Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Si...Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.展开更多
The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and signi...The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and significantly variable gas contents of the drilled shales.Excitingly,the first major breakthrough in deep and ultra-deep Lower Cambrian shale gas was made recently in the well Z201 in the southern Sichuan Basin,with a gas yield exceeding 73×10^(4)m^(3)/d.The success of well Z201 provides a favorable geological case to reveal the distinct enrichment mechanism of deep and ultra-deep Lower Cambrian shale gas.In this study,at drilling site of well Z201,fresh shale core samples with different gasin-place contents were collected,and their geochemical,pore development and water-bearing characteristics were analyzed systematically.The results showed that the Z201 organic-rich shales reached an overmature stage,with an average Raman maturity of 3.70%.The Z201 shales with high gas-in-place contents are mainly located in the Qiongzhusi 12section and the upper Qiongzhusi 11section,with an average gas-in-place content of 10.08 cm^(3)/g.Compared to the shales with low gas-in-place contents,the shales with high gas-in-place contents exhibit higher total organic carbon contents,greater porosities,and lower water saturations,providing more effective pore spaces for shale gas enrichment.The effective pore structures of the deep and ultra-deep Lower Cambrian shales are the primary factors affecting their gas-in-place contents.Similar to the shales with high gas-in-place contents of well Z201,the deep and ultra-deep Lower Cambrian shales in the Mianyang-Changning intracratonic sag,especially in the Ziyang area,generally developed in deep-water shelf facies with high total organic carbon contents and thick sedimentary thickness,providing favorable conditions for the development and preservation of effective pores.Therefore,they are the most promising targets for Lower Cambrian shale gas exploration.展开更多
Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and developm...Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and development.Herein,we investigated the Fengcheng Formation(P_(1)f)in Mahu Sag.This study integrated geochemistry,Soxhlet extraction,scanning electron microscopy,gas adsorption,and nuclear magnetic resonance T_(1)-T_(2)spectroscopy to elucidate the microscopic oil occurrence mechanisms in shales.Results indicate the presence of felsic shale,dolomitic shale,lime shale,and mixed shale within the P_(1)f.Matrix pores and microfractures associated with inorganic minerals are the predominant pore types in P_(1)f.Adsorbed oil primarily resides on the surfaces of organic matter and clay minerals,while free oil predominantly occupies inorganic pores and microfractures with larger pore sizes.Variations exist in the quantity and distribution of shale oil accumulation across different scales,where free oil and adsorbed oil are governed by dominant pores with diameters exceeding 10 nm and ineffective pores with diameters below 10 nm,respectively.Shale oil occurrence characteristics are influenced by organic matter,pore structure,and mineral composition.Felsic shale exhibits a high abundance of dominant pores,possesses the highest oil content,predominantly harbors free oil within these dominant pores,and demonstrates good mobility.Fluid occurrence in dolomitic shale and lime shale is intricate,with low oil content and a free oil to adsorbed oil ratio of 1:1.Mixed shale exhibits elevated clay mineral content and a scarcity of dominant pores.Moreover,ineffective pores contain increased bound water,resulting in medium oil content and limited mobility predominantly due to adsorption.Presently,shale oil mainly occurs in the dominant pores with a diameter larger than 10 nm in a free state.During the exploration and development of alkaline lacustrine shale oil resources,emphasis should be placed on identifying sweet spots within the felsic shale characterized by dominant pores.展开更多
Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the we...Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the well logging data,core samples,outcrops,and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin.Our analysis focused on the lake basin evolution and the migration characteristics,paleoenvironmental features,formation mechanisms,and developmental model of the black shales.The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration,with an overall thickening trend from east to west.Within the 1st Member of the formation,black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region.Multiple sets of shale developed within the 2nd and 3rd members,and these had lower thicknesses than the 1st Member and migrated toward central Sichuan.Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales.A semi-humid climate influenced the deposition of black shales,bringing abundant freshwater,terrigenous debris,and nutrients into the basin.Decomposition of organic matter consumed oxygen in sediment and bottom water,causing localized oxygen deficiency in the strata.展开更多
Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of th...Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of these targets and associated risks.Assessing shale depositional environments is also challenging due to the fine-grained nature of the sediments and subtle compositional variations.Herein,marine black shales of the Lower Cambrian Shiyantou(SYT)Formation(Fm)and Yu'anshan(YAS)Fm are investigated through a series of experiment,including thin sections,scanning electron microscopy,and major and trace elements analysis.Results show that five lithofacies can be identified in the SYT and YAS shales:(1)calcareous mudstone;(2)wavy-laminated sand,silt,and clay bearing mudstone;(3)laminated and massive mudstone;(4)planar-laminated pyritic mudstone,and(5)thin bedded sand and siltstone.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of SYT Fm are 57.03%,12.74%,4.20%,3.97%,3.93%,3.35%,1.09%,0.68%,0.28%,and 0.05%,respectively.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of Yu'anshan Fm are 54.93%,14.52%,5.26%,6.00%,3.77%,3.88%,0.15%,0.63%,0.19%,and 0.10%,respectively.Samples from SYT Fm are enriched in Li,V,Cr,Co,Zr,Cs,and U relative to Upper Continental Crust(UCC)and most of shale samples from YAS Fm are enriched in Li,V,Co,and U relative to UCC.The marine black shales are deposited in dynamic anoxic to oxic environment in upper Yangtze Plate,which indicated the seabed had already oxidized in the Cambrian Stages 2 and 3.The Chemical Index of Alteration(CIA)values ranged 51.84–79.46 indicate a warm and humid climate in the 2 stages.These findings are consistent with the region's paleogeography and previous studies.They hold significance for sedimentologists,paleontologists,and other researchers involved in petroleum geology.展开更多
High-temperature thermal simulation experiments(500-1000℃)were conducted with samples from the Lower Cambrian Niutitang Formation shale to investigate its mineral evolution and pore development.Integrated analyses,in...High-temperature thermal simulation experiments(500-1000℃)were conducted with samples from the Lower Cambrian Niutitang Formation shale to investigate its mineral evolution and pore development.Integrated analyses,including total organic carbon(TO C)content determination,X-ray diffraction(XRD),Scanning Electron Microscopy(SEM),and pore structure characterization,reveal that clay minerals progressively decompose and transform into quartz during heating,with a new mineral phase mullite produced at a temperature above 800℃.Concurrently,organic matter undergoes thermal evolution and shrinkage,creating distinctive shrinkage-induced fractures that enhance pore development.Clay mineral decomposition produces a more complex internal pore structure and fragmented reservoir matrix,generating pores at various scales.This process increases the number and size of micropores,mesopores,and macropores,creating intricate pore networks favorable for shale reservoir development.The study illuminates the intrinsic relationship between mineral transfo rmation and pore development in highly mature marine shales exposed to elevated temperatures.展开更多
