An investigation of static and dynamic data using multistage triaxial tests

Bilal, Abdullah; Myers, Michael T.; Hathon, Lori

doi:10.1190/segam2016-13969660.1

Cited by 3 publications

(2 citation statements)

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“…Previous research on the comparison of static and dynamic properties mainly focuses on sandstone, limestone, and carbonate [6,17,21,22]. In this paper, we focus on measuring and comparing the static and dynamic elastic properties of Eagle Ford Shale.…”

Section: Introductionmentioning

confidence: 99%

Static and Dynamic Mechanical Properties of Organic-Rich Gas Shale

Dong

et al. 2021

Geofluids

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Rock mechanical properties are critical for drilling, wellbore stability, and well stimulation. There are usually two laboratory methods to determine rock mechanical properties: static compression tests and acoustic velocity measurements. Rocks are heterogeneous, so there are significant differences between static elastic constants and the corresponding dynamic ones. Usually, static test results are more representative than dynamic methods but the static tests are time consuming and costly. Dynamic methods are nondestructive and less expensive, which are practical in the laboratory and field. In this paper, we compare the static and dynamic elastic properties of Eagle Ford Shale by triaxial compressive tests and ultrasonic velocity tests. Correlations between static and dynamic elastic properties are developed. Conversion from dynamic mechanical properties to static mechanical properties is established for better estimating reservoir mechanical properties. To better understand the relationship of static and dynamic mechanical properties, 30 Eagle Ford Shale samples were tested. According to the test results, the dynamic properties are considerably different from the static counterparts. For all tested samples, static Young’s modulus is lower than dynamic Young’s modulus, ranging from 55% to 90%. The difference of the static and dynamic Young’s moduli decreases with the increasing of confining pressure. The reason may be because the microcracks closed in high confining pressure. Correlations between static and dynamic Young’s modulus are developed by regression analysis, which are crucial to understand the rock mechanical properties and forecast reservoir performance when direct measurement of static mechanical properties is not available or expensive. There are no strong correlations between static and dynamic Poisson’s ratios observed for the tested samples. Two potentially major reasons for the discrepancy of the static and dynamic properties of Eagle Ford Shale are discussed. Lithology and heterogeneity may be the inherent reasons, and external causes are probably the difference in strain amplitude and frequency.

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Section: Introductionmentioning

confidence: 99%

Static and Dynamic Mechanical Properties of Organic-Rich Gas Shale

Dong

et al. 2021

Geofluids

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“…A similar method was presented by (Bilal et al 2016). In their work, the stress-strain curves were fitted with a quadratic polynomial function, with the quadratic component representing the non-elastic contribution.…”

Section: Introductionmentioning

confidence: 99%

From Static to Dynamic Stiffness of Shales: Frequency and Stress Dependence

Lozovyi

Bauer

2019

Rock Mech Rock Eng

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The relation between static and dynamic stiffness in shales is important for many engineering applications. Dynamic stiffness, calculated from wave velocities, is often related to static stiffness through simple empirical correlations. The reason for this is that dynamic properties are often easier to obtain; however, it is the static properties that define the actual subsurface response to stress or pore pressure changes. Rocks are not elastic media, and stiffness depends on the stress state, stress-change amplitude, loading rate, drainage conditions, fluid saturation, and scale. All these factors require consideration when static and dynamic stiffness properties are to be related. Two mechanisms that may have a strong effect on the stiffness of shales were studied in this experimental work: (i) a reduction of undrained static stiffness with an increase in stress amplitude and (ii) a frequency dependence (or dispersion) of dynamic stiffness. Laboratory tests were performed on four fully brine-saturated undrained field shales from different overburden formations. Experiments were conducted using a low-frequency apparatus-a triaxial loading cell with the ability to measure dynamic stiffness at seismic frequencies (1-150 Hz) and ultrasonic velocities (500 kHz). Shale anisotropy was characterized by testing differently oriented core plugs. Static and dynamic stiffness of shales The results demonstrated that all the tested shales exhibited a dispersion of dynamic stiffness from seismic to ultrasonic frequencies. Young's modulus dispersion for the tested shales ranged from nearly 30% to above 100%. Wave velocity dispersion was on the order of 10-20% for P-waves and 20-40% for S-waves. In static tests, the undrained rock stiffness gradually decreased with increasing stress amplitude. For one shale, the static undrained Young's modulus was reduced by 50% when amplitude of the loading-unloading measurement cycle was increased from 1 MPa to 3 MPa. This finding is explained by non-elastic deformations that increase with the stress level. A method of zero-stress extrapolation of static stiffness was used to obtain the purely elastic response. The stiffness for the limit of zero stresschange amplitude agreed well with the dynamic response at seismic frequency, providing a link between static and dynamic stiffness.

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