organic geochemistry of oils and condensates in the kekeya field southwest depression of the tarim basin china this study shows that the oils and condensates in the kekeya field in the tarim basin nw china belong to a single family most likely derived from marine shale source rocks deposited under oxic suboxic conditions with mixed terrigenous and algal bacterial organic inputs the maturity data clearly indicate that the paraffinic condensates were not formed by thermal cracking of oil during late catagenesis ro 1 2 both the oils and condensates were generated within the normal oil window whereas addition of gaseous hydrocarbons from a separate source resulted in migration fractionation and hence spuriously high heptane indices age specific biomarkers show that the oils and condensates were not generated from the mesozoic cenozoic strata but from the carboniferous permian sections 1d basin modeling results are consistent with this interpretation suggesting that the mesozoic eocene strata are currently immature with respect to hydrocarbon generation and expulsion deep seated faults may have provided routes for upward fluid migration at the time of active deformation during several pulses of the himalayan orogeny the favored targets for further petroleum exploration in front of the kunlun mountains include the deep structures within the carboniferous permian strata for indigenous petroleum accumulations and anticlines and stratigraphic traps within the mesozoic cenozoic sections that are cut by deep seated thrust faults where secondary petroleum accumulations most likely occurred

low frequency vibroseis data with maximum displacement sweeps several recent advances in land seismic acquisition equipment and processing algorithms have encouraged exploration geophysicists to reconsider the potential benefits of energetic low frequencies for geophysical applications imaging beneath high velocity and highly absorbing formations deep imaging acoustic impedance inversion velocity model estimation in geophysically complex areas and inversion of surface waves to characterize near surface elastic properties

permian sedimentary tuff tight reservoirs in the santanghu basin nw china abstract sedimentary tuffs comprise important tight oil reservoirs in the middle permian tiaohu formation in the santanghu basin this paper describes three research advances made on these reservoirs 1 there are many sets of sedimentary tuff in the second member of the tiaohu formation and they are the sweet section for tight oil exploration vitric crystal vitric and argillaceous tuffs are the main reservoir types of which the first two are more favorable 2 a model was established to show how the volcanic edifice controls the type and distribution of the volcanic lacustrine tuff deposition the crystal vitric tuff is distributed in the lacustrine deposits nearest to the volcanic crater and the vitric tuff is distributed on both sides of the active volcanic belt a certain distance from the crater and this is the most favorable distribution area for sedimentary tuff later devitrification resulted in formation of a large number of micro pores and this is the main reason for the presence of favorable reservoirs 3 the sedimentary tuff reservoir has undergone successive geological processes from formation of secondary dissolution pores then hydrocarbon charge and accumulation to compaction the tight oil accumulation is the result of the coupling of the diagenetic evolution of the tuff in the tiaohu formation and the hydrocarbon generation and charging from the shale in the lucaogou formation

oil and gas developments in western canada in 1989 there were 5513 wells drilled in western canada during 1989 30 fewer than in 1988 total meterage drilled was 6 459 797 m for an average well depth of 1172 m exploratory drilling in 1989 dropped by 13 and development drilling by 40 from 1988 levels british columbia was the only area in western canada with increased activity the industry continued to acquire more acreage for less total bonus at provincial crown sales throughout western canada during 1989 3 564 827 ha were acquired for a total bonus of 484 872 000 footnote 5 although the total disposition of crown lands decreased only 4 the average bonus dropped to 136 ha down 26 from 1988 in alberta the most active exploration areas were the southern and eastern mesozoic gas play the western deep devonian gas play the oil plays on and adjacent to the peace river arch and the middle devonian carbonate oil plays in the northwest in british columbia the most active exploration areas were the mesozoic and paleozoic gas plays in the northeastern portion of the province for the first time in 5 years crown drilling rights were issued within the fraser valley in the southwest there was a focus on gas exploration in the province as pipeline reversal was implemented permitting access to canadian and california markets through the alberta transportation network in manitoba exploration and development activity continued to decline in northern canada exploratory drilling success offering of crown lands for exploration approval of gas exports and indications that many of the native lands claims may be approaching settlement all provided exploration encouragement for the next decade exploration activities occurred throughout the northwest territories from the offshore beaufort to the southern border in saskatchewan active exploration areas were shallow mesozoic gas plays in the western portions of the province and deep paleozoic oil plays in the south

harmonic distortion reduction on seismic vibrators to improve seismic resolution using vibroseis vibrators must output the ground force energy with minimum harmonic distortion four main sources within the vibrator system cause the ground force to suffer severe harmonic distortion the nonlinear servo valve flow pressure character istics the servo valve characteristics near null the fluctuations in the hydraulic pressure and the nonlinear contact stiffness between the baseplate and the ground modeling was undertaken to investigate and quantify harmonic distortion from each source as a result three modifications have been made to reduce the harmonic distortion of the ground force

