A new method for production data analysis of tight and shale gas reservoirs during transient linear flow period

• We used a correction factor for square root of time plot for tight/shale gas reservoirs.
• We developed an iterative method for calculation of the correction factor.
• The correction factor corrects the considerable error in the existing methods for tight/shale gas reservoirs.
• The method is applicable for any reservoir fluid type.

Pseudo-pressure has historically been used in analytical solutions of the diffusivity equation for analysis of real gas flow in conventional gas reservoirs. The accuracy of analytical solutions during the transient flow period is contingent on the validity of the assumption of constant hydraulic diffusivity which is implicit in the background formulations. However, the assumption of pseudo-pressure-independent hydraulic diffusivity during transient flow is not valid for the cases of high pressure drawdown at the wellbore. For tight and shale gas reservoirs, this dependency is more pronounced due to the complexities associated with non-Darcy flow, adsorption/desorption phenomena, stress-sensitivity of permeability and porosity, and condensation in porous media.The current study focuses on rate transient analysis of tight and shale gas reservoirs during transient linear flow period for a single fractured well producing under constant well bottom-hole pressure. The results of the analytical solution of real gas flow in porous media are corrected for the effects of high pressure drawdown, non-static permeability, and condensate formation. The method proposed in this study includes three key elements: introducing a measure of nonlinearity (departure of dimensionless hydraulic diffusivity from linearity); differential and integral formulation of the correction factor (used to correct the slope of the square-root-of-time plot); implementing the iterative integral method for solution of flow equation; and evaluating the correction factor for constant-pressure production during transient linear flow period. The results show that the correction factor becomes more important for higher values of drawdown, permeability modulus, and condensate saturation.