Understanding the concept including connotation and extension and category for different hydrocarbon accumulations is fundamental for further study and application,with the development of petroleum exploration and research work,and the increasingly enriched types of discovered reservoirs.In this paper,we discuss the concepts and category of lithological and stratigraphic accumulations,and the distinctions from continuous-type accumulation as well.We come up with three sufficient and necessary conditions for continuous hydrocarbon accumulation outside the source extent,that is,an unconventional (tight) reservoir,a wide-distributed high-quality source rock,and a configuration that the reservoir should overlap the source rock tightly and seamlessly.In addition,there are two identification markers,namely the essential attributes in terms of trap-forming conditions and percolation and accumulation mode.
From the reservoir geological characteristics,rock composition and diagenesis,physical properties,pore types and so on,this paper analyzes the particularity of sandstone reservoirs in the member 6 to the member 4+5 of the upper Triassic Yanchang Formation from the Hujianshan area of Ordos basin,and discusses the reservoir characteristics and their relationship with oil accumulation.The sand body with strong heterogeneity develops in submarine distributary channel of delta front.The sandstones are mainly feldspathic lithic fine sandstone with strong diagenesis and low physical property values as a whole.Most of the reservoirs are low porosity and low permeability\|tight and the effective pore types are mainly intergranular pore,dissolution pore and intracrystalline pore.Oil accumulates in the reservoir layers with different physical properties and many aquifers have high porosity and permeability.So reservoir characteristics itself can not afford a decisive role in the petroleum gathering.There must have a good assemblage of higher physical property value reservoir,conduct pathway and oil surce can form oil pool.
Based on Sr concentration,the ratios of Sr/Br and Th/U,and biogliph fossil,we discuss the water condition and paleoclimate for the deposition of Chang7 oil layer in the Ordos basin.The results show that the ratio of Sr/Br and Th/U is from 0.19 to 0.65,and 0.36 to 5.03,respectively,indicating the water during the Chang7 Period was continental freshwater.The V/Ni ratio of 1.75-5.53 is fallen into the score of the reducing environment.The element assemblage,biogliph fossil,and Co quantitative match indicate that the water depth at the Chang7 Period was half-deep to deep lake,with the maximum depth of 50, 120m.The paleoclimate was confirmed as warm and humid climate by sporopollen assemblage.
Based on measurement of thin section,casting thin section,scanning electron microscope,and X-ray diffraction for Chang 101 sandstone reservoir,we use the quantitatively calculating methods to study the diagenesis of Chang 101 sandstone reservoir in the Ansai oilfield. The feldspar sandstone is dominant n the sandstone.The diagenesis of sandstone reservoir is fallen into the middle degree stage B.The actions for the poor-quality reservoir are both early compaction and cementation of several minerals.Dissolution (especially feldspar and laumontite dissolution) is a factor for improving the reservoir property.Considering diagenetic types and quantitative characters,five kinds of diagenetic facies are classified.the diagenetic facies control the distribution of the highly permeable reservoir.
Generally,the time of natural gas accumulation is late.But the filling history of the Carboniferous natural gas in the Dinan uplift\|Wucaiwan of Junggar basin gives a special sample.Natural gas has low dryness coefficient of 0.92 and N2 content of 3.04%,but the δ13C1 value of -32.12‰ indicates that natural gas would be at the highly mature stage.By means of genetic origin of natural gas and recovery of filling history,we consider that natural gas was formed at early stage but accumulate at late stage in the Dinan uplift\|Wucaiwan of Junggar basin.There are three stages of gas accumulation,including late Hercynian,late Indo\|Chinese and middle Yanshan,but the Yanshan is the main stage of gas accumulation.At Yanshan Era,natural gas was derived from the Carboniferous source rock with thermal maturity of 0.8％-1.2％RO,causing methane enriched in 13C.
