tricyclic terpane maturity parameters response to heating by an igneous intrusion the effects of thermal maturation upon the abundance and composition of the tricyclic terpanes have been investigated within a single sedimentary horizon within the dun caan shale member isle of skye scotland intruded by a 0 9 m thick tertiary dolerite dyke heating by the igneous body caused the concentrations of all 13 h 14 h and 13 h 14 h tricyclic terpanes to increase towards or within the effective oil window recording generation from abundant non hydrocarbon precursors such as kerogen and asphaltene bound components progressive changes in tricyclic terpane composition accompany these concentration changes an increase in the c23 maturity parameter towards the dyke resulted from the relatively greater rate of generation of the isomer combined with the earlier decline in concentration by degradation or isomerisation of the component the tricyclics tricyclics hopanes parameter shows a dramatic increase within the latter part of the oil window due to the greater relative thermal stability of the tricyclic terpanes the quantitative data demonstrate the importance of the processes of generation from non hydrocarbon fractions of the sedimentary organic matter and thermal degradation in the operation of tricyclic terpane maturity parameters

episodic petroleum fluid migration in fault zones of the northwestern junggar basin northwest china evidence from hydrocarbon bearing zoned calcite cement hydrocarbon bearing zoned calcite cements occur widely in jurassic cretaceous fault zone cores and sandstone outcrops of the northwestern junggar basin northwest china hydrocarbon bearing bands alternate with nearly hydrocarbon free bands at a micron scale analytical results from biomarker organic geochemistry fourier transform infrared microspectroscopy and trace element geochemistry on these zoned cements suggest that at least three different types of fluids have participated in their formation the first fluid type is probably primary unmodified lacustrine formation water from which the hydrocarbon poor bands are formed and are characterized by mg rich calcite the other two types of fluids include basinal fluids e g hot hydrocarbon bearing fluids and meteoric water the hydrocarbon rich bands in which the hydrocarbons have been biodegraded and the mn content is relatively high suggest a mixture of hydrocarbon bearing basinal fluid and meteoric water the alternating growth of hydrocarbon bearing and hydrocarbon free bands of calcite cements implies that the cement formation is episodic it is related to alternating episodes of mixed petroleum bearing fluid and unmodified primary formation waters respectively the fault appears to have been a mixing zone where seismic pumping during the movement of associated regional faults occurred thus in the northwestern junggar basin the micron scale hydrocarbon bearing zoned structure of the calcite cements is likely a reflection of episodic petroleum fluid migration in fault zones

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

predicting gas oil and water intervals in niger delta reservoirs using gas chromatography formation evaluation experts usually have little difficulty in interpreting wireline logs to assess the type of reservoir fluid oil gas water in sand shale sequences this assessment is usually accomplished by a combination neutron density tool that detects low hydrogen and low electron densities typical of gas zones and the repeat formation tester rft which uses both the pressure gradient and sample acquisition techniques to evaluate reservoir fluid in the niger delta however many of the sands exhibit a poor neutron density response to gas and rft testing has been largely eliminated because poor hole conditions commonly result in stuck tools oil fingerprinting of residual hydrocarbons from sidewall core extracts can provide an independent means of identifying eservoir fluid type in conjunction with the nigerian national petroleum company we completed numerous chromatographic analyses on solvent extracts of sidewall core samples from various wells in the mefa field offshore west niger delta oil fingerprints of sidewall core extracts clearly reflect the type of hydrocarbons in the reservoir fingerprints of oil saturated sands are typical of topped c15 whole oils whereas fingerprints of hydrocarbons extracted from the gas dominated sands show an abbreviated hydrocarbon distribution more typical of gas condensates fingerprints of extracts from water productive intervals show a further abbreviated signature suggesting that higher molecular weight hydrocarbons did not migrate into these intervals these signatures are distinct and intact despit poor sample preservation due to prolonged storage of up to 3 yr additional applications of this technique include the reevaluation of older wells that lack modern wireline measurements but have sidewall or conventional core material available and in thin or low permeability sands that may not yield definitive rft or wireline log responses application potential for this technology is worldwide and includes the gulf coast of the united states canada indonesia and papua new guinea

