Abstract

Understanding pore structure would enable us to obtain a deeper insight into the fluid mechanism in porous media. In this research, multifractal analysis by various experiments is employed to analyze the pore structure and heterogeneity characterization in the source rock in Ordos Basin, China. For this purpose, imaging apparatus, intrusion tests, and nonintrusion methods have been used. The results show that the objective shale reservoir contains complex pore network, and minor pores dominant the pore system. Both intrusion and nonintrusion methods detected pore size distributions show multifractal nature, while the former one demonstrates more heterogeneous features. The pore size distributions acquired by low temperature adsorption and nuclear magnetic resonance have relatively good consistence, indicating that similar pore network detection method may share the same mechanism, and the full-ranged pore size distributions need to be acquired by multitechniques. Chlorite has an obvious impact on the heterogeneity of pore structure in narrow pore size range, while illite and I/S mixed layer influence that in wide range. Kerogen index is the fundamental indicators of geochemical parameters. With the decrease of averaged small and middle/large pore radius, the heterogeneity of pore structures increase in narrow and wide ranges, respectively. This work employed a comprehensive methodology based on multitechniques and helps to explore how pore networks affect reservoir quality in shale reservoirs.

Highlights

  • Shale oil exploration and development enhance the necessity of determining the pore structures [1,2,3,4]

  • Based on the three-end diagram of the compositions of different minerals, it was demonstrated that the Chang 7 Member (C7) shales were mainly classified into two groups: brittle mineral high shales (BMHS) and clay mineral high shales (CMHS)

  • Where T2 is the relaxation time, Fs refers to the pore shape factor, ρ2 stands for relaxivity, and r represents pore radius

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Summary

Introduction

Shale oil exploration and development enhance the necessity of determining the pore structures [1,2,3,4]. The combination of various experiments and the calculation of the percentage of pores with different radius were important to the analysis of the characterization of shale pore structure [15,16,17] After those steps, the multifractal characteristics, origin of subpore features (for example, surface roughness and heterogeneity) could be investigated from the perspective of relationships among multifractal dimensions, mineral compositions, and pore structures [16]. The multifractal characteristics, origin of subpore features (for example, surface roughness and heterogeneity) could be investigated from the perspective of relationships among multifractal dimensions, mineral compositions, and pore structures [16] These trends were of great importance to probe the pore network distribution rules and evaluate the reservoir qualities

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