diagenesis and hydrocarbon accumulation brent sandstone jurassic bergen high area north sea diagenesis of brent group sandstones in the bergen high area was studied and related to the history of hydrocarbon maturation and pore fluid environment calcite and kaolinite are low temperature diagenetic precipitates that formed as meteoric pore water entered the brent at the end of brent deposition and later during late cimmerian erosion a major period of feldspar dissolution associated with quartz and illite cementation occurred at huldra field precipitation of diagenetic illite in brent sandstones was closely linked with hydrocarbon maturation in the adjacent viking graben and accumulation of generated fluids in traps at structural highs at huldra field illite k ar ages suggest onset of illite diagenesis in the latest cretaceous initial reservoiring of hydroca bons during the latest paleocene to early eocene 58 ma and filling of the reservoir by early oligocene 38 ma pore water character during illite diagenesis interpreted from oxygen isotope and quartz overgrowth fluid inclusion data was warmer than predicted by burial history analysis and one and a half to two times seawater salinity the incursion of saline isotopically evolved fluids at huldra suggests replacement of paleometeoric water by basin compaction fluid illite k ar ages from veslefrikk field indicate a minimum age of hydrocarbon accumulation at about 30 ma modern pore water chemistry in the brent at veslefrikk is unlike the suggested water chemistry at huldra and indicates that migrating compaction water did not completely displace older fresh connate water this sugge ts that hydrocarbons migrated into veslefrikk as a discrete phase without great volumes of associated compaction water

diagenesis in north sea hpht clastic reservoirs consequences for porosity and overpressure prediction upper jurassic clastic reservoirs of the fulmar formation in the central north sea possess anomalously high porosities for their present day depth of burial reservoirs with the highest overpressures have the highest porosities possess less macroquartz cement and have significant secondary porosity quartz cementation in hpht high pressure high temperature reservoirs has been inhibited by a combination of factors high overpressure limited fluid movement presence of early grain coating cements high pore fluid salinity and possibly petroleum migration secondary porosity has contributed to reservoir quality with an average of 4vol extra porosity created quantitative prediction of porosity would require an improved depositional model for the fulmar accurate thermal and pressure modelling and detailed knowledge of field filling and leakage histories theoretical calculations indicate that diagenetic reactions occurring in the fulmar formation smectite illitisation and quartz cementation did not generate significant overpressure because seal permeabilities were too high and the rate of volume increase associated with the reactions too small therefore diagenetic reactions can effectively be ignored when modelling overpressure generation in the central north sea although cementation will affect rock permeability and rates of fluid dissipation

effect of dolomitization on isotopic records from neoproterozoic carbonates in southwestern mongolia abstract carbon isotope values from shallow marine carbonate rocks including those from many dolomitized successions are the primary lens through which we interpret the ancient carbon cycle carbon isotopes are typically regarded as being robust to alteration during dolomitization due to the high carbon content of the rock compared to the fluid however chemostratigraphic studies of the neoproterozoic tsagaan olom group in southwestern mongolia exhibit 3 12 differences in carbon isotopes between stratigraphically equivalent limestone and dolomitized successions to understand the origins of this geochemical variation we conducted detailed geological mapping petrographic isotopic 13c 18o 44 40ca and 26mg and fluid inclusion analyses of carbonates in the taishir ol and shuurgat formations of the tsagaan olom group stratigraphic and textural constraints distinguish fabric retentive early dolomitization dolomitization event 1 that occurred in the taishir and ol formations during and soon after deposition of the ca 635 ma marinoan cap dolomite of the ol formation and fabric destructive dolomitization that occurred after the deposition of the younger shuurgat formation dolomitization event 2 either prior to or during early cambrian foreland basin formation the dolomitizing fluids moved through porous stratigraphic units bound by impermeable shale of the khongor and zuun arts formations dolomitization homogenized the isotopic records of all neoproterozoic tsagaan olom group dolomites undolomitized successions show more extreme negative excursions from more positive background values the salinity and isotopic values of seawater the dolomitizing fluids and the original platform carbonate were estimated from fluid inclusion data and a numerical model of diagenetic dolomitization these results demonstrate that both early and late dolomitization can have a profound effect on carbon isotopic records of carbonates however with a multi isotope approach the original carbon isotopic composition of platform top carbonate can be distinguished from that of seawater and other dolomitizing fluids

reply to a discussion of evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields by osborne and haszeldine 1993

accumulation in coastal west antarctic ice core records and the role of cyclone activity cyclones are an important component of antarctic climate variability yet quantifying their impact on the polar environment is challenging we assess how cyclones which pass through the bellingshausen sea affect accumulation over ellsworth land west antarctica where we have two ice core records we use self organizing maps soms an unsupervised machine learning technique to group cyclones into nine som nodes differing by their trajectories 1980 2015 the annual frequency of cyclones associated with the first som node som1 which generally originate from lower latitudes over the south pacific ocean is significantly p 0 001 correlated with annual accumulation with the highest seasonal correlations p 0 001 found during autumn while significant p 0 01 increases in vertically integrated water vapor over the south pacific ocean coincide with this same group of cyclones we find no indication that this has led to an increase in moisture advection into nor accumulation over ellsworth land over this short time period

