Based on the chemical compositions and steady carbon isoto pe of natural gases from Taizhou formation in Yancheng sag, Subei basin, and com bined with the results of carbon isotope of gases from the thermal simulation of K2t and Ef2 source rocks with different organic matter type s, the natural gases are dry gas derived from thermal cracking of type-Ⅲ kerogen. They are mainly generated from the underlying upper Paleozoic source rocks .The condensates accompanying with dry gases are primarily derived from K2t source rocks. The formation of condensates is related to gas washi ng which results in the fractionation of crude oils in upper oil reservoirs.
Xiamaling Formation of Qingbaikou System of later Proterozoic in North China is relatively more abundant in organic matter in marine sedimentary stratigraphies from Proterozoic to later Paleozoic in North China area. The content of organic matter is beyond 16% at most. The analyzing result of main elements, trace eleme nts and organic matter content of Xiamaling Formation shows that the content of SiO2 is apparently higher in organic matter rich mud rock than organic poor mu d rock, the content of SiO2 has a positive correlation with TOC content, and h as a negative correlation with TiO2 content (indicator of land matter input). The ratio of Si/(Si Al Fe) has a positive correlation with TOC content, too. In organic matter rich stratigraphy, there is apparently higher element content of P, Cu, Zn, Co, Ni, V which are related to thermal fluid activity in ocean floor, and the ratio of Ba/Sr is far more than 1. These characteristics indicate that during the organic matter rich stratigraphy of Xiamaling Formation was depositin g, there is thermal fluid activity in ocean floor at the same time. The activity of thermal fluid can provide organism a lot of nutrition, such as N, P, K, SiO2 and so on, it also can provide much energy for organism to grow. As a result , it leads to apparently better accumulation of organic matter in depositional s tratigraphy of thermal fluid active area in ocean floor.
Geochemical characteristics of crude oils of Suqiao-Wenan and Chaheji area in Jizhong depression have been analyzed and studied systemati cally by various of geochemical techniques and methods for molecular information , the results suggest these crude oils can be fall into three groups of coal-fo rmed oil, Paleocene Tertiary oil and mixed oil. The characteristics of coal-for med oil in Suqiao-Wenan are that saturated hydrocarbons amounts to about 80% of the bulk composition and Pristane/Phytane ratios more than 2.0, the contents of tricyclic terpanes with low carbon number(C19-C21) and C24 tetracyclic terpane are abundant, but gammacerane indices is low. In contrast, ch aracteristics of Paleocene Tertiary oils in Chaheji area in Jizhong depression a re that pristane/phytane ratio is low, contents of tricyclic terpanes with highe r carbon numbers(C23-C24) are abundant, but the gammacerane amount is abundant. However, geochemical characteristics of mixed oils from Suqiao-Wen an area in Jizhong depression are between coal-formed oils in Suqiao-Wenan are a and Paleocene Tertiary oils in Chaheji area.
The analysis of fluid inclusion is a very effective method in studying oil and gas migration and the pool-forming time. The authors were systemically carried out an investigation of the type, the distribution characte ristics, homogenization temperature, freezing point, salinity and the compositio n of fluid inclusions in Ordovician carbonate reservoirs in central Ordos basin in this paper. The pool-forming time and migration direction of natural gas fr om Ordovician weathered crust gas reservoirs were also discussed. The type and c haracteristics of fluid inclusions in Ordovician carbonate reservoirs are relati ve complex in central Ordos basin. There are about 5%～80% organic inclusion con tent, 70～180℃ homogenization temperature, -1.0～-13.5℃ freezing point, more t han 5.0wt.% salinity, and 0.922～1.065 density in Ordovician carbonate reservoir s in central Ordos basin. It is suggested that there would have been at least tw o stages for the formation of natural gas pools in central Ordos basin, which th e main pool-forming time was probably the end of late Triassic period and the e nd of the early Cretaceous period. Natural gas at the two stages generally migra ted from east to west and from south to north.
Hydrocarbon source rock of carboniferous is mainly developed in Keluke formation of upper carboniferous, its carbonate attain evalution standard of source rock, mudstone is middle-good source rock, and coal is poor source rock. Thinking ov er the influences of evolution and weathering, the results that carbonate and mu dstone is good hydrocarbon source rock is conjectured in the northern margin of Chaidamu basin, and its organic matter is in evolution stage of maturation-high maturation. The analytical data show that carboniferous possesses better oil an d gas exploration prespects.