With the development of unconventional hydrocarbon, how to improve the shale oil and gas recovery become urgent. Therefore hydraulic fracturing becomes the key due to the complicated properties of the reservoirs. The ...With the development of unconventional hydrocarbon, how to improve the shale oil and gas recovery become urgent. Therefore hydraulic fracturing becomes the key due to the complicated properties of the reservoirs. The pore structure not only plays an essential role in the formation of complex fracture networks after fracturing but also in resource accumulation mechanism analyses. The lacustrine organicrich shale samples were selected to carry out petrophysical experiments. Scanning Electron Microscopy(SEM) and X-ray Diffraction were performed to elucidate the geology characteristics. MICP, 2D NMR, CT,and N2adsorption were conducted to classify the pore structure types. The contribution of pore structure to oil accumulation and hydrocarbon enrichment was explained through the N2adsorption test on the original and extracted state and 2D NMR. The results show that micropores with diameter less than20 nm are well-developed. The pore structure was divided into three types. Type Ⅰ is characterized by high porosity, lower surface area, and good pore throat connectivity, with free oil existing in large pores,especially lamellation fractures. The dominant nano-pores are spongy organic pores and resources hosted in large pores have been expelled during high thermal evolution. The content of nano-pores(micropores) increases and the pore volume decreases in Type Ⅱ pore structure. In addition, more absorbed oil was enriched. The pore size distribution of type Ⅱ is similar to that of type Ⅰ. However, the maturity and hydrocarbon accumulation is quite different. The oil reserved in large pores was not expelled attributed to the relatively low thermal evolution compared with type Ⅰ. Structural vitrinite was observed through SEM indicating kerogen of type Ⅲ developed in this kind of reservoir while the type of kerogen in pore structure Ⅰ is type Ⅱ. Type Ⅲ pore structure is characterized by the largest surface area,lowest porosity, and almost isolated pores with rarely free oil. Type Ⅰ makes the most contribution to hydrocarbon accumulation and immigration, which shows the best prospect. Of all of these experiments,N2adsorption exhibits the best in characterizing pores in shales due to its high resolution for the assessment of nano-scale pores. MICP and NMR have a better advantage in characterizing pore space of sandstone reservoirs, even tight sandstone reservoirs. 2D NMR plays an essential role in fluid recognition and saturation calculation. CT scanning provides a 3D visualization of reservoir space and directly shows the relationship between pores and throats and the characteristics of fractures. This study hopes to guide experiment selection in pore structure characterization in different reservoirs. This research provides insight into hydrocarbon accumulation of shales and guidance in the exploration and development of unconventional resources, for example for geothermal and CCUS reservoirs.展开更多
The microscopic occurrence characteristics primarily constrain the enrichment and mobility of shale oil.This study collected the lacustrine shales from the Palaeogene Funing Formation in the Gaoyou Sag, Subei Basin. C...The microscopic occurrence characteristics primarily constrain the enrichment and mobility of shale oil.This study collected the lacustrine shales from the Palaeogene Funing Formation in the Gaoyou Sag, Subei Basin. Conventional and multistage Rock-Eval, scanning electron microscopy, and nuclear magnetic resonance(NMR) T1-T2were performed to analyze the contents and occurrence characteristics of shale oil. Low-temperature nitrogen adsorption-desorption(LTNA/D) experiments were conducted on the shales before and after extraction. The relationships between shale oil occurrence with organic matter and pore structures were then discussed. Predominantly, the shale oil in the Funing Formation is found within fractures, with secondary occurrences in interparticle pores linked to brittle minerals and sizeable intraparticle pores associated with clay minerals. The selected shales can be categorized into two types based on the nitrogen isotherms. Type A shales are characterized by high contents of felsic and calcareous minerals but low clay minerals, with larger TOC and shale oil values. Conversely, Type B shales are marked by abundant clay minerals but diminished TOC and shale oil contents. The lower BET specific surface area(SSA), larger average pore diameter, and simpler pore surfaces and pore structures lead to the Type A shales being more conducive to shale oil enrichment and mobility. Shale oil content is predominantly governed by the abundance of organic matter, while an overabundance of organic matter typically equates to a reduced ratio of free oil and diminished fluidity. The BET SSA, volumes of pores less than 25 and 100 nm at extracted state all correlate negatively with total and adsorbed oil contents but display no correlation with free oil, while they have positive relationships with capillary-bound water.Consequently, pore water is mainly saturated in micropores(<25 nm) and minipores(25-100 nm), as well as adsorbed oil, while free oil, i.e., bound and movable oil, primarily exists in mesopores(100-1000 nm) and macropores(>1000 nm). These findings may enhance the understanding of the microscopic occurrence characteristics of shale oil and will contribute to guide resource estimation and shale oil sweet spot exploitation in the Gaoyou Sag, Subei Basin.展开更多
To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay...To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.展开更多
Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a mor...Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a more complex pore water distribution.However,previous studies have focused on the water vapor sorption of gas shales rather than liquid pore water.This study clarifies the occurrence and distribution of pore water and the controlling factors by conducting thermogravimetry(TGA)under liquid water saturation and water vapor sorption experiments on four gas shales from the Wufeng Formation in South China.Nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies were used to monitor the dynamic changes and states of moisture,and the microscopic pore structures during water vapor sorption were detected using low-temperature nitrogen adsorption-desorption.The results indicate that TGA is adequate for determining the adsorbed,bound,and movable water contents.These four gas shales are characterized by high adsorbed and movable water contents,and some bound water.The adsorbed water primarily occurs in tiny pores(<100 nm),controlled by organic matter,followed by clay mine rals.The movable water,typically associated with quartz,primarily exists in pores of>100 nm,particularly macropores of>1000 nm.The bound water predominantly correlates with pores ranging from 10 to 2000 nm in clay minerals.The water vapor sorption process of the gas shale is well clarified.Water molecules primarily adsorb on the clay mineral's hydrophilic surface,followed by oxygen functional groups in the organic matter.Therefore,clay mine rals control water vapor sorption at low relative humidity(RH<0.75),whereas organic matter primarily affects vapor sorption at high RH.The TGA of liquid wate r-saturated gas shales can clarify the water distributions in full-scale pore networks,whereas the water vapor sorption method primarily discloses the moisture in small nanopores(<100 nm)but ignores most bound and movable water.This paper provides insight into liquid water distribution and occurre nce states within shale pore netwo rks,contributing to a better understanding of gas-wate r-rock interaction systems in-situ and hydraulic fracturing shale gas formations.展开更多
