The accumulation and productivity of shale gas are mainly controlled by the characteristics of shale reservoirs;study of these characteristics forms the basis for the shale gas exploitation of the Lower Cambrian Niuti...The accumulation and productivity of shale gas are mainly controlled by the characteristics of shale reservoirs;study of these characteristics forms the basis for the shale gas exploitation of the Lower Cambrian Niutitang Formation(Fm),Southern China.In this study,core observation and lithology study were conducted along with X-ray diffraction(XRD)and electronic scanning microscopy(SEM)examinations and liquid nitrogen(N2)adsorption/desorption and CH4 isothermal adsorption experiments for several exploration wells in northwestern Hunan Province,China.The results show that one or two intervals with high-quality source rocks(TOC>2 wt%)were deposited in the deep-shelf facies.The source rocks,which were mainly composed of carbonaceous shales and siliceous shales,had high quartz contents(>40 wt%)and low clay mineral(<30 wt%,mainly illites)and carbonate mineral(<20 wt%)contents.The SEM observations and liquid nitrogen(N2)adsorption/desorption experiments showed that the shale is tight,and nanoscale pores and microscale fractures are well developed.BJH volume(VBJH)of shale ranged from 2.144×10^-3 to 20.07×10^-3 cm^3/g,with an average of 11.752×10^-3 cm3/g.Pores mainly consisted of opened and interconnected mesopores(2–50 nm in diameter)or macropores(>50 nm in diameter).The shale reservoir has strong adsorption capacity for CH4.The Langmuir volume(VL)varied from 1.63 to 7.39 cm^3/g,with an average of 3.95 cm^3/g.The characteristics of shale reservoir are controlled by several factors:(1)A deep muddy continental shelf is the most favorable environment for the development of shale reservoirs,which is controlled by the development of basic materials.(2)The storage capacity of the shale reservoir is positively related to the TOC contents and plastic minerals and negatively related to cement minerals.(3)High maturity or overmaturity leads to the growth of organic pores and microfractures,thereby improving the reservoir storage capacity.It can be deduced that the high percentage of residual gas in Niutitang Fm results from the strong reservoir storage capacity of adsorbed gas.Two layers of sweet spots with strong storage capacity of free gas,and they are characterized by the relatively high TOC contents ranging from 4 wt%to 8 wt%.展开更多
In order to evaluate the geological characteristics and gas-bearing factors of Niutitang Formation within the Lower Cambrian of northern Guizhou,the Huangping area located at the southern edge of the ancient uplift be...In order to evaluate the geological characteristics and gas-bearing factors of Niutitang Formation within the Lower Cambrian of northern Guizhou,the Huangping area located at the southern edge of the ancient uplift belt of Xuefeng Mountain was selected as the target area,and Well Huangdi 1 was drilled for the geological survey of shale gas.Through geological background analysis and well logging and laboratory analysis such as organic geochemical test,gas content analysis,isothermal adsorption,and specific surface area experiments on Well Huangdi 1,the results show that the Niutitang Formation is a deep-water shelf,trough-like folds and thrust fault.The thickness of black shale is 119.95 m,of which carbonaceous shale is 89.6 m.The average value of organic carbon content is 3.55%,kerogen vitrinite reflectance value is 2.37% and kerogen type is sapropel-type.The brittle mineral content is 51%(quartz 38%),clay mineral content is 38.3%.The value of porosity and permeability are 0.5%and 0.0014 mD,which the reservoir of the Niutitang Formation belongs to low permeability with characteristics of ultra-low porosity.The gas content is 0.09‒1.31 m^3/t with a high-value area and a second high-value area.By comparing with the geological parameters of adjacent wells in the adjacent area,the accumulation model of“sediment control zone,Ro control zone,structure controlling reservoir”in the study area is proposed.Therefore,deep-water shelf-slope facies,Ro is between high maturity-early stage of overmaturity and well-preserved zones in the Niutitang Formation in this area are favorable direction for the next step of shale gas exploration.展开更多
