Study on the distribution of extractable organic matter in pores of lacustrine shale: An example of Zhangjiatan Shale from the Upper Triassic Yanchang Formation, Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF109-SF126 ◽  
Author(s):  
Yuxi Yu ◽  
Xiaorong Luo ◽  
Ming Cheng ◽  
Yuhong Lei ◽  
Xiangzeng Wang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Oil And Gas ◽  
Storage Capacity ◽  
Ordos Basin ◽  
Organic Content ◽  
Capacity Control ◽  
Yanchang Formation ◽  
Geochemical Characterization ◽  
Extractable Organic Matter

Shale oil and gas have been discovered in the lacustrine Zhangjiatan Shale in the southern Ordos Basin, China. To study the distribution of extractable organic matter (EOM) in the Zhangjiatan Shale ([Formula: see text] ranges from 1.25% to 1.28%), geochemical characterization of core samples of different lithologies, scanning electron microscope observations, low-pressure [Formula: see text] and [Formula: see text] adsorption, and helium pycnometry were conducted. The content and saturation of the EOM in the pores were quantitatively characterized. The results show that the distribution of the EOM in the shale interval is heterogeneous. In general, the shale layers have a higher EOM content and saturation than siltstone layers. The total organic content and the original storage capacity control the EOM content in the shale layers. For the siltstone layers, the EOM content is mainly determined by the original storage capacity. On average, 75% of the EOM occurs in the mesopores, followed by 14% in the macropores, and 11% in the micropores. The EOM saturation in the pores decreases with the increase in pore diameter. The distribution of EOM in the shale pores is closely related to the pore type. Micropores and mesopores developed in the kerogens and pyrobitumens and the clay-mineral pores coated with organic matter are most favorable for EOM retention and charging.

Hydrocarbon storage space within lacustrine gas shale of the Triassic Yanchang Formation, Ordos Basin, China

2015 ◽  
Vol 3 (2) ◽  
pp. SJ15-SJ23 ◽  
Author(s):  
Xiangzeng Wang ◽  
Lixia Zhang ◽  
Chengfu Jiang ◽  
Bojiang Fan
Keyword(s):  
Organic Matter ◽  
Oil And Gas ◽  
Ordos Basin ◽  
Storage Space ◽  
Oil Accumulation ◽  
Abrupt Decrease ◽  
Thin Sections ◽  
Yanchang Formation ◽  
Oil Generation ◽  
Gas Supply

The Triassic Yanchang Formation lacustrine shale is a source of conventional oil accumulation in the Ordos Basin, China. The Yanchang Formation, a hybrid system of organic-rich shale, interbedded silty shale, and siltstone, is believed to be a potential unconventional oil and gas play. Our crossdisciplinary investigation of the storage space included the outcrop description, core observation, thin sections, and scanning electron microscope pore imaging. We evaluated the results from these techniques to reveal that the storage space within the Yanchang Formation shales included primary intergranular pores, secondary generated pores, tectonic fractures, and bedding-parallel fractures. We conducted adsorption experiments, combined with burial and thermal history, in which the primary migration process can be divided into three stages. In the Early Jurassic, organic matter did not reach the oil generation threshold. From the Late Jurassic to the Early Cretaceous, organic matter entered the oil generation window, and gas was generated and stored as adsorbed gas, dissolved gas, and free gas. From the Middle to Late Cretaceous, the storage of shale gas was dynamically transformed by tectonic uplift. Variations in chemical and carbon isotopic compositions from canister-core desorption were directly related to the gas supply in shales. An abrupt decrease in gas dryness and positive [Formula: see text] values indicated the depletion of gas supply drainage. Our ultimate recovery factor reached 70%.