The Wufeng-Longmaxi Formation shales with burial depths > 3 500 m in the southern Sichuan Basin are believed to have large shale gas potentials.However,the reservoir properties and gasin-place(GIP) contents of thes...The Wufeng-Longmaxi Formation shales with burial depths > 3 500 m in the southern Sichuan Basin are believed to have large shale gas potentials.However,the reservoir properties and gasin-place(GIP) contents of these shales exhibit variations across different sublayers.In this study,a set of Wufeng-Longmaxi shales with burial depths of 4 000–4 200 m was derived from the Well Y101H2 in the Luzhou area,and the differences in geological and geochemical characteristics,porosity,water saturation and GIP content of various sublayer shales were investigated.The results indicate that the TOC content and effective porosity of the upper(LMX1-4) and lower(LMX1-3) sublayer shales of the first member of the Longmaxi Formation are better than those of the Wufeng Formation(WF) shales,which results in the LMX1-4 and LMX1-3 shales having higher GIP contents than the WF shales.The GIP contents of the LMX1-3 shales are higher than those of the LMX1-4 shales,and this is likely because the organic matter of the LMX1-3 shales had more aquatic organisms and was preserved in a stronger reductive environment,which leads to a stronger gas generation potential.In contrast to the middle-shallow LMX1-4 shales in the Sichuan Basin,the deep LMX1-4 shales in the Luzhou area have advantageous reservoir properties and GIP contents,and thus it is promising to synchronously exploit the deep LMX1-4 and LMX1-3 shales in some regions of the southern Sichuan Basin.展开更多
Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of the...Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of thermal maturity and OM types within the geological conditions.A suite of 16 core samples were taken from Type-Ⅲ Longtan shales and Type-Ⅱ Dalong shales from two wells covering a ma-turity(Ro,vitrinite reflectance)ranging from 1.22%to 1.43%and 2.62%to 2.97%,respectively.Integrated analysis of the shale samples was carried out,including field-emission scanning electron microscopy(FESEM),low-pressure N2 and CO2 adsorption,high-pressure CH4 adsorption,and mercury intrusion capillary pressure(MICP)analysis.The fluid inclusions of liquid and gas hydrocarbons trapped in calcite vein samples in Dalong shales of two wells were studied using laser Raman and fluorescence spectroscopy.FE-SEM images indicated that OM pores in different formations varied substantially in terms of shape,size,and distribution density.OM pores in Type-Ⅱ Dalong shales of Well XY1 were mainly micropore,sparsely distributed in the gas-prone kerogen with a spot-like and irregular shape,while bitumen rarely developed observable pores.In contrast,the morphology of OM pores in Type-Ⅲ Longtan shales were significantly different,which was due to differences in the OM type.The primary OM pores in some terrestrial woody debris in Longtan shales had a relatively larger pore diameter,ranging from hundreds of nanometers to a few micrometers and were al-most all rounded in shape,which might be one of the factors contributing to larger pore volume and gas adsorption capacity than Dalong shales of Well XY1.Comparing Dalong shales of Well XY1 with relatively lower thermal maturity,there were abundant spongy-like pores,densely developed in the pyrobitumen in Type-Ⅱ Dalong shales of Well EY1,with an irregular shape and diameter ranging from several to hundreds of nanometers.Many blue fluorescent oil inclusions and a small number of CH4 inclusions mixed with C2H6 could be observed within calcite veins in Dalong shales of Well XY1,whereas only CH4 inclusions could be identified within calcite veins in Dalong shales of Well EJ1.Therefore,thermal maturity not only controlled the type of hydrocarbons generated,but also makes a significant contribution to the formation of OM pores,resulting in larger pore volumes and adsorption capacity of Type-Ⅱ shale samples in the dry gas window.展开更多
One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method w...One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.展开更多
The marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed ...The marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17‰（relative to PDB）, which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events（T-OAE） in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic-anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox-sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo-and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea-level rise and an increase of surface water productivity.展开更多
The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on....The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province （China）. All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 （C 23 for sample Gzh00-1）. The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values （0.7） suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise.展开更多
To investigate pore characteristics and the factors controlling lacustrine shales,geochemical,mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songli...To investigate pore characteristics and the factors controlling lacustrine shales,geochemical,mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songliao Basin,China.A comparison of mercury injection capillary pressure(MICP)and low-temperature N2 adsorption pore-size distribution showed that MICP has a higher pore-size distribution(PSD)line in its overlapping pore diameter range,which may be elevated by the higher pressure of MICP.Therefore,in the overlapping range,low-temperature N2 adsorption data were preferred in pore characterization.Negative correlations were observed between pore volumes and TOC content,indicating organic matter pores are not well-developed in the studied samples.This may be related to their low grade of maturity and type I kerogens.There existed negative relationships between pore volumes and S1,which illustrated that liquid hydrocarbons occupied some pore space.Micropore volume had a better correlation with S1 than mesopore and macropore volumes,which suggests that liquid hydrocarbons preferentially occur in micropores.No obvious relationships between pore volumes and quartz or feldspar were observed,while pore volumes increased with the increasing clay mineral content.These relationships indicate that intraparticle pores in clay minerals represent the principal pore type.展开更多
