Multi-stage Hydraulically Fractured Shale Gas Well Production Decline Analysis

With the rapid developments in drilling technique and hydraulic technique in horizontal wells, shale gas reservoir has drawn researchers' attentions due to the abundance reserves, huge development potential and long operating time, becoming the important point in solving energy shortage problems. As the theoretical basis of shale gas wells forecasting, multi-stage hydraulically fractured shale gas well production decline analysis(PDA) is of great significance in fully understanding production performance and promoting shale gas well yield.To enhance the study, two factors resulting in complex fracture geometry after hydraulically fracturing were analyzed, including reservoir quality and completion quality. Based on different fracture geometry, varies flow stages in production were discussed. Dimensionless pseudo-pressure and dimensionless pseudo-time were employed to eliminate the influence of viscosity and Z-factor caused by changed formation pressure. And total compressibility considering desorption was used in describing shale gas flow. According to kinds of fracture geometry, mathematical models were established which include linear dual porosity model, linear triple porosity model and model with three linear flow. The analytical solutions in Laplace space and numerical solution in real space were solved, and the production decline curves and type curves were plotted. Three models can be adopted in different conditions respectively. Factors influencing production decline curves and flow stages were studied from reservoir condition and completion. Results shown different factors influence different flow stages, and different completion conditions caused different flow stages, therefore applicable of mathematical models in PDA was discussed qualitatively and quantitatively. Moreover, production data obtained by Eclipse and theoretical models using same parameters were compared. Good fitting demonstrated the validity of mathematical models in this thesis and application potential in field site. Finally, in order to match field data and have a good estimate of the sought reservoir or well parameters including permeability and fracture half length, optimization fitting method was constructed based on least squares regression method.Mathematical models and PDA curves study in varies reservoir and completion conditions can promote the efficiency of PDA method by choosing models based on field conditions directly. At the same time, optimization fitting realize the solution of complex parameters in multi-stage hydraulically fractured shale gas wells. Study on PDA will become the foundation of multi-stage hydraulically fractured shale gas operation.