Summary

The composition and structure of clay minerals play a major role in controlling the physical and chemical properties of shale. Understanding the relationship between clay mineralogy and the physical parameters of shale such as the wettability, fracability, and permeability is crucial in characterizing and developing a shale reservoir. Typically, the higher the amount of clay minerals present the lower will be the material brittleness/fracability, whereas a lower clay abundance is usually associated with improved reservoir permeability. Determining the clay composition in shales is a significant challenge considering the chemical complexity and heterogeneous nature of the shale. In this paper, we report on the preliminary characterization of Permo-Triassic shale reservoir samples from the Perth Basin using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The suitability and performance of FTIR and XRD for determining clay mineralogy was evaluated. Both FTIR and XRD revealed that kaolinite was the dominant clay species in most of the samples from the Permo-Triassic shale reservoir. It was shown that XRD is able to identify and quantify many different minerals in the shale samples, while FTIR helped provide complimentary information on some minerals along with information concerning the amorphous organic matter.

Introduction

The extraction and production of gas from shale has become an attractive energy source in Australia over the last decade. There are a number of factors that determine if a particular shale will develop into a gas resource. The following three factors have been suggested to be important with respect to a shale gas becoming a significant resource play:

  • organic matter content, type and thermal maturity;

  • pore size distribution and porosity-permeability relationships; and

  • brittleness and its association with mineralogy and rock fabric (Josh et al. 2012).

Despite improved conditions for exploration and development, there has been very little activity in targeting shale reservoirs in the Perth Basin (i.e. Kockatea and Carynginia formations). This formation is currently being explored as a potential shale gas resource (Figure 1).

A number of papers have been published which show that the fluid flow and oil recovery are determined by rock properties (Bustin and Bustin, 2012). The physical (i.e., permeability, fracability, wettability) and chemical properties of shale rocks depend strongly on the type and amount of clay minerals present. Clay particles can be distributed in a shale according to three general locations such as pore-lining clays (mixed layer clays), pore-bridging clays (illite), and discrete particles (kaolinite). According to Morris and Shepperd (1982) the clay particle size is an important factor influencing the permeability of shales. Others have shown that the water content and the swelling ability depends significantly on the type of clay minerals present (Bennion and Thomas, 1992). It has been found that a low amount of clay minerals results in a high fracability within shales (Sondergeld et al., 2010).

URTeC 1619333

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