The differences in organic matter abundance and rock composition between shale and mudstone determine the discrepancy of their contributions to the formation of conventional and shale oil/gas reservoirs.The evaluation...The differences in organic matter abundance and rock composition between shale and mudstone determine the discrepancy of their contributions to the formation of conventional and shale oil/gas reservoirs.The evaluation criteria of source rocks are different in the future exploration in self-sourced petroleum systems.Shales are deposited in deep/semi-deep lacustrine,with low sedimentation rate and chemical depositions of various degrees,while mudstones are mostly formed in shallow lacustrine/lakeside,with high deposition rate and density flow characteristics.Three factors contribute to the enrichment of organic matter in shales,including the"fertility effect"caused by volcanic ash deposition and hydrothermal injection,excessive and over-speed growth of organisms promoted by radioactive materials,and deep-water anaerobic environment and low sedimentation rate to protect the accumulation of organic matter from dilution.Lamellations in shales are easy to be stripped into storage space,and acid water produced during hydrocarbon generation can dissolve some particles to generate new pores.The massive mudstones with high clay content are of poor matrix porosity.Shales with high total organic carbon,developed laminations,relatively good reservoir property,and high brittle mineral content,are the most favorable lithofacies for shale oil exploration and development.It is necessary to conduct investigation on the differences between shale and mudstone reservoirs,to identify resources distribution in shale and mudstone formations,determine the type and standard of"sweet-spot"evaluation parameters,optimize"sweet-spot areas/sections",and adopt effective development technologies,which is of great significance to objectively evaluate the total amount and economy of shale oil resources,as well as the scale of effective exploitation.展开更多
Production performance of the Wufeng-Longmaxi shales varies significantly among Fuling,Weirong,and Wulong fields in the Sichuan Basin.Total organic carbon(TOC)content,mineralogy,and organic matter(OM)pore characterist...Production performance of the Wufeng-Longmaxi shales varies significantly among Fuling,Weirong,and Wulong fields in the Sichuan Basin.Total organic carbon(TOC)content,mineralogy,and organic matter(OM)pore characteristics are investigated to identify key factors governing sweet spots.Siliceous shales with good preservation conditions in the Fuling Field exhibit large thickness,high TOC content and thin-section porosity(TSP),and well-developed OM macropores,thus high initial production and estimated ultimate recovery(EUR).Thin carbonate-containing siliceous shales with good preservation conditions in the Weirong Field feature medium-to-high TOC and well-developed OM macropores but low TSP,leading to high initial production but low EUR.Siliceous shales with poor preservation conditions in the Wulong Field are characterized by large thickness,high TOC,low TSP and poorly-developed OM macropores,causing low initial production and EUR.Both sedimentary and preservation conditions are intrinsic decisive factors of sweet spots,as they control the mineral composition,TOC,and OM macropore development.Deep-water shales in transgressive systems tracts(TSTs)exhibit better-developed OM macropores and greater TOC compared to highstand systems tracts(HSTs).OM macropores are most prevalent in siliceous shales,followed by carbonate-containing siliceous shales and then argillaceous shales.Furthermore,good preservation conditions are conducive to retain OM macropores with low pore aspect ratio(PAR).Comparison among the three fields shows that high-TOC silicious shales with good preservation conditions are the highest in TSP and EUR.Therefore,organic richness,lithofacies,and preservation conditions are the major factors which determine OM pore development,governing the sweet spots of the Wufeng-Longmaxi shales.展开更多
In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened ...In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The H rka formation which hosts bituminous shale deposits is a volcanosedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of BS（1.83/2.62 ppm） are much lower than averages of UC, NASK and PAAS（uranium： 2.70/2.66/3.10 ppm; thorium： 8.50/12.30/14.60 ppm）. Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of BS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites（e.g. gneiss, schist） which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals（e.g. autunite, torbernite） which occur in granite, gneiss and schist. BS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma-Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements.展开更多
The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool...The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool for evaluating rocks with comparison and analysis both quantitatively and qualitatively.In our study,20 MHz NMR Relaxometry is used as a key technique to study the changes of water and oil behaviors in Chinese lacustrine Qingshankou shales under different saturated states(imbibition and evaporation without pressure).The results show that variation in different proton populations(water,oil and organic)can be distinguished using 2D T_(1)-T_(2)maps.The comparison among T_(1)-T_(2)maps with different saturated states shows that different signal regions changed during oil and water migrations,which the 1D NMR Relaxometry may be not easy to approach.Combined with the pyrolysis analysis,T2 shift and differences of signal regions in T_(1)-T_(2)maps can reflect properties such as wettability and composition(organic matter,clay and magnetic minerals)to some extent.This study provides better insight into oil and water behaviors in lacustrine oil shales with further understanding of 20 MHz NMR 2D T_(1)-T_(2)maps both in qualitative and quantitative analysis.展开更多
基金supported by the project of“Shale Gas Resources Investigation and Evaluation in the Baoshan Block”from Sinopec Exploration Company and the National Natural Science Foundation of China(41925014 and 42172192)。
文摘Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.
基金supported by the National Natural Science Foundation of China(41925014).
文摘The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and significantly variable gas contents of the drilled shales.Excitingly,the first major breakthrough in deep and ultra-deep Lower Cambrian shale gas was made recently in the well Z201 in the southern Sichuan Basin,with a gas yield exceeding 73×10^(4)m^(3)/d.The success of well Z201 provides a favorable geological case to reveal the distinct enrichment mechanism of deep and ultra-deep Lower Cambrian shale gas.In this study,at drilling site of well Z201,fresh shale core samples with different gasin-place contents were collected,and their geochemical,pore development and water-bearing characteristics were analyzed systematically.The results showed that the Z201 organic-rich shales reached an overmature stage,with an average Raman maturity of 3.70%.The Z201 shales with high gas-in-place contents are mainly located in the Qiongzhusi 12section and the upper Qiongzhusi 11section,with an average gas-in-place content of 10.08 cm^(3)/g.Compared to the shales with low gas-in-place contents,the shales with high gas-in-place contents exhibit higher total organic carbon contents,greater porosities,and lower water saturations,providing more effective pore spaces for shale gas enrichment.The effective pore structures of the deep and ultra-deep Lower Cambrian shales are the primary factors affecting their gas-in-place contents.Similar to the shales with high gas-in-place contents of well Z201,the deep and ultra-deep Lower Cambrian shales in the Mianyang-Changning intracratonic sag,especially in the Ziyang area,generally developed in deep-water shelf facies with high total organic carbon contents and thick sedimentary thickness,providing favorable conditions for the development and preservation of effective pores.Therefore,they are the most promising targets for Lower Cambrian shale gas exploration.
