The abiogenic gas resource can be classified as major abiogenic gas and minor abiogenic gas,based on the commercial resource and the proportion of natural gas components.In the major abiogenic gas resource,the abiogenic gases(CO_2 and CH_4) take the most part of natural gas,even whole.Whereas,the abiogenic gases concentration(He)in the minor abiogenic gas resource is low,or extreme low. Most of the major abiogenic gas accumulations which have the high concentration of CO_2 and gaseous hydrocarbons are discovered.
The paper discusses sources and formation mechanism of microbial gas,thermogenic gas,deep gas and abiogenic gas.Pointing out deferent source,deferent formation mechanism and gas formation environment make various origin types and a non-continue characteristics,support to a broad prospect for investigating and seeking natural gas resources.Reviewing advances in abiogenic natural gas studies and a prospect for abiogenic gas resource.Discussing the mechanism an abiogenic origin via polymerization and kinetic.
The possible mechanism of abiogenic hydrocarbon formation and organics generation in deep strata via F-T synthesis and catalytic reactions over metals from carbon,hydrogen and methane was discussed in this paper.
To better understand genesis of crude oil and bitumen,a comprehensive study of Pb,Sr,and Nd isotopic systematics was undertaken for kerogen,crude oil and bitumen from Karamay Oilfield,Tarim Basin and Liaohe Oilfield.Pb isotopic compositions of bitumen and crude oil from Karamay,Liaohe and Tarim all show features of crust-mantle interaction.They are evidently different from Pb isotopic composition of kerogen,which mostly show crustal signatures.Radiometric isotopic systems can be preserved in the bitumen.
The geological processes and degassing processes of the earth are discussed in the article.The author thinks the earth has five gas-spheres al least,such as atmosphere,gas-sphere in the upper crust,gas-sphere in the middle crust,gas-sphere in the upper mantle and gas-sphere in the outer core.Mantle liquid(mantle ichor),which is a complex compound system,is the source of the gas of all gas-spheres in the earth.The gas-sphere in the middle crust has huge natural gas resource.In the author’s opinion that gas.
Mantle fluids in supercritical state possess high dissolving and diffusing capac ity, which are the important transporting carrier of energy in earth interior, t heir chemical compositions vary in a large range with the evolution processes of mantle, and can be distinguished as the primitive fluid in upper mantle, the fl uid of mantle metasomatism and etc. The chemical composition of primitive fluid in upper mantle are related to the mantle reservoir, the primitive fluid in uppe r mantle with a primitive mantle-like reservoir is dominated by CO with seconda ry amounts of CO2 and H2; a depleted mantle reservoir shows a dominant CO2 with minor amounts of CO and H2 in primitive fluid in upper mantle, and an en riched mantle reservoir is enriched in H2. Meanwhile the fluids of mantle meta somatism were mixed by the recycled crustal fluid components beneath eastern Chi na. Mantle fluids have preserved a certain amount light hydrocarbon, such as CH4, C2H6 etc. and high weight hydrocarbon, including an amount of primordia l hydrocarbon, moreover, mantle fluid enriched in H-2 and heat can provide the ample hydrogen and heat sources in hydrocarbon generation of kerogen and promote source rocks to expel hydrocarbons and migration.
This paper deal with the advances and research status, exploration expectation, the coupling and differences of deep oil/gas and abiogenic oil/gas. Deep oil/gas and abiogenic oil/gas researches are the important research and exploration are a in oil and gas exploration domain and will be of important theoretical signifi cance and extensive exploration expectation in the future. Deep oil/gas and abio genic oil/gas are fundamentality different in their formation mechanism, but they also have much similarity in their physical and chemical conservation environm ent. Both deep oil/gas and abiogenic oil/gas were also going through much simila r thermal maturity process in the deep higher temperature and higher pressure en vironments. We need also pay some attention on the abiogenic oil/gas during the deep oil/gas exploration process.