A series of black marine oils with similar chemical compos ition distributed in Hade 4 Oilfield and correlative areas, which are derived fr om the similar source rocks showed by oil source correlation studies based on ag e-specific biomarkers. By the studies of qualitative and quantitative analysis, it can be shown that the concentration and internal composition of terpenoids, such as drimanes, tricyclicterpanes and hopanes, to some extent, are related to oil maturity. In this point, the characteristics of terpanes occurence can be us ed as a reference for the oil source correlation studies of mature marine oils. When ratios of C15-8β(H)-drimane to C16-8β(H)- and ratios of t ricyclicterpanes to hopanes are used for the purpose of oil source correlation s tudy, great attention should be paid to the phenomenon characterized by occurren ce of terpanes in Hade 4 Oilfield and correlative areas.
Mango parameters and the evolution of parents and its children indicate that cru de oil exists difference in Ledong and Dongfang area. It show they come from dif ferent source rock or have distinguishable effect during forming reservoir. The light hydrocarbon parameters of crude oil coming from Ya 13-1 structure vary be tween the parameters of two area crude oil which indicates kerogen matrix types and depositional environment are different. The difference of hydrogen and carbo n isotope composition in Ledong and Dongfang crude oil shows the depositional en vironment of their source rock or changeable effect during forming reservoir are different. The biomarks parameters also make sure the discrepancy of crude oil property in two area and prove the same oil source that come from Ya 13-1 struc ture. The study of aromatic hydrocarbon and fatty acid obtained the same results .
The oil cracked gas has been identified in Kekeya region based on the geochemica l characteristics of oil and gas. Overall, integrated analysis results show that the oil and gas are in the stage of high maturity that oil cracking occurs. Bes ides, the abundant diamondoid hydrocarbon and absent of pyrrolic nitrogen compou nds in associated crude oils are very similar to the characteristics of associat ed oil for oil cracked gas reported in the other region. Moreover, the methane content increased as the depth of formation, etc. All these result shows that oil cracking is very important process for the generation of natural gas in this region.
The natural gas in well Yingnan 2 is mostly composed of hydrocarbons. As heavy hydrocarbon is higher, this kind of natural gas is regarded as wet gas. The content of nitrogen in gas is high,while carbon dioxide is minor. The characters of carbon isotope indicates that it belongs to high or over-mature sapropelic source rock-derived gas. Further more this article studies the reason why wet gas and higher of nitrogen are formed.
The asphaltenes of the heavy oils from Lunnan, Tahe oilfie lds and TD2 well were studied by ruthenium-ions-catalyzed oxidation. The subst ituted functions bounded on the aromatic structure of the asphaltene were domina ted by n-alkyl chains, with n-alkyl bridges secondary. A certain amount of bra nched alkanes and biomarkers were also identified. Most of these compounds were bounded on the asphaltene through C-C bounds. The aromatic systems of the aspha ltenes were dominated by naphthalene, phenantherne and biphenyl, with little hig hly condensed aromatic system. The products of the asphaltene RICO with high n- alkanoic/di-n-alkanoic acid ratios and the isomeric ratio of the steranoic aci d great than 0.4 suggested that the oils have high maturity. The distributions o f n-alkanoic and steranoic acids of the products of asphaltenes RICO of heavy o ils from Lunnan, Tahe oilfields showed great difference from that of the oils fr om TD2 well, a typical oil from the Cambrian, indicating the heavy oils from Lun nan and Tahe oilfields were originated from middle-upper Ordovician.
