New Prediction Model for Individual Well Productivity in Tight Sandstone Gas Reservoir after Reservoir Reconstruction

Abstract Tight sandstone reservoir has low permeability and natural productivity. To enhance the productivity of individual wells in tight sandstone formations, reservoir reformation is often employed, with extensive hydraulic fracturing being a key method. Given the intricate nature of the physical characteristics inherent in this kind of reservoir, phenomena such as the slippage effect, the sensitivity to stress, and the initial pressure gradient are frequently observed. Moreover, the effectiveness of engineered fractures is contingent upon a multitude of factors, including the durability of the proppant, the particle size distribution, the concentration of sand spread, the pressure required to close the fractures, the embedding of proppant within the fractures, and the deformation of both the proppant and the fracture walls. These factors have more influence on the individual well productivity of tight sandstone gas reservoir after reconstruction. At present, the research on single well productivity prediction model of tight sandstone gas reservoir after reservoir reconstruction considering multiple factors is still insufficient. This paper presents a novel approach to categorizing the gas well control area into three distinct seepage zones: ① the fracturing fracture zone, which serves as the primary fracture resulting from artificial fracturing; ② the reconstruction zone, comprising secondary fractures and matrix generated during the fracturing process, influenced by the reconstruction activities; and ③ the unmodified zone, primarily consisting of the unaffected matrix. Leveraging the unique characteristics of each region, we develop a new predictive model for single well productivity in tight sandstone gas reservoirs, grounded in Darcy’s law and percolation mechanics. This model takes into account various factors, including the high-speed non-Darcy effect, stress sensitivity, slippage effect, startup pressure gradient, and changes in the conductivity of supporting fractures. It also considers the combined impact of proppant strength, particle size, sand concentration, closure pressure, proppant insertion, fractures, and the deformation of proppants and fracture walls on the fracturing process. Moreover, when water is present in certain gas wells, the gas phase’s relative permeability takes a hit as the aqueous phase commandeers the flow channels and the reservoir’s affinity for water comes into play. Post-fracturing, the induced fractures can be a mixed blessing; they significantly enhance the permeability of compact sandstone formations, creating advantageous pathways for oil and gas to flow. However, they can also connect with underlying or peripheral water, hastening the increase of water cut in individual wells and complicating efforts to enhance the productivity of gas wells. This study delves into the influence of water production on the performance of gas wells in water-bearing formations following reservoir stimulation. It formulates a productivity equation tailored to scenarios where water breakthrough occurs post-reconstruction. When tested against real-world gas reservoir data, the model demonstrates minimal discrepancies between predicted and actual single-well productivity values. The findings suggest that the new model’s predictive accuracy is well-suited for practical field applications. The findings offer guidance for forecasting productivity of individual wells and assessing fracturing outcomes in reconstructed tight sandstone gas formations.