Pyrolysis of coal measure source rocks at highly to over mature stage and its geological implications

Besides coal seam, the source rocks including dark mudstone, carbon mudstone and so on account for a large proportion in the coal measures. Based on the complex geothermal evolution history, the majority of coal measure organic matters with the peak of gas generation have a good potential of gas. Therefore, shale gas in coal measure is an important part of the shale gas resources. There are good conditions including the thickness of coal measures, high proportion of shale rocks, rich in organic matter content, high degree of thermal evolution, high content of brittle mineral and good conditions of the porosity and permeability for the generation of shale gas in Wuli area, the south of Qinghai province. Also the direct evidence of the gas production has been obtained from the borehole. The evaluation of shale gas in coal measure resources could broaden the understanding of the shale gas resources and promote the comprehensive development of the coal resources.

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Fluid geochemistry of the Jurassic Ahe Formation and implications for reservoir formation in the Dibei area, Tarim Basin, northwest China

Energy Exploration & Exploitation ◽

10.1177/0144598718759560 ◽

2018 ◽

Vol 36 (4) ◽

pp. 801-819 ◽

Cited By ~ 1

Author(s):

Shuangfeng Zhao ◽

Wen Chen ◽

Zhenhong Wang ◽

Ting Li ◽

Hongxing Wei ◽

...

Keyword(s):

Natural Gas ◽

Tarim Basin ◽

Oil And Gas ◽

Northwest China ◽

Source Rocks ◽

Coal Measure ◽

Hydrocarbon Generation ◽

Gas Reservoirs ◽

Isotopic Analyses ◽

Jurassic Coal

The condensate gas reservoirs of the Jurassic Ahe Formation in the Dibei area of the Tarim Basin, northwest China are typical tight sandstone gas reservoirs and contain abundant resources. However, the hydrocarbon sources and reservoir accumulation mechanism remain debated. Here the distribution and geochemistry of fluids in the Ahe gas reservoirs are used to investigate the formation of the hydrocarbon reservoirs, including the history of hydrocarbon generation, trap development, and reservoir evolution. Carbon isotopic analyses show that the oil and natural gas of the Ahe Formation originated from different sources. The natural gas was derived from Jurassic coal measure source rocks, whereas the oil has mixed sources of Lower Triassic lacustrine source rocks and minor amounts of coal-derived oil from Jurassic coal measure source rocks. The geochemistry of light hydrocarbon components and n-alkanes shows that the early accumulated oil was later altered by infilling gas due to gas washing. Consequently, n-alkanes in the oil are scarce, whereas naphthenic and aromatic hydrocarbons with the same carbon numbers are relatively abundant. The fluids in the Ahe Formation gas reservoirs have an unusual distribution, where oil is distributed above gas and water is locally produced from the middle of some gas reservoirs. The geochemical characteristics of the fluids show that this anomalous distribution was closely related to the dynamic accumulation of oil and gas. The period of reservoir densiﬁcation occurred between the two stages of oil and gas accumulation, which led to the early accumulated oil and part of the residual formation water being trapped in the tight reservoir. After later gas filling into the reservoir, the fluids could not undergo gravity differentiation, which accounts for the anomalous distribution of fluids in the Ahe Formation.

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Oil and gas potential assessment for coal measure source rocks on absolute concentration of n-alkanes and aromatic hydrocarbons

Science in China Series D Earth Sciences ◽

10.1007/s11430-009-5021-9 ◽

2009 ◽

Vol 52 (S1) ◽

pp. 51-58 ◽

Cited By ~ 2

Author(s):

HongJing Zhao ◽

Min Zhang ◽

ZhiYong Wang

Keyword(s):

Aromatic Hydrocarbons ◽

Oil And Gas ◽

Source Rocks ◽

Coal Measure ◽

Absolute Concentration ◽

Gas Potential

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Petrography and Organic Geochemistry Characterizations of Lower Paleozoic Organic-Rich Shale in the Northwestern Upper Yangtze Plate: Niutitang Formation and Longmaxi Formation, Dabashan Foreland Belt

