Development of new type curves for production analysis in naturally fractured shale gas/tight gas reservoirs

• New models are developed for multi-stage fractured horizontal well in tight rock.
• The un-stimulated reservoir is modelled as a dual porosity system.
• The solutions are more general for type curve analysis.
• We have developed new type curves for shale/tight gas production analysis.

As a result of ultra-low rock permeability and hydraulic fracturing, both shale gas and tight gas production exhibit long-term transient and linear flow behaviour. Previous studies have introduced the type curves for linear flow reservoir and assumed that the production is dominated by the stimulated reservoir volume (SRV). Later the type curves were extended to include the production contribution from un-stimulated region which has been assumed to be a homogeneous system. At present, no type curves have been developed for naturally fractured shale gas/tight gas reservoirs in which the un-stimulated region has double porosity flow behaviour.In the current study, we have developed new analytical solutions for shale gas/tight gas reservoirs with multi-stage fractured horizontal well in order to account for the un-stimulated region as a dual porosity system. The solutions are more general for type curve analysis and applicable in both homogeneous and naturally fractured reservoirs. Numerical models were used to validate the analytical solutions and obtained an excellent agreement. We have also developed new type curves for shale gas/tight gas evaluation. The flow regimes are identified to show linear flow and transition flow alternately, and are more complicated than the assumption of homogeneous un-stimulated reservoir in late period. We have compared the new type curves with the curves based on SRV and Brohi's solutions. It is concluded that the double porosity behaviour of un-stimulated region has a positive effect on production even if the fracture permeability is in the order of matrix permeability and the matrix bulk shape factor is low.