It′s difficult to analyze the particle texture characteristics of coarse clastic rocks (conglomerate,conglomerate-sandstone,etc.) by using existing methods of particle size analysis.A method of combining macroscopic core delineation with microscopic thin-section identification was used.Probability cumulative grain size curves from gravel to sand were established.The parameters of particle texture were calculated,and the characteristics of particle texture among different lithofacies assemblages in near-shore subaqueous fan were studied quantitatively.According to the characteristics of rock structure,sedimentary structure and rock color,the sandy conglomerate bodies are separated into 11 types of lithofacies as well as 14 types of lithofacies assemblages of upper Es4 in the Yanjia area,Dongying Depression.On the basis of parameters of particle texture such as φ5,Mz,So,gravel contents and the characteristics of their vertical degradation degree,the types of lithofacies assemblages are divided into three categories and six subcategories.Generally,with the distance from near to distant from the fault boundary in source direction,particle size turns fine,sorting becomes better,gravel contents decrease and vertical degradation degree increases at first then decreases.
Although the Darcy′s law with applicable speed limit was proposed in classical percolation mechanics,the non-Darcy percolation law is not clear under the low speed condition.7 groups of seepage simulation experiments of the Xujiahe tight gas reservoir in the Sichuan Basin were carried out with highest gas injection pressure of 10MPa and confining pressure higher than the injection pressure of 2-3MPa in order to ensure that the gas migrated along the tight sandstone rather than along the inner wall of the core and blessings.10-15 flow data points were determined in each experiment.The experiments of the complete process of gas migration in tight sandstone effectively explore the tight gas seepage mechanism.Results of the experiments indicate that the seepage process of tight gas has 3 stages (very low-velocity & non-linear stage,low-velocity & non-linear seepage,low-velocity & linear stage),and 4 seepage curve models (composite type,concave type,convex type,linear type).
The degree of oxidation and reduction of sedimentary environment and sedimentation rates are two vital factors impacting the preservation of organic matter.The author has attempted to study their impaction by instance of Erlian Basin in northern China and found that the strong reducing environment and high sedimentation rates are favorable for the preservation of organic matter.By comprehensive analysis,the author found that the preservation of organic matter is not controlled by a single factor,for example in some sags with their sedimentary environments proximal to oxidation,if the sedimentation rates were higher,the rapid burial of organic matter could shorten the time of degradation;in other sags with lower sedimentation rates,if their sedimentation environment was reducing,organic matter can also be well preserved.In summary,the preservation of organic matter is affected synthetically by the degree of oxidation and reduction and sedimentation rates.They play a role of “mutual complementation” during the preservation of organic matter.Previous research on the preservation of organic matter only analyzed single factor such as the degree of oxidation and reduction or sedimentation rates,which is somewhat partial.
Exploration practice shows that the middle-shallow layer from the upper Ganchaigou Formation to the lower Youshashan Formation have great potential for oil and gas exploration in the Yingxiong Mountain in the western Qaidam Basin.Based on the systematical analysis of the mouth bar and distal bar sandstones of the lower Youshashan Formation from the Yingdong faulted anticline to Wudong slope in the eastern Yingxiong Mountain in the western Qaidam Basin from the aspects of its development scale,horizontal distribution,varying regulation,major fault flat form,extend range,trap development condition,oil source condition and oil/gas show,it is suggested that the area from the east of the well Sha39 in Yingdong faulted anticline to the north of the well Wu 28 in Wunan fault nose has good oil-gas geological condition.This area has geological conditions favorable for the development of structural traps and lithologic traps with tectonic settings.It is the important succeeding region of the following oil and gas exploration.
The Hadson Oilfield,whose main reservoir is Carboniferous Donghe sandstones,has the problems of strong heterogeneity in reservoir fluid properties and complex oil-water relationships.Aimed to interpret the differences between interlayers and their around normal reservoirs in Donghe sandstones,through detailed core samples observation and analysis of well testing data,this article analyzed the geometry of interlayers,their petrologic elements and diagenesis,and pointed out their influences on fluid flow and materials interchange.This study indicates that elements of rock skeleton in calcareous interlayers and their around reservoirs are basically unanimous.However,because of the differences in diagenesis process,the cements in interlayers are usually calcite,dolomite and anhydrite.The cements can make the physical property of calcareous interlayers very poor,and they can also make significant property differences in crude oil and formation water which located above and below the interlayers.Based on the above analysis,the barrier effects on fluid flow of the interlayers of different degree lead to the properties of uneven distribution of fluid and complex fluid flow in the Donghe sandstone in the Hadson Oilfield.