The purpose of this study was to examine the sedimentary facies characteristics of lower Cambrian Niutitang Formation(∈1n)in South China,to reveal the mechanism of organic matter enrichment,and to guide exploration o...The purpose of this study was to examine the sedimentary facies characteristics of lower Cambrian Niutitang Formation(∈1n)in South China,to reveal the mechanism of organic matter enrichment,and to guide exploration of shale gas.Macro investigation and experimental analyses were used to assess the lithology in detail,total organic matter mass fraction w(TOC),mineral composition,and trace element characteristics of∈1n.The influencing factors of organic matter enrichment were discussed extensively,and a sedimentary facies mode was suggested.In the early stage of∈1n,the locations of Well E’yangye 1,Well Ciye 1,Well Changye 1,and Well Anye 1 respectively develop,platform inner sag,outer shelf,Jiangnan slope belt,and South China detention basin.In the late stage of∈1n,the sedimentary facies evolve with decreasing sea level.The study area presents a complete three-step basin in the Early Cambrian.In the early stage of∈1n,the first step is the Yangtze carbonate platform,the second step is the outer shelf and slope,and the third step is the deep-water basin.From the Yangtze carbonate platform to the deep-water basin,w(TOC)and the mass fraction of quartz gradually increase,the mass fraction of carbonate mineral decreases,and the mass fraction of clay mineral is higher in the second step.The sea level fluctuation results in a higher w(TOC)vertically in the lower∈1n shale,and the paleogeographic(provenance)conditions lead to better horizontal development of organic matter in the outer shelf,slope and detention basin.Trace elements are abundant in the lower∈1n,and w(TOC)is correlated positively with many trace elements.In the outer shelf,slope,and adjacent areas,hydrothermal activity and upwelling current bring nutrient-rich material and promote organic matter enrichment under a strong reducing condition.Deep-shelf,slope and deep-water basin are the best facies for the formation and preservation of organic matter,especially deep-water basin facies.It remains necessary to strengthen the exploration of shale gas in the deep-water basin of∈1n in central Hunan,China.展开更多
The Terreneuvian Epoch（541-521 Ma）is also an important period for metallogenesis in South China, as was represented by the widespread occurrences of Ni-Mo polymetallic layers on the antecedent shallow platform margi...The Terreneuvian Epoch（541-521 Ma）is also an important period for metallogenesis in South China, as was represented by the widespread occurrences of Ni-Mo polymetallic layers on the antecedent shallow platform margin and the V-enriched black shales in deeper slope-basin settings. In this study, we have measured Re-Os isochron ages of Ni-Mo polymetallic layers（Songlin, Niuchang, Sancha, Chuanpengwan）, V-rich black shales（Bahuang）, and non-metalliferous black shales（Shuidong） in the basal Niutitang Formation in Guizhou and Hunan province, South China. The Ni-Mo polymetallic layers and V-enriched black shales have similar Re-Os isochron ages, suggesting concurrent deposition of these two types of metalliferous ores. This suggestion is consistent with the traditional stratigraphic correlation by using the nodular phosphorite bed directly underlying these metalliferous layers as a stratigraphic marker. Furthermore, the metalliferous ores and non-metalliferous black shales have similar initial ^（187）Os/^（188） Os ratios of 0.8-0.9, arguing for a dominant seawater origin with minor contribution of hydrothermal activity. Furthermore, Re-Os isotopic data also imply that Ni-Mo and V ore might have derived from the same source. We suggest that the spatial distribution of metalliferous ores can be explained by the development of non-sulfidic anoxic-suboxic wedge（NSASW） in the slope-basin and sulfidic wedge in the previous platform margin. Upwelling of deep water first transects the mildly reduced, organic rich NSASW, in which V（V） is reduced to V（IV）, and is preferentially removed from seawater by organometallic complex formation. As a result, V-rich black shale deposits in the slope-basin of Yangtze Platform. Further movement of deep water into the sulfidic platform margin results in Ni-Mo polymetallic layer formation.展开更多
