Upscaling Fractured Media and Streamline HT-Splitting in Compositional Reservoir Simulation

We present two approaches devoted to speeding up reservoir simulations. The first approach deals with permeability upscaling for fractured media. The basic problem of any upscaling procedure, which consists of how to formulate the boundary-value conditions for a cell problem, is solved by the method of splitting the global pressure field into two components in such a way that one component may be neglected, while the second one may be calculated in the analytical way. In addition to this, we have developed a new fast method of solution to the cell problem, which is based on splitting the contribution of fractures and a tight matrix. The second approach is devoted to streamline simulations for a compositional flow. The low e.ciency of any streamline simulation in this case is reduced due to the lack of fast analytical solutions to 1D flow problems. We suggest a new asymptotic compositional flow model which ensures a total splitting between the thermo- and hydrodynamics. As a result, such a splitting leads to an analytical or semianalytical solution for the multicomponent flow problem along the streamlines

Evaluation of multiple reduced-order models to enhance confidence in global sensitivity analyses

Variance-based global sensitivity analysis (e.g., the Sobol' sensitivity index) can be used to identify the important parameters over the entire parameter space. However, one often cannot afford the computational costs of sampling-based approaches in combination with expensive high-fidelity forward models. Reduced-order models (ROM) can substantially accelerate calculation of these sensitivities. However, it is usually difficult to determine what type of ROM should be used and how accurately the ROM represents the high-fidelity model (HFM) results. In this paper, we propose to concurrently use multiple ROMs as a way to assess the robustness of the model-reduction method. Two sets of HFM simulations are needed, one set for building ROMs and the other for validating ROMs. Our goal is to keep the total number of HFM simulations to a minimum. Ideally some of the HFM simulations in the first set can be shared by different ROMs. Based on validation results, the ROMs can be combined with different schemes. We demonstrate that we can achieve the goal by using four different ROMs and still considerably save computational time compared to using traditional HFM simulation for calculating sensitivity indices. We apply the approach to an example problem of a large-scale geological carbon dioxide storage system, in which the objective is to calculate a sensitivity index to identify important parameters. For this problem, the locally best ROM provides better estimates than the weighted average from all ROMs

Optimization of Medium-Deep Borehole Thermal Energy Storage Systems

Arrays of medium-deep borehole heat exchangers are characterized by their slow thermal response and large storage capacity. They represent suitable thermal energy storage systems for seasonally fluctuating heat sources such as solar energy or district heating grids. However, the economic feasibility of these systems is compromised by high investment costs, especially by the expensive drilling of the boreholes. This study presents an approach for the simulation and optimization of borehole thermal energy storage systems. To exemplify the concept, a software tool is used to optimize the number and length of borehole heat exchangers with regard to a specific annual heat demand. The tool successfully determines the ideal size of the thermal energy storage. Furthermore, the prediction of the system’s performance also indicates that borehole thermal energy storage systems only operate efficiently in large-scale applications. With the presented tool, many aspects of borehole thermal energy storage systems can be simulated and optimized