Current gas well decline analysis under boundary-dominated flow(BDF)is largely based on the Arps'empirical hyperbolic decline model and the analytical type curve tools associated with pseudo-functions.Due to the n...Current gas well decline analysis under boundary-dominated flow(BDF)is largely based on the Arps'empirical hyperbolic decline model and the analytical type curve tools associated with pseudo-functions.Due to the nonlinear flow behavior of natural gas,these analysis methods generally require iterative calculations.In this study,the dimensionless gas rate(qg/qgi)is introduced,and an explicit method to determine the average reservoir pressure and the original gas in place(OGIP)for a volumetric gas reservoir is proposed.We show that the dimensionless gas rate in the BDF is only the function of the gas PVT parameters and reservoir pressure.Step-by-step analysis procedures are presented that enable explicit and straightforward estimation of average reservoir pressure and OGIP by straight-line analysis.Compared with current techniques,this methodology avoids the iterative calculation of pseudo-time and pseudo-pressure functions,lowers the multiplicity of type curve analysis,and is applicable in different production situations(constant/variable gas flow rate,constant/variable bottom-hole pressure)with a broad range of applications and ease of use.Reservoir numerical simulation and field examples are thoroughly discussed to highlight the capabilities of the proposed approach.展开更多
Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-st...Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-stage accumulation processes.This study investigates the origin of natural gas in deep hydrothermal dolomite reservoirs of the Maokou Formation,eastern Sichuan Basin,using hydrocarbon inclusion analysis,radiometric U-Pb dating of calcite cements,maturity modeling of potential source rocks,and constraints on reactivation periods of the nearby No.15 Fault System.Results indicate an oil charging event at approximately 246.9 Ma,followed by two episodes of gas charging at 222.4 Ma and 175.2 Ma.Furthermore,the oil and gas charging events occurred synchronously with activities of the No.15 Fault System,suggesting that its reactivation induced episodic hydrocarbon migration.Maturity modeling indicates that during the oil charging period,source rocks in the Qiongzhusi,WufengLongmaxi,and first member of the Maokou formations reached the stages of dry gas generation,significant oil generation,and the threshold of oil generation,respectively.During the subsequent twoepisode gas charging periods,the Qiongzhusi and Wufeng-Longmaxi formations progressed to dry and wet gas generation stages,respectively,while the first member of the Maokou Formation attained the oil generation stage.The hydrocarbon charging time and maturity history of potential source rocks indicate that:1)oil in hydrothermal dolomite reservoirs predominantly originated from the Wufeng-Longmaxi Formation at approximately 246.9 Ma;2)during the subsequent gas charging episodes,the WufengLongmaxi Formation could contribute wet gas,while the Qiongzhusi Formation likely supplied cracking gas from kerogen and residual liquid hydrocarbon;3)all oil in the hydrothermal dolomite reservoirs underwent thermal cracking to gas at approximately 110 Ma.This study indicates that gas pools in(ultra-)deep carbonate reservoirs of the Sichuan Basin have mixed genetic origins,with contributions from multiple sources.The multidisciplinary approach,combining direct dating of hydrocarbon charge events and simulation of hydrocarbon generation,proves robust and effective in identifying the origin of natural gas in(ultra-)deep reservoirs.展开更多
The different reservoirs in deep Songliao Basin have non-homogeneous lithologies and include multiple layers with a high content of hydrogen gas.The gas composition and stable isotope characteristics vary significantl...The different reservoirs in deep Songliao Basin have non-homogeneous lithologies and include multiple layers with a high content of hydrogen gas.The gas composition and stable isotope characteristics vary significantly,but the origin analysis of different gas types has previously been weak.Based on the geochemical parameters of gas samples from different depths and the analysis of geological settings,this research covers the diverse origins of natural gas in different strata.The gas components are mainly methane with a small amount of C_(2+),and non-hydrocarbon gases,including nitrogen(N_(2)),hydrogen(H_(2)),carbon dioxide(CO_(2)),and helium(He).At greater depth,the carbon isotope of methane becomes heavier,and the hydrogen isotope points to a lacustrine sedimentary environment.With increasing depth,the origins of N_(2)and CO_(2)change gradually from a mixture of organic and inorganic to inorganic.The origins of hydrogen gas are complex and include organic sources,water radiolysis,water-rock(Fe^(2+)-containing minerals)reactions,and mantle-derived.The shales of Denglouku and Shahezi Formations,as source rocks,provide the premise for generation and occurrence of organic gas.Furthermore,the deep faults and fluid activities in Basement Formation control the generation and migration of mantle-derived gas.The discovery of a high content of H_(2)in study area not only reveals the organic and inorganic association of natural-gas generation,but also provides a scientific basis for the exploration of deep hydrogen-rich gas.展开更多
