A mathematical model for predicting the productivity of fractured horizontal wells of tight sandstone gas: A case study in the Sulige gas field

The Sulige tight sandstone gas reservoir is marked by low permeability, intricate pore structures, and notable lateral heterogeneity, making it difficult to predict the productivity of fractured horizontal wells in the reservoir. In this study, a productivity prediction model for fractured horizontal wells is developed based on the characteristics of the Sulige gas reservoir, including its high start-up pressure gradient, strong stress sensitivity, obvious non-Darcy flow, and typical slippage and diffusion effects. This new model fully accounts for each hydraulic fracture in the horizontal wells based on the superposition principle and Green's function. This model facilitates efficient productivity calculations and enables rapid quantitative analysis of the influencing factors specific to horizontal wells with hydraulic fractures, fully integrating the specific characteristics of the Sulige gas field. The accuracy of this model is tested against field data from Wells LX1 and LX2 in the Sulige field, indicating good agreement between the predicted values and field data. Well LX2 is used as a case study to analyze the influences of geological and engineering factors on well productivity. The following conclusions are drawn: 1) Well productivity is notably influenced by the start-up pressure gradient and stress sensitivity, with a minor impact from non-Darcy effects. 2) Productivity linearly decreases with increased hydraulic fracture spacing. 3) Productivity increases, and the increment rate gradually decreases, with increases in the length and conductivity of the hydraulic fractures. This model provides valuable guidance on predicting productivity in tight sandstone gas reservoirs, such as that of the Sulige gas field.