Flow diagnostics are constructed based on a (single-phase) pressure solution and can be used as efficient tools for assessing flow patterns and well allocation factors. The 'diagnostics' module in MRST offers a computationally inexpensive alternative to performing full-featured multiphase simulations in order to rank, compare, and validate reservoir models and production scenarios.
The basic diagnostic routine computes the following information:
Time-of-flight and tracer partitions are often associated with streamlines, but in the 'diagnostics' module they are computed using a standard first-order, upstream, finite-volume method. This way, these quantities can easily be computed in a robust manner on general unstructured grids. However, the resulting values will not be very representative in a pointwise sense, in particular in cells that contain flow paths with significantly different residence times. More accurate values are obtained if one computes averaged time-of-flight per tracer region.
Based on time-of-flight, the module can also compute three quantities that can be used to assess the heterogeneity of a reservoir model:
The upper figure shows how the Lorenz coefficient can be used to predict the oil recovery for different permeability and well configurations. The oil recovery simulated for four different fluid models is plotted as a function of the Lorenz coefficient for all the 85 horizontal layers in Model 2 from the SPE 10 Comparative Solution Project.
The lower figure shows flow and storage capacity diagram for two different well configurations. The blue line represents the F-Phi curve of a standard five-spot well configuration. The green line shows the F-Phi curve of an alternative well placement that has been obtained by rigorous mathematical optimization with the Lorenz coefficient as objective function. Because the green curve lies much closer to a linear curve corresponding to an ideal linear displacement, one can expect the optimized well placement to give significantly higher recovery, which was also confirmed by a full simulation.
The most obvious use of tracer partitions and time-of- flight values is to use these cell-based values as a basis to provide improved visualization of flow patterns. Drainage and sweep volumes can be defined using a majority vote over tracer concentrations so that each cell is assigned to a specic injector or producer. Communication between wells is obtained by intersecting drainage and swept volumes, and the resulting volume partition can be used to identify the pore volume associated with each well pair, or to compute well allocation factors, i.e., the fraction of the producer's inflow that can be attributed to a given indicator. A very intuitive visualization of the evolution of injected fluids is obtained by combining swept volumes with the forward time-of-flight.
The upper plot shows the sweep volumes associated with a single injector delineated and colorized by injector-producer connections. The lower plot shows pore volumes assigned to each producer (left) and the allocation factors per depth (right), which makes it easy to estimate influences between well pairs.
In MRST, all these ideas are combined in an interactive viewer that makes it easy to look at allocation factors, drainage/flood volumes for well pairs and so on for specific regions of time-of-flight. Because the flow diagnostics is so quick to compute, the user may use these measures to interactively adjustment well positions and rates, experiment with adding new infill wells, etc. Likewise, a simple preview of future production can be obtained by visualizing the fluid distribution inside the drainage volume of a given producer as function of the reverse time-of-flight.
The two figures below exemplify how flow diagnostics can be used to pre-process and post-process more comprehensive multiphase simulations to gain better insight into flow patterns and volumetric connections in a reservoir model
This module is included with MRST from version 2012b and onwards under the name 'diagnostics'.
Published October 1, 2012
Examples of various uses of flow diagnostics. Enlarge the picture
Tutorial: compute time-of-flight and stationary tracer as well as three different measures for heterogeneity. Read more..
Tutorial: visualize drainage and flooded volumes and compute well-pair diagnostics. Read more..
Tutorial: use well-allocation factors to assess the quality of upscaling. Read more..
Tutorial: use SAIGUP geomodel realization to set up a simulation model and then launche the interactive diagnostics tool. Read more..
Example of injection tracer region superimposed on a well-allocation map for the SAIGUP data set. Click to enlarge..
Youtube video demonstrating interactive visualization and flow diagnostics in MRST.