Tracing of natural gas migration by light hydrocarbons:A case study of the Dongsheng gas field in the Ordos Basin,NW China

Based on the analysis of light hydrocarbon compositions of natural gas and regional comparison in combination with the chemical components and carbon isotopic compositions of methane,the indication of geochemical characteristics of light hydrocarbons on the migration features,dissolution and escape of natural gas from the Dongsheng gas field in the Ordos Basin is revealed,and the effect of migration on specific light hydrocarbon indexes is further discussed.The study indicates that,natural gas from the Lower Shihezi Formation(Pix)in the Dongsheng gas field displays higher iso-C5-7contents than n-C5-7contents,and the C6-7light hydrocarbons are composed of paraffins with extremely low aromatic contents(<0.4%),whereas the C7light hydrocarbons are dominated by methylcyclohexane,suggesting the characteristics of coal-derived gas with the influence by secondary alterations such as dissolution.The natural gas from the Dongsheng gas field has experienced free-phase migration from south to north and different degrees of dissolution after charging,and the gas in the Shiguhao area to the north of the Borjianghaizi fault has experienced apparent diffusion loss after accumulation.Long-distance migration in free phase results in the decrease of the relative contents of the methylcyclohexane in C7 light hydrocarbons and the toluene/n-heptane ratio,as well as the increase of the n-heptane/methylcyclohexane ratio and heptane values.The dissolution causes the increase of isoheptane values of the light hydrocarbons,whereas the diffusion loss of natural gas in the Shiguhao area results in the increase of n-C5-7contents compared to the iso-C5-7contents.

Geochemical characteristics of noble gases in natural gas and their application in tracing natural gas migration in the middle part of the western Sichuan Depression, China

Noble gases in natural gas, from Xiaoquan, Xinchang, Hexingchang and Fenggu gas reservoirs in the middle part of the western Sichuan Depression, China, were analysed. Results show that the volume content of crustal noble gases accounts for 97.9% to 99.7% of the total noble gas content, indicating that the noble gases in the study area are very largely derived from the crust. Moreover, the 40Ar time-accumulating effect of source rocks is used to determine the complex relationship between gases and source rocks in this area, and the results agree well with that from analysis of source rock light hydrocarbons. Due to the short migration distance, the separation of 4He and 40Ar is not significant in Xujiahe natural gas and Lower and Middle Jurassic natural gas, so it is difficult to trace natural gas migration. However, this separation characteristic of 4He and 40Ar in Middle and Upper Jurassic natural gas is significant, which indicates that natural gas migration was from the Middle Jurassic to Upper Jurassic formations. In addition, the variation trends of 3He/4He ratio and δ13C1 value indicates that natural gas migration is from the Xujiahe formation to the Jurassic layer in the study area.

A Study of the Migration and Accumulation Efficiency and the Genesis of Hydrocarbon Natural Gas in the Xujiaweizi Fault Depression

In order to investigate the migration and accumulation efficiency of hydrocarbon natural gas in the Xujiaweizi fault depression, and to provide new evidence for the classification of its genesis, a source rock pyrolysis experiment in a closed system was designed and carried out. Based on this, kinetic models for describing gas generation from organic matter and carbon isotope fractionation during this process were established, calibrated and then extrapolated to geologic conditions by combining the thermal history data of the Xushen-1 Well. The results indicate that the coal measures in the Xujiaweizi fault depression are typical ＂high-efficiency gas sources＂, the natural gas generated from them has a high migration and accumulation efficiency, and consequently a large-scale natural gas accumulation occurred in the area. The highly/over matured coal measures in the Xujiaweizi fault depression generate coaliferous gas with a high δ^13C1 value （〉 -20‰） at the late stage, making the carbon isotope composition of organic alkane gases abnormally heavy. In addition, the mixing and dissipation through the caprock of natural gas can result in the negative carbon isotope sequence （δ^13C1 〉δ^13C2 〉δ^13C3 〉δ^13C4） of organic alkane gases, and the dissipation can also lead to the abnormally heavy carbon isotope composition of organic alkane gases. As for the discovery of inorganic nonhydrocarbon gas reservoirs, it can only serve as an accessorial evidence rather than a direct evidence that the hydrocarbon gas is inorganic. As a result, it needs stronger evidence to classify the hydrocarbon natural gas in the Xujiaweizi fault depression as inorganic gas.

