subtidal open marine region low energy tidal flats developed on the protected flank of the barrier facing the lagoon lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model the outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts in addition the spatial heterogeneity was captured in multiple time slices i e during different phases of cyclic base level fluctuations in general the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top establishing low energy subtidal conditions across the whole platform and when the accommodation space was filled with tidal flat facies heterogeneity increased during deposition of the relief building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation cycles commonly are composed of a thin transgressive tidal flat unit followed by coated grain rudstone bar facies lateral to the bar facies pisoidal grainstone beach deposits accumulated these bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand there the bars either graded into supratidal pisoidal facies with tepees when accommodation space was filled or were capped by subaerial exposure due to a sea level fall modified embedded markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval constant depositional mode analysis of individual sections did not reveal any ordering which may be related to the limited thickness of these sections composite sections however rejected the null hypothesis of randomness the addition of stratigraphically significant information to the markov analysis such as exposure surfaces and lateral dimensions of facies bodies strengthens the verdict of unambiguous preferential ordering through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation 2009 the authors journal compilation 2009 international association of sedimentologists

formation and evolution of silurian paleo oil pools in the tarim basin nw china the formation and evolution of silurian sandstone reservoirs which are characterized by the coexistence of reservoir bitumen with different types of commercial oil pools in a very extensive area around the slope and uplift areas of the manjiaer depression in the tarim basin nw china are still in question in this paper we report our investigations on the geological and geochemical characteristics of this reservoir the results show there are four types of oil shows in the reservoir severely biodegraded solid bitumen biodegraded heavy oil normal oils and light oils with slight biodegradation three suites of petroleum inclusions were identified in the reservoir which were formed during the early devonian triassic to cretaceous and late tertiary respectively petroleum in the silurian sandstone reservoirs mainly originated from the mid lower cambrian source rock and mid upper ordovician source rock the thermal maturity evolution of the source rocks in slope areas has shown that there were three main stages of oil generation that controlled the formation of the above three stages of petroleum inclusions this evidence indicates that the silurian reservoir has experienced three petroleum charge events during its geological history the first charge event occurred during the early devonian and it resulted in giant paleopools which gradually evolved into the presently widespread bitumen due to the combination of biodegradation and thermal alteration the second charge covered a long period from triassic to cretaceous and probably was related to both the mid lower cambrian source rock and the mid upper ordovician source rock the petroleum generated during this stage mixed and interacted with the low matured residual bitumen and eventually formed the present soft bitumen and some residual heavy oils in the reservoirs the third charge event mainly associated with the mid upper ordovician source rocks occurred mainly during late tertiary and accounted for most of the present commercial petroleum pools mainly normal and light oils

simulation and characterization of pathway heterogeneity of secondary hydrocarbon migration carriers are important links between sources and traps for hydrocarbon migration and accumulation in a petroleum system oil and gas commonly migrate along narrow and irregular pathways in porous media even in macroscopically homogeneous media a migration simulator based on the invasion percolation theory which couples the buoyancy of a hydrocarbon column as the driving force with capillary pressure as the resisting force satisfactorily explains migration processes in heterogeneous media in macroscopically homogeneous carriers migration pathways are generally perpendicular to equipotential lines but locally the pathways can be irregular because of the influence of microscopic heterogeneity the degree of irregularity of these pathways depends on the difference between competing driving and resisting forces when numerous pathways form in a migration accumulation system the flux of migrating hydrocarbons may vary among these pathways in macroscopically heterogeneous carriers the irregularity of migration pathways is exacerbated when the driving force is relatively weak hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large these pathways differ from those predicted only on the basis of flow potential simulation of the migration process in the middle jurassic carrier beds of the paris basin demonstrates the characteristics of the migration simulator in the analysis of migration pathway heterogeneity results are comparable to or superior to those achieved with previous simulation approaches

an anaerobic 3400 ma shallow water microbial consortium presumptive evidence of earth s paleoarchean anoxic atmosphere abstract a microbial consortium preserved in shallow water carbonaceous chert of the paleoarchean 3400 ma strelley pool formation pilbara craton northwestern western australia is composed of copiously abundant globular cobweb like swirls of randomly oriented filaments intermingled with laterally extensive flat laminated masses of subparallel filaments the shallow water possibly mudflat like habitat of the biocoenose is established by its geological setting and intimately intermixed association with millimetric quartz radiating laths and rosettes interpreted to be pseudomorphs after evaporitic gypsum anhydrite the indigenousness and syngenicity of the permineralized fossils to the encompassing chert their uncompacted minimally altered life like spatial distribution and their biogenicity and bacterial affinity are shown by optical microscopic raman spectroscopic and confocal laser scanning microscopic analyses in situ that document the mineralogy of their embedding matrix and their cylindrical filamentous morphology cellularity and kerogenous composition by comparison with mid precambrian and modern sulfur cycling ecosystems and consistent with sulfur isotopic data and their intimate co existence with copious microgranular pyrite and pseudomorphs evidently after sulfate the swirled aggregates are interpreted to be anaerobic sulfuretums in contrast the intermixed flat laminated components like microbes of fossil and modern stromatolitic mat communities are interpreted to be co occurring light requiring phototrophs whether such phototrophs were anoxygenic photosynthesizers like extant photosynthetic bacteria e g chloroflexaleans or facultatively anaerobic cyanobacteria cf oscillatoria limnetica their anoxygenic metabolism seems plausibly established given its great age shallow water habitat and anaerobic microaerophilic physiology this evidently first reported occurrence from the fossil record of anoxygenic phototrophs and of a microbial sulfuretum phototroph consortium is consistent with the supposition that earth s paleoarchean environment was essentially anoxic and suggests that o2 producing photosynthesis may have been a later evolutionary innovation

