Pressure Transient Analysis of Shale Gas Reservoirs Considering Stimulated Reservoir Volume Using Elliptical Flow

Most shale gas reservoirs are naturally fractured with dual-porosity characteristics. After fracturing or re-fracturing, the stimulated reservoir volume (SRV) always exists around the wellbore. This paper demonstrates a composite elliptical mathematical model to analyze the pressure transient and rate transient behaviors in shale gas reservoirs with SRV considering desorption, diffusion, and viscous flow. This model focuses on two main dual-porosity media regions which are the inner region and outer region divided based on micro-seismic observation. The inner region which has higher flow capacity characterizes the SRV. The inter-porosity flow between matrix and fracture was assumed as unsteady flow for both the inner region and outer region. We solve the model with the elliptical flow model and using Mathieu modified functions, Laplace transform, and Stehfest algorithm comprehensively. We presented the pressure transient and rate transient type curves based on which six flow regimes were recognized including the early wellbore storage period, skin factor period, linear flow period, first radial flow period, transition flow period, and later radial flow period. Then, effect of related parameters including SRV size, desorption, diffusion, inner region and outer permeability ratio on shale gas transient behavior were investigated. The presented model and obtained results can enrich the production performance analysis methods for shale gas reservoirs.