upper permian lacustrine oil shales southern junggar basin northwest china upper permian organic rich lacustrine mudstones oil shales that crop out in the southern junggar basin rank among the richest and thickest petroleum source rock intervals in the world with maximum toc values reaching 34 and rock eval pyrolytic yields s 2 up to 200 kg hc t rock lacustrine sedimentary facies define an overall transgressive regressive cycle of approximately 2000 m gross thickness which includes approximately 800 m of source rocks averaging 4 1 toc and 26 2 kg hc t rock basinal facies comprise silicic organic rich laminated lacustrine mudstones and interbedded siltstones organic matter contained in the mudstones ranges in composition from type i to type iii basinal facies were deposited in a deep oxygen deficient stratified lake lake margi facies consist of nonlaminated siliciclastic mudstones rippled dolomitic siltstones and sandstones and minor limestones maximum toc values are approximately 6 desiccation cracks are common in the marginal facies but evaporite minerals are rare or absent biomarker correlation parameters measured from rock extracts exhibit significant stratigraphic variability but strongly support the hypothesis that upper permian lacustrine oil shales charge the giant karamay field in the northwestern junggar basin karamay oils are characterized by high relative abundances of beta carotane this characteristic is restricted to desiccated facies in the outcrop sections however we therefore propose that an abundance of beta carotane indicates elevated environmental salinities during deposition of the oil shales orographic precipitation induced by a paleo tian shan range may have provided fresh water to the southern areas of the basin while more evaporative conditions prevailed to the north outcrop oil seeps confirm that the outcrop sections have attained sufficient thermal maturity to generate oil t max values range from 431 to 451 degrees c vitrinite reflectances range from 0 73 to 0 88 and sterane isomerization ratios range from 0 30 to 0 48 20s 20s 20r matoil registered trademark computer modeling of burial history and thermal maturity of the outcrop sections indicates that approximately 4 5 km of triassic jurassic cover was needed to bring the oil shales to their current maturity the major phase of hydrocarbon generation in this area appears to have preceded the creation of traps by neogene thrusting which may account for the lack of discoveries in the southern junggar basin most of the oil discovered so far is trapped in structures which originated duri g the late paleozoic or mesozoic

petroleum migration and mixing in the northwestern junggar basin nw china constraints from oil bearing fluid inclusion analyses abstract abundant oil bearing fluid inclusions are present in four reservoir sandstone samples from the slope and fault zone areas in the northwestern margin of the junggar basin nw china free oil in intergranular pores adsorbed oil on grain surfaces and petroleum in inclusions hosted by mineral grains of these samples were analyzed by gas chromatography and gas chromatography mass spectrometry analytical results indicate similar biomarker distributions in the three bitumen fractions of the samples collected from the slope area which correlate well with characteristic of the source rocks in the lower permian fengcheng formation this is in contrast to the fault zone where the three bitumen fractions vary significantly in their geochemical signatures suggesting that all of the three permian source sequences rocks including the lower permian jiamuhe and fengcheng formations and the middle permian lower wuerhe formation have been mature and contributed to the oils in the fault zone the presence of an unresolved hydrocarbon hump and a full range of unaltered n alkanes in the gas chromatograms of samples collected from the fault zone indicate an earlier hydrocarbon biodegradation and subsequent injection of fresh oils distinctly different from that in the slope area petrographic and microthermometric investigations of oil bearing fluid inclusions suggest a single oil charge in the slope area to the lower triassic reservoir occurring during the late triassic to early jurassic time in the fault zone oil migration and mixing took place mainly during the late triassic to early jurassic and cretaceous followed by gas migration in the tertiary period the different petroleum migration and mixing histories in the slope and fault zones are attributed to the effect of fault controlled oil and gas migration

