Decline Behavior of Hydraulically Fractured Horizontal Wells at Different Production Stages in Continental Shale Oil Reservoirs: A Case Study of the Qingcheng Oilfield

Production decline in hydraulically fractured horizontal wells in continental shale oil reservoirs is jointly controlled by reservoir heterogeneity, fracture-system evolution, and changes in development practices. It commonly exhibits pronounced stage-dependent characteristics, making it difficult for a single decline model to accurately characterize the full-life-cycle production dynamics. To address this issue, this study focuses on hydraulically fractured horizontal wells in the Qingcheng Oilfield, Ordos Basin. Based on production performance data and staged decline analysis, a full-life-cycle decline-analysis workflow based on production-stage identification was established. First, the production process of individual wells was divided into an early quasi-stable stage, an early decline stage, and a middle-to-late decline stage according to the evolution of the daily oil-rate decline and the relative growth rate of cumulative oil production. Subsequently, the Hu–Chen–Zhang (HCZ), Duong, and Arps models were used to fit the three stages, respectively, thereby constructing a full-life-cycle segmented decline curve. On this basis, the decline behavior of different well types was comparatively analyzed in combination with the production responses of representative wells. The results indicate that the production dynamics of hydraulically fractured horizontal wells in the study area exhibit clear stagewise evolution throughout their life cycles. The HCZ, Duong, and Arps models show good applicability to the early quasi-stable stage, early decline stage, and middle-to-late decline stage, respectively. The combined decline model constructed from these three models can effectively characterize the complete production process of an individual well, including initial high-rate production release, rapid decline, and gradual late-time depletion. For a representative well, the full-life-cycle fitting results yielded a coefficient of determination (R2) of 0.95, a root mean square error (RMSE) of 0.69, and a mean absolute percentage error (MAPE) of 7.34%. According to their decline-dynamic characteristics, the hydraulically fractured horizontal wells in the study area can be classified into two types: medium-to-high initial-rate decline wells and continuously low-rate wells. The former exhibit strong initial production-release capacity but rapid production loss during the early decline stage, whereas the latter are characterized by relatively low initial production rates and persistently low-rate, gradual-decline behavior throughout the production process. The results provide a reference for understanding decline behavior and forecasting production performance of hydraulically fractured horizontal wells in the Qingcheng Oilfield.