Acoustic and Petrophysical Evolution of Organic-Rich Chalk Following Maturation Induced by Unconfined Pyrolysis

Shitrit, O.; Hatzor, Yossef H.; Feinstein, Shimon; Vinegar, Harold J

doi:10.1007/s00603-017-1325-9

Cited by 7 publications

(5 citation statements)

References 48 publications

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“…Given the economic importance of fracking and the rising energy demands worldwide, the geophysical and geochemical processes underlying the chemical transformation of organic precursors into usable hydrocarbons has been a major interest for understanding the evolution of quality oil shale plays. − Until recently, these models have been primarily limited to the effects that macroscopic properties, such as temperature, depth, pressure, and time, have on the quality of an oil shale reservoir. − These factors are generally well-understood and contribute to our estimations of recoverable oil shale reserves. Recent studies have begun to introduce more complex parameters into their models, such as total organic content, clay content, microcracks, anisotropy, level of thermal maturation, and overall porosity. − Special attention has been given to the effect of structural heterogeneity on the mechanical properties (modulus) of source rocks. , However, such models are incomplete as they are often based on results from scanning electron microscopy (SEM), Rock-Eval pyrolysis, and vitrinite reflectance measurements . These conventional methods have intrinsic limitations which prevent them from recovering important information at spatial scales below the optical diffraction limit.…”

mentioning

confidence: 99%

Spectro-Mechanical Characterizations of Kerogen Heterogeneity and Mechanical Properties of Source Rocks at 6 nm Spatial Resolution

Jakob

Wang

et al. 2019

Anal. Chem.

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In situmeasurements of the chemical compositions and mechanical properties of kerogen help understand the formation, transformation, and utilization of organic matter in oil shale source rocks. However, the optical diffraction limit prevents attainment of nanoscale resolution using conventional spectroscopy and microscopy. Here, we developed peak force infrared (PFIR) microscopy for multimodal characterization of kerogen in organic shales. PFIR microscopy provides correlative infrared imaging, mechanical mapping, and broadband infrared spectroscopy capabilities with 6 nm spatial resolution within the frequency region of 2400−4000 cm −1 . We have observed nanoscale heterogeneity in the chemical composition, aromaticity, and the level of maturity of the kerogens from source rocks obtained from the Eagle Ford shale play in Texas. The level of aromaticity of the kerogen positively correlates with the local mechanical moduli of the surrounding inorganic matrix, offering insights into the effect of kerogen heterogeneity on the nanoscale mechanical properties of the source rock. Our method and investigation advances the understanding toward the origin and transformation of kerogen in geological settings.

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confidence: 99%

Spectro-Mechanical Characterizations of Kerogen Heterogeneity and Mechanical Properties of Source Rocks at 6 nm Spatial Resolution

Jakob

Wang

et al. 2019

Anal. Chem.

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“…Zhao et al (2016), for example, described the matrix as a composition of clay minerals, non-clay minerals, and kerogen, with the pore space filled with water, oil, and gas. Another approach considers the sample as a solid phase of minerals and kerogen with pores partially filled with air and oil/bitumen (Shitrit et al, 2017). We use the measurements to determine the proportions using the second approach.…”

Section: Petrophysical Relationsmentioning

confidence: 99%

“…Suwannasri et al (2018) reported increasing porosity and sensitivity of propagation velocities to pressure in a series of Eagle Ford samples maturated by dry pyrolysis. Shitrit et al (2017) applied a rock physics model (RPM) to analyze the effects of maturation and composition in chalk samples from the Ghareb and the Mishash formations with generation induced by dry pyrolysis.…”

Section: Introductionmentioning

confidence: 99%

“…There are studies that model the porosity as inclusions (Zhao et al, 2016) and fractures (Liu et al, 2020), with fluid effects considered after using Gassmann equations (Zhao et al, 2016). The maturation effects on the elastic properties can be obtained as the summation of all previous parameters, in addition to the structural modification from load bearing to filling kerogen considered by some authors (Zhao et al, 2016;Shitrit et al, 2017). Regarding the complexity of the models, Dvorkin et al (2021) suggested that elaborated models can lead to a high number of unknown inputs and proposed a "simple as possible" theoretical approach to reduce free parameters and the use of unmeasured properties.…”

Section: Introductionmentioning

confidence: 99%

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On the evolution of artificially maturated hydrocarbon source rocks

Lacerda¹,

Mörschbächer²,

Justen³

et al. 2023

Front. Earth Sci.