基金financially supported by the State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development(33550000-22-ZC0613-0006)National Natural Science Foundation of China(42202133)+2 种基金CNPC Innovation Fund(2022DQ02-0106)Strategic Cooperation Technology Projects of the CNPC and CUPB(ZLZX2020-01-05)Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences),Ministry of Education,China(TPR-2023-05)。
文摘Alkaline lacustrine shale is highly heterogeneous,and the complex relationship between the organicinorganic porosity network and hydrocarbon occurrence restricts the effectiveness of shale oil exploration and development.Herein,we investigated the Fengcheng Formation(P_(1)f)in Mahu Sag.This study integrated geochemistry,Soxhlet extraction,scanning electron microscopy,gas adsorption,and nuclear magnetic resonance T_(1)-T_(2)spectroscopy to elucidate the microscopic oil occurrence mechanisms in shales.Results indicate the presence of felsic shale,dolomitic shale,lime shale,and mixed shale within the P_(1)f.Matrix pores and microfractures associated with inorganic minerals are the predominant pore types in P_(1)f.Adsorbed oil primarily resides on the surfaces of organic matter and clay minerals,while free oil predominantly occupies inorganic pores and microfractures with larger pore sizes.Variations exist in the quantity and distribution of shale oil accumulation across different scales,where free oil and adsorbed oil are governed by dominant pores with diameters exceeding 10 nm and ineffective pores with diameters below 10 nm,respectively.Shale oil occurrence characteristics are influenced by organic matter,pore structure,and mineral composition.Felsic shale exhibits a high abundance of dominant pores,possesses the highest oil content,predominantly harbors free oil within these dominant pores,and demonstrates good mobility.Fluid occurrence in dolomitic shale and lime shale is intricate,with low oil content and a free oil to adsorbed oil ratio of 1:1.Mixed shale exhibits elevated clay mineral content and a scarcity of dominant pores.Moreover,ineffective pores contain increased bound water,resulting in medium oil content and limited mobility predominantly due to adsorption.Presently,shale oil mainly occurs in the dominant pores with a diameter larger than 10 nm in a free state.During the exploration and development of alkaline lacustrine shale oil resources,emphasis should be placed on identifying sweet spots within the felsic shale characterized by dominant pores.
基金funded by Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX050103).
文摘Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the well logging data,core samples,outcrops,and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin.Our analysis focused on the lake basin evolution and the migration characteristics,paleoenvironmental features,formation mechanisms,and developmental model of the black shales.The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration,with an overall thickening trend from east to west.Within the 1st Member of the formation,black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region.Multiple sets of shale developed within the 2nd and 3rd members,and these had lower thicknesses than the 1st Member and migrated toward central Sichuan.Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales.A semi-humid climate influenced the deposition of black shales,bringing abundant freshwater,terrigenous debris,and nutrients into the basin.Decomposition of organic matter consumed oxygen in sediment and bottom water,causing localized oxygen deficiency in the strata.
基金Supported by the National Natural Science Foundation of China(Nos.42130206,41302076)the Ministry of Science and Technology of the People’s Republic of China(MOST)Special Fund+1 种基金the State Key Laboratory of Continental Dynamics,Northwest University(No.201210128)the Major Scientific and Technological Projects of Changqing Oilfield(No.ZDZX-2021-03)。
文摘Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of these targets and associated risks.Assessing shale depositional environments is also challenging due to the fine-grained nature of the sediments and subtle compositional variations.Herein,marine black shales of the Lower Cambrian Shiyantou(SYT)Formation(Fm)and Yu'anshan(YAS)Fm are investigated through a series of experiment,including thin sections,scanning electron microscopy,and major and trace elements analysis.Results show that five lithofacies can be identified in the SYT and YAS shales:(1)calcareous mudstone;(2)wavy-laminated sand,silt,and clay bearing mudstone;(3)laminated and massive mudstone;(4)planar-laminated pyritic mudstone,and(5)thin bedded sand and siltstone.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of SYT Fm are 57.03%,12.74%,4.20%,3.97%,3.93%,3.35%,1.09%,0.68%,0.28%,and 0.05%,respectively.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of Yu'anshan Fm are 54.93%,14.52%,5.26%,6.00%,3.77%,3.88%,0.15%,0.63%,0.19%,and 0.10%,respectively.Samples from SYT Fm are enriched in Li,V,Cr,Co,Zr,Cs,and U relative to Upper Continental Crust(UCC)and most of shale samples from YAS Fm are enriched in Li,V,Co,and U relative to UCC.The marine black shales are deposited in dynamic anoxic to oxic environment in upper Yangtze Plate,which indicated the seabed had already oxidized in the Cambrian Stages 2 and 3.The Chemical Index of Alteration(CIA)values ranged 51.84–79.46 indicate a warm and humid climate in the 2 stages.These findings are consistent with the region's paleogeography and previous studies.They hold significance for sedimentologists,paleontologists,and other researchers involved in petroleum geology.
基金supported by the National Natural Science Foundation of China(No.52474056)the Forward-Looking Project of the State Key Laboratory,China(No.PRE/indep-2406)。
文摘High-temperature thermal simulation experiments(500-1000℃)were conducted with samples from the Lower Cambrian Niutitang Formation shale to investigate its mineral evolution and pore development.Integrated analyses,including total organic carbon(TO C)content determination,X-ray diffraction(XRD),Scanning Electron Microscopy(SEM),and pore structure characterization,reveal that clay minerals progressively decompose and transform into quartz during heating,with a new mineral phase mullite produced at a temperature above 800℃.Concurrently,organic matter undergoes thermal evolution and shrinkage,creating distinctive shrinkage-induced fractures that enhance pore development.Clay mineral decomposition produces a more complex internal pore structure and fragmented reservoir matrix,generating pores at various scales.This process increases the number and size of micropores,mesopores,and macropores,creating intricate pore networks favorable for shale reservoir development.The study illuminates the intrinsic relationship between mineral transfo rmation and pore development in highly mature marine shales exposed to elevated temperatures.
