Geophysical Monitoring for Geologic Carbon Storage. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
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Жанр произведения: География
Год издания: 0
isbn: 9781119156840
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      where we used α F ~ 1 and η M ~ φ F /K f , and φ F ~ 1.

Schematic illustration of changes in the uniaxial Skempton coefficients B/3 and BF/3 during Frac IIb scCO2 injection test.

      When the two mechanisms (near‐monotonic decreases in the modulus and increases in attenuation from the heterogeneous invasion of scCO2 in the matrix, and nonmonotonic changes in the modulus and attenuation from interactions between the matrix and the fracture) are combined, the observed complex behavior of the sample's dynamic properties can be explained. However, dynamic poroelastic modeling of the scCO2‐invasion‐induced dynamic rock property changes would be needed for their quantitative validation.

      In this chapter, we presented a series of laboratory experiments on the seismic property changes of fractured Carbon Tan sandstone cores during supercritical CO2 injection. The use of a modified resonant bar technique (Split‐Hopkinson Resonant Bar method) allowed us to make the measurements at crosshole seismic survey frequencies, at approximately 1.4–1.5 kHz for longitudinal waves (or Young's modulus) and 800–900 Hz for torsional waves (or shear modulus). Evolving distributions of water and scCO2 in the samples were also determined via X‐ray CT imaging.

      The experiments showed that CO2 injection resulted in little to no changes in the overall Young's modulus of the sample when the fracture was highly compliant and parallel to the core axis. In contrast, samples containing a core‐perpendicular fracture exhibited large decreases in the Young's modulus, particularly when the leading edge of the invading scCO2 reached the fracture by fast passing along high‐permeability features in the sample. In both cases, large increases in the attenuation were observed. However, the attenuation in the latter samples showed a sudden decrease when the scCO2 reached the fracture, corresponding to the maximum rate of decrease in the Young's modulus.

      The laboratory‐observed changes in seismic velocity and attenuation during scCO2 injection were strongly dependent upon the orientation of the fractures. Particularly, there is an indication that preferential saturation of a fracture by scCO2, oriented perpendicular to the compressional wave direction, can result in sudden decreases in the seismic velocity and attenuation. Because fracture orientation has a dominant effect on the migration of scCO2 and its saturation in reservoir rock, the observed changes can be used for improved assessment of the scCO2's behavior from seismic measurements. Caution must be used in their applications, however, because the pressure diffusion length in reservoir rock is often very short even at the surface seismic exploration frequencies, limiting some of the laboratory‐observed fluid‐substitution‐induced changes in the rock properties (seismic properties) to a small volume around the fractures. Additionally, observed changes in seismic waves in the field are averaged over the effects from multiple fractures with different mechanical properties and orientations.

      Initial experimental work in this research was supported by the Assistant Secretary for Fossil Energy, Office of Natural Gas and Petroleum Technology, CSRP Program, through the National Energy Technology Laboratory. Additional experiments (Frac IIb test) and the rock‐physics analyses were supported by the Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences of the U.S. Department of Energy, under the U.S. DOE Contract No. DE‐AC02‐05CH11231.

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