Attenuation of P- and S-waves in Lower Cretaceous carbonate rocks

Seismic attenuation is expected to be more sensitive to rock properties than velocity and may present a better correlation with permeability. However, the relation between attenuation and rock properties are not well understood yet, especially in carbonates. This paper presents attenuation measurements of P and S-waves at ultrasonic frequencies in forty-seven Lower Cretaceous carbonate samples. These samples were measured room-dry and full saturated with deionized water under differential pressure of 30 MPa. The pulse transmission technique and spectral ratio method were used to determine the quality factor (Q) values. We observe that attenuation is much more scattered than velocity at a given porosity for both P- and S-waves. Four reservoir rock types (RRT) are proposed for the studied samples. The rock typing scheme utilizes a porosity cutoffof 20 % in combination with dominant pore type and textural classification to distinguish samples with distinct porosity-permeability relations. RRT-4 samples are recognized by their grain-dominated texture along with high porosity (>20 %) and high permeability (>10 mD) values and have high 1/Q values. RRT-1 and RRT-2 samples have abundant lime-mud matrix resulting in low to intermediate permeability (< 10 mD); 1/Q values for these two RRT are low. Attenuation characteristics of RRT-3 samples are somewhere more complex because of their large-scale heterogeneous fabrics.