Minerals ◽

10.3390/min8100439 ◽

2018 ◽

Vol 8 (10) ◽

pp. 439 ◽

Cited By ~ 1

Author(s):

Delu Li ◽

Rongxi Li ◽

Di Zhao ◽

Feng Xu

Keyword(s):

Gas Chromatography ◽

Organic Matter ◽

Organic Geochemistry ◽

Source Rocks ◽

Gas Chromatography Mass Spectrometry ◽

Mature Stage ◽

Type I ◽

Lower Paleozoic ◽

Longmaxi Formation ◽

Niutitang Formation

Measurements of total organic carbon, Rock-Eval pyrolysis, X-ray diffraction, scanning electron microscope, maceral examination, gas chromatography, and gas chromatography-mass spectrometry were conducted on the organic-rich shale of Lower Paleozoic Niutitang Formation and Longmaxi Formation in Dabashan foreland belt to discuss the organic matter characteristic, organic matter origin, redox condition, and salinity. The results indicate that the Niutiang Formation and Longmaxi Formation organic-rich shale are good and very good source rocks with Type I kerogen. Both of the shales have reached mature stage for generating gas. Biomarker analyses indicate that the organic matter origin of Niutitang Formation and Longmaxi Formation organic-rich shale are all derived from the lower bacteria and algae, and the organic matter are all suffered different biodegradation degrees. During Niutitang Formation and Longmaxi Formation period, the redox conditions are both anoxic with no stratification and the sedimentary water is normal marine water.

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LAND-PLANT SOURCE ROCKS FOR OIL AND THEIR SIGNIFICANCE IN AUSTRALIAN BASINS

The APPEA Journal ◽

10.1071/aj81012 ◽

1982 ◽

Vol 22 (1) ◽

pp. 164 ◽

Cited By ~ 5

Author(s):

B. M. Thomas

Keyword(s):

Depositional Environment ◽

Land Plant ◽

Source Rocks ◽

Coal Measure ◽

Terrestrial Plants ◽

Geological Time ◽

Close Relationship ◽

Jurassic Coal ◽

Paraffin Waxes ◽

Gippsland Basin

Many Australian oils are rich in paraffin waxes which are derived from the remains of terrestrial plants. Although the land-plant contribution to oils, particularly those found in a paralic or deltaic environment, is well established, opinion is divided on the ability of non-marine coaly sediments to generate and expel commercial quantities of oil. It appears that some coal measure sequences have generated mainly gas whilst others are the source of large oil accumulations. The composition of coals deposited in Australia has varied through geological time as a result of differences in climate, geological setting, depositional environment and stage of floral evolution. Consequently, most Australian pre-Jurassic coal measure sequences are deficient in exinite macerals and are therefore mainly gas-prone. In contrast, Jurassic to Tertiary coal-rich sequences often contain abundant exinite and may have substantial potential to generate oil in commercial quantities, as demonstrated by the well-known Gippsland Basin (Bass Strait) oilfields.A similar trend is observed worldwide, where, despite the extraordinary global abundance of Late Palaeozoic coals, only minor amounts of crude oil of land-plant origin are known to be associated with them. However, there appears to be a close relationship between the occurrence of waxy, land-plant-derived crudes and coaly sediments of Cretaceous and Tertiary age. This is thought to be a result of the dominance of conifers in swamp floras of these periods, together with the evolution of the angiosperms (flowering plants) in the Late Cretaceous.

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THE OTWAY BASIN

The APPEA Journal ◽

10.1071/aj88034 ◽

1989 ◽

Vol 29 (1) ◽

pp. 417 ◽

Cited By ~ 1

Author(s):

S. Laing ◽

C.N. Dee ◽

P.W. Best

Keyword(s):

