A novel EUR prediction model for fractured horizontal shale gas wells based on material balance theory

Accurately predicting the estimated ultimate recovery (EUR) of shale gas wells is key to formulating a shale gas reservoir development plan. However, in practice, determining the EUR remains challenging due to the complex dynamic characteristics of shale gas production, which first decreases rapidly and then slowly. In this study, based on material balance theory and equivalent seepage resistance theory and considering crucial factors including primary water, adsorption, and pore effects, a new production model for fractured horizontal shale gas wells is developed. The calculation process is designed by using Newton's iterative method. The shale gas well EUR prediction method is verified, and the factors influencing the EUR are analyzed. The results show that adsorption has a significant effect on production, especially on the Langmuir volume. Moreover, ignoring the influence of primary water, which exists in shale gas reservoirs in the form of bound water, results in an overestimation of the EUR. Furthermore, production positively correlates with the fracture half-length and the number of fractures, but the action mechanisms of these two factors differ. Unlike the number of fractures, which predominantly affects the initial stage of production, the fracture half-length has a more nuanced role. It is capable of altering the stimulated reservoir volume zone, thereby exerting influence over the entire production life cycle.