High Maturity Stage Research Articles

Origin and Source of Deep Natural Gas in Nanpu sag, Bohai Bay Basin, China

Abstract:Natural gas exploration in Nanpu sag, Bohai Bay Basin, has achieved breakthroughs in recent years, and a number of natural gas and condensate wells with high yield have been found in several structures in the beach area. Daily gas production of single wells is up to 170,000 m3, and high‐yield wells are mainly distributed in the Nanpu No. 1 structural belt. Studies have shown that these natural gases are mainly hydrocarbon gases, with methane content about 80% to 90% and ethane 6%–9%, so they are mainly wet gas; and non‐hydrocarbons are at a low level. Carbon isotopes of methane range from −42‰ to −36‰, and ethane from −28‰ to −26‰. Calculated maturity based on the relationship between δ13C and R0 of natural gas, the gases are equivalent to those generated from organic matter when R0 is 1.0%–1.7% (mainly 1.25%–1.32%). The natural gas is oil‐type gas generated from the source rocks at mature to high mature stage, associated with condensate, so carbon isotopes of the gases are heavier. Natural gas in the Nanpu No.1 structural belt is mainly associated gas with condensate. The analysis of the origin and source of natural gas and condensate, combined with the monomer hydrocarbon carbon isotopes and biomarker, indicated that the main source rocks in the Nanpu No.1 structural belt were Es3 (the lower member of the Shahejie Formation), followed by Es1 (the upper member of the Shahejie Formation). The high‐mature hydrocarbons from source rocks in the deep sag mainly migrated through deep inherited faults into shallow traps and accumulated to form oil and gas pools. Therefore, there is a great potential for exploring gas in deep layers.

Evaluation of hydrocarbon generation of the Xiamaling Formation shale in Zhangjiakou and its significance to the petroleum geology in North China

The semi-closed pyrolysis simulation system under constant pressure was conducted to explore the characteristics and mechanisms of hydrocarbon generation from Xiamaling Formation shale in Xiahuayuan, North China. The experiment results indicate the oil generated by the Xiamaling Formation shale in oil window should be classified as “aromatic-intermediate” type, whereas the decreasing of dry coefficient can be ascribed to the cracking of residual bitumen in source rock in the stage of high to post maturity. The amount of hydrocarbon gas generated from residual bitumen can be up to 1–2 m3 per ton rock in high to post mature stage by calculating hydrogen contents in the kerogen, the expelled hydrocarbon, and the residual hydrocarbon. This reveals the importance of residual bitumen as a gas source during high to post mature stage of the kerogen evolution, and also as the broad exploration prospect of these gases. This research highlights the attention should be paid to oil/gas reservoirs sourced from residual bitumen of organic-rich source rock in high mature stage, even the primary oil/gas reservoirs considered as the main exploration targets in middle-upper Proterozoic sediments of North China.

Geologic Characteristics of Reservoir Accumulation in Suganhu Depression in North Margin of Qaidam Basin

Based on the analysis and testing data of rocks, the basic geologic characteristics of Suganhu depression is discussed. It is concluded that the 200m thickness dark mudstone of inshore shallow lake face in the middle–lower Jurassic stratum is the only source rock of this region. It has the characteristics of high abundance of organic matter and in high mature stage. And the type of organic matter is Ⅱ2.The reservoir properties is controlled by the influences of both the sedimentation and the diagenesis and belong to the low porosity and low permeability ones. The mudstone of Upper Jurassic is the local cap, the ones of braided river face and braided river delta face which existed in the up-middle of the middle Jurassic can be qualified as sealing bed between the sand bodies. Paleocene–eocene mudstone is the regional cap rock. The ability of upper Jurassic sealing bed is good because of the low porosity and permeability and high break pressure. The regional cap rock has the characteristics of big thickness and large area. Both the local and regional cap rock had been able to seal the petroleum and gas before the time of hydrocarbon accumulation of middle Jurassic. In general, Mesozoic formed reservoir–cap combination with the features of lower–generation and upper–reservoir, upper–cap.