Along with the research progress on Precambrian, the Molar tooth carbonates (briefly called MT, or called microsparite carbonates or MT st ructure) being formed in mid-late Proterozoic become a target of crossing firer ecently. The Proterozoic Molar-tooth (MT) carbonate rocks refer to those Meso- to Neoproterozoic (1 700～650 Ma) carbonates with MT structure, being a series o f pecular, ptygmatically folded and spar-filled cracks in fine-grained carbona tes of Precambrian age, located in the environment of mid-to inner ramp and sha llow platform. Like a bridge, MTS connected the inorganic world with the organic one and is closely related to the evolution of the paleo-oceans, the atmospher e and the biosphere. Their development and/or recession are related to the origi n of life and the abruption of sedimentary geochemistry of marine carbonates. By using of morden instruments and testing methods adequately in this paper, cont ents of sandstone oxides and the model curve of REE distribution were measured; the 87Sr/86Sr isotopic ratio obtained an accurate value, tha t is, the age of MT formation is about 750～900 Ma; C and O isotopes of some fre sh micrite limestone samples were analyzed; the energy spectrum analysis found t hat MT consists of microspar calcite mainly, while chemical composition of the m atrix is abundantly of peaks Ca, M, Al, Si, K.The geochemical indicators proved that the MT carbonates of Neoproterozoic in the Ji-Liao region developed in the margin of the stable continent, formed in the torrid zone and the paleo-temper atures were about 50℃, the sea water was normal salinity when MT formed during the wanlong period in the southern Jilin, the Yingchengzi period and the Xingmin cun period in the eastern Liaoning. the sedimentary environment located in the i nner ramp. In summary, it is of important significance for the origin of the MT, also for the paleo-climate, the paleo-environment, ascertaining the age and t he stratigraphy division and correlation of the Proterozoic to study the geochem ical features of the MT carbonates and its formation environment.
In this article, the two geo-microbiological te chniques applied to oil and gas industry, the Microbial Prospecting of Oil and G as (MPOG) and the Microbial Enhancement of Oil Recovery (MEOR), are systematical ly summarized, in the meanwhile the experimental methods, main characteristics a nd so on are briefly depicted, at last the successful case histories of the Germ any, American, Russian and Chinese experience are numerated. Through practice of MPOG and MEOR, it should be paid much attention to the basic theoretical resear ch, and at the same time, it will have fundamental influence on the great improv ement of Chinese oil and gas prospecting and oil recovery to train large amount of multiple-discipline scientists of geology and microbiology and to develop ou r own a set of geo-bio-tech.
Microbial prospecting of oil and gas (MPOG) is paid more a nd more attention by the whole exploration field, because of its many advantages such as direct display, effectiveness, economics and less multi-interpretation . With the new method of the microbial prospecting of natural gas, which is one of MPOG, applied to Manite depression of Erlian basin, the samples are collected and the methane oxidizing bacteria are cultivated, the following abnormal zones are classified. The two gas abnormal zones are north-western abnormal zone and middle-southern abnormal zone. Comparing the microbial results with the drille d wells in studied area, the accordance between them is satisfactory. Meanwhile, through the microbial prospecting of natural gas practices, the influence of th e soil surface and subsurface faults as well as the objectivity of the analytic results are concluded and discussed, which have much significance for Chinese co mplicated subsurface geo-structural natural fields to explore oil & gas. At las t, on the basis of the microbial results of gas indicator and combining with man y conditions such as traps and oil source, etc. The oil and gas potentiality is analyzed, and the optimal drilling site is also provided which are needed to be clarified in the future well drilling.
Reservoirs of hydrogen sulfide bearing gas are distribute d widely in globally. The natural gas with H2S content have been discovered in several petroliferous basins of China which include Sichuan, Bohai bay, E rdos, Tarim and Zhungaer, etc. Among them, the north-eastern gas area of Sichua n basin and the Zhaolanzhuang gas field located in North China, together with th e Luojia gas field located in Shengli oil field of eastern China, are all belong to gas fields with high H2S contents. According to the analysis and summary o f the current research status of H2S at home and abroad, based on the probing into the genetic mechanism of H2S and its classification and combining the geo logical features of the gas fields with high H2S content, it can be concluded that the above three gas fields were originated mainly from the thermochemical s ulfate reduction (TSR).
In the aerobic condition, the structure of crude oils were changed by hydrocarbon-oxidizing bacteria. The structure of crude oils was also changed by sulphate-reducing bacteria in the anaerobic condition. Sulphat e-reducing bacteria can make use of crude oils as sole carbon source. After tre atment of crude oils, the sample was analyzed with gas chromatograph(GC).The res ult of GC show the lighter compounds of crude oils decrease, but the more high w eight compounds increase. The sulfate-reducing bacteria were detected in the oi lfield water of Tarim basin. Its numbers were up to 104 cells/ml. The resu lts support the view that H2S is the origin of biology.