Pearl River Mouth basin undergoes two large tectonic movements from Late Oligocene to Early Miocene.The earthquakes induced by multiphase tectonic activity generate serious seismic-related soft-sediment deformation structures of seismite autochthonous system.The vertical superposition relationship of these structures within transgressive sediment sequence indicates the reworking on original sedimentary sequence during the different earthquake intensity stages.The vertical seismites succession includes 7 sections from bottom to top: Section A is coastal sandstone with primary stratification,as basal interval of seismites succession deposit during pediocratic before the earthquake happened;Section B is meandering liquefaction dyke,when unconsolidated sandish debris are liquefied during the period of strong earthquake activities;Section C is a series of sand shale interbedded with liquefied fold deformed lamination;Section D is step micro-fault,as a result of differential settlement of the rapid accumulation of sediments in the depletion period of earthquake;Section E is pinch and swell structure which is characterized by discontinuous sandish belt,because of thin sand in mudstone stretch or compress when earthquakes tend to stop;Section F is load structure driven by gravity at the end of earthquakes;Section G is continental shelf mudstone with microscopic horizontal bedding developed at the stagnant period of earthquakes.Seismic events can be favorable for forming lithostratigraphic traps.The properties of reservoirs can be greatly improved by fissures and liquefaction sandstone dyke caused by seismic actions.And seismism has a positive influence on hydrocarbon migration.But seismic activities can destroy the sealing ability of cap rocks in some degree.To strengthen the research on paleoseismic records will provide a new perspective for hydrocarbon exploration in Pearl River Mouth basin.
Using seismic,logging and geochemical data combined with basin modeling,this paper discussed tectonic evolution,paleotemperature and overpressure evolution in Oujiang Sag.The results show that tectonic evolution stage of the Oujiang Depression experiences a rift,depression and regional deposition,which controls the development and distribution of depositional systems.It deposits three sets of source rocks,Yue Guifeng Formation,Lingfeng Formation and Mingyuefeng Formation,in which the Yueguifeng Formation is the main source rocks.Paleotemperature field of the study area has experienced the evolution of burial warming-uplift cooling-burial warming,and the paleo-temperature of west subsag is higher than the east subsag.Because of this thermal evolution difference,the source rocks maturity in the west subsag is higher than that in the east subsag.Abnormal high pressure experiences a supercharge-decompression-supercharge process in Oujiang Sag.Abnormal high pressure can provide a driving force for oil and gas migration.The abnormal high pressure decompression process occurs in Late Eocene,which is the importance time of oil and gas migration.The coupling of the tectonic evolution,the accumulation of the dynamic pressure and release,heat flow and hydrocarbon controls the formation of oil-gas reservoir in Oujiang Sag.
In Amu-Darya Basin of Northern Afghanistan,the oil and gas distribution shows significant difference,i.e.,gas pools are located in the north and the oil ones in the south,while in between are the oil pools and gas pools with oil ring.By analyzing the geological elements of oil and gas accumulation,the controlling factors of oil and gas differential distribution are approached.From north to south,trap fill,gas component and reservoir-cap assemblage differ specially.Southward,the trap fill and content of CO2 decease,while CH4 increases.Bounded by the Upper Jurassic salt,the reservoir-cap assemblage in the north and south is subsalt Upper Jurassic carbonate and supra-salt Lower Cretaceous clastic ones,respectively,and in-between both assemblages develop.The distribution range of gypsum and salt is the key factor controlling the differential distribution of oil and gas.Then the corresponding mode is established and the exploration targets in the research area are evaluated,which indicate that in the north of the research area where salt exists the Upper Jurassic gas pools are the targets,while in the south where anhydrite is absent the oil pools should be focused,and in between both Upper Jurassic gas pools and Lower Cretaceous oil pools and gas pools are the potential targets.
Baram Delta Province is located at the NW Borneo active margin.It has the features of different zones in north and south: the overlap-thrusting belt under compression in north,extensive subsiding belt generated by extension in middle and compressive inverting belt in south.Different fromthe area developing Cenozoic deltas located on the passive-margin,its total shortening in compression province goes beyond 1.8% compared with the stretching in extension province and this can not be explained by the ideal delta system.Based on the regional tectonic setting analysis and stress features in the study area,it regards the far-field compression and the function driven by gravity during delta growing process as the mechanism for this phenomenon.For the effection of tetonic division,the upper,middle and lower oil-gas reservoir-forming assemblages distributed in different tectonic zone; different stress background generated unique structural trap in various tectonic belt and the fault with long-term activity provided major pathways for hydrocarbon migration.Thus,the conclusion will be helpful for the research of hydrocarbon formation and further hydrocarbon exploration in Baram Delta area.
