the effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate gas reservoirs abstract thermochemical sulfate reduction tsr is a well known process that can lead to sour h2s rich petroleum accumulations most studies of tsr have concentrated upon gas chemistry in this study we have investigated palaeoformation water characteristics in a deep anhydrite bearing dolomite sour gas reservoir of permian age in abu dhabi using fluid inclusion stable isotope petrographic and gas chemical data the data show that low salinity isotopically distinct water was generated within the reservoir by reaction between anhydrite and methane the amount of water added to the reservoir from tsr indicated by reduced fluid inclusion salinity and water 18o values varied systematically with the extent of anhydrite reaction with methane water salinity and isotope data show that the original formation water was diluted by between four and five times by water from tsr thus we have shown that large volumes of very low salinity water were generated within the gas reservoirs during diagenesis following gas emplacement the salinity of formation water in evaporite lithologies is therefore not necessarily high modelling based upon a typical khuff gas reservoir rock volume suggests that initial formation water volumes can only be increased by about three times as a result of tsr the extreme local dilution shown by the water salinity and 18o data must therefore reflect transiently imperfect mixing between tsr water and original formation water the creation of large volumes of water has important implications for the mechanism and rate of thermochemical sulphate reduction and the interpretation of gas volumes using petrophysical logging tools

new absolute time scale for the quaternary climate in the chinese loess region by grain size analysis continuous loess sequences in china provide not only information for paleoclimatic reconstructions but also permit the establishment of a reliable absolute time scale for the quaternary an empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short well dated reference section step 1 this relationship is extrapolated to the complete quaternary section step 2 after derivation of the sedimentation rate by measuring the grain size in all the layers of the sequence the duration of deposition of each layer is obtained by dividing thickness by sedimentation rate and subsequently the age of each point in the sequence is calculated by adding together all the duration values of the overlying layers the chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them

gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

geochemical identification of marine and terrigenous condensates a case study from the sichuan basin sw china abstract condensates are extensively produced from the marine lower permian maokou formation and the lower triassic jialingjiang formation the main marine condensate producing strata in southern sichuan basin and also in the terrigenous upper triassic xujiahe formation in the central and southern sichuan basin based on the analyses of light hydrocarbons biomarkers and stable carbon isotopic compositions of marine and terrigenous condensates and the light hydrocarbon composition of natural gases in the jialingjiang fm and xujiahe fm in the sichuan basin the following conclusions are drawn a condensates produced from the carbonate reservoirs of jialingjiang fm and the maokou fm marine condensates belong to a single oil family and the condensates from the terrigenous xujiahe fm terrigenous condensates belong to another family b marine condensates were generated from sapropelic organic matter in the late stage of high maturation and the biomarker composition indicates that they were derived from the lower silurian shale and the lower permian carbonate while the terrigenous condensates were generated from mature humic source rocks c most of the marine condensates and gases encountered in the lower permian maokou fm and lower triassic jialingjiang fm were generated from the same source and a few of the gases in the jialingjiang fm contain admixtures of coal derived gas while terrigenous condensates and gases were generated from the xujiahe fm humic source rocks d effects that could be related to evaporative migration and biodegradation are not evident in the examined condensates

migration induced compositional changes in oils and condensates of a single field thirty one oils and condensates from the vermilion 39 field offshore louisiana u s gulf coast are examined using techniques of elemental isotopic and molecular geochemistry in an effort to determine the causes of compositional differences among them compositional variability in elemental concentration carbon isotope ratios and molecular distributions suggests that at least two sub groups occur in the sample set the sub groups are characterized by differences in n c 15 content relative to n c 15 pristane phytane ratio 13 c sulfur and nitrogen concentration and s n ratio although the separation into these two sub groups is superficially indicative of distinct sources and or variable levels of thermal maturity interpretation of the data set as a whole indicates that source influences maturity differences and biodegradation do not control observed variations in composition reliable source e g r c 27 29 sterane distribution and maturity e g 20s 20s 20r parameters provide clear evidence of a common source and constant maturity level for all 31 oils condensates the remaining geochemical differences including various molecular pristane phytane isotopic 13 c oil and elemental s n parameters correlate with the extent of migration fractionation that each sample has undergone as measured by the relative amount of n c 15 in each sample the migration fractionation process in the vermilion 39 field is facilitated by fault initiated pressure releases within reservoirs that originally contained full range crudes vertical migration of the released saturated hydrocarbon gases has led to a concentration of lighter components in the most fractionated samples this geochemical interpretation is supported by geologic data inasmuch as the extent of fractionation is least in the deepest samples and greatest in the shallowest samples the results presented here indicate the potential for misinterpretation of geochemical parameters previously considered to be influenced solely by source influence or thermal maturity

