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Acoustic impedance in carbonates is influenced by factors such as porosity, pore structure/fracture, fluid content, and lithology. Occurrence of moldic and vuggy pores, fractures and other pore structures due to diagenesis in carbonate rocks can greatly complicate the relationships between impedance and porosity. Using a frame flexibility factor ($\gamma$) derived from a poroelastic model to characterize pore structure in reservoir rocks, we find that its product with porosity can result in a much better correlation with sonic velocity ($V_p$ = $A-B\ast \varphi \ast \gamma$) and acoustic impedance ($AI$ = $C-D\ast \varphi \ast \gamma )$, where A, B, C and D is 6.60, 0.03, 18.3 and 0.09, respectively for the deep low-porosity carbonate reservoir studied in this paper. These new relationships can also be useful in improving seismic inversion of ultra-deep hydrocarbon reservoirs in other similar environments.

In this study, $\mathrm{\text{bismuth}}+\mathrm{\text{carbonate}}$ co-doped and pure hydroxyapatites (HAp) were coated on rough surfaces of Ti6Al4V plates by biomimetic method. Prepared samples were investigated with SEM, EDS, FTIR, XRD and ICP. Furthermore, mechanical scratch tests, profilometer tests and in vitro cell studies were carried out. In order to explore the antibacterial characteristics of the coating, the survival rate of a bacteria named Staphylococcus epidermidis was determined. Structural investigations showed that HAp nucleation began four days after the immersion, expectedly nucleation developed collaterally with the incubation period and co-dopants had considerable effect on surface characteristics. Besides, the pretreatment procedure and dopants had notable impact on mechanical qualifications of the coatings. The critical load values obtained for coating failure were detected above 100mN in all types of coatings (max. critical load was obtained from 0.3mM co-doped coatings). Cancerous bone cells (SaOS-2) on prepared coatings were evaluated in terms of biological properties. 0.1-C7 and 0.3-C7 exhibited highest reduction percentage among all co-doped samples. Further increase in dopants concentrations up to 0.5mM lead to increase in toxicity and decrease in cell proliferation. Antibacterial test results showed the most antibacterial samples were 0.1-C7 and 0.3-C7, the results conformed with cell culture findings.