Shales from the Lower Cambrian Niutitang Formation of Yangtze Platform have been widely investigated due to its shale gas potential.To better illustrate the pore structure and fractal characteristics of shale,a series...Shales from the Lower Cambrian Niutitang Formation of Yangtze Platform have been widely investigated due to its shale gas potential.To better illustrate the pore structure and fractal characteristics of shale,a series of experiments were conducted on outcrop samples from the Lower Cambrian Niutitang Formation on Yangtze Platform,including X-ray diffraction(XRD),field-emission scanning electron microscopy(FE-SEM) and low-temperature nitrogen adsorption.Frenkel-Halsey-Hill(FHH) model was adopted to calculate the fractal dimensions.Furthermore,the relationships between fractal dimensions and pore structure parameters and mineral composition are discussed.FE-SEM observation results show that interparticle pores are most developed in shale,followed by intraparticle pores.This study identified the fractal dimensions D1(ranging from 2.558 0 to 2.710 2) and D2(ranging from 2.541 5 to 2.765 2).The pore structure of the Niutitang Formation shale is primarily controlled by quartz and clay content.Fractal dimensions are able to characterize the pore structure complexity of Niutitang Formation shale because D1 and D2 correlate well with average pore diameter and quartz content.展开更多
The lower Cambrian Niutitang Formation is of crucial importance for shale gas target reservoirs in western Hubei,China;however,little work has been done in this field,and its shale gas accumulation and enrichment mech...The lower Cambrian Niutitang Formation is of crucial importance for shale gas target reservoirs in western Hubei,China;however,little work has been done in this field,and its shale gas accumulation and enrichment mechanism are still unclear.Based on survey wells,outcrop data,and large numbers of tests,the geological conditions of shale gas accumulation were studied;moreover,the factors that influence the gas content were thoroughly discussed.The results show that the Niutitang Formation(Є1n)can be divided into three sections:the first section(Є_(1)n^(1)),the second section(Є_(1)n^(2)),and the third section(Є1n3).TheЄ_(1)n^(2) is the main shale gas reservoir.The deep shelf facies is the main sedimentary facies and can be divided into three main lithofacies:argillaceous siltstone,carbonaceous shale and carbonaceous siliceous rock.The total organic carbon(TOC)content shows gentle growth trends until bottom of theЄ_(1)n^(2) and then decreases rapidly within theЄ_(1)n^(1),and the TOC content mainly ranges from 2%to 4%horizontally.The calcite and dolomite dissolution pores,clay intergranular pores and organic pores are the main pore types and the micropore types are clearly related to the mineral compositions and the TOC content.Vertically,the gas content is mainly affected by the TOC content.Horizontally,wells with high gas contents are distributed only southeast of the Huangling anticline,and the combination of structural styles,fault and fracture development,and the distribution of the regional unconformity boundary between the upper Sinian Dengying Formation(Z2d)and theЄ_(1)n^(2) are the three most important factors affecting the gas content.The favorable areas must meet the following conditions:a deep shelf environment,the presence of theЄ_(1)n^(1),wide and gentle folds,far from large normal faults that are more than 5 km,moderate thermal evolution,and greater than 500 m burial depth;this includes the block with the YD2–ZD2 wells,and the block with the Y1 and YD4 wells,which are distributed in the southern portion of the Huangling anticline and northern portion of the Xiannvshan fault.展开更多
The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock.However,hydrocarbon-forming organisms of these organic-rich shales was poorly understood.In this paper,the result...The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock.However,hydrocarbon-forming organisms of these organic-rich shales was poorly understood.In this paper,the results of palynofacies analysis and hydrocarbon-forming organism characteristics of the Niutitang Formation from the Yangtze Block are reported for the first time,and the sedimentary environment is discussed in combination with geochemical data.Palynofacies analysis show that the organic matter(OM)of the Niutitang Formation is mainly composed of amorphous organic matter(AOM),with a small amount of structural organic matter(STOM)and palynomorphs(PL).The results of CONISS(stratigraphically constrained incremental sum of squares)cluster analysis show that the PL can be divided into three zones in the ascending order:Leiosphaeridia-Micrhystridiumfungal zone,algal bloom zone and fungal development zone,corresponding to three stages:transgression,high-stand and regression,respectively.The principal component analysis(PCA)shows that the main hydrocarbon-forming organisms include planktonic green microalgae or dinoflagellates that are related to Leiosphaeridia and Microcystidium.Palynofacies analysis and geochemical data show that the Niutitang Formation was deposited under anoxic or dysoxic condition which was favorable to the enrichment of organic matter.展开更多