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

hydrocarbon filling and leakage history of a deep geopressured sandstone fulmar formation united kingdom north sea diagenetic minerals in a water filled borehole from the jurassic fulmar formation united kingdom central north sea record two phases of hydrocarbon filling and emptying initial oil charge was during the late cretaceous at shallow burial depths of about 1 5 km 0 9 mi as we consider that hydrocarbon has preserved porosity during burial this has implications for the understanding of the porosity evolution of the fulmar formation which in other locations is an important hydrocarbon reservoir the early oil charge as recorded by illite k ar ages progressively filled the structure from 84 to 59 ma and possibly precipitated bitumen because of biodegradation the first oil predated many of the burial diagenetic reactions within the sandstone after leak off at ca 60 ma diagenetic reactions continued in an open geochemical system with possible import of co2 products of these reactions include ankerite and quartz overgrowth cements hydrocarbon staining postdates these phases and provides evidence of a hydrocarbon charge probably gas condensate the second hydrocarbon charge also leaked off and the sandstone is now water bearing previous work on the fulmar formation has incorrectly placed all the diagenetic reactions as predating the first arrival of hydrocarbon the present day pore fluids are high salinity high 18o fluids derived from the underlying permian zechstein evaporates these fluids entered the reservoir during a phase of overpressure release that caused fracturing of the framework quartz grains possibly coincident with the second phase of hydrocarbon leak off at 2 5 ma mark wilkinson studied sandstone hosted calcite concretions for his ph d and has subsequently tried to take a more holistic view of the diagenesis of sedimentary basins his career has been funded by a variety of oil companies although he is currently involved in geological disposal of some of the co2 that he was partly responsible for producing stuart haszeldine is a professor at edinburgh university he received his ph d on clastic and coal sedimentology in 1981 from the university of strathclyde after an attempted reeducation in the oil industry he has collaborated with many companies to research on hydrocarbon reservoir quality radioactive waste disposal and coal resources he currently heads the united kingdom s largest group investigating carbon dioxide sequestration tony fallick was educated at the university of glasgow scotland in physics b sc and chemistry ph d he did research at mcmaster university ontario canada and cambridge england before moving in 1980 to the scottish universities research and reactor center where he is currently the director

a new possible giant hydrocarbon generated formation the upper triassic source rock in southwestern junggar basin nw china abstract the triassic formation is a possible new giant hydrocarbon generated formation in northwest china and mid asia taking the upper triassic formation in the sikeshu sag in junggar basin as an example based on the comprehensive analysis on the geochemical characteristics of the cores and the dark mudstone of the outcrops and reservoir formation conditions we have evaluated the upper triassic source rocks by comparing with those in the ulungu depression and reached the following findings firstly the upper triassic formation is mainly composed of dark mudstone and sandy mudstone deposits and the hydrocarbon source rock is mainly distributed in the middle and upper parts with a thickness range of 100 150 m and area of 3500 km 2 secondly the source rock moderate in organic matter abundance with toc range of 1 3 has the material basis for hydrocarbon generation thirdly the organic matter has high percentage of sapropelinite and is dominated by type ii 2 fourthly the degree of the thermal evolution is moderate and the source rock with r o higher than 0 7 has a distribution area of about 1800 km 2 providing the conditions of massive hydrocarbon generation fifthly the source rock has great burial depth and wide distribution the source rock with a r o of higher than 0 7 and thickness of more than 100 m has an area of around 1400 km 2 implying huge resource potential sixthly the next step exploration should focus on highly mature hydrocarbon generation central area in the upper triassic lower jurassic in the east of the sag to search for and confirm favorable traps the research findings have important reference value for promoting the resource status of deepening the understanding of reservoir formation and clarifying the exploration direction in the sikeshu sag and other periphery mid asia areas

