Bitumen In Rocks Research Articles

Biomarker Hydrocarbons and Carbon Isotopes of Individual n-Alkanes in Paraffin Oils and Bitumens of the Middle Devonian–Lower Frasnian Terrigenous Complex of the Timan–Pechora Basin

Abstract ––The objects of study were bitumens of sedimentary rocks and paraffin oils of the Middle Devonian–lower Frasnian terrigenous complex of the Timan–Pechora basin. We studied the composition of biomarker hydrocarbons and the carbon isotope composition of individual n-alkanes of bitumens from the cores of the wells of the Omra–Lyzha saddle. The results were compared with similar data on the composition of paraffin oils from the south of the Pechora–Kozhva megaswell. The generation potential and thermal maturity of organic matter were studied by the Rock-Eval pyrolysis method. The maturity of organic matter in the rocks of the studied complex in the Omra–Lyzha saddle and the Pechora–Kozhva megaswell corresponds to the oil window. Data on the carbon isotopy of n-alkanes and on the composition of biomarker hydrocarbons do not contradict the possible genetic relationship between paraffin oils and the organic matter of the host sedimentary complex. Both the studied paraffin oils and the rock bitumens contain early eluting rearranged hopanes atypical of oils of other petroliferous complexes and show high contents of n-alkanes relative to iso-alkanes and polycyclic biomarkers. The content of 13C tends to decrease with an increase in the number of carbon atoms in the n-alkane molecule in both oils and bitumen rocks.

Petroleum Potential and Organic-Matter–Oil Correlation in the Rocks of the Upper Riphean Iremeken Formation in the Kamo Arch of the Baikit Anteclise (Siberian Platform)

Abstract —A complex of laboratory studies of Riphean rocks and oils was carried out by the organic-geochemistry methods to construct a basin model for the Kamo arch of the Baikit anteclise of the Siberian craton. We compared the parameters of the organic matter (OM) and oils of the Upper Riphean Iremeken carbonaceous member by biomarker hydrocarbons. Analysis of the obtained chromatography–mass spectrometry data showed an unordinary group hydrocarbon composition of extracts from the OM and oils and low contents of cheilanthanes and steranes in them. Within the Kamo arch, the Upper Riphean Iremeken OM-enriched deposits with a high petroleum potential might have reached the peak of petroleum generation only in the deepest part of the Madra trough; thus, the traps could not be completely filled with oil. The distribution of tricyclic terpanes in the rock bitumens from the studied wells testifies to immature OM in the Iremeken Formation. However, in the most submerged zones of the Kamo arch and in the adjacent areas, oil was generated from the OM of the Iremeken Formation. This is evidenced by the oils of the Upper Iremeken Subformation in the Kuyumbinskoe field and the Ter’-Kamo license area.

Short-chain A-ring methylated steroidal hydrocarbons

Short-chain A-ring methylated steroidal hydrocarbons

On the origin of 3-methyl steroids and diasteranes

The potential origin of 3-methyl steroids is investigated through comparison of their carbon number distributions with those of their desmethyl counterparts using GC-MS and GC-MS-MS analysis of a range of oils and some immature source rock bitumens. There is a close genetic link between desmethyl and 3-methyl steranes, consistent with competition between methylation and hydrogenation at C-3 in the shared steroidal precursors, producing strongly positively correlated carbon number distributions within the two series. The absence (or possibly very low levels) of detectable 3-methyl diasteroids in immature bitumen samples suggests that these compounds are not formed in the free bitumen during diagenesis in amounts capable of explaining their abundance in oils. It is possible that they are produced by a limited degree of rearrangement of steroids after they are bound into kerogen or upon cleavage from kerogen and methylation during catagenesis. Support for this proposition is provided by the previous detection of desmethyl diasterenes in the hydropyrolysate of pre-extracted algal biopolymers, as well as the high diasterane/sterane ratios reported in several studies of hydrous pyrolysis of kerogen. Competition between methylation and hydrogenation during catagenetic formation of diasteranes might explain the lower diasterane/regular sterane ratio observed for 3-methyl compared to desmethyl species.