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

imprint of the north american plate in siberia revealed by gps 1 gps observations in east siberia combined with global observations collected 1995 2002 place constraints on the geometry and motions of the eurasian north american and pacific plates in east asia by comparing velocities relative to eurasia and to north america we conclude that east siberia to the east of the cherskiy range belongs to the north american plate hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity smaller plates in east asia such as okhotsk and amurian can neither be resolved nor excluded by the gps velocities

crustal deformation rates in central and eastern u s inferred from gps analysis of continuous gps observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern united states suggests that the area is generally stable seven of the 62 stations show anomalous velocities but there is reason to suspect their monument stability assuming the remaining 55 stations are stable with respect to interior north america we have found the north america itrf97 euler vector 1 88 1 04 n 77 67 0 39 w 0 201 0 004 myr 1 that minimizes the rms station velocity referred to fixed north america all of these velocities are less than 3 2 mm yr 1 motion of several stations suggests the mississippi embayment may be moving southward away from the rest of the continent at a rate of 1 7 0 9 mm yr 1 the motion of the embayment produces a large gradient in velocity which in turn implies the highest seismic moment accumulation rate that we found although the highest rate is only marginally significant the fact that it occurs near new madrid where earthquake risk is thought to be high argues that the anomaly may be real nevertheless the identification of the anomaly remains tentative

rifting process of the xihu depression east china sea basin abstract having a maximum depositional depth up to 15 km the ne trending xihu depression is evolved from a deep paleogene continental margin rifting along the present day east china sea continental shelf in this paper we use deep seismic reflection well logging and gravity data to synthesize early rifting process of the depression to study the regional tectonic subsidence history we developed a computer program that performs backstripping and simultaneous inversion for stretching factor initial lithospheric thickness and incipient age of thermal subsidence tectonic subsidence analyses of 40 industrial wells reveal nonuniform stretching preferential crustal extension along the depocenter but preferential mantle extension at the western flank uniform extension may have occurred only somewhere between the central inversion zone and the western margin in the early rifting stage subdued initial subsidence or initial uplift is observed on several wells near the western margin due possibly to flexural isostatic balance the initial mechanical lithospheric thicknesses from subsidence inversion seem to vary from about 55 km to almost 130 km suggesting significant longitudinal segmentation as well as transverse variation in the prerifting lithosphere it is likely that the southern part of the xihu depression was developed initially on a region of relatively thin lithosphere a statement conformable to geological evidences nw se trending deep seismic profiling clearly reveals the deep basement structure of the depression as well as the synrift and postrift sedimentary packages separated by a breakup unconformity crustal layer thicknesses are independently estimated from gravity modeling inversion tectonic subsidence analyses and deep seismic profiling respectively these methods all arrive at very small present day thicknesses of the crustal layer beneath the depocenter of the xihu depression

chernobyl fallout and radionuclide activity in bottom sediments at the river adige estuary northern adriatic sea italy the artificial radionuclides 137cs 134cs and 106ru have been determined up to 16 cm deep in two sediment cores collected in march 1988 at the river adige estuary in the northern adriatic sea interdependent relations between the properties of the sediment levels and the activity of radionuclides have been investigated using multivariate statistical analysis the interactions between radiocontaminants and the particulate matter or water phase are discussed during their transfer processes from the river to the estuary and the marine environment diffusion phenomena within the sedimentary column have also been considered the vertical distribution of the artificial radionuclides due to chemobyl fallout in sediment cores from the river adige mouth compared to those from similar estuarine environments in the adriatic sea point out a general rapid accumulation of river borne solid material in coastal zones of the north adriatic sea

an investigation of the in reservoir conversion of oil to gas compositional and kinetic findings from closed system programmed temperature pyrolysis abstract the thermal alteration of reservoired petroleum upon burial was simulated by closed system non isothermal pyrolysis samples of a medium gravity oil from the norwegian north sea central graben were pyrolysed in microscale sealed glass or quartz vessels at heating rates of 0 1 0 7 and 5 0 k min 1 up to temperatures varying from 300 to 650 c the composition of the oil and gas in each vessel was determined by a single step on line gas chromatographic analysis with increasing rate of heating the onset of all oil degradation reactions was shifted to higher temperatures the same successive compositional changes occurred in each case increase in the total yield of gc detectable compounds significant gas c1 c4 generation accompanied by a decrease in yield of heavy components aromatisation and attainment of maximum gas yield and finally a cracking of the c2 gas components the stable final mixture consisted of methane aromatic hydrocarbons pyrobitumen and possibly hydrogen kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal mol assigning 35 of the total gas potential 460 mg per g of oil to an energy of 66 kcal mol and 29 to 67 kcal mol pre exponential factor 1 1 1016 s 1 by extrapolation to natural maturation conditions the onset of gas generation is predicted to occur between 160 and 190 c for geological heating rates between 0 53 and 5 3 k ma 1 predictions from the model are in accordance with the observed preservation of liquid hydrocarbons in a deep hot 165 c petroleum reservoir from the saga 2 4 14 well norwegian continental shelf

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

an assessment of analytical techniques for the size analysis of fine grained sediments abstract an evaluation of techniques for the size analysis of fine grained sediments revealed that the malvern laser sizer e3600 electrozone particle counter model 112 micromeritics sedigraph 5000e and hydrophotometer work well for the analysis of sorted silt differences in results may be attributed to the particle property being measured by each instrument the malvern laser sizer and electrozone particle counter are sizing techniques the hydrophotometer and sedigraph determine sedimentation diameter through particle settling there was less agreement among these instruments for unsorted natural sediments containing greater than 15 percent clay by weight clay content of less than or equal to 8 percent does not appear to decrease the resolution of silt sized particles

chemical changes of fluid inclusion oil trapped during the evolution of an oil reservoir jabiru 1a case study timor sea australia abstract this study of the jabiru oil field timor sea australia shows how the variability of visual properties of fluid inclusions in palaeo oil zones can be mapped to identify internal structures that result from fluid interactions in the reservoir variability in the attributes of oil inclusion assemblages oias is greater within an inferred palaeo gas cap zone 1 and current residual zone zone 3 and less within the current oil zone zone 2 in zone 3 where water imbibed a higher proportion of oias with visual white fluorescing oil inclusions correlates with less mono aromatic compounds and a higher abundance of polar compounds determined on a bulk extract of inclusion oil using high performance liquid chromatography hplc the ch 2 ch 3 ratios and water contents determined by fourier transform infrared spectroscopy ft ir are higher in zone 1 where gas drained there is a higher proportion of oias with visual yellow fluorescing oil inclusions and these correlate with low hplc mono aromatic and moderate polar contents and low ft ir ch 2 ch 3 ratios and water contents interpretation of the grains with oil inclusions goi and pressure volume temperature composition pvtx fluid inclusion data suggests that a gas saturated blue fluorescing palaeo oil was present in the three zones at the same pressure temperature fluid inclusion forming event pt 1 lighter gas saturated blue fluorescing oil was present in zone 2 but was rarer in zones 1 and 3 at the later fluid inclusion forming event pt 2 the yellow and white inclusion oils trapped in zones 1 and 3 respectively are gas depleted and interpreted to result from the interaction between non movable residual oil around grains with the surrounding gas and water respectively comparison between the pvtx data and the published burial curve suggests that most of the fluid inclusions were trapped during two different hot fluid flow events the full oil column is interpreted to have been present during early mid tertiary the palaeo oil column was reduced during the late miocene by imbibition of water in the present residual zone and drainage of gas at the top of the reservoir

natural gas formation in the western nile delta eastern mediterranean thermogenic versus microbial abstract the offshore part of the nile delta is an emerging gas and condensate province and one of the most promising areas for future petroleum exploration and supply in northern africa while the nile delta s hydrocarbon potential and its geological and stratigraphic pattern has been the focus of numerous studies the origin of its gas has been poorly studied in order to characterize the natural gas and to determine whether microbial or thermogenic processes are the dominant generation pathways of methane a regional geochemical study was performed on 38 test gases collected from 9 neogene western nile delta discoveries main constituents of the gases are methane 89 4 99 4 up to pentane with traces of carbon dioxide and nitrogen methane carbon isotopic composition ranges from 66 0 to 39 6 displaying a mixed microbial and thermogenic character for most of the gases microbial gas contributions range from 15 to 95 the mixed and the more thermogenic gases are frequently accompanied by light oils and condensates 41 59 api calculated maturities of the thermogenic gas proportions suggest source rock maturities between 0 8 and 1 4 ro which are actually present in the pre miocene section evidence for microbial alteration of petroleum accumulations in the nile delta is largely manifested in anomalously heavy isotopic compositions of both wet gas components propane and n butane and preferential removal of higher n alkanes from condensates the hydrocarbon accumulations affected by biodegradation are trapped within shallow pliocene reservoirs

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

geodetic constraints on the rigidity and relative motion of eurasia and north america gps observations in northeastern asia when combined with observations from the global network for the period 1992 1999 yield an angular rotation vector between eurasia and north america consistent with and a factor of two more precise than estimates derived using gps or vlbi data previously available from only western eurasia the new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the nuvel 1a global plate model suggesting a significant change in the relative motion of eurasia and north america over the past 3 myr the standard deviations of horizontal velocities from rigid plate motion for nineteen stations in eurasia and ten in north america are less than 1 mm yr the observations place an upper bound of 2 mm yr at 95 confidence for relative motion between western and eastern eurasia

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

geochemistry of oil in fluid inclusions in a middle proterozoic igneous intrusion implications for the source of hydrocarbons in crystalline rocks abstract the ca 1280 ma dolerite sill within the mesoproterozoic roper group in the roper superbasin australia contains evidence for at least two episodes of hydrocarbon migration represented respectively by solid bitumen with a ketone rich extract and a mixture of a high maturity gas condensate and a lower maturity oil within oil bearing fluid inclusions the ketone isomers are formed by flash pyrolysis of kerogen during the intrusion of the dolerite sill org geochem 21 1994 829 and represent the first and oldest phase of hydrocarbon migration the gas condensate and oil were subsequently trapped as a mixture within fluid inclusions at diagenetic temperatures and pressures of around 110 c and 250 bars significantly after cooling of the sill and likely during the neoproterozoic reactivation of the roper superbasin either 1 these fluids migrated together and mixed in the reservoir or 2 an earlier oil charge was flushed by a later condensate charge and the oil condensate mixture was trapped within single fluid inclusions oil inclusions occur chiefly within albitised zones of labradorite laths within the dolerite matrix and within transcrystalline microfractures cutting vein calcite and rarely vein quartz oil inclusions trapped in the vein calcite are accompanied by hypersaline ca mg brines gas chromatography mass spectrometry of oil extracted from inclusions within the dolerite matrix shows that the oil is non biodegraded and was therefore trapped relatively quickly within the host minerals trace amounts of biomarkers indicate that the inclusion oil is of a biogenic origin and excludes any abiotic processes that are apparent sources of hydrocarbons in many crystalline rocks monomethylalkanes pentacyclic terpanes chiefly comprising hopanes and diahopanes and very low concentrations of steranes and diasteranes indicate input from cyanobacterial organic matter with a minor contribution from eukaryotes the hydrocarbons are likely derived from proterozoic source rocks such as the directly overlying velkerri formation and or the underlying barney creek formation from the mcarthur group the study has implications for the source of hydrocarbons in non sedimentary rocks and suggests that fluid inclusions can be used not only to distinguish between biogenic and abiogenic sources of hydrocarbons but also to provide critical information about the composition of the biomass fluid migration events and conditions under which hydrocarbons in different geological settings are trapped