When petroleum is formed from disperse organic matter, it will encounter a serie s of inorganic sedimentary components, such as, water, clay minerals, inorganic salts and some metal elements etc. Inorganic components can serve as reactant or catalyst, and participate in the processes of the formation of petroleum. Petro leum, reductive state matter in geological system, migrate and accumulate in spa tial system formed by inorganic minerals, when it encounters mineral oxidants (i ron-bearing minerals), which can react with inorganic components, moreover, pet roleum physical properties and chemical compositions have been changed during th is process, and the reservoir properties of a rock have also probably been modif ied by products derived from the reactions between organic and inorganic matter. Although some reaction mechanisms of organic-inorganic interactions are still not known by geologists, they have important affect on the petroleum formation a nd accumulation, studies on this fact will enhance our ability to predict the oc currence of petroleum and evaluation of petroleum sources.
The content of CO2 in associated gas of Daqing placanticline has increased greatly after the 90s of 20th century.The CO2 content of the whole amount of associated gas reached 2.87%(V/V)in 2003,the content of CO2 today is about ten times higher than that of in 80s of last century and it’s increasing trend is obvious.By analysing δ13CCO2 of the CO2 in associated gas,the values of three samples are all higher than +3‰.The figure indicates that the origin of this CO2 is the pyrolysis of carbonate.The origin of this CO2 perha ps associate with the pyrolysis of carbonate rock in Permo-Carboniferous.
There was no H2S in the associated gas of Daqing placanticline before the 80s of last century. By the middle of 90s, the content of H2S in the associated ga s was detected. At the year of 2002, the content of H-2S reached 200 mg/m3 an d many oil pipes were eroded. By analyzing the 8 samples(H2S gas and FeS powde r) collected from Daqing placanticline, the values of δ34S of 8 samples v ary at the range of +12.73‰～+16.10‰. The isotope feature of this H2S is qui te different compare with the H2S which generated by bacterial sulfate reducti on(BSR) in other oilfield. The H2S maybe associate with the Thermochemical Sul fate Reduction(TSR) in the rock of Permo-Carboniferous in the basement of Songl iao basin.
Natural gas pools with high content of CO2 were discovered during the hydrocarbon exploration in Fushan depression,Beibuwan basin.The carbon isotopic composition of CO2,Helium and Argon isotopic composition of noble gas indicate that the CO2 is curst-mantal source.Magma activities frequently occurred since Cenozoic.In this area.The first epoch associated by Zhuqiong Motion,occurred in 45 Ma with basalt eruption and part of diabase formed by shallow intrusion.The next three epochs occurred in 30,10~5 and 1Ma associated by Nanhai and Dongsh a Motions respectively. The basalt and diabase of Liushagang formed in Eocene ma inly occur in Huachang, F8 and F10 blocks, which just coincide with the occurren ce of natural pools with high contents of CO2. This indicates that the magma activity occurred in Eocene is the mainly controlling factors that caused the ge neration and accumulation of CO2 gas. The difference between the third member and the first member of Liushagang Formation in CO2 accumulation indicate tha t the distribution and activity of fault systems is another important factors th at controls the accumulation of CO2.
Based on the analysis of the 4000m deep horizontal slice and the Mesozoic(J-K)Xiwa formation residual isopach map of Jiyang sag,the Mesozoic original basin was preliminarily restored in the paper.The results show that the original basin exists three types,that is,the first one is the northwestern type,which is located at the east of the sag;the second one is the northeastern type,which is located at the west of the sag;and the third one is the nearly east-west type,which is located at the center of the sag.Through the further analysis of the slice and its tectonic stereo-gram (including the distribution of the fault and symon fault), the main controlling factors of the Msozoic basin is northeastern andno rthwestern structures (including faults and symon fsult). It is very significant of these points in the paper for the guide of trapping advantageous objects in the next oil-gas exploitation of Jiyang sag.