organic geochemical identification of reservoir oil gas water layers in the junggar basin nw china abstract the identification of reservoir oil gas water layers is a fundamental task in petroleum exploration and exploitation but is difficult especially in cases of complex hydrocarbon migration and accumulation in such cases hydrocarbon remigration and dysmigration take place very commonly leading to the presence of residual or paleo oil accumulations and layers which cannot be easily identified or misinterpreted as oil layers by conventional logging and geophysical data in this paper based on a case study in the luxi area of the central junggar basin nw china we seek to characterize such layers in terms of organic geochemistry we suggest specific indicator parameters of organic geochemistry such as the chloroform bitumen content of reservoir extracts which is usually 1 0 in oil layers we explore the application of grains containing oil inclusions goi the ratio of mineral grains containing oil inclusions to the total number of mineral grains for the identification of oil gas water layers in the junggar basin for the first time this method has been used elsewhere the maximum goi values for the oil layers oil water layers water layers and dry layers are 11 7 11 6 7 and c21 c23 in contrast the typical characteristic of the heavy oil layers is the presence of 25 norhopanes in reservoir bitumen extracts these specific indicators can be applied in the junggar basin and in similar settings elsewhere

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

geochemical evidence for mudstone as the possible major oil source rock in the jurassic turpan basin northwest china abstract geologists and geochemists have debated whether hydrocarbons from jurassic coal measures are derived from the mudstones or the coals themselves this paper identifies mudstones as the possible major source rock of hydrocarbons in the jurassic basins in northwest china the turpan basin is used as a representative model mudstones in the middle lower jurassic are very well developed in the basin and have an average genetic potential from 2 to 4 mg g the vitrinite reflectance of the source rocks ranges from 0 6 to 1 3 exhibiting sufficient thermal maturity to generate oil and gas biomarkers in crude oils from the basin are similar to those in mudstones from the coal bearing strata with a low tricyclic terpane cheilanthane content a relatively high content of low carbon number less than c22 tricyclic terpanes and a low content of high carbon number tricyclic terpanes relatively high ratios of ts tm and c29 ts 17 h c29 norhopane and low ratios of tm 17 h c30 hopane and 17 h c31 homohopane 17 h c30 hopane these characteristics and the distribution of steranes and terpanes in the crude oil and mudstone differ significantly from those of the jurassic coals and carbonaceous shales of the basin indicating mudstone is possibly the major source rock of the oils in the turpan basin

geochemistry and origins of natural gases in the central junggar basin northwest china abstract the petroliferous central junggar basin in northwest china is predominantly an oil exploration region however its gas exploration also might have good prospects thus to assist in gas exploration the geochemistry and origins of gases are discussed in this paper based on relatively comprehensive analyses of compositions carbon isotopes and light hydrocarbons of gases based on the results the gas genetic types are grouped into families and combined with the geological setting e g biomarkers of retrograde condensates and source rock characteristics we show that there are four representative genetic types of gases the first consists of gases derived from permian lacustrine mudstones with type i ii kerogen and type iii kerogen sources in the penyijingxi sag their representative geochemical feature is 13c2 ranging from 31 4 to 24 7 the second is gas sourced from carboniferous tufaceous mudstones of type iii kerogen in the dishuiquan sag whose representative geochemical feature is the heaviest values of 13c1 in the studied samples ranging from 32 0 to 30 4 the third consists of gases sourced from jurassic coals and mudstones in the shawan fukang sag the light hydrocarbon fingerprints of these gases are similar to those of gases and oils typically derived from jurassic source rocks in the southern junggar basin the fourth is gas most likely generated from the degradation of crude oil it is mainly found in the luliang area and has dryness values as much as 0 999 and 13c1 ranging from 54 8 to 43 2 among these four types of gases the first mainly sourced from the permian lacustrine mudstones in the penyijingxi sag is the predominant type