Novel low-field NMR method for characterization content and SARA composition of bitumen in rocks

In the oil industry, there is a need for fast and non-invasive methods for determining the bitumen content and group composition in rock samples. Determination of bitumen saturation of reservoir or source rocks has some difficulties due to existing methods limitations. For this purpose, the novel method is based on a combination of free induction decay (FID) and modified Carr-Purcell-Meilboom-Gill (CPMG) measurements using a low-frequency nuclear magnetic resonance (NMR) relaxation technique was developed. It allows obtaining the content and group composition (SARA fractions) of bitumen directly in the porous media without extraction. FID data fitting based on a combination of Voigt and exponential functions for liquid phase, as well as Abragam and exponential functions for solid phase components respectively was proposed. The developed method was tested on 20 rock samples collected from the productive formation (horizon M) located at the depth of 601–708 m of the wellbore 3001 of the Boca de Jaruco oilfield (Republic of Cuba). The bitumen content in the samples was obtained and compared with data determined by thermogravimetric analysis (TGA) and Rock-Eval pyrolysis. A good agreement of NMR results with TGA and pyrolysis was shown (R2 = 0.99 and 0.97 respectively). The values of liquid HC components (saturates, aromatics and resins) and solid HC components (asphaltenes) were compared with TGA data (R2 = 0.97 and 0.98 respectively). Finally, the proposed NMR method was applied to determine the SARA composition of the bitumen in the samples. To assess the accuracy of determining the SARA composition by the NMR method, SARA analysis (ASTM D4124-09) of extracts from the samples 632, 638, 658, 676, 689, 708 was carried out. NMR and conventional SARA analysis showed close results. To assess the completeness of the bitumen extraction from the mineral matrix, microCT and FIB-SEM were performed before and after extraction. It was found that after extraction the part of the bitumen remains in the pores, which distorts the results of SARA analysis. The proposed NMR method can be used to calculate the bitumen saturation and SARA composition for characterization of bitumen, selecting and modeling the effectiveness of applying the optimal EOR without destroying the samples. Also, the method is promising for the operational control of technological processes of oil production.

Fractionation of hydrocarbons and NSO-compounds during primary oil migration revealed by high resolution mass spectrometry: Insights from oil trapped in fluid inclusions

The composition of oil trapped in fluid inclusions (FI), occurring in mineral cements, can provide valuable insights into oil migration. Here, FI oils in a calcite vein (representing expelled fluids) and source rock (SR) extracts (representing retained bitumen) from the Hosszúhetény Calcareous Marl Formation (HCMF) in the Mecsek Mountains area of Hungary were investigated to assess how organic compounds are fractionated during primary migration. Biomarkers analyzed by gas chromatography–mass spectrometry and gas chromatography-stable carbon isotope ratio mass spectrometry were used to demonstrate that the FI oils had been expelled from the HCMF marl (calculated vitrinite reflectance of ~0.74% Rc). Fourier transform-ion cyclotron resonance-mass spectrometry then provided insights into polar compound geochemistry, showing that O1, N1, N1O1 and S1O1 compound classes are preferentially retained in the source rock bitumen, while less polar compounds like aromatic hydrocarbons (HCs) and S1 compounds are assumed to be preferentially expelled. Independent of the compound class, compounds with higher double bond equivalents (DBEs) are enriched in the retained source rock bitumen. Thus, besides the molecular polarity determined by the functional groups, the molecular size and the degree of aromaticity appear to be the most important factors affecting the migration and retention behavior of the petroleum HCs and NSO-compounds in the HCMF. Moreover, the enrichment of high DBE compounds with shorter alkyl chains in the SR extracts infers that shielding effects could have played a major role for compound retention and expulsion during primary oil migration.

Mechanical behaviors of asphalt mixtures modified with European rock bitumen and waste cooking oil

• ERB improve the high temperature and aging performance of asphalt mixture. • WCO improve the low temperature performance of asphalt mixture. • WCO compensates for the low temperature performance of ERB modified mixtures. • To realize the effective utilization of waste cooking oil resources. The use of modifiers as an effective solution to improve the performance of asphalt pavement has been gaining popularity in recent years. The objective of this research was to investigate the effect of compound modification of asphalt using European rock bitumen (ERB) and waste cooking oil (WCO) on the macroscopic mechanical properties of asphalt mixtures. WCO can effectively improve the low-temperature performance of the compound-modified asphalt, and ERB can make up for the adverse effects of waste cooking oil on high-temperature performance. The experimental plan considered asphalt mixture AC-13 with four ERB/WCO modified asphalt combinations (18% ERB + 0% WCO, 2% WCO + 18% ERB, 4% WCO + 18% ERB and 4% WCO + 12% ERB) and Marshall test, rutting test, indirect tensile strength test at low temperature, freeze-thaw splitting test, and the long-term aged test, were conducted to evaluate the properties of the asphalt mixture in the work. The modified asphalt (18% ERB + 0%WCO, 2%WCO + 18%ERB, 4%WCO + 18%ERB, and 4%WCO + 12%ERB), could effectively improve the high-temperature stability, water stability, low-temperature stability, and aging resistance of the asphalt mixture. According to the overall behavior, 4%WCO + 18%ERB was the best combination.

