Effects of Kerogen Content on Elastic Properties‐Based on Artificial Organic‐Rich Shale (AORS)

Abstract

Quantitative rock physical approaches are becoming increasingly important for both geophysical exploration and geological interpretation. One limiting factor is that experimental measurements in natural rock tend to be restricted by the availability of natural materials particularly if they are obtained from core holes. Artificial physical models that allow for control of composition and structure provide opportunities to carry out many more experiments on a range of samples with different characteristics. In this study, a hot‐pressing technique that includes temperature and pressure control is developed to construct artificial organic‐rich shales (AORS). The compositions of the AORS were developed from known natural samples and include mixtures of relevant minerals and appropriate organic matter considering grain sizes and shapes. The microstructures of the samples as observed in the scanning electron microscope and the petrophysical properties (density, porosity, permeability, and pressure sensitivity) are similar to those observed in the natural shales and support use of these samples as shale analogs. A total of 10 AORS samples with kerogen contents (KC) ranging from 1.71% to 14.8% was constructed to evaluate the effects of KC on elastic properties. A cross‐plot of the VP/VSH ratio versus the acoustic impedance indicates patterns that may be useful in remotely assessing KC content. Similarly, cross‐plots using the Lamé parameters of λρ versus μρ at various confining pressure may also be an effective tool in predicting KC. The linear correlations between the sum of weight percentage of KC and porosity and acoustic impedance tend to be strengthened during the pressurized procedure.

Experimental Investigation of Stress Sensitivity of Elastic Wave Velocities for Anisotropic Shale in Wufeng–Longmaxi Formation

“…This is because the microfractures were almost completely closed at the initial pressure loading stage, and the directional arrangement of the mineral particles caused a wave velocity change in the elastic stage. The arrangement of clay minerals is the key factor causing the high anisotropy of shale [5,6]. The higher clay content in the mineral composition renders a greater anisotropy [68].…”

“…The elastic properties and mechanical behavior of shale have attracted great interest in geological engineering [5][6][7][8][9][10][11]. Vernik et al [12,13] pointed out that there is a high correlation between in situ stress, porosity, permeability parameters, organic matter content, and shale acoustic wave velocity.…”

Geomechanics of Organic Matters Contained in Shales: A Molecular-Level Investigation

“…These values were in good agreement with those of previous studies conducted on an experimental and computational basis. 20,41 The calculated porosities of the kerogens were between 0.13 and 0.15, and the highest corresponded to the most mature one (II-D).…”

Attenuation of Seismic Waves in Partially Saturated Berea Sandstone as a Function of Frequency and Confining Pressure

“…Since the observed attenuation might result from the combination of squirt flow and patchy saturation, we could model our data using the double double-porosity model proposed by Ba et al (2017). Besides, we could test analog materials whose physical properties could be thoroughly controlled (e.g., Xie et al, 2019). Nevertheless, results and modeling presented here suggest that in near-surface sedimentary terrains, where the effective stress is low -e.g., < 20 MPa -and partial saturation is likely to be present, attenuation and dispersion might strongly affect the propagation of seismic waves like suggested by field observations (e.g., Abercrombie, 1997).…”