Artificial bacterial degradation and hydrous pyrolysis of suberin: Implications for hydrocarbon generation of suberinite

The organic maceral suberinite is widely believed to be a contributor to immature or low mature oils with Ro<0.5% in some coal and terrigenous sequences. However, its evolution of hydrocarbon generation, especially in the relatively high maturation stage of Ro>0.5%, has not been sufficiently characterized. This issue was addressed herein using periderm cork tissues of the modern angiosperm Quercus suber (suberin), which is a possible bio-precursor of suberinite, in artificial bacterial degradation and hydrous pyrolysis experiments. Integrated studies were conducted, including analyses on the compositions of hydrocarbon yields and the content variations that were generated during the experiments, gas chromatography (GC) analyses of generated oils and spectral fluorescence observations, and Rock-Eval and Fourier Transform Infrared (FTIR) microspectroscopic studies on solid residues. Analytical results indicate that suberin and suberinite have long and complex hydrocarbon generation histories. In general, the hydrocarbon that is generated during bacterial degradation is predominantly gas and present in relatively limited amounts, while the oils mainly are generated during hydrous pyrolysis. Furthermore, the oil generation has two peaks that correspond to Ro of approximately 0.35–0.50% and 0.80–1.10%. In composition, the early generated oil mainly consists of long chain waxy and oxygen containing compounds, while the late generated oil is relatively enriched in aromatic compounds. These features can be ascribed to the chemical nature (e.g., composition and structure) of suberin. It is a type of insoluble and high molecular weight polyester compound that contains large quantities of long chain structure dicarboxylic acids and alcohols. Consequently, the deoxygenization of these compounds can take place under relatively low thermodynamic conditions, generating liquid oil that is dominated by a long chain structure and oxygen-containing waxy compounds. In contrast, the degradation of the phenolic compounds results in the second oil generation peak. Therefore, suberinite has a two stage and relatively long oil generation history and is a good bio-precursor for coal-derived oil generation.

A case study of the internal structures of gossans and weathering processes in the Iberian Pyrite Belt using magnetic fabrics and paleomagnetic dating

In the Rio Tinto district of the Iberian Pryrite Belt of South Spain, the weathering of massive sulfide bodies form iron caps, i.e., true gossans and their subsequent alteration and re-sedimentation has resulted in iron terraces, i.e., displaced gossans. To study the stucture and evolution of both types of gossans, magnetic investigations have been carried out with two foci: (1) the characterisation and spatial distribution of magnetic fabrics in different mineralised settings, including massive sulfides, gossans, and terraces, and (2) paleomagnetic dating. Hematite has been identified as the suceptibility carrier in all sites and magnetic fabric investigation of four gossans reveals a vertical variation from top to bottom, with: (1) a horizontal foliation refered to as “mature” fabric in the uppermost part of the primary gossans, (2) highly inclined or vertical foliation interpreted as “immature” fabric between the uppermost and lowermost parts, and (3) a vertical foliation interpreted to be inherited from Hercynian deformation in the lowermost part of the profiles. In terraces, a horizontal foliation dominates and is interpreted to be a “sedimentary” fabric. Rock magnetic studies of gossan samples have identified goethite as the magnetic remanence carrier for the low-temperature component, showing either a single direction close to the present Earth field (PEF) direction or random directions. Maghemite, hematite, and occasionally magnetite are the remanence carriers for the stable high-temperature component that is characterized by non PEF directions with both normal and reversed magnetic polarities. No reliable conclusion can be yet be drawn on the timing of terrace magnetization due to the small number of samples. In gossans, the polarity is reversed in the upper part and normal in the lower part. This vertical distribution with a negative reversal test suggests remanence formation during two distinct periods. Remanence in the upper parts of the gossans is older than in the lower parts, indicating that the alteration proceeded from top to bottom of the profiles. In the upper part, the older age and the horizontal “mature” fabric is interpreted to be a high maturation stage of massive sulfides’ alteration. In the lower part, the age is younger and the inherited “imature” vertical Hercynian fabric indicates a weak maturation stage. These two distinct periods may reflect changes of paleoclimate, erosion, and/or tectonic motion.

