Shale gas has become a significant resource play in the USA over the past few years, and oil companies are now evaluating the shale gas potential of many sedimentary basins. The successful development of these shale gas systems has led to a strong exploration campaign in Saudi Arabia to investigate its several onshore basins. These "shales" have complex and varying mineralogies and require intensive petrophysical analysis to determine even basic characteristics. The renewed focus on rock sequences has necessitated the development of workflows and methods for characterizing these shale rocks. With the deployment of new methods comes the need for interpretation frameworks to understand properties from diverse measurements. We investigated the use of two techniques, the dielectric dispersion technique and nuclear magnetic resonance (NMR), as potential tools for systematic shale characterization and examined their applicability to reservoir evaluation in shale plays.

Dielectric properties were measured on a suite of shale gas rock samples selected from several wells across the Silurian source rock formation. The frequency range of 10 MHz to 1 GHz covers the different polarization types of the electric field within the rock samples. The dependence of minerals in the shale-gas rocks on the interpretation of the dielectric response was studied. The dual-range Fourier transform infrared (FTIR) technique was used to accurately quantify the mineralogical composition of the studied samples, including pyrite. Pyrite has an obvious effect on the dielectric responses, and an accurate estimation of its volume is crucial for an enhanced interpretation of the dielectric response. The dependence of the effective matrix permittivity to the shale-gas minerals was well investigated in this work. A workflow was developed to accurately estimate the effective permittivity of the rock matrix to enhance the estimate of water volume from the dielectric response. The high-resolution retort was also used for the quantification of water content, and the results were compared to the water saturations from dielectric dispersion. NMR T2 was also measured on the selected shale gas rock samples using very short echo spacing to capture all the inorganic and organic porosity at the nanometer scale. An accurate estimation of total porosity from NMR and total water content from dielectric dispersion enhances the estimation of the total gas in place of the shale-gas rocks.

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