Liquid hydrocarbon characterization of the lacustrine Yanchang Formation, Ordos Basin, China: Organic-matter source variation and thermal maturity

2017 ◽  
Vol 5 (2) ◽  
pp. SF225-SF242 ◽  
Author(s):  
Xun Sun ◽  
Quansheng Liang ◽  
Chengfu Jiang ◽  
Daniel Enriquez ◽  
Tongwei Zhang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Ordos Basin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Type I ◽  
Hydrocarbon Generation ◽  
Type Ii ◽  
Thermal Maturity ◽  
Yanchang Formation

Source-rock samples from the Upper Triassic Yanchang Formation in the Ordos Basin of China were geochemically characterized to determine variations in depositional environments, organic-matter (OM) source, and thermal maturity. Total organic carbon (TOC) content varies from 4 wt% to 10 wt% in the Chang 7, Chang 8, and Chang 9 members — the three OM-rich shale intervals. The Chang 7 has the highest TOC and hydrogen index values, and it is considered the best source rock in the formation. Geochemical evidence indicates that the main sources of OM in the Yanchang Formation are freshwater lacustrine phytoplanktons, aquatic macrophytes, aquatic organisms, and land plants deposited under a weakly reducing to suboxic depositional environment. The elevated [Formula: see text] sterane concentration and depleted [Formula: see text] values of OM in the middle of the Chang 7 may indicate the presence of freshwater cyanobacteria blooms that corresponds to a period of maximum lake expansion. The OM deposited in deeper parts of the lake is dominated by oil-prone type I or type II kerogen or a mixture of both. The OM deposited in shallower settings is characterized by increased terrestrial input with a mixture of types II and III kerogen. These source rocks are in the oil window, with maturity increasing with burial depth. The measured solid-bitumen reflectance and calculated vitrinite reflectance from the temperature at maximum release of hydrocarbons occurs during Rock-Eval pyrolysis ([Formula: see text]) and the methylphenanthrene index (MPI-1) chemical maturity parameters range from 0.8 to [Formula: see text]. Because the thermal labilities of OM are associated with the kerogen type, the required thermal stress for oil generation from types I and II mixed kerogen has a higher and narrower range of temperature for hydrocarbon generation than that of OM dominated by type II kerogen or types II and III mixed kerogen deposited in the prodelta and delta front.

THE GEOCHEMICAL CHARACTERIZATION OF AUSTRALIAN CRUDE OILS

1972 ◽  
Vol 12 (1) ◽  
pp. 125
Author(s):  
T.G. Powell ◽  
D.M. McKirdy
Keyword(s):  
Organic Matter ◽  
Organic Material ◽  
Depositional Environment ◽  
Land Plant ◽  
Crude Oils ◽  
Geochemical Characterization ◽  
Marine Organic Matter ◽  
Show Evidence ◽  
Lower Palaeozoic

Australian oils are generally light by world standards. They have API gravities greater than 35°, low sulphur and asphalt contents, and are of paraffinic or naphthenic base. The geochemical similarity of oils from the Bowen-Surat Basin, with the notable exception of the Conloi crude, is most marked in the fraction boiling above 250 °C. Oils from the Cooper, Gippsland and Otway Basins are probably derived from terrestrial organic material, but differ in their degree of maturation as indicated by n-alkane patterns. Samples from the Perth Basin exhibit a similar variation in maturity. In the Carnarvon Basin, the Windalia crude differs from those in deeper reservoirs in containing a higher proportion of oxygen-bearing, nitrogen-bearing, and sulphur-bearing compounds, another sign of a less mature oil. The East Mereenie oil displays an odd-even predominance in its n-alkane distribution which is characteristic of some Lower Palaeozoic crudes. A Papuan Basin condensate is the only available sample produced from a limestone reservoir. This probably accounts for its higher sulphur content. Two seeps obtained from the Papuan Highlands are inspissated residues which may have suffered microbiological alteration.A major control of the composition of Australian crude oils appears to be the depositional environment of the source rock. Most of the oils show evidence of having been generated, at least in part, from terrestrial (as opposed to marine) organic matter. The location of all but one of the reservoirs within sequences dominated by the sandstone - shale association is consistent with the likely contribution of land plant detritus to their source environment. Likewise, low sulphur and asphalt values reflect the scarcity of favourable carbonate-evaporite source and reservoir situations in Australia.