The Qilian permafrost of the South Qilian Basin(SQB)has become a research focus since gas hydrates were discovered in 2009.Although many works from different perspectives have been conducted in this area,the origin of...The Qilian permafrost of the South Qilian Basin(SQB)has become a research focus since gas hydrates were discovered in 2009.Although many works from different perspectives have been conducted in this area,the origin of gas from gas hydrate is still controversial.Molecular composition and carbon isotope of 190 samples related to gas hydrates collected from 11 boreholes allowed exploration of genetic type,thermal maturity,biodegradation,as well as gas-source correlation of alkane gases from gas hydrates and free gases.Results indicate that alkane gases biodegraded after the formation of natural gas.According to differences in carbon isotopes of methane and their congeners(CH4,C2H6,C3H8),the thermal maturity(vitrinite reflectance,VRo)of most alkane gases ranges from 0.6%to 1.5%,indicating a mature to high mature stage.The thermal maturity VRo of a small part of alkane gas(in boreholes DK5 and DK6)is higher than 1.3%,indicating a high mature stage.Alkane gases were mainly produced by secondary cracking,consisting of crude oilcracking gases and wet gases cracking to dry gases.Genetic types of alkane gases are primarily oil-type gases generated from shales and mudstones in the upper Yaojie Formation of Jurassic,with less coal-type gases originated from the mudstones in the Triassic Galedesi Formation and the lower Yaojie Formation of Jurassic.Carbon dioxides associated with alkanes from gas hydrates and free gases indicate the thermal decomposition and biodegradation of organic matter.The origins of natural gases from gas hydrates and free gases shed light on the evaluation of petroleum resource potential,deeply buried sediments,and petroleum resource exploration in the SQB.展开更多
The composition and isotopic values of natural gas in the Sinian Dengying Fm,Cambrian Qiongzhusi Fm,Longwangmiao Fm and Xixiangchi Fm in the Sichuan Basin exhibit different features in different tectonic position,caus...The composition and isotopic values of natural gas in the Sinian Dengying Fm,Cambrian Qiongzhusi Fm,Longwangmiao Fm and Xixiangchi Fm in the Sichuan Basin exhibit different features in different tectonic position,causing controversy over its origin and sources.The geochemical features of the natural gases in this area were compared based on previous research results and large amounts of drilling data of new exploration wells.The results show:(1)The natural gas is typical dry gas on the whole,with hydrocarbon gas in dominance,and a methane content of 74.85%-97.35%,mostly 83.0%-96.0%;due to different clay contents in source rocks,the difference in non-hydrocarbon gas mainly lies in N_(2)and He content,with gas in Weiyuan and Ziyang areas having high contents of N_(2)and He,while gas in Gaoshiti and Moxi areas having low N_(2)and He.(2)Natural gases in different regions differ greatly in carbon isotope value(δ^(13)C_(1)andδ^(13)C_(2)).Theδ^(13)C_(1)of natural gas in Cambrian system of Ziyang area is the lightest,from-38.0‰to-35.5‰,and that in other regions is from-33.9‰to-32.0‰,indicating different capture stages of natural gases.For example,gas captured in early stage is relatively light in carbon isotope;the carbon isotope value(δ^(13)C_(2))of gas from Sinian and Cambrian system in Weiyuan is from-36.5‰to-32.7‰;that from the Longwangmiao Fm in Gaoshiti and Moxi is from-33.6‰to-31.8‰,but that in the Dengying Fm in Gaoshiti-Moxi area is from-29.1‰to-26.8‰,quite different from the above natural gases,which mainly shows the differences in kerogen types.(3)Light hydrocarbons of C_(6)-C_(7)mainly consist of cyclanes and isomerization alkanes,which is the feature of oil cracking gas.展开更多
