Elastic Properties of Great Bahama Bank From Platform Top to the Toe-of-Slope
The need for thorough rock mechanical description of carbonates is paramount for models of fracture generation or structural restoration. Plug samples from cores, acquired during the Bahamas Drilling Project and ODP Leg 166 across the margin of western Great Bahama Bank provide a comprehensive database to classify and map dynamic elastic properties of different facies (reef, platform, upper, and lower slope), texture (mud-, wacke-, pack-, grainstone), diagenetic zone (meteoric, mixed, and marine diagenesis), and major pore type (connected molds, intercrystalline, micropores, mixed connected/isolated pores, and vuggy to cavernous). Platform and reefal environments have higher median elastic moduli than upper and lower slope facies. Mudrock has the largest elastic moduli of all lithologies. The medians of wacke-, pack-, and grainstone are not statistically different (p-value > 0.05). However, lithologies that let fluids circulate easily are also more prone to diagenetic overprint, and therefore with increasing grain size the elastic properties show tendencies for larger scatter with highest variations possible for grainstone. Ultimately, where vuggy to cavernous pores are dominant, higher elastic properties dominate as well. Intercrystalline, connected molds, and mixed connected/isolated pores show similar median values, but smaller ranges, respectively. We observe a strong influence of diagenesis on the elastic properties. High scatter is observed for depositional environments which are prone to heterogeneous diagenetic alterations and changing geological environment; i.e. reef, margin, and upper slope. For platform and lower slope facies, significantly less dispersion of these parameters is observed. Meteoric and marine burial diagenesis result both in similar ranges for the parameters, but statistically significant differences in their median values (which distinguishes the two zones). In the mixing zone, parameters are always higher compared to median parameter values in zones of meteoric and marine diagenesis. Facies, lithology, diagenetic zone, and major pore type all show characteristic parameter patterns and ranges for their elastic properties. It is therefore viable to make assumptions about parameters when a generic and diagenetic context is given or can be determined. That this catalogue of dynamic elastic parameters for carbonates shows significant differences permits better determination of input parameters for geomechanical models.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017