cement stratigraphy of pennsylvanian holder formation sacramento mountains new mexico cyclic strata of the holder formation virgilian new mexico were deposited across a pennsylvanian shelf to basin transition during a time when sea level fluctuated over tens of meters cement stratigraphy studies indicate abundant calcite precipitation from low temperature fresh water within shelf shelf crest and shelf edge marine limestones freshwater cementation occurred during 15 periods of intraformational subaerial exposure these early cements are least abundant in basin and lagoon limestones the distribution of the early cement zones suggests that cementation was controlled by paleotopography stratigraphic position below subaerial exposure surfaces lithology and configuration of the paleoaquifer system distribution of early calcite cements provides new data for interpretation of cycles diagenetic systems and porosity evolution in petroleum reservoirs trace element analyses support a low temperature freshwater origin for the early cements cement stratigraphy studies fluid inclusion analyses and trace element analyses indicate a later cement that occluded remaining limestone porosity precipitated from a sodium and calcium rich brine at a temperature of about 100 c stratigraphic reconstruction dates this cementation as cretaceous or later fluorescent oil filled fluid inclusions were trapped along fractures in the late cement indicating oil migration during or after late stage cementation

a 308 year record of climate variability in west antarctica 1 we present a new stable isotope record from ellsworth land which provides a valuable 308 year record 1702 2009 of climate variability from coastal west antarctica climate variability at this site is strongly forced by sea surface temperatures and atmospheric pressure in the tropical pacific and related to local sea ice conditions the record shows that this region has warmed since the late 1950s at a similar magnitude to that observed in the antarctic peninsula and central west antarctica however this warming trend is not unique more dramatic isotopic warming and cooling trends occurred in the mid nineteenth and eighteenth centuries suggesting that at present the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past 300 years

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

ice core reconstruction of sea ice change in the amundsen ross seas since 1702 a d antarctic sea ice has been increasing in recent decades but with strong regional differences in the expression of sea ice change declining sea ice in the bellingshausen sea since 1979 the satellite era has been linked to the observed warming on the antarctic peninsula while the ross sea sector has seen a marked increase in sea ice during this period here we present a 308 year record of methansulphonic acid from coastal west antarctica representing sea ice conditions in the amundsen ross sea we demonstrate that the recent increase in sea ice in this region is part of a longer trend with an estimated 1 northward expansion in winter sea ice extent sie during the twentieth century and a total expansion of 1 3 since 1702 the greatest reconstructed sie occurred during the mid 1990s with five of the past 30 years considered exceptional in the context of the past three centuries

precipitation pathways for five new ice core sites in ellsworth land west antarctica ice cores provide a wealth of information about past climate and atmospheric circulation however a good understanding of the precipitation patterns potential source regions and transport pathways is essential in their interpretation here we investigate the precipitation pathways for a transect of five new ice cores drilled in the southern antarctic peninsula and ellsworth land we utilize in situ observations from automatic weather stations to confirm that the european centre for medium range weather forecasts era interim reanalysis data adequately captures annual and sub annual variability with evidence of a slight cold bias in the 2 m temperatures back trajectory analysis from the british atmospheric data centre trajectory service reveals that warm and snowy years are associated with air masses that originate 5 days before reaching the site from the amundsen bellingshausen sea while cold and dry years are associated with air masses from the antarctic continent there is a clear seasonal migration in the trajectories at each site reflecting the east to west migration of the amundsen sea low known to have a strong influence on climate in this region

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

an integrated thermal and isotopic study of the diagenesis of the brent group alwyn south u k north sea abstract the petrography fluid inclusion thermometry and isotope geochemistry of diagenetic cements are used to reconstruct the pore fluid history of the middle jurassic brent group reservoir sandstones in the alwyn south area of the u k north sea the study focuses on a relatively limited area of three adjacent reservoir compartments at successively higher structural levels the cement assemblage of kaolinite quartz and illite has resulted in severe deterioration of otherwise good reservoir quality early precipitation of vermiform and late blocky kaolinite was succeeded by a period of relatively intense illite precipitation temperature estimates for kaolinite precipitation of 80 c and 18o of 15 3 suggest co existing fluids of 18o 3 quartz cementation overlapped both kaolinite and illite formation fluid inclusion data indicate that quartz cementation took place at temperatures of 109 7 c pore fluid salinities were 4 wt nacl with a h2o o isotopic composition of 1 o 0 5 smow the fluids which precipitated coexisting illite were compositionally homogeneous with equilibrium 18o water compositions of 0 5 smow illite sd values range from 33 to 50 smow these fluid inclusion and isotopic data suggest that both quartz and illite were precipitated from pore waters with a uniform marine signature this is consistent with the predominantly marine to paralic depositional context of the brent group in alywn south illite precipitation was followed by hydrocarbon emplacement between the middle eocene and lower oligocene

recent climate and ice sheet changes in west antarctica compared with the past 2 000 years west antarctic temperature and pressure observations begin onlyin 1957 and reliable satellite observations of antarctic sea icedate to 1979 comprehensive observations of glacier dynamicsin the most rapidly changing areas were initiated in the 1990s borehole temperature data from the wais although confirmingthe recent rapid rise in temperature do not resolve decadal scalevariability in the past

