Effect of solid bitumen on pore structure of ultra-deep carbonate reservoir and its logging calculation method

Abstract

An amount of highly evolved bitumen has been discovered in carbonate reservoirs during ultra-deep oil and gas exploration. This bitumen damages the pore structure and is difficult to dissolve using chemical reagents. To address the gap in studying highly evolved bitumen’s impact on carbonate reservoirs. This study utilized samples from the second member of the Dengying Formation (referred to as Deng 2) in Sichuan Basin. Using thin-section observation, and full-diameter CT scanning, were employed to establish two digital models: with bitumen and without. The study aims to observe bitumen distribution characteristics, compare physical properties and pore structures of two digital cores, clarify bitumen content and its impact on the reservoir, and establish a regression equation. The results indicate: (1) Bitumen in Deng 2 exhibits three states: semi-filled, fully filled, and combined cementation; (2) Properties of the bitumen-containing model decline, with significant reductions in pore and throat numbers. Bitumen primarily occupies large-pore spaces with high coordination numbers and blocks large-radius, long-throat spaces; (3) A bitumen calculation model was established using digital core analysis and well logging parameters, demonstrating good applicability. In conclusion, this approach offers guidance for studying the impact of bitumen on ultra-deep reservoirs and quantitative well logging analysis.

Keywords:

• Dengying formation
• log response
• pore structure
• Sichuan basin
• solid bitumen

Author contributions

All authors contributed to the study conception and design. Yuyu Wu and Qiang Lai wrote the manuscript, Yong Li and Rong Yin analyzed the data, Xinggang Liu and Zeyu Wang completed the relevant experiments, and Liyuan Luo and Nan Zhang drew the corresponding figures.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data generated or analyzed during this study are included in this published article.

Additional information

Funding

This study was jointly sponsored by the National Natural Science Fund of China (42302164), CNPC Innovation Fund (2022DQ02-0105, 2020CX030000).