formation distribution and resource potential of the sweet areas sections of continental shale oil in china abstract shale oil refers to oil stored in organic rich shale it is an important part of unconventional oil and provides a large amount of resources based on the systematic study of the geological characteristics of shale oil in china s major continental basins the geological connotation of the sweet area section in shale oil is proposed in this paper and it refers to areas sections that can be preferentially explored and developed in oil bearing shale formations under current economic and technical conditions the formation conditions and distribution characteristics of continental shale oil in china are analyzed with a focus on the geological properties of the triassic yanchang formation in the ordos basin the cretaceous qingshankou formation in the songliao basin and the permian lucaogou formation of the jimusar sag in the junggar basin it is found that the sweet areas of shale oil with medium high maturation are mainly located in thick shales with a ro greater than 0 9 and the sweet sections are mainly located in the middle and lower parts of the shale formation the geological resources of continental shale oil in the major continental basins in china are estimated to be approximately 3700 108 tons the in situ conversion process icp may be a key technology for the effective development of medium to low mature shale oil the scale maximum burial depth and present depth of the organic rich shale are proposed as the three key parameters for the optimization of pilot sites by taking the triassic yanchang formation in the ordos basin as an example using icp it is expected that the recoverable resources of china s continental shale oil will be approximately 400 500 108 tons the terminology of man made reservoir is proposed in this paper in an man made reservoir the overall industrial output of the sweet areas sections is formed by artificial intervention and the construction of an underground fracture network system with man made permeability continental shale oil may be another revolutionary source of unconventional oil and is expected to be first successfully produced in china

lithostratigraphy of the volcanic sequences at hole 917a leg 152 se greenland margin abstract an overall high recovery rate up to 52 and 450 m of continuous logging data of good quality at odp hole 917a leg 152 se greenland margin allow us to refine the petrological descriptions made onboard and to establish a precise lithostratigraphy of the palaeocene volcanic succession changes in the dips of the flow banding between the upper series and the middle and lower series coincide with the transition from continental magmatism to post breakup volcanism established by the geochemistry

seismic vibrator control and the downgoing p wave while the need for phase compensation is well established the best method to measure the seismic vibrator output is not phase control of the force exerted by a seismic vibrator upon the earth s surface ground force is shown to be useful in producing consistent downhole p wave signatures experimental results are presented which compare the downhole correlation wavelets produced by phase locking to ground force reaction mass acceleration and baseplate acceleration as changes in vibrator type sweep bandwidth drive level and coupling medium are made the empirical results support earlier theoretical work which predicts with suitable assumptions that ground force and far field particle displacement are in phase except for a time delay

how good is the weighted sum estimate of the vibrator ground force vibroseis sources are the principal nonimpulsive sources used in land seismic exploration to achieve an improved image of the subsurface with higher accuracy and better resolution it is necessary to take the true ground force as the reference in calculating the cross correlation function with the far field data instead of using the theoretical reference signal the true ground force is defined as the total compressive force exerted by the earth upon the vibrator baseplate theoretically it can be calculated by integrating the compressive stress over the surface area that contacts the baseplate in practice it is very difficult to quantify the true ground force accurately as the vibrator shakes on highly variable surfaces such as desert sand dunes the vibrator will generate more harmonic distortion at the same time the baseplate will flex and rock this results in poor repeatability of source signatures this means that the true ground force varies from place to place and becomes impossible to determine

structural evolution of organic matter and implications for graphitization in over mature marine shales south china abstract to characterize the degree of organic matter graphitization in the over mature lower paleozoic marine shales from south china a suite of kerogen samples covering different maturity ro ranging from 1 2 to 4 2 were analyzed by laser raman microprobe lrm transmission electron microscope tem and fourier transform infrared spectroscopy ftir techniques chemical structures and related major changes caused by thermal evolution history were systematically discussed the results indicate that with the thermal maturity increasing the aliphatic side chains fall off gradually and the aromatic rings increase continuously the ordered structure of shales continues to enhance leading to the increasing of graphitization degree the parameters of lrm i e position of g and d bands peak position difference rbs full width at half maximum fwhm and intensity ratio id ig highlight the turning point at maturity level around rmcro 3 5 which represents the chemical structure jump of the kerogen this chemical structure jump can be characterized by the continuous decreasing of amorphous carbon before the rmcro exceeded 3 5 and the sharp increasing degree of aromatic conjugation after that point tem analysis indicates that the carbon layers of shale samples with rmcro exceeds 3 5 show better ordering and continuity than that of low maturity shale samples the ftir analysis suggests that there are relatively high aromatics c c chains and very few aromatic c h chains in the high maturity samples this critical chemical structure jump at rmcro 3 5 could be interpreted as the structure of organic matter begins to transform from amorphous carbon to crystalline graphite in shales due to the increasing degree of graphitization graphitized shale is characterized by stable chemical structure condensed and orderly carbon layer constructure and ultra low resistivity