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

detailed 3 d depositional architecture of late jurassic carbonate anhydrite cycles brightling mine weald basin uk abstract quantifying the geometries of evaporite deposits at a 13 c and 18 o isotope analysis the stratigraphic interval contains five facies in stratigraphic order these include supratidal porphyritic nodular evaporite shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite subtidal shale and subtidal laminar marl capped by nodular anhydrite the interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal tidal flat facies and subtidal shallow marine facies laterally passed into the evaporative sabkha the cycles are interpreted as meter scale shoaling upward sequences likely controlled by localized high frequency changes in relative sea level and or sabkha hydrology spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam the variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution eolian processes and coastal erosion these observations indicate a similar mode of deposition to the modern day sabkha of the persian gulf we conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses but largely continuous lateral bedding at an interwell scale

sabkha facies and the preservation of a falling stage systems tract at the sauk ii iii supersequence boundary in the late cambrian eilean dubh formation nw scotland the durness group of northwest scotland represents a nearly one kilometer thick succession of mid cambrian to lower middle ordovician carbonates these rocks crop out in a narrow belt along the foreland of the caledonian orogen and in the moine thrust zone stretching some 170 km from loch eriboll southwestwards to the isle of skye the cambrian parts of the succession represent deposition on a paleo southeast facing low latitude passively subsiding continental margin situated at around 20 s carbonate deposition in scotland formed part of the extensive great american carbonate bank the sauk ii iii supersequence boundary occurs above an interval of thin meter scale shallowing upward peritidal cycles containing intraclast dolorudstones stromatolites tepees siliciclastic sand and surface karst evidence of former evaporites in the succession comprises pseudomorphs of nodular and bedded anhydrite crystal shaped calcite filled vugs representing growth of sulfate dissolution breccias and local halite casts these features represent sabkha facies arranged into cycles that constitute a preserved falling stage systems tract fsst the top of the fsst is marked by a pronounced karst surface of sandstone filled fissures the section preserves a rare snapshot of a seldom preserved environment on the cambrian laurentian margin its preservation during a time of falling relative sea level under slow tectonic subsidence is discussed

carbonate evaporite sequences of the late jurassic southern and southwestern arabian gulf the carbonate evaporite sequences of the upper jurassic arab and overlying hith formations in the southern and southwestern arabian gulf form many supergiant and giant fields that produce from the arab formation and are excellent examples of a classic reservoir seal relationship the present day sabkha depositional setting that extends along most of the southern and southwestern coasts of the arabian gulf provides an analog to these upper jurassic sedimentary rocks in fact sabkha related diagenesis of original grain supported sediments in the arab and hith formations has resulted in five distinct lithofacies that characterize the reservoir seal relationship 1 oolitic peloidal grainstone 2 dolomitic grainstone 3 dolomitic mudstone 4 dolomitized grainstone an 5 massive anhydrite interparticle porosity in grainstones and dolomitic grainstones and intercrystalline porosity in dolomitized rocks provide the highest porosity in the study area these sediments accumulated in four types of depositional settings 1 supratidal sabkhas 2 intertidal mud flats and stromatolitic flats 3 shallow subtidal lagoons and 4 shallow open marine shelves the diagenetic history of the arab and hith formations in the southern and southwestern arabian gulf suggests that the anhydrite and much of the dolomitization are a result of penecontemporaneous sabkha diagenesis the character and timing of the paragenetic events are responsible for the excellent porosity of the arab formation and the lack of porosity in the massive anhydrites of the hith which together result in the prolific hydrocarbon sequences of these formations

a generalized growth model for simulating initial migration of dense non aqueous phase liquids modeling the migration of spilled non aqueous phase liquids napls is currently difficult because the physics governing their movement is complex and knowledge of the local geology is always incomplete napl movement is subject to buoyancy capillary and viscous forces in addition to being directed by the particular structural and hydraulic properties of the porous medium consideration of buoyancy forces suggests that the flow regime diagram of lenormand et al 1988 can be expanded to a third dimension we develop a generalized growth model based on invasion percolation that captures the essential physics of initial napl migration but is simple enough computationally that simulations can be conducted much faster than by using continuum simulation models that attempt to capture all details of the physics in comparison with available experimental data our model realistically simulates movement of a napl for a wide range of values of bond and capillary numbers in any kind of porous medium because this approach allows much faster and simpler simulation than other approaches a higher spatial resolution and or the use of monte carlo methods to reduce the effect of geological uncertainty becomes a realistic possibility

reconstruction of palaeohydrological conditions in a lagoon during the 2nd zechstein cycle through simultaneous use of δd values of individual n alkanes and δ 18 o and δ 13 c values of carbonates for the first time 18o and 13c values from carbonates and d values of individual n alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the central european zechstein basin cezb a 12 m core covering the complete ca2 interval and adjacent anhydrites a1 and a2 was analyzed for 18o and 13c values of dolomitized carbonates and d values of individual n alkanes 18ocarb values 2 to 5 vs vpdb were strongly influenced by evaporation and temporal freshwater input into the lagoon the 13ccarb values 1 to 4 vs vpdb were controlled mainly by changes in primary production both isotopic ratios show an inverse relationship throughout most of the core contradicting diagenetic alteration since 13ccarb values are not altered significantly during dolomitization assuming a temperature range of 35 40 c in the lagoon 18ocarb values of 2 5 to 8 vs vsmow for the lagoonal water can be reconstructed the lagoon may have desiccated twice during the ca2 interval as indicated by very high 18ocarb and low 13ccarb values coinciding with increasing amount of anhydrite in the analyzed sample these events seem to reflect not just local but a regional intra ca2 cyclicity measured d values of the short chain n alkanes namely n c16 and n c18 which are widely used as indicators for photosynthetic bacterial and algal input reflect the isotopic composition of the lagoonal water assuming constant fractionation during incorporation of hydrogen into lipids of 160 an average d value of 70 vs vsmow can be reconstructed for the lagoonal water accounting for very arid conditions the long chain n alkanes n c27 n c28 n c29 and n c30 thought to be derived from the leaf waxes of terrestrial higher plants were shown to be depleted in d relative to the short chain alkanes therefore indicating a different hydrogen source terrestrial plants in arid areas mainly use water supplied by precipitation by using a smaller fractionation of 120 due to evaporation processes in the leaves reconstructed values vary between 74 and 9 vs vsmow these values are not indicating extremely arid conditions implying that the long chain n alkanes were transported trough wind and or rivers into the lagoon at the zechstein sea coast dwater values reconstructed using the n c16 alkane and 18o water values independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon altogether our results indicate that hydrogen isotopic ratios of n alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction

minimum saturations and buoyancy in secondary migration percolation theory it is often argued requires a minimum nonwetting phase saturation of approximately 15 for hydrocarbon migration but field measurements usually fail to find residual oil on the pathway taken during hydrocarbon migration from a source to a reservoir we use numerical simulations and experiments to show that percolation theory when applied to the process of oil invading a pore space leads to the conclusion that field scale saturations in secondary migration can be on the order of 1 or less our capillary invasion experiments on berea sandstone and numerical simulations of fluid invasion on networks show that the minimum saturation for flow of the nonwetting phase decreases as the reciprocal square root of the linear size this result applies to cyli drical samples that have height equal to diameter our numerical simulations include the effects of sample aspect ratio buoyancy and pore size distribution all the numerical results reduce to a single relation between threshold saturations and sample size normalized by a function of the pore size distribution we find that a pore size distribution that has many more small pores than large pores as is typical in rocks and soils substantially reduces the influence of buoyancy on threshold saturations the common practice of using uniform flat pore size distributions to simulate rocks overestimates the effects of buoyancy experiments show that for larger samples the permeability at threshold for flow is higher than conventionally expected in a typical geological situation this h gh permeability is large enough to carry oil to a reservoir over geologic time at saturations of less than 1 of the pore volume our laboratory permeability and saturation experiments confirm the expectations of percolation theory including the fractal dimension of the first invasion path size dependent saturation is the prediction of invasion percolation theory the percolation model is applicable to the secondary migration problem as well as to migration of gas in reservoirs migration of gas or fluids from radioactive waste repositories and migration of nonaqueous phase liquid pollutants in groundwater