petrographic and geochemical evidence for origin of paleospeleothems new mexico implications for the application of fluid inclusions to studies of diagenesis abstract solution pockets in the mississippian lake valley formation of new mexico occur below the sub pennsylvanian unconformity large masses of columnar calcite spar form within the solution pockets the calcite shows fine growth banding stalagmitic and stalaclitic fabrics coarse detrital inclusions and truncation of crystal terminations indicating a vadose zone or speleothem origin for the spar the calcite is twinned and cross cut by both stylolites and forroan calcite filled fractures indicating deeper burial after precipitation near the surface the mean 13c of 7 29 and 18o of 3 06 pdb of the speleothem calcite defines the light carbon end member of an inverted j shaped curve of isotopic compositions of pre pennsylvanian components in the host limestone the isotopic relationship between speleothems and pre pennsylvanian components suggests a pre pennsylvanian age for the speleothems the isotopic composition and low magnesium content of speleothem calcite reflects precipitation from meteoric water altered little by stabilization of components of the host rock primary fluid inclusions are either one phase all liquid which indicate calcite precipitation below about 40 50 c or two phase with variable ratios of vapor to liquid the two phase inclusions formed by high temperature reequilibration of low temperature fluid inclusions and entrapment of air and water in the vadose zone the petrographic characteristics and one atmosphere pressure of some of the fluid inclusions suggest precipitation of speleothems in the vadose zone some secondary fluid inclusions are two phase with rather consistent ratios of vapor to liquid these inclusions indicate a late history of relatively high temperatures of the primary fluid inclusions 74 of the two phase population have been refilled with brines of deeper burial and 26 retain fresh water for the one phase fluid inclusions 100 are fresh water therefore the one phase all liquid inclusions in partially reequilibrated low temperature fluid inclusion populations should be viewed as reliable indicators of temperature and salinity of cement precipitation in this and other diagenetic studies

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

a doubling in snow accumulation in the western antarctic peninsula since 1850 1 we present results from a new medium depth 136 metres ice core drilled in a high accumulation site 73 59 s 70 36 w on the south western antarctic peninsula during 2007 the gomez record reveals a doubling of accumulation since the 1850s from a decadal average of 0 49 mweq y 1 in 1855 1864 to 1 10 mweq y 1 in 1997 2006 with acceleration in recent decades comparison with published accumulation records indicates that this rapid increase is the largest observed across the region evaluation of the relationships between gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong temporally stable and positive relationship with the southern annular mode sam furthermore the sam is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site r 0 66 the association between gomez accumulation and enso is complex while sometimes statistically significant the relationship is not temporally stable thus at decadal scales we can utilise the gomez accumulation as a suitable proxy for sam variability but not for enso

airborne radar and ice core observations of annual snow accumulation over thwaites glacier west antarctica confirm the spatiotemporal variability of global and regional atmospheric models 1 we use an airborne radar method verified with ice core accumulation records to determine the spatiotemporal variations of snow accumulation over thwaites glacier west antarctica between 1980 and 2009 we also present a regional evaluation of modeled accumulation in antarctica comparisons between radar derived measurements and model outputs show that three global models capture the interannual variability well r 0 9 but a high resolution regional model racmo2 has better absolute accuracy and captures the observed spatial variability r 0 86 neither the measured nor modeled accumulation records over thwaites glacier show any trend since 1980 although an increase in accumulation may potentially accompany the observed warming in the region the projected trend is too small to detect over the 30 year record

quartz veins record vertical flow at a graben edge fulmar oil field central north sea the fulmar oil field lies at the faulted western margin of the central graben in the central north sea chalcedony and quartz and later dolomite occur as diagenetic cements in veins within the upper jurassic fulmar formation quartz in one particular vein contains primary aqueous fluid inclusions with homogenization temperatures ranging from 85 degrees to 140 degrees c with a mean of 117 degrees c the measured d18o of the authigenic quartz ranges from 25 1 to 27 1o oo smow the d18o of the water from which most of the quartz precipitated is calculated to have been around 8o oo which is significantly more positive than the measured present day formation water d18o of 4o oo quartz and chalcedony cements in the vein are postdated texturally by dolomite that has a d18o of 23 5o oo smow high salinities are recorded in the fluid inclusions in the quartz the majority ranging from 15 to 19 wt nacl equivalent also the quartz contains inclusions of anhydrite high salinity aqueous inclusions combined with anhydrite inclusions in the quartz and the 18o enriched calculated water composition suggest that the quartz precipitated from an evaporite influenced fluid the same fluid contributed mg for dolomite precipitation more deeply buried sections including the permian zechstein evaporites underlying the fulmar field are the most obvious source of an 18o enriched saline fluid mineralization of the vein resulted from cross formational flow of warm fluids from depth through the zechstein and into the jurassic succession over vertical distances of 600 2000 m fluids most probably migrated up faults and fractures during episodes of salt movement or overpressure release

pore fluid evolution in the kimmeridge clay formation of the uk outer moray firth implications for sandstone diagenesis abstract carbonate concretions in upper jurassic kimmeridge clay formation from three overpressured wells provide a detailed record of pore fluid evolution in the outer moray firth northern central graben the concretions contain multiple generations of septarian cements with morphologies ranging from simple cracks to complex fractures discrepancy exists between diagenetic studies which indicate these concretions formed during the initial 1 1 5 km of burial and palaeotemperature predictions based on a thermal history calibrated from the vitrinite reflectance kinetic model which indicate formation at much greater depths of between 1 5 and 2 5 km modelling undertaken for this study indicate that the concretions formed during the initial stages of burial under high heat flows fitting the early diagenetic model for their formation these conclusions have important implications for understanding the cementation of adjacent sandstone reservoirs where cement sequences have similar mineralogy and isotopic compositions with precipitation in the same temperature range from mudrock derived pore fluids early cementation of these sandstones is implied by analogy with the mudrock concretions

methane depletion in both polar regions of uranus inferred from hst stis and keck nirc2 observations abstract from space telescope imaging spectrograph stis observations of uranus in 2012 when good views of its north polar regions were available we found that the methane volume mixing ratio declined from about 4 at low latitudes to about 2 at 60 80 n this depletion in the north polar region of uranus in 2012 is similar in magnitude and depth to that found in the south polar regions in 2002 this similarity is remarkable because of the strikingly different appearance of clouds in the two polar regions we have never seen any obvious signs of convective activity in the south polar region while the north has been peppered with numerous small clouds thought to be of convective origin keck and hubble space telescope imaging observations close to equinox at wavelengths of 1080 nm and 1290 nm with different sensitivities to methane and hydrogen absorption but similar vertical contribution functions imply that the depletions were simultaneously present in 2007 and at least their gross character is probably a persistent feature of the uranus atmosphere the depletion appears to be mainly restricted to the upper troposphere with the depth increasing poleward from about 30 n reaching 4 bars at 45 n and perhaps much deeper at 70 n where it is not well constrained by our observations the latitudinal variations in degree and depth of the depletions are important constraints on models of meridional circulation our observations are qualitatively consistent with previously suggested circulation cells in which rising methane rich gas at low latitudes is dried out by condensation and sedimentation of methane ice particles as the gas ascends to altitudes above the methane condensation level then is transported to high latitudes where it descends and brings down methane depleted gas since this cell would seem to inhibit formation of condensation clouds in regions where clouds are actually inferred from spectral modeling it suggests that sparse localized convective events may be important in cloud formation a more complex meridional circulation pattern may be necessary to reproduce the observed cloud distribution but microwave observations appear to be most compatible with a single deep circulation cell the small scale latitudinal variations we found in the effective methane mixing ratio between 55 n and 82 n have significant inverse correlations with zonal mean latitudinal variations in cloud reflectivity in near ir keck images taken before and after the hst observations if the ch4 h2 absorption ratio variations are interpreted as local variations in para fraction instead of methane mixing ratio we find that downwelling correlates with reduced cloud reflectivity while there has been no significant secular change in the brightness of uranus at continuum wavelengths between 2002 and 2012 there have been significant changes at wavelengths sensing methane and or hydrogen absorption with the southern hemisphere darkening considerably between 2002 and 2012 by 25 at mid latitudes near 827 nm for example while the northern hemisphere has brightened by 25 at mid latitudes at the same wavelength

evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields abstract quartz is a major pore occluding cement in north sea oilfield reservoir sandstones fluid inclusions yield homogenization temperatures t h which have been thought to represent growth temperatures for the host quartz however early diagenetic inclusions from the detrital grain overgrowth boundary yield excessively high palaeotemperatures which do not match the growth temperatures calculated from the depth of cementation the temperatures of these inclusions increase with present day depth of burial and approach present day reservoir temperatures this suggests that the inclusions have begun to reset towards present day pressure temperature conditions the t h of the inclusions hence represent burial temperatures rather than growth temperatures for the quartz experimental studies indicate that the amount of resetting undergone by an inclusion varies depending on its size shape and fluid composition a relationship between inclusion t h and these variables has been observed in inclusions from deeply buried quartz cements in the north sea

reequilibration of fluid inclusions in low temperature calcium carbonate cement calcium carbonate cements precipitated in low temperature near surface vadose environments contain fluid inclusions of variable vapor to liquid ratios that yield variable homogenization temperatures cements precipitated in low temperature phreatic environments contain one phase all liquid fluid inclusions neomorphism of unstable calcium carbonate phases may cause reequilibration of fluid inclusions stable calcium carbonate cements of low temperature origin which have been deeply buried contain fluid inclusions of variable homogenization temperature and variable salt composition most inclusion fluids are not representative of the fluids present during cement growth and are more indicative of burial pore fluids therefore low temperature fluid inclusions probably reequilibrate with burial fluids during progressive burial reequilibration is likely caused by high internal pressures in inclusions which result in hydrofracturing the resulting fluid inclusions population could contain a nearly complete record of burial fluids in which a particular rock has been bathed

reservoir architecture and diagenesis in downthrown fault block plays the lowlander prospect of block 14 20b witch ground graben outer moray firth uk north sea

diagenesis of the sherwood sandstone group in the southern east irish sea basin blocks 110 13 110 14 and 110 15 constraints from preliminary isotopic and fluid inclusion studies

the characteristic variability and connection to the underlying synoptic activity of the amundsen bellingshausen seas low 1 recent studies have noted an asymmetrical climate change across antarctica with significant warming in west antarctica and the antarctica peninsula and primarily insignificant trends in east antarctica due to its proximity variations in the position and intensity of the amundsen bellingshausen seas low absl are a suspected atmospheric mechanism here we investigate the absl to understand its characteristic variability and underlying synoptic scale influences based on three reanalysis data sets the absl is defined as the minimum monthly pressure in the 45 75 s 180 60 w domain using this criterion a significant north south and east west progression is noted in the climatological 1979 2001 average absl which is strongly tied to the location of the maximum cyclone system density and minimum cyclone central pressures more than 550 cyclones a year were identified in the vicinity of the absl during spring significant trends in their central pressures are noted in the ross sea the implied changes in temperature advection by these stronger systems are consistent with the warming in west antarctica the strongest cyclone events i e the ten with the deepest central pressures also demonstrate a connection to the climatological absl albeit weaker moreover these strong cyclone events are significantly linked to the southern annular mode sam particularly in their annual frequency and location steering in the summer this shows that large scale forcing such as from the sam may influence the strongest cyclones in the region and could allow for the prediction of such events

synthetic fluid inclusions vi quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure h2o synthetic inclusions formed by healing fractures in natural quartz three different modes of non elastic deformation referred to as stretching leakage or partial decrepitation and total decrepitation have been observed the internal pressure required to initiate non elastic deformation is inversely related to inclusion size according to the equation internal pressure kbar 4 26 d 0 423 where d is the inclusion diameter in microns regularly shaped inclusions require a higher internal pressure to initiate non elastic deformation than do irregularly shaped inclusions of similar size heating inclusions through the quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion long term heating experiments 2 years suggest that the internal pressure required to initiate non elastic deformation does not decrease significantly with time and indicates that short lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature inclusions that do exhibit decreased density higher homogenization temperature are however always accompanied by a change in shape from irregular to that of a negative crystal observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals these results indicate that an inclusion will not be influenced by a neighbouring inclusion or other defect in the host phase as long as the distance between the two is 2 4 diameters of the larger of the two inclusions

geothermometry and geobarometry of overpressured lower paleozoic gas shales in the jiaoshiba field central china insight from fluid inclusions in fracture cements the wufeng longmaxi organic rich shales host the largest shale gas fields of china this study examines sealed fractures within core samples of the wufeng longmaxi shales in the jiaoshiba shale gas field in order to understand the development of overpressures in terms of magnitude timing and burial in wufeng longmaxi shales and thus the causes of present day overpressure in these paleozoic shale formations as well as in all gas shales quartz and calcite fracture cements from the wufeng longmaxi shale intervals in four wells at depth intervals between 2253 89 m and 3046 60 m were investigated and the fluid composition temperature and pressure during natural fracture cementation determined using an integrated approach consisting of petrography raman spectroscopy and microthermometry many crystals in fracture cements were found to contain methane inclusions only and aqueous two phase inclusions were consistently observed alongside methane inclusions in all cement samples indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid homogenization temperatures of methane saturated aqueous inclusions provide trends in trapping temperatures that th values concentrate in the range of 198 5 c 229 9 c 196 2 c 221 7 c for quartz and calcite respectively pore fluid pressures of 91 8 139 4 mpa for methane inclusions calculated using the raman shift of c h symmetric stretching v1 band of methane and equations of state for supercritical methane indicate fluid inclusions trapped at near lithostatic pressures high trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of wufeng longmaxi shales at maximum burial and the early stage of the yanshanian uplift which can provide a key evidence for understanding the formation and evolution of overpressure our results demonstrate that the main cause of present day overpressure in shale gas deposits is actually the preservation of moderate high overpressure developed as a result of gas generation at maximum burial depths

a fluid inclusion study of quartz cemented sandstones from offshore mid norway possible evidence for continued quartz cementation during oil emplacement abstract jurassic sandstones from the oil zone in a well from the haltenbanken area offshore mid norway contain both aqueous and hydrocarbon fluid inclusions within quartz overgrowths homogenization temperatures for the inclusions range from 92 c up to the present formation temperature of approximately 118 c since the inclusions mostly are located at the boundaries between quartz clasts and quartz overgrowths the homogenization temperatures indicate that quartz cementation started at temperatures slightly below 92 c poikilotopic ferroan calcite cement usually predates formation of quartz overgrowths and most calcite cement must be precipitated at temperatures below 90 c although in one calcite cemented zone ferroan calcite encloses quartz overgrowths with inclusions trapped at temperatures of up to 105 c none of the examined hydrocarbon inclusions homogenized below 102 c and this suggests that oil started entering the reservoir at temperatures of around 100 c the burial history of the examined sandstones indicates that temperatures of 100 c were not reached before the late pliocene and that filling of the reservoir has taken place during the last few million years homogenization temperatures approximately equal to present formation temperature suggest that quartz cementation may still be in progress and that emplacement of oil did not necessarily stop precipitation of quartz cement possible continued quartz cementation after oil filled the reservoir could be explained by dissolution of quartz at stylolites and grain contacts as transport of dissolved quartz from these sources might possibly take place by diffusion through irreducible water

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

oxygen isotope microanalysis by secondary ion mass spectrometry suggests continuous 300 million year history of calcite cementation and dolomitization in the devonian bakken formation calcite cementation and dolomitization are key diagenetic processes in many sedimentary systems unravelling detailed histories and timescales of cementation and replacement is however often compromised by the limited spatial resolution of many analytical techniques in some cases multiple grains are co analyzed so that diagenetic histories are blurred and reaction periods are difficult to establish in this study we have used 10 micrometer resolution in situ secondary ion mass spectrometry to determine the oxygen isotope composition of 197 individual 10 50 micrometer size crystals of dolomite and calcite from six samples in a single core of upper devonian middle bakken member siltstones and sandstones the major tight oil formation of the williston basin usa this amount of data places important constraints on the range of temperatures and times that carbonate cementation and replacement occurred petrographic data show that microcrystalline calcite cement is an early phase and combined with mineralogical data suggest that much of the dolomite replaces calcite over spatial scales of less than a centimeter analyses of individual calcite crystals have a range of 5 for 18o in the group of crystals and for the group of individual dolomite crystals 10 these sub centimeter ranges are as great as those observed in previous studies of carbonate cements sampled over many meters and remind us that previous low resolution studies may have inadvertently analyzed mixed phases there is no relationship between dolomite texture and isotopic composition at this spatial scale microscale backscattered electron imagery and scanning electron microscopy cathodoluminescence zoning is seen but cannot be resolved with a 10 micrometer spot size assuming since it is an early cement that calcite precipitated from seawater 18o 1 5 it formed at ca 15 40 c mainly at the lower temperatures present day formation waters in devonian rocks in this region have oxygen isotope compositions of 7 8 vsmow using these values as a likely dolomitizing fluid we suggest that dolomitization occurred continuously between 40 and 140 c over 150 200 million years most likely in a fluid with a high mg ca ratio resulting from gypsum formation in local evaporites we suggest that this exceptionally low rate of dolomitization was controlled by the low rate of supply of mg in a very sluggish flow regime dolomitization is incomplete because of a limited supply of mg