pressure seals their diagenetic banding patterns abstract pressure seals are economically significant geological phenomena since they play an important role in deep natural gas entrapment identified in basins worldwide they offer a new frontier for exploration of natural gas reservoirs below 10 000 ft 3000 m pressure seals are low permeability envelopes which enclose abnormally pressured reservoirs there are three different types of seals basal lateral and top basal seals which define the bottom of abnormal pressure compartments usually follow a stratigraphic horizon lateral seals are generally associated with faults top planar seals may parallel or cut across time stratigraphic boundaries they may be developed in any lithology the southeastern portion of the anadarko basin displays a layered sequence of abnormally pressured fluid compartments at depths ranging from 3 000 to 13 500 ft 900 to 4150 m these compartments are separated from each other by pressure seals in mcclain county a top pressure seal separating two abnormally pressured compartments is located between 10 000 ft 3000 m to 12 000 ft 3650 m within the simpson group ordovician the seal zone is characterized by alternating cemented and porous intervals silica and carbonate cements comprise a diagenetic laminated and banded pattern the compositional and textural heterogeneity within this structure evolved through diagenetic processes active during the seal evolution

top seal development in the shale dominated upper devonian catskill delta complex western new york state the preferential generation of vertical natural hydraulic fractures at the contact of the upper devonian hanover gray shale and overlying dunkirk black shale of the catskill delta complex western new york state suggests that the latter served as a hydraulic top seal to formation fluids migrating upward from deeper in the sediment pile petrophysical properties and small scale textural characteristics of these siliceous fine grained rocks confirm the crucial role of depositional environment and sequence stratigraphic position of a shale lithotype in determining its sealing capacity the especially high sealing capacity of the basal interval of the dunkirk shale inferred early high stand systems tract hst strata reflects the anoxic depositional environment of these deposits that favored the preservation of their abundant organic matter and finely laminated depositional texture the absence of bioturbation enabled the undisrupted sediment notably carbonaceous clay rich laminae to undergo rapid mechanical compaction platy grain reorientation and porosity reduction compaction induced squeezing of ductile organic matter into void spaces further reduced pore throat diameters immediately underlying heavily bioturbated deposits of the organic lean hanover shale inferred upper hst or low stand wedge sediments accumulated in a dysoxic depositional environment disruption of layering and homogenization of sediment by burrowing organisms produced a more porous and permeable microfabric through which formation fluids moved only to be arrested by the high capillary entry pressures at the base of the dunkirk shale natural hydraulic fractures some of which propagated into the dunkirk shale formed when fluid pressure at the top of the hanover shale reached the fracture gradient the high sealing capacity of the basal dunkirk shale was probably enhanced by its finely laminated nature and the generation of biogenic methane both of which contributed to the formation of a near impermeable gas capillary seal

petroleum secondary migration and accumulation in the central junggar basin northwest china insights from basin modeling the timing of petroleum generation migration and accumulation in the central junggar basin has been evaluated using basin modeling technology to decipher the processes of petroleum secondary migration and accumulation in the jurassic carrier beds during the yanshan and himalayan orogenies during the early yanshan orogeny j2 j3 crude oils sourced mainly from the permian source rocks migrated laterally from depocenters to adjacent structural high points during the late yanshan orogeny cretaceous eocene the hydrocarbon secondary migration pattern changed significantly specifically in the cretaceous a large scale regional second phase of generation and migration occurred in the western part of the central junggar basin in the eastern part of the central junggar basin crude oils emplaced in the depressions migrated mainly to the eastern uplifts in the early tertiary oils in the source kitchens generally began migrating to the north and mixed with the jurassic generated hydrocarbons during the himalayan orogeny neogene quaternary this migration was strengthened continually the modeled results agree with migration associated geochemical information of the jurassic accumulations integration of the regional geological setting and some petroleum geology data suggest that the jurassic tectonic high points and facies change and unconformity associated subtle traps are of crucial importance for current oil exploration both overpressured bodies in the triassic and permian systems and volcanic rock reservoirs of the carboniferous basement in the uplifts have important implications for future natural oil and gas exploration this work should help reduce exploration risk in this region