Lacustrine Sediments ◽

South Australia ◽

Commercial Production ◽

Source Rocks ◽

Mature Stage ◽

Tectonic Events ◽

Late Tertiary ◽

Marine Carbonates ◽

Initial Deposition ◽

Commercial Oil

The Otway Basin covers an area of some 150 000 km2 both onshore and offshore southwestern Victoria and southeastern South Australia. Exploration within the basin is at a moderately mature stage by Australian standards (though immature by world standards), with a well density of one per 1500 km2, including offshore areas.Formation of the Otway Basin commenced in the late Jurassic with the initiation of rifting between Australia and Antarctica. As rifting continued, a number of depositional cycles occurred. Initial deposition comprised fluvio- lacustrine sediments, followed by marine transgressions and associated regressive deltaic cycles. As subsidence continued into the Late Tertiary, a series of marine carbonates and marls were deposited. The Otway Basin is structurally complex as a result of the superposition of a number of tectonic events which occurredboth during and after the development of the basin.The Otway Basin is a proven gas province, with commercial production at Caroline 1 (carbon dioxide) and North Paaratte Field (methane). Although no commercial oil production has yet been established in the basin, oil has been recovered at Port Campbell 4, Lindon 1 and Windermere 1. The presence of excellent reservoir units within the basin, mature source rocks and adequate seals, together with a number of untested play types and favourable economics, augurs well for the prospectivity of the Otway Basin.

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THE STRUCTURAL DEVELOPMENT AND HYDROCARBON POTENTIAL OF PALAEOZOIC SOURCE ROCKS IN THE ADAVALE BASIN REGION

The APPEA Journal ◽

10.1071/aj83031 ◽

1984 ◽

Vol 24 (1) ◽

pp. 393 ◽

Cited By ~ 2

Author(s):

V. L. Passmore ◽

M. J. Sexton

Keyword(s):

Middle Devonian ◽

Oil And Gas ◽

Structural Features ◽

Source Rocks ◽

Geochemical Data ◽

Mature Stage ◽

Hydrocarbon Generation ◽

Structural Development ◽

Seismic Reflection Data ◽

Basin Region

The Adavale Basin of southwestern Queensland consists of a main depression and several isolated synclinal extensions, traditionally referred to as troughs. The depressions and troughs are erosional remnants of a once more extensive Devonian depositional basin, and are now completely buried by sediments of the overlying Cooper, Galilee and Eromanga Basins. Geophysical and drilling investigations undertaken since 1959 are the only source of information on the Adavale Basin. A single sub-economic discovery of dry gas at Gilmore and a few shows of oil and gas are the only hydrocarbons located in the basin to date.In 1980, the Bureau of Mineral Resources in cooperation with the Geological Survey of Queensland commenced a major, multidisciplinary investigation of the basins in southwestern Queensland. Four long (> 200 km) seismic lines from this study over the Adavale Basin region and geochemical data from 20 wells were used to interpret the Adavale Basin's development and its present hydrocarbon potential.The new seismic reflection data allow the well-explored main depression to be correlated with the detached troughs, some of which have little or no well information. The BMR seismic data show that these troughs were previously part of one large depositional basin in the Devonian, the depocentre of which lay east of a north-trending hingeline. Structural features and Devonian depositional limits and patterns have been modified from earlier interpretations as a result of the new seismic coverage. The maximum sediment thickness is re-interpreted to be 8500 m, considerably thicker than previous interpretation.recognised. The first one, a diachronous Middle Devonian unconformity, is the most extensive, and reflects the mobility of the basement during the basin's early history. The second unconformity within the Late Devonian Buckabie Formation reveals that there were two phases of deformation of the basin sediments.The geochemical results reported in this study show that most of the Adavale Basin sediments have very low concentrations of organic carbon and hydrocarbon fractions. Maturity profiles indicate that the best source rocks of the basin are now in the mature stage for hydrocarbon generation. However, at Gilmore and in the Cooladdi Trough, they have reached the dry gas stage. The maturity data provide additional evidence for the marked break in deposition and significant erosion during the Middle Devonian recognised on the seismic records, and extend the limits of this sedimentary break into the northern part of the main depression.Hydrocarbon potential of the Adavale Basin is fair to poor. In the eastern part of the basin, where most of the data are available, the prospects are better for gas than oil. Oil prospectivity may be improved in any exinite-rich areas that exist farther west, where palaeo-temperatures were lower.

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