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

petroleum systems in the offshore xihu basin on the continental shelf of the east china sea xihu basin is one of the cenozoic sedimentary basins within the continental shelf of the east china sea within which eight oil and gas fields and four hydrocarbon bearing structures have been found our systematic analysis of potential petroleum systems in the basin has identified the eocene pinghu formation as the most important source rock in the basin the eocene pinghu formation consists of mudstone and coal deposited in an embayment and tidal flat environment and is characterized as containing type iii kerogen the pinghu formation is mature and at the present time is within the oil and wet gas windows with determined vitrinite reflectance values in the range of 0 55 2 2 measured vitrinite reflectance rom modeling results suggest that the main stage of hydrocarbon expulsion occurred during the miocene the main reservoir consists of fine grained sandstones of the huagang and pinghu formations deposited within shallow lacustrine and estuarine environments the measured porosity from core samples of reservoir rock ranges from 10 to 35 whereas permeability values range from 1 to 4000 md both porosity and permeability decrease with depth the mudstones of the upper huagang and longjing formations also occur as regional seals which developed overpressure zones as determined by two way sonic transit times the overburden includes all the oligocene miocene pliocene and quaternary strata the hydrocarbon traps in the basin are mainly structural traps including faulted blocks faulted structural noses and anticlines most traps were developed at the ends of the eocene or oligocene hydrocarbons produced from the xihu basin are predominantly natural gases with minor amounts of crude oil the crude oil in the basin is characterized by a low density low sulfur low wax low vanadium nickel ratio a low resin and asphaltene content and a high proportion of saturated hydrocarbons the natural gas in the basin is composed predominantly of methane with an average c1 c1 5 ratio of 0 89 and a c1 c2 5 ratio of 8 6 two petroleum systems have been identified in the basin the known pinghu huagang and the hypothetical huagang huagang systems the pinghu huagang is the major petroleum system and most important for oil and natural gas exploration in the basin

fluid inclusions and pvtx modelling examples from the garn formation in well 6507 2 2 haltenbanken mid norway abstract fluid inclusions study and multi techniques quantitative analyses have been coupled to reconstitute pvtx conditions of aqueous and petroleum fluid entrapment of a local haltenbanken area well 6507 2 2 from the garn formation unusual low temperature behaviour showing the liquid portion separating into two liquids has been described this behaviour is typical of a gas condensate volatile mixture with high methane content and heavy alkanes the variable liquid vapour ratio compositions and morphologies of all petroleum inclusions can be interpreted as a result of a combination of heterogeneous trapping and necking down thus all petroleum inclusions can be related to a single petroleum source three main episodes of fluid entrapment can be distinguished the first one corresponds to the water trapped within detrital quartz microfractures at around 50 c and 50 bar the second to the petroleum fluid arrival in the biphase field of a critical system around 100 120 c and 190 230 bar the third one to the main trapping of present day petroleum inclusions during the recrystallisation of quartz cements around 110 160 c and 230 280 bar within the last few million years of a short and relatively rapid burial

global positioning system measurements from eastern tibet and their implications for india eurasia intercontinental deformation we present and interpret global positioning system gps measurements of crustal motions for the period 1991 1998 for a network encompassing the eastern part of the tibetan plateau and its foreland relative to a eurasian frame defined by minimizing the velocities of 16 gps stations in europe central asia and siberia stations within all parts of the plateau foreland in south china move 6 10 mm yr east southeast indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland north of the plateau foreland stations move northeastward at 10 mm yr indicating that the northern boundary of the deformation zone lies north of the plateau with this realization of a eurasian frame the velocity of the gps station at bangalore in southern india implies that the northward motion of india is 5 12 mm yr slower than that predicted from the nuvel 1a plate reconstruction viewed relative to the south china block stations of the northeast plateau bounded on the north by the qilian shan and the altyn tagh fault move nne to ne with velocities ranging from 19 mm yr within the plateau to 5 11 mm yr in its foreland the altyn tagh fault shows left lateral slip of 10 mm yr at 95 e and shortening across the fault of 5 mm yr stations south and west of the xianshuihe xiaojiang fault system define a crustal fragment rotating clockwise at 10 mm yr relative to the south china block around the eastern himalayan syntaxis the gps measurements indicate no significant shortening 3 mm yr within the longmen shan of the central eastern plateau and its adjacent foreland although the longmen shan rise over 6 km in 100 km horizontal distance geological studies indicate that the deformational field was established diachronously in late miocene to pliocene time was characterized by no east west shortening of tibetan crust and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes

geochemical characteristics of tertiary coal bearing source rocks in xihu depression east china sea basin abstract this study aims at investigating hydrocarbon generation potential and biological organic source for the tertiary coal bearing source rocks of pinghu formation middle upper eocene in xihu depression east china sea shelf basin another goal is to differentiate coal and mudstone with respect to their geochemical properties the coal bearing sequence has a variable organofacies and is mainly gas prone the coals and carbonaceous mudstones in comparison with mudstones have a higher liquid hydrocarbon generation potential as reflected by evidently higher hi values averaging 286 mg hc g c and h c atomic ratios round 0 9 the molecular composition in the coal bearing sequence is commonly characterized by unusually abundant diterpenoid alkanes dominant c29 sterane over c27 and c28 homologues and high amount of terrigenous related aromatic biomarkers such as retene cadalene and 1 7 dimethylphenanthrene indicating a predominantly terrigenous organic source the source rocks show high pr ph ratios ranging mostly from 3 5 to 8 5 and low mdbts mdbfs ratios

