Evolution and organic geochemical significance of bicyclic sesquiterpanes in pyrolysis simulation experiments on immature organic-rich mudstone

Sesquiterpanes are ubiquitous components of crude oils and ancient sediments.Liquid saturated hydrocarbons from simulated pyrolysis experiments on immature organic-rich mudstone collected from the Lower Cretaceous Hesigewula Sag were analyzed by gas chromatography-mass spectrometry(GC-MS).C14 bicyclic sesquiterpanes,namely,8β(H)-drimane,8β(H)-homodrimane,and 8 a(H)-homodrimane were detected and identified on basis of their diagnostic fragment ions(m/z123,179,193,and 207),and previously published mass spectra data,and these bicyclic sesquiterpanes presented relatively regular characteristics in their thermal evolution.The ratios 8β(H)-drimane/8β(H)-homodrimane,8β(H)-homodrimane/8 a(H)-homodrimane,and 8β(H)-drimane/8 a(H)-homodrimane all show a clear upward trend with increasing temperature below the temperature turning point.Thus,all these ratios can be used as evolution indexes of source rocks in the immature-lowmaturity stage.However,the last two ratios may be more suitable than the first ratio as valid parameters for measuring the extent of thermal evolution of organic matter in the immature-low-maturity stage because their change amplitude with increasing temperature is more obvious.

Discovery of Hesigewula Sag on the western margin of Da Hinggan Mountains in China and its significance in petroleum geology

With Songliao Basin in northeast China entering the middle-late stage of the exploration and development of oil and gas resources,it is urgent to open up new areas for oil and gas exploration on the periphery of the basin.Five sedimentary sags have been discovered in the western margin of the Da Hinggan Mountains through high-precision gravity,magnetic,and electrical prospecting engineering.According to the conditions of the 5 sags such as buried depth,area,and the scale of source rock,Hesigewula Sag was preferentially selected to deploy two-dimensional seismic prospecting and drilling.As a result,the stratigraphic distribution and structure of Hesigewula Sag were preliminarily ascertained,the main sedimentary facies developed in Aershan Formation-Tengger Formation of the Lower Cretaceous was summarized,and the assessment parameters of source rock of Hesigewula Sag were obtained.According to the research results,the Hesigewula Sag can be divided into 3 second-order tectonic units including the western bulge,the central sag,and the eastern bulge respectively,and the sag was formed mainly subject to the west fractures.Three sedimentary facies including fan delta facies,braided river delta facies,and lacustrine facies have been identified in the Aershan Formation-Tengger Formation of the sag.The source rock in the first member and second member of Tengger Formation in the sag features high abundance of organic matter,meeting the standards of good source rocks.The kerogen of the source rock is mainly of type Ⅱ1-Ⅱ2.The organic matter in the source rock is characterized by low maturity and it entered the evolution stage of low maturity from the second member of Tengger Formation.Furthermore,Hesigewula Sag bears a strong similarity to other petroliferous sags in Erlian Basin in structure,sedimentation,source rock,and other characteristics.Therefore,it can be preliminarily determined that Hesigewula Sag boasts great potential for oil and gas resources.

Identification and geochemical significance of unusual C24 tetracyclic terpanes in Shahejie Formation source rocks in the Bozhong subbasin,Bohai Bay Basin

C_(24)tetracyclic terpanes are common compounds in source rocks and crude oils,and C_(24)17,21-secohopane is the most common and widely used source-related indicator.In this study,three unusual C_(24)tetracyclic terpanes were detected on the m/z 191 chromatogram of saturated hydrocarbons in the Shahejie Formation source rocks in the Bozhong subbasin.Based on the mass spectra characteristics,diagnostic ion fragments,retention time and comparisons with published literature,three unusual C_(24)tetracyclic terpanes were identified as 10β(H)-des-A-oleanane,10β(H)-des-A-lupane and C_(24)des-Ahopane.To the best of our knowledge,this is the first study to detect and publicly report these three compounds in source rock samples from the Shahejie Formation of the Bozhong subbasin,Bohai Bay Basin.The results indicated that 10β(H)-des-A-oleanane and 10β(H)-des-A-lupane likely originated from terre strial angiosperms,while C_(24)des-A-hopane likely originated fro m prokaryotic o rganisms.Te rrestrial angiosperms provide the material basis for the generation of compounds A and B,and the distribution and concentration of these two compounds are affected by thermal maturity.In the low maturity stage(0.5%<R_(0)<0.7%),compounds A and B are relatively enriched in the source rocks.

Composition and distribution of NSO compounds in two different shales at the early maturity stage characterized by negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry

Gas chromatography/mass spectrometry （GC/MS） can only analyze volatile molecular compounds, and it has limitations when applied to determine the complex components of crude oils and hydrocarbon source rocks. Based on Fourier transform ion cyclotron resonance mass spectrometry （FT-ICR-MS） and GC/MS analyses, the molecular compositions of NSO compounds in extracts from the Permian Dalong Formation, Sichuan Basin and the Permian Lucaogou Formation, Junggar Basin in China were compared. Analyses of types of heteroatoms present （S~, $2, $3, OS, OS2, 02S, NS, and NOS compounds） suggest that marine shales from the Dalong Formation are mainly composed of carboxylic acids （02 com- pounds） with a high abundance of fatty acids, indicating a marine phytoplankton organic source. However, lacustrine shales from the Lucaogou Formation are dominated by pyrrolic compounds （N1 compounds） with abundant dibenzocar- bazole. It suggests that the organic source materials may be derived from lower aquatic organisms and lacustrine algae. Overall, FT-ICR-MS has potential for applications in analyses and determination of depositional environments and organic sources in petroleum geology.