Geothermal regime and hydrocarbon kitchen evolution of the offshore Bohai Bay Basin, North China

The offshore Bohai Bay Basin, located in the central Bohai Bay Basin, north China, one of the most petroliferous basins in China. In this article, based on formation-testing temperature, drill-stem tests, and bottom-hole temperature data, 80 thermal gradient values at the depth interval of 0 to approximately 3000 m (~9843 ft) in the offshore Bohai Bay Basin were obtained. The basinwide average thermal gradient is 31.8 4.6C/km. Based on the above thermal gradient data and the corresponding average weighted thermal conductivity data, 80 measured terrestrial heat flow values were obtained. These values range from 33.5 to 84.0 mW/m2, with an average value of 60.8 8.7 mW/m2. The heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags. A thermal history, derived from vitrinite reflectance and apatite fission-track) data, indicates that Paleogene cooling occurred after a period of much higher paleogeothermal gradient (3854C/km). Tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the Paleogene followed by subsequent thermal subsidence since the Neogene. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation. The maturation and hydrocarbon expulsion histories of the Paleogene Shahejie 3 Formation (E2s3), which is the most important source rock in the offshore Bohai Bay Basin, are modeled. Results show that the Shahejie 3 Formation is in a high mature stage at the present day, and the Bozhong and Qikou sags are the most important kitchens. The Huanghekou sag became the third most important hydrocarbon kitchen in the early Neogene. Based on this hydrocarbon kitchen evolution, oil and gas mainly accumulated after 12 Ma. The evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore Bohai Bay Basin.

Combination and superimposition of source kitchens and their effects on hydrocarbon accumulation in the hinterland of the Junggar Basin, west China

In the hinterland of the Junggar Basin, there are multiple depressions with multiple sets of source rocks. Therefore, the conditions of hydrocarbon sources are complex, and the geochemical characteristics and sources of hydrocarbon vary in different structural belts. The evolution of the Che-Mo palaeohigh affected the formation of hydrocarbon source kitchens and hydrocarbon migration. We studied the combination and superimposition of hydrocarbon source kitchens, using as an example the hinterland of the Junggar Basin (including the Yongjin, Zhengshacun, Moxizhuang and Luliang uplift areas). The study was based on geochemical analyses of crude oil and fluid inclusions, and the histories of tectonic evolution and hydrocarbon generation. The results indicated that before the Paleogene there were two hydrocarbon-generating depressions: the Western Well Pen1 depression and the Changji depression on the south and north sides of the Che-Mo palaeohigh, respectively. The Permian source kitchen had been generating hydrocarbon continuously since Triassic and reached high maturity stage in the Cretaceous period. After Paleogene, the adjustment of the Che-Mo palaeohigh led to the subsidence of the Changji depression and the Jurassic source rocks reached mature stage and became the main source kitchens. However, the Jurassic source rocks in the Western Well Pen1 depression were still in a low maturity stage and did not generate oil because of the adjustment of tectonic movements. As a result, in the central and southern parts of the Junggar Basin, Jurassic source rocks generated oil, but in the Luliang uplift, the crude oil was from the Permian source rocks in the Western Well Pen1 depression and the Jurassic source rocks did not contribute. The crude oil in the central Zhengshacun-Moxizhuang belt was from the Permian source rocks in two depressions, and partially from the Jurassic source rocks. The crude oil in the Luliang uplift was from the source rocks of the lower Permian Fengcheng Formation and middle Permian Wuerhe Formation, which is characterized by superimposition of two sets of source kitchens and three accumulation stages. The crude oil in the Yongjin tectonic belt was from the lower Permian, middle Permian and Jurassic source rocks, which is characterized by superimposition of three sets of source kitchens and two accumulation stages. The crude oil in the Zhengshacun tectonic belt was from a combination of source kitchens of lower Permian and middle Permian in the Western Well Pen1 depression in the early stage and from the superimposition of Jurassic source rocks in the Changji depression in the late stage.