The Triassic sedimentary facies of well W16 in northwest margin of Junggar basin are studied by core observation,thin section analysis,and mud logging and well logging data.Results indicate that fan delta front sub-facies is the main sedimentary system of Karamay Formation in W16 well area.The underwater distributary channel deposit and underwater inter\|distributary deposit are main sedimentary microfacies in the studied area.The underwater distributary channel deposit is the main reservoir sand.Analyses of the evolution and the distribution of the microfacies in beds suggest that the accumulation of oil and gas is controlled by microfacies,and the underwater distributary channel deposit is the major oil and gas accumulation of Karamay Formation.
The upper Paleozoic source rocks include dark mudstone in coal measures,coal,and carbonaceous mudstone in the southern north China.In the primary sedimentary settings,the thickness of Carboniferous and Permian source rocks in the southern north China is larger than that in the north Bohai Bay basin.The upper Paleozoic source rock went through three times of hydrocarbon generation: early Indosinian,Yanshanian,and late Himalayan.In some places (i.e Kaifeng sag,Luoyang\|Yichuan,Hefei basin,Qiuxian-Guanxian sag,Huangkou sag,Tangzhuang\|Shenqiu sag),the hydrocarbon source rock reached the highest thermal maturity and the maximum hydrocarbon generation at the Yanshan Period and ceased the hydrocarbon generation at the Himalayan Period.In the Bohai Bay basin,the late hydrocarbon generation potential of source rocks in the areas of HuiMing,DongPu,DongYing,ZhanHua is large,but general in the areas of Chezheng,north Xinxian sag,Luyi,and Niqiuji.
Hyperstable heavy minerals with little diversity in different members were dominated in the upper Triassic Xujiahe Formation of Sichuan basin.Heavy mineral measurement is not only helpful to accurate restoration of depositional systems and ancient water systems,but also reveal the rock\|tectonic attribute of Longmen Shan and recovery of tectonic uplift history.Q\|cluster and principal factor show that the parent rock in the Xujiahe Formation is dominated by sedimentary rocks and low\|level metamorphic rocks,as well as low content of high-grade metamorphic rocks.The content of high-grade metamorphic rocks increases from section bottom to top.ZTR index shows that 4 main source areas in the late Triassic Sichuan basin are located in south-west,north\|west,north-east and south\|east of Sichuan basin,respectively.The distribution of source areas exist inherited.Based on tectonic belt and sedimentology of previous research,the Longmen Shan fold belt begin to form at late Triassic Period.At the second phase of Xujiahe Formation,the northern section of Longmen Shan had been exposed and eroded,but the southern section was still underwater or not yet uplifted.At the fourth phase,the northern section of Longmen Shan continued uplift and suffered erosion,whereas the southern section started uplift and erosion and provided the sediments toward the basin.At the sixth phase,the Longmen Shan was uplifted fully and provided sediments to the basin.
It is generally considered Ordovician break\|slope of Tarim basin with advantage of hydrocarbon accumulation,may directly dominate the distribution of reservoirs after the exploration breakthrough of discovery of Tazhong Ⅰ break-slope.Therefore,we have a series of studies aiming at break-slope.Analyses of characteristics of hydrocarbons and inclusions from wells in Gucheng and Luoxi areas suggest that the original reservoirs in Tadong break-slope have been damaged and the type of late filling hydrocarbons is obvious different from that of original.The divergences of hydrocarbon accumulations in Gucheng and Luoxi are mainly caused by the differences of source kitchen thermal history,structural and fault evolutions of two areas.And the north part of Gucheng break slope zone and the plateau frontier slope of the west part of Luoxi break slope zone are possibly beneficial oil and gas exploration orientation.