During the progressive exploration of the Jingbian Gas Field in the Ordos Basin,multiple gas-bearing regions have been discovered in the dolomite reservoirs in the Middle Ordovician assemblages of Lower Paleozoic in J...During the progressive exploration of the Jingbian Gas Field in the Ordos Basin,multiple gas-bearing regions have been discovered in the dolomite reservoirs in the Middle Ordovician assemblages of Lower Paleozoic in Jingxi area,but these gas-bearing regions and intervals are significantly different in terms of gas enrichment degrees.So far,however,the reasons for the difference have not been figured out.In this paper,the origin and source of natural gas in the Middle Ordovician assemblages in Jingxi area was investigated on the basis of geochemical data(e.g.natural gas composition and carbon isotope),and then the main factors controlling the gas accumulation were analyzed.It is shown that the natural gas in the Middle Ordovician assemblages in the Middle Ordovician assemblages in Jingxi area is similar to that in the Upper Ordovician assemblages and Upper Paleozoic reservoir in terms of genesis and sources,and they are mainly the Upper Paleozoic coaliferous gas with some oil-derived gas.Under the influence of hydrocarbon generation center of coal source rocks and the source-rock-reservoir contact relationship,the proportion of coaliferous gas increases areally from the north to the south and vertically from Ma55 sub-member of the Lower Ordovician Majiagou Fm.It is concluded that the natural gas enrichment degree is controlled by the gas charging capacity at the hydrocarbon-supplying windows.Second,the vertical migration and distribution of natural gas is dominated by the differences of Ma_(5)^(5)-Ma_(5)^(10)transport pathways.And third,the lateral migration direction of natural gas and the range of gas accumulation are controlled by the superimposition relationship between structures and reservoirs.展开更多
For an improved understanding of gas enrichment mechanism in the eastern Sichuan Basin,South China,twelve natural gas samples were obtained from carbonate reservoirs of the Upper Permian strata to analyze the hydrocar...For an improved understanding of gas enrichment mechanism in the eastern Sichuan Basin,South China,twelve natural gas samples were obtained from carbonate reservoirs of the Upper Permian strata to analyze the hydrocarbon and non-hydrocarbon gas compositions,stable carbon and hydrogen isotopes ratios of hydrocarbons,and noble gas isotope ratios.The gas samples in the Upper Permian reservoirs principally consist of alkane gas with a dryness ratio ranging from 127.9 to 1564.4.The carbon isotope ratio of methane(δ^(13)C_(1))was almost constant at-34.1 to-31.3‰,but the carbon isotope ratio of ethane(δ^(13)C2)varied from-36.6‰to-25.8‰.The hydrogen isotope ratio of methane(δ^2HC_(1))also displayed a wide range from-137‰to-127‰.The large variations in the dryness ratio,δ^(13)C_(2),andδ^2HC_(1)with almost constantδ^(13)C_(1)suggest the mixing of sapropelic and humic origins for hydrocarbon gases in these reservoirs.A high concentration of hydrogen sulfide(H_(2)S)originated from the thermochemical sulfate reduction(TSR),which was positively correlated withδ^(13)C_(1)(orδ^(13)C_(2))in individual gas fields.TSR alteredδ^(13)C_(1)(orδ^(13)C_(2))and resulted in the abnormal character of isotopic reversal in the individual samples.Theδ^(13)C_(1)(orδ^(13)C_(2))in most gas samples,independent of H_(2)S concentration,further displayed reversed carbon isotopes because of the mixture of thermogenic gases with various thermal maturity levels.The measured argon isotope ratio(^(40)Ar/^(36)Ar)varied from 310 to 1225,which suggests that the oldest 320 Ma source rock age corresponds to Permian shales.The analysis of the gas origin and the identification of primary source rock have made a significant contribution to further understanding the resource potential and distribution of natural gas in the Upper Permian,and have great implications for gas exploration in the eastern Sichuan Basin.展开更多
The Ordovician of the Tazhong area in the Tarim Basin has suffered multi-cyclic hydrocarbon charging, making Tazhong a typical condensate gas district. In this paper, production and test data were gathered and a detai...The Ordovician of the Tazhong area in the Tarim Basin has suffered multi-cyclic hydrocarbon charging, making Tazhong a typical condensate gas district. In this paper, production and test data were gathered and a detailed comparison was conducted on the geology and the fluid distribution and characteristics between the eastern and western Tazhong area. Eastern and western regions exhibit significant differences in tectonic structure, fluid distribution, and physical-chemical properties of oil and gas. Compared with the eastern region, the western part has a greater development of discordogenic gas associated with strike-slip faults which, combined with the Tazhong No. 1 fault zone, control the fluid distribution. The eastern region is mainly controlled by the Tazhong No. 1 fault zone. Fluid have markedly homogeneous properties in the east, but are heterogeneous in the west. The origins of oil and gas are different between the east and the west. In the east, hydrocarbons are mainly from Ordovician source rocks and natural gas is mostly derived from kerogen pyrolysis. In the west, the hydrocarbons mainly originated from Cambrian source rocks, and the gas was mostly generated by crude oil cracking. In sum, the east region is dominated by primary condensate gas reservoirs, and the western region is dominated by secondary condensate gas reservoirs. Because of the different geological settings and fluid physical properties, differences in the condensate gas reservoirs in the eastern and the western Tazhong area have been analyzed, and appropriate formation mechanisms for condensate gas origins are established.展开更多