Evaluating maturity of source rocks by aromatic compounds: A case from Dongling Block, Songliao Basin

Abstract The characteristics of the thermal evolution of aromatic maturity parameters, such as methyl phenanthrene, alkylated dibenzothiophene, dehydroxy-tocopherol and triaromatic-sterane series compounds are discussed on the basis of molecular organic geochemistry and GC-MS analysis of the source rocks in the Dongling area of the Songliao Basin. The distribution characteristics of aromatic hydrocarbon chromatography, the methyl phenanthrene index (MPI), the ratio of β/γ dehydroxy-tocopherol, 4-/1-MDBT, 4,6-/1,4-DMDBT, TASC27 (20R)/C28 (20R), the content of the triaromatic-sterane series and vitrinite reflectance measurements all suggest that the Lower Cretaceous Quantou Formation source rock is in the middle stage of maturity, whereas the Lower Cretaceous Yingcheng Formation and the Upper Jurassic Huoshiling Formation source rocks have reached a high maturity stage.

Aromatic hydrocarbons as indicators of origin and maturation for light oils from Panyu lower uplift in Pearl River Mouth basin

Aromatic fractions of six light oils and two source rock samples from Panyu (番禺) lower uplift of Pearl River Mouth basin were analyzed using GC-MS (gas chromatography-mass spectrometric) technique. Thirteen aromatic series of hydrocarbons detected such as biphenyls, naphthalenes, phenanthrenes, dibenzothiophenes (more than two hundred aromatic hydrocarbon compounds) were used to analyze the origin and maturity of the light oils. This study indicates that the distribution of aromatic hydrocarbon compounds in the light oils of wells L1 and P1 differs from those of wells P2, P3 and P4. The light oil samples from wells L1 and P1 contain more dibenzofuran and fluorence hydrocarbons and less naphthalene hydrocarbons. The contents of fluorene, dibenzothiophene and dibenzofuran in the two groups of light oils also show their difference in sedimentary environment. Moreover, the diversity of the relative distributions of biphenyl and naphthalene is apparent between the two groups of light oils. As mentioned above, the origin of the light oils from wells L1 and P1 varies from that of wells P2, P3 and P4. According to the result of oil-source correlation, the light oils from wells P2, P3 and P4 mainly originated from the source rocks in the Enping (恩平) Formation. Accordingly, the light oils from wells L1 and P1 may have been derived from the lacustrine shales in the Wenchang (文昌) Formation or from the mixed source of the Wenchang Formation and the Enping Formation. Applying maturity parameters of methylnaphthalenes, methylphenanthrenes and methyldibenzothiophenes from the aromatic hydrocarbons to the study of the maturity of light oils from Panyu lower uplift indicates that the maturity has reached the high mature stage.

Compositional and geochemical characteristics of light hydrocarbons for typical marine oils and typical coal-generated oils in China

Different types of crude oils have different light hydrocarbon compositional and geochemical characteristics. Based on the light hydrocarbon data from two kinds of oils, i.e., coal-generated oils and marine oils in China, light hydrocarbons in marine oils in the Tazhong area are generally relatively enriched in n-heptane, and coal-generated oils from the Turpan Basin are enriched in methylcyclohexane. The K1 values, reported by Mango (1987), range from 0.97 to 1.19 in marine oils, basically consistent with what was reported by Mango on light hydrocarbons in terms of the majority of the crude oil data. But the K1 values of coal-generated oils are particularly high (1.35–1.66) and far greater than those of marine oils; heptane values in marine oils, ranging from 32.3% to 45.4%, and isoheptane values, ranging from 1.9 to 3.7, are respectively higher than those of coal-generated oils, indicating that the oils are in the high-maturity stage. In addition, expulsion temperatures of coal-generated oils from the Turpan Basin are obviously lower than those of marine oils from the Tazhong area.

Analysis of Single, Purified Inclusions as a Novel Approach to Understand Methamphetamine Neurotoxicity

A variety of neurodegenerative diseases leading to movement disorders such as Parkinson's disease (PD) are characterized by neuronal inclusions. Despite evidence of the presence of these intrusions, these intracellular bodies have been poorly investigated because of the technical limits of reproducing them in experimental models and the difficulties in isolating these ultrastuctures. Here, we describe a simple method for the isolation of single, purified inclusion bodies using immunomagnetic separation. We profited from the high number and maturation stage of inclusions produced in vitro by methamphetamine (METH) in cultured PC12 cells; in fact, this experimental condition is highly reproducible and has a limited number of experimental variables, while it is predictive of what is described in vivo in dopamine neurons.