The occurrence of the Quaternary in Sanhu area of Qaidam basin,which has trapped the largest biologic gas field,is the product of migration of basin depositional center from west to east under the tectonic movements at the end of Tertiary.In recent years,lithologic gas reservoirs have been found in this area and been divided into three types including sand updip pinch\|out,sand lens and sand property change in the lateral direction.The distribution regularities of lithologic gas reservoirs in the Sanhu area are summarized as distribution in the northern slope,development on the tectonic background,location below the marker bed k9,accumulation in thin sandstone and limitation to a certain depth.At last,according to the distribution regularity of lithologic gas reservoir,the authors point out favorable exploration areas of lithologic gas reservoir.This study has important theoretical and practical significances for lithologic gas reservoirs exploration in the Sanhu area of Qaidam basin.
Yinggehai basin is a Cenozoic extended and transformational sedimentary basin.This unique geological condition causes the different behaviors of gas migration and accumulation.These different behaviors are displayed in the basinal scale,zone scale and transformation scale.The tree-shape transformation system in the central diapirs belt made the deep natural gas migrate alone the mud\|fluid diaper faults and accumulate the surrounding shallow and moderate deep sandstone reservoir at the top of diapirs or its surrounding.The transformation pathway is the vertical conductive fault and fissure.Yingdong slope as a complex transformation system is composed of sand body,unconformity and faults.The transformation system in the Yingdong slope is characterized as segmentation distribution associated with the gradual increase of conductive performance among northern,middle and southern sections in turns.These different transformation behaviors in the extended and transformational sedimentary basin obviously control the natural gas migration and accumulation.The tree-shape on mud-fluid transformation system is favorable of natural gas accumulation around the diapirs.The composite transformation system caused the natural gas migration and accumulation through the different pathways in the Yingdong slope,and the behaviors of natural gas migration and accumulation at each segment in the Yingdong slope were different.
Neotectonism occurred in the Qiongdongnan basin under regional stress field action controlled by deep seated structure,movements of adjacent plates and spreading of South China Sea.Neotectonism plays an important role in the thermal evolution of source rock,reservoir development,and trap formation.A lot of faults,which was formed later under the Neotectonism action,caused the deep hydrocarbon source interconnect with the shallower reservoirs.The vertical interconnection of hydrocarbon source and reservoir is favorable for hydrocarbon accumulation in Paleogene and Neogene.The neotectonisms widely exist in the east and south of Qiongdongna basin, such as Lingnan uplift,Songnan uplift,Changchang uplift,and northern slope of Baodao sag.The good assemblages of reservoir and seal in Neogene and Paleogene exist in these areas above.The late-formed faults made the hydrocarbons migrating upward and accumulating in the Paleogene and Neogene reservoirs,suggesting the good exploration in the future.
Based on the dissections of the typical high content CO2 gas pools in Changling fault-depression,south Songliao basin,a comparative analysis was taken on the genesis,distribution characteristics and their differences of the gases of Changshen 1,2,4,6,7 high content CO2 gas pools in deep layer.Results showed that the type of basement faults determined the relative good or bad conditions for mantle-derived CO2 and hydrocarbon gas accumulations,which further determined the CO2 content in gas pools and the accumulation layer of CO2 -containing gas.The model of gas migration and accumulation in Changling fault-depression was established,which reasonably explains the gas exploration status and complex distribution problems.What's more,it provides a theoretical basis for prediction of CO2 and hydrocarbon gas before drilling.
The large scale of magma activity in Hailaer-Tamuchge basin happened during the period of Hercynian and Yanshanian,which formed the igneous rocks including andesite,basalt and tuff with the age distribution of 84-129Ma.Natural gas pools with high content of CO2 were discovered in central fault zone of Hailaer-Tmuchage basin.The carbon isotopic composition of CO2,Helium and Argon isotopic composition of associated noble gas indicate that the CO2 located in Surennouer rupture structural belt,Wunan subbasin and Bayantala rupture structural belt is curst-mantal source,whose distributional region is not same as the distribution of magma in Yanshanian.The authors consider that most of the CO2 polls,but not all,are relevant to the volcanic magmatism belt.The reservoir forming characteristics of CO2 in S2 well indicate that the distribution and activity of fault systems are another important factors controlling the accumulation of CO2.Meanwhile,this paper cautions that Nantun Formation and Tongbomiao Formation which are connected by the discordogenic fault are the favorable direction for furthering exploration.
