Uncertainty assessment of Vapex performance in heterogeneous reservoirs using a semi-analytical proxy model

While compositional simulators are available for modeling the recovery performance of Vapex process, computational constraints often preclude detailed numerical solution of the flow and transport differential equations, as implemented in traditional flow simulators, using an entire suite of geostatistical realizations that represent the uncertainty due to reservoir heterogeneity occurring at different scales. Proxy models that are based on analytical formulations provide efficient alternatives to expensive detailed flow simulations. l semi-analytical proxy has been developed to model solvent transport in Vapex at isothermal conditions. Detailed analytical formulations were derived and implemented in a calculation procedure to advance the solvent–oil interface and estimate producing oil rate with time. A mass penetration parameter was formulated, and its change with time was tracked. Results obtained from the proxy were validated against experimental data available in the literatures as well as detailed compositional simulation studies (Shi and Leung, 2014a, 2014b). Later, a suite of geostatistical realizations are ranked based on their cumulative oil production using this proxy, and the results demonstrate good agreement with those based on detailed compositional simulations but with significant savings in computational costs. Finally, this proxy is employed to assess impacts of uncertainty in subscale heterogeneity. ortant contribution from this work is that process physics are built directly into this proxy; it represents an advantage over other alternative modeling approaches (i.e., regression) that are driven only by data. This proposed proxy can be easily integrated in existing reservoir management workflows to optimize production scenarios in a quick and robust manner. It can be applied to rank numerous geostatistical realizations and quickly identify a smaller, more manageable subset of realizations for further simulation analysis. It presents an important tool for assessing the uncertainty in reservoir properties on effective mass transfer and the ensuing recovery performance, as well as assisting decisions-making for future pilot and field development planning.