To evaluate the accumulation conditions and gas-bearing properties of shale gas in the Lower Cambrian Niutitang Formation,northwestern Hunan Province,the first shale gas parameter well(Well Changye-1)that takes the Ni...To evaluate the accumulation conditions and gas-bearing properties of shale gas in the Lower Cambrian Niutitang Formation,northwestern Hunan Province,the first shale gas parameter well(Well Changye-1)that takes the Niutitang Formation as the target horizon in the Hunan Province was selected preferably and drilled,cumulatively revealing the thickest dark shale horizon of the Niutitang Formation among the single-well drillings in China,with a true vertical thickness of 674.5m.Through analyzing the core samples in terms of organic geochemistry,rock mineralogy and reservoir properties,the black shale horizons in the Niutitang Formation of Well Changye-1 have high organic carbon content(average 3.9%),moderate maturity(equivalent Ro average 2.6%),high brittle mineral content(quartz content average 50.1%),low clay mineral content(average 32.4%),low porosity(1.7%)and low permeability(1.32×10^(-3)mD),and well-developed meso to micro-pores and fractures,indicating good conditions for shale gas accumulation.Field desorption and laboratory isothermal adsorption measurements on core samples show that Well Changye-1 has good gas-bearing properties,and gas content generally increases with depth.The black shale horizons at the depth of 1100-1250m have an average organic carbon content up to 10.1%,total gas content of 0.5-2.1m^(3)/t and 3.7-6.4m^(3)/t,and this is the most favorable depth for shale gas development,indicating that the Niutitang Formation has good a prospect for shale gas exploration.Due to huge sedimentary thickness,the black shale in the middle-lower part of the Niutitang Formation should be given priority for exploration.展开更多
基金granted by the National Natural Science Foundation of China (41603046)the Natural Science Foundation of Hunan Province (2017JJ1034)
文摘The accumulation and productivity of shale gas are mainly controlled by the characteristics of shale reservoirs;study of these characteristics forms the basis for the shale gas exploitation of the Lower Cambrian Niutitang Formation(Fm),Southern China.In this study,core observation and lithology study were conducted along with X-ray diffraction(XRD)and electronic scanning microscopy(SEM)examinations and liquid nitrogen(N2)adsorption/desorption and CH4 isothermal adsorption experiments for several exploration wells in northwestern Hunan Province,China.The results show that one or two intervals with high-quality source rocks(TOC>2 wt%)were deposited in the deep-shelf facies.The source rocks,which were mainly composed of carbonaceous shales and siliceous shales,had high quartz contents(>40 wt%)and low clay mineral(<30 wt%,mainly illites)and carbonate mineral(<20 wt%)contents.The SEM observations and liquid nitrogen(N2)adsorption/desorption experiments showed that the shale is tight,and nanoscale pores and microscale fractures are well developed.BJH volume(VBJH)of shale ranged from 2.144×10^-3 to 20.07×10^-3 cm^3/g,with an average of 11.752×10^-3 cm3/g.Pores mainly consisted of opened and interconnected mesopores(2–50 nm in diameter)or macropores(>50 nm in diameter).The shale reservoir has strong adsorption capacity for CH4.The Langmuir volume(VL)varied from 1.63 to 7.39 cm^3/g,with an average of 3.95 cm^3/g.The characteristics of shale reservoir are controlled by several factors:(1)A deep muddy continental shelf is the most favorable environment for the development of shale reservoirs,which is controlled by the development of basic materials.(2)The storage capacity of the shale reservoir is positively related to the TOC contents and plastic minerals and negatively related to cement minerals.(3)High maturity or overmaturity leads to the growth of organic pores and microfractures,thereby improving the reservoir storage capacity.It can be deduced that the high percentage of residual gas in Niutitang Fm results from the strong reservoir storage capacity of adsorbed gas.Two layers of sweet spots with strong storage capacity of free gas,and they are characterized by the relatively high TOC contents ranging from 4 wt%to 8 wt%.