The tectonic activity and exploration potential analysis of subduction-accretionary belt at plate convergent margins are always difficult problems in oil geologic field.Myanmar is a favorite place for the study,which lies in the conjunction area of the Eurasian Plate and Indian Plate.The tectonic evolution,structural domain division and petroleum exploration prospects are studied based on the carefully study on the wells,outcrops,seismic data and regional background information.It can be divided into three structural domains:Accretionary wedge,slope basin and trench.The hydrocarbon accumulation condition is favorable in Bengal fan trench region,and hunting for turbidite sand bodies and subtle reservoirs is the key to petroleum exploration.
Based on drilling core,bore well,well logs and seismic data,we use the calssical Vail theory of sequence stratigraphy to identify six sequence boundaries in Paleogene Baiju sag,which is divided into one first-order sequence,two second\|order sequences,and five three-order sequences.The third-order sequences of SQ1-SQ4 and SQ5 are corresponding to the basin's subsiding-fault depressing stage and strong fault-depressing stage.We use the isochronous correlation to establish the Paleogene sequence stratigraphic framework in the Baiju sag,and discuss the relationship between source-reservoir-cap rock assemblages and third-order sequences.The low water level and later high water level system fields are the favorable place of reservoir development.The transgressive and early high water lelve system fields are the profitable place of source and cap rock formation.Three sets of source-reservoir-cap assemblages are formed among these fields,and the lower assemblage is the best one in Paleogene in the Baiju sag.
The hydrous pyrolysis experiments for potential hydrocarbon sources in the marine sequence of south China were subjected in the high pressure and geological condition simulation vessels.The results indicate that the productivity of hydrocarbon gas generation for hydrocarbon sources is various,the highest productivity for crude oil (light oil and condensate),the secondary productivity for the dispersed soluble organic matter (solid bitumen and heavy oil),and the poor productivity for kerogen.The yield of hydrocarbon gas products for hydrocarbon sources is positively related with total organic carbon,soluble organic matter and organic matter type,but negatively with thermal maturity.The carbon isotopes of hydrocarbon sources inhibit the tendency of methane carbon isotopes.The carbon isotopic composition of methane derived from the hydrocarbon source with the lighter carbon isotope is lighter than that of methane from the hydrocarbon sources having the heavier carbon isotope.With thermal maturity increase,δ13C value of methane increases but is less than that of its hydrocarbon sources.Theδ13C values of ethane and propane in the pyrolysate products also increase with pyrolysis temperature increase,gradually approaching of the carbon isotope of their sources at the peak stage of hydrocarbon generation.At high-over mature stages,the δ13C values of ethane and propane are often more than that of their sources.Thus the carbon isotope of heavy hydrocarbon gases would be ineffective as gas genetic indicators.The contents and isotope compositions of carbon dioxide are different between kerogens and dispersed soluble organic matter.The carbon isotope fractionation between carbon dioxide and methane derived from soluble organic matter is greater than that from kerogen.During the process of hydrocarbon generating for hydrocarbon sources,the carbon isotope compositions of kerogen and liquid hydrocarbons are mainly controlled by precursor type,tracing their sources.Therefore,the carbon isotope compositions of kerogen and liquid hydrocarbons can be used to perform oil-source correlation and tracing hydrocarbon sources.