Study on the restitution coefficient of original total organic carbon for high mature marine source rocks

On the basis of the results of hydropyrolysis simulations for about 90 different types of immature to mature source rocks selected from about 5 000 marine source rocks in China, along with the natural thermal evolution profiles, the following conclusions were obtained. (1) Total organic carbon (TOC) content of excellent marine source rocks does not change obviously when Ro 1.3%, and the residual TOC content is decreasing gradually with the maturity increase at 0.8% 1.3%), the decreased maximums of residual TOC content for the kerogen of sapropel (I), II1, and II are usually 40%, 32% and 24%, respectively, and their TOC restitution coefficient is, respectively, 1.68, 1.48 and 1.32. (3) Both the TOC decreasing amplitude and the restitution coefficient decrease gradually with the decrease of TOC content for the source rocks with low organic matter abundance (usually 0.3% 30%) also require no restitution at the high mature stage. Such kind of TOC restitution is further supported by the coincidence of the decrease of residual TOC with the decreasing of S1 + S2 and the increasing of hydrocarbon quantity during the experimental simulation of hydrocarbon generation and expulsion for marine source rocks (0.3% < TOC < 30%) in natural thermal evolution profiles.

Linking steroid hormone levels to sexual maturity index and energy reserves in Nereis diversicolor from clean and polluted estuaries

The objective of this work was to compare seasonal variations of reproduction physiology of the ragworm Nereis diversicolor —a key species in estuarine ecosystems—originating from a clean (Authie) and multi-polluted (Seine) estuaries. A particular attention was carried out in female worms, on relationships between sexual maturity stages, energy reserves (glycogen and lipids) and steroid hormone levels (progesterone, 17β-estradiol, and testosterone). Sexual maturity index (SMI), energy reserves and steroid hormones are clearly influenced by season in worms from both sites. Depleted steroid hormone levels were depicted in specimens exhibiting high sexual maturity stage and energy reserves. Intersite analysis has revealed all over the sampling period:—a sexual precocity in worms from Seine,—glycogen concentrations generally higher in worms from Authie,—no clear tendency for lipids,—no differences in steroid hormone levels. Sexual precocity and lower glycogen levels in Seine could be explained by a specific strategy above all devoted to reproduction in these worms. Chemical stress could be a possible explanation of these observations.

Influence of pressure on stable carbon isotope ratio and production yield of coal-derived methane

Two immature coals have been pyrolyzed in confined gold reactors from 250 to 600 °C, but at different constant heating rates (2 and 20 K/h) and under different pressures (30 and 65 Mpa). Yields of coal-derived methane show significant differences under different pressures even with the same analytical procedure. Generally speaking, increasing pressure can result in an increasing yield of methane, even though the experiment did show a slight decrease at low temperatures (≤400 °C) with high heating rates. The range of activation energies for methane generation is obviously narrower at 65 Mpa than at 30 MPa. Under high pressure conditions of 65 MPa, methane relatively depleted in 13C would be induced at the major stage of methane generation. However, our kinetic modeling results show that isotope-specific kinetic parameters, activation energies and frequency factors of methane at high pressure are almost the same as those at low pressure. The isotope ratios for methane precursors in two coals studied were also similar to each other but with some variances under the two different pressure circumstances. The modeled δ 13C of cumulative methane by using two pressure-based series of kinetic parameters under geological conditions at 2 K/Myr exhibits less differences, which manifests that the effect of pressure can be regarded as being negligible. The modeled δ 13C values of instantaneously generated methane at two different pressures under geological conditions are, however, significantly distinctive, and this is especially the case at high maturation stage of coal.

