Permanent Down-hole Gauges (PDG) have been widely installed in oil and gas reservoirs. These systems monitor the real-time down-hole information continuously. In this way, real time reservoir management and production can be significantly improved.

The key in analysing long term transient data from PDG is the flowing rate history. Accurate flowing rate history is not always available in oilfield, especially in the multiphase reservoir. The multi-phase flow meters are not only expensive but also inaccurate and unstable. The common practice is that several wells are measured together through manifold, and total cumulative production is given without flowing rate details for each individual well. How to recover accurate flowing rate history is a challenge for reservoir engineers.

This paper presents the study results of recovering flowing rate history using the Wavelet Transform (WT) method in oil and water two-phase flowing reservoir. At first, the transient pressure from PDG is processed by HAAR wavelet. The WT will yield frequency amplitude changes when flow events happen, so the time of flow events will be identified. Then, with the relationship between liquid rate change and the corresponding WT frequency amplitude changes, the flowing rate history can be recovered with high accuracy.

The developed algorithms were demonstrated through two kinds of simulation models, i.e., constant water cut and increasing water cut after water breaking though. In addition, the relationship between water cut change and WT frequency amplitude is developed. The effects of skin, wellbore storage and reservoir heterogeneities are considered, and the study results have demonstrated the robustness of this method and its promising future application in practice.

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