modelling and modal analysis of seismic vibrator baseplate the vibroseis method must be extended to its limits as the search for oil and gas continues on land to successfully improve vibroseis data quality it is crucial to evaluate each element in the vibroseis data acquisition system and ensure that the contribution from each element is successful vibroseis systems depend greatly upon the ability of vibrators to generate synchronous repeatable ground force sweeps over a broad frequency range this requires that the reaction mass and the baseplate of the vibrator move as rigid bodies however rigid body motion is not completely true for high frequency vibrations especially for the vibrator baseplate in order to accurately understand the motion of the vibrator baseplate a finite element analysis model of the vibrator baseplate and the coupled ground has been developed this model is useful for simulating the vibrator baseplate dynamics evaluating the impact of the baseplate on the coupled ground and vibrator baseplate design model data demonstrate that the vibrator baseplate and its stilt structure are subject to six significant resonant frequencies in the range of 10 80 hz due to the low rigidity of the baseplate the baseplate stilt structure experiences severe rocking motions at lower frequencies and the baseplate pad experiences severe flexing motions at higher frequencies flexing motions cause partial decoupling which gives rise to increased levels of harmonic distortion and less useable signal energy in general the baseplate pad suffers more bending and flexing motions at high frequencies than low frequencies leading less efficiency in transmitting the useable energy into the ground

generation and evolution of overpressure caused by hydrocarbon generation in the jurassic source rocks of the central junggar basin northwestern china the jurassic black mudstone and coal beds in the central junggar basin northwestern china are the major source rocks for the basin with type ii2 and type iii gas prone kerogens widespread overpressures are developed in the jurassic stratigraphic interval sonic and resistivity logs display strong characteristic responses of overpressure in the mudstones with anomalously high acoustic traveltimes and low resistivity compared with the normally pressured mudstones the overpressured jurassic sediment sequences appear to have undergone normal compaction because the mudstones exhibit no anomalously low bulk density the overpressured mudstones deviate from the normally pressured mudstones in density effective vertical stress space the overpressure in the jurassic source rocks is therefore not caused by disequilibrium compaction the overpressured jurassic sandstone reservoirs are predominantly oil and gas saturated or oil bearing the well log responses of the overpressured mudstones and seismic velocity characteristics indicate that the top depth of the overpressure zone ranges from 3800 to 4600 m 12 500 to 15 100 ft corresponding to formation temperatures of approximately 94 c to 111 c 201 f to 232 f with estimated vitrinite reflectance values of 0 6 to 0 75 the jurassic source rocks with overpressure are capable of generating hydrocarbons at present and are currently overpressured all the evidence suggests that the overpressure in the jurassic source rocks in the central junggar basin is caused by hydrocarbon hc generation the overpressure evolution was modeled quantitatively in response to pressure changes caused by hc generation during basin evolution the results indicate that multiple episodes of overpressure development and release occurred within the jurassic source rocks suggesting multiple episodes of hc expulsion the timing and numbers of these episodes of hc expulsion were thus determined from the modeled overpressure evolution

geophysical benefits from an improved seismic vibrator the seismic vibrator has become a very important source for land data acquisition and there have been dramatic improvements in recent times in the application of the vibroseis technique these improvements have led to much increased productivity and in many cases much denser source sampling at the same time the vibrator itself has seen little improvement over the last couple of decades there are needs in a few areas where an improvement in the vibrator itself can bring benefits to the quality of the seismic data acquired this paper describes progress in four such areas low frequency performance high frequency performance an improved estimate of the vibrator groundforce and source signature consistency over variable ground conditions each of these vibrator characteristics will be discussed in turn meanwhile two field test results in which the performance of two different vibrators in these four areas are compared

on the accuracy of the ground force estimated in vibroseis acquisition for a linear elastic earth the time derivative of the ground force is considered proportional to the far field wavelet under the assumption that the baseplate is stiff and the bending forces of the baseplate are negligible the ground force is also approximated by the sum of the accelerations of the baseplate and the reaction mass weighted by the respective masses combining these two assumptions the time derivative of the weighted sum is considered proportional to the far field wavelet this result often referred to as the far field wavelet assumption although convenient and most often employed is not always valid we explore its validity using the spectral harmonic ratios of recorded data which are used extensively in data filtering and analysis of vibratory data we show that the far field wavelet assumption fails particularly for harmonic components of even order more compact soil after repeated shots further invalidates this assumption non linear modelling of the ground under the vibrator point may provide a direction towards solving this discrepancy finally we describe a method for the estimation of the harmonic spectral ratios