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The elastic moduli are a function of properties that could vary between samples and change during maturation. Consequently, the effects of organic matter maturation on the elastic wave velocities of organic-rich rocks are challenging to describe. This work analyzes the isolated maturation effects on the organic content, pore volume, microstructure, and propagation velocities of elastic waves. To avoid any initial rock heterogeneity, we prepared a series of homogeneous samples from a unique outcrop block collected on the Eagle Ford formation with mineral composition initially determined using X-ray diffraction. From the initial set, four samples were held in their original condition and four were artificially maturated by hydropyrolysis until transformation rates were up to 95%. Then, the evolution of the sample properties was examined using an association of LECO TOC, Rock-Eval pyrolysis, vitrinite reflectance, mercury intrusion porosimetry (MIP), and ultrasonic pulse propagation. In addition, scanning electron microscopy images registered the microstructure evolution. To evaluate the effects of maturation on pore geometry and the organic matter elastic moduli, we analyze the relationship between the measured quantities using a rock physics inclusion model with the unmeasured properties taken as fitting parameters. The hydropyrolysis maturation increases the vitrinite reflectance from the initial 0.55% to 1.34% on the most matured sample. A total organic carbon reduction from 4.2% to 2.1% and a porosity increase from 9.2% to 21% are associated with observed maturation. The geochemical characterization on cleaned samples reveals an initial increment of soluble organic matter followed by a monotonical reduction related to oil migration out of bulk volume. The measurement of wave propagation velocities as a function of confining pressure displays an increasing pressure sensitivity with a downward trend in both velocity moduli. The petrophysical analysis indicates that the porosity increases through organic matter consumption and pore creation. The rock physics diagnoses indicate a decrease in the pore aspect ratio with an increase in the elastic modulus of the organic matter with maturation.

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“…This results in Young's modulus of 6.4 GPa, which leads to bulk modulus of 7.1 GPa and shear modulus of 2.4 GPa. The organic material in the immature state is approximately 94% kerogen and 6% bitumen (further detailed in Shitrit et al 2017). Using the elastic moduli of bitumen (Table 1), the bulk and shear moduli of the entire organic phase are estimated to be 6.9 and 2.3 GPa, respectively.…”

Section: Ultrasonic Wave Velocities and Dynamic Modulimentioning

confidence: 99%

Static and dynamic elastic moduli of organic‐rich chalk

Shitrit

Hatzor

Feinstein

et al. 2019

Geophysical Prospecting

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The elastic moduli and anisotropy of organic‐rich rocks are of great importance to geoengineering and geoprospecting of oil and gas reservoirs. In this paper, we probe into the static and dynamic moduli of the Ghareb–Mishash chalk through laboratory measurements and new analytical approaches. We define a new anisotropy parameter, ‘hydrostatic strain ratio’ (Ω), which describes the differential contraction of anisotropic rocks consequent to hydrostatic compression. Ω depends on the C11, C12, C13 and C33 stiffness constants of a transversely isotropic material, and therefore enables a unique insight into the anisotropic behaviour of TI rocks. Ω proves more sensitive to anisotropy within the weak anisotropy range, when compared with Thomsen's ε and γ parameters. We use Ω to derive static moduli from triaxial compression tests performed on a single specimen. This is done by novel employment of a hydrostatic‐deviatoric combination for transversely isotropic elastic stiffnesses. Dynamic moduli are obtained from acoustic velocities measurements. We find that the bedding‐normal velocities are described well by defining kerogen as the load‐supporting matrix in a Hashin–Shtrikman model (‘Hashin–Shtrikman (HS) kerogen’). The dynamic moduli of the Ghareb–Mishash chalk in dry conditions are significantly higher than the static moduli. The dynamic/static moduli ratio decreases from ∼4 to ∼2 with increasing kerogen content. Both the static and dynamic moduli decrease significantly with increasing porosity and kerogen content. The effect of porosity on them is two times stronger than the effect of kerogen.

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Acoustic and Petrophysical Evolution of Organic-Rich Chalk Following Maturation Induced by Unconfined Pyrolysis

Cited by 7 publications

References 48 publications

Spectro-Mechanical Characterizations of Kerogen Heterogeneity and Mechanical Properties of Source Rocks at 6 nm Spatial Resolution

Spectro-Mechanical Characterizations of Kerogen Heterogeneity and Mechanical Properties of Source Rocks at 6 nm Spatial Resolution

On the evolution of artificially maturated hydrocarbon source rocks

Static and dynamic elastic moduli of organic‐rich chalk

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