An experimental study to investigate the physical and dynamic elastic properties of Eagle Ford shale rock samples

Abstract

Unconventional resources, such as Eagle Ford formation, are commonly classified for their ultra-low permeability, where pore sizes are in nano-scale and pore-conductivity is low, causing several challenges in evaluating unconventional-rock properties. Several experimental parameters (e.g., diffusion time of gas, gas injection pressure, method of permeability measurement, and confining pressure cycling) must be considered when evaluating the ultra-low permeability rock's physical and dynamic elastic properties measurements, where erroneous evaluations could be avoided. Characterizing ultra-low permeability samples' physical and elastic properties helps researchers obtain more reliable information leading to successful evaluations. In this study, 24 Eagle Ford core samples' physical and dynamic elastic properties were evaluated. Utilizing longer diffusion time and higher helium injection pressure, applying complex transient method, and cycling confining pressure were considered for porosity, permeability, and velocities measurements. Computerized tomography (CT) scan, porosity, permeability, and ultrasonic wave velocities were conducted on the core samples. Additionally, X-ray Diffraction (XRD) analysis was conducted to determine the mineralogical compositions. Porosity was measured at 2.07 MPa injection pressure for 24 h, and the permeability was measured using a complex transient method. P- and S-wave velocities were measured at two cycles of five confining pressures (up to 68.95 MPa). The XRD analysis results showed that the tested core samples had an average of 81.44% and 11.68% calcite and quartz, respectively, with a minor amount of clay minerals. The high content of calcite and quartz in shale yields higher velocities, higher Young's modulus, and lower Poisson's ratio, which enhances the brittleness that is an important parameter for well stimulation design (e.g., hydraulic fracturing). The results of porosity and permeability showed that porosity and permeability vary between 5.3–9.79% and 0.006–12 µD, respectively. The Permeability–porosity relation of samples shows a very weak correlation. P- and S-wave velocities results display a range of velocity up to 6206 m/s and 3285 m/s at 68.95 MPa confining pressure, respectively. Additionally, S-wave velocity is approximately 55% of P-wave velocity. A correlation between both velocities is established at each confining pressure, indicating a strong correlation. Results illustrated that applying two cycles of confining pressure impacts both velocities and dynamic elastic moduli. Ramping up the confining pressure increases both velocities owing to compaction of the samples and, in turn, increases dynamic Young's modulus and Poisson's ratio while decreasing bulk compressibility. Moreover, the results demonstrated that the above-mentioned parameters' values (after decreasing the confining pressure to 13.79 MPa) differ from the initial values due to the hysteresis loop, where the loop is slightly opened, indicating that the alteration is non-elastic. The findings of this study provide detailed information about the rock physical and dynamic elastic properties of one of the largest unconventional resources in the U.S.A, the Eagle Ford formation, where direct measurements may not be cost-effective or feasible.

Nanoscale Analysis of Shale Matrix Alteration after Supercritical CO2Treatment: Implications for scCO2Fracturing in Shales

“…The average modulus was 47.53 GPa, which was within the range of the modulus values of the Eagleford shale. 1,47 Comparing the stats of this area before and after scCO 2 treatment (Figure 7d,e), the average modulus was reduced by around 15.76% to 40 GPa. The standard deviation of all the indented points in area 3 decreased by approximately 27% after scCO 2 treatment, indicating that the overall distribution of the indentation modulus has compacted toward the center.…”

Supercritical methane adsorption measurement on shale using the isotherm modelling aspect

“…The Eagle Ford is a carbonate-rich shale hydrocarbon play where mineralogy based on XRD consists of; 40-60% calcite, 10-30% quartz, and clays with less than 20%. 79 The XRD results show that calcite is the dominant mineral in all samples. The mineral distributions in all the samples are shown in Fig.…”

“…The Eagle Ford is a carbonate-rich shale hydrocarbon play where mineralogy based on XRD consists of; 40–60% calcite, 10–30% quartz, and clays with less than 20%. 79 …”

Geophysical logging in brittleness evaluation on the basis of rock mechanics parameters: a case study of sandstone of Shanxi formation in Yanchang gas field, Ordos Basin

“…However, in situations where brittle minerals contain cuttings, the brittleness evaluation method is no longer accurate (Zhang et al 2018). In the rock mechanics parameter method, elastic modulus and Poisson's ratio are used to calculate brittleness (Fan et al 2015;Qin et al 2016;Wang et al 2020;Altawati et al 2021;Lu et al 2022). There are mainly two ways to obtain rock mechanics parameters.…”