There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feix-ianguan Formation in the Eastern Sichuan Basin.This seriously restricts the study of natural gas dy-namics in the Fe...There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feix-ianguan Formation in the Eastern Sichuan Basin.This seriously restricts the study of natural gas dy-namics in the Feixianguan Formation and thus hampers natural gas exploration in the region,so further study is urgently required.Using experimental tests of natural gas composition,stable isotopes,and noble gas isotopes with gas chromatography(GC)and mass spectrometry(MS)studies of source rock and reservoir asphalt saturated hydrocarbons,the natural gas geochemical characteristics,the genetic identification and a gas-source comparison of the Feixianguan Formation were studied.Then,con-strained by the thermal history,the histories of gas generation and expulsion were restored by basin simulation technology.Finally,a gas accumulation model was established for the Feixianguan Formation.The results showed that(1)the H_(2)S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin,respectively.The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs.(2)The natural gas of the Feixianguan Formation is organic thermogenic gas,which is mainly oil-type gas generated by the secondary cracking of crude oil.The gas-generating parent material is mainly type II kerogen.(3)The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argil-laceous source rocks of the Upper Permian Longtan Formation.(4)Natural gas accumulation occurred as follows:the paleo-structure heights were filled with crude oil in the Early Jurassic,and paleo-oil res-ervoirs were formed in the Feixianguan Formation;during the Middle-Late Jurassic,the paleo-oil res-ervoirs were cracked when the reservoir temperatures rose above 160 C,and paleo-gas reservoirs were formed.Since the end of the Late Jurassic,the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs.These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.展开更多
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 char...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.展开更多
Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized： low sulfur content, low refl...Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized： low sulfur content, low reflectance （LSLR） solid bitumens in sandstone reservoirs in the Xujiahe Formation and high sulfur content, high reflectance （HSHR） solid bitumens in the carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing formations. Solid bitumens in the Upper Triassic Xujiahe Formation correlate well with extracts from the Upper Triassic to Jurassic nonmarine source rocks in isotopic composition of the saturated and aromatic fractions and biomarker distribution. Solid bitumens in the Feixianguan and Changxing formations are distinctly different from extracts from the Cambrian and Silurian rocks but display reasonable correlation with extracts from the Upper Permian source rocks both in isotopic composition of the saturated and aromatic fractions and in biomarker distribution, suggesting that the Permian especially the Upper Permian Longtan Formation was the main source of solid bitumens in the carbonate reservoirs in the Feixianguan and Changxing formations in the Puguang gas field. Chemical and isotopic composition of natural gases indicates that the majority of hydrocarbon gases originated from sapropelic organic matter and was the products of thermal cracking of accumulated oils. This study indicates that source rock dominated by sapropelic organic matter existed in the Upper Permian and had made major contribution to the giant Puguang gas field, which has important implication for petroleum exploration in marine sequences in South China.展开更多
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 ho...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.展开更多
Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysi...Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.展开更多
Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaw...Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.展开更多
基金supported by the Young Elite Scientist Sponsorship Program by Beijing Association for Science and Technology,China(No.BYESS2023262)the Science Foundation of China University of Petroleum(Beijing),China(No.2462022BJRC004).
