Pore Characteristics of Lacustrine Shale Oil Reservoir in the Cretaceous Qingshankou Formation of the Songliao Basin, NE China

Xiaomeng Cao,Sha Song,Shuangbiao Han,Lei Kang,Jingwei Cui,Chengshan Wang,Yuan Gao

doi:10.3390/en13082027

Abstract

Shale oil is hosted in nanopores of organic-rich shales, so pore characteristics are significant for shale oil accumulation. Here we analyzed pore characteristics of 39 lacustrine shale samples of the Late Cretaceous Qingshankou Formation (K2qn) in the Songliao Basin, which is one of the main shale oil resource basins in China, using field emission-scanning electron microscopy (FE-SEM), and low-pressure nitrogen adsorption. We accomplished fractal analysis, correlation analysis using correlation matrix and multidimensional scaling (MDS), and prediction of fractal dimensions, which is the first time to predict pore fractal dimensions of shales. Interparticle pores are highly developed in K2qn. These shales have mesoporous nature and slit-shaped pores. Compared with the second and third members (K2qn2,3), the first member of the Qingshankou Formation (K2qn1) has a larger average pore diameter, much smaller surface area, fewer micropores, simpler pore structure and surface indicated by smaller fractal dimensions. In terms of pore characteristics, K2qn1 is better than K2qn2,3 as a shale oil reservoir. When compared with marine Bakken Formation shales, lacustrine shales of the Qingshankou Formation have similar complexity of pore structure, but much rougher pore surface. This research can lead to an improved understanding of the pore system of lacustrine shales.

Highlights

With the increasing energy demands of the world, the transition from conventional petroleum to unconventional petroleum is inevitable [1,2,3,4,5,6]
Four types of pores were recognized in this study, including organic-matter pores, interparticle pores, intraparticle pores, and micro-fractures
Some gridded-like pores are found within organic matter, which coexists with clay minerals, calcite grains, and pyrite particles (Figure 2i)

Summary

Introduction

With the increasing energy demands of the world, the transition from conventional petroleum to unconventional petroleum is inevitable [1,2,3,4,5,6]. As a kind of unconventional petroleum resource, is attracting growing attention [7,8,9,10]. Multistage-fractured horizontal drilling dramatically enhances the production performance of shale reservoirs [11]. Natural fracture spacing significantly affects shale reservoir performance [11]. A shale oil reservoir is a kind of self-contained source-reservoir system. The pores and micro-fractures in inorganic minerals and organic matter constitute a complicated pore-fracture system in shales [1,2,12,13]. Shale oil is stored in four types of pores, i.e., intraparticle (intraP) pores, Energies 2020, 13, 2027; doi:10.3390/en13082027 www.mdpi.com/journal/energies

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Conclusion