in situ stress orientation near the san andreas fault preliminary results to 2 1 km depth from the cajon pass scientific drillhole stress induced wellbore breakouts were analyzed in the cajon pass scientific drillhole 4 3km ne of the san andreas fault to determine the orientation of the principal horizontal stresses using borehole televiewer digitized data in the depth interval 1750 2115 m the mean orientation of the maximum horizontal stress is 073 the scatter in the orientation of breakouts is as much as 37 and variations occur with wavelengths of few hundred meters in this interval reflecting either true changes in stress orientation with depth or the variability of rock anisotropy all the measured orientations however result in left lateral shear stress resolved onto planes parallel to the san andreas fault contrary to its post miocene right lateral slip of 300 km the stress orientation is consistent however with reported left lateral displacement across the cleghorn fault 3 km northeast of and possibly subparallel to the san andreas near cajon pass since the pleistocene the cajon pass stress orientation may reflect the current state of stress across the san andreas fault in which case it should change prior to right lateral slip on this fault or a shallow local perturbation to the san andreas stress field in which case it should rotate couterclockwise with depth determination of the stress orientations at greater depths in the cajon pass drillhole will better sample the near field of the san andreas fault and help resolve this question

well logging methods in groundwater surveys of complicated aquifer systems bohemian cretaceous basin geophysical well logging methods including borehole flow logging can significantly contribute to a detailed understanding of hydrogeological conditions in basins with complicated sedimentary structure in studies undertaken to make optimal use of water sources or to protect those resources from contamination it is a common practice to delineate geological and hydrogeologic conditions at the scale used in geological maps and surface surveys however there is a need for more detailed descriptions of basin structure for many tasks related to water resources management and hydrologic research this paper presents four specific examples of boreholes in complex hydrogeologic settings where useful information was provided by geophysical logging 1 identification of large scale upward cross flow between aquifer horizons in an open borehole 2 confirmation of continuous permeability throughout a long borehole interval 3 identification of leakage into a test well via a defective casing joint 4 evidence for downward flow in open boreholes and 5 identification of permeable beds associated with water inflows during aquifer tests these borehole geophysical measurements provide important information about the detailed lithological profiles of aquifers especially in the absence of core enabling the optimization of groundwater monitoring resource use and wellhead protection activities

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

origin and mechanism of the formation of the low oil saturation moxizhuang field junggar basin china implication for petroleum exploration in basins having complex histories the moxizhuang field is a small oil field in the central junggar basin containing several low saturation low resistivity oil reservoirs which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs biomarker associations of crude oil and grains containing oil inclusions gois of both the present day water bearing zones water zones and the oil and water bearing zones low oil saturation pay zones were analyzed to investigate the mechanisms for the formation of the low saturation low resistivity oil accumulations the biomarker assemblage and hierarchical cluster analysis indicate that oil in the moxizhuang field was mostly generated from permian source rock deposited in brackish to hypersaline anoxic environments the pay zones and several water zones display goi values as much as 38 greater than the generally accepted threshold goi value for an oil column 5 these goi values are similar to those for high saturation oil reservoirs in the bohai bay basin and oil zone samples from australian basins suggesting that both pay zones and water zones were high saturation oil reservoirs in the geologic past geologic history analysis shows that the moxizhuang field was located on the north wing of a paleoanticline during oil charge in the late cretaceous to paleogene this anticline has gradually evolved into a south dipping monocline since the neogene causing northward remigration of accumulated oil differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high goi values completely drained reservoirs and the low saturation low resistivity pay zones partially preserved reservoirs and caused the complex correlation between oil saturation and porosity and permeability compared with other postaccumulation physicochemical alteration processes lateral leakage has rarely been recognized recognizing differential lateral leakage of accumulated petroleum with the existence of high quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories

atomic h c ratio of kerogen as an estimate of thermal maturity and organic matter conversion in recent years the atomic h c hydrogen to carbon ratio of kerogen as a way to assess the quality of organic matter in source rocks has been overlooked in favor of the more easily determined rock eval hydrogen index rock eval pyrolysis provides fast inexpensive quantitative mg hc g rock data without requiring kerogen isolation from the rock because of the general scatter in the data many source rock interpreters consider rock eval pyrolysis to be a screening analysis in this paper i describe the benefits of using h c ratios in source rock evaluations and present new correlations between atomic h c ratios and thermal maturity organic matter conversion and expulsion volumetrics atomic h c ratios of pyrolyzed kerogens have been correlated to the extent of thermal conversion of organic matter for both type i and type ii kerogens the excellent agreement between stoichiometric calculated hydrogen and carbon loss to observed losses from hydrous pyrolysis maturation experiments suggests that kerogen h c ratios are excellent indicators of thermal maturity for end member kerogen types these data also offer a method to estimate percent organic matter conversion provided that both the initial and present h c ratios of the kerogen are known present h c ratios can be measured and initial h c ratios can be reasonably estimated from microscopic organic analysis of kerogen for oil prone source rocks typical immature type i kerogens have h c ratios of 1 35 1 50 whereas type ii kerogens have h c ratios of 1 20 1 35 correlations of the amount of expelled oil in hydrous pyrolysis experiments to atomic h c ratio of the spent kerogen offer exploration geologists a quick estimate of oil expulsion volumes based on hydrous pyrolysis experiments measured h c ratios and calculated original toc total organic carbon values first order volumetric approximations were made on three basins containing mature source rocks results compared favorably with published approximate oil in place estimates for the williston basin bakken shale los angeles basin nodular shale and the illinois basin new albany shale

hydrocarbon migration in the multiple sourced petroleum system in the northwestern junggar basin northwestern china constraint from geochemical and phase fractionation analysis oil mixing and absence of source rock samples make it difficult to identify the hydrocarbon migration routes in a petroleum system we provide a case study in the northwestern junggar basin to show that combined geochemical and phase fractionation analyses are robust tools to unravel the complex hydrocarbon migration processes the study rebuilds a migration history that multiple sourced hydrocarbons migrated mixed accumulated and fractionated along the evolution of regional tectonics in detail the shawan and mahu sags expelled the early stage hydrocarbons during the late triassic and late jurassic respectively because of their variable subsidence these hydrocarbons charged the entire area based on the evidence from bitumen and oil inclusions during the early cretaceous both sags subsided rapidly and expelled their late stage hydrocarbons these hydrocarbons first mixed along unconformities in the sags which generated mixed source oils and induced gas washing subsequently they further mixed with or displaced the encountered early stage oils during migration along the basal unconformity of the upper permian into the area causing a horizontal distribution of oil maturity zones in addition gases flowing through the early stage oils induced gas washing again creating heavy oils condensate oils and mixed gases after the late stage oils finally accumulated in fractured volcanics migration fractionation caused the remigration of light end compositions this study also shows the strong control of structures on hydrocarbon migration the unconformity network provided opportunities for long distance migration and widespread mixing of multiple sourced hydrocarbons whereas the paleoridge line of the zhongguai high defined the boundary of regional migration

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

attenuation of p and s waves as a method of distinguishing gas and condensate from oil and water compressional and shear wave attenuation data were calculated from sonic waveforms in three wells the results show that at similar porosities and at in situ conditions gas and condensate sandstone reservoirs exhibit higher p wave attenuation lower p wave quality factor q p than either fully water or partially oil water saturated sandstones however s wave attenuation and quality factor q s do not show such a strong dependence on pore fluids furthermore q p q s 1 indicates presence of gas or condensate while q p q s i indicates full water or oil water saturation these field data are consistent with laboratory data and theoretical predictions by various researchers the crossovers of p swave attenuation and q p q s quality factors proved useful for distinguishing gas and condensate from oil and water reservoirs they may be used in conjunction with vp vs and other logs as an aid in formation evaluation for the detection of gas condensate and oil several case studies in the literature report high p wave energy absorption at seismic frequencies below gas and condensate pools this suggests that it is not unreasonable to assume that this method could also be used in seismic exploration as an aid for distinguishing gas and condensate from oil and water formations