文摘Current gas well decline analysis under boundary-dominated flow(BDF)is largely based on the Arps'empirical hyperbolic decline model and the analytical type curve tools associated with pseudo-functions.Due to the nonlinear flow behavior of natural gas,these analysis methods generally require iterative calculations.In this study,the dimensionless gas rate(qg/qgi)is introduced,and an explicit method to determine the average reservoir pressure and the original gas in place(OGIP)for a volumetric gas reservoir is proposed.We show that the dimensionless gas rate in the BDF is only the function of the gas PVT parameters and reservoir pressure.Step-by-step analysis procedures are presented that enable explicit and straightforward estimation of average reservoir pressure and OGIP by straight-line analysis.Compared with current techniques,this methodology avoids the iterative calculation of pseudo-time and pseudo-pressure functions,lowers the multiplicity of type curve analysis,and is applicable in different production situations(constant/variable gas flow rate,constant/variable bottom-hole pressure)with a broad range of applications and ease of use.Reservoir numerical simulation and field examples are thoroughly discussed to highlight the capabilities of the proposed approach.
基金financially supported by National Natural Science Foundation of China(No.92255302)the Joint Funds of the National Natural Science Foundation of China(No.U20B6001)。
文摘Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-stage accumulation processes.This study investigates the origin of natural gas in deep hydrothermal dolomite reservoirs of the Maokou Formation,eastern Sichuan Basin,using hydrocarbon inclusion analysis,radiometric U-Pb dating of calcite cements,maturity modeling of potential source rocks,and constraints on reactivation periods of the nearby No.15 Fault System.Results indicate an oil charging event at approximately 246.9 Ma,followed by two episodes of gas charging at 222.4 Ma and 175.2 Ma.Furthermore,the oil and gas charging events occurred synchronously with activities of the No.15 Fault System,suggesting that its reactivation induced episodic hydrocarbon migration.Maturity modeling indicates that during the oil charging period,source rocks in the Qiongzhusi,WufengLongmaxi,and first member of the Maokou formations reached the stages of dry gas generation,significant oil generation,and the threshold of oil generation,respectively.During the subsequent twoepisode gas charging periods,the Qiongzhusi and Wufeng-Longmaxi formations progressed to dry and wet gas generation stages,respectively,while the first member of the Maokou Formation attained the oil generation stage.The hydrocarbon charging time and maturity history of potential source rocks indicate that:1)oil in hydrothermal dolomite reservoirs predominantly originated from the Wufeng-Longmaxi Formation at approximately 246.9 Ma;2)during the subsequent gas charging episodes,the WufengLongmaxi Formation could contribute wet gas,while the Qiongzhusi Formation likely supplied cracking gas from kerogen and residual liquid hydrocarbon;3)all oil in the hydrothermal dolomite reservoirs underwent thermal cracking to gas at approximately 110 Ma.This study indicates that gas pools in(ultra-)deep carbonate reservoirs of the Sichuan Basin have mixed genetic origins,with contributions from multiple sources.The multidisciplinary approach,combining direct dating of hydrocarbon charge events and simulation of hydrocarbon generation,proves robust and effective in identifying the origin of natural gas in(ultra-)deep reservoirs.
基金supported by the National Natural Science Foundation of China(Grant No.42072168)the National Key R&D Program of China(Grant No.2019YFC0605405)the Fundamental Research Funds for the Central Universities(Grant No.2023ZKPYDC07)。
文摘The different reservoirs in deep Songliao Basin have non-homogeneous lithologies and include multiple layers with a high content of hydrogen gas.The gas composition and stable isotope characteristics vary significantly,but the origin analysis of different gas types has previously been weak.Based on the geochemical parameters of gas samples from different depths and the analysis of geological settings,this research covers the diverse origins of natural gas in different strata.The gas components are mainly methane with a small amount of C_(2+),and non-hydrocarbon gases,including nitrogen(N_(2)),hydrogen(H_(2)),carbon dioxide(CO_(2)),and helium(He).At greater depth,the carbon isotope of methane becomes heavier,and the hydrogen isotope points to a lacustrine sedimentary environment.With increasing depth,the origins of N_(2)and CO_(2)change gradually from a mixture of organic and inorganic to inorganic.The origins of hydrogen gas are complex and include organic sources,water radiolysis,water-rock(Fe^(2+)-containing minerals)reactions,and mantle-derived.The shales of Denglouku and Shahezi Formations,as source rocks,provide the premise for generation and occurrence of organic gas.Furthermore,the deep faults and fluid activities in Basement Formation control the generation and migration of mantle-derived gas.The discovery of a high content of H_(2)in study area not only reveals the organic and inorganic association of natural-gas generation,but also provides a scientific basis for the exploration of deep hydrogen-rich gas.