Abundant subtle oil and gas reservoir,which tied up with slope-break,were embedded in Jiyang depression.Further studying of the grouping type of Slope-break is favor of more effective forecasting of abundant subtle oil and gas reservoir.The studying of the slope-break in Jiyang depression indicated that much factor,such as geometry style of profile,grouping style,subsidence factor,location and genesis et al.not one factor should be considered when the division of slope-break.In term of these factors,the slope-break in Jiyang depression was divided into three la rge grouping types, and eight small grouping types. The three large grouping typ es were flat style, spade style and slope-flat style. The eight small grouping types were successional subsidence type of flat style with one step, intermitten t subsidence type of flat style with mul-steps, tilted-book type of flat style with mul-steps,broom type of flat style with mul-steps, one-step type of spade style, mul-st ep type of spade style, basin margin type of slope-flat style, basin inner type of slope-flat style. The control of slope-break on Lowstand system tract was different with its type. And different subtle traps were formed. The type of s lope-break should be first judged, and combining with well data for subtle tra ps forecasting when practical exploration.
It’s a significant meaning to looking for anticline trap of roller anticline through confirming geometry of normal listric a fault,poor seismic data in deeper section usually bothers researchers during their exploring process.A inclined shear technique by rotating tangent of antithetic subsidiary fault could result in more accurate extension,thus tracing fault trajectories.We have had a great achievement in tracing trajectories of listric of 639 profile in Jiyang sag.
To research vertical transporting natural gas efficiency of fault transportation system,this paper defines transporting coefficient of fault transportation system by analysis impacting factors of fault transporting capacity.Base on the effectiveness of natural gas migration and accumulation process,evaluation standard on transporting efficiency of fault transportation system is established and applied to evaluate transporting efficiency of fault transportation system in the north belt of Kuche depression.The evaluating conclusion displays that there are better relativity between distribution of natural gas and transporting coefficient of fault transportatio n system, which indicates that it is feasible to evaluate the transporting effic iency of fault transportation system by using this evaluating method.
Based on gas potential distribution and evolution in geologically history periods,thinking of relation between with fluid dynamic and hydrocarbon migration accumulation.According of principia which hydrocarbon migration and accumulation systems is compartmentalized,nature gas migration and accumulation systems of lower Cretaceous period Jidike is compartmentalized and studied,nature gas accumulation is discussed,at the same time,according of the migration and accumulation systems and the distribution and evolution characteristic of lower poten tial area and center location which hydrocarbon is formed and development situa tion of fault, nature gas migration direction is analyzed synthetically.
The carbonate rocks of Ordovician in Lunnan area are generally not reservoirs,but the deuterogenous karstificated holes,pores and seams can serve as valid reservoirs.On the base of analyzing the controlling factors of the development of karsts and the stages of karstification,the distribution of two series of three types reservoirs of Ordovician in Lunnan area was studied,and the differences between them were also discussed by the authors.Through analyzing the distributing rules of the oil and gas reservoirreservoirs of Ordovician and the special occurring state of the liquids in the carbonate rocks, it is believed that the distribution of the oil and gas in Ord ovician in Lunnan area is generally controlled by the development of the reservo irs, and the distinct regional distributing rules of the oil and gas are mainly caused by the varying insulated and closed oil (gas) or water in different types of reservoirs.
Lianmuqin Formation of Cretaceous,Shengbei structure zone of Shengbei Sag,Turban-Harmy basin,belongs to typical fan-deltaic front sedimentary system of north sediment source.The sandstone bodies of this sedimentary system are buried in shallow position and in good quality of porosity and permeability.Shengbei structure zone and its south flank are the main position for sandstone and available for the north pinch out subtle traps development.Combined the background of upheaval in sag and cling to the strike--shift faults of Shengbei F3 and F4, which join the hydrocarbon source rocks of coal-bearing series of Shuixigou group, lower-middle Jurassic and lacustrin e mudstone of Qiketai formation of middle Jurassic, the Shengbei structure zone and its south flank are favorable shallow position for secondary subtle traps ex ploration of Cretaceous in Shengbei sag.