The analyses of alkylcarbazoles in the oils from the Pearl River Mouth Basin show that the ratio of 1,3-dimethylcarbazole (DMC) to 1,6-D MC displays a remarkable invariance (about 1) independent of their absolute conc entrations. This may indicate that 1,3- and 1,6-DMC had a common precursor: 1-methylc arbazole. The formation of 1,3- and 1,6-DMC resulted from methylation at ring carbon 3 and 6, which have identical reaction activities, in 1-methylcarbazole in kerogen matrix with identical rate. The 1,4- and 1,5-DMC contents display q uite uniform variance trends as that of 1,3- and 1,6-DMCs in the oils, which indicated during the methylation of 1-methylcarbazole a competitive reaction oc curred between ring carbon 3, 6 and ring carbon 4, 5 in 1-methylcarbazole.
Nitrogen isotopic samples of oils in Tarim basin were prep ared with Kjeldahl method and the ratios were measured. The results show that δ15N values of oil and source rock can be correlated but vary with ge ological age and different tectonic zones. Oil δ15N in Tazhong zone is lo west with most values below 1‰; it has some higher value in Tabei zone but stil l near zero on the whole. Whereas the δ15N distribution in Kuche zone is d iscrete with value maximum 18.11‰ and minimum 2.77‰,the difference being 15.34 ‰. Oil δ15N in Ordovician formation of YH5 well is lower than that in Te rtiary Formation, which suggests that oil in the zone is a mixer of two differen t sources. Oil δ15N values in different formations of well Lunnan 14 decr ease from bottom to the top reservoir gradually so it is speculated that hydroca rbon migration may have occurred vertically.
Organonitrogen compounds in oil has been widely us ed to study oil migration distance. Many foreign scholars and some Chinese schol ars have done much work in this field. In the meantime, quite many attempts have been made and /or some results achieved in the studies particularly during rece nt twenty years. Nevertheless, there are still many issue in organonitrogen comp ounds studies which need further exploration, such as extent which original sour ce material, paleoenvironment and thermal maturity have influence on the p arameter of neutral nitrogen compounds, validity of application of pyrrolic comp ounds parameters during oil migration. Based on these problems, lots of new prog ress have been achieved by some scholars in recent years and some important conc lusions have been made so as to benefit the development of organonitrogen compou nds studies.
The outp ut proporation of fo ur multi-oil zone co-recovery wells in Wenchang 13-1 oilfield has been calculated based on highly accurate and repeated technology of Gas Chromatograp hy (GC) for quantitative analysis on fingerprinting crude oil, random GC fingerp rint differentia selection, the most similarity of GC fingerprint in the same oi l zone, the most differentia of GC fingerprint among the different oil zones, an d numeric simulation program of least square method. Through the method of “bac k to back”, namely on-site testing and laboratory calculation going on respect ively, the results of on-site testing and laboratory calculation have been comp ared, and having evaluated the creditability of the method. The absolute differe nce of two oil zone co-recovery well is about 5%, while that of three oil zone co-recovery well between 5%~10%.
Advanced GC fingerprint technique provides an economy, sim ple and valid method for reservoir dynamic monitor. It is used for allocating of 2(3) end members of commingled production wells based on GC fingerprint charact er. It was applied to the condensed oil and heavy oil in Banqiao oilfield, Tianj in City. The coincidence of the results and production data indicates a good pro spect of GC fingerprint in production monitoring.
By survey of filed geological section and many of core and analysis of well-log ging data and microfacies in the microscope, we think that formation of Kangcun group in Neogene period in area of Dawanqi，Tarim basin are a delta sedimentary system which form where a lowsinuosity river flew into an in-land lake with ver y shallow water. The sand bodies are made of lithical sandstone with different size. Delta place subfacies and delta front subfacies has been distinguish in the range of oil fields, they were subdivided into 8 kinds of microfacies. Reservoi r sand body mainly consist of distributary channel sand，subaqueous distributary channel sand and distributary mouth bar sand．They are vertically characterized by multiple superimposition and laterally by frequent migration, tapering out a nd lower continuity.
In H-152 well block in Huachi Oilfield, there were dril ling cores of 10 wells been detailed observed and single well sedimentary facies es, profile facieses and plane facieses of over 200 wells been analyzed. It was held that the Chang +3 -3 sand group is a suit of meandering stream's delta dep osition system. And two subfacies including meandering stream's delta front and prodelta could be found. And its sedimentary microfacies were also deep studied.
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