Development of New Type Curves for Production Analysis in Naturally Fractured Shale Gas/Tight Gas Reservoirs

As a result of ultra-low rock permeability and hydraulic fracturing, both shale gas and tight gas exhibit long-term transient and linear flow behaviour. Previous studies have introduced type curves for linear flow and assumed that the production is dominant by the stimulated reservoir volume (SRV). The more recent type curves are developed to include the production contribution from un-stimulated region which has been assumed to be a homogeneous system. We know that some tight or shale gas reservoirs are naturally fractured and unstimulated zone is not homogeneous. In current study, we have developed new analytical solutions (type curves) applicable for both natural fractured and hydraulic fractured shale gas/tight gas reservoirs in which both SRV and non SRV regions have double porosity flow behavior. Our developed type curves are more general and applicable for both homogenous 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 homogenous un-stimulated reservoir in late period. The parameters sensitivity of type curves was also investigated and analysed. It is shown that the reservoir size, interporosity coefficient and fracture permeability ratio have great influence on type curves while the effect of storativity ratio is not such significant because fracture porosity is very low compared to matrix porosity. We have compared the new type curves with the curves based on SRV and Brohi’s solutions. It is concluded that double porosity behaviour of un-stimulated region has positive effect on production even if the fracture permeability is in the order of matrix permeability and the matrix bulk shape factor is low.