Hydrocarbon-generating characteristics of barkinite-rich coals from Late Permian Longtan Formation, South China

Leping coal (including barkinite-rich coal) is a unique kind of coal, which is widely distributed in the Late Permian Longtan Formation, South China. In this paper, Rock-Eval, Py-GC and simulation experiment via an open-system were used to study the hydrocarbon-generating potential, hydrocarbon composition, and hydrocarbon-generating model of barkiniterich coals from the Shuicheng coal field of Guizhou Province, Southwest China. The results show that barkinite-rich coals have high hydrocarbon-generating potential, with S1 + S2 being 211 – 311mg/g, and can produce large amounts of hydrocarbon at the high-maturity stage, mostly within the temperature range of 420 – 450°C (corresponding to VR0 1.1 – 1.5%); barkinite-rich coal is one of the better oil sources and light hydrocarbon and wet gas are the major hydrocarbon components, which account for 45% and 33% of the total hydrocarbons, respectively. These characteristics are of importance for exploring oil and gas resources in the Late Permian Longtan Formation coals, Southwest China.

Effect of maturity stages on the content of ash components in raw, frozen and canned broad beans

The aim of the present work was to determine the level of ash, potassium, phosphorus, calcium, magnesium, iron, zinc, manganese, and copper in fresh and preserved broad bean seeds at the stage of milk-wax maturity. The experiments included two broad bean cultivars, four stages of seed maturity being differentiated in each. With the higher maturity stages, the contents of ash, potassium, phosphorus, calcium, and magnesium gradually increased in fresh matter of the two cultivars. The contents of zinc and copper showed a slight decreasing tendency, while the levels of iron and manganese varied. Frozen and canned broad bean seeds of milk-wax maturity, prepared for consumption, were a valuable source of mineral compounds. The more mature the seeds, the greater were the contents of potassium, phosphorus, calcium, magnesium, and manganese, and smaller less so for copper, while the levels of iron and zinc varied. Boiled frozen seeds contained more potassium, phosphorus, magnesium, zinc, manganese, and copper than canned products, no differences being found in the contents of calcium and iron. The dehulled seeds contained more phosphorus but less calcium than the intact ones.

The process of glauconitization: chemical and isotopic evidence

Sequential leaching experiments were made on Recent glauconies and clay fractions of the associated mud from off-shore Africa near the estuary of the Congo River. Analyses of major/rare earth elements (REE) and Nd isotopic compositions on the resulting leachate and residue pairs allow identification of at least three important and isotopically distinct components which contributed to the glauconitization process: (1) a detrital component with relatively high 87Sr/86Sr and relatively low 143Nd/144Nd isotopic ratios; (2) a phosphate phase rich in REE and Sr with sea water Sr and Nd isotopic characteristics; (3) a component rich in organic matter and Ca with a sea water Sr isotopic signature, a relatively low Nd isotopic composition and elevated Sm/Nd ratios. This latter component probably represents the suspended organic and carbonate-rich river load. The detrital and the river components were mixed up in the muddy off-shore sediment, ingested by worms, and integrated into faecal pellets. The resulting material has Sr and Nd isotopic signatures intermediate between those of the detrital and river components, and represents the precursor of the glaucony minerals. During the subsequent dissolution-crystallization process, the glauconitic pellets remain isotopically closed to any external supply, but expulsion of Sr and Nd with increasing degree of maturation is observed without any effect on the Sr and Nd isotopic compositions. At a higher maturation stage (K2O>4.5%), the Sr and Nd isotopic compositions tend to decrease and increase, respectively, approximating the isotopic composition values of the phosphate-rich phase. Because the Sr and Nd concentrations decrease, the evolution of the glauconies toward lower Sr and higher Nd isotopic compositions can only be explained by expulsion of Sr and Nd of the detrital component with high Sr and low Nd isotopic signatures. Dissolution of the chemically unstable, wormdigested clay material from mud may be responsible for the liberation of these elements. Consequently, the phosphate-rich phase with sea water Sr and Nd isotopic signatures becomes increasingly important for the isotopic characteristics of the maturing glauconite grains, and sea water isotopic signatures can be reached during the stage of mature glauconite (K2O>6.5%), without chemical exchange with the depositional environment.

Methylphenanthrenes from the MITI Takada-heiya well and thermally altered Kusanagi shales by dolerite intrusion in Northeast Japan.