Geological reservoir and resource potential(10^(13)m^(3))of gas hydrates in the South China Sea

A detailed understanding of the distribution and potential of natural gas hydrate(NGHs)resources is crucial to fostering the industrialization of those resources in the South China Sea,where NGHs are abundant.In this study,this study analyzed the applicability of resource evaluation methods,including the volumetric,genesis,and analogy methods,and estimated NGHs resource potential in the South China Sea by using scientific resource evaluation methods based on the factors controlling the geological accumulation and the reservoir characteristics of NGHs.Furthermore,this study compared the evaluation results of NGHs resource evaluations in representative worldwise sea areas via rational analysis.The results of this study are as follows:(1)The gas hydrate accumulation in the South China Sea is characterized by multiple sources of gas supply,multi-channel migration,and extensive accumulation,which are significantly different from those of oil and gas and other unconventional resources.(2)The evaluation of gas hydrate resources in the South China Sea is a highly targeted,stratified,and multidisciplinary evaluation of geological resources under the framework of a multi-type gas hydrate resource evaluation system and focuses on the comprehensive utilization of multi-source heterogeneous data.(3)Global NGHs resources is n×10^(15)m^(3),while the NGHs resources in the South China Sea are estimated to be 10^(13)m^(3),which is comparable to the abundance of typical marine NGHs deposits in other parts of the world.In the South China Sea,the NGHs resources have a broad prospect and provide a substantial resource base for production tests and industrialization of NGHs.

Gas Sources of Natural Gas Hydrates in the Shenhu Drilling Area, South China Sea: Geochemical Evidence and Geological Analysis

The Shenhu gas hydrate drilling area is located in the central Baiyun sag, Zhu I! depression, Pearl River Mouth basin, northern South China Sea. The gas compositions contained in the hydrate-bearing zones is dominated by methane with content up to 99.89% and 99.91%. The carbon isotope of the methane （δ^13C1） are -56.7%0. and -60.9%0, and its hydrogen isotope （δD） are -199%0 and -180%0, respectively, indicating the methane from the microbial reduction of CO2. Based on the data of measured seafloor temperature and geothermal gradient, the gas formed hydrate reservoirs are from depths 24-1699 m below the seafloor, and main gas-generation zone is present at the depth interval of 416-1165 m. Gas-bearing zones include the Hanjiang Formation, Yuehai Formation, Wanshan Formation and Quaternary sediments. We infer that the microbial gas migrated laterally or vertically along faults （especially interlayer faults）, slump structures, small-scale diapiric structures, regional sand beds and sedimentary boundaries to the hydrate stability zone, and formed natural gas hydrates in the upper Yuehai Formation and lower Wanshan Formation, probably with contribution of a little thermogenic gas from the deep sedments during this process.

Thermodynamic Modeling of Fluid-Bearing Natural Gas Inclusions for Geothermometer and Geobarometer of Overpressured Environments in Qiongdongnan Basin, South China Sea

It is a very difficult problem to directly determine fluid pressure duringhydrocarbon migration and accumulation in sedimentary basins. pVt modeling of coupling hydrocarbonfluid inclusion of its coeval aqueous fluid inclusion provides a powerful tool for establishing therelationship of formation pressure evolution with time. Homogenization temperature of fluidinclusion can routinely be measured under microthermometric microscopy. Crushing technique has beenemployed to obtain the composition of fluid inclusions, and the commercial software VTFLINC easilyand rapidly completes the construction of p-t phase diagram. The minimum trapping pressure ofhydrocarbon fluid inclusion would be then determined in the p-t space. In this paper, three samplesof YC21-1-1 and YC21-1-4 wells at YC21-1 structural closure, Qiongdongnan basin, South China Sea,were selected for the pVt modeling practice, and the formation pressure coefficient (equals to fluidpressure/hydrostatic pressure) changing trend with time has primarily been established. Themodeling results also indicate that the reservoirs of Ling-shui and Yacheng formations in YC21-1structure are within a very high potential system and would have undergone a discharging of thermalfluids through top seal rupture, which depicts that there is a very high risk for natural gasexploration in this area.