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

overpressure generation and evolution in lower paleozoic gas shales of the jiaoshiba region china implications for shale gas accumulation abstract overpressured shale gas plays have been found in the lower paleozoic marine shales of jiaoshiba region in the sichuan basin china the black shales from the upper ordovician wufeng group o3w and the lower part of lower silurian longmaxi group s1l are the producing reservoirs overpressure is widespread in the o3w s1l shales with the pressure coefficient up to 1 74 fluid inclusion microthermometric and raman spectroscopic techniques pvt and basin modeling are used to investigate overpressure generation and evolution in the o3w s1l shales the results show that thermocatalytic dry gas generation is the main genetic mechanism for overpressure development in the o3w s1l shales with specific characteristics as follows 1 the maximum burial depth of overpressured shales is more than 6200 m without anomalously low density and high primary porosity according to wireline log and core data 2 the over mature o3w s1l shales with the mean toc values ranging from 3 36 wt to 4 48 wt and the vitrinite reflectance values of 2 7 2 9 ro determined by kerogen ftir fourier transform infrared spectroscopy characteristics has excellent potential to produce dry gas 3 overpressured reservoirs are characterized by high gas saturations and the pressure coefficients positively correlate with gas saturation 4 the abnormally high pressures recorded in the fluid inclusions are coincident with high homogenization temperatures which is supportive of overpressure occurring during dry gas generation and provides convincing in situ evidence for gas generation overpressuring the calculated pore fluid pressures for methane inclusions within the maximum buried o3w s1l shales are approximately 90 3 139 4 mpa suggesting that gas generation produced a maximum pressure gradient of 23 1 mpa km which is equivalent to the lithostatic magnitudes the overpressure evolution in the o3w s1l shales is noticed to have evolved through four stages a rapidly increasing overpressure caused by thermocatalytic gas generation 145 85 ma a rapid pressure release 85 61ma overpressure preservation 61 20 ma and a relatively slow pressure release 20 ma present during post generation evolution 85 ma present of the o3w s1l shales both the overpressure and pressure coefficients decreased with time due to the intensive tectonic uplifts and denudation and approximately 19 0 28 5 of the initial total gas content was continuously released until the present day overpressure state the study of overpressure evolution in the o3w s1l shales provides basic information for the further study of the conversion between adsorbed gas and free gas and the method and technique used in this study to stress the overpressure generation and evolution may be generally applied to other overpressured or normally pressured shale gas systems

a model for diagenetic mass transfer between adjacent sandstone and shale abstract there are numerous suggestions that mass transfer between sandstone and shale is an important factor in the diagenesis of sandstone reservoirs however advective transport models for mass transport have not produced results that support these proposals a model is developed that overcomes the problems of advective transport models by assuming that diffusive mass transfer is the principle transport mechanism the process occurs when the rate of dissolution of reactive detrital components exceeds the local rate of diffusive transport at that point in the burial history units with greater amounts of a reactive component will generate more solute per unit time than units with less reactive component the process forms chemical gradients that can rapidly transfer mass equivalent to several vol of rock over distances of at least 5 m the observed transport of potassium and silica between adjacent sandstone and shale in the north sea during late stage illitization was correctly predicted using this conceptual approach the conceptual framework from the illite model can be extended to other diagenetic reactions and suggests that the burial of adjacent sandstone shale units could produce episodic diffusion gradients that transfer mass and form multiple generations of cement in sandstone reservoirs

how do hydraulic vibrators work a look inside the black box in order to have realistic expectations of what output is achievable from a seismic vibrator an understanding of the machine s limitations is essential this tutorial is intended to provide some basics on how hydraulic vibrators function and the constraints that arise from their design with these constraints in mind informed choices can be made to match machine specifications to a particular application or sweeps can be designed to compensate for performance limits