CO2 and CH4 play a significant role in the global climate change and carbon circulation and can be used to monitor their origin and tectonic activity.In this paper,we carried out investigations on the gas compositions,carbon isotope ratios of CO2 and CH4 ,and He isotope compositions from the Qiangtang Basin and its adjacent areas.Our results show gas samples from Beiluhe,Bucha Lake,and eastern Tuotuo River are N2-rich with N2 over 75%.The contents of CO2andCH4 are only 3.45%-20.91% and 0-3.58%,respectively.CO2/3He and CH4/3He and carbon isotopic values of CO2and CH4 suggest that both CO2 and CH4 from Bucha Lake are biotic without mantle-derived CO2 and He,whereas those of Beiluhe and eastern Tuotuo River are abiotic.Southern Erdaogou Depot,branch of Tuotuo River,and Tanggula Mountain Depot are enriched in CO2 with more than 96%.TheCO2 was at least partially originated from mantle,trace amount of CH4 was abiotic and derived from mantle-derived CO2;He was primarily originated from crust with only 2.15%-5.66% of mantle-derived origin.These results show that the emitting of large quantity of mantle-derived CO2 is likely to be ascribed to the presence of Bangong Lake-Nujiang River,Hoh Xil-Jinsha River sutures and the Cenozoic volcanism in northern Tibet.Nevertheless,the estimated small fraction of mantle-derived He may result from the low opening degree at the bottom of fault zones and possibly reflect a geological setting of strong extrusion and an increase in crustal thickness.
In order to ascertain whether there exists natural gas hydrate in Wuli premofrost of Tibet Plateau and to investigate the gas source of gas hydrate,based on the analysis of organic carbon content,rock pyrolysis and vitrinite reflectance measurement on the potential source rocks and combined with molecular biomarker analysis technology,a preliminary study on organic sources,depositional environment and the thermal evolution degree was made on the Permian and Triassic mudstones,carbonaceous mudstones and coals from Wuli area.The results illustrated that the potential source rocks of this area were developed in reducing environment of marine-terrigenous facies,and most organic material was a mixture of lower aquatic organism and higher terrigenous plants.However,biogensis of some samples was mainly originated from lower hydrobiont.The isomerization parameter values of C29steranes and C32 homohopanes reached equilibrium point except individual sample.The organic carbon content in some mudstone intervals of Nayixiong Formation was relatively high and the coal-bearing sequence was relatively thick in the Upper Permian.and generally at over-mature stage.Therefore,they could be as gas source rocks.However,because of limited distribution in the west of eighty-five track section,the coal-bearing strata of the Upper Triassic Bagong Formation might merely be local gas source.
Natural gas and small amount of condensates were obtained in Rub Al Khali Basin.The Ordovician condensates from well A2,with carbon isotopic value from -26.55‰ to -27.70‰,was dominated by the alkanes with carbon numbers smaller than 17.The condensates has high saturated fraction with no asphaltene.The content order of group composition is as follows: saturated fraction > aromatic fraction>non-hydrocarbon fraction.The heptane and isoheptane values of the condensates are 22% and 2.38,respectively.The biomarker contents of the condensate are low,with hopane dominating in the terpanes and C23 tricyclic terpane dominating in tricyclic terpane,and low content of C24tetracylic terpane.The condensates have high content of diasterane,with regular sterane distribution being C29≈C27>C28.The biomarker distribution of the Ordovician condensates is similar to that of the Paleozoic oils sourced from Silurian hot shale.The maturity parameters of biomarker and diamondoids suggest the condensates to be mature to high mature.All the natural gases from different time in Block B are wet gas of organic origin.The maturity of these gases ranges from 0.75% to 1.35%.Due to the similar maturity between the condensate and natural gas,it is suggested that the oil-cracking may not be the only gas origin.Condensates and natural gas may be mainly sourced from the thermal cracking of Silurian hot shale.
Through core observation,thin section identification,grain size analysis and seismic attributes research,the sedimentary facies model of Middle Es3 Formation in Pucheng tectonic belt,Dongpu Depression was established.According to the geological characteristics of “high uplifts & deep sags” and the rule of wave impedance inversion on sandstone and mudstone varing from different burial depth,the wave impedance inversion method of expressed compaction controlled by sedimentary facies model was put forward and used for reservoir prediction.The results showed that the sedimentary systems in the study area was fan delta,lacustrine mudstone and beach bar facies.Two fan deltas were developed in the down throw side of Lanliao fault and beach bar sands in shore-shallow lacustrine were found in Pucheng anticline belt.The result of reservoir prediction showed that sand thickness was bigger in the area where developed fan deltas,beach bar or area between the two fan deltas.Sandstone distribution was fit to the rule of sedimentation.Fan delta front and the beach bar between the two fan deltas in the slope area between Pucheng anticline belt and Pucheng Subsag were favorable to exploration where were easy to form up dip wedge-out reservoir and lenticular reservoir.
