The horizontal well with multiple transverse fractures has proven to be an effective strategy for shale gas reservoir exploitation. However, to improve the well design it is important to quantify the reservoir permeability and the extent of the stimulated reservoir volume (SRV) defined by the created hydraulic fractures.
Rate-normalized pressure (RNP) is easily computed from production data and is more straightforward to interpret than pressure normalized rate. Pseudolinear flow before pressure interference happens between two adjacent transverse fractures, seen as a ½ slope trend in the RNP derivative, and pseudo pseudosteady state, seen as a straight trend with slightly less than unit slope, are key to the analysis. When only pseudolinear flow appears, a minimum extent for the SRV is indicated as well as a maximum value for the shale permeability. The appearance of pseudo pseudosteady state flow provides an estimate for the pore volume of the SRV and a minimum value for the shale permeability. When both pseudolinear and pseudo pseudosteady state flow regimes appear, permeability and the average half-length and spacing of created fractures can be estimated.
We illustrate the analysis procedure with field data from key shale gas plays. Estimates for both the expected ultimate recovery and recovery efficiency as a fraction of the gas in place in the SRV are possible using this interpretation technique. Sensitivity of the analysis to uncertainties in shale thickness, porosity, and adsorption parameters are explored.