Shale oil resource evaluation with an improved understanding of free hydrocarbons:Insights from three-step hydrocarbon thermal desorption

The pyrolysis parameter S1,which indicates the amount of free hydrocarbons present in shale,is often underestimated due to hydrocarbon loss during sample handling and measurement processes.To remedy this issue,we strongly recommend an immediate three-step hydrocarbon thermal desorption(HTD)approach to be conducted on oil shale at the drilling site.This approach measures S_(g),S_(O),and S_(1)^(*),which refer to gaseous,light,and free hydrocarbons,respectively.The new shale oil content value,calculated from the total of these three parameters,is far more precise and reliable than traditional pyrolysis S1.Moreover,we thoroughly investigated the components and microscopic occurrence features of hydrocarbons thermally desorbed at three temperature stages using gas chromatography(GC)and X-ray microcomputed tomography(CT).For example,we selected Chang 7_(3)mud shale.Our experimental results irrefutably indicate that the ultimate shale oil content of poor resource rocks is significantly impacted by evaporative loss,with this effect being greater when the total organic carbon(TOC)is lower.Additionally,C_(1-5)and C_(1-7)hydrocarbons constitute almost all of S_(g)and S_(O),respectively.S_(g)and S_(O)are predominantly composed of C_(1-3)gaseous hydrocarbons,with a maximum proportion of 42.93%.In contrast,S_(1)^(*)contains a substantial amount of C_(16-31)hydrocarbons.A three-dimensional reconstruction model of an X-ray micro-CT scan shows that while the amount of shale organic matter greatly decreases from the frozen state to 300℃,the pore volume significantly increases,particularly between 90 and 300℃.The increased pore volume is mainly due to macropores and fractures.It is imperative to note that the shale oil triple-division boundaries must be adjusted based on more accurate oil content,although this would not affect the resource zones to which the samples already belong(ineffective,low-efficient,and enriched resources).In conclusion,we strongly advise conducting an immediate well-site analysis or utilizing preservation procedures,such as deep freezing or plastic film wrapping followed by core waxing,to minimize volatile loss.

Sediment supply mechanism and its influence on hydrocarbon accumulation in the Paleogene of the northern Huanghekou Sag,Bohai Bay Basin,China

Tectonic activity and sediment supply have significantly affected the rifted basin fillings and hydrocarbon accumulations.The Huanghekou Sag in the southeastern Bohai Bay Basin is a hydrocarbon rich sag and was bounded by the Bonan Uplift to the north in the Paleogene,which strongly affected sediment disribution and hydrocarbon accumulation in this region.The sediment supply mechanism of the Paleogene parent rocks in this area has not been revealed yet.Therefore,the Huanghekou Sag is a natural laboratory to reveal the relationship between the tectonic activties and hydrcoarbon accumulations in a rifted basin.In this study,the tectonic evolution characteristics of the Bonan Uplift in different geological periods are revealed during the main fault depression periods.Then,the direction of the provenance and distribution of the depositional system of the Bonan Uplift are analyzed based on the sedimentary system and mineralogy analysis.Finally,the sediment supply in the Bonan Uplift in different geological periods has been systematically studied.The results indicated that sediment supply is the dominant factor of hydrocarbon accumulation in the Paleogene in the Huanghekou Sag.During the Paleocene-Middle Eocene,extensive denudation occurred in the Bonan Uplift,sediments were mainly sourced from the Bonan Uplift in the northern margin of the Huanghekou Sag.During the Late Eocene to Early Oligocene,the Bonan Uplift had a large angle rotation and subsidence due to the strong rifting of the Bozhong Sag in the north,and the sand supply capacity was seriously reduced.Due to the different sediment supply in different geological periods,high quality reservoir and cap conditions were formed in the Paleogene in the central and northern parts of the Huanghekou Sag,which is conducive to the accumulation and preservation of oil and gas.

Chemically synthesizing exchange-coupled SmCo_(5)/Sm_(2)Co_(17) nanocomposites

A new strategy to chemically synthesize exchange-coupled SmCo_(5)/Sm_(2) Co_(17) nanocomposites by in situ decomposition of SmCox(5<x<8.5)is reported in this work.Our synthesis starts with the fabrication of Co/Sm_(2) O_(3)(Sm to Co atomic ratio of Sn/Co=1:4.2),which can be reduced into 40-nm SmCo_(5) single crystal nanoparticles by Ca under the protection of CaO,showing a high coercivity of 2.85 T and saturation magnetization(Ms)of 0.0671 A·m^(2)·g^(-1).By changing the Sm/Co to 1:4.5,1:4.8 and 1:5.2,SmCo_(5)/Sm_(2) Co_(17) nanocomposites with different proportions were acquired using the same process.Owing to the in situ decomposition of SmCo_(x) intermediate,the small size(both of their size less than 10 nm)and uniform phase distribution were achieved in our nanocomposites.Thus,the as-prepared nanocomposites display a strong exchange-coupling interaction.As a consequence,SMCo_(5)/Sm_(2)Co_(17)(Sm/Co=1:5.2)exhibits a coercivity of 1.23 T and enhanced M7 T(magnetization at 7 T)of 0.0812 A·m^(2)·g^(-1),increasing by 21%than pure SmCo_(5).Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites.