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Approximately 40 different reservoir and surface rock samples were lased using high power COIL (1.315 micrometer), CO2 (wavelength = 10.6 micrometer) and Nd:YAG (wavelength = 1.06 micrometer) lasers. Spectrum of the samples (sandstones, shales, and limestones) in the wavelength region from 0.35 to 15.387 wavelength were obtained. Spectral signatures and optic coefficients of the reservoir and surface sandstones were discussed by the authors in a previous paper (SPIE 5273-97). In this contribution, a detailed study of the spectral properties and optic signatures of shale and limestone samples is presented. The optic coefficients (extinction/reflection (E), scattering (S), absorption (K) and emission (F)) of these rocks are mathematically and statistically calculated and are critically investigated against rock chemistry, grain size, porosity, cementing matrix and rock textures, and total organic content.
Our investigations show that: 1) Porosity and grain size are the only rock properties that exhibited a strong statistical relation with the absorption and reflection coefficients. 2) Rocks with high porosity have greater reflection coefficients (at the COIL and Nd:YAG wavelengths) compared to those having lower porosity. 3) The reflectance at the CO2 laser wavelength (10.6 wavelength) is not a function of porosity or grain size. 4) Surface and reservoir shales have almost the same spectral features and hence similar optic coefficients. This indicates that mode of occurrence does not influence the spectral signatures of rocks. 5) Spectrum of limestones is dominated by the four (v1 v2, v3, and v4) fundamental stretching carbonate absorption bands.
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