Impact of saturation changes on acoustic velocities of carbonate rocks

  • El Amin Mokhtar

Student thesis: Master's Thesis

Abstract

To assess the effect of saturation on acoustic velocities of carbonate rocks, laboratory measurements of compressional waves (Vp), and shear waves (Vs) at dry, almost full and partial brine/oil saturation at ambient pressure and temperature on seventeen samples were conducted. NMR T2 analysis, CT scan imaging, thin sections petrography, porosity and permeability measurements were also carried out. Cross plots of acoustic velocities versus porosity, permeability and NMR T2 mean were generated to study potential correlations. Furthermore, comparisons between existing fluid substitution models and acoustic velocity measurements at different brine/oil saturations were investigated. The study indicates that porosity is the leading rock property influencing acoustic velocities in carbonate rocks and displays an inverse relationship with acoustic velocities. Permeability shows a weaker correlation. Rock fabrics, pore types and sizes tend to have a secondary influence on acoustic velocities as indicated by the NMR T2 distributions, thin sections and CT scan images. Acoustic velocity measurements conducted at different combinations of brine and oil saturations indicate that changes beyond the estimated margin of error can be observed in both Vp and Vs measurements. These changes reveal that Vp tend to increase from oil to brine saturation. Vp also follows five trends that resemble exclusively or partly the Gassmann and Patchy saturation models. Furthermore, comparing lab and sonic data show that they follow similar trends with depth. However, lab velocities consistently displayed lower velocities than the sonic logs due to differences in pressure and temperature. In conclusion, this study demonstrates that meaningful changes in acoustic velocities due to fluid saturations changes can be measured in the laboratory. These changes also seem to exclusively or partly follow Gassmann and Patchy saturation models and are influenced by porosity, rock fabrics, pore types and sizes.
Date of Award2014
Original languageAmerican English
SupervisorSandra Vega (Supervisor)

Keywords

  • Earth sciences
  • Petroleum Geology
  • 0583:Petroleum Geology

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