Bitumen geochemistry and producibility in the Upper Cretaceous Niobrara Formation shale oil play

In the Upper Cretaceous Niobrara Formation shale oil play, considerable oil fractions are produced directly from C14+ bitumen in place (e.g., extractable organic matter). This paper provides new insights on the geochemistry and producibility of C14+ bitumen by integrating the full process of generation, retention, conversion, expulsion, and production, as a whole, in the Niobrara shale oil system. Hydrocarbons are found not to be generated primarily from kerogen but rather from the secondary conversion of polar compounds. Maturation is essentially the underlying driving force that determines the geochemistry of C14+ bitumen in source rocks. However, the in situ cracking of C14+ bitumen does not occur in chalk reservoirs at the maturity stage investigated (430°C–465°C for the reading temperature at the maximum rate of petroleum generation by Rock-Eval 2 pyrolysis on a solvent-extracted sample). Instead of maturation, the geochemistry of C14+ bitumen present in reservoirs is principally determined by migration and associated fractionation. The intraformational migration has fractionated the generated oil into a higher saturated fluid; therefore, C14+ bitumen accumulated in chalk reservoirs is more producible than that retained in source rocks. In comparison, the bulk fractionation effect associated with production is not as pronounced as that of expulsion. Therefore, the bulk compositions of chalk bitumen strongly resemble those of crude oils. Among the least mobile nitrogen-, sulfur-, and oxygen-containing compounds, N1 species are nevertheless partitioned into crude oils during production, and the molecular weight exhibits a less apparent effect on their producibility than chemical affinity (i.e., aromaticity and aliphaticity). Accordingly, a relative enrichment of C5+ heavier carbazoles into crude oils rather than the lighter C1–5 carbazoles was documented.

Triaromatic dinosteroids – Isomeric distributions and their geochemical significance

• Identification of triaromatic dinosteroid isomers and absence of seventh early eluting peak. • Effects of age, depositional environment, biodegradation, maturity and metamorphism. • Implication of co-eluants in m / z 245 chromatograms for oil source age inferences. The distribution of triaromatic dinosteroids in a range of oils and some source rock bitumens was determined by GC–MS selected ion monitoring and GC–MS-MS in order to investigate possible ambiguity in the observed distribution of isomers, including those related to maturation and alteration processes commonly affecting oil accumulations. The results confirm that the eight possible isomers for the triaromatic dinosteroids and their 28-nor equivalents (triaromatic 23,24-dimethylcholesteroids) in post-Paleozoic samples are consistently represented by six peaks on commonly used GC stationary phases, although the fifth eluting is broadened and probably represents a pair of isomers. The presence of a seventh, early eluting, triaromatic dinosteroid isomer occasionally encountered in m / z 245 mass chromatograms in the literature was not substantiated. Closely co-eluting compounds can give the seemingly misleading impression that one or two triaromatic dinosteroid isomers (including the last eluting) are present at low levels in pre-Mesozoic samples and in younger oils from dominantly higher plant sources, so care is required in inferring source age for such samples. The relative abundance and retention time pattern observed for the triaromatic dinosteroids is duplicated by their 28-nor analogues. Triaromatic dinosteroid isomer distributions vary little throughout the oil window, based on data from Norwegian North Sea oils representing a range of mean maturities. Overall abundance of the series seems to decline in a similar way to other biomarkers towards the end of the oil window. In source rock bitumen corresponding to maturities of ≤0.5% vitrinite reflectance, when diasterenes are still abundant, the second eluting triaromatic dinosteroid peak was enhanced and the fifth depleted in the limited set of samples studied (Late Jurassic marine shales from the Norwegian continental shelf). Both dinosteroid series appear particularly resistant towards biodegradation and metamorphism, with no obvious change in isomeric distributions compared to unaltered oil. As a consequence, their relative abundances, as represented by age parameters that ratio each series to their 24-ethyl counterparts, increase when alteration is severe. Lacustrine oils can be difficult to date because post-Paleozoic samples do not always contain detectable dinosteroids and, when they are present, they can vary significantly in abundance. Unambiguous age resolution at the Period level was not possible for the Triassic-Tertiary oils studied, neither could depositional environments be distinguished with confidence.

Recognition of in situ oil cracking in the Precambrian–Lower cambrian petroleum systems of sichuan basin, southwestern China

Determining the place of paleo-oil cracking is crucial to understanding the formation mechanism of the gas reservoirs in the Precambrian–Cambrian strata. For the old strata the attainable information is limited because most paleo-oil have been cracked to gas at high thermal maturity, such as the Anyue giant gas field in the Moxi–Gaoshiti Bulge of Sichuan Basin, Southwestern China. In this study, the place of paleo-oil cracking was discussed based on solid bitumen found in the reservoirs. Numerous solid bitumen from the deep boreholes in the Precambrian Dengying (Z2dn2 and Z2dn4) and Lower Cambrian Longwangmiao (Є1l) formations of the Moxi–Gaoshiti Bulge were analyzed. Elemental and carbon isotope analyses and optical microscopic observations, such as Raman spectroscopy, scanning electron microscopy, and electronic probe, were performed on these solid bitumen samples. The obtained parameters, including the reflectance of the solid bitumen, parameters I(D)/I(G) and S(D)/S(G) from the Raman spectra, the compositions and carbon isotope of gas, burial history, and the predicted “equivalent vitrinite reflectance Ro” (EqVRo) for reservoirs, jointly support that solid bitumen are epigenetic bitumen in reservoirs other than primary bitumen in source rocks. This study provides a relatively solid evidence of in situ cracking of paleo-oil and the thermochemical sulfate reduction reaction between paleo-oil and dolomite reservoirs. Pyrite were found both in carbonate rocks and argillaceous rock, and the sulfur in pyrite is perceived as a pathway of H2S formation. The results provide a basis for understanding the formation mechanism of the deep huge gas field that was derived from paleo-oil cracking, and may contribute to future petroleum exploration in deep Precambrian–Lower Cambrian systems.

Geochemical characteristics and significance of the bitumen in Sinian reservoirs in Sichuan basin and its periphery

The bitumen of Doushantuo Formation distributed along fractures has been firstly discovered in the dolomite reservoirs of Dou-3 Member in Zigui region, Yichang, Hubei. Research has been conducted using multiple methods on the characteristics of the newly discovered bitumen of Doushantuo Formation, bitumen of Dengying Formation-Longwangmiao Formation in Anyue gas field in Sichuan Basin, and bitumen of Sinian and source rocks of Sinian-Cambrian in Northeast Sichuan. The results show:①The reflectivity of the bitumen of Dou-3 Member is about 2.8%; ② The carbon number of n-alkanes in the bitumen of Dou-3 Member is C13-C33, where nC17 is the main peak; the relative proportion of the regular steranes is C27≈C29>C28, and C27, C28 and C29ααα20R steranes are distributed in “L” shape; abundant tricyclic terpanes and pentacyclic triterpanes have been detected, and the abundance of gammacerane is high; Aromatics are mainly phenanthrene series compounds. ③ The heteroatomic compounds in the bitumen of Dou-3 Member are mainly O2 carboxylic acids, and the oxygen compounds in the bitumen of Dengying Formation in Anyue gas field are close to those of the source rocks of Doushantuo Formation. The research results are of vital guiding significance to the study of potential source rocks of Doushantuo Formation in Sichuan Basin and the exploration of oil and gas from the source rocks of Doushantuo Formation.

INCREASING PERFORMANCE OF ROAD LAYERS FROM POROUS ASPHALT

Statement of the problem. Studies of the degree of influence of the content of polymer-modified bitumen, adhesive additives and mineral materials of various rocks on the physic-mechanical and operational properties of draining asphalt have been conducted. Results. The results of the mathematical planning of a three-factor experiment are presented in the process of studying the operational properties of porous asphalt. Conclusions. The composition of the draining asphalt mix on mineral materials of various types and types of rocks and polymer-modified bitumen PMB 50/70 with an adhesive additive that provides an increase in the abrasion service life, reaction rate and water resistance has been developed and justified.

О происхождении углеводородов доюрского комплекса Ханты-Мансийского месторождения

The origin of hydrocarbon deposits in Jurassic and pre-Jurassic complexes of the Khanty-Mansiysk area, located within the Frolov depression, in the local compression zone of the West Siberian plate — the suture zone, is established. The core and crude oil of Jurassic and pre-Jurassic complexes from prospecting wells of the Khanty-Mansiyskoe field is studied. The content and molecular mass distribution of hydrocarbons, including n-alkanes, n-alkylbenzenes, naphthalene’s and phenanthrenes, is determined in bitumen of rocks and oils by chromatography-mass spectrometry. Lithological and petrographic characteristics of rocks is determined by optical microscopy. For oil deposits of the pre-Jurassic complex “source of hydrocarbons” is not reliably established, the parent rocks were not clearly identified in this research. In the lower horizons of the Jurassic section, there is a layer of highly permeable gritstone of the Gorely formation, in which organic matter is localized, presumably making the main contribution to the hydrocarbon deposits of the lower Jurassic and pre-Jurassic complexes. As a possible “source of Paleozoic oil”, it is proposed to collect hydrocarbons from scattered organic matter of Paleozoic rocks at a significant depth (not covered by core drilling) in the areas of tectonic block crushing of foundation.

A geochemical investigation into the resource potential of the Lawn Hill Platform, northern Australia

The Lawn Hill Platform (LHP) is a sedimentary province in north-eastern Northern Territory and north-western Queensland that hosts a significant Paleoproterozoic–Mesoproterozoic sequence, often referred to as 'the ‘Isa Superbasin’, and includes the overlying South Nicholson Group. Shale gas resources and base-metals mineralisation are known in north-west Queensland, but the larger basin is underexplored. The Australian Government’s Exploring for the Future (EFTF) 2016−2020 program aims to boost resource exploration in northern Australia. New precompetitive geochemical data obtained in this program includes source rock geochemistry, kerogen kinetics, bitumen reflectance, biomarker and δ13C n-alkanes for understanding the petroleum potential, organic geochemistry of source rocks and fluids, stratigraphic correlations and mineralogy to determine the brittleness of shales. All data and derived reports are accessible on the EFTF portal (www.eftf.ga.gov.au), providing a central location for informed decision making. The results in this study demonstrate fair to excellent source rocks in multiple supersequences that are brittle and favourable to hydraulic stimulation. A comparison to the greater McArthur Basin demonstrates, that although there are many similarities in bulk geochemistry, LHP mudstones are largely heterogeneous, reflecting local variations that may be inherited from variations in contributing biomass, microbial reworking, depositional environment, sediment input and paleoredox conditions.

Free and kerogen-bound biomarkers from late Tonian sedimentary rocks record abundant eukaryotes in mid-Neoproterozoic marine communities.

Lipid biomarker assemblages preserved within the bitumen and kerogen phases of sedimentary rocks from the ca. 780-729Ma Chuar and Visingsö Groups facilitate paleoenvironmental reconstructions and reveal fundamental aspects of emerging mid-Neoproterozoic marine communities. The Chuar and Visingsö Groups were deposited offshore of two distinct paleocontinents (Laurentia and Baltica, respectively) during the Tonian Period, and the rock samples used had not undergone excessive metamorphism. The major polycyclic alkane biomarkers detected in the rock bitumens and kerogen hydropyrolysates consist of tricyclic terpanes, hopanes, methylhopanes, and steranes. Major features of the biomarker assemblages include detectable and significant contribution from eukaryotes, encompassing the first robust occurrences of kerogen-bound regular steranes from Tonian rocks, including 21-norcholestane, 27-norcholestane, cholestane, ergostane, and cryostane, along with a novel unidentified C30 sterane series from our least thermally mature Chuar Group samples. Appreciable values for the sterane/hopane (S/H) ratio are found for both the free and kerogen-bound biomarker pools for both the Chuar Group rocks (S/H between 0.09 and 1.26) and the Visingsö Group samples (S/H between 0.03 and 0.37). The more organic-rich rock samples generally yield higher S/H ratios than for organic-lean substrates, which suggests a marine nutrient control on eukaryotic abundance relative to bacteria. A C27 sterane (cholestane) predominance among total C26 -C30 steranes is a common feature found for all samples investigated, with lower amounts of C28 steranes (ergostane and crysotane) also present. No traces of known ancient C30 sterane compounds; including 24-isopropylcholestanes, 24-n-propylcholestanes, or 26-methylstigmastanes, are detectable in any of these pre-Sturtian rocks. These biomarker characteristics support the view that the Tonian Period was a key interval in the history of life on our planet since it marked the transition from a bacterially dominated marine biosphere to an ocean system which became progressively enriched with eukaryotes. The eukaryotic source organisms likely encompassed photosynthetic primary producers, marking a rise in red algae, and consumers in a revamped trophic structure predating the Sturtian glaciation.

Characterization and comparison of high-modulus asphalt mixtures produced with different methods

Abstract It is well known that rutting is one of the major distresses for asphalt pavements. To enhance the rutting resistance of asphalt pavements, different approaches have been developed, among which using high-modulus asphalt mixtures (HMAM) has been proved effective. The main objective of this study is to characterize and compare the performances of using hard binders, HMAM additives, and polyester fiber, in producing HMAM. To achieve this objective, the rheological properties of four hard binders, including rubberized bitumen, lake bitumen and SBS collectively modified asphalt binder, rock bitumen and SBS collectively modified asphalt binder, and hard-grade asphalt binder, were first tested. Then, three modulus parameters, namely resilient moduli, dynamic moduli and stiffness moduli, of seven mixtures, including four mixtures prepared with the four hard binders, one SBS modified mixture, one SBS modified mixture with an HMAM additive, PR.M., and one SBS modified mixture with polyester fiber, were measured and compared, followed by comprehensive laboratory performance tests, including rutting resistance, low-temperature cracking resistance, fatigue resistance, and moisture damage resistance tests, and binder-mixture performance correlation analysis. It was found that all the four hard binders can produce mixtures with high modulus as expected. Among different mixtures, rubberized asphalt mixture was provided best overall performance. For the purpose of rutting treatment, rubberized asphalt mixture, the mixture collectively modified by SBS and rock bitumen, and the SBS modified asphalt mixture with PR.M. additive are the better candidates in consideration of their superior rutting resistance and relatively more balanced performance properties.

Distribution and characteristics of paleo-oil reservoirs in Cambrian Longwangmiao Formation in Anyue area of Sichuan Basin, China

The Anyue gas field is a giant marine gas field with the largest reserves of a single reservoir and the oldest strata in China. In this area, the proved gas reserves in the Cambrian Longwangmiao Formation are 4, 404×108 m3, which are believed to originate from crude oil cracking according to substantial evidences. The paleo-oil reservoirs in the area have been destroyed, and their fluid properties, scale and other characteristics are unclear, despite of the distribution preliminarily determined. In this paper, the paleo-oil reservoirs in the Cambrian Longwangmiao Formation in the Moxi–Gaoshiti area were analyzed thoroughly through conventional microscopic observation, together with quantitative grain fluorescence (QGF), total scanning fluorescence (TSF), and micro-laser Raman analysis. The study results indicate that the Longwangmiao Formation contains bitumen, which is mainly distributed in four types of pore space, i.e. vein-like fractures, dissolution pores, intergranular pores, and intercrystalline pores. The bitumen in vein-like fractures was formed mostly in relation to hydrocarbon migration, while the bitumen in dissolution pores, intergranular pores and intercrystalline pores was formed by in-situ cracking of petroleum, mostly as a result of thermal alteration. The QGF index suggests the existence of paleo-oil reservoirs in certain scale in the study area, and the high QGF-E intensity indicates the property of residual bitumen. The laser Raman spectroscopy reveals the maturity of the extensive solid bitumen in reservoir rocks. The well-cross section illustrates that the paleo-oil reservoirs are mainly layered, have experienced mostly in-situ cracking, and match with the present gas reservoirs.

Thermal analysis methods to study the reservoir bitumens

The bitumen-containing reservoir rocks taken from Devonian terrigenous formation of Romashkino and Bavly oil fields (Russia) were sampled and investigated using thermal analysis methods. It was shown that thermal analysis methods allow to characterize the bitumen-containing rocks in whole, taking into account both soluble and insoluble parts of bitumen and mineral composition of rocks. It was established that the soluble part of reservoir bitumen (bitumen extract) had heavy fractional composition and was enriched with asphaltenes and asphaltene-like particles prone to formation of carbene–carboid compounds (compounds insoluble in the used solvents). When the soluble bitumen was extracted, there was insoluble organic matter on the rock, which, likely, was carbene–carboid compounds dropped out of bitumen system. It was shown that carbene–carboid compounds, in contrast to the asphaltenes, are poor in hydrogen, more carbonized and heat resistant. The assumption was made that the redistribution of the carbene–carboid compounds in the oil reservoir—in the reservoir rock or within bitumen—can indicate the mechanisms of formation of phase-migration series bitumens.

Origin of conventional and shale gas in Sinian–lower Paleozoic strata in the Sichuan Basin: Relayed gas generation from liquid hydrocarbon cracking

Large amounts of natural gas have been discovered recently, both in carbonate reservoirs and in shales in the Sinian–Silurian strata of the Sichuan Basin, southern China. Although numerous studies have been conducted to learn about the accumulation of conventional and shale gas, the gas generation history, the origins of the two types of gas, and gas resources in the basin remain unclear. In this study, the hydrocarbon generation histories of Cambrian and Silurian source rocks were reconstructed on the basis of thermal history and hydrocarbon generation kinetic parameters. Intensive cracking of crude oil to generate considerable amounts of secondary cracking gas in Silurian and Cambrian formations occurred during deep burial. The high abundance of overmature pyrobitumen in carbonate reservoirs and shale demonstrates the occurrence of large-scale in situ cracking of liquid hydrocarbons. A mixing model was proposed to quantitatively determine the contribution of kerogen and oil-cracking gas in shale gas accumulations. The mixing of two thermogenic gases with different maturities resulted in a reversal and a rollover of the carbon isotope compositions of shale gas. Moreover, gas resources from the cracking of three occurrence states of liquid hydrocarbons—including dispersed residual bitumen in source rocks, dispersed oil outside the source, and accumulated oil in reservoirs—were evaluated in Sinian–Cambrian and Silurian petroleum systems in the Sichuan Basin, providing a guide for future deep gas exploration of similar formations in China and elsewhere.

Solid bitumen in shales: Petrographic characteristics and implications for reservoir characterization

Abstract The presence of solid bitumen strongly affects hydrocarbon storage and expulsion from a source rock as it might either cause blockage of pore throats leading to lower effective gas permeability, or contribute to hydrocarbon storage and provide migration pathways when a continuous network of hydrocarbon-wet organic matter (OM) pores is formed. Furthermore, organic matter transformation reactions are suggested to influence mineral diagenesis as well. In an attempt to characterize different solid bitumen types and transformation stages over a broad maturity interval (0.5–2.7%Ro) and for varying primary kerogen compositions, we reviewed optical and scanning electron microscopy (SEM) data of 35 solid bitumen-rich shale samples with a Cambrian to Triassic age. We were able to identify in-situ pre-oil solid bitumen, as well as remobilized post-oil solid bitumen at various maturity stages from the early oil window onwards. Solid bitumen is the main host for SEM-visible organic matter porosity; onset of porosity development in solid bitumen differs considerably between predominantly oil-prone (e.g., alginites, amorphous OM from algal and bacterial precursors) and gas-prone (vitrinite-rich) kerogen compositions. Furthermore, solid bitumen (pyrobitumen) in rocks with a terrestrially dominated OM composition seems to be considerably less mobile within the source rock compared to pre- and post-oil solid bitumen in oil-prone rocks, and less reactive in terms of porosity generation. In most samples, several solid bitumen populations with varying fluorescence properties and bitumen reflectance were observed, complicating the use of these petrographic maturity indicators. The apparently different solid bitumen populations often form continuous networks at the SEM-scale. Microstructural features such as irregularly distributed sponge-like porosity or detrital and authigenic mineral inclusions in the sub-micrometer scale were found to have a great influence on texture and reflectance under reflected light microscopy. The formation of authigenic minerals (quartz, various carbonate phases with different Ca/Mg/Fe proportions, magnetite in Cambrian samples) was observed frequently in post-oil solid bitumen of oil-prone rocks, indicating a close genetic relationship between transformation products formed during hydrocarbon generation (e.g., acetate, carbon dioxide and methane) and the dissolution and precipitation of minerals during diagenesis. In some cases, stylolite-like features in the sub-micrometer scale were found, showing that processes well-known from reservoir characterization at core-scale also play a role at the micrometer-scale. Furthermore, the observed strong interaction between organic matter transformation and mineral authigenesis indicates a substantial aqueous component even in pores filled apparently exclusively with solid bitumen.