We investigated the effect of porosity, pore geometry, and diagenetic history on the elastic properties of dry, tightly cemented grainstones whose pore space consists dominantly of intragranular microporosity within micritic grains. The integration of laboratory petrophysical measurements (porosity, P- and S-wave velocity), petrographic analysis and scanning electron microscope (SEM) imaging of micropore space of 80 Lower Cretaceous microporous carbonate samples from Provence (south-east France) allows (1) the changes in porosity and pore geometry during the diagenetic history to be related to changes in elastic properties, and (2) the impact of micritic grain diagenesis on the elastic properties of microporous grainstones to be quantified by means of fitting parameters derived from equivalent elastic medium modeling. The Urgonian microporous cemented grainstones are elastically equivalent to a homogeneous calcitic host with spherical calcitic inclusions comprising spheroidal pores. The best fit is obtained when porous spheres are modelled using the differential effective medium (DEM) approach and the whole composite using the self-consistent (SC) method (DEM-SC model). At lower porosity values (<20%), when the micropore volume is controlled by intercrystalline cementation processes without compaction, the equivalent pore aspect ratio (EPAR) derived from DEM-SC modelling is nearly constant and averages 0.15. At higher porosities, changes in micropore space architecture related to leaching processes result in slightly increasing EPAR. The recognition of EPAR-preserving versus EPAR-non preserving elastic property evolution is proposed as a tool for diagenetic pattern detection in microporous carbonate reservoirs.

New high-quality multibeam and seismic data image the western slope of the Great Bahama Bank and the adjacent floor of the Straits of Florida. The extensive survey reveals several unexpected large- and small-scale morphologies. These include bypass areas, channel-leveelobe systems, gullied slopes, and products of slope instabilities at various scales, including long slump scars at the lower slope and mass transport complexes that extend ~30 km into the adjacent basin floor. The toe of the slope is irregularly covered with deep-water carbonate mounds. The abundance of the individual morphological features varies from north to south. From 26°00'N to 25°20'N, the slope is dissected by numerous deep canyons that abruptly end southward, where the slope is characterized by a smooth lower portion and small regularly spaced furrows in its upper part. Further south, two long (25-50 km) scars document instability at the lower slope. One of these scars is the source area of a large mass transport complex. In addition to this large-scale feature, several types of gravity-induced sedimentary processes are revealed. Most of the morphologies and inferred processes of this carbonate system are similar to those observed in siliciclastic systems, including mass transport complexes, gravity currents initiated by density cascading, and overspilling channeled turbidity currents. For the first time, a clear asymmetric channel-levee system has been identified along the slope, suggesting similitude in sorting processes between carbonate and siliciclastic systems and enhancing the reservoir-bearing potential of carbonate slopes. Notable differences with siliciclastic systems include: the lack of connection with the shallow and emerged part of the system (i.e., bank top), and the small size of the sedimentary system. © 2012 Geological Society of America

The equivalent pore aspect ratio provides a tool to detect pore types by combining compressional and shear wave velocities, porosity, bulk density, and mineralogical composition of carbonate rocks. The integration of laboratory measurements, well logs, and petrographic analysis of carbonate rocks from various depositional and diagenetic settings (Lower Cretaceous presalt nonmarine carbonates from offshore Brazil; Lower Cretaceous shallow-water platform carbonates from southeast France; and Upper Cretaceous deep-water carbonate from the Gargano Peninsula, Italy) allowed the acoustic signature of a wide range of pore types to be quantified. The equivalent pore aspect ratios are shown to be independent of pore volume and mineralogy. They can, therefore, be regarded as relevant parameters for discriminating selected pore network architectures in carbonate reservoirs. Interparticle and intercrystalline microporosity and macroporosity may include a variety of distinct pore network structures and a wide range of acoustic signatures depending on particle shape, nature of contacts, packing, and cementation (intergranular macroporosity in a densely packed granular sediment, secondary pseudofenestral, etc.). The acoustic response of moldic pores appears to be mainly controlled by the shape of the dissolved allochems. The present work reveals also that correct pore type detection from acoustic and porosity measurements is highly dependent on the pore type classification used. A selection of petrographic and diagenetic features to be considered for the construction of a suitable pore type classification is proposed to improve the detection of the pore type effect on the acoustic properties of carbonate reservoirs at plug and well log scale.