Numerical simulation study of gob air leakage field and gas migration regularity in downlink ventilation

Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influence of natural wind pressure to analyze the stope face differential pressure, gob air leakage field distribution and gas migration regularity theoretically. Established a two-dimensional physical model with one source and one doab, and applied computational fluid dynamics analysis software Fluent to do numerical simulation, analyzed and contrasted to the areas of gob air leakage on size and gas emission from gob to working face on strength when using the downlink ventilation and uplink ventilation. When applied downward ventilation in stope face, the air leakage field of gob nearly working face, and the air leakage intensity were smaller than uplink, this can effectively reduce the gas emission from gob to working face; when used downlink ventilation, the air leakage airflow carry the lower amount of gas to doab than uplink ventilation, and more easily to mix the gas, reduced the possibility of gas accumulation in upper comer and the stratified flows, it can provide protection to mine with safe and effective production.

Experimental study on solid particle migration and production behaviors during marine natural gas hydrate dissociation by depressurization

Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate(NGH)reservoirs.Particle migration within the NGH reservoir dominates sand production behaviors,while their relationships were rarely reported,severely constrains quantitative evaluation of sand production risks.This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time.Theoretical evolutionary modes of sand migration are established based on experimental observations,and its implications on field NGH are comprehensively discussed.Five particle migration regimes of local borehole failure,continuous collapse,wormhole expansion,extensive slow deformation,and pore-wall fluidization are proved to occur during depressurization.The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation.In contrast,the depressurization mainly dominates the transmission rate of the particle migration regimes.Furthermore,both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate(MH)saturation.Discontinuous gas bubble emission,expansion,and explosion during MH dissociation delay sand migration into the wellbore.At the same time,continuous water flow is a requirement for sand production during hydrate dissociation by depressurization.The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications.Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.

Origin of a giant fuzzy reflection zone and its implication for natural gas exploration in the southwestern Qiongdongnan Basin of the South China Sea

The southwestern depression of the Qiongdongnan Basin(QDNB)hosts thick Cenozoic sediments and awaits major hydrocarbon discovery.Multichannel seismic(MCS)profile CFT2011 across the southwestern QDNB reveals a~60-km-wide fuzzy reflection zone(FRZ)within the sediments,but its origin and distribution remain unclear.Here ocean bottom seismometer(OBS)data of Line CFT2011 are processed with focus on the velocity structures by traveltime tomography inversion and analyzed together with the coincident and adjacent MCS profiles.The OBS velocity results show that the giant FRZ features lower velocity with difference up to 1.5 km/s and smaller vertical velocity gradient than the surrounding sedimentary sequences at the same depth,likely resulting from enhanced fluid infilling.The MCS profile exhibits that the giant FRZ is about 3-9-km thick and extends from the Paleogene strata rich in organic matters upward to the lower Pleistocene sediments.Within the shallow overlying sediments,multiple bright spots with reverse polarity are imaged and their reflection amplitudes increase with offset,consistent with the features of gas-charged sediments.They are probably shallow gas reservoirs with gases sourced from the deep FRZ.Therefore,the FRZ is proposed to be a giant gas-charged zone,which probably contains lots of hydrocarbon gases migrated vertically from the deep Paleogene source rocks through the boundary faults of the depressions and the minor fractures generated under overpressure.This FRZ is also imaged on the adjacent MCS profiles MCS-L1 and MCS-L2 with the width of about 40 km and 68 km,respectively.It is roughly estimated to cover an area of~1900 km2 and host a volume of~11400 km3 assuming an average thickness of 6 km,implying huge natural gas potential in the sedimentary depression of the southwestern QDNB of the South China Sea.