relative sea level change climate and sequence boundaries insights from the kimmeridgian to berriasian platform carbonates of mount saleve e france the present study analyses the stratal architecture of the late jurassic kimmeridgian to early cretaceous berriasian sedimentary succession of mount saleve e france and four berriasian stratigraphic intervals containing four sequence boundary zones reflecting lowering trends of the relative sea level evolution massive kimmeridgian limestones characterized by the presence of colonial corals appear to be stacked in an aggrading pattern these non bedded thick deposits which are interpreted to have formed in balance between relative sea level rise and carbonate accumulation suggest a keep up transgressive system above well bedded tithonian to berriasian peritidal carbonates reflect a general loss of accommodation these strata are interpreted as a highstand normal regressive unit during the early phase of this major normal regression the vertical repetition of upper intertidal lower supratidal lithofacies indicates an aggrading depositional system this is in agreement with an early stage of a highstand phase of relative sea level the berriasian sequence boundary zones investigated up to 4 m thick developed under different climatic conditions and correspond to higher frequency forced and normal regressive stages of relative sea level changes according to the classical sequence stratigraphic principles these sequence boundary zones comprise more than one candidate surface for a sequence boundary three sequence boundary zones studied in early berriasian rocks lack coarse siliciclastic grains contain a calcrete crust as well as marly levels with higher abundances of illite with respect to kaolinite and exhibit fossilized algal microbial laminites with desiccation polygons these sedimentary features are consistent with more arid conditions a sequence boundary zone interpreted for the late berriasian corresponds to a coal horizon the strata above and below this coal contain abundant quartz and marly intervals with a higher kaolinite content when compared to the illite content accordingly this late berriasian sequence boundary zone was formed under a more humid climate the major transgressive regressive cycle of relative sea level identified and the climate change from more arid to more humid conditions recognized during the late berriasian have been reported also from other european basins therefore the kimmeridgian to berriasian carbonate succession of mount saleve reflects major oceanographic and climatic changes affecting the northern margin of the alpine tethys ocean and thus constitutes a reliable comparative example for the analysis of other coeval sedimentary records in addition the stratigraphic intervals including sequence boundary zones characterized in this study constitute potential outcrop analogues for sequence boundary reflectors mapped on seismic profiles of subsurface peritidal carbonate successions the detailed sedimentological analyses provided here highlight that on occasions the classical principles of sequence stratigraphy developed on seismic data are difficult to apply in outcrop a sequence boundary reflector when seen in outcrop may present successive subaerial exposure surfaces which formed due to high frequency sea level changes that were superimposed on the longer term trend of relative sea level fall

coastal sabkha and salt pan deposition of the lower clear fork formation permian texas abstract middle permian leonard series evaporites carbonates and red beds of the lower clear fork formation in the texas panhandle display many features common to modern coastal and continental sabkha facies similarities among lithofacies patterns and sequences sedimentary structures and anhydrite halite textures and fabrics of both the lower clear fork formation and modern sabkha facies permit construction of a model of halite deposition in coastal sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins inferred coastal sabkha and marine inner shelf environments and lithofacies recognized in the lower clear fork formation are largely based upon analogous modern depositional se tings and include the following 1 red siltstone to mudstone deposited in a wadi or desert alluvial eolian plain and inner sabkha mud flats both passing basinward into 2 chaotic mudstone halite of an inner sabkha saline mud flat which flanked 3 inner sabkha salt pans bearing banded to massive halite and laminated anhydrite and 4 nodular nodular mosaic and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments salt pans may have formed in the inner sabkha as a result of displacive gypsum anhydrite growth and jacking up of the marginal sabkha surface which impeded seaward drainage of floodwater off the sabkha modern process sediment analogs include alluvial fans saline mud flats and salt pans of the coastal sabkhas in baja mexico the trucial coast and kutch india evaporites and terrigenous clastics in bristol dry lake california exhibit many features analogous with the permian suggesting that this setting though strictly continental serves as a process analog bromide values in lower clear fork halite average 40 ppm which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis upward decreasing values in the lower clear fork upper cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite

eustatic controls on carbonate facies in reservoirs and seals associated with mesozoic hydrocaron fields of the arabian gulf and the gulf of mexico abstract abundant subsurface data for mesozoic and cenozoic sections of the us gulf coast and the middle east make it possible to track the relationship of shelf carbonates and evaporites associated with minor amounts of clastics to eustasy our contention is that because the sedimentary deposition for both regions was in part controlled by gentle tectonic subsidence punctuated by eustatic variations the major hydrocarbon fields which occur here can be related to sea level behaviur at the time of deposition of the reservoir sections and their early diagenesis with the exception of chalks most of these carbonate hydrocarbon fields can be related to highstand system tracts and include the following 1 1 keep up reservoirs with sheet like geometry formed when carbonate accumulation matched sea level rise aggrading to form shoaling upward cycles during sea level highstands 2 2 give up and catch up reservoirs with lense like carbonate geometry formed on drowned shelves during and following rapid sea level rises often downslope from carbonate margins give up reservoirs occur when carbonate accumulation was unable to match sea level rise and catch up reservoirs form where carbonate accumulation was initially unable to keep pace with the sea level rise but then aggraded to sea level 3 3 reservoirs with the prograded discontinuous clinoform geometry of the platform margin formed during stillstands by carbonate accumulation that not only kept up with the sea level rise but also advanced in a seaward direction source rocks for these carbonate reservoirs are often formed during rapid sea level rises while the reservoir seals are usually transgressive shales dense transgressive limestones and or highstand evaporites

