Controls on sonic velocity in carbonates
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Compressional and shear-wave velocities (Vp andVs) of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore-fluid pressures. The lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones. The velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy, porosity, pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations.
Pure carbonate rocks show, unlike siliciclastic or shaly sediments, little direct correlation between acoustic properties (Vp andVs) with age or burial depth of the sediments so that velocity inversions with increasing depth are common. Rather, sonic velocity in carbonates is controlled by the combined effect of depositional lithology and several post-depositional processes, such as cementation or dissolution, which results in fabrics specific to carbonates. These diagenetic fabrics can be directly correlated to the sonic velocity of the rocks.
At 8 MPa effective pressureVp ranges from 1700 to 6500 m/s, andVs ranges from 800 to 3400 m/s. This range is mainly caused by variations in the amount and type of porosity and not by variations in mineralogy. In general, the measured velocities show a positive correlation with density and an inverse correlation with porosity, but departures from the general trends of correlation can be as high as 2500 m/s. These deviations can be explained by the occurrence of different pore types that form during specific diagenetic phases. Our data set further suggests that commonly used correlations like “Gardner's Law” (Vp-density) or the “time-average-equation” (Vp-porosity) should be significantly modified towards higher velocities before being applied to carbonates.
The velocity measurements of unconsolidated carbonate mud at different stages of experimental compaction show that the velocity increase due to compaction is lower than the observed velocity increase at decreasing porosities in natural rocks. This discrepancy shows that diagenetic changes that accompany compaction influence velocity more than solely compaction at increasing overburden pressure.
The susceptibility of carbonates to diagenetic changes, that occur far more quickly than compaction, causes a special velocity distribution in carbonates and complicates velocity estimations. By assigning characteristic velocity patterns to the observed diagenetic processes, we are able to link sonic velocity to the diagenetic stage of the rock.
Key WordsSonic velocity carbonates physical properties porosity diagenesis compaction
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- Anselmetti, F. S., Eberli, G. P., Sellami, S., andBernoulli, D.,From outcrops to seismic profiles: An attempt to model the carbonate platform margin of the Maiella, Italy. InAbstract with Programs (Geol. Society of America, Annual Meeting, San Diego 1991).Google Scholar
- Biddle, K. V., Schlager, W., Rudolph, K. W., andBush, T. L. (1992),Seismic Model of a Progradational Carbonate Platform, Picco di Vallandro, the Dolomites, Northern Italy, American Association of Petroleum Geologists Bull.76, 14–30.Google Scholar
- Biot, M. A. (1956),Theory of Propagation of Elastic Waves in a Fluid-saturated Porous Solid, I. Low Frequency Range, II. Higher Frequency Range, J. Acoust. Soc. Am.28, 168–191.Google Scholar
- Birch, F. (1960),The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 1, J. Geophys. Res.65, 1083–1102.Google Scholar
- Burns, S. J., andSwart, P. K. (1992),Diagenetic Processes in Holocene Carbonate Sediments: Florida Bay Mudbanks and Islands, Sedimentology39, 285–304.Google Scholar
- Campbell, A. E., andStafleu, J. (1992),Seismic Modelling of an Early Jurassic, Drowned Platform: The Djebel Bou Dahar, High Atlas, Morocco, American Association of Petroleum Geologists Bull.76, 1760–1777.Google Scholar
- Christensen, N. I., andSzymanski, D. L. (1991),Seismic Properties and the Origin of Reflectivity from a Classic Palsozoic Sedimentary Sequence, Valley and Ridge Province, Southern Appalachians, Geol. Soc. Am. Bull.103, 277–289.Google Scholar
- Coyner, K. B. (1984),Effects of Stress, Pore Pressure, and Pore-fluids on Bulk Strain, Velocity and Permeability in Rocks (Ph.D. Thesis, Massachusetts Institute of Technology).Google Scholar
- Crescenti, U., Crostella, A., Donzelli, G., andRaffi, G. (1969),Stratigrafia della serie calcarea dal Lias al Miocene nella regione Marchigiano-Abruzzese, Parte II—Litostratigrafia, Biostratigrafia, Paleogeografia, Mem. Soc. Geol. It.8, 343–420.Google Scholar
- Dawans, J. M., andSwart, P. K. (1988),Textural and Geochemical Alterations in Late Cenozoic Bahamian Dolomites, Sedimentology35, 385–403.Google Scholar
- Eberli, G. P.,Physical properties of carbonate turbidite sequences surrounding the Bahamas: Implications for slope stability and fluid movements. InProceedings of the Ocean Drilling Program, Scientific Results 101 (eds. Austin, J. A., Jr., and Schlager, W.) (1988) pp. 305–314.Google Scholar