teleconnections between the tropical pacific and the amundsen bellinghausens sea role of the el nino southern oscillation 1 tropical pacific high southern latitude teleconnections are shown to be caused by rossby wave dynamics and are sensitive to the exact pattern of sea surface temperature sst anomalies forcing anomalous ascent further the signal becomes obscured by local natural variability at higher southern latitudes here it is shown that a rossby wave with a source in the tropical pacific can explain the general pattern of teleconnection found during the southern winter upper level divergence associated with deep convection in the tropical pacific plays a major role in the generation of these rossby waves sst anomalies associated with el nino southern oscillation force the tropical deep convection however the relationship between deep convection and sst anomalies is complex and modeling experiments show that in areas of large scale subsidence positive sst anomalies would have to be larger than any observed anomalies 4 c before they have any effect on the vertical motion large variations are observed between the high latitude response to el nino with apparently similar tropical forcings this makes accurate prediction of the high latitude response to tropical change difficult ensemble gcm runs show that variations due to the natural variation of the zonal flow in the southern hemisphere can swamp the signal resulting from changes in the rossby wave source region

central west antarctica among the most rapidly warming regions on earth the west antarctic ice sheet is contributing to sea level rise but temperature trends in the region have remained uncertain a complete temperature record for byrd station in central west antarctica spanning from 1958 to 2010 establishes west antarctica as one of the fastest warming regions globally

snow precipitation at four ice core sites in east antarctica provenance seasonality and blocking factors snow precipitation is the primary mass input to the antarctic ice sheet and is one of the most direct climatic indicators with important implications for paleo climatic reconstruction from ice cores provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites dome c law dome talos dome and taylor dome in east ant arctica were analysed with air mass back trajectories cal culated using the lagrangian model and the mean composite data for precipitation geopotential height and wind speed field data from the european centre for med ium range weather forecast from 1980 to 2001 on an annual basis back trajectories showed that the atlantic indian and ross pacific oceans were the main provenances of precipitation in wilkes land 80 and victoria land 40 respectively whereas the greatest influence of the ice sheet was on the interior near the vostok site 80 and in the southwest ross sea 50 an effect that decreased towards the coast and along the antarctic slope victoria land received snowfall atypically with respect to other antarctica areas in terms of pathway eastern instead of western seasonality summer instead of winter and velocity old air age geopotential height patterns at 500 hpa at low 10 days and high 2 6 days frequen cies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the tasman sea eastern indian ocean at higher latitudes 60 70s than normal this could be considered part of an atmospheric blocking event with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low frequency positive anomalies

new evidence for the origin of quartz cements in hydrocarbon reservoirs revealed by oxygen isotope microanalyses quartz cements degrade hydrocarbon reservoir quality by choking off fluid flow paths therefore it is important to understand the sources and timing of quartz cementation we present in situ microanalyses of oxygen isotope ratios in quartz cements from a jurassic hydrocarbon reservoir located offshore norway showing systematic variations that reveal the isotopic history of the pore fluids that precipitated the quartz earliest quartz cements have 18o values of 20 26 subsequent cements drop in 18o value as low as 13 but then increase back to 23 with increasing cement thickness this isotopic trend was observed in multiple overgrowths with temperatures constrained by fluid inclusions and the burial history of the reservoir the isotopic composition of porewaters can be estimated from the measured isotopic ratios in quartz cement results indicate that 97 of the quartz cement precipitated from negative 18o waters originally meteoric that were gradually modified by burial diagenetic reactions as temperatures increased precipitation began in the middle to late cretaceous however the rate of quartz precipitation increased dramatically in the last 3 5 ma as the reservoir was rapidly buried the data show that quartz precipitation is a continuous process during burial and that silica is derived locally from silicate reactions occurring within the sandstone reservoir the isotopic data do not record evidence of episodic cementation from convection driven hot basinal fluids

twentieth century increase in snowfall in coastal west antarctica the amundsen sea sector of the west antarctic ice sheet has been losing mass in recent decades however long records of snow accumulation are needed to place the recent changes in context here we present 300 year records of snow accumulation from two ice cores drilled in ellsworth land west antarctica the records show a dramatic increase in snow accumulation during the twentieth century linked to a deepening of the amundsen sea low asl tropical sea surface temperatures and large scale atmospheric circulation the observed increase in snow accumulation and interannual variability during the late twentieth century is unprecedented in the context of the past 300 years and evidence that the recent deepening of the asl is part of a longer trend

