A newly developed mathematical model has been used for formation damage analyses of two hydraulically fractured horizontal wells in the Daqing field, China, and twelve vertical wells in the naturally fractured reservoirs of the Spraberry Trend Area, West Texas. Application of the model to Daqing horizontal wells indicated that these wells should have 4 to 5 times higher oil production rates if the formation was not damaged. The use of the model has captured the characteristics of rapid decline in productivity of the Spraberry vertical wells. Comparisons between the effects of matrix skin and fracture permeability indicated that stress-sensitive fracture permeability is responsible for the productivity loss of these wells. This paper provides reservoir engineers with a practical tool for analyzing inflow performance of wells intersecting long fractures.