Sang, Liqin (2016-05). Seismic Attenuation in Carbonate Rocks and Rock Physics Models of Clay-Bearing and Organic-Rich Formations. Doctoral Dissertation. | Thesis individual record

Accurate prediction of key reservoir rock properties (lithology, porosity and permeability) with seismic techniques requires a comprehensive understanding of how these rock properties are related to their seismic response (wave velocities and attenuation). In this dissertation, I first study the P- and S-wave attenuation of carbonate rocks to relate attenuation to rock types and permeability; I then investigate rock physics models of clay-bearing and organic rich formations to incorporate the effect of clay and organic matter on the effective elastic properties of these formations.

Parameters that control the attenuation properties of carbonate rocks were investigated by laboratory ultrasonic measurements of P- and S-wave attenuation and petrophysical characterization of forty-seven core samples. The measurements reveal that at similar porosities within the range of 20%-30%, attenuation of samples with grain-dominated matrix and interparticle macro-pores is approximately twice as much as that of samples with homogenous muddy texture and abundant microporosity. Attenuation also strongly correlates to permeability. S-wave attenuation increases from room-dry to fully water-saturated conditions, whereas no significant difference in P-wave attenuation occurs between dry and saturated rocks. These results could be helpful for further quantitative studies on the mechanisms of seismic attenuation in carbonate rocks.

Velocity-porosity relationship for clay-bearing and organic-rich formations is largely affected by clay and kerogen content. A two-stage rock physics model is proposed to describe the elastic properties of these formations. The model considers the large moduli contrast between clay or kerogen and other matrix minerals and the structural effect of the clay or kerogen occupied space on matrix properties. Results from the studied clay-bearing formations suggest that the relative difference in estimates of total matrix moduli between the Voigt-Reuss-Hill model and the two-stage model can be as much as 40% for a modulus ratio of 0.13 between clay and other matrix minerals. For the studied organic-rich formations, the kerogen volume fraction is typically 0-0.1(v/v), and the relative difference in total matrix moduli estimates between the two models are 0-8% for shear modulus and 0-24% for bulk modulus, respectively, for a modulus ratio of 0.07-0.08 between kerogen and other stiff minerals.

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