Lossless progressive compression of meshes for upscaling and upgridding in reservoir simulation with HexaShrink, European Association of Geoscientists and Engineers, EAGE 2019, Dynamic Reservoir Characterization and Modelling II , June 2019 http://www.laurent-duval.eu/opus-hexashrink-multiscale-mesh-representation-compression-wavelet-modelet.html Manipulation of large data volumes is becoming a concern in the field of simulation. In reservoir simulation, grids are complex structures composed of heterogeneous objects, with a potentially large number of cells. HexaShrink is a perfectly reversible multiscale decomposition tool based on 3D wavelet transformation, dedicated to structured hexahedral meshes. It provides a representation of mesh geometry and properties at different resolutions, coherently preserving discontinuities such as fault networks. This lossless compression method was initially designed for storage and transfer. Here we evaluate its suitability in the context of two-phase flow simulations. Initial results demonstrate comparable impacts of low-resolution grids on injected water. This suggests that embedding low resolution meshes can serve accelerated appromixate simulation results with little overhead, in a consistent upscaling and upgriding fashion.