division of fine grained rocks and selection of sweet sections in the oldest continental shale in china taking the coexisting combination of tight and shale oil in the permian junggar basin abstract the permian formation in the junggar basin contains the oldest continental shale in china and has abundant petroleum resources the lithofacies and lithology of the shale strata in the lucaogou formation which are characterized by two sets of coexisting combinations of tight oil and shale oil in the jimsar sag eastern junggar basin are studied via experiments to explore their petrophysics geochemistry reservoir pores and oil bearing properties the results show that 1 the lucaogou formation in the jimsar sag consists of shallow deep lacustrine sediments and can be divided into six stratigraphic units vertically 2 fine grained sediments in the sag composed of shale dolomite and siltstone can be specifically divided into carbonate mudstone cm siliceous mudstone sm carbonate rock cc carbonate sandstone cs and siliceous sandstone ss 3 cm and sm are good source rocks for shale oil and p 2 l 2 and p 2 l 5 are the sweet sections for shale oil cc cs and ss are reservoirs of tight oil and p 2 l 1 and p 2 l 4 are the sweet sections for tight oil finally definitions are discussed and proposed for tight oil and shale oil

the permian hybrid petroleum system in the northwest margin of the junggar basin northwest china in this paper we define the concept of a hybrid petroleum system for the permian petroleum system in the northwest margin of the junggar basin by documenting the complexity in its formation and evolution it is termed hybrid because there are three source rock sequences seven reservoir caprock combinations and three petroleum events and multiple source rocks source the same reservoir and the same source rocks also feed multiple reservoirs the mahu sag centre is the petroleum source area with three sets of source rocks dark shale of the lower permian jiamuhe formation black shale of the lower permian fengcheng formation and black shale of the middle permian lower wuerhe formation the reservoir rocks include volcanic and clastic rocks of upper carboniferous to lower cretaceous age mainly characterized by alluvial conglomerate and sandstone there are three sets of ultimate caprocks among which the mudstone of the upper triassic baijiantan formation is the most important due to its wide distribution throughout almost the whole northwest margin and greatest thickness up to 300 m whereas the lower jurassic and lower cretaceous mudstone acts as an effective seal oil and gas were generated mainly during the middle late permian late triassic and middle jurassic early cretaceous the reconstruction of the oil filling history shows that the three source rocks charged reservoirs mainly in three geologic intervals with common mixing of oils from different sources and or with different maturities these three hydrocarbon charges coincide with the three main stages of petroleum generation related to the hercynian indosinian and yanshannian orogenies during these three petroleum events oil and gas migrated along the migration framework controlled by faults unconformities and good permeability reservoir rocks the faults are mainly well developed and episodically active thrust faults and secondary faults as a result the permian petroleum system in the northwest margin of the junggar basin is hybrid

heat flow and thermal maturity modelling in the northern carnarvon basin north west shelf australia abstract the northern carnarvon basin is located at the southern end of the north west shelf of australia it was developed by rifting during the jurassic earliest cretaceous heat flow and thermal maturity in seven wells from three sub basins rankin platform and exmouth plateau of the northern carnarvon basin were modelled using basinmod 1d program multiple thermal maturity parameters were used to constrain the influence of anomalously low vitrinite reflectance those t max data with reliable quality can be applied to correlate with vitrinite reflectance establish thermal maturity and calibrate the modelled results the modelled results indicated that the measured maturity data in some wells were consistent with the rift heat flow model jarvis mckenzie associated with the jurassic rift and the earliest cretaceous seafloor spreading events the maximum values of heat flow were in the range from 67 mw m 2 jurabi 1 to 105 mw m 2 bowers 1 in the exmouth and barrow sub basins on the exmouth plateau the maximum values of heat flow were modelled to be 72 mw m 2 in the jupiter 1 well and 78 mw m 2 in the investigator 1 well these maximum values were modelled to occur during syn rift phase which were 29 88 and 33 37 greater than their current heat flow values in the sub basins and on the exmouth plateau respectively this study suggests that maturity indicators are less diagnostic of rifting thermal histories if the maximum thermal effect is associated with cretaceous and cainozoic burial in this basin