Reservoirs of Yingcheng group of Wangjiatun Gasfield are strong non-homogeneous volcanic reservoirs with low porosity and low permeability,in which cracks play a very important role for the communication between porosity and corrosion holes.Because of the dual media features of pores and cracks,between which configuration relations are complex and diverse,using post-stack data has been unable to meet the demands of gas reservoir evaluation to make further fine description of crack and quantitatively identify small-scale cracks.In this study,we resorted azimuth before processing the seismic data,extracted transverse difference properties which are not affected by fluid,finally we characterized the attribute parameter changes after processing in the form of strength,and predicted the development of the of cracks;Using multi-azimuthal AVO crack detection technology,we predicted the fracture development of the volcanic reservoir of Yingcheng Group of Wangjiatun region.Compared to conventional coherent technology,multi-azimuthal AVO crack detection technology has characteristics of high resolution and identification of small-scale cracks.The predicted results also have a high degree of agreement with actual well interpret results.
P-wave velocity and S-wave velocity are the bridge of petrophysical property and seismic exploration.Through the study of P-wave velocity and S-wave velocity,we can get the effective identification of lithology,physical property and fluid.However,there is often lack of S-wave data in actual study,so S-wave velocity prediction is necessary.Now s-wave velocity prediction in clastic reservoir has developed very well,but in the carbonate reservoir,because the lithology and pore systems are very complex,the prediction accuracy is low and the development of prediction is slow.Xu-Payne model considered the effect of different pore type to elastic wave which can be used in carbonate reservoir theoretically.In this article,we introduce the method of S-wave velocity prediction which is based on rock physics,and analyze the effect of pore type on P-wave and S-wave velocity,such as stiff pores,inter-particle pores and crack.Also we compare it with other models,the prediction accuracy of Xu-Payne model is 2.9% higher than that by Xu-White model,so it is more consistent to the measured S-wave log.
Drilled well demonstrated that the Carboniferous Xiaohaizi Formation develops bank complex at the Qunkuqiake structural belt in western Maigaiti slope,and anomalous seismic responses have been discovered in the south of Qunkuqiake structural belt.For exploring the geology properties of anomalous seismic response,according to drilled wells,seimic and regional geology data,the bank complex's sedimentary environment in Xiaohaizi Formation is investigated.It is pointed out that the sedimentary model of Xiaohaizi Formation in western Maigaiti slope is carbonatite gentle slope.On the basis of the research of sedimentary facies,the seismic facies' characteristics of different sedimentary facies are analyzed,and the characteristics of anomalous seismic responses are depicted and interpreted.Research results show that bank complex has two kinds of typical reflection characteristics,i.e.,abnormal thickening of the reflection time thickness and the decrease of amplitude.It forms four anomalous seismic responses which are imbricate retrograding reflection,lenticular reflection,low frequency weak amplitude reflection and wave-miniliform noncontinuous reflection.Bank complex mainly developed in banding of NEE trending at middle gentle slope facies belt whose thickness changed obviously.Bank complex has major distribution range and scale.
Permeability is an important physical parameter,which determines the fluid flow ability.Take shale reservoir matrix and fracture as the research object,combine the new research results from home and abroad,two kinds of diffusion in the matrix were presented:Knudsen diffusion and Fick diffusion.Knudsen diffusion is caused by the collisions between gas molecules and the hole wall while Fick diffusion is due to the effect of concentration difference.Taking two diffusion effects into account in the matrix,the new gas permeability model in the matrix was deduced to analyze the Knudsen diffusion and Fick diffusion effects on permeability in the matrix.To amend the P & M model,the Klinkenberg effect was also considered in the model,the permeability change model under the influence of different mechanisms were presented.And then the influence of the Klinkenberg effect on the permeability of fracture was analyzed.Results show that:(1)For matrix permeability model,when the pore radius is small,Knudsen diffusion has a great influence on permeability;Furthermore,the impact of Fick diffusion on matrix permeability is remarkable at low pressure and small matrix permeability.(2)For fracture permeability model,the impact of Klinkenberg effect emerges only at low pressure.
Adsorbed gas content is essential to the calculation of shale gas reserves,and adsorbed gas desorption process is directly related to the production of shale.Isothermal adsorption and desorption experiments under different conditions were carried out with Longmaxi shale samples collected from south of Sichuan and Zhaotong area.The results show that the maximum adsorption volume VL decreases with the increase of temperature and the desorption ratio increases with the increase of temperature,which both showed a good linear relationship with the temperature. TOC and clay mineral content will affect the shale gas adsorption capacity.The shale maximum adsorption volume has a positive correlation with TOC in shale with high TOC content,while the maximum adsorption volume and clay mineral content was positively correlated in shale with low TOC content.The presence of water will reduce the shale adsorption capacity and also the desorption ratio.The remaining adsorption volume after desorption increases with the moisture content.
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