Shale operators are finding it increasingly critical to find a reservoirs' sweet spot, choose the optimum landing point, geo-steer the well within the best rock, and run the optimal completion hardware in order to exceed investor expectations. Due to geological structures that vary across the field or geo-steering quality issues, many wells suffer severe sinuosity which potentially impairs completions and inhibits productivity. This study presents a comprehensive evaluation of hydraulically-fractured wellbore productivity compared with relatively smooth and highly-sinuous wells of similar reservoir quality. The sharp contrast leads to the engineering investigation by coupling a reservoir model which imbeds a representative complex fracture network with a transient multiphase wellbore simulator. The integrated model provides insight behind the flow instability in horizontal wells that produce hydrocarbons from unconventional reservoirs and the remedy completion and production strategy by considering reservoir and wellbore coupled performance. Hydraulically-fractured horizontal wells in shale reservoirs have unstable flow dynamics because of low effective productivity index, small fluid velocity (due to large production string), and multiphase flow under bubble-point pressure, etc. We found that all these reasons lead to vigorous terrain slugging for any toe-up or toe-down wellbore geometries. Furthermore, this flow assurance issue determines more serious problems while encountering a certain level of wellbore sinuosity. In fact, we observed how the stagnation of fluid may isolate entire sections of the lateral and lead to a huge impairment of well deliverability.