A Numerical Well-Test Model of Oil-Gas Two-Phase Flow Based on an Improved Embedded Discrete Fracture Model

Pressure transient analysis is one of the most important methods for understanding well performance. However, there is currently limited research on pressure transient analysis of oil-gas two-phase flow. To address this issue, we propose an oil-gas two-phase numerical well-test model for pressure transient analysis of multi-stage fractured horizontal wells (MFHWs) based on an improved Embedded Discrete Fracture Model (EDFM). Firstly, the oil-gas two-phase flow is considered and the conductivity between matrix and fractures is modified in the EDFM to establish the improved EDFM. The accuracy of the proposed model is then verified by comparing the results with those obtained from standard pressure transient analysis software. Finally, the effects of fluid properties, including dissolved gas/oil ratio, bubblepoint pressure and oil viscosity, on the pressure response are analysed. The results show that the flow stages of a MFHW can be classified as: wellbore storage and skin effect, bilinear flow, linear flow, transition flow, oil-gas flow and boundary dominated flow. As the bubblepoint pressure and oil viscosity increase, the onset of the oil-gas flow stage occurs earlier and the pressure derivative curve during this stage becomes more concave. In addition, the higher the dissolved gas/oil ratio, the deeper the concave in the pressure derivative curve during the oil-gas flow stage. This work may provide insights into the pressure transient analysis of oil-gas two-phase flow.