Distribution and Thermal Maturity of Devonian Carbonate Reservoir Solid Bitumen in Desheng Area of Guizhong Depression, South China

Abstract

The distribution of solid bitumen in the Devonian carbonate reservoir from well Desheng 1, Guizhong Depression, was investigated by optical microscope and hydrocarbon inclusions analysis. Vb and chemical structure indexes measured by bitumen reflectance, laser Raman microprobe (LRM), and Fourier transform infrared spectroscopy (FTIR) were carried out to determine the thermal maturity of solid bitumen. Based on the solid bitumen thermal maturity, the burial and thermal maturity history of Devonian carbonate reservoir were reconstructed by basin modeling. The results indicate that the fractures and fracture-related dissolution pores are the main storage space for the solid bitumen. The equivalent vitrinite reflectance of solid bitumen ranges from 3.42% to 4.43% converted by Vb (%) and LRM. The infrared spectroscopy analysis suggests that there are no aliphatic chains detected in the solid bitumen which is rich in aromatics C=C chains (1431-1440 cm −1 ). The results of Vb (%), LRM, and FTIR analysis demonstrate that the solid bitumen has experienced high temperature and evolved to the residual carbonaceous stage. The thermal evolution of Devonian reservoirs had experienced four stages. The Devonian reservoirs reached the highest reservoir temperature 210-260 ∘ C during the second rapid burial-warming stage, which is the main period for the solid bitumen formation.

Maturity assessment of solid bitumen in the Sinian carbonate reservoirs of the eastern and central Sichuan Basin, China: Application for hydrocarbon generation modelling

“…Some representative Raman spectrums of solid bitumen with VR eq values ranging from 4.09% to 4.89% reported by Liu et al (2013) and Hou et al (2017) were characterized by the height of the D band being higher than that of the G band. Some Raman spectrums of solid bitumen in the eastern Sichuan Basin are similar to those of solid bitumen with VR eq values ranging from 4.09% to 4.89%, while all Raman spectrums of solid bitumen in the central Sichuan Basin are similar to that of solid bitumen with a VR eq value of 3.75%, indicating that the thermal maturity of solid bitumen in the eastern Sichuan Basin is higher than that in the central Sichuan Basin.…”

“…881-879 cm À1 , and 783-727 cm À1 , and weak bands at 3020 cm À1 , 2900-2890 cm À1 , 2520 cm À1 , 1670-1660, cm À1 and 1570-1560 cm À1 were also detected (Figure 8). According to extensive investigations on FTIR spectrums of kerogen and solid bitumen (Christy et al, 1989;Ganz & Kalkreuth, 1991;Hou et al, 2017;Liao & Geng, 2001;Liu et al, 1998;Małachowska et al, 2019;Pejcic et al, 2021;Yang et al, 2021), the important functional groups represented by absorption bands are as follows:…”

“…(g) Solid bitumen with a VR eq value from 4.08% to 4.14% in the Qianbei depression (Zhang et al, 2017). (h) Solid bitumen with a VR eq value of 3.42%-3.79% in the Guizhong depression (Hou et al, 2017). (i) Solid bitumen with a VR eq value of 4.88% in the Northwest Hunan province (Cao et al, 2013) strong absorption characteristic of the C C group in the region ranging from 1570 to 1560 cm À1 and a weak absorption characteristic of the C O group in the region between 1670 and 1660 cm À1 (Figure 8a-d).…”

“…(g) Solid bitumen with a VR eq value of 3.75% (Liu et al, 2013). (h) Solid bitumen with a VR eq value of 4.09% in the Guizhong depression (Hou et al, 2017). (i) Solid bitumen with a VR eq value of 4.89% (Liu et al, 2013) T A B L E 1 Raman spectral parameters and calculated vitrinite reflectance equivalent (VR eq ) of solid bitumen and bitumen inclusions in the Sichuan Basin…”

“…Some functional groups of solid bitumen, such as CH 2 and CH 3 aliphatic groups, aromatic CH bands, and oxygenated CO groups are sensitive to thermal maturity. Many studies suggest that thermal maturation can result in the increase in the amount of aromatic CH bands of solid bitumen whereas decrease in the amount of CH 2 and CH 3 aliphatic groups and heteroatom functional groups in solid bitumen (Craddock et al, 2015; Hou et al, 2017; Liu et al, 1998). Artificial maturation experiments also reveal that oxygenated CO groups are enriched in solid bitumen formed at low maturity levels (R o <0.8%) whereas become depleted at higher maturity levels (R o >0.8%) (Craddock et al, 2015).…”