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

stream scanning laser system electric sensing counter and settling grain size analysis a comparison using reference materials and marine sediments abstract surface and deep sea core sediments and two sets of standards were measured by three different techniques galai cis 1 laser system coulter counter ta ii and micromeritics sedigraph 5000d in order to compare the galai results with the other two the differences between the three types of measuring device turned out to be greater in sediments than in standards and were attributed to the physical properties shape density and composition of the particles complexity of the matrix comparison of moment statistics showed that the galai determines coarser grain sizes than the coulter and finer than the sedigraph particularly as regards analysis of surface sediments the relationships between galai and sedigraph were estimated using analysis of variation residuals within individual intervals the analysis showed a higher variability of residuals for the coarser fractions 8 16 m and 16 32 m with respect to the finer 2 4 m and 4 8 m fractions the

initial results from wing the continuous gps network in the western pacific area to investigate tectonic deformation in the western pacific a continuous gps tracking network has been established and named the western pacific integrated network of gps wing between 1995 and march 1997 we establised ten new sites data for the period july 1995 to october 1996 were analyzed together with data from international gps service for geodynamics igs global sites to estimate daily coordinates a fiducial free approach was used to obtain the most accurate baseline estimates to fix the estimated coordinates to the terrestrial reference frame the tsukuba igs site is assumed to be moving westward relative to the stable eurasian continent at 2 cm yr according to heki s 1996 estimate we find that 1 velocities of sites well within oceanic plates are in good agreement with rigid plate motion models 2 sites close to plate boundaries are all affected by the deformation at those boundaries among which back arc rifting spreading is clearly visible at the mariana and okinawa troughs 3 sites in eastern asia are moving east to east southeast relative to the stable eurasian continent suggesting long distance effects of the northward collision of india with asia

hydrocarbon accumulation processes in the dabei tight gas reservoirs kuqa subbasin tarim basin northwest china the dabei gas field is a recently discovered giant tight gas field in the kuqa subbasin western china the reservoir porosity and permeability mainly range from 1 to 8 and from 0 01 to 1 md respectively the hydrocarbon both gas and light oil accumulation processes in the tight sandstone reservoirs were studied based on detailed reservoir characterization thermal maturity of both gas and light oil hydrocarbon charge history regional tectonic compression and thrusting two episodes of oil and one episode of natural gas charge were delineated in the tight sandstone reservoir as evidenced by 1 similar sources but different maturities for the gas and light oil 2 the presence of abundant bitumen in the tight sandstone reservoir 3 the presence of both hydrocarbon gas inclusions and oil inclusions with two distinct fluorescence colors and 4 the presence of two groups of aqueous inclusions coeval with the petroleum inclusions with contrasting homogenization temperatures and salinities the oil inclusions with the blue white fluorescence color were determined to have been trapped at 5 4 ma whereas the gas charge may have occurred at circa 3 2 ma corresponding to a salinity change recorded in the aqueous inclusions the hydrocarbon accumulation processes appeared to be controlled by the tectonic compression of the south tianshan mountains intense tectonic compression caused thrust fault reactivation which provided pathways for hydrocarbon migration overpressure evolution of the reservoir indicates that an intense tectonic compression began at circa 5 ma which caused thrust activation and concomitant oil charge into the relatively porous part of the reservoir subsequent tectonic compression caused uplift and erosion associated with thrusting at the end of the kuqa formation deposition ca 3 ma with thrust faults and fractures acting as major migration pathways for the gas accumulation in the already tight sandstone reservoir resulting from both compaction and tectonic compression

hydrocarbon migration and accumulation of the suqiao buried hill zone in wen an slope jizhong subbasin bohai bay basin china abstract the hydrocarbon migration and accumulation of the suqiao deep buried hill zone in the jizhong subbasin the bohai bay basin eastern china was investigated from the perspective of paleo fluid evidence by using fluid inclusions quantitative fluorescence techniques qgf total scanning fluorescence method tsf and organic geochemical analysis results show that the current condensate oil gas reservoirs in the study area once were paleo oil reservoirs in addition the reservoirs have experienced at least two stages of hydrocarbon charge from different sources and or maturities during the deposition of the oligocene dongying formation ed the deep ordovician reservoirs were first charged by mature oils sourced from the lacustrine shale source rocks in the fourth member of shahejie and kongdian formations es4 ek and then adjusted at the end of ed period subsequently by virtue of the tectonic movement since the deposition of the neogene minghuazhen formation nm the reservoirs were mainly charged by the gas that consisted of moderate to high maturity condensate and wet gas sourced from the es4 ek lacustrine shale source rocks and mature coal derived gas sourced from the carboniferous permian c p coal bearing source rocks meanwhile the early charged oil was subjected to gas flushing and deasphalting by the late intrusion of gas the widely distributed hydrocarbon inclusions the higher qgf index and foi the frequency of oil inclusions values in both gas oil and water zone are indicative of early oil charge in addition combined with the homogenization temperatures of the fluid inclusions

