Productivity Prediction for Fractured Wells in Tight Sand Gas Reservoirs Accounting for Non-Darcy Effects

Abstract

AbstractReliable prediction of production profile for fractured wells is important for hydraulic fracturing optimization. Contribution of Russian researchers (Hristianovich, Zheltov, Goldstein, Entov) in hydraulic fracturing is worldwide recognized. The production profile includes early transient period that is followed by pseudo-steady-state production. Usually, the transition period for conventional reservoirs lasts for months while for tight sands with permeabilities far below millidarcy, it can exceed years. Therefore, two regimes are important for production profile prediction in tight sand reservoirs.Drawdown values in tight sands significantly exceed those for conventional reservoirs, so gas velocity in well fractures is also exceedingly higher. At high Reynolds numbers, inertia effects have the same order of magnitude that the viscous (Darcy's) pressure losses. It results in well productivity decrease. Therefore, it is important to account for non-Darcy effects in fractured well modelling.In the current paper, the inertia non-Darcy pressure losses are incorporated in the mathematical model for gas production via fractured well in tight sand reservoirs by including the quadratic term into momentum balance equation for gas flow in fracture. The model is based on matching of semi-analytical solutions for transient and pseudo-steady-state flows towards well and extends the previous research by considering non-Darcy effects. The iterative procedure allows predicting production profile up to 15 years in fields with permeability 0.005-0.2 md. The model developed aims optimization of hydraulic fracturing in tight sand gas fields.