基金granted by the National Natural Science Foundation of China(Grant nos.4170214441802212)+1 种基金the State Key Laboratory of Organic Geochemistry,GIGCAS(Grant no.SKLOG-201908)the Fundamental Research Funds for the Central Universities(Grant no.2652018234)。
文摘The Qilian permafrost of the South Qilian Basin(SQB)has become a research focus since gas hydrates were discovered in 2009.Although many works from different perspectives have been conducted in this area,the origin of gas from gas hydrate is still controversial.Molecular composition and carbon isotope of 190 samples related to gas hydrates collected from 11 boreholes allowed exploration of genetic type,thermal maturity,biodegradation,as well as gas-source correlation of alkane gases from gas hydrates and free gases.Results indicate that alkane gases biodegraded after the formation of natural gas.According to differences in carbon isotopes of methane and their congeners(CH4,C2H6,C3H8),the thermal maturity(vitrinite reflectance,VRo)of most alkane gases ranges from 0.6%to 1.5%,indicating a mature to high mature stage.The thermal maturity VRo of a small part of alkane gas(in boreholes DK5 and DK6)is higher than 1.3%,indicating a high mature stage.Alkane gases were mainly produced by secondary cracking,consisting of crude oilcracking gases and wet gases cracking to dry gases.Genetic types of alkane gases are primarily oil-type gases generated from shales and mudstones in the upper Yaojie Formation of Jurassic,with less coal-type gases originated from the mudstones in the Triassic Galedesi Formation and the lower Yaojie Formation of Jurassic.Carbon dioxides associated with alkanes from gas hydrates and free gases indicate the thermal decomposition and biodegradation of organic matter.The origins of natural gases from gas hydrates and free gases shed light on the evaluation of petroleum resource potential,deeply buried sediments,and petroleum resource exploration in the SQB.
基金Special and Significant Project of National Science and Technology“Development of Large Oil/gas Fields and Coalbed Methane”(No.2011ZX05007-002)Project of CNPC Key Laboratory of Gas Reservoir Formation and Development.
文摘The composition and isotopic values of natural gas in the Sinian Dengying Fm,Cambrian Qiongzhusi Fm,Longwangmiao Fm and Xixiangchi Fm in the Sichuan Basin exhibit different features in different tectonic position,causing controversy over its origin and sources.The geochemical features of the natural gases in this area were compared based on previous research results and large amounts of drilling data of new exploration wells.The results show:(1)The natural gas is typical dry gas on the whole,with hydrocarbon gas in dominance,and a methane content of 74.85%-97.35%,mostly 83.0%-96.0%;due to different clay contents in source rocks,the difference in non-hydrocarbon gas mainly lies in N_(2)and He content,with gas in Weiyuan and Ziyang areas having high contents of N_(2)and He,while gas in Gaoshiti and Moxi areas having low N_(2)and He.(2)Natural gases in different regions differ greatly in carbon isotope value(δ^(13)C_(1)andδ^(13)C_(2)).Theδ^(13)C_(1)of natural gas in Cambrian system of Ziyang area is the lightest,from-38.0‰to-35.5‰,and that in other regions is from-33.9‰to-32.0‰,indicating different capture stages of natural gases.For example,gas captured in early stage is relatively light in carbon isotope;the carbon isotope value(δ^(13)C_(2))of gas from Sinian and Cambrian system in Weiyuan is from-36.5‰to-32.7‰;that from the Longwangmiao Fm in Gaoshiti and Moxi is from-33.6‰to-31.8‰,but that in the Dengying Fm in Gaoshiti-Moxi area is from-29.1‰to-26.8‰,quite different from the above natural gases,which mainly shows the differences in kerogen types.(3)Light hydrocarbons of C_(6)-C_(7)mainly consist of cyclanes and isomerization alkanes,which is the feature of oil cracking gas.