development of algebra algorithms for automated generation of grain size distribution maps the grain size distribution of sediments is a fundamental characteristic in understanding the earth s surface environments and an essential tool in classifying sedimentary environments grain size data provide important information on the energy and dynamics of depositional environments and aid our understanding of sediment transport ternary diagrams tds are useful and conventional tools to classify sediments on the basis of relative grain size i e gravel sand mud or sand silt clay the development of spatial modelling in a geographical information system gis can assist in treating computing and displaying sedimentological data such as grain sizes in this work four map algebra ma algorithms are written in a gis environment to automatically produce maps depicting the spatial distribution of sediment texture classes based on the most frequently used grain size tds the shepard classification and flemming classification for sand silt clay components and the folk et al classification and blair and mcpherson classification for sand gravel mud components the proposed method allows rapid assessments by producing map distributions of the parameters most widely used in sedimentology copyright 2007 john wiley sons ltd

effect of water washing on crude oil compositions crude oils from venezuela oklahoma and new mexico were water washed in the laboratory at temperatures from room temperature to 80 c and with water salinities from 0 to 300 000 mg l in experiments lasting from 7 to 338 hours the effects of water washing were determined by gas chromatographic and gas chromatography mass spectrometric analysis of the residual oil these experiments show that water washing is particularly effective for the c15 fraction and hydrocarbons are removed in the sequence aromatics then n alkanes then naphthenes in the c15 fraction no loss of pristane phytane steranes or terpanes occurs but some aromatics and sulfur compounds especially dibenzothiophene are depleted although water washing reduces api gravity water washing is unlikely to produce tar layers the effects of water washing were simulated with a numerical model based on the equation of diffusion predicted oil water ratios were in good agreement with the experimental values for the light ends and the model suggests that water washing is very fast in the subsurface comparison of oils that appeared to have been water washed in nature with the equivalent unwashed oils showed the expected compositional trends water washing is probably the dominant process affecting crude oil composition in the subsurface when water flows past oils under conditions where bacterial degradation is precluded by temperature 80 c or by lack of dissolved oxygen and the temperatures are too low for thermal cracking

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

the 2000 mw 6 8 uglegorsk earthquake and regional plate boundary deformation of sakhalin from geodetic data 1 interseismic gps velocities in sakhalin indicate that the island moves to the west at 3 4 mm yr with respect to the eurasian plate which is about half of the relative eurasia north america plate convergence rate gps measurements across the central sakhalin fault system provide evidence of compressive and strike slip strain accumulation at a rate 3 mm yr coseismic vertical displacements produced by the august 4 2000 mw 6 8 uglegorsk earthquake in sakhalin were analyzed by constrained nonlinear inversion which provided evidence for a reverse faulting mechanism on an east dipping fault plane

genetic origin of gas condensate in permian and triassic strata in the southern sichuan basin sw china abstract gas condensate is produced from permian and triassic marine strata in the southern sichuan basin where the lower triassic jialingjiang formation is one of the major gas condensate reservoirs condensate gas pools are mainly distributed laterally in the core area and the flank of the luzhou paleo uplift abundant reservoir bitumen and high goi grains containing oil inclusions total grains 100 values have been found in the permian maokou formation and the triassic jialingjiang formation which indicate that both formations once hosted oil accumulations very high methyldiamantane contents and gas to oil ratios gor were found in the condensate pools and the carbon isotopic values of the saturates and the whole condensates both become increasingly enriched from the core area to the flank of the luzhou paleo uplift these lines of evidence indicate that the condensates were generated by intensive oil cracking oil reservoirs in the jialingjiang formation were destroyed in the middle triassic period by uplift and erosion the maokou formation was buried to greater depths and oil reservoirs in it experienced intensive oil cracking in the middle jurassic and later cretaceous periods these oils were transformed into gas condensates much of the gas condensate in the maokou formation migrated upward along the faults and accumulated in the jialingjiang formation reservoirs during the himalayan period 65 0 ma

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

geodynamics of the baikal rift zone and plate tectonics of asia the baikal rift zone stretches from the southern termination of lake baikal as far as 118 e and includes the baikal basin and the barguzin upper angara and muysk grabens that form its easterly continuation coincident with the rift zone is a narrow seismic belt which extends further east along the stanovoy range to the okhotsk sea this belt can be considered as the boundary between the eurasian and amurian lithospheric plates earthquake focal mechanism solutions that show a consistent orientation of extensional axes across the strike of the rift zone indicate the behaviour of the eurasian and amurian plates as rigid bodies from 83 focal mechanism solutions the pole of rotation of the eurasian and amurian plates was computed to lie at the point 56 95n 117 45e the angular rate estimated from the amount of baikal opening is about 1 10 7 deg year the position of the pole at the eastern termination of the rift zone accounts for the dying out of the rift zone and for the appearance east of the pole of compressive structures in the stanovoy range to the southwest the baikal rift zone is replaced by the mosaic of microplates in central asia that occupy the space between the eurasian and indian lithospheric plates prominent are the mongolian dzungarian alashan tarim tibetan and pamir microplates earthquakes in central asia are dispersed although higher concentrations of earthquakes associated with microplate boundaries are prominent the tectonics of central asia are considered to be due to the interaction of rigid microplates assuming that plastic deformations occur within the relatively wide zones along the microplate boundaries by considering the strike slip faults to define the trajectories of microplate motions the parameters of relative movements of the microplates have been computed the microplate mosaic of central asia is moving northeasterly as a result of the collision and continued convergence of india and eurasia the mosaic acts as a wedge splitting off the amurian plate from eurasia causing it to rotate counterclockwise so opening the baikal rift