Application of butane geochemistry of natural gas in hydrocarbon exploration

In order to distinguish the source and migration direction of natural gas by geochemical characteristics of butane,the components and carbon isotopes of natural gas from major hydrocarbonbearing basins in China were analyzed.The results showed that：（1） Oil-type gas has i-C 4 /n-C 4 0.8,δ 13 C butane -28‰,δ 13 C i-butane -27‰,δ 13 C n-butane -28.5‰,whereas coal-type gas has i-C 4 /n-C 4 0.8,δ 13 C butane -25.5‰,δ 13 C i-butane -24‰,δ 13 C n-butane -26‰.（2） When δ 13 C i-butane-δ 13 C n-butane is greater than 0,the maturity of oil-type gas is generally more than 2.4% and that of coal-type gas is greater than 1.4%,whereas when the difference is less than 0,the maturity of oil-type gas is generally less than 1.1% and that of coal-type gas is less than 0.8%.（3） When natural gas migrates through dense cap rocks,the value of i-C 4 /n-C 4 increases,whereas when it migrates laterally along a reservoir,the value of i-C 4 /n-C 4 decreases.（4） Sapropelic transition zone gas with composition and carbon isotopic signatures similar to those of oil-type gas in the low thermal evolution stage is found to have a relatively high butane content.（5） The values of i-C 4 /n-C 4 and δ 13 C n-butane δ 13 C i-butane of gas which has suffered biological degradation are significantly higher than those obtained from thermogenic and bio-thermocatalytic transition zone gas.Thus,natural gas of different genetic types can be recognized through component analysis and carbon isotopic signatures of butane,the natural gas maturity can be estimated from the difference in carbon isotopic content between isobutane and n-butane,and the migration direction of natural gas can be determined from i-C 4 /n-C 4 ratios and transport conditions,which can also be used to thermogenic and bio-thermocatalytic transition zone gas.

Gas source of the Middle Jurassic Shaximiao Formation in the Zhongjiang large gas field of Western Sichuan Depression:Constraints from geochemical characteristics of light hydrocarbons

The Zhongjiang gas field is a typical large gas field in terrigenous strata of the Western Sichuan Depression.It remains debatable which member of the Upper Triassic Xujiahe Formation served as the source rocks and how significant the member contributed to the gas accumulations in the Zhongjiang gas field.In this study,we analyzed the essential characteristics of the Lower Jurassic source rocks and the geochemical features of light hydrocarbons in natural gas from the 2nd(T_(3)χ^(2))and 4th members(T_(3)χ^(4))of the Upper Triassic Xujiahe Formation(T_(3)χ),as well as the Middle Jurassic Shaximiao(J_(2)s)and Qianfoya(J_(2)q)formations.Based on this,we explored the sources of the natural gas in the Zhongjiang gas field and determined the natural gas migration patterns and their effects on the properties of light hydrocarbons in the natural gas.The results indicate that the Lower Jurassic lacustrine source rocks of the Zhongjiang gas field contain humic organic matter,with vitrinite reflectance(R_(0))values ranging from 0.86%to 0.98%.Samples meeting the criterion for effective source rocks[total organic carbon(TOC)content≥0.75%]exhibited an average TOC content of merely 1.02%,suggesting significantly lower hydrocarbon generation potential than source rocks in the underlying T3x,which show higher thermal maturity and TOC contents.For natural gas samples from T_(3)χ^(2),T_(3)χ^(4),J_(2)s,and J_(2)q reservoirs,their C_(5-7)iso-alkane content was significantly higher than their n-alkane content,and their methylcyclohexane(MCH)index ranged from 59.0%to 77.3%,indicating the predominance of methylcyclohexane in C_(7)light hydrocarbons.As indicated by the origin identification and gas-source correlation based on the geochemical features of light hydrocarbons,the natural gas in the Zhongjiang gas field is typical coal-derived gas.The gas from the primary pay zone of the Shaximiao Formation,with significantly high K_(1),(P_(2)+N_(2))/C_(7),and P_(3)/C_(7)values,predominantly originated from the 5th member of the T3x and migrated in the free phase,with a small amount possibly sourced from the Lower Jurassic source rocks.The dissolution and adsorption during gas migration led to a decrease in the aromatic content in C_(6-7)light hydrocarbons and an increase in the isoheptane values.Therefore,their effects must be considered when determining the gas origin and thermal maturity based on the aromatic content in C_(6-7) light hydrocarbons and iso-heptane values.

Research progress on isotopic fractionation in the process of shale gas/coalbed methane migration

