Shale oil reservoir of the Palaeogene Shahejie Formation in the Dongpu Sag: Petrology and pore microstructural characteristics

doi:10.13745/j.esf.sf.2022.10.15

Abstract

Abstract:

Shale petrology and pore microstructures are key performance evaluation indicators for shale oil and gas reservoirs. In this study, the petrological and oil compositional characteristics of shale oil reservoir and reservoir lithofacies types, pore/fracture types and pore-throat distribution in the Shahejie Formation in the Dongpu Sag are investigated by core observation, thin section analysis, scanning electron microscopy, mercury injection-liquid nitrogen adsorption and microCT-guided 3D reconstruction methods. Results show that the shale oil reservoir contains mainly clay and carbonate minerals and some felsic minerals. The main lithofacies includes laminated limestone/clay stone/calcareous fine-grained mixed rocks/argillaceous fine-grained mixed rocks, and massive clay stone/dolomite. The reservoir pore space is mainly provided by a combination of intergranular/intragranular dissolution/clay mineral intergranular/organic pores. The microfractures can be divides into diagenetic and tectonic fractures, and the laminated limestone/calcareous fine-grained mixed rocks developed various high porosity pore spaces. Lithofacies and bedding structure are important factors influencing pore development and pore quality. Laminated rocks, except clay stone, possess large pore space and show good pore connectivity, relatively developed microfractures and high oil content and mobility, and laminated limestone is the most favorable lithofacies. These rocks are key shale oil exploration targets in the Dongpu Sag.

Key words: shale oil, fine-grained sedimentary rock, petrological characteristics, microscopic reservoir, Dongpu Sag

CLC Number:

PENG Jun, SUN Ningliang, LU Kun, XU Yunlong, CHEN Faliang. Shale oil reservoir of the Palaeogene Shahejie Formation in the Dongpu Sag: Petrology and pore microstructural characteristics[J]. Earth Science Frontiers, 2023, 30(4): 128-141.

Figures/Tables 12

Fig.1 Regional structural map and tectonic units of the Dongpu Sag

Fig.2 Schematic stratigraphic column of the Palaeogene Shahejie Formation

Fig.3 Lithofacies classification diagram for fine-grained sedimentary rocks in the upper 3rd and lower 4th members of the Dongpu Sag

Fig.4 Main lithofacies types of fine-grained sedimentary rocks of the Shahejie Formation

Fig.5 Core-based comprehensive stratigraphic column of lower 4th member of the Shahejie Formation of well V456

Fig.6 Lithofacies-dependent main pore types in shale oil reservoir of the Shahejie Formation

Fig.7 Lithofacies-dependent micro-fracture types in the Shahejie shale oil reservoir

Fig.8 Lithofacies-dependent pore diameter distribution characteristics in the Shahejie shale oil reservoir

Fig.9 Thin sections (A, C, E) and 3D models (by MicroCT-guided 3D reconstruction) (B, D, F) of three shale samples with different lithofacies from the Shahejie shale oil reservoir

Fig.10 Relationship between S1 and TOC in shale samples with different lithofacies

Fig.11 Relationship between TOC and OSI in shale samples with different lithofacies

Fig.12 Shale oil occurrence types in the Shahejie Formation in the Dongpu Sag

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