Reason Analysis for Higher or Lower Productivity of MFHW in Tight Gas Reservoirs Based on Well Testing Theory

Abstract Field data indicate that the production capacity of single wells in tight sandstone gas reservoirs can be significantly enhanced through large-scale, multi-stage hydraulic fracturing. However, production anomalies have been consistently observed in fractured gas wells during subsequent production phases. These anomalies are typically reflected in either higher or lower than expected well productivity. At present, effective methods for the rapid identification and systematic interpretation of such production anomalies in multi-stage fractured horizontal wells (MFHWs) remain inadequate. To address this limitation, an integrated analytical method was established based on well testing and seepage theory. In this method, production performance data were coupled with linear flow analysis to systematically diagnose the causes of production anomalies. Firstly, an improved trilinear flow model was established to describe the seepage characteristics of each reservoir zone after hydraulic fracturing in tight sandstone gas reservoirs. The non-uniqueness of parameter inversion was constrained using the rate-normalized pressure (RNP) diagnostic plot. As a result, reasonable interpretations of reservoir parameters, fracture parameters and Ak were obtained. Then, cumulative gas production and fracturing parameters were normalized for individual wells. Based on these, normalized cumulative production plots under different influencing factors were constructed to quickly identify abnormal gas wells. Sensitivity plots between Ak and various fracturing parameters were generated using data from 206 typical wells. The correlations between fracturing parameters and Ak were analyzed to evaluate the fracturing scale. In addition, the reasons for higher or lower well productivity were explained based on these plots. Finally, the reliability of the interpretation results was verified using multiple datasets, including post-fracture flowback data. The results indicate that high or low production abnormal wells can be rapidly identified based on the normalized cumulative production plots. A positive correlation between Ak and fracturing parameters was observed from the sensitivity analysis plots. In addition, the possible causes of production anomalies in fractured wells can also be interpreted using these plots. Specifically, the abnormal high or low gas production is attributed to the mismatch between the theoretical fracturing scale and the actual fracturing effectiveness.