Several techniques,including GC,GC-MS and GC-IRMS,are used to study the molecular geochemistry and origin of oil (filled joint and cavern in limestone) of T1f1 in the Changjianggou profile of the northwest of the Sichuan basin.The data show that the petroleum δ13C values for bulk oil and group compositions are less than -30 ‰.The crude oil has not suffered the secondary change such as bacterial decomposition,water leaching and so on.The isotope fractionation effect for the group compositions is small.The distribution of normal paraffin alkane is single peak,with nC22 prominent peak.Pr/Ph ratio (isoprenoid) is 0.75,with the Pr and Ph prominent predominance comprised with nC17and nC18respectively.The aromatic hydrocarbons present a shape of camel shoulder suggesting complicate domponents,and the phenanthrene is the prominent peak.Based on the methyl phenanthrene index (MPI1),RO for the crude oil is about 0.83%.The carbon number for the tricyclene is distributed from C19to C30,with C23prominent peak.C30 is the prominent peak in hopanoid and γ-wax alkane is the medium intensity content.The C29steroid is predominant in the sterane series,with the “V” shape distribution of C29>C27>C28.The values of maturity parameter C2920S/(20S+20R) and C29ββ/(ββ+αα) are 0.39 and 0.31 respectively,which not reach the isomerization equilibrium.On the basis of regional geology,source rock characteristics of T1f1,geochemical characteristics of petroleum and oil\|source correlation,we consider that the crude petroleum is a product of Cambrian source rock at the oil generation peak and the occurrence of crude petroleum in the limestone cave and seam is a result of tectonic destroys after the early oil accumulation.
There are three sets of source rocks in the Qiongdongnan basin,including Eocene lacustrine source rock,Oligocene and Miocene marine gas layers.Since the Eocene unit has not yet been met during the drilling,it can only be considered as potential source rock in Oligocene.The total organic carbon (TOC) and hydrocarbon generation in the Oligocene source rocks in the Qiongdongnan basin reach the assessment standard of good source rock.The mudstone in the Oligocene source rocks of Yacheng and Lingshui Formations have the high TOC,associated with a certain hydrocarbon generation potential.The mudstone in the Oligocene source rocks of Yacheng and Lingshui Formations have a dominant vitrinite component,and minor sapropelic and exinite.Kerogen type of source rock is mainlyⅡ2 or Ⅲ,and prone to generate gas.The n-alkane series of Yacheng Formation dark mudstone are characterized by high carbon number prominence,high Pr/Ph ratio,and low gammacerane index,showing the source rock had formed in oxygenated conditions.High abundance of oleanane detected in the hopane series of compounds shows the input of high plants.The C27,C28,C29 regular steranes in the coal extract occur as opposite “L” pattern,indicating that the organic matter would be originated from the lacustrine high plants.But in the Yacheng Formation and Lingshui Formation mudstone,the sterane series are distributed as “V” pattern,suggesting there would be some of the algae inputs in addition to high plants.The algae input in some parts of Lingshui Formation source rocks greatly increased,indicating the more favorable conditions for generating hydrocarbon.
We comparatively studied the geochemical characteristics of C6-C7 light hydrocarbons in natural gas from Lishu fault depression in Songliao basin for the first time.Combined with characteristics of carbon isotope,results showed that natural gas from Lishu fault depression is very poor in aromatic hydrocarbon but rich in chain alkanes.Among the components of C6-7 light hydrocarbon,n-alkanes have the content advantage and naphthenes have the lowest content.The distribution characteristics suggested that the natural gas originated from sapropelic organic matter.The ratio K1 is around 1 and the three\|ring preference (3RP) is greater than 5RP and 6RP in C7 light hydrocarbon from lacustrine facies source [JP2]rocks,which were basically consistent with the conclusion of light hydrocarbons by Mango.The high value of paraffin index and heptane index indicated that the natural gas is mainly pyrolysis gas which coincides with the high value of δ13C1.