century scale perspectives on observed and simulated southern ocean sea ice trends from proxy reconstructions since 1979 when continuous satellite observations began southern ocean sea ice cover has increased whilst global coupled climate models simulate a decrease over the same period it is uncertain whether the observed trends are anthropogenically forced or due to internal variability or whether the apparent discrepancy between models and observations can be explained by internal variability the shortness of the satellite record is one source of this uncertainty and a possible solution is to use proxy reconstructions which extend the analysis period but at the expense of higher observational uncertainty in this work we evaluate the utility for change detection of 20th century southern ocean sea ice proxies we find that there are reliable proxies for the east antarctic amundsen bellingshausen and weddell sectors in late winter and for the weddell sea in late autumn models and reconstructions agree that sea ice extent in the east antarctic amundsen and bellingshausen seas has decreased since the early 1970s consistent with an anthropogenic response however the decrease is small compared to internal variability and the change is not robustly detectable we also find that optimal fingerprinting filters out much of the uncertainty in proxy reconstructions the ross sea is a confounding factor with a significant increase in sea ice since 1979 that is not captured by climate models however existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection

deformation by solution deposition and re equilibration of fluid inclusions in crystals depending on temperature internal pressure and stress abstract changes of shape and density of fluid inclusions in crystals were demonstrated when these crystals were subjected to temperatures and internal pressures greater than those of their growth experimental relations have been established between the rate of length change of the inclusions and the different parameters of the experiment nature of the crystal temperature and internal pressure state of stress on the crystal geometric characters of the inclusion length width orientation of the inclusion with respect to the optical axes of host mineral it is essentially the effect of the variation of surface energy with the curvature around the cavity which causes a mass transfer of the host crystal by diffusion through the fluid under pressure the rate of length change is limited by the rate of dissolution at the median part of elongate inclusions this change of shape and density is known to occur in naturally deformed crystals an example of such a behaviour is given which allowed us to use the inclusions as markers of the conditions of temperature and pressure subsequent to the growth of crystal

improving ice core interpretation using in situ and reanalysis data 1 back trajectory analysis provided by the british atmospheric data centre using meteorological parameters from the european centre for medium range weather forecasts ecmwf reanalysis era 40 1980 2001 and operational analysis 2002 2006 is used to investigate transport pathways and source regions of climate proxies preserved in a new ice core gomez from the southwestern antarctic peninsula the ecmwf data are compared with automatic weather station data and ice core annual accumulation records to demonstrate that the ecmwf data capture a large proportion of the annual and subseasonal precipitation variability at the site the back trajectories reveal that precipitation preserved in the ice core accumulation record and hence climate proxies contained therein originate from the low pressure systems from the bellingshausen sea transported via circumpolar westerly winds hence precipitation dependent ice core proxies such as isotopic composition will be influenced by both localized sea ice extent and large scale circulation changes such as the southern annular mode sea ice proxies from the ice core are expected to be dominated by sea ice extent in the bellingshausen sea but also influenced by sea ice in the weddell sea with a small proportion of air mass trajectories originating from this region during the summer comparison with other ice core sites reveals a stronger influence of easterly transport at more northerly locations thus explaining the observed differences in snow accumulation records between ice cores and the poor correlation with instrumental records at these sites

topographic effects on the mean tropospheric flow patterns around antarctica abstract topographically induced flows around antarctica in a rotating tank experiment with both homogeneous and stratified fluid are analyzed and compared with the mean tropospheric circulation a circular tank of fluid was brought to a state of near rigid clockwise rotation and a topographic model of the antarctic continent was then rotated counterclockwise to simulate a mean westerly zonal wind stratification was chosen to give the same ratios of topographic and dynamical length scales as in the atmosphere as was the rossby number based on the ratio of rotation rates after the onset of the relative rotation of the antarctic model cyclonic eddies evolved in the coastal areas with in the homogeneous case anticyclonic eddies over the antarctic dome after about ten tank rotation periods a dominant wavenumber 3 structure with cyclonic eddies in the ross and weddell seas and prydz bay is observed as an approximately steady state flow over the topography is relatively stagnant with weak anticycloni

quartz cementation history of sandstones revealed by high resolution sims oxygen isotope analysis abstract evaluating the timing and origin of quartz cement is central to understanding how porosity is lost in sandstones during burial kinetic models of quartz cementation have been calibrated using large scale datasets but have never been tested at the microscopic level at which cement forms here we use high precision in situ oxygen isotope analyses on sandstone from the jurassic ness formation from the north sea to reveal the growth history of single quartz overgrowths to a resolution of 2 m measured 18o cement range from 28 to 20 v smow in early to late cement and are consistent with quartz cementation models that propose the bulk of quartz precipitates as a continuous process beginning at 60 70 c quantitative x ray diffraction analyses and clay mineralogical analysis of interbedded shales are inconsistent with a silica source from shale implying that silica for the cement is sourced internally to the sand these isotope data are broadly consistent with predictive conceptual quartz cementation models and provide a critical link from micron scale measurements to basin scale predictions and observations

dating diagenesis in a petroleum basin a new fluid inclusion method the final porosity and permeability of sandstone petroleum reservoirs is greatly affected by the diagenetic growth of minerals after deposition for example a sand may be deposited with a porosity of 25 and a permeability of 5 000 mdarcy md 1 diagenetic growth of quartz around detrital sand grains may leave a rock with only 10 porosity and later growth of clays may partly fill these remaining pores and block inter pore connections reducing permeability to 100 md ref 2 if the depth and timing of such diagenetic alteration can be measured and the extent of diagenesis estimated then prediction of the diagenetic state of undrilled sandstones may become possible and diagenesis related more closely to the timing of hydrocarbon migration and the formation of hydrocarbon traps we present an example of a new method for estimating the date of quartz diagenesis using a combination of techniques from thin section petrography fluid inclusion thermometry organic geochemical thermometry and sedimentary basin stratigraphic analysis these results suggest that quartz in the beatrice oilfield was precipitated from moving and cooling pore fluids at a temperature between 68 c and 94 c in the late jurassic

fluid inclusion constraints on temperatures of petroleum migration from authigenic quartz in bitumen veins abstract solid bitumens in fracture systems commonly contain microscopic crystals of authigenic quartz which were precipitated coevally with the bitumen early in the paragenesis of the fracture fillings the quartz contains primary fluid inclusions both aqueous and hydrocarbon yielding homogenization temperatures particularly in the range 95 130 c indicating minimum temperatures of entrapment during petroleum migration volumes of up to 50 entrained quartz and a predominance of aqueous inclusions indicate that the petroleum fluid had a substantial aqueous component

