A Chart-Based Diagnostic Model for Tight Gas Reservoirs Based on Shut-in Pressure during Hydraulic Fracturing

A precise diagnosis of the complex post-fracturing characteristics and parameter variations in tight gas reservoirs is essential for optimizing fracturing technology, enhancing treatment effectiveness, and assessing post-fracturing production capacity. Tight gas reservoirs face challenges due to the interaction between natural fractures and induced fractures. To address these issues, a theoretical model for diagnosing fractures under varying leak-off mechanisms has been developed, incorporating the closure behavior of natural fractures. This model, grounded in material balance theory, also accounts for shut-in pressure. The study derived and plotted typical G-function charts, which capture fracture behavior during closure. By superimposing the G-function in the closure phase of natural fractures with pressure derivative curves, the study explored how fracture parameters-including leak-off coefficient, fracture area, closure pressure, and closure time-impact these diagnostic charts. Findings show that variations in natural fracture flexibility, fracture area, and controlling factors influence the superimposed G-function pressure derivative curve, resulting in distinctive "concave" or "convex" patterns. Field data from Well Y in a specific tight gas reservoir were used to validate the model, confirming both its reliability and practicality.