Although the Naiman depression has made a breakthrough and gotten the commercial oil flow during 20 years petroleum exploration,the geochemistry of natural gas and its origin is not reported.Based on the chemical and carbon isotopic compositions of natural gas for 38 gas samples from the Naiman 1 block，we discuss the geochemical characteristic of hydrocarbon gases and their origin,in combination with geological background.Natural gas was derived from sapropelic organic matter at low-mature or mature stage,whose origin is of oil-type gas.Natural gas has the dominant CH4 concentration and moderate heavy hydrocarbon gas,with low dry coefficient,showing the typical wet gas.Based on stable carbon isotope and thermal maturity for hydrocarbon gases，we consider that natural gas in this study is oil-associated gas.Values of δ13C1，C1/C1-5,iC4/nC4 and iC5/nC5 in the natural gas from the upper part of Jiufotang Formation more than those from the lower part is related to thermal maturity.
Based on porous media and Terzaghi effective stress principle,we build the model of coal constitutive framework in the coal bed methane (CBM) production and interpret the stress deformation of coal matrix.We setup the dynamic model of the porosity and permeability so as to get the changes of the physical properties of coal seams during CBM production.The seeping equation of coal fluid is obtained based on hydromechanics continuity equation.Finally we present the mathematical model of single phase and multiphase fluid-solid coupling seepage in the CBM production by means of auxiliary equation and formed conditions.
Based on principle and method of seismic AVO inversion,the inversion for some known coal-gas outburst points is integrated.Single point analysis shows that the absolute AVO intercept and gradient at the coal-gas outburst point is greater than that at the non-outburst point,suggesting that the AVO abnormity would be resulted from coal-gas outburst points.According to AVO response at the coa-gas outburst points,the prediction of coal-gas outburst area is gotten by AVO crossplot and integrative index.As a new predicting technology,the comprehensive analysis of the regional geology should be involved practically so as to avoid the multi\|solutions of AVO inversion.
The Santanghu basin is one of low-rank coal-bearing basins which have become the hotspot of coal bed methane exploration areas.Based on the analyses and discussions of geologic characteristics of this area,such as developmental characteristics of coal,coal evolution characteristics,coal bed methane content,micropetrological unit,the adsorption isotherm characteristics of coal,Hydrogeological conditions of effect and so on,we consider that the basin has abundant coal bed methane exploration foundation and the northern margin of Tiaohu Malangng sag in Shuixigou Group is the preferred field for coal bed methane exploration.
Five coalbed methane productive and enriching types are examined in China,including structural high of coal\|rich zone,upslope with stable regional direct cap rock,uplift of depressions in regional active volcanic zone,well-sealed thick coal zone with low coal rank and faulting & secondary cleat developed zone.The productivity and enrichment of coalbed methane are based on the following three conditions: cap rocks control gas content;stress field controls permeability;structure and coal types control enrichment zone.The controlments of sedimentary environment on coalbed methane enrichment are also analyzed,including the coal-forming precursor,sealing ability and reservoir quality.Woody plants are better than herbs in coalbed methane generation and preservation.Shallow sea-coastal barrier and lake environments have better sealing ability.Coals with lower ash content,higher vitrinite content and developed microfracture have better reservoir quality.Further,key parameters of coalbed methane productivity and enrichment are analyzed.The production characteristics of coalbed methane are elaborated,and the productive conditions of directional pinnate horizontal wells are emphatically analyzed.Three types of coalbed water including internal water,interlayer water and external water are described.
The study for geological storage of CO2 has been more than ten years in China,but the optimization system of CO2 geological storage target area is not established yet.This embarrass situation has been restricting the development of the applications of geological storage of CO2.Based on the references of CO2 geological storage and the previous research results,we analyze the effect of the geological background,basinal resource and reservoir characteristics upon the CO2geological storage,and establish the evaluation system for the CO2 geological storage.By AHP to determine weights,we make the indicator standardization using dimensionless index approach,and evaluate the target areas using the weighted average model.Finally,we evaluate and sort some CO2 geological storage areas in China.The application results show optimization system can effectively guide the use of CO2geological storage to improve the efficiency of reservoir exploitation.
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