scholarly journals Imaging‐Based Characterization of Perthite in the Upper Triassic Yanchang Formation Tight Sandstone of the Ordos Basin, China

2019 ◽  
Vol 93 (2) ◽  
pp. 373-385 ◽  
Author(s):  
Shuheng DU ◽  
Guoxin SHI ◽  
Xinjian YUE ◽  
Gen KOU ◽  
Bo ZHOU ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Upper Triassic ◽  
Tight Sandstone ◽  
Yanchang Formation ◽  
The Ordos Basin

Fractures in continental shale reservoirs: a case study of the Upper Triassic strata in the SE Ordos Basin, Central China

2015 ◽  
Vol 153 (4) ◽  
pp. 663-680 ◽  
Author(s):  
WENLONG DING ◽  
PENG DAI ◽  
DINGWEI ZHU ◽  
YEQIAN ZHANG ◽  
JIANHUA HE ◽  
...  
Keyword(s):  
Organic Matter ◽  
Shale Gas ◽  
Mineral Content ◽  
Ordos Basin ◽  
Total Content ◽  
Upper Triassic ◽  
Thin Sections ◽  
Yanchang Formation ◽  
Fracture Development ◽  
Shale Reservoirs

AbstractFractures are important for shale-gas reservoirs with low matrix porosity because they increase the effective reservoir space and migration pathways for shale gas, thus favouring an increased volume of free gas and the adsorption of gases in shale reservoirs, and they increase the specific surface area of gas-bearing shales which improves the adsorption capacity. We discuss the characteristics and dominant factors of fracture development in a continental organic matter-rich shale reservoir bed in the Yanchang Formation based on observations and descriptions of fracture systems in outcrops, drilling cores, cast-thin sections and polished sections of black shale from the Upper Triassic Yanchang Formation in the SE Ordos Basin; detailed characteristics and parameters of fractures; analyses and tests of corresponding fracture segment samples; and the identification of fracture segments with normal logging. The results indicate that the mineral composition of the continental organic-matter-rich shale in the Yanchang Formation is clearly characterized by a low brittle mineral content and high clay mineral content relative to marine shale in the United States and China and Mesozoic continental shale in other basins. The total content of brittle minerals, such as quartz and feldspar, is c. 41%, with quartz and feldspar accounting for 22% and 19% respectively, and mainly occurring as plagioclase with small amounts of carbonate rocks. The total content of clay minerals is high at up to 52%, and mainly occurs as a mixed layer of illite-smectite (I/S) which accounts for more than 58% of the total clay mineral content. The Upper Triassic Yanchang Formation developed two groups of fracture (joint) systems: a NW–SE-trending system and near-E–W-trending system. Multiple types of fractures are observed, and they are mainly horizontal bedding seams and low-dip-angle structural fractures. Micro-fractures are primarily observed in or along organic matter bands. Shale fractures were mainly formed during Late Jurassic – late Early Cretaceous time under superimposed stress caused by regional WNW–ESE-trending horizontal compressive stress and deep burial effects. The extent of fracture development was mainly influenced by multiple factors (tectonic factors and non-tectonic factors) such as the lithology, rock mechanical properties, organic matter abundance and brittle mineral composition and content. Specifically, higher sand content has been observed to correspond to more rapid lithological changes and more extensive fracture development. In addition, higher organic matter content has been observed to correspond to greater fracture development, and higher quartz, feldspar and mixed-layer I/S contents have been observed to correspond to more extensive micro-fracture development. These results are consistent with the measured mechanical properties of the shale and silty shale, the observations of fractures in cores and thin-sections from more than 20 shale-gas drilling wells, and the registered anomalies from gas logging.

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