基金This research was financially supported by the National Science and Technology Major Project(2016ZX05034)project of China Gelogical Survey(DD20160181).
文摘In order to evaluate the geological characteristics and gas-bearing factors of Niutitang Formation within the Lower Cambrian of northern Guizhou,the Huangping area located at the southern edge of the ancient uplift belt of Xuefeng Mountain was selected as the target area,and Well Huangdi 1 was drilled for the geological survey of shale gas.Through geological background analysis and well logging and laboratory analysis such as organic geochemical test,gas content analysis,isothermal adsorption,and specific surface area experiments on Well Huangdi 1,the results show that the Niutitang Formation is a deep-water shelf,trough-like folds and thrust fault.The thickness of black shale is 119.95 m,of which carbonaceous shale is 89.6 m.The average value of organic carbon content is 3.55%,kerogen vitrinite reflectance value is 2.37% and kerogen type is sapropel-type.The brittle mineral content is 51%(quartz 38%),clay mineral content is 38.3%.The value of porosity and permeability are 0.5%and 0.0014 mD,which the reservoir of the Niutitang Formation belongs to low permeability with characteristics of ultra-low porosity.The gas content is 0.09‒1.31 m^3/t with a high-value area and a second high-value area.By comparing with the geological parameters of adjacent wells in the adjacent area,the accumulation model of“sediment control zone,Ro control zone,structure controlling reservoir”in the study area is proposed.Therefore,deep-water shelf-slope facies,Ro is between high maturity-early stage of overmaturity and well-preserved zones in the Niutitang Formation in this area are favorable direction for the next step of shale gas exploration.
基金Project(2017GK2233)supported by the Science and Technology Innovation Program of Hunan Provine,ChinaProject(2017JJ1034)supported by the Natural Science Foundation of Hunan Province,China。
文摘The purpose of this study was to examine the sedimentary facies characteristics of lower Cambrian Niutitang Formation(∈1n)in South China,to reveal the mechanism of organic matter enrichment,and to guide exploration of shale gas.Macro investigation and experimental analyses were used to assess the lithology in detail,total organic matter mass fraction w(TOC),mineral composition,and trace element characteristics of∈1n.The influencing factors of organic matter enrichment were discussed extensively,and a sedimentary facies mode was suggested.In the early stage of∈1n,the locations of Well E’yangye 1,Well Ciye 1,Well Changye 1,and Well Anye 1 respectively develop,platform inner sag,outer shelf,Jiangnan slope belt,and South China detention basin.In the late stage of∈1n,the sedimentary facies evolve with decreasing sea level.The study area presents a complete three-step basin in the Early Cambrian.In the early stage of∈1n,the first step is the Yangtze carbonate platform,the second step is the outer shelf and slope,and the third step is the deep-water basin.From the Yangtze carbonate platform to the deep-water basin,w(TOC)and the mass fraction of quartz gradually increase,the mass fraction of carbonate mineral decreases,and the mass fraction of clay mineral is higher in the second step.The sea level fluctuation results in a higher w(TOC)vertically in the lower∈1n shale,and the paleogeographic(provenance)conditions lead to better horizontal development of organic matter in the outer shelf,slope and detention basin.Trace elements are abundant in the lower∈1n,and w(TOC)is correlated positively with many trace elements.In the outer shelf,slope,and adjacent areas,hydrothermal activity and upwelling current bring nutrient-rich material and promote organic matter enrichment under a strong reducing condition.Deep-shelf,slope and deep-water basin are the best facies for the formation and preservation of organic matter,especially deep-water basin facies.It remains necessary to strengthen the exploration of shale gas in the deep-water basin of∈1n in central Hunan,China.