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

seasonality of airmass pathways to coastal antarctica ramifications for interpreting high resolution ice core records abstractunderstanding airmass pathways is critical for ice core interpretation and the ability to determine the broadscale characteristics and seasonality of synoptic scale flow using paleoclimate records offers great potential to improve the understanding of past atmospheric circulation the dominant airmass pathways to a coastal antarctic ice core site at the whitehall glacier in the ross sea are modeled using snowfall and high resolution stable isotope data between 1979 and 2006 combined with back trajectories produced from both ncep ncar and ecmwf interim re analysis era interim data back trajectories generated from both datasets produce comparable results they show that high snowfall is associated with cyclonic airflow in the ross sea with a strong meridional component along the western ross sea coast over a 28 yr time frame trajectories also reveal a clear distinction between flow paths associated with above and below average annual temperatures high and low d in the ice core record in

diagenesis and reservoir quality prediction the modern concept of diagenesis was introduced by walther one hundred years ago to encompass the postdepositional processes that affect sediments from deposition to low grade metamorphism since walther 1893 diagenetic studies have been concerned with an extraordinary variety of chemical and physical interactions each of which has the potential to significantly affect the final composition and texture of a sedimentary rock the issues to which those studies have been applied are equally varied and include 1 improved techniques to predict the producibility of hydrocarbon reservoirs 2 improved techniques to predict subsurface fluid pressures 3 better constraints on the timing of fluid flow events 4 reconstruction of global climate change and 5 evaluation of groundwater contamination commercial applications of diagenetic studies have traditionally focused on the producibility of hydrocarbon reservoirs as such a review of this topic serves as an effective illustration of how basic research has been commercialized and a useful focus for the following dicussion however it is worth noting that decreased industrial research funding coupled with increased government funding for environmental research have recently resulted in a gradual evolution of diagenetic publications away from the producibility of hydrocarbon reservoirs toward the producibility of uncontaminated groundwater and other environmental issues despite the shift in emphasis many of the basic research issues remain unchanged whether one is focused on deep hydrocarbon reservoirs or shallow aquifers

microspectrofluorimetric and microthermometric evidence for variability in hydrocarbon fluid inclusions in quartz overgrowths implications for inclusion trapping in the alwyn north field north sea abstract hydrocarbon inclusions trapped in quartz cement from alwyn north field sandstones of well 3 9a 6 north sea have been analyzed using microthermometric and microspectrofluorimetric methods they are two phased with consistent gas oil ratios and mainly occur along the detrital grain overgrowth boundary their homogenization temperatures vary from 60 to 129 c with a great variability within a single fluid inclusion assemblage up to 40 c the fluorescence colour of the hydrocarbon inclusions has been characterized using a microspectrofluorimeter which allows the analysis of very small inclusions 1 7 m with good reproducibility hydrocarbon inclusions display large variations in their fluorescence colour converted in chromaticity coordinates even within a single fluid inclusion assemblage moreover they are concentrically distributed within the detrital grain overgrowth interface according to the relationship between api gravity and fluorescence colour established with reference to crude oils from alwyn north field this observation is interpreted as representing compositional variations such compositional variability in a single fluid inclusion assemblage could result from either the progressive entrapment of oils in which api gravity evolves through time and or the fractionation of hydrocarbons at the time of trapping

investigation of oil pool formation from the homogenization temperatures of fluid inclusions and biomarkers in reservoir rocks a genetic model for the deng 2 oil pool in the jiyuan depression abstract the jiyuan depression is a frontier area for oil and gas exploration in henan province china in recent years oil was discovered in the deng 2 well in the lower tertiary though the tectonics and petroleum geology of the depression are very complex a series of experiments on fluid inclusions in the oil bearing sandstones from the deng 2 well were made that included measurement of the homogenization temperatures of gas liquid inclusions and gc ms analysis of biomarkers either in the sandstone pores or in the fluid inclusions the deng 2 oil reservoir was formed at about 78 c corresponding to a burial depth of about 2200 m the present burial depth is about 700 m because of erosion and fault block uplift in oligocene time although oil in the sandstone pores is now heavily biodegraded the biomarkers in the inclusions show slight biodegradation representing a watering and biodegradation process that did not occur before formation of the deng 2 oil pool having investigated the structural evolution of the deng 2 trap it is concluded that the oil discovered in the tertiary reservoir of deng 2 well migrated from mesozoic reservoirs through active faults around the deng 2 trap as the oil migrated from the mesozoic to the tertiary reservoir the deng 2 trap was uplifted close to the depth of active biodegradation subsurface temperature lower than 80 c and to a burial depth shallower than 2250 m from the thermal gradient of 3 1 c 100 m so that the oil in the inclusions shows a slight biodegradation because of the continuous uplift of the deng 2 trap during the tertiary and quaternary the reservoired oil has been more heavily biodegraded compared to that in the inclusions