Rock Physics and Seismic Inversion to identify stratification within salt section supporting velocity, facies modeling and geomechanical analysis

Abstract

Challenges in oil producing from Pre-salt field go beyond reservoir characteristics. Pre-salt reservoir is located in ultra-deep water. They are carbonates, most formed by microbiolite, coquina, volcanoclastic, with vertical and lateral heterogeneity. Fluid in these rocks may vary from low to high CO2 content with large differences related to gas-oil ratio. Moreover, to reach these reservoir, up to 3000 m of evaporite section must be drilled. Evaporites are particular rocks resulting from chemical precipitation in a restricted environment and high rate of water evaporation. Under high pressure and overburden, evaporite rocks impose drilling challenges. Under these circumstances, salt formations have mobile nature. In a short time, due to higher deformation rate than sedimentary rocks, well stability and safety are unsteady affecting well bore stability. Creep behavior of salt rock can lead to hole closure and borehole collapse. Undoubtedly, to achieve the goals of development and monitoring of these field through a well drilling campaign, salt rock must be known. To achieve this aim, we purpose in these paper a workflow which takes into account geological, well log and seismic information. Flowing steps are purposed and accomplished: get rock physics relation from well log information; perform seismic inversion in order to get elastic property; derive probabilistic facies through Bayesian classification and, at length, make quantitative seismic interpretation of these data with geological, geophysical and engineering integration.