基金supported by the National Natural science Foundation of China (Nos. 41203037, 41272017, 41472089, 41402025)the Chinese Geological Survey Program (Nos. 12120113015500, 12120114039701, 1212010633903, 1212011120622, J(2010)KP010705)+2 种基金Laboratory of Paleontology and Stratigraphy Open-lab grant (133103)the Science and Technology Foundation of Guizhou (No. QKHJZ(2012)2163)the Talents Introduction Foundation of Guizhou University (No. GDRJHZ(2011)17)
文摘The Terreneuvian Epoch（541-521 Ma）is also an important period for metallogenesis in South China, as was represented by the widespread occurrences of Ni-Mo polymetallic layers on the antecedent shallow platform margin and the V-enriched black shales in deeper slope-basin settings. In this study, we have measured Re-Os isochron ages of Ni-Mo polymetallic layers（Songlin, Niuchang, Sancha, Chuanpengwan）, V-rich black shales（Bahuang）, and non-metalliferous black shales（Shuidong） in the basal Niutitang Formation in Guizhou and Hunan province, South China. The Ni-Mo polymetallic layers and V-enriched black shales have similar Re-Os isochron ages, suggesting concurrent deposition of these two types of metalliferous ores. This suggestion is consistent with the traditional stratigraphic correlation by using the nodular phosphorite bed directly underlying these metalliferous layers as a stratigraphic marker. Furthermore, the metalliferous ores and non-metalliferous black shales have similar initial ^（187）Os/^（188） Os ratios of 0.8-0.9, arguing for a dominant seawater origin with minor contribution of hydrothermal activity. Furthermore, Re-Os isotopic data also imply that Ni-Mo and V ore might have derived from the same source. We suggest that the spatial distribution of metalliferous ores can be explained by the development of non-sulfidic anoxic-suboxic wedge（NSASW） in the slope-basin and sulfidic wedge in the previous platform margin. Upwelling of deep water first transects the mildly reduced, organic rich NSASW, in which V（V） is reduced to V（IV）, and is preferentially removed from seawater by organometallic complex formation. As a result, V-rich black shale deposits in the slope-basin of Yangtze Platform. Further movement of deep water into the sulfidic platform margin results in Ni-Mo polymetallic layer formation.
基金supported by the National Natural Science Foundation of China(Nos41690131,41572327,41273001)the Program of Introducing Talents of Discipline to Universities(No.B14031)
文摘Shales from the Lower Cambrian Niutitang Formation of Yangtze Platform have been widely investigated due to its shale gas potential.To better illustrate the pore structure and fractal characteristics of shale,a series of experiments were conducted on outcrop samples from the Lower Cambrian Niutitang Formation on Yangtze Platform,including X-ray diffraction(XRD),field-emission scanning electron microscopy(FE-SEM) and low-temperature nitrogen adsorption.Frenkel-Halsey-Hill(FHH) model was adopted to calculate the fractal dimensions.Furthermore,the relationships between fractal dimensions and pore structure parameters and mineral composition are discussed.FE-SEM observation results show that interparticle pores are most developed in shale,followed by intraparticle pores.This study identified the fractal dimensions D1(ranging from 2.558 0 to 2.710 2) and D2(ranging from 2.541 5 to 2.765 2).The pore structure of the Niutitang Formation shale is primarily controlled by quartz and clay content.Fractal dimensions are able to characterize the pore structure complexity of Niutitang Formation shale because D1 and D2 correlate well with average pore diameter and quartz content.