biotic and abiotic processes in the formation and diagenesis of permian dolomitic stromatolites zechstein group ne england abstract the crinkly bed of the upper permian zechstein group succession roker formation hauptdolomit z2c in northeast england is a distinctive 1 4 meter thick unit that has been interpreted as a stromatolite of microbial origin or alternatively as the result of purely abiotic precipitation close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the zechstein basin the internal structure of the crinkly bed consists of fine millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt size peloids with rare hollow spheroids the lamination is extremely regular in thickness and laterally persistent for up to 4 meters a microbial community composed of coccoid and filamentous microorganisms inferred from fossil evidence colonized the original sediment surface it is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae the peloids are consequently interpreted as autochthonous this interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite which constitutes both the continuous micritic laminae and the peloids themselves primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters mediated by bacterial metabolism similar to the process that operates in modern intertidal microbial mats the crinkly bed shows macro structures that vary along a continuum from symmetrical to asymmetrical centimeter scale ripple like structures some showing interference patterns through to domical and conical structures more typical of stromatolites the more ripple like structures have a lamination of microbial origin identical to that within the domal conical stromatolites there is no internal cross lamination their origin is equivocal they could be the result of physical current or wave induced deformation of a surficial biofilm or their form could be inherited from true mechanically deposited ripples not observed that provided a template for biofilm growth changes in the nature and strength of the wave and or current regime and possibly in the community structure of the microbial mat produced this array of microbially induced macrostructures miss the latter plus the absence of desiccation features indicative of intertidal to supratidal deposition suggest subtidal sedimentation at a depth of several meters intergranular gypsum cement precipitated during early diagenesis and ferroan sparry dolomite precipitated during burial tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre existing dolomite probably via the biological mediation of heterotrophic bacteria the interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record

an experimental study of secondary oil migration in a three dimensional tilted porous medium a three dimensional physical experiment was conducted to study secondary oil migration under an impermeable inclined cap light colored oil was released continuously at a slow rate of about 0 1 ml min from a point at the base of an initially water saturated porous model with buoyancy as a primary driving force a vertical cylindrical shape of an oil migration pathway was observed first and then a layer shaped lateral migration pathway was observed beneath the top inclined sealing plate once the oil cluster had reached the top cap magnetic resonance imaging was used to observe the migration processesmdashfor example morphology of the migration pathway intermittency of oil bubbles and variation of oil saturation within the migration paths results show that the snap off phenomenon related to fast local imbibition processes occurred more commonly during vertical migration than it did during lateral migration the lateral migration pathway that parallels to the top inclined cap has a typical vertical thickness of 2 to 4 cm 0 8ndash1 6 in i e roughly 40ndash80 pores this thickness is consistent with the prediction derived from scaling laws related to pore size and bond number along the lateral migration direction the sectional area and the horizontal width of the migration pathway fluctuate significantly although the average oil saturation along the pathway remains almost the same after stopping the initial oil injection the sectional area of the migration pathway shrinks significantly therefore we believe that this significant shrinking of the migration pathway is the main reason why only a relatively small volume of oil and gas has been lost during secondary migration

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

buoyancy and interfacial force effects on two phase displacement patterns an experimental study modeling secondary migration of oil currently is difficult because the physics governing the movement is complex and information on heterogeneity of carrier beds is always incomplete to better understand the basic physical process of secondary migration we discuss displacement patterns based on relative magnitudes among buoyancy interfacial and viscous forces using the results of one dimensional vertical oil water displacement experiments oil was injected at a constant rate from the lower inlet of a glass tube packed with sorted glass beads the injection pressure and oil outflow rate were measured while we observed the displacement pattern runs were done using different grain sizes and injection rates two displacement patterns were recognized during the experiments type a consisted of stable piston like displacement and type b consisted of capillary fingering the difference coincided with the relative magnitudes of the driving forces which can be characterized by the dimensionless modified bond bo and capillary ca numbers type a pattern was produced for high ca bo ratios and type b pattern for low ca bo ratios a flow regime diagram showing the regions of the two displacement patterns was constructed in ca bo space including the effects of gravity our results also showed that excess pressure for the nonwetting phase fluid to intrude into a porous medium was rate dependent

facies patterns and depositional models of permian sabkha complex red cave formation texas panhandle abstract the red cave formation permian leonard series in the texas panhandle consists of cyclic red bed clastic and carbonate evaporite members that were deposited in an extensive coastal sabkha desert wadi plain and a carbonate inner shelf which bordered the northern midland basin evaporite members were deposited in carbonate evaporite crustal sabkhas and clastic members were deposited in mud rich coastal to continental sabkhas north to south red bed wadi plain facies pass into coastal sabkha facies and inner shelf dolomite facies in a randall county core vertical sequences commonly include slightly fossiliferous faintly laminated to burrowed dolomitic mudstone and pellet wackestone overlain by cross laminated oolitic or pellet packstone to grainstone followed by algal laminated dolomitic mudstone and nodular anhydrite in dolomite matrix a progradational carbonate shoreline is inferred with supratidal or sabkha evaporite to intertidal algal mat and sand flat environments passing seaward into a shallow muddy subtidal inner shelf mud rich sabkha sequences culminate with red to green mudstone and anhydrite above shoreline carbonates carbonate and evaporite facies pinch out generally toward the northwe t and northeast into wadi plain red beds these facies include ripple drift cross laminated siltstone and sandstone deposited in braided fluvial channels adhesion rippled siltstone and red to green mudstone deposited in mud flat and interchannel environments desiccation features intraclasts root zones and paleosol horizons attest to subaerial exposure and probable nonmarine conditions large scale cyclicity of red bed clastic and carbonate evaporite members probably was controlled by the relative supply or fluctuating input of clastics to sabkhas by way of fluvial systems rather than by absolute sea level changes partial modern analogs to red cave sabkha depositional models are the coastal mud flats and alluvial fans in the northwestern gulf of california tidal flats and an ephemeral stream delta wooramel delta in gladstone embayment shark bay australia and the trucial coast sabkhas in the persian gulf each setting has certain facets that are remarkably similar to intepreted paleoenvironments and lithofacies of the red cave formation end of article last page 761

sedimentation distribution and diagenesis of organic matter in a recent carbonate environment abu dhabi u a e abstract in the modern hypersaline carbonate lagoon and sabkha sedimentary environments of abu dhabi united arab emirates three types of organic matter originate respectively from microbial mat avicennia mangrove and halodule lagoonal seagrass the study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo sedimentary facies based on geochemical and sedimentological criteria this permits the construction of an organo sedimentary sequence which expresses the holocene sedimentary record involving a transgressive and a regressive sequence the various organic facies occur in both sequences heterogeneity within the individual organic facies reflects several factors including sedimentation dynamics mineral matrix oxidation and reduction and selective organic and mineral diagenesis these parameters are discussed in terms of depositional environment and location within the organo sedimentary sequence changes in distribution quantity and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates

revealing oil migration in the frontier bight basin australia abstract the bight basin along the southern margin of australia represents one of australia s most prospective deep water frontier hydrocarbon exploration regions however its 15 km thick sedimentary succession remains largely untested whilst there is some evidence of oil from shows fluid inclusions and natural strandings of asphaltite along the basin margin it is unclear if any hydrocarbons were generated in the deep water ceduna sub basin fluid inclusions offer a unique method to test for petroleum migration that would otherwise remain hidden and a study using csiro s grains with oil inclusion goi technique was undertaken on gnarlyknots 1a along with other historic exploration wells with the exception of jerboa 1 in the eyre sub basin the goi results

coeval versus reciprocal mixed carbonate siliciclastic deposition middle devonian baltic basin eastern europe implications from the regional tectonic development the middle devonian narva succession in the baltic basin represents a significant turnaround in the history of the basin the detailed study of core and outcrop sections and the three dimensional correlations across the baltic basin reveal a carbonate dominated mixed retrogressive succession overlain by a siliciclastic dominated progradational succession the palaeogeographic reconstructions show how the shallow tide influenced basin expanded from south west to north east and later during the transgression also to the north south and east the transgressive portion of the basin fill is dominated by carbonate rich sabkha and supratidal to intertidal deposits on the basin margins and subtidal carbonates in the basin centre siliciclastic material was derived by tidal currents and storm waves from the south west through a tidal inlet and flood tidal delta complex this initial transgressive phase is characterized by the lack of subsidence or even episodic uplifts in the northern north western part of the basin margin shown by convergence of timelines and the thin 30 m transgressive succession in contrast on the southern margin the facies associations stack vertically into a 70 to 80 m thick succession indicating significantly higher subsidence rates the upper part of the transgressive phase indicates subsidence across the whole basin the upper progradational portion of the basin fill is dominated by coarse siliciclastic tide influenced deltaic deposits that rapidly prograded from north west to south east this detailed study on the narva succession shows that siliciclastic and carbonate deposition was coeval and that mixing occurred at different temporal and spatial scales the mixing was controlled by grain size volume and location of siliciclastic input rather than relative sea level changes as suggested in widely used reciprocal mixing models it is suggested that the forebulge of the scandinavian caledonian fold and thrust belt migrated to the north western margin of the baltic basin during the earliest eifelian as indicated by the lack of subsidence and probable uplift in the northern north western margin during the early transgressive phase the forebulge migration ceased although the forebulge had already started to subside during the later stages of the transgressive phase the deltaic progradation is interpreted to be associated with the orogenic collapse and uplift in the scandinavian caledonides that caused the erosion of the foreland basin fill and the coarse sediment transport into the baltic basin

quantification of carbonate ramp sedimentation and progradation rates for the late holocene abu dhabi shoreline abstract we utilize new radiocarbon dates and detailed sedimentological logging of the abu dhabi sabkha to produce the first well constrained internally consistent rates for late holocene carbonate ramp sediment accumulation and progradation for the southern shore of the persian gulf these data are applied to test the hypothesis that in low angle carbonate ramp systems ramp geometry is the primary control on sedimentation and progradation rates and therefore estimates acquired from other depositional environments cannot be applied to low angle carbonate ramp systems average calculated progradation rates of 0 75 m yr are higher than progradation rates proposed for other late holocene and recent carbonate settings a relationship that is explained by the lack of accommodation space in the low angle laterally extensive ramp system in the sedimentary record such relatively high progradation rates would produce laterally extensive lithologically uniform units with little or no evidence of progradational features and would appear to be largely contemporaneous across their extent the total average sediment accumulation rate of 0 029 cm yr is lower than those proposed from most other late holocene to recent shallow water carbonate depositional environments again a relationship interpreted to result from the limited accommodation space of low angle carbonate ramp systems calculated sediment accumulation rates show little variation over the past 1 400 years yet the calculated progradation rates exhibit a sharp decline from a maximum of 1 03 m yr before 677 946 cal bp to 0 70 m yr afterwards this is interpreted to reflect a rise in relative sea level or distal steepening of the ramp system applying the progradation rates proposed in this paper the lagoon system in the study area would be completely infilled in less than 4 000 years calculated sediment accumulation rates for syndepositional and early postdepositional interstitial displacive evaporite formation are higher than those for carbonate and microbial mat intervals continued precipitation of evaporite minerals during burial would result in a further increase in their relative contribution to the sediment pile conversely compaction particularly of microbial mat intervals will result in a decrease in apparent sediment accumulation rates for non evaporite intervals these processes need to be considered when modeling the basin evolution of mixed evaporite carbonate sequences in the stratigraphic record during calculation of sedimentation rates it is important to consider both a correction for compaction and a correction for evaporite formation

environmental and sequence stratigraphic implications of anhydrite textures a case from the lower triassic of the central persian gulf abstract the lower triassic kangan formation in the persian gulf south pars gas field and its adjacent areas are composed of carbonate evaporite sequences these sediments were deposited in a shallow marine homoclinal ramp study of the anhydrite bearing intervals shows various structures and textures the anhydrite structures are mainly bedded massive chicken wire and nodular type and the main textures are felted sparse crystal needle shape lath shape equant and fibrous pervasive and poikilotopic cement together with replacement and porphyroblastic gypsum are accounted as the most common diagenetic features in anhydrite evaluation of anhydrite occurrences and features support both primary and secondary formations the nodular to chicken wire anhydrite formed under synsedimentary sabkha conditions whereas anhydrite cements occurred during the late stages of diagenesis shallow burial stage massive to bedded anhydrite could have been formed under subaqueous conditions or originated by coalescing and continued growth of anhydrite nodules in the sabkha zone anhydrite fabrics impose a significant control on the reservoir quality of the kangan carbonates at the south pars gas field thick massive and bedded anhydrite could have been formed as an intraformational seals and anhydrite cements occluded pore spaces and reduced the poroperm values the sequence stratigraphic analysis revealed two depositional sequences in the studied intervals which are composed of tst and hst investigation of anhydrite throughout depositional sequences indicates a change in the content and style of anhydrite texture anhydrite content volume decreases upward through transgressive system tract sea level rise whereas it enhances during highstand system tract sea level fall pervasive and poikilotopic anhydrite cements together with replacement by anhydrite are prevalent features during transgressive and early highstand system tract at the late hst with a progradational stacking pattern anhydrite value increases and felted radial equant crystalline and mosaic texture are the most common anhydrite fabrics sequence boundaries that indicate maximum sea level fall and exposure of successions are marked by the broad anhydrite deposits with massive to bedded and chicken wire structures and various textures that located in late hst package there is an unambiguous relationship between the microfacies associations the evaporite textures and the sea level fluctuations this relationship could lead to a predictable pattern that can be of use as a general guide for the sequence stratigraphic interpretations in the area

