HR: 0800h
AN: MR31C-0529    [Abstracts]
TI: Seismic Response of Carbonate Cemented Sandstones
AU: * Dutta, T
EM: tanima@stanford.edu
AF: Stanford University, 397 Panama Mall, Mitchell Building, Stanford, CA 94305, United States
AU: Mukerji, T
EM: mukerji@pangea.stanford.edu
AF: Stanford University, 397 Panama Mall, Mitchell Building, Stanford, CA 94305, United States
AU: Mavko, G
EM: mavko@stanford.edu
AF: Stanford University, 397 Panama Mall, Mitchell Building, Stanford, CA 94305, United States
AB: This study focuses on how carbonate cementation precipitated at the key sequence stratigraphic surfaces impact the seismic impedance. Our goals are two-fold: (1) to identify the sedimentological variations within carbonate- cemented sandstones and (2) to quantify their effects on P-impedance. To accomplish this goal, we identify the relationship between carbonate cementation and key stratigraphic surfaces, such as, the incision surfaces and the flooding surfaces. Next, we use effective medium models to quantify the impact of sediment parameters on P- impedance. We find that the carbonate cemented sandstones are extremely heterogeneous in nature, even within a depth interval of 60 meter in our study area offshore Equatorial Guinea, West Africa. Their grain-size, sorting, mineralogy, clay-content, amount of cement and degree of leaching vary considerably. We identify two distinct clusters of data in the P-impedance vs. porosity plane. The carbonate cemented sandstones from the base of incision are usually associated with lower shaliness, lower porosity and higher P-impedance. On the contrary, data from the top of flooding surfaces exhibit higher shaliness, higher porosity and lower P-impedance. The contact cement model fails to predict the trend shown by the later cluster of data. The predictions using the constant cement model with 1% constant carbonate cement, and the modified stiffsand model with 15% critical porosity agree reasonably well with the data. Furthermore, we find that the modified differential effective media model with 40% percolation porosity, and Berryman's self consistent model with 20% percolation porosity fit P- impedance vs. porosity trend of the carbonated cemented sandstones. In conclusion, the carbonate cements are different than the siliciclastic cements in terms of sedimentological parameters, and the commonly used rock physics model for quartz cemented sandstones are not always suitable to predict P-impedance vs. porosity trends for the carbonate cemented sandstones. We recommend testing the predictions of rock physics models against data, classified by key stratigraphic surfaces.
DE: 4255 Numerical modeling (0545, 0560)
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 9305 Africa
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting