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Practical Implementation of Stratigraphic Compartmentalization in Turbidite Lobe Reservoirs

Antoine Bertoncello

In sheet-sand reservoirs, the presence of shale draping the lobes tends to compartmentalize the reservoir sand into multiple flow units. This stratigraphic compartmentalization has dramatic implications in term of field development and hydrocarbons recovery, and has to be characterized as early as possible in the field life. Geochemistry and fluid pressure analyses along the well path are common tools to identify the different flow units (a flow unit corresponding typically to a lobe) but they provide an incomplete description of the full 3-D reservoir compartmentalization. A traditional approach to achieve a complete reservoir description from sparse data is to use geostatistical algorithms. However, geostatistics are ill-equipped to integrate compartmentalization information and to generate the corresponding shale drape geometry.

In this study, we propose a 2-point geostatistical workflow that overcomes this limitation. First, the geometry of each lobe (i-e compartment) observed in the wells is propagated in the geocellular grid by Sequential Indicator Simulation. The lobes shapes are controlled by the algorithm input parameters. A probability map of shale occurrence is then computed. High probabilities are assigned to the surface of the previously simulated lobes, where the shale drapes are found. Using this probability map, a 2-point geostatistical facies modeling step is performed. The simulated shale, which is therefore located at the lobes surfaces, forms drapes and compartmentalizes the reservoir as observed in the well data.

This workflow is stochastic in nature and generates models in seconds. For that reason, it can be easily used to assess reservoir compartmentalization uncertainty. The method is successfully applied to a real turbidite reservoir in offshore Gulf of Mexico composed of 6 wells and 8 identified lobes. The geological consistency of the resulting models is compared to an outcrop considered an analog of the reservoir and located in Frazier Park, California.

AAPG Search and Discovery Article #90179©2013 AAPG Geosciences Technology Workshop, Houston, Texas, August 6-7, 2013