SCAL Workflow for Heterogeneous Pre-salt Carbonate Rocks

Pre-salt carbonates are amongst the most relevant reservoirs in Brazil. The reservoirs are highlyheterogeneous, with large variations in porosity and permeability and often contain significant amounts ofsolid hydrocarbons inside the pores or on the pore throats, all of these making it challenging to properlydescribe the reservoirs. Moreover, the complexity of the fluids, often rich in light components, adds to thedifficulty of accurately estimating reserves and forecasting production or to selection of the most optimalproduction strategy. In our view, Advanced Special Core Analysis (SCAL) techniques and integratedworkflows are necessary for a better understanding on how these complexities impact the recovery processand the production strategies. In the Shell Rocks & Fluids laboratory in Amsterdam, we combinedinnovative technologies, including imaging with CT, NMR/MRI, SEM, etc. with coreflooding performedusing in-situ saturation monitoring (ISSM), to obtain reliable fluid flow parameters such as relativepermeability, capillary pressure, trapping properties for these challenging carbonates. In this article, weprovide a detailed description of the integrated SCAL workflow used for the pre-salt carbonate rocks. Thisincludes careful selection of the samples for SCAL tests, characterization using a multitude of techniques,a research study on selecting the most optimal solvent for effective cleaning (while preserving the integrityof the reservoir rock, including of solid hydrocarbons), as well as an assessment on how heterogeneityimpacts the interpretation of coreflooding tests used to extract relative permeabilities. The X-ray basedISSM played a key role in execution and interpretation of the steady-state coreflooding tests (for water-oildisplacing process) and the unsteady state coreflooding tests (for water-gas displacement). Multispeedcentrifuge tests were performed in parallel to obtain imbibition capillary pressure. All experimental testswere history matched using in-house numerical simulations techniques, in order to accurately interpret theresults, and to extract reliable input parameters for further upscaling to the static and dynamic models usedfor field development plans of pre-salt carbonates portfolio.