Development of organic pores in the Longmaxi Formation overmature shales: Combined effects of thermal maturity and organic matter composition
Development of organic pores in the Longmaxi Formation overmature shales: Combined effects of thermal maturity and organic matter composition
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DOI：
10.1016/j.marpetgeo.2020.104314
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Liao Zhiwei
中科院分区：
文献类型：
--
作者：
Hu Guang;Pang Qian;Jiao Kun;Hu Chaowei;Liao Zhiwei
Organic pores are considered to be the dominant contributors to total porosity and hydrocarbon storage in many.source rock unconventional reservoirs. In this study, organic petrology, focused ion beam–environmental.scanning electron microscopy (FIB-SEM), and low-pressure N2 adsorption and desorption were used to analyze.six shale samples obtained from the Shuanghe section (Changning County) and wells YS118 and JY2 in the.Sichuan Basin, China. Results of point-counting under the microscope show that alginite including type I and II is.most abundant followed by bitumen and zooclasts of graptolites. The contents of alginite I, alginite II, and.bitumen range from 12 vol% to 48 vol%, from 5 vol% to 35 vol%, and from 30 vol% to 48 vol%, respectively..Only few pores were found in graptolites. Thermal maturity, macerals, and palynomorphs have strong influences.on the development of organic pores. In the analyzed samples, organic pores (> 10 nm) in shale with a maturity.of<2.5% Ro are larger and rounder than those in shale with a maturity of>2.5% Ro. In addition, characteristics.of organic pore in different maceral types are studied based on SEM and low-pressure N2 adsorption.and desorption. Generally, alginite I and solid bitumen have larger and more abundant organic pores than other.macerals. Alginite I and solid bitumen have approximately same porosity (~13.0 vol%) and same mean pore size.(~180 nm). Pores in a lginite I are elongated and lattice-like arranged, however, pores in bitumen are spongy.and vesicle pores. With respected to alginite I, alginite II has a more complicated pattern of organic-pore development..Some unicellular alginite II grains contain very few nanopores, whereas some aggregated alginite II.host plenty of nanoscale organic pores. Detailed studies on the palynomorphs of macerals suggested that alginite.I is sourced from benthic algae and alginite II are derived from phytoplankton. By comparing the development of.organic pores in different palynomorphs, it was concluded that palynomorphs derived from different algae.precursors and with distinct hydrocarbon potentials and hydrocarbon-generating characteristics affect the development.of organic pores in alginite macerals in the over-mature stage.