are post seismic effects of the m 8 4 bolnay earthquake 1905 july 23 still influencing gps velocities in the mongolia baikal area summary gps measurement campaigns in the mongolia baikal area show that 1 the baikal rift zone is currently opening at 4 5 mm yr 1 in a nw se direction and 2 the western part of the amurian north china block is moving eastward relative to eurasia at 5 7 mm yr 1 these results are consistent with recent geodetic studies in asia and indicate that crustal motions in mongolia and north china derived from geodetic measurements are significantly faster than those proposed by most deformation models of asia using a numerical model we test whether post seismic deformation caused by viscoelastic relaxation in the lower crust following the tsetserleg bolnay earthquake sequence mw 7 9 and 8 4 1905 july can explain this discrepancy we find that surface velocities at the gps sites presented here for the 1997 2000 time period can reach 4 mm yr 1 depending on the earthquake source parameters and the rheology used in the models using a model based on our best current knowledge of lithospheric structure and rheology in the mongolia baikal area we find that the contribution of post seismic effects to the gps velocities presented here is less than 2 mm yr 1 for the mongolian sites and less than 1 mm yr 1 for the baikal sites we therefore conclude that the post seismic effects of the mw 8 4 1905 bolnay earthquake cannot explain why the gps derived crustal motions in mongolia and the baikal rift zone are significantly larger than those proposed by deformation models of asia this discrepancy must therefore be sought in processes not accounted for in most of these deformation models such as the farfield contribution of the pacific subduction zones and or the effect of gravitational forces on intracontinental deformation

strain response and re equilibration of ch4 rich synthetic aqueous fluid inclusions in calcite during pressure drops abstract aqueous fluids in sedimentary basins often contain dissolved methane particularly in petroleum environments pvtx pressure volume temperature composition reconstructions performed using fluid inclusion data are largely based on the assumption that inclusions do not change from the time of trapping until the present many authors however consider that fluid inclusions can re equilibrate particularly in fragile minerals like calcite in order to understand this re equilibration phenomenon in the metamorphic domain previous experiments have been performed under high pt conditions but few have been performed at low to medium pt conditions such as those associated with sedimentary burial diagenesis and no previous studies have examined ch 4 bearing aqueous inclusions in calcite an experimental study of the preservation modification of ch 4 rich synthetic fluid inclusions in calcite during isothermal decompression was conducted an autoclave was used for accurate ptx control allowing equilibrium between liquid and vapour in the ch 4 h 2 o system ptx conditions were maintained at four stages of decreasing pressure with each stage held for 7 days to simulate an isothermal pressure drop in order of decreasing pressure the pressure temperature conditions monitored were 276 10 bar at 180 7 c 176 10 bar at 180 7 c 76 10 bar at 180 7 c and 10 3 bar at 180 15 c at the end of the experiment the calcite was recovered and analyzed by microthermometry and raman microspectroscopy for ptx reconstruction a careful procedure was adopted to limit re equilibration of inclusions during analytical procedures four types of inclusion shapes and four types of strain patterns were differentiated classification of the petrographic strain patterns was carried out these strain patterns were associated with inclusion stretching and or leakage regarding ch 4 t h and p h compared to experimental conditions factors controlling the preservation or acquisition of strain patterns included the initial shape and size of the inclusion and the pressure differential p between the confining pressure p cf and the internal pressure p i within the inclusion most fluid inclusions seemed to be trapped during the first 7 days of the experiment although few 4 of these preserved the initial pt conditions of 276 10 bar whereas 8 preserved the second and third run of pt conditions overall the majority of inclusions 88 did not reflect accurately the ptx trapping conditions a petrographic guide to the inclusions is presented here that allows strain identification for pvt reconstructions re equilibration patterns and evidence for preferential methane leakage from aqueous inclusions in calcite are important findings revealed by this study and may be useful for the reconstruction of post trapping events in investigations of natural samples and in other experiments using synthetic inclusions in calcite

aspects of petroleum basin evolution due to gas advection and evaporative fractionation abstract criteria are proposed for the recognition of depletion by evaporative fractionation in reservoir fluid analyses pvt data the characteristics of original as generated molar concentration profiles of marine oils are postulated oils derived from clastic or carbonate sediments bearing respectively type ii or iis kerogens in unaltered marine oils two decreasing exponential concentration series occur separated by a discontinuity between p5 the 5 carbon pseudo component and p6 such that p6 exceeds p5 rendering the profile abruptly bimodal a suite of 195 detailed pvt analyses c1 to p30 of reservoir fluid oils shows that concentrations in the p6 fraction are frequently perturbed the maximum migrating to p7 p8 or a higher carbon number alteration attributable to additive gas advection followed by evaporative fractionation in the subject oils four variables are adduced which track these changes c1 c2 p4 p8 e3 a light gas liquid heavy end ratio and e7 a gasoline range heavy end ratio increase in c1 c2 is accompanied by decreasing values of p4 p8 for which there is no a priori rationale other than the precepts of evaporative fractionation involving the advection of highly mature dry gas dividing a suite of 535 pvt analyses detailed analyses plus 340 analyzed to p7 of world wide provenance into seven subsets on the basis of c1 c2 ratios a well defined separate regression of gas oil ratio on saturation pressure is revealed in each subset such correlations depend primarily upon the processes involved in evaporative fractionation the curves embrace the full commonly encountered range of combinations of gas oil ratio and saturation pressure both of which correlate poorly with level of maturity expressed in a liquid fraction slope factor these observations lead to the hypothesis that progressive evaporative fractionation is a widespread if not universal evolutionary process in petroleum basins