The research progress of isotopic fractionation in the process of shale gas/coalbed methane migration has been reviewed from three aspects: characteristics and influencing factors, mechanism and quantitative characterization model, and geological application. It is found that the isotopic fractionation during the complete production of shale gas/coalbed methane shows a four-stage characteristic of “stable-lighter-heavier-lighter again”, which is related to the complex gas migration modes in the pores of shale/coal. The gas migration mechanisms in shale/coal include seepage, diffusion, and adsorption/desorption. Among them, seepage driven by pressure difference does not induce isotopic fractionation, while diffusion and adsorption/desorption lead to significant isotope fractionation. The existing characterization models of isotopic fractionation include diffusion fractionation model, diffusion-adsorption/desorption coupled model, and multi-scale and multi-mechanism coupled model. Results of model calculations show that the isotopic fractionation during natural gas migration is mainly controlled by pore structure, adsorption capacity, and initial/boundary conditions of the reservoir rock. So far, the isotope fractionation model has been successfully used to evaluate critical parameters, such as gas-in-place content and ratio of adsorbed/free gas in shale/coal etc. Furthermore, it has shown promising application potential in production status identification and decline trend prediction of gas well. Future research should focus on:(1) the co-evolution of carbon and hydrogen isotopes of different components during natural gas migration,(2) the characterization of isotopic fractionation during the whole process of gas generation-expulsion-migration-accumulation-dispersion, and(3) quantitative characterization of isotopic fractionation during natural gas migration in complex pore-fracture systems and its application.

A natural gas hydrate-oil-gas system in the Qilian Mountain permafrost area, northeast of Qinghai-Tibet Plateau

Natural gas hydrate,oil and gas were all found together in the Qilian Mountain permafrost area,northeast of Qinghai-Tibet Plateau,China.They are closely associated with each other in space,but whether they are in any genetic relations are unknown yet.In this paper,a hydrocarbon gas-generation series,gas-fluid migration series and hydrocarbon gas-accumulation series are analyzed to probe the spatial,temporal and genetic relationships among natural natural gas hydrate,oil and gas.The subsequent results show that natural gas hydrate,oil and gas actually form a natural gas hydrate-oil-gas system.Based on the Middle Jurassic and the Upper Triassic hydrocarbon gas-generation series,it is divided into four major sub-systems in the study area:(1)A conventional Upper Triassic gas-bearing sub-system with peak hydrocarbon gas-generation in the late Middle Jurassic;(2)a conventional Middle Jurassic oil-bearing sub-system with low to mature hydrocarbon gas-generation in the late Middle Jurassic;(3)a natural gas hydrate sub-system with main gas source from the Upper Triassic gas-bearing sub-system and minor gas source from the Middle Jurassic oil-bearing sub-system as well as little gas source from the Middle Jurassic coal-bed gas and the microbial gas;(4)a shallower gas sub-system with microbial alteration of the main gas source from the Upper Triassic gas-bearing sub-system.This natural gas hydrate-oil-gas system and its sub-systems are not only theoretical but also practical,and thus they will play an important role in the further exploration of natural gas hydrate,oil and gas,even other energy resources in the study area.

Removal from Water and Adsorption onto Natural Quartz Sand of Hydroquinone

Hydroquinone (HQ) is the most important hydroxy aromatic compound which is produced on a large scale. Understanding its fate in the environment is therefore of primary importance to prevent its migration in the soil and/or the contamination of the aquatic ecosystems. Here we present a column based method to investigate the physicochemical processes controlling the removal from the aqueous phase and the adsorption onto natural quartz sand (NQS), of organic pollutant such as HQ molecules. We will focus on the interactions that occur between the organic pollutant and the NQS substrate. Thus, column reactors filled with NQS were used to investigate the influence of physicochemical parameters such as the ionic strength, the pH, the flow rate, and the nature of the electrolyte cation, on the HQ adsorption from water onto NQS substrate. The data indicate that, when divalent instead of monovalent cations, are present in the effluent water injection phase, and/or when the ionic strength of the effluent increases, the adsorbed HQ amount decreases. Similar decrease of the adsorbed HQ amount was also observed, at constant ionic strength, by increasing either, the pH from 3 to 9, the flow rate Q from 1 to 3 ml·mn-1, or by decreasing the HQ initial concentration, C0 from 30 to 6 mg·L-1. Further, large amount of the organic pollutant (up to 93 wt% of HQ molecules) was removed from the effluent water phase by using NQS column. The overall data seem to indicate that the adsorption of HQ molecules on the NQS surface is mainly controlled by electrostatic interaction forces occurring between the organic molecule polar groups and the inorganic matrix silanol groups.

