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Laboratory tests were conducted to analyze the ultrasonic velocity response to the pressure change in dry carbonate rocks from the Weyburn oilfield, Canada. Twenty-four samples are from seven wells with helium porosities ranging from 1% to 29%. Thin-section images, SEM and mercury intrusion porosimetry were performed to show their inner structures and pore throat size distributions. P- and S-wave velocities (Vp and Vs) measurements were first done under hydrostatic loading and then while unloading, with confining pressures varying between 3 and 35 MPa. The results indicate that Vp and Vs in these samples follow a linear relation independent of the pressure change. The ratio Vp/Vs is more responsive to pressure change irrespective of the pore volume. One-third of the carbonate samples show abnormal Vp/Vs reduction with the increase in the effective pressure. The pressure dependence of velocities (PDV) of Weyburn carbonate rocks varies widely even for samples from the same formation with similar sedimentary history. Samples with loosely packed crystals and/or relatively large dominant pore diameter have higher PDV. The exponential empirical model V = A - C e D P e was tested; therein, V is the elastic wave velocity, Pe is the effective confining pressure, and A, C and D are the best fitting coefficients determined by curve fitting. The model gives good fits for most of the Weyburn carbonate samples. From a statistical point of view, there is no difference between the Vp- and Vs-derived exponential coefficient D. [ABSTRACT FROM AUTHOR]

Evaluating the adsorbed gas content in shale gas reservoirs is crucial for calculating total gas production potential of the reservoir. In this study, we analyzed the chemical composition and total organic carbon content of the black shale samples collected from different depths in the Liard Basin, Canada. The samples were identified as siliceous-rich shale samples; specifically, organic-rich black shale with a total organic carbon content of more than approximately 3%. We also analyzed the adsorbed methane gas content and the pore structure of the shale samples. We conducted a mechanistic study to identify the important factors affecting the amount of adsorbed CH 4 gas in the shale by evaluating the correlation between the adsorbed CH 4 gas content and quantitative pore structure results (i.e., specific surface area and micropore, mesopore, and macropore volume). The results indicate that the micropore volume can be effectively used to predict the content of adsorbed CH 4 gas in organic-rich black shale samples from the Liard Basin. [Display omitted] • Black shales were collected from the Laird Basin natural gas deposit in Canada. • Organic-rich black shales exhibited similar chemical compositions and TOC contents. • The correlation between shale pore structure and adsorbed CH 4 content was analyzed. • Micropore volumes were relatively well correlated with adsorbed CH 4 contents. • Small pores are significant as an important factor in predicting the adsorbed CH 4 content in shale. [ABSTRACT FROM AUTHOR]