- Eberli, G. P., andGinsburg, R. N.,Cenozoic progradation of Northwestern Great Bahama Bank, a record of lateral platform growth and sea-level fluctuations. InControls on Carbonate Platform and Basin Development (SEPM Special Publication No. 44 1989) pp. 339–351.Google Scholar
- Eberli, G. P.,Growth and demise of isolated carbonate platforms: Bahamian controversies. InControversies in Modern Geology (Academic Press Limited 1991) pp. 231–248.Google Scholar
- Eberli, G. P., Bernoulli, D., Sanders, D., andVecsei, A. (1993),From aggradation to progradation: The Maiella platform (Abruzzi, Italy). InAtlas of Cretaceous Carbonate Platforms (eds. Simo, J. T., Scott, R. W., and Masse, J.-P.) Amer. Assoc. of Petroleum Geologist Memoir56, 213–232.Google Scholar
- Enos, P., andSawatsky, L. H. (1981),Pore Networks in Holocene Carbonate Sediments, J. Sed. Petrol.51, 961–985.Google Scholar
- Enos, P., andPerkins, R. D. (1979),Evolution of Florida Bay from Island Stratigraphy, Geol. Soc. Am. Bull.90, 59–83.Google Scholar
- Gardner, G. H. F., Gardner, L. W., andGregory, A. R. (1974),Formation Velocity and Density: The Diagnostic Basics for Stratigraphic Traps, Geophysics39, 770–780.Google Scholar
- Gassmann, F. (1951),Elastic Waves through a Packing of Spheres, Geophysics16, 673–685.Google Scholar
- Hamilton, E. L. (1971),Elastic Properties of Marine Sediments, J. Geophys. Res.76/2, 579–604.Google Scholar
- Hamilton, E. L., (1980),Geoacoustic Modeling of the Sea-floor, J. Acoust. Soc. Am.68, 1313–1340.Google Scholar
- Japsen, P. (1993),Influence of Lithology and Neogene Uplift on Seismic Velocities in Denmark: Implications for Depth Conversion of Maps, American Association of Petroleum Geologists Bull.77, 194–211.Google Scholar
- Kenter, J. A. M., Ginsburg, R. N., Eberli, G. P. McNeill, D. F., andLidz, B. H. (1991),Mio-Pliocene Sea-level Fluctuations Recorded in Core Borings from the Western Margin of Great Bahama Bank, Abstract, GSA Annual Meeting, San Diego, California.Google Scholar
- Laughton, A. S. (1957),Sound Propagation in Compacted Ocean Sediments, Geophysics22, 233–260.Google Scholar
- Marion, D., Nur, A., Yin, H., andHan, D. (1992),Compressional Velocity and Porosity in Sand-clay Mixtures, Geophysics57, 554–563.Google Scholar
- Milholland, P., Manghani, M. H., Schlanger, S. O., andSutton, G. H. (1980),Geoacoustic Modeling of Deep-sea Carbonate Sediments, J. Acoust. Soc. Am.68/5, 1351–1360.Google Scholar
- Nur, A., andSimmons, G. (1969),The Effect of Saturation on Velocity in Low Porosity Rocks, Earth and Planet. Sci. Lett.7, 183–193.Google Scholar
- Nur, A., Marion, D., andYin, H.,Wave velocities in sediments. InShear Waves in Marine Sediments (Kluwer Academic Publishers 1991) pp. 131–140.Google Scholar
- Rafavich, F., Kendall, C. H. St. C., andTodd, T. P. (1984),The Relationship between Acoustic Properties and the Petrographic Character of Carbonate Rocks, Geophysics49, 1622–1636.Google Scholar
- Sanders, D. G. K. (1994),The Cenomanian to Miocene Evolution of a Carbonate Platform to Basin Transition: Montagna della Maiella Abruzzi, Italy (unpubl. Diss. ETH Zürich, Switzerland).Google Scholar
- Schlanger, S. O., andDouglas, R. G.,The pelagic ooze-chalk-limestone transition and its implications for marine stratigraphy. InPelagic Sediments (eds. Hsu, K. J., and Jenkyns, H. C.) (Special Publication Int. Assoc. of Sedimentologists 1 1974) pp. 117–148.Google Scholar
- Sellami, S., Barblan, F., Mayerat, A.-M., Pfiffner O. A., Risnes, K., andWagner, J.-J. (1990),Compressional Wave Velocities of Samples from the NFP-20 East Seismic Reflection Profile, Mém. Soc. Géol. Suisse1, 77–84.Google Scholar
- Urmos, J., andWilkens, R. H., (1993),In situ Velocities in Pelagic Carbonates: New Insights from Ocean Drilling Program Leg 130, Ontong Java Plateau, J. Geophys. Res.98/B5, 7903–7920.Google Scholar
- Vecsei, A. (1991),Aggradation und Progradation eines Karbonatplattform-Randes: Kreide bis Mittleres Tertiär der Montagna della Maiella, Abruzzen, Mitteilungen aus dem Geologischen Institut der Eigdenössischen Technischen Hochschule und der Universität Zürich, 294.Google Scholar
- Vernik, L., andNur, A. (1992),Petrophysical Classification of Siliciclastics for Lithology and Porosity Prediction from Seismic Velocities, American Association of Petroleum Geologists Bull.76, 1295–1309.Google Scholar
- Vidlock, S. (1983),The Stratigraphy and Sedimentation of Cluett Key, Florida Bay, M.S. Thesis, University of Connecticut.Google Scholar
- Wang, Z., Hirsche, W. K., andSedgwick, G. (1991),Seismic Velocities in Carbonate Rocks, J. Can. Petr. Tech.30, 112–122.Google Scholar
- Wilkens, R. H., Fryer, G. F., andKarsten, J. (1991),Evolution of Porosity and Seismic Structure of Upper Oceanic Crust: Importance of Aspect Ratios, J. Geophys. Res.96, 17981–17995.Google Scholar
- Wilson, J. L.,Carbonate Facies in Geologic History (Springer, New York 1975).Google Scholar
- Wood, A. B. (1941),A Textbook of Sound (Macmillan, New York 1941).Google Scholar
- Wyllie, M. R., Gregory, A. R., andGardner, G. H. F. (1956),Elastic Wave Velocities in Heterogeneous and Porous Media, Geophysics21/1, 41–70.Google Scholar