the importance of wind as a driver of earthen heritage deterioration in dryland environments abstract dryland regions are exposed to extreme environmental conditions that create hotspots of weathering and erosion many earthen heritage sites are located in these dryland regions and experience extensive deterioration driven by interactions with environmental processes however previous research has focused largely on the role of rain as a driver of deterioration this study combines approaches from geomorphology with understandings of earthen materials from heritage science to investigate the relative importance of wind and rain in driving earthen heritage deterioration in drylands we use geomorphological signatures to infer the environmental histories of earthen walls with a range of known ages at suoyang ancient city china using semi quantitative deterioration assessments we find rain driven deterioration features to be associated with the loss of larger volumes of material and to have higher persistence than wind driven deterioration features however we argue that the high frequency nature of wind events means that wind is an important initiator of deterioration across the site in addition walls exposed to the prevailing wind are dominated by wind driven deterioration features outcomes from this study present an opportunity for earthen heritage conservation to investigate potential strategies to minimise wind speed at earthen heritage sites in drylands

quantitative assessment of petroleum loss during secondary migration in the yaojia formation ne songliao basin ne china abstract in the nw songliao basin ne china petroleum is produced from fluvio deltaic sandstones in the upper cretaceous yaojia formation source rocks are dark colored lacustrine shales of the qinshankou formation in this paper two models were developed to characterize the petroleum migration pathways in the lower member member 1 of the yaojia formation in the first model which applies to the northern region of the study area petroleum migrates only in the lowermost carrier bed in member 1 immediately above the area of the source kitchen and later in multiple carrier beds outside this area in the second model which represents migration patterns in the central and southern regions of the study area petroleum migrates in multiple carrier beds both within and outside the area of the source kitchen pressures in the yaojia formation were inferred to be hydrostatic while petroleum expulsion and migration took place therefore seven migration accumulation i e local palaeo drainage systems were defined according to the fluid potential gradients migration loss was found to vary markedly between migration accumulation systems in the study area and was controlled by factors including the shape width and area of the effective source rocks the thickness and distribution of carrier beds inside the source area the migration distance outside the source area and the number of carrier beds involved in petroleum migration using these two models petroleum loss during secondary migration was estimated the loss during secondary migration was approximately 5 21 billion bbl of petroleum which is approximately 6 of the petroleum expelled into the first member of the yaojia formation nearly 80 of the total migration loss occurred in all the carrier beds above the source area

shelf petroleum system of the columbus basin offshore trinidad west indies ii field geochemistry and petroleum migration model abstract petroleum migration patterns in the present day shelf area of the columbus basin reflect a complex interaction of structural evolution stratigraphic architecture and fault seal behavior thermogenic charge access is ultimately controlled by the geographic distribution of sand prone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits migration in this system consists of two components cross stratal migration through mud dominated deep water slope and basin floor sediments followed by horizon parallel flow along laterally extensive sand prone shelf carrier beds thermogenic charge access to any individual sand occurs only in a linear geographic area where that sand is not shielded from vertical migration by stratigraphically older sands the geochemical characteristics of the trapped petroleum in this system are primarily a reflection of migration distance with the earliest expelled lowest maturity products having progressed farthest along the migration pathway because of the stratigraphic architecture and structural geometry involved a pattern of increasing thermogenic content and maturity with depth at any location is created despite the fact that a significant portion of the migration is horizon parallel in parts of the basin this simple pattern has been overprinted by complex mixing of maturity fractions in single accumulations as a result of late stage differential source rock uplift the observations are inconsistent with previously proposed models for this basin that emphasize petroleum fractionation accompanying vertical migration through the shelf stratigraphic section

a review of the origin and setting of tepees and their associated fabrics carbonate hardgrounds often occur at the surface of shallow subtidal to supratidal lacustrine and subaerial carbonate shelf sediments these are commonly disrupted and brecciated when the surface area of these crusts increases in the subtidal environment megapolygons form when cementation of the matrix causes the surface area of the hardgrounds to expand similar megapolygons form in the supratidal lacustrine and subaerial settings when repeated incremental fracturing and fracture fill by sediment and or cement also causes the area of the hardgrounds to expand the arched up antiform margins of expansion megapolygons are known as tepees the types of tepees found in the geological record include 1 submarine tepees which form in shallow carbonate saturated waters where fractured and bedded marine grainstones are bound by isopachous marine phreatic acicular and micritic cements the surfaces of these brecciated crusts have undergone diagenesis and are bored unlike tepees listed below they contain no vadose pisolites or gravity cements 2 peritidal and lacustrine tepees are formed of crusts characterized by fenestral pisolitic and laminar algal fabrics this similarity in fabric makes these tepees of different origins difficult to separate peritidal tepees occur where the marine phreatic lens is close to the sediment surface and the climate is tropical they are associated with fractured and bedded tidal flat carbonates their fracture fills contain geopetal asymmetric travertines of marine vadose origin and or marine phreatic travertines and or terra rossa sediments the senile form of these peritidal tepees are cut by labyrinthic dissolution cavities filled by the same material lacustrine tepees form in the margins of shallow salinas where periodic groundwater resurgence is common they include groundwater tepees which form over evaporitic boxwork carbonates and extrusion tepees which also form where periodic groundwater resurgence occurs at the margins of shallow salinas but the dominant sediment type is carbonate mud these latter tepee crusts are coated and crosscut by laminated micrite the laminae extend from the fractures downward into the underlying dolomitic micrite below the crust both peritidal and lacustrine tepees form where crusts experience alternating phreatic and vadose conditions in time intervals of days to years cement morphologies reflect this and the crusts often contain gravitational meniscus vadose cements as well as phreatic isopachous cement rinds 3 caliche tepees which are developed within soil profiles in a continental setting they are formed by laminar crusts which contain pisolites and fractures filled by micritic laminae microspar spar and terra rossa most of the cements are gravitational and or meniscoid in ancient carbonates when their cementation and diagenetic fabric can be interpreted tepee structures can be used as environmental indicators they can also be used to trace the evolution of the depositional and hydrological setting