Different Hydrocarbon Accumulation Histories in the Kelasu-Yiqikelike Structural Belt of the Kuqa Foreland Basin

The Kuqa foreland basin is an important petroliferous basin where gas predominates. The Kela-2 large natural gas reservoir and the Yinan-2, Dabei-1, Tuzi and Dina-11 gas reservoirs have been discovered in the basin up to the present. Natural gases in the Kelasu district and the Yinan district are generated from different source rocks indicated by methane and ethane carbon isotopes. The former is derived from both Jurassic and Triassic source rocks, while the latter is mainly from the Jurassic. Based on its multistage evolution and superposition and the intense tectonic transformation in the basin, the hydrocarbon charging history can be divided into the early and middle Himalayan hydrocarbon accumulation and the late Himalayan redistribution and re-enrichment. The heavier carbon isotope composition and the high natural gas ratio of C1/C1-4 indicate that the accumulated natural gas in the early Himalayan stage is destroyed and the present trapped natural gas was charged mainly in the middle and late Himalayan stages. Comparison and contrast of the oils produced in the Kelasu and Yinan regions indicate the hydrocarbon charging histories in the above two regions are complex and should be characterized by multistage hydrocarbon migration and accumulation.

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

Migration and accumulation of natural gas in Kela-2 gas field

With the guidance of petroleum system theory,the dynamic filling history of natural gas in the Kela-2 gasfield is analyzed by using a large suite of oil and gas geo-chemistry evidence in combination with the tectonic evolu-tion history and reservoir evolution history. It concludes thatthe Kela-2 gas field was formed by capturing the gas gener-ated during the main gas generation period, while the latekerogen cracking gas contributed a little to the gas field. Itsuggests that the gas generated during the main gas genera-tion accumulated in the early-formed wide-gentle anticline,which is the necessary condition for natural gas to re-migrateand enrich late to form the large-scale gas reservoir. Thenewest research shows that the filling history of gas in theDabei-1, Yinan-2, Tuziluoke and Dina-2 gas fields was re-lated with the natural gas accumulation in the early wide-gentle anticline as well as late re-migration and enrichmentof natural gas.

A New Method for Quantitative Simulating Hydrocarbon Expulsion and Its Application

We should understand that the content of chlo-roform bitumen“A”from source rocks at any depth(or period)is not the content of residuary oil,but it is the oil content of source rocks in a condition of dynamic equilibrium of generation and expulsion in an 1nstant.Sc can be measured by laboratory experiment and determined from the curve of S-A"versus depth for the same source rock.(Fig.l)

Effect of hydrophilic silica nanoparticles on hydrate formation during methane gas migration in a simulated wellbore

Natural gas hydrates are mostly formed in low-permeability and fractured muddy sedimentary formations.Adding suitable nanoparticles to the drilling fluid system can improve its filtrate resistance and fracture plugging,and effectively weaken the invasion of drilling fluid into the reservoir.However,it is likely that nanoparticles promote hydrate formation and accumulation in wellbores which will induce accidents.Therefore,this study investigated the effect of hydrophilic silica nanoparticles with particle sizes of 30 nm,60 nm,and 80 nm and concentrations of 0.5e4.0 wt%on hydrate formation during upward migration of methane gas using a dynamic simulation system for hydrate formation in a wellbore.The experimental results show that under the condition of methane gas migration,hydrophilic silica nanoparticles inhibit hydrate formation.The inhibition effect increased with the growth in the particle size under a constant concentration,whereas it first increased and then decreased with increasing nanoparticle concentration under a constant particle size.The strongest inhibition effect was observed at a hydrophilic silica nanoparticle concentration of 2.0 wt%.The influence of hydrophilic silica nanoparticles on hydrate formation may be mainly determined by their hydrophilic properties,heat and mass transfer,and gas migration in the wellbore.Our research indicates that hydrophilic silica nanoparticles can be added to hydrate drilling fluid systems if their concentration can be properly controlled.

川中地区须家河组天然气成藏机制研究

以天然气形成时期研究、天然气地球化学特征分析及运移地质条件分析为基础,对川中地区上三叠统须家河组天然气成藏机制进行了系统研究。研究认为川中地区须家河组气藏为2期气相充注,在燕山末期—喜山期构造抬升过程中,储层水溶气脱溶可能性小、残余气相的卸压膨胀具有一定贡献;虽然须家河组砂岩厚度大、分布广,但储层强烈的非均质性以及较平缓的区域地层,限制了油气进行长距离运移;天然气及凝析油等地球化学特征表现为近距离运聚成藏特点。从而为川中地区须家河组构造—岩性气藏的勘探提供了新的依据。