Investigation of Oil-Bearing Pore Size Distribution—Take Damintun Sag for Example

Abstract

Damintun Sag is located in Liaohe Depression, Bohai Bay, in China, covering an area of about 800 km². The production data shows good shale oil potential in E₂S₄² shale of Damintu sag.

A general understanding of the oil-bearing pore size distribution (PSD) in shale is important for optimizing the dessert area of shale oil. Unfortunately, the oil-bearing PSD has not been completely revealed to the best of our knowledge. In the previous studies, researchers tried to reveal the oil-bearing PSD by comparing the NMR T₂ distribution of the shale samples with different oil/water saturation (Fleury, 2014; 2015). However, it is the saturated oil/water PSD rather than the original oil PSD that can be obtained, which are inconsistent with each other because of the difference of the charging mode. The impact of chloroform extraction on the PSD of shale has been qualitatively discussed (Li et al., 2016), however, the difference on the PSD between extracted and unextracted shale samples has not been quantitatively linked to the oil content or the oil-bearing PSD. Therefore, the quantitative investigation of the oil-bearing PSD in shale is urgently needed.

we revealed the oil-bearing PSD in shale of Damintun sag at the peak oil generation stage by comparing the PSD between the extracted and un-extracted shale samples, and by linking the difference on the PSD between the extracted and un-extracted shale samples to the oil content in shale. It is found that while the specific pore volume (SPV) of meso pores are nearly 8 times as large as that of micro pores, the macro pores contribute to the majority of the pore volume in lacustrine shale at the peak oil generation stage. The SPVs of the extracted samples are generally larger than that of the un-extracted samples, and the oil-bearing PSD in pores with the size up to 80 nm are obtained by subtracting SPVs of un-extracted samples from that of the extracted samples in the specific pore size intervals. The oil-bearing mechanism is further investigated by linking the oil-bearing PSD to the total oil content obtained from the pyrolysis experiments. It is found that the content of oil residing in the micro and meso pores is significantly less than the total oil content, indicating that the oil is mainly contained in the macro pores rather than in the micro or meso pores. Therefore, the abundance and distribution of macro pores in lacustrine shale at the peak oil generation stage is a critical factor of a shale oil reservoir.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018