A simple spreadsheet model has been develped to estimate Original Gas In Place (OGIP), layer productivity and recoverable reserves for wells with commingled production, completed in multi-layered tight gas reservoirs. Differentiating the productivity between multiple layers of contrasting permeability is old technology. This model, however, replicates the observed material balance trend while also honouring total well productio data by varying layer properties. The P/Z trend of the higher permeability layers and lower permeability layers is mapped to "envelope" the productivity index (PI) weighted P/Z curve that is used to match historical data.
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