geomorphological changes in the coastal area of farasan al kabir island saudi arabia since mid holocene based on a multi proxy approach abstract the geomorphological evolution of the southeastern coastal area of farasan al kabir island saudi arabia is revealed by the mapping of modern landforms and a multi proxy and high spatial resolution study including grain size particulate organic carbon mineralogy element geochemistry benthic foraminifera analysis and radiocarbon dating of a 3 3 m long sediment core the modern geomorphological features comprise a variety of arid landforms such as plateau cliffs and pediments of pleistocene coral limestones playa depressions located on plateau surfaces alluvial fans butte and sandy beaches the mid holocene evolution of the borehole area is resulted from the detailed analysis of five sedimentary units detected along the core matar 1 and includes three distinct stages a from 5253 223 y cal bp to 3138 223 y cal bp carbonate coarse grained material consisting of coral fragments molluscs calcareous algae and benthic foraminifera are deposited on a shallow marine fringing reefal platform which becomes progressively a nearshore backreef around 3675 215 y cal bp and later around 3138 223 y cal bp a reef ramp b since 3040 220 y cal bp the borehole area obtains the characteristics of a high energy beach that receives increasing inputs of terrigenous material c subsequently a supratidal backshore setting is established influenced mostly by terrestrial processes and occasionally by marine processes as it is indicated by the decreasing and sometimes sporadic presence of benthic foraminifera and recently a sedimentary veneer consisting of terrigenous carbonate and evaporite material is formed by terrestrial mainly wadi and aeolian processes

numerical simulation of hydrocarbon migration in tight reservoir based on artificial immune ant colony algorithm a case of the chang 81 reservoir of the triassic yanchang formation in the huaqing area ordos basin china abstract the hydrocarbon migration in tight reservoirs is a complex process the fluid flow patterns of which are notably different from those of conventional reservoirs therefore specific mathematical models are needed to simulate the secondary hydrocarbon migrations this study presents a numerical simulation method based on artificial immune ant colony algorithm aiaca to simulate the secondary hydrocarbon migrations in tight reservoirs it consists of three core parts 1 the release modes of artificial ants based on the intensity of hydrocarbon generation 2 the wandering patterns of artificial ants under the control of the dynamic field and the distribution of pheromones 3 the updating modes of pheromones based on the changes in reservoir wettability the simulation of secondary migration can be realized by the observing the dynamic movements and accumulations of the artificial ants the method has been tested in the chang 8 1 tight sandstone reservoir which is part of the triassic yanchang formation in the huaqing area ordos basin in china and proved to be successful in matching the current data in exploration and development

cenozoic paleo environmental evolution of the pamir tien shan convergence zone abstract the retreat of the tethys sea and the uplift of the tibetan plateau play the critical roles in driving asian climatic changes during the cenozoic in the pamir tien shan convergence zone over 3000 m of cenozoic successions consisting of marine deposits in the lower continental clay and fine sand in the middle and molasse in the upper part record the evolution of the tethys sea the asian aridification and the deformation of the pamir in this work the existing biostratigraphic subdivisions and new electronic spinning resonance dating results were used to assign ages to formations within the ulugqat section sedimentary facies analysis and multi proxy indices were used to reconstruct the paleo environmental evolution the results show 1 the pamir tien shan convergence zone has undergone progressive environmental changes from shallow marine before 34 ma to arid land at 23 ma and finally to inter mountain basin by 5 3 ma 2 the overall increase in mean size of grains decrease in redness in magnetic susceptibility and in proportion of the ultrafine component of the sediments studied revealed a long term strengthening in potential energy to transporting medium cooling and enhanced continental aridity respectively 3 the easternmost edge of the tethys sea prevailed in the western tarim basin from late cretaceous to early cenozoic and finally retreated from this region around the eocene oligocene transition which in turn strengthened the asian aridification 4 accumulation of molasse with an upper age of 1 ma suggests that the deformation front of the pamir migrated to this area at or before that time

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

quantitative evaluation of the oil leg potential in the oliver gas field timor sea australia oil bearing fluid inclusions in sandstone cores and cuttings represent hidden oil shows the frequency of quartz grains containing these inclusions the goi number reflects the maximum paleo oil saturation experienced in a sandstone reservoir irrespective of the present fluid phase samples that have been exposed to high oil saturation have goi numbers at least one order of magnitude greater than samples that have demonstrably low oil saturation in this way these fluid inclusion data can be used to identify paleo oil columns and to map original oil water contacts in wells where oil has been displaced by a later gas charge moreover the use of detailed goi mapping to accurately define the location of the original oil water contact allows the height of the paleocolumn to be determined and an estimate to be made of original oil in place the oliver oil and gas discovery located in the timor sea australia presently contains a hydrocarbon column of 178 5 m composed of 164 m of gas over a 14 5 m oil leg and is filled to spillpoint in well oliver 1 goi mapping has delineated a gross paleo oil column of between 99 and 132 m within the present gas leg this corresponds to original oil in place of up to 200 million bbl considerably greater than the 45 million bbl of oil presently reservoired the displacement of up to 155 million bbl of oil from this structure has high graded the prospectivity of tilted fault blocks updip from the oliver structure goi mapping is an innovative approach to reservoir characterization that can reliably detect paleo oil accumulation in hydrocarbon traps that are presently filled by gas these data allow the oil leg potential of both gas discoveries and nearby untested structures to be addressed in a quantitative manner before additional drilling is commissioned

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

material balance assessment of the new albany chesterian petroleum system of the illinois basin the new albany chesterian petroleum system of the illinois basin is a well constrained system from which petroleum charges and losses were quantified through a material balance assessment this petroleum system has nearly 90 000 wells penetrating the chesterian section a single new albany shale source rock accounting for more than 99 of the produced oil well established stratigraphic and structural frameworks and accessible source rock samples at various maturity levels a hydrogen index hi map based on rock eval analyses of source rock samples of new albany shale defines the pod of active source rock and extent of oil generation based on a buoyancy drive model the system was divided into seven secondary migration catchments each catchment contains a part of the active pod of source rock from which it derives a petroleum charge and this charge is confined to carrier beds and reservoirs within these catchments as accountable petroleum petroleum losses or undiscovered petroleum a well constrained catchment with no apparent erosional or leakage losses is used to determine an actual petroleum charge from accountable petroleum and residual migration losses this actual petroleum charge is used to calibrate the other catchments in which erosional petroleum losses have occurred petroleum charges determined by laboratory pyrolysis are exaggerated relative to the actual petroleum charge rock eval charges are exaggerated by a factor of 4 14 and hydrous pyrolysis charges are exaggerated by a factor of 1 7 the actual petroleum charge provides a more meaningful material balance and more realistic estimates of petroleum losses and remaining undiscovered petroleum the total petroleum charge determined for the new albany chesterian system is 78 billion bbl of which 11 4 billion bbl occur as accountable in place petroleum 9 billion bbl occur as residual migration losses and 57 6 billion bbl occur as erosional losses of the erosional losses 40 billion bbl were lost from two catchments that have highly faulted and extensively eroded sections anomalies in the relationship between erosional losses and degree of erosion suggest there is potential for undiscovered petroleum in one of the catchments these results demonstrate that a material balance assessment of migration catchments provides a useful means to evaluate and rank areas within a petroleum system the article provides methodologies for obtaining more realistic petroleum charges and losses that can be applied to less data rich petroleum systems

facies and sedimentary environment of the permian carbonates khuff formation in the united arab emirates abstract the late permian to early triassic khuff formation of the united arab emirates is a 625 970 m thick sequence of shallow water carbonates dolomites limestones and dolomitic limestones with subordinate anhydrite it can be subdivided into ten facies units distinguished on the basis of their depositional textures that represent an overall regressive carbonate evaporite sequence based on the paleoecology sedimentary structures and lithology four distinct depositional settings can be recognized supratidal sabkha lagoon shoal and shallow shelf the khuff formation has both primary interparticle and secondary dissolution vugs and intercrystalline porosities

the carbonate evaporite lagoon of al dakhirah qatar an example of a modern depositional model controlled by longshore transport the southern coast of the arabian gulf is considered a good example of an arid carbonate depositional system the objective of this field investigation is to better elucidate the dynamic controls on the character and pattern of the depositional belts in a carbonate evaporite lagoonal setting the interpretation of this lagoon is based on combined field examination and laboratory analyses of surface samples and this has resulted in an updated depositional model for carbonate evaporite lagoonal settings this study highlights the effects of sediment transport by longshore currents with the formation of sand spits that gradually closed the lagoon during their southwards migration the associated narrow and elongated back barrier settings consist of tidal dominated muddy sediments affected by a network of tidal channels this wave dominated high energy system has generated several carbonate barrier and back barrier units that migrated southwards and seawards during the last few thousands of years this updated depositional model significantly differs from shoreline parallel facies tracts of the classical trucial coast model where the dominant wind is orientated perpendicular to the coastline conversely to the sediment belts of the trucial coast the al dakhirah lagoon displays a strongly asymmetrical pattern of the sediment belts marked by a southwards and seawards migration

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

flow regime associated with vertical secondary migration secondary migration is defined as the movement of hydrocarbons through relatively permeable rocks from source to trap a two phase flow within a porous medium depending on the geometry and capillary pressure distributions of carrier beds secondary migration has both vertical and lateral components the present paper focuses on that part of the migration where the movement is mainly vertical its objective is to propose a description of the dynamics governing the vertical part of secondary migration based on the main physical aspects of two phase flow in a homogeneous porous medium the study is illustrated by laboratory observations performed in a vertical 2 d hele shaw cell filled with a transparent porous medium where the flow of dyed oil invading a wetting fluid is visually observed these observations help us to understand the effect of buoyant capillary and viscous forces on the resulting flow the relative importance of which is characterized by non dimensional numbers extrapolating these observations to natural media it is proposed that vertical secondary migration can be described as a percolation of disconnected and vertically elongated stringers these stringers do not move continuously but as a succession of snap off and re feeding events which result in a jerky upward movement using parameters characterizing the physical properties of the fluid and of the porous medium the geometry and the dynamic behavior of the stringers are estimated the width of stringers occurring during secondary migration in geological media is centimetric and their vertical size ranges from several centimeters to a few meters an upper limit of the mean upward velocity of stringers is proposed as well as an estimate of their spatial density and of the minimum average horizontal distance decametric between two stringers the stringers are sparsely distributed resulting in a low average oil loss and a high efficiency of the vertical migration process

petroleum migration and accumulation modeling and applications subsurface hydrocarbon observations at any scale serve as critical clues to understand and reconstruct migration pathways and charge histories through geological time to assess the risk of petroleum exploration targets hydrocarbon migration commonly occurred millions of years ago and the pathways can rarely be observed in wells or in outcrops therefore hydrocarbon migration modeling tools are important to test and quantify the processes and elements which impact hydrocarbon migration this paper presents a new method of analyzing migration in superimposed basins which have experienced multiple stages of basin subsidence and inversion during which multiple episodes of hydrocarbon generation migration and accumulation occurred the new modeling method first identifies the character of the migration and accumulation units by synthesizing geological factors such as heterogeneity of carrier beds and reservoirs second hydrocarbon migration is analyzed as a geologic process for which the invasion percolation ip migration method seems to be most suitable the ip migration method demonstrates a good relationship between migration driving and resisting forces along pathways and thus can be used to reasonably model hydrocarbon migration processes at any scale of units in a basin the new migration method provides insights into quantitative methods that can be applied to petroleum system analysis the new method has been applied to several chinese basins and has proven to be useful for defining exploration targets and resource assessments in mature frontier and especially tectonically complex basins a case study of the upper triassic chang 7 and chang 8 units in the southern ordos basin central china is presented to demonstrate a multistage hydrocarbon accumulation unit modeling results show that the same pairs of reservoir seal sets contained different accumulation units in the geological past with different styles of hydrocarbon migration and different accumulation patterns it can be concluded that the style and character of early hydrocarbon migration have significantly affected the more recent hydrocarbon migration and the present day distribution of hydrocarbons

stochastic evaluation of fluvial to marginal marine sealing facies abstract hydrocarbon top seal analyses are particularly difficult in fluvial and marginal marine settings although these settings often contain beds comprised of a low permeability clay rich lithology associated with high quality seals their presence does not guarantee an effective seal because individual beds within the stratal unit may be laterally discontinuous lateral facies changes truncation of fine grained beds or the presence of crevasse splays may provide cross stratal migration pathways reducing the effective sealing capacity to a magnitude less than the closure height to evaluate probable bed seal capacities in such a setting we have calculated 75 statistically equivalent geologic models of a heterogeneous bed seal based upon facies interpretations derived from measured data measured capillary and hydraulic properties of rocks in each facies were then fit to gaussian distributions we populated the geologic models with flow properties by randomly selecting from these distributions two realizations of the rock property distributions were performed for each of the 75 object based geologic models gas charge was simulated in each of the rock property model trials using a percolation based hydrocarbon migration software program the results of the simulations return a probability distribution of bed seal capacities measured in equilibrium gas column heights from which cumulative frequency diagrams and percentile rankings may be derived channel amalgamation by incision juxtaposing levee overbank and or channel facies formed the most common type of cross stratal leak point a factor of 10 difference in the p50 seal capacity was observed by varying the net volume fraction of channels from 10 to 30 higher seal capacity realizations were found to have a low density of channels near the structural crest a variable which outweighs all other stochastic parameters these results highlight the importance of a risking based methodology to account for variability in bed seal stratigraphy in fluvial to marginal marine settings