Fractal Analysis of Microscale and Nanoscale Pore Structures in Carbonates Using High-Pressure Mercury Intrusion

Peiqing Lian,Zhichao Liu,Fuyong Wang,Liang Jiao,Jian Gao,Jiuyu Zhao

doi:10.1155/2018/4023150

Peiqing Lian, Zhichao Liu + Show 4 more

Open Access

https://doi.org/10.1155/2018/4023150

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Abstract

This paper investigated fractal characteristics of microscale and nanoscale pore structures in carbonates using High-Pressure Mercury Intrusion (HPMI). Firstly, four different fractal models, i.e., 2D capillary tube model, 3D capillary tube model, geometry model, and thermodynamic model, were used to calculate fractal dimensions of carbonate core samples from HPMI curves. Afterwards, the relationships between the calculated fractal dimensions and carbonate petrophysical properties were analysed. Finally, fractal permeability model was used to predict carbonate permeability and then compared with Winland permeability model. The research results demonstrate that the calculated fractal dimensions strongly depend on the fractal models used. Compared with the other three fractal models, 3D capillary tube model can effectively reflect the fractal characteristics of carbonate microscale and nanoscale pores. Fractal dimensions of microscale pores positively correlate with fractal dimensions of the entire carbonate pores, yet negatively correlate with fractal dimensions of nanoscale pores. Although nanoscale pores widely develop in carbonates, microscale pores have greater impact on the fractal characteristics of the entire pores. Fractal permeability model is applicable in predicting carbonate permeability, and compared with the Winland permeability model, its calculation errors are acceptable.

Highlights

Compared with sandstones, carbonate pore structures are usually more complex
It could be concluded that though nanoscale pores are predominant in the Y carbonate reservoir, petrophysical properties are mainly dominated by microscale pores
The following conclusions can be drawn from this study: (i) The calculated fractal dimensions strongly depend on the fractal models used

Summary

Introduction

Carbonate pore structures are usually more complex. There are many diverse types of pore space in carbonates such as intergranular pores, intraparticle pores, moldic pores, fractures, and vugs. Mercury intrusion method has been extensively used to study fractal characteristics of pore structures in sandstones [9,10,11] and coals [12,13,14]. Based on the tortuous and fractal tubular bundle model, Buiting and Clerke [25] developed a different fractal permeability model, which had been verified with more than 500 carbonate core samples, but empirical parameters were introduced. With more than 200 carbonate core samples, Nooruddin et al [26] compared nine different permeability models using mercury intrusion capillary pressure data, and they found that Swanson and Winland permeability models gave the best carbonate permeability prediction results. Porosity-permeability correlation is very weak, indicating high heterogeneity of carbonate core samples. Pore structures and pore size distributions of carbonate core samples were characterized with HPMI technique.

Methodology Description

Fractal Dimension Calculation

Fractal Characteristic Analysis

Carbonate Permeability Modelling

Findings

Conclusion