Compositional changes of phenanthrene (P) and methylphenanthrenes (MP) in mudstones received burial diagenesis and contact thermal alteration were examined to test their usefulness as thermal indicators. Mudstone samples were obtained from the MITI Takada-heiya well (Neogene Takada basin, Niigata, Japan) and from outcrops of the Kusanagi formation (Neogene, Yamagata, Japan), where the thermal alteration by dolerite intrusion occurred in Miocene time. Concentrations of MP increased in the sediments deeper than the peak of oil generation in both the MITI Takada-heiya well and the thermally altered Kusanagi shales. The main formation zone of MP seems to correspond to the relatively higher maturation stage (mean vitrinite reflectance: %Rm > 1.0; JNOC, 1988) and the wet gas generation zone. Relative abundances of 2- and 3-MP to P and/or other MP isomers (MPI1 by Radke et al., 1982a; MPI3 by Angelin et al., 1983) increased with increasing maturity in the oil and wet gas generation zone in both the MITI Takada-heiya well and the thermally altered shales. However, the MPI vs. %Rm relationships in burial diagenesis (the MITI Takada-heiya well) and in contact thermal alteration (Kusanagi shales) were different from each other. Markedly different heating rate and temperature may be the major reasons for the difference. In the overly matured zone from 2.0%Rm to 3.0%, MPI3 may indicate the apparent equilibrium for methyl-shift of MP.

A novel type of oil-generating organic matter — Crystal-enclosed organic matter

The comparative study of organic matter in carbonate rocks and argillaceous rocks from the same horizon indicates that the organic thermal maturities of carbonate rocks are much lower than those of argillaceous rocks. And extensive analysis of extracted and inclused organic matter from the same sample shows that inclused organic matter is different from extracted organic matter, and the thermal maturity of the former is usually lower than that of the latter in terms of biomarker structural parameters. It seems that carbonate minerals could preserve organic matter and retard organic maturation. The inclused organic matter, abundant in most carbonate rocks, will be released from minerals and transformed into oil and gas during the high thermal maturity stage.

Effects of Deep-Seated Igneous Intrusions in Northwest Germany on Generation of Hydrocarbons in Lower Jurassic Source Strata: ABSTRACT

In the Lower Saxony basin of northwest Germany several deep seated batholithic intrusions are indicated by pronounced gravity and magnetic anomalies. At considerable distance from these intrusions, the igneous heat has significantly advanced the rank of coaly particles finely dispersed in shales and siltstones of Upper Carboniferous to Lower Cretaceous-age strata, and isorank patterns have been documented in the literature. The results of a detailed geochemical study of kerogens and extractable low and high molecular weight hydrocarbons in Lower Jurassic Pliensbachian-age source bed-type shales involving a multitude of analytical methods (solvent extraction, MPLC, HPLC, capillary gas chromatography of saturated and polycyclic aromatic hydrocarbons, GC/MS of steranes and t iterpanes, hydrogen stripping/thermovaporization of light hydrocarbons, Rock-Eval pyrolysis and reflectance microscopy) are reported in this paper. A reconstruction of the pre-intrusive burial and maturation history based on a modified Lopatin method allowed, for this sourcerock unit, estimation of temperature and maturity increase associated with the intrusion. The main conclusion from this study concerns a significant influence which the high heating rate exercised, during the period of cooling of the intrusions, on the evolution of hydrocarbon generation processes in these Lower Jurassic source beds. The established relationship between stages of petroleum hydrocarbon generation and maturity progress (expressed, e.g., as vitrinite reflectance), as it has been documented for many case histories worldwide and referred to as window, cannot be seen in this rapidly heated source rock series. The liquid window is shifted toward higher maturity stages and extends up to 1.75% Rm. This is documented on the basis of maturity trends for the evolution of yields and compositional patterns of the extractable hydrocarbons. The most li ely explanation for these observations is that the reaction rate causing vitrinite reflectance to increase is more temperature-dependent than the rates of the hydrocarbon generation reactions. In kinetic terms this means that, although the processes are highly complex, the effective activation energy of the vitrinite reaction is higher than that of the hydrocarbon generation reactions. End_of_Article - Last_Page 796------------