Microseismicity may be fluid-induced or it may be caused by changing stress conditions in the reservoir, therefore not all seismicity will contribute to production. Development of a microseismic-based DFN model can describe fracture networks which have been activated during stimulation, but further interpretation is required to determine how these fractures will impact reservoir drainage. This interpretation starts with an examination of stimulated reservoir volume (SRV).
Effective Fluid Flow from Microseismic Estimates of SRVs have evolved over the lifetime of the technology. Early attempts to define SRV by using envelope functions around microseismic event distributions generally resulted in large overestimates of the stimulated zone by incorrectly accounting for outlier events and an inability to distinguish between fluid-induced and stress induced events. Further refining SRV to an estimate of the most seismically deformed volume addressed the issue of outliers, but does not incorporate knowledge of failure mechanisms or activated fracture sets. By considering that stimulated fractures can form a number of intersections the stimulated volume can be interpreted in terms of fracture complexity (FC).
A final consideration to the stimulated reservoir volume is to determine where fracture complexity allows for a part of the reservoir to be well connected back to the perforations, in essence providing a drainage pathway. Using advanced SMTI analysis, high-quality events can be inverted for a general solution, which enables determination of whether mixed-mode shear-tensile events exhibit fracture opening or closing components. With reference to a geomechanical model, the amount of net opening within the fracture networks defines a volume of enhanced fluid flow (EFF) in the reservoir. By evaluating the orientation, density and size of fractures as they intersect within the fracture network, it is possible to better delineate drainage pathways within the reservoir.