It is confirmed by drilling and oil testing that there are many vertical oil & gas layers,many oil & gas types and complex accumulation patterns in Shengbei area.This paper analyses the correlation between known oil-gas reservoir and source-reservoir-cap,the lithology of upper strata and the oil-gas reservoir as well as its production,the position of oil-gas reservoir and the structure in Shengbei area,figuring that J_2q is the major stratum in oil & gas assemblage of self-generation and self-accumulation,and J3k, K1 and K1lshould be regarded as the major prospect object in the oil & gas assemblage of injection migration; It also concludes th at most oil & gas is stored at the top of sand unit and its production has clo se relations with the upper cap, and that the geological strata will ascend with structural position. These conclusions have certain significance to the cogniti on of the vertical distribution of oil & gas in the whole basin and target evalu ation and optimization, and can well guide hydrocarbon detection by integrating multiple seismic attributes geologically.
Studies on the geological conditions and process of hydrocarbon accumulation and the formation and the evolution of the structure in Shanle structural province show that the main factors controlling hydrocarbon accumulation are the disposal of source rock,reservoir and covering strata,and the form of ancestral structure,the space time relation of trap and source rock,and faults.However faults are fundamental factor in all this factors through controlling the connectivity of source rock,trap formation and envelop oil and gas. Generalize the accumulation patterns of gas and oil, according the analysis of the control fact ors and the period of hydrocarbon accumulation, which is of significance to guid e the petroleum prospecting efforts in Shanle structural province.
Turpan-Hami basin is a multicycle and multiplex basin with the overriding characteristic of multistage and multitype,which has his characteristic distinction.Studies of the division and the correlation of Turpan-Hami basin by using the theory of high resolution sequence stratigraphy shows that the shallow formation of Cretaceous system-Tertiary system can be divided to six succession of strata.Three of which are hyper-perennial,the others are perennial,and the former five perennial succession of strata can be further divided to sixteen medium-term succession of strata.
The depth of Mesozoic strata of I depression in northern Yellow Sea Basin was great and the strata imbedded deep.Its distribution was steady and the condition of hydrocarbon accumulation was better.The research of trapping characters of Mesozoic strata was importantly significant in clarifying the character of the play of I depression,the law of oil/gas accumulating,the searching of objective structure and the collocation of exploration well location.By the researching synthetically of physical geography and the analyzing of regional geology, we identified 2 kinds, 3 subkinds and 5 types of trapping in the Mesozoic strata. Their characters are as follows:① the main trapping type was the structure trapping; ②there was little excursion of highest point of trapping structure was; ③on the plane the distribution was obviously controlled by the type;④the forming periods are concentrative.⑤the c ondition of hydrocarbon accumulation of anticlines trapping, faulted anticlines trapping and parts of faulted nose trapping was good.
Based on the measuring of out section and the analysis of inner data,the petrologic character,lithologic association,sedimentary structure,palaeourrent directions,and distribution of sandstone, the sedimentary character of the Jinci sandstone in Baode area is studied systematically.The authors considered that the sedimentary environment of the Jinci sandstone is meandering river.
The palaeo-structrual pattern of Ordovician are three uplifts and two neks and one depress in Ordos basin.Three uplifts control together sedimentary system of Ordovician,at the same time control the development of the original reservoir.After sedimentary of Ordovician,sedimentary are interrupted about a hundred million years,karst reservoir developed widely.From benxi formation to middle Trias,the up-and-down configurations of Ordovician weathered crust peak are very steady,namely high in the middle and bellow in the east. There are a abrupt slop e between uplift and depress, it is important to evolution of karst reservoir. L ate trias, the up-and-down configurations of Ordovician weathered crust peak a re high on the west-north and low on the east-south, oil-gas moved to west-n orth. The middle Jurassic, the up-and-down configurations of Ordovician weathe red crust peak are high on the east and low on the west, oil-gas adjusted again , moved to east.
