Production forecast of deep shale gas wells based on gas-water two-phase flow

Two-phase flow of gas and water is vital for the production capacity of deep shale gas wells, and it is of great significance to investigate the two-phase production performance of gas and water, for evaluating the reservoir stimulation effects. The production forecast model of multi-stage fractured horizontal wells of deep shale gas was built, considering the two-phase gas-water flow in the fracturing fluid-invaded zone (water invasion zone) and fractures. The presented model was combined with the material balance equation, and the semi-analytical solutions of this model were obtained via the successive iteration approach. The liability and practicability of this model were validated using both the commerical numerical simulator and field production data, and the effects of the sensitive parameters of the water invsion zone (width, water saturation and permeability of the water invasion zone) on production capacity of wells were analyzed. The results showed that the built model can deliver reasonable prediction of production capacity of deep shale gas wells. The shale gas production drops with the expanding width and increasing water saturation of the water invasion zone, and yet climbs up, with the growing permeability of the water invasion zone. The shale gas production capacity is subjected to the joint effects of the multiple parameters of the water invasion zone. Specifically, among the width, water saturation and permeability of the water invasion zone, the water invasion zone width has the largest effects on the 20-year cumulative gas production and water production time, while the intial gas production is most affected by the water saturation of the water invasion zone. The new model provides a theoretical basis and scientific basis for improving the accuracy of productivity prediction in deep shale gas wells.