geochemistry characteristics and significance of two petroleum systems near top overpressured surface in central junggar basin nw china abstract most hydrocarbons discovered in the central junggar basin are endowed in limited areas below and above top overpressured surface by studying geochemical and distribution characteristics of hydrocarbons in reservoirs near top overpressured surface it was found that the lacustrine dark mudstone in middle lower permian and coal measures in jurassic are the major source rocks crude oils from these two sets of source rocks have apparently different geochemical indexes their maturity values are 0 7 1 0 higher in permian the natural gas is mainly coal derived wet gas from jurassic formation with general maturity of 0 9 1 0 hydrocarbons in tectonic units have different distribution features depending on sources crude oil above top overpressured surface in western well pen 1 sag is from both middle and lower permian while crude oil in overpressure compartment is mainly from middle permian and natural gas is from hybrid sources crude oil near top overpressured surface in western changji sag is mainly from middle permian including some oil from hybrid sources the natural gas is mainly coal derived wet gas hydrocarbons in northern dongdaohaizi sag and eastern changji sag are mainly coal derived oil and gas in overpressure compartment hydrocarbons in the central junggar basin underwent two stages of accumulation and experienced two large scale chargings at the later stage to summarize geochemical and distribution characteristics of hydrocarbons in reservoirs near top overpressured surface in the central junggar basin can provide reference for understanding hydrocarbon accumulation regularity and predicting favorable exploration targets near top overpressured surface in this region and similar high overpressure and hydrocarbon generation basins

broadband seismic amplitude variation with offset inversion abstractseismic amplitude variation with offset avo inversion is well known as a popular and pragmatic tool used for the prediction of elastic parameters in the geosciences low frequencies missing from conventional seismic data are conventionally recovered from other geophysical information such as well log data for estimating the absolute rock properties which results in biased inversion results in cases of complex heterogeneous geologic targets or plays with sparse well log data such as marine or deep stratum broadband seismic data bring new opportunities to estimate the low frequency components of the elastic parameters without well log data we have developed a novel avo inversion approach with the bayesian inference for broadband seismic data the low frequency components of the elastic parameters are initially estimated with the proposed broadband avo inversion approach with the bayesian inference in the complex frequency domain because seismic inversion in the complex frequency domain is he

stable carbon and hydrogen isotopes of natural gases sourced from the xujiahe formation in the sichuan basin china abstract the compound specific hydrogen and carbon stable isotope ratios of alkanes in natural gases from the xujiahe and jurassic formations in the western sichuan basin were investigated to distinguish between coal derived and oil associated gases all gases were determined to be coal derived and sourced from the xujiahe formation thermal maturities of the source rocks are expected to vary from 0 8 1 8 vitrinite reflectance ro according to the empirical relationship between the measured 13cch4 values and ro which is within the scope of the maturities of source rocks 0 7 2 1 in particular c1 3 alkanes of primary coal derived gases which have not undergone any secondary alteration become more enriched in deuterium with increasing molecular mass and the dch4 values increase with increasing thermal maturity of source rocks in the sichuan basin d values of coal derived gases sourced from terrigenous source rocks of the xujiahe formation are more negative than those of oil associated gases sourced from marine organic matter of the sinian permian and triassic formations

integrated study of the judy field block 30 7a an overpressured central north sea oil gas field the triassic reservoirs of the judy field an overpressured petroleum accumulation in the central north sea have been studied to determine their pressure and petroleum filling history the magnitude of overpressure in the pre cretaceous aquifer is similar across the field at about 24 mpa 3500 psi but with some higher pressure laterally in areas closest to the major depocentres pressure modelling shows that the magnitude of the overpressure can be attributed almost entirely to disequilibrium compaction and largely due to late rapid tertiary burial although modelling does require nanodarcy i e shale like permeability in the cretaceous chalk section the contributions from other mechanisms which may be relevant in this setting i e gas generation and lateral transfer appear to be small the existence of both aqueous and petroleum phases in secondary fluid inclusions in microfractures in quartz and feldspar grains allows estimation of palaeopressure the data show fracture healing from 115 to 136 c during a time when reservoir palaeopressures were above hydrostatic reconstruction of the temperature history of the reservoir places the timing of the fluid inclusion formation during fracture healing at between 3 and 1 my ago coincident with a period of rapid burial the palaeopressure estimation using fluid inclusions validates the pressure modelling studies which are derived independently from commercial basin modelling software the fluid inclusions also revealed a low gor oil over the whole field prior to late stage flooding by gas leading to the variable low to high gor fluids plus gas condensates within the field today