基金supported by the Scientific Research project of Department of Natural Resources of Hubei Province(No.ZRZY2020KJ10)Hubei Geological Bureau(No.KJ2019-3)+2 种基金the Shale Gas Geological Survey Projects of Department of Natural Resources of Hubei Province(Nos.HBCZ-17060223-170397 and DTCG-190409)We also thank the funds provided by Youth Foundation of the Northeast Petroleum University(No.2019QNL-21)Opening Fund of the Coal Reservoir Laboratory of National Engineering Research Center of CBM Development&Utilization,China University of Geosciences(Beijing)(No.2019MCQ02001)。
文摘The lower Cambrian Niutitang Formation is of crucial importance for shale gas target reservoirs in western Hubei,China;however,little work has been done in this field,and its shale gas accumulation and enrichment mechanism are still unclear.Based on survey wells,outcrop data,and large numbers of tests,the geological conditions of shale gas accumulation were studied;moreover,the factors that influence the gas content were thoroughly discussed.The results show that the Niutitang Formation(Є1n)can be divided into three sections:the first section(Є_(1)n^(1)),the second section(Є_(1)n^(2)),and the third section(Є1n3).TheЄ_(1)n^(2) is the main shale gas reservoir.The deep shelf facies is the main sedimentary facies and can be divided into three main lithofacies:argillaceous siltstone,carbonaceous shale and carbonaceous siliceous rock.The total organic carbon(TOC)content shows gentle growth trends until bottom of theЄ_(1)n^(2) and then decreases rapidly within theЄ_(1)n^(1),and the TOC content mainly ranges from 2%to 4%horizontally.The calcite and dolomite dissolution pores,clay intergranular pores and organic pores are the main pore types and the micropore types are clearly related to the mineral compositions and the TOC content.Vertically,the gas content is mainly affected by the TOC content.Horizontally,wells with high gas contents are distributed only southeast of the Huangling anticline,and the combination of structural styles,fault and fracture development,and the distribution of the regional unconformity boundary between the upper Sinian Dengying Formation(Z2d)and theЄ_(1)n^(2) are the three most important factors affecting the gas content.The favorable areas must meet the following conditions:a deep shelf environment,the presence of theЄ_(1)n^(1),wide and gentle folds,far from large normal faults that are more than 5 km,moderate thermal evolution,and greater than 500 m burial depth;this includes the block with the YD2–ZD2 wells,and the block with the Y1 and YD4 wells,which are distributed in the southern portion of the Huangling anticline and northern portion of the Xiannvshan fault.
基金supported by the National Natural Science Foundation of China(No.41430101)the State Special Fund from Ministry of Science and Technology(No.2017ZX05036002)。
文摘The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock.However,hydrocarbon-forming organisms of these organic-rich shales was poorly understood.In this paper,the results of palynofacies analysis and hydrocarbon-forming organism characteristics of the Niutitang Formation from the Yangtze Block are reported for the first time,and the sedimentary environment is discussed in combination with geochemical data.Palynofacies analysis show that the organic matter(OM)of the Niutitang Formation is mainly composed of amorphous organic matter(AOM),with a small amount of structural organic matter(STOM)and palynomorphs(PL).The results of CONISS(stratigraphically constrained incremental sum of squares)cluster analysis show that the PL can be divided into three zones in the ascending order:Leiosphaeridia-Micrhystridiumfungal zone,algal bloom zone and fungal development zone,corresponding to three stages:transgression,high-stand and regression,respectively.The principal component analysis(PCA)shows that the main hydrocarbon-forming organisms include planktonic green microalgae or dinoflagellates that are related to Leiosphaeridia and Microcystidium.Palynofacies analysis and geochemical data show that the Niutitang Formation was deposited under anoxic or dysoxic condition which was favorable to the enrichment of organic matter.
文摘To evaluate the accumulation conditions and gas-bearing properties of shale gas in the Lower Cambrian Niutitang Formation,northwestern Hunan Province,the first shale gas parameter well(Well Changye-1)that takes the Niutitang Formation as the target horizon in the Hunan Province was selected preferably and drilled,cumulatively revealing the thickest dark shale horizon of the Niutitang Formation among the single-well drillings in China,with a true vertical thickness of 674.5m.Through analyzing the core samples in terms of organic geochemistry,rock mineralogy and reservoir properties,the black shale horizons in the Niutitang Formation of Well Changye-1 have high organic carbon content(average 3.9%),moderate maturity(equivalent Ro average 2.6%),high brittle mineral content(quartz content average 50.1%),low clay mineral content(average 32.4%),low porosity(1.7%)and low permeability(1.32×10^(-3)mD),and well-developed meso to micro-pores and fractures,indicating good conditions for shale gas accumulation.Field desorption and laboratory isothermal adsorption measurements on core samples show that Well Changye-1 has good gas-bearing properties,and gas content generally increases with depth.The black shale horizons at the depth of 1100-1250m have an average organic carbon content up to 10.1%,total gas content of 0.5-2.1m^(3)/t and 3.7-6.4m^(3)/t,and this is the most favorable depth for shale gas development,indicating that the Niutitang Formation has good a prospect for shale gas exploration.Due to huge sedimentary thickness,the black shale in the middle-lower part of the Niutitang Formation should be given priority for exploration.