基金Project supported by the PetroChina's Key Special Petroleum S&T Project“PetroChina's Fourth Assessment of Oil&Gas Resources”(No.2013E-050207).
文摘During the progressive exploration of the Jingbian Gas Field in the Ordos Basin,multiple gas-bearing regions have been discovered in the dolomite reservoirs in the Middle Ordovician assemblages of Lower Paleozoic in Jingxi area,but these gas-bearing regions and intervals are significantly different in terms of gas enrichment degrees.So far,however,the reasons for the difference have not been figured out.In this paper,the origin and source of natural gas in the Middle Ordovician assemblages in Jingxi area was investigated on the basis of geochemical data(e.g.natural gas composition and carbon isotope),and then the main factors controlling the gas accumulation were analyzed.It is shown that the natural gas in the Middle Ordovician assemblages in the Middle Ordovician assemblages in Jingxi area is similar to that in the Upper Ordovician assemblages and Upper Paleozoic reservoir in terms of genesis and sources,and they are mainly the Upper Paleozoic coaliferous gas with some oil-derived gas.Under the influence of hydrocarbon generation center of coal source rocks and the source-rock-reservoir contact relationship,the proportion of coaliferous gas increases areally from the north to the south and vertically from Ma55 sub-member of the Lower Ordovician Majiagou Fm.It is concluded that the natural gas enrichment degree is controlled by the gas charging capacity at the hydrocarbon-supplying windows.Second,the vertical migration and distribution of natural gas is dominated by the differences of Ma_(5)^(5)-Ma_(5)^(10)transport pathways.And third,the lateral migration direction of natural gas and the range of gas accumulation are controlled by the superimposition relationship between structures and reservoirs.
基金supported by the National Natural Science Foundation of China(Nos.42072184 and 41702157)the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance。
文摘For an improved understanding of gas enrichment mechanism in the eastern Sichuan Basin,South China,twelve natural gas samples were obtained from carbonate reservoirs of the Upper Permian strata to analyze the hydrocarbon and non-hydrocarbon gas compositions,stable carbon and hydrogen isotopes ratios of hydrocarbons,and noble gas isotope ratios.The gas samples in the Upper Permian reservoirs principally consist of alkane gas with a dryness ratio ranging from 127.9 to 1564.4.The carbon isotope ratio of methane(δ^(13)C_(1))was almost constant at-34.1 to-31.3‰,but the carbon isotope ratio of ethane(δ^(13)C2)varied from-36.6‰to-25.8‰.The hydrogen isotope ratio of methane(δ^2HC_(1))also displayed a wide range from-137‰to-127‰.The large variations in the dryness ratio,δ^(13)C_(2),andδ^2HC_(1)with almost constantδ^(13)C_(1)suggest the mixing of sapropelic and humic origins for hydrocarbon gases in these reservoirs.A high concentration of hydrogen sulfide(H_(2)S)originated from the thermochemical sulfate reduction(TSR),which was positively correlated withδ^(13)C_(1)(orδ^(13)C_(2))in individual gas fields.TSR alteredδ^(13)C_(1)(orδ^(13)C_(2))and resulted in the abnormal character of isotopic reversal in the individual samples.Theδ^(13)C_(1)(orδ^(13)C_(2))in most gas samples,independent of H_(2)S concentration,further displayed reversed carbon isotopes because of the mixture of thermogenic gases with various thermal maturity levels.The measured argon isotope ratio(^(40)Ar/^(36)Ar)varied from 310 to 1225,which suggests that the oldest 320 Ma source rock age corresponds to Permian shales.The analysis of the gas origin and the identification of primary source rock have made a significant contribution to further understanding the resource potential and distribution of natural gas in the Upper Permian,and have great implications for gas exploration in the eastern Sichuan Basin.