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

improved understanding of petroleum migration history in the hongche fault zone northwestern junggar basin northwest china constrained by vein calcite fluid inclusions and trace elements calcite veins and cements occur widely in carboniferous and permian reservoirs of the hongche fault zone northwestern junggar basin in northwest china the calcites were investigated by fluid inclusion and trace element analyses providing an improved understanding of the petroleum migration history it is indicated that the hongche fault behaved as a migration pathway before the early cretaceous allowing two oil charges to migrate into the hanging wall fault core and footwall reservoirs across the fault since the late cretaceous the hongche fault has been sealed as a consequence meteoric water flowed down only into the hanging wall and fault core reservoirs the meteoric water incursion is likely an important cause for degradation of reservoir oils in contrast the footwall reservoirs received gas charge the third hydrocarbon event following the late cretaceous this helps explain the distribution of petroleum across the fault this study provides an example of how a fault may evolve as pathway and seal over time and how reservoir diagenetic minerals can provide clues to complex petroleum migration histories

quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history abstract two new fluorescence techniques quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e can detect palaeo oil zones and current residual oil zones in petroleum wells respectively qgf and qgf e measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts qgf is measured on dry disaggregated reservoir grains after a cleaning procedure involving solvent hydrogen peroxide and acid whereas qgf e is measured on the solvent extract from the qgf cleaned grains palaeo oil zones have distinct qgf spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated current and residual oil zones have distinct qgf e spectra with spectral peaks at around 370 nm and elevated qgf e intensities compared with that for current water zones both qgf and qgf e responses increase upwards from the palaeo oil water and residual oil water contacts respectively an oil producing well from timor sea nw australia was investigated in detail using the qgf and qgf e techniques to illustrate how they can be used to reconstruct hydrocarbon migration history

late cenozoic tectonic activity and its significance in the northern junggar basin northwestern china abstract the dingshan area located in the northern part of the junggar basin of northwestern china is a significant prospect area for sandstone type uranium deposits in china where mainly cenozoic rocks were deposited the cenozoic strata can be divided into four units according to the prior data and our own field observation sedimentary studies indicate that most cenozoic strata were deposited under a hot and arid climate in a continental environment the sedimentary facies are alluvial fan meandering fluvial and fluvio lacustrine field investigation and interpretation of satellite images suggest that cenozoic tectonics in the area is characterized by reactivation of early deep seated thrusts resulting in extensional fractures and formation of many small depressions in the shallow crustal level measurement of joint orientations suggests that regional shortening direction trends in north south in the middle pleistocene as indicated by the esr electronic spin resonance age of 0 1 0 4 ma obtained from fault gouge and gypsum deposits a four stage sedimentation tectonic evolution model of the northern junggar basin during the late cenozoic can be established based on reconstruction of sedimentary filling processes and cenozoic tectonic movements we suggest that landform evolution and groundwater movement are controlled by active tectonics indicating that late cenozoic tectonic activities may also play important roles in the formation of sandstone type uranium deposits therefore a new metallogenic model for sandstone type uranium deposits is proposed

bed level adjustments in the arno river central italy abstract two distinct phases of bed level adjustment over the last 150 years are identified for the principal alluvial reaches of the arno river upper valdarno and lower valdarno the planimetric configuration of the river in these reaches is the result of a series of hydraulic works canalization rectification artificial cut offs etc carried out particularly between the 18th and the 19th centuries subsequently a series of interventions at basin level construction of weirs variations in land use intense instream gravel mining after world war ii and the construction of two dams on the arno river caused widespread degradation of the streambed since about 1900 total lowering of the channel bed is typically between 2 and 4 m in the upper valdarno reach and between 5 and 8 m in some areas of the lower valdarno reach bed level adjustments with time are analyzed for a large number of cross sections and described by an exponential decay function this analysis identified the existence of two main phases of lowering the first triggered at the end of the past century the second triggered in the interval 1945 1960 and characterized by more intense degradation of the streambed the first phase derived from changes in land use and land management practices the second phase is the result of the superimposition of two factors intense instream mining of gravel and the construction of the levane and la penna dams