gas washing of oil along a regional transect offshore louisiana abstract gas chromatogram data for 219 oils in a 190 km n s transect offshore louisiana reveal a spatially coherent pattern of compositional change which is caused by gas washing near the louisiana shoreline as much as 91 of the original n alkanes have been removed from the oils the maximum intensity of depletion decreases southward in a nearly regular fashion to nil at the jolliet field 190 km offshore the oils show a parallel change in the maximum carbon number of the removed n alkanes implying that the pressure at which gas washing took place also decreased in the offshore direction the systematic change in maximum extent of depletion crosscuts tectonostratigraphic boundaries as well as oil source provinces models of gas washing suggest that the maximum depth of washing reflects the distribution of deeply buried continuous sands suggesting deep sands may have provided sites for efficient gas oil interaction

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

natural gas washing induces condensate formation from coal measures in the pinghu slope belt of the xihu depression east china sea basin insights from fluid inclusion geochemistry and rock gold tube pyrolysis abstract a systematic study into the origin and potential formation processes of condensates in the pinghu slope belt of the xihu depression east china sea basin was conducted using fluid inclusion analysis petroleum geochemistry and rock gold tube pyrolysis grains containing oil inclusions goi technique well logging and formation testing together indicate that the present day gas condensate layer has evolved from a paleo oil layer biomarkers from oil inclusions indicate that these paleo oils were generated from coal measures at a moderate maturity level based on organic macerals elemental ratios of kerogens rock eval pyrolysis and results from gold tube pyrolysis experiments the coal measures are evaluated as source rocks prone to gas generation and capable of oil formation at moderate levels of maturity this maturity level coincides with present day condensate maturities determined from a series of molecular maturity ratios vitrinite reflectance 0 7 1 0 ro biomarkers related to specific sources suggest that the condensates are also coal derived these observations suggest that the condensates are derived from secondary alteration following paleo oil accumulation rather than being related to the thermal degradation of resin rich organic matter at a low maturity level or the thermal cracking of kerogen at a high maturity level some condensates are characterized by a significant loss of n alkanes with low carbon numbers and relatively high toluene n heptane tol nc7 ratios this indicates that the paleo oil reservoirs have been subjected to varying degrees of gas washing which resulted in condensate formation as opposed to the process of oil cracking under high temperatures subsequent interactions between gas and paleo oils resulted in oil inclusions showing fluorescence varying from near yellow to blue variable vapor volume fractions measured in the same oil assemblage are the result of two phase trapping of oil and gas the widely observed presence of bitumen asphaltene in the reservoir pores and bitumen bearing oil inclusions is considered to be due to gas deasphalting homogenization temperatures th of associated aqueous inclusions and burial thermal curves suggest that the initial paleo oil reservoirs formed in the late miocene excess gas composed of local mature gas and heterochthonous high to over mature gas migrated into the paleo oil reservoirs later in the quaternary this process not only resulted in the formation of condensates but also led to vertical differentiation of density and wax content in the reservoirs

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

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

geochemical comparison of oil bearing fluid inclusions and produced oil from the toro sandstone papua new guinea abstract a detailed study was carried out to compare the geochemistry of the crude oil in the lower cretaceous toro sandstone reservoir in the iagifu 7x well with oil trapped in fluid inclusions in this sandstone in the iagifu 7x and p nyang 2x wells in the papuan fold belt the drill stem test dst oils and the oils trapped in fluid inclusions show different source and maturity dependent geochemical parameters biomarkers suggest that the dst oils at iagifu 7x were derived from clay rich mixed marine terrestrial source rocks deposited under oxic conditions probably middle to late jurassic mudstones the fluid inclusion oils were derived from a less terrestrially influenced marine source rock deposited under less oxic conditions the fluid inclusion oils contain 1 2 7 trimethylnaphthalene and oleanane biomarkers indicative of angiosperm input and a cretaceous or younger source rock these oils are more mature calculated reflectance rc 1 02 than the reservoired oil at iagifu 7x rc 0 84 and condensate at p nyang 2x rc 0 84 source and thermal maturity parameters for all three fluid inclusion samples are similar suggesting that they were derived from similar source rock facies furthermore samples with predominantly blue vs white fluorescing oil inclusions have no discernible geochemical maturity difference suggesting that the use of fluorescence colours as a qualitative guide to the maturity of the trapped oil is not valid in this case fluid inclusion oils were trapped prior to charge of the reservoir with oil at the iagifu 7x and gas condensate at the p nyang 2x wells the fluid inclusion oils therefore represent an early oil charge from a deeply buried probably cretaceous source rock which started migrating into the toro sandstone during the miocene at iagifu this early oil was probably diluted by a larger volume of jurassic oil generated at the end of the miocene the absence of fluid inclusions with compositions like the currently reservoired oil is interpreted to be due to oil charging an already oil saturated zone when diagenesis is likely to have been inhibited at the p nyang well the transition from oil as represented by the oil inclusions to gas condensate was most likely caused by gas displacement