Molecular nitrogen encountered in varying amounts(up to >90%) in natural gas reservoirs may be derived from two potential sources,thermal liberation from the organic and/or inorganic constituents of sediments(crustal source) and accumulation of upward migrating deep (mantle) nitrogen.Different types of pyrolysis experiments show that nitrogen is produced not only at low temperatures,but also at high temperature levels.A variety of different release mechanisms are involved.It is well known that proteins areare hydrolysed to amino acids during the early, diagenetic stage of maturat ion (Ro<0.6 %). However, amino acids are generally unstable and are prefer entially transformed to NH3 under the catalysis of clay minerals which then may be further oxidized to N2, nitrate or nitrite. The bulk of nitrogen in coals at higher ranks occurs in condensed aromatic units as pyridinic and pyrrolic structures of high thermal stability.Natural gases from different depositional environments are characterized by nitr ogen isotope ratios. The =δ15N values are usually lower than +3‰ in continental deposits whereas they are higher +4‰ in marine deposits. Different ni trogen isotope compositions are indicative for specific origins. Generally δ15N vaues of biogenic nitrogen are below -10‰whereas for nitrogen from pyro lysis experiments δ15N values are higher than -10‰. The N2/Ar of gases produced by microbial processes and thermal pyrolysis is often higher than 84. The δ15N of N2 resulting from high temperature metamorphism of N-conta ining minerals ranges from +1.0‰ to +3.5‰, with N2/Ar＞84. The δ15N composition of nitrogen from the upper mantle and/or the deep crust is between -2 0‰ and +1‰，with 40Ar/36Ar＞2000 and 3He/4He＞1.39×10-6.
Bonan sub-sag is the main target of the exploration in deep beds of Jiyang depression,the 4th member of shahejie formation is the principal oil and gas generating series,and the Bonan sub-sag is still in its primary stage of exploration at present.This paper presents the organic matter content and types and maturity of organic matter in the source rocks,and reveals that there is a high carbon abundance in the source rocks in the 4th member of shahejie formation with mainly type-I and type- III,just situatin in mature to post-mature phases. According to analysis on the sedimentar y facies and source rocks of the well Boshen-4 and Boshen-5, organic facies of source rocks in the 4th member of shahejie formation were analyzed.
By means of whole rock thermal simulating experiment in the open system,the authors have studied the effect of different heating-rate to the hydrocarbon generation of source rock(grey-black mudstone of Trias from well Ha 2 in Tarim basin).The result of experiment indicate the hydrocarbon generation of high heating-rate is near to that of low heating-rate between 350℃~500℃,while after 500℃,the hydrocarbon generation of high heating-rate is more than that of low heating-rate.In the course of heating-rate enhancing,the secondary react ion in molecules of organic matter will increase,so the hydrocarbon generation i s higher than that of low heating-rate. The result of this experiment is in op position to that of the predecessor, because the environment and course of react ion in the open system are different from that in close system. The effect of h eating-rate to the hydrocarbon generation have relation to the system of expe riment.
The analysis of reservoir-forming terms and its procesure of Shengtuo oilfield in Dongying sag proves that the northern steep slop zone of Dongying sag has the geological condition of two terms of reservoir-forming.The crude oil biologic criteria and petrphysical characteristics and the result of oil and source rock correlation for all the oil-bearing formations provides direct geochemical evidence.The Shengtuo oilfield in Dongying sag under goes two procesures: accumulation and breakdown in the early time(Oligocene), th e 2nd accumulation and adjustment in the later time (Pliocene). The two terms of reservoirforming has an obvious effect on the reserves distribution in Shengtuo oilfield.
In this paper,we described the process of establishing natural gases information system of China using the ArcIMS software based on the natural gas geochemical database.Temporal and spatial distribution and geochemial characters of natural gases in china were discussed by using the data of this system.Taking the natural gas in Ordovician as an example,we discussed its geochemial characteristics and gas source in China and implemented the primary application of the information system.
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