基金financially supported by the National Natural Science Foundation of China (Grant No. 42002133)Science Foundation of China University of Petroleum,Beijing No.2462024XKBH009+1 种基金the 2022 AAPG Foundation Grants-in-Aid ProgramChina National Postdoctoral Science Foundation(BX20240425 and 2024M753611)
文摘With the development of unconventional hydrocarbon, how to improve the shale oil and gas recovery become urgent. Therefore hydraulic fracturing becomes the key due to the complicated properties of the reservoirs. The pore structure not only plays an essential role in the formation of complex fracture networks after fracturing but also in resource accumulation mechanism analyses. The lacustrine organicrich shale samples were selected to carry out petrophysical experiments. Scanning Electron Microscopy(SEM) and X-ray Diffraction were performed to elucidate the geology characteristics. MICP, 2D NMR, CT,and N2adsorption were conducted to classify the pore structure types. The contribution of pore structure to oil accumulation and hydrocarbon enrichment was explained through the N2adsorption test on the original and extracted state and 2D NMR. The results show that micropores with diameter less than20 nm are well-developed. The pore structure was divided into three types. Type Ⅰ is characterized by high porosity, lower surface area, and good pore throat connectivity, with free oil existing in large pores,especially lamellation fractures. The dominant nano-pores are spongy organic pores and resources hosted in large pores have been expelled during high thermal evolution. The content of nano-pores(micropores) increases and the pore volume decreases in Type Ⅱ pore structure. In addition, more absorbed oil was enriched. The pore size distribution of type Ⅱ is similar to that of type Ⅰ. However, the maturity and hydrocarbon accumulation is quite different. The oil reserved in large pores was not expelled attributed to the relatively low thermal evolution compared with type Ⅰ. Structural vitrinite was observed through SEM indicating kerogen of type Ⅲ developed in this kind of reservoir while the type of kerogen in pore structure Ⅰ is type Ⅱ. Type Ⅲ pore structure is characterized by the largest surface area,lowest porosity, and almost isolated pores with rarely free oil. Type Ⅰ makes the most contribution to hydrocarbon accumulation and immigration, which shows the best prospect. Of all of these experiments,N2adsorption exhibits the best in characterizing pores in shales due to its high resolution for the assessment of nano-scale pores. MICP and NMR have a better advantage in characterizing pore space of sandstone reservoirs, even tight sandstone reservoirs. 2D NMR plays an essential role in fluid recognition and saturation calculation. CT scanning provides a 3D visualization of reservoir space and directly shows the relationship between pores and throats and the characteristics of fractures. This study hopes to guide experiment selection in pore structure characterization in different reservoirs. This research provides insight into hydrocarbon accumulation of shales and guidance in the exploration and development of unconventional resources, for example for geothermal and CCUS reservoirs.
基金supported by the National Natural Science Foundation of China(42302160)the Sanya City Science and Technology Innovation Project(2022KJCX51)the Support Plan for Outstanding Youth Innovation Team in Shandong Higher Education Institutions(2022KJ060).
文摘The microscopic occurrence characteristics primarily constrain the enrichment and mobility of shale oil.This study collected the lacustrine shales from the Palaeogene Funing Formation in the Gaoyou Sag, Subei Basin. Conventional and multistage Rock-Eval, scanning electron microscopy, and nuclear magnetic resonance(NMR) T1-T2were performed to analyze the contents and occurrence characteristics of shale oil. Low-temperature nitrogen adsorption-desorption(LTNA/D) experiments were conducted on the shales before and after extraction. The relationships between shale oil occurrence with organic matter and pore structures were then discussed. Predominantly, the shale oil in the Funing Formation is found within fractures, with secondary occurrences in interparticle pores linked to brittle minerals and sizeable intraparticle pores associated with clay minerals. The selected shales can be categorized into two types based on the nitrogen isotherms. Type A shales are characterized by high contents of felsic and calcareous minerals but low clay minerals, with larger TOC and shale oil values. Conversely, Type B shales are marked by abundant clay minerals but diminished TOC and shale oil contents. The lower BET specific surface area(SSA), larger average pore diameter, and simpler pore surfaces and pore structures lead to the Type A shales being more conducive to shale oil enrichment and mobility. Shale oil content is predominantly governed by the abundance of organic matter, while an overabundance of organic matter typically equates to a reduced ratio of free oil and diminished fluidity. The BET SSA, volumes of pores less than 25 and 100 nm at extracted state all correlate negatively with total and adsorbed oil contents but display no correlation with free oil, while they have positive relationships with capillary-bound water.Consequently, pore water is mainly saturated in micropores(<25 nm) and minipores(25-100 nm), as well as adsorbed oil, while free oil, i.e., bound and movable oil, primarily exists in mesopores(100-1000 nm) and macropores(>1000 nm). These findings may enhance the understanding of the microscopic occurrence characteristics of shale oil and will contribute to guide resource estimation and shale oil sweet spot exploitation in the Gaoyou Sag, Subei Basin.
基金financially supported by the National Natural Science Foundation of China (Grant No. 42072150)
文摘To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.
基金This study was financially supported by the National Natural Science Foundation of China(42302160)the PhD Scientific Research and Innovation Foundation of the Education Department of Hainan Province Joint Project of Sanya Yazhou Bay Science and Technology City(HSPHDSRF-2024-07-001)Educational Reform of Hainan Higher Education Institutions(Hnjg2024-276)。
文摘Connate water strongly restricts shale gas enrichment and production,and most artificially injected water is confined in shale pore networks owing to low water recovery during hydraulic fracturing,which leads to a more complex pore water distribution.However,previous studies have focused on the water vapor sorption of gas shales rather than liquid pore water.This study clarifies the occurrence and distribution of pore water and the controlling factors by conducting thermogravimetry(TGA)under liquid water saturation and water vapor sorption experiments on four gas shales from the Wufeng Formation in South China.Nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies were used to monitor the dynamic changes and states of moisture,and the microscopic pore structures during water vapor sorption were detected using low-temperature nitrogen adsorption-desorption.The results indicate that TGA is adequate for determining the adsorbed,bound,and movable water contents.These four gas shales are characterized by high adsorbed and movable water contents,and some bound water.The adsorbed water primarily occurs in tiny pores(<100 nm),controlled by organic matter,followed by clay mine rals.The movable water,typically associated with quartz,primarily exists in pores of>100 nm,particularly macropores of>1000 nm.The bound water predominantly correlates with pores ranging from 10 to 2000 nm in clay minerals.The water vapor sorption process of the gas shale is well clarified.Water molecules primarily adsorb on the clay mineral's hydrophilic surface,followed by oxygen functional groups in the organic matter.Therefore,clay mine rals control water vapor sorption at low relative humidity(RH<0.75),whereas organic matter primarily affects vapor sorption at high RH.The TGA of liquid wate r-saturated gas shales can clarify the water distributions in full-scale pore networks,whereas the water vapor sorption method primarily discloses the moisture in small nanopores(<100 nm)but ignores most bound and movable water.This paper provides insight into liquid water distribution and occurre nce states within shale pore netwo rks,contributing to a better understanding of gas-wate r-rock interaction systems in-situ and hydraulic fracturing shale gas formations.
基金supported by the National Natural Science Foundation of China (Nos.41925014,42173031)the Natural Science Foundation of Guangdong Province (No.2021A1515011381)the Project of PetroChina Southwest Oil and Gas Fields (No.XNS-YYY-JS2021-49)。
文摘The Wufeng-Longmaxi Formation shales with burial depths > 3 500 m in the southern Sichuan Basin are believed to have large shale gas potentials.However,the reservoir properties and gasin-place(GIP) contents of these shales exhibit variations across different sublayers.In this study,a set of Wufeng-Longmaxi shales with burial depths of 4 000–4 200 m was derived from the Well Y101H2 in the Luzhou area,and the differences in geological and geochemical characteristics,porosity,water saturation and GIP content of various sublayer shales were investigated.The results indicate that the TOC content and effective porosity of the upper(LMX1-4) and lower(LMX1-3) sublayer shales of the first member of the Longmaxi Formation are better than those of the Wufeng Formation(WF) shales,which results in the LMX1-4 and LMX1-3 shales having higher GIP contents than the WF shales.The GIP contents of the LMX1-3 shales are higher than those of the LMX1-4 shales,and this is likely because the organic matter of the LMX1-3 shales had more aquatic organisms and was preserved in a stronger reductive environment,which leads to a stronger gas generation potential.In contrast to the middle-shallow LMX1-4 shales in the Sichuan Basin,the deep LMX1-4 shales in the Luzhou area have advantageous reservoir properties and GIP contents,and thus it is promising to synchronously exploit the deep LMX1-4 and LMX1-3 shales in some regions of the southern Sichuan Basin.
基金We would like to thank the National Key R&D program of China(No.2017YFE0103600)the National Natural Science Foundation of China(Nos.41830431,41672139)the China National Science and Technology Major Projects(No.2016ZX05034002-003)for financial assistance to this research.
文摘Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of thermal maturity and OM types within the geological conditions.A suite of 16 core samples were taken from Type-Ⅲ Longtan shales and Type-Ⅱ Dalong shales from two wells covering a ma-turity(Ro,vitrinite reflectance)ranging from 1.22%to 1.43%and 2.62%to 2.97%,respectively.Integrated analysis of the shale samples was carried out,including field-emission scanning electron microscopy(FESEM),low-pressure N2 and CO2 adsorption,high-pressure CH4 adsorption,and mercury intrusion capillary pressure(MICP)analysis.The fluid inclusions of liquid and gas hydrocarbons trapped in calcite vein samples in Dalong shales of two wells were studied using laser Raman and fluorescence spectroscopy.FE-SEM images indicated that OM pores in different formations varied substantially in terms of shape,size,and distribution density.OM pores in Type-Ⅱ Dalong shales of Well XY1 were mainly micropore,sparsely distributed in the gas-prone kerogen with a spot-like and irregular shape,while bitumen rarely developed observable pores.In contrast,the morphology of OM pores in Type-Ⅲ Longtan shales were significantly different,which was due to differences in the OM type.The primary OM pores in some terrestrial woody debris in Longtan shales had a relatively larger pore diameter,ranging from hundreds of nanometers to a few micrometers and were al-most all rounded in shape,which might be one of the factors contributing to larger pore volume and gas adsorption capacity than Dalong shales of Well XY1.Comparing Dalong shales of Well XY1 with relatively lower thermal maturity,there were abundant spongy-like pores,densely developed in the pyrobitumen in Type-Ⅱ Dalong shales of Well EY1,with an irregular shape and diameter ranging from several to hundreds of nanometers.Many blue fluorescent oil inclusions and a small number of CH4 inclusions mixed with C2H6 could be observed within calcite veins in Dalong shales of Well XY1,whereas only CH4 inclusions could be identified within calcite veins in Dalong shales of Well EJ1.Therefore,thermal maturity not only controlled the type of hydrocarbons generated,but also makes a significant contribution to the formation of OM pores,resulting in larger pore volumes and adsorption capacity of Type-Ⅱ shale samples in the dry gas window.
基金This work is supported by the National Key Basic Research Program （2006CB701406）；Natural Science Foundation of China for Youth （40403003） ；Key Project of the Natural Science Foundation of China （40332020）, and is a contribution to IGCP 463.
文摘One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.
基金supported by the National Natural Science Foundation of China(grants No.41102066,41572095 and 41572089)Opening Foundation of the State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences(grant No.201008)State Key Laboratory of Marine Geology,Tongji University(grant No.MGK1703)
文摘The marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17‰（relative to PDB）, which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events（T-OAE） in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic-anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox-sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo-and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea-level rise and an increase of surface water productivity.
基金supported by the "CAS Hundred Talents"Foundation of the Chinese Academy of Sciences to H.Z.,National Natural Science Foundation of China (Grant No.41102066, 40972084)Natural Science Foundation Project of CQ CSTC (Grant No. 2009BB7383)Opening Foundation of the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences
文摘The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province （China）. All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 （C 23 for sample Gzh00-1）. The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values （0.7） suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise.
基金co-funded by the National Science Foundation of China(41972161,41502144)the Petro China Science and Technology Special Project(2011A-0203)。
文摘To investigate pore characteristics and the factors controlling lacustrine shales,geochemical,mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songliao Basin,China.A comparison of mercury injection capillary pressure(MICP)and low-temperature N2 adsorption pore-size distribution showed that MICP has a higher pore-size distribution(PSD)line in its overlapping pore diameter range,which may be elevated by the higher pressure of MICP.Therefore,in the overlapping range,low-temperature N2 adsorption data were preferred in pore characterization.Negative correlations were observed between pore volumes and TOC content,indicating organic matter pores are not well-developed in the studied samples.This may be related to their low grade of maturity and type I kerogens.There existed negative relationships between pore volumes and S1,which illustrated that liquid hydrocarbons occupied some pore space.Micropore volume had a better correlation with S1 than mesopore and macropore volumes,which suggests that liquid hydrocarbons preferentially occur in micropores.No obvious relationships between pore volumes and quartz or feldspar were observed,while pore volumes increased with the increasing clay mineral content.These relationships indicate that intraparticle pores in clay minerals represent the principal pore type.
基金Supported by the China National Science and Technology Major Project(2016ZX05046,2017ZX05001)
文摘The differences in organic matter abundance and rock composition between shale and mudstone determine the discrepancy of their contributions to the formation of conventional and shale oil/gas reservoirs.The evaluation criteria of source rocks are different in the future exploration in self-sourced petroleum systems.Shales are deposited in deep/semi-deep lacustrine,with low sedimentation rate and chemical depositions of various degrees,while mudstones are mostly formed in shallow lacustrine/lakeside,with high deposition rate and density flow characteristics.Three factors contribute to the enrichment of organic matter in shales,including the"fertility effect"caused by volcanic ash deposition and hydrothermal injection,excessive and over-speed growth of organisms promoted by radioactive materials,and deep-water anaerobic environment and low sedimentation rate to protect the accumulation of organic matter from dilution.Lamellations in shales are easy to be stripped into storage space,and acid water produced during hydrocarbon generation can dissolve some particles to generate new pores.The massive mudstones with high clay content are of poor matrix porosity.Shales with high total organic carbon,developed laminations,relatively good reservoir property,and high brittle mineral content,are the most favorable lithofacies for shale oil exploration and development.It is necessary to conduct investigation on the differences between shale and mudstone reservoirs,to identify resources distribution in shale and mudstone formations,determine the type and standard of"sweet-spot"evaluation parameters,optimize"sweet-spot areas/sections",and adopt effective development technologies,which is of great significance to objectively evaluate the total amount and economy of shale oil resources,as well as the scale of effective exploitation.
文摘Production performance of the Wufeng-Longmaxi shales varies significantly among Fuling,Weirong,and Wulong fields in the Sichuan Basin.Total organic carbon(TOC)content,mineralogy,and organic matter(OM)pore characteristics are investigated to identify key factors governing sweet spots.Siliceous shales with good preservation conditions in the Fuling Field exhibit large thickness,high TOC content and thin-section porosity(TSP),and well-developed OM macropores,thus high initial production and estimated ultimate recovery(EUR).Thin carbonate-containing siliceous shales with good preservation conditions in the Weirong Field feature medium-to-high TOC and well-developed OM macropores but low TSP,leading to high initial production but low EUR.Siliceous shales with poor preservation conditions in the Wulong Field are characterized by large thickness,high TOC,low TSP and poorly-developed OM macropores,causing low initial production and EUR.Both sedimentary and preservation conditions are intrinsic decisive factors of sweet spots,as they control the mineral composition,TOC,and OM macropore development.Deep-water shales in transgressive systems tracts(TSTs)exhibit better-developed OM macropores and greater TOC compared to highstand systems tracts(HSTs).OM macropores are most prevalent in siliceous shales,followed by carbonate-containing siliceous shales and then argillaceous shales.Furthermore,good preservation conditions are conducive to retain OM macropores with low pore aspect ratio(PAR).Comparison among the three fields shows that high-TOC silicious shales with good preservation conditions are the highest in TSP and EUR.Therefore,organic richness,lithofacies,and preservation conditions are the major factors which determine OM pore development,governing the sweet spots of the Wufeng-Longmaxi shales.
基金supported by Ankara University Scientific Research Projects Coordination Unit(Project No:09B4343013)
文摘In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The H rka formation which hosts bituminous shale deposits is a volcanosedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of BS（1.83/2.62 ppm） are much lower than averages of UC, NASK and PAAS（uranium： 2.70/2.66/3.10 ppm; thorium： 8.50/12.30/14.60 ppm）. Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of BS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites（e.g. gneiss, schist） which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals（e.g. autunite, torbernite） which occur in granite, gneiss and schist. BS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma-Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements.
基金supported by the Opening Fund of Key Laboratory of Continental Shale Accumulation and Development(Northeast Petroleum University,China)the National Natural Science Foundation of China(Grant No.51605089,Grant No.41972156)
文摘The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool for evaluating rocks with comparison and analysis both quantitatively and qualitatively.In our study,20 MHz NMR Relaxometry is used as a key technique to study the changes of water and oil behaviors in Chinese lacustrine Qingshankou shales under different saturated states(imbibition and evaporation without pressure).The results show that variation in different proton populations(water,oil and organic)can be distinguished using 2D T_(1)-T_(2)maps.The comparison among T_(1)-T_(2)maps with different saturated states shows that different signal regions changed during oil and water migrations,which the 1D NMR Relaxometry may be not easy to approach.Combined with the pyrolysis analysis,T2 shift and differences of signal regions in T_(1)-T_(2)maps can reflect properties such as wettability and composition(organic matter,clay and magnetic minerals)to some extent.This study provides better insight into oil and water behaviors in lacustrine oil shales with further understanding of 20 MHz NMR 2D T_(1)-T_(2)maps both in qualitative and quantitative analysis.