基金financially supported by a Chinese National 973 Program (Nos.2011CB201100-03, 2006CB202302)Chinese National Oil and Gas Program (Nos.2011ZX05005-004-HZ06, 2011ZX05009-002-402)
文摘The Ordovician of the Tazhong area in the Tarim Basin has suffered multi-cyclic hydrocarbon charging, making Tazhong a typical condensate gas district. In this paper, production and test data were gathered and a detailed comparison was conducted on the geology and the fluid distribution and characteristics between the eastern and western Tazhong area. Eastern and western regions exhibit significant differences in tectonic structure, fluid distribution, and physical-chemical properties of oil and gas. Compared with the eastern region, the western part has a greater development of discordogenic gas associated with strike-slip faults which, combined with the Tazhong No. 1 fault zone, control the fluid distribution. The eastern region is mainly controlled by the Tazhong No. 1 fault zone. Fluid have markedly homogeneous properties in the east, but are heterogeneous in the west. The origins of oil and gas are different between the east and the west. In the east, hydrocarbons are mainly from Ordovician source rocks and natural gas is mostly derived from kerogen pyrolysis. In the west, the hydrocarbons mainly originated from Cambrian source rocks, and the gas was mostly generated by crude oil cracking. In sum, the east region is dominated by primary condensate gas reservoirs, and the western region is dominated by secondary condensate gas reservoirs. Because of the different geological settings and fluid physical properties, differences in the condensate gas reservoirs in the eastern and the western Tazhong area have been analyzed, and appropriate formation mechanisms for condensate gas origins are established.
基金supported by the National Natural Science Foundation of China(Grant No.41972109)the Chengdu University of Technology Postgraduate Innovative Cultivation Program(CDUT2022BJCX004).
文摘There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feix-ianguan Formation in the Eastern Sichuan Basin.This seriously restricts the study of natural gas dy-namics in the Feixianguan Formation and thus hampers natural gas exploration in the region,so further study is urgently required.Using experimental tests of natural gas composition,stable isotopes,and noble gas isotopes with gas chromatography(GC)and mass spectrometry(MS)studies of source rock and reservoir asphalt saturated hydrocarbons,the natural gas geochemical characteristics,the genetic identification and a gas-source comparison of the Feixianguan Formation were studied.Then,con-strained by the thermal history,the histories of gas generation and expulsion were restored by basin simulation technology.Finally,a gas accumulation model was established for the Feixianguan Formation.The results showed that(1)the H_(2)S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin,respectively.The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs.(2)The natural gas of the Feixianguan Formation is organic thermogenic gas,which is mainly oil-type gas generated by the secondary cracking of crude oil.The gas-generating parent material is mainly type II kerogen.(3)The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argil-laceous source rocks of the Upper Permian Longtan Formation.(4)Natural gas accumulation occurred as follows:the paleo-structure heights were filled with crude oil in the Early Jurassic,and paleo-oil res-ervoirs were formed in the Feixianguan Formation;during the Middle-Late Jurassic,the paleo-oil res-ervoirs were cracked when the reservoir temperatures rose above 160 C,and paleo-gas reservoirs were formed.Since the end of the Late Jurassic,the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs.These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.
基金Supported by the National Natural Science Foundation of China(42172149,U2244209)Sinopec Science and Technology Research Project(P23230,P22132)。
文摘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.
文摘Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized： low sulfur content, low reflectance （LSLR） solid bitumens in sandstone reservoirs in the Xujiahe Formation and high sulfur content, high reflectance （HSHR） solid bitumens in the carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing formations. Solid bitumens in the Upper Triassic Xujiahe Formation correlate well with extracts from the Upper Triassic to Jurassic nonmarine source rocks in isotopic composition of the saturated and aromatic fractions and biomarker distribution. Solid bitumens in the Feixianguan and Changxing formations are distinctly different from extracts from the Cambrian and Silurian rocks but display reasonable correlation with extracts from the Upper Permian source rocks both in isotopic composition of the saturated and aromatic fractions and in biomarker distribution, suggesting that the Permian especially the Upper Permian Longtan Formation was the main source of solid bitumens in the carbonate reservoirs in the Feixianguan and Changxing formations in the Puguang gas field. Chemical and isotopic composition of natural gases indicates that the majority of hydrocarbon gases originated from sapropelic organic matter and was the products of thermal cracking of accumulated oils. This study indicates that source rock dominated by sapropelic organic matter existed in the Upper Permian and had made major contribution to the giant Puguang gas field, which has important implication for petroleum exploration in marine sequences in South China.
基金funded by the National Natural Science Foundation of China(No.42172149,No.U2244209)the SINOPEC Science and Technology Project(No.P22132,No.P21077-1).
文摘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.
文摘Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.
基金Supported by NSFC project No. 40372066 and SRFDP No. 20030183042
文摘Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.
