Understanding of Naturally Fractured Geothermal Reservoirs Using Data Assimilation

Abstract

Naturally fractured reservoirs can pose challenges for geothermal energy production where a clear understanding of mass and heat transfer is essential for developing and successfully managing operations. The dynamic behavior of these reservoirs is greatly affected by fracture properties such as orientation and aperture, whose magnitude is mainly influenced by the stresses on the reservoir rocks. Methodologies for accurate modeling of thermal multiphase flow within fractured reservoirs are limited. Therefore, simulating fractures and their behavior tends to be computationally intensive, which often limits the use of data assimilation methods for uncertainty quantification. However, recent advances in Discrete Fracture Models (DFM) have successfully overcome computational complexity and allow for the explicit inclusion of discrete fractures in reservoir simulations. This study explore the use of data-assimilation techniques to help quantify uncertainties of energy production from naturally fractured reservoirs. We combine a recent implementation of DFM in the Delft Advanced Research Terra Simulator (DARTS) with both ensemble and gradient-based data-assimilation methods. The data assimilation workflow is first developed with a synthetic naturally fractured reservoir and then tested on a real outcrop based reservoir model. Our results show that data assimilation can help to understand the main dynamic characteristics of geothermal energy production from fractured reservoirs. Using this technique, we obtain a more accurate representation of the stresses acting on the reservoir and how they affect the fracture